DECLARATION I, …………………………………………… declare that my thesis, entitled …………………………………………………………………………………… …………………………………………………………. is identical in content and form to my thesis of the same title presented at the TDK conference in the year of ……………. Budapest, 20………………… …………………………………. student's name and signature Astrid Deverre Astrid Deverre Astrid Deverre Clinical presentation of coxofemoral joint luxation in horses: a case series Astrid Deverre 2025 Astrid Deverre 25 Astrid Deverre Astrid Deverre University of Veterinary Medicine Budapest Department of Equine Medicine Clinical presentation of coxofemoral joint luxation in horses a case series Astrid Deverre Supervisor: Dr. Nagy Annamária, associate professor Departement of Equine Medecine 2025 1 Abstract Coxofemoral joint luxation is rare in full-sized horses, and literature on clinical presentation is limited. This study aimed to describe details of history, clinical signs, gait patterns, diagnostic approaches, and outcomes in horses with confirmed coxofemoral joint luxation. Data were collected via an electronic questionnaire send to veterinarians who had diagnosed coxofemoral luxation or subluxation. Twelve horses with sufficient detail on clinical presentation were included. One horse developed lameness after a traumatic recovery from general anaesthesia, six became lame following routine activities such as bucking, jumping, or playing and in two there was no known incident. The duration of lameness was ≥4 months in five horses; 1 week–3 months in two and five horses presented within hours to a few days after the onset of lameness. Lameness was moderate to severe in all horses. Common clinical features included outward limb rotation (n=8), proximal position of the tuber calcanei (n=7), reduced range of passive motion of the coxofemoral joint (n=8), muscle atrophy of the gluteal, biceps femoris, and quadriceps muscles (n=6) and audible and/or palpable crepitus (n=8). Diagnosis was achieved by radiography and/or ultrasonography in all cases. Outcomes were poor; seven horses were euthanized, one retired, and four were lost to follow-up. In conclusion, horses with coxofemoral joint luxation can present with variable history and lameness duration; recognition of common clinical features described in this study may aid earlier diagnosis. 2 Table of content 1 Introduction .............................................................................................................. 3 2 Literature Review ...................................................................................................... 3 2.1 Anatomy of the coxofemoral joint .............................................................................. 3 2.2 Biomechanics of the coxofemoral joint ....................................................................... 5 2.3 Pathologies involving the coxofemoral joint ............................................................... 6 2.3.1 Osteochondrosis ................................................................................................................... 6 2.3.2 Osteoarthritis ........................................................................................................................ 6 2.3.3 Round ligament injuries ........................................................................................................ 7 2.3.4 Coxofemoral luxation and subluxation .................................................................................. 8 2.4 Diagnosis of coxofemoral luxation .............................................................................. 9 2.4.1 Clinical examination ............................................................................................................. 9 2.4.2 Ultrasonography ................................................................................................................. 10 2.4.3 Radiography ....................................................................................................................... 11 2.4.4 Computed tomography........................................................................................................ 12 2.4.5 Scintigraphy ....................................................................................................................... 12 2.5 Treatment options and prognosis of coxofemoral luxation...................................... 12 2.6 Conclusion ................................................................................................................. 13 3 Objectives ................................................................................................................ 14 4 Material and methods ............................................................................................. 14 5 Results..................................................................................................................... 17 5.1 Signalment................................................................................................................. 17 5.2 History ....................................................................................................................... 18 5.3 Clinical signs ............................................................................................................. 18 5.4 Gait evaluation .......................................................................................................... 20 5.5 Diagnostic imaging .................................................................................................... 20 5.6 Treatment and outcome ............................................................................................ 22 5.7 Post-mortem examination ......................................................................................... 22 6 Discussion ............................................................................................................... 24 7 Summary ................................................................................................................. 30 8 References............................................................................................................... 31 9 Acknowledgements.................................................................................................. 34 3 1 Introduction The coxofemoral joint connects the hindlimb to the pelvis. It allows a wide range of motion while also providing stability, necessary for athletic performance and daily activities. Disorders affecting the coxofemoral joint are rare and luxation is considered to be a particularly uncommon pathology in full-sized horses. Diagnosis of coxofemoral joint luxation can be challenging. The limited literature and case reports on this condition are largely based on ponies rather than horses, which contributes to the difficulty of establishing a reliable diagnosis in adult horses. Gait abnormalities associated with coxofemoral luxation in full-sized horses are scarcely described in the veterinary literature. 2 Literature Review 2.1 Anatomy of the coxofemoral joint The coxofemoral joint, also referred to as the hip joint is a composite spheroidal joint and forms the connection between the pelvis and the hindlimbs [1]. The main movements are extension and flexion, but some abduction and adduction can also occur [1]. The bony pelvis is composed of a right and left os coxae which are fused at the crista symphysialis and are joined dorsally by the os sacrale [1]. Each os coxae is made from the fusion of the ossa ilium, pubis and ischium (cranial to caudal) [1]. These three bones join and form the acetabulum, the articular surface (socket) for the coxofemoral joint that connects with the head of the femur [2]. The coxofemoral joint is stabilized by three principal ligaments: the femoral head ligament (also referred to as the round ligament), the transverse acetabular ligament, and the accessory ligament [3]. The femoral head ligament and accessory ligament run through the acetabular notch (incisura acetabuli) [1]. The ligamentum transversum acetabuli runs over this notch, acting as a bridge and supporting the other ligaments [2]. The acetabular notch is found between the craniodorsal and caudodorsal margins of the facies lunata, near the foramen obturatum [2]. 4 The acetabulum is bordered by the margo acetabuli [2]. Along the margins, the fibrous labrum deepens the acetabulum and thus increases the stability of the joint [1]. Deep in the socket lies the fossa acetabuli, where the ligamentum capitis ossis femoris attaches [2]. The articular surface has a crescent shape, which is reflected in its name, facies lunata [2]. On the ventral surface of the os pubis there is a groove in which runs the accessory ligament [1]. This ligament originates from the tendon of the rectus abdominis, runs through the acetabular notch and inserts on the femoral head [1]. There is a small depression on the femoral head, the fovea [1]. It is a relatively large triangular surface, with an apex close to the center of the femoral head and a base near the medial border [1]. It is the insertion site of the ligamentum capitis ossis femoris (near the apex) and the ligamentum accessorium ossis femoris (near the base) [2]. The coxofemoral joint is supported by powerful muscle groups that provide both stability and movement [4]. The gluteal muscles are the primary extensors of the hip, with the middle gluteal muscle being the most powerful. It originates from the lumbar region (ilium, sacrum and lumbar fascia) and inserts on the greater trochanter of the femur and plays a crucial role in propulsion during locomotion. In contrast, the iliopsoas muscle functions primarily as a flexor of the hip [4]. It originates from the ventral aspect of the lumbar vertebrae and the ilium and inserts on the proximal part of the femur [4]. The tensor fasciae latae and superficial gluteal muscle are the primary flexors of the hip, both originate from the tuber coxae [4]. The tensor fasciae latae inserts on the patella and the superficial gluteal muscle on the third trochanter of the femur [3, 4]. Additional flexor muscles include the quadriceps femoris group. The rectus femoris originates from the pubis and the vastus femoris from the femur, and both insert on the patella [4]. The pectineus muscle runs from the ipsilateral and contralateral pecten ossis pubis and iliopubic eminence to the pectineal line of the femur. The sartorious muscle originates from the iliac fascia and psoas minor muscle and inserts on the medial surface of the proximal tibia, by the fascia cruris. The quadriceps femoris muscle originates from the ilium and femur and inserts on the tibial tuberosity. These muscles also contribute to flexion of the hip [3]. During weightbearing, the semitendinosus, semimembranosus, gluteus and biceps femoris muscles contribute to extension of the hip [1]. They originate either from the ischium or the sacrum and insert on the distal part of the femur and proximal tibia [4]. 5 The gracilis muscle extends from the pubic symphysis to the medial aspect of the tibia, while the adductor muscles originate from the pubic symphysis and insert on the caudal surface of the femur [1]. Located on the medial aspect of the thigh, they contribute to adduction of the hindlimbs [4]. 2.2 Biomechanics of the coxofemoral joint In biomechanics, a lever is defined as a system in the body composed of a rigid part (the bone), a pivot (the joint) and an effort (the muscle making the movement possible). According to Denoix (2014), horses use two types of lever: the “first-type” is utilized during the propulsion phase and the “second-type” in the swing phase. In the hindlimb “first-type levers” include the trochanteric, patellar and calcanean levers, and “second-type levers” include the iliopsoas and caudal femoral levers [4]. The trochanteric and iliopsoas levers contribute to movement of the coxofemoral joint [4]. The trochanteric lever pivots around the coxofemoral joint; the greater trochanter acts as an arm to establish motion [4]. The movement is initiated by contraction of the middle gluteal muscle, which extends the limb caudally [4]. The middle gluteal muscle is the strongest of the gluteal muscles, and the most efficient extensor muscle in the equine body [4]. It plays a crucial role in hindlimb impulsion and propulsion [4]. In addition to hip extension, the gluteal muscles are also responsible for the abduction of the hindlimbs [4]. Flexion of the hip is carried out by the iliopsoas lever, of which the most important muscle is the iliopsoas, which belongs to the sublumbar muscle group [4]. This muscle flexes the lumbosacral intervertebral joint and is the strongest flexor of the coxofemoral joint. It also has a major role in in engaging the hindquarters [4]. Other muscles contributing to coxofemoral joint flexion were described earlier in the anatomy section. These muscles also have a role in protraction and abduction of the hindlimbs [1]. During the stance (weightbearing) phase of the stride, muscle groups contract eccentrically to prevent the joints from collapsing under the weight of the body [4]. Contraction of the middle gluteal and caudal femoral muscles antagonizes flexion of the hip that would naturally occur in weightbearing position [4]. During midstance, lengthening of the gluteal and femoral muscles contributes to the loading of energy that will be essential during the subsequent propulsion phase [4]. In the final part of the stance phase, powerful extension of 6 the hip occurs following concentric contraction of the large middle gluteal and caudal femoral muscles [4]. During the swing (non-weightbearing) phase, flexion of the hip is essential to bring the hindlimb cranially and beneath the trunk [4]. Flexion of the hip requires concentric contraction of the previously stated muscles [4]. In the midswing phase, maximal flexion of the coxofemoral joint occurs through the concentric contraction of cranial femoral and iliopsoas muscles [4]. During the protraction phase, when the limb hits the ground, the coxofemoral joint is not mobilized as much as the other joints, in order to lengthen the limb to the fullest for better engagement [4]. 2.3 Pathologies involving the coxofemoral joint The coxofemoral joint can be affected by developmental, degenerative, traumatic and septic conditions [5]. 2.3.1 Osteochondrosis Osteochondrosis is a developmental abnormality that can occasionally involve the coxofemoral joint [5]. Affected foals are typically younger than 4 months old, with a typical hindlimb lameness, characterized by a low foot arc and shortened cranial phase of the stride [5]. Pain can be elicited on deep palpation of the greater trochanter [5]. Radiography can confirm the diagnosis [5]. Radiographic abnormalities include osteochondral fragments and abnormal (shallow and/or irregular) contour of the acetabulum [5]. Arthroscopic debridement of osteochondrosis lesions offers the best outcome, but prognosis for athletic function is poor [5]. 2.3.2 Osteoarthritis Osteoarthritis can develop as a consequence to nearly any pathology occurring in the joint [5]. It can also develop following soft tissue trauma of the region, which does not have to include intraarticular damage [5]. Horses usually exhibit a pronounced lameness with a low arc of foot flight and a shortened cranial phase of the stride [5]. It can present at any age but is somewhat more prevalent in older horses with a history of chronic lameness [5]. Firm and painful osseous swelling over the greater trochanter might be seen in case of chronic cases [5]. 7 To confirm the diagnosis of coxofemoral osteoarthritis, intra-articular anaesthesia, radiography and ultrasonography are the most valuable tools [5]. Radiography can detect periarticular bone modeling and osteophytes, however the size of mature horses is a major limitation [5]. Cutaneous and transrectal ultrasound may also be used to identify joint effusion and periarticular modelling [5, 6]. In mild cases and at early stages of the disease diagnosis remains challenging [5]. Non-Steroidal Anti-Inflammatory Drugs and intra-articular corticosteroids, polysulfated glycoaminoglycans or nutraceutical therapies might result in improvement in mild cases [5]. Prognosis is poor even for mild osteoarthritis; lameness tends to recur or persist [5]. Non-iatrogenic infectious arthritis can occur in foals [5]. The coxofemoral joint is less frequently involved than other joints [5]. Infections are usually of hematogenous origin and are most often caused by Gram negative bacteria [5]. Due to muscle coverage, it may be difficult to detect heat, focal pain and joint effusion on clinical examination [5], but ultrasound readily confirms joint effusion and facilitates synovial fluid sample collection [6]. Prognosis is usually poor as by the time the diagnosis is achieved, severe joint abnormalities and osteomyelitis are likely to have developed [5]. 2.3.3 Round ligament injuries Rupture of the round ligament (ligamentum capitis ossis femoris) can occur with or without luxation of the coxofemoral joint [7]. Clinical signs can be very similar and it is crucial to establish the presence of concurrent joint subluxation or luxation [7]. Shortening of the limb is often seen in coxofemoral joint luxation but not in horses with round ligament rupture alone [7]. Differentiation can be particularly challenging in cases of chronic coxofemoral luxation, where secondary changes such as muscle atrophy, fibrosis, and modeling appear similar to other hip pathologies [7]. 8 2.3.4 Coxofemoral luxation and subluxation Luxation of a joint is a complete displacement of the anatomical parts composing the joint [8], while subluxation is an incomplete displacement of the anatomical structures [9]. Horses suffering from coxofemoral subluxation can show two different clinical pictures: some present with an acute onset, severe lameness, while in other cases the disease and clinical signs are progressive [10]. Subluxation of the coxofemoral joint can occur due to trauma causing rupture or injury to the round ligament, but also as a chronic process preceded by an acetabular fracture [10]. Coxofemoral luxation in full-sized horses is most commonly the result of trauma causing acetabular or iliac fractures, as the femoral head is otherwise deeply seated within the acetabulum [7]. Traumatic events such as falls, during which the stifle becomes hyperextended and the femur is positioned vertically, can lead to luxation or femoral head fractures [7]. Luxation has also been reported as a complication of full-limb casting, where horses may panic and injure themselves while attempting to free the immobilised limb [7]. Non-traumatic causes include congenital or anatomical abnormalities, such as the absence of key stabilising ligaments particularly the round ligament and the accessory ligament [7]. Additionally, a genetic predisposition has been proposed in cases of coxofemoral joint dysplasia, particularly in Friesian foals, where osteochondral dysplasia leads to joint instability [11]. Foals with this condition may show clinical signs similar to luxation, including a shortened hindlimb gait, and structural abnormalities such as a shallow acetabulum, joint surface erosion, and subchondral bone changes increase the likelihood of luxation [11]. In ponies, upward fixation of the patella has been linked to coxofemoral luxation [7]. This condition is sometimes described as secondary upward fixation of the patella, occurring as a consequence of coxofemoral joint luxation [12]. The outward rotation and change in anatomy of the limb can interfere with normal muscle function; e.g., the rectus femoris muscle is unable to release the patella [13]. The opposite scenario occurs when the stifle is locked in an extended position due to upward fixation of the patella [14]. In this case, the quadriceps muscles may contract forcefully enough to cause luxation of the coxofemoral joint [14]. 9 2.4 Diagnosis of coxofemoral luxation 2.4.1 Clinical examination Coxofemoral joint pathology can be challenging to diagnose correctly. Many horses present pathognomic clinical signs; however, in others, especially in mild cases, diagnosis is less straightforward [10]. In general, regardless of the type of pathology, horses experiencing coxofemoral joint pain tend to move with their limb rotated outwards and abducted [5]. Visual examination of the pelvis and hindquarters is crucial [15]. The symmetry of osseous and soft tissue structures of the pelvis should be evaluated. The presence of any swelling or atrophy of specific muscle groups should be noted [15]. Injuries of the coxofemoral joint are rarely associated with swelling which can be visually identified (unless horses are examined shortly after injury), but the deep palpation of the area may elicit pain reaction [15]. Horses may stand and walk with the stifle rotated outwards and toed out [15]. The affected limb appears to be shorter and if observed from the side, it also appears straighter than the unaffected limb [15]. A more proximal position of tuber calcanei when looking from behind, which results in the impression of a shortened limb, is related to craniodorsal displacement of the femur [7]. Most causes of hindlimb lameness are associated with a shortened cranial phase of the stride is usually observed in horses suffering from hindlimb lameness [7]. However, in horses with pelvic injuries often a shortened caudal phase of the stride is seen [7]. To elicit pain arising from the coxofemoral joint, manipulation into flexed, abducted and extended position can be performed by holding the metatarsus and listening (with a stethoscope if needed) for crepitation [15]. In horses with coxofemoral joint region pain, repeating the manipulation will commonly lead to reaction in attempt to avoid pain and accentuated lameness [15]. The crepitation that can be heard is due to rubbing of the femur and acetabular margins. [7] 10 Manipulation of the limb can also be helpful to feel if the coxofemoral joint is in its anatomical position [16]. With a hand placed between the tuber ischiadicum and the greater trochanter of the femur, slow and controlled rotation of the leg can be performed [16]. In a healthy joint, this motion moves the hand out of its position, however in a luxated joint it moves the greater trochanter [16]. Many horses with coxofemoral joint pathology are reluctant to bear weight on the affected hindlimb only and it can be difficult or impossible to pick up the contralateral limb. 2.4.2 Ultrasonography Ultrasonography is a quick, reliable and cheap diagnostic imaging tool [17]. In foals and small ponies, transcutaneous ultrasonography examination of the pelvis is easier than in adult horses, and images are of better quality, due to a thinner layer of muscle fibers [18]. However, very important and valuable information can be gained in most full-sized horses as well. Transcutaneous ultrasonography, performed with a curvilinear (macroconvex) probe, offers assessment of the ilium, acetabular rim, greater trochanter, femoral neck, coxofemoral joint, and lateral pelvic surfaces [19]. Transcutaneous ultrasonography is considered the most effective for diagnosing coxofemoral luxation [19]; femoral head displacement, joint capsule changes and soft tissue abnormalities can be detected [10]. Transrectal ultrasonography provides detailed pelvic imaging using a linear transducer, allowing visualization of the axial aspects of the ilium, ischium and acetabulum, the ventral surface of the sacrum and the dorsal surface of the pubis [19]. In foals, the articular cartilage of the femoral head appears as a thick, hypoechoic band with a smooth surface [18], compared to a thinner and anechoic appearance in adult horses [20]. This is a very important difference to be aware of, as what is present in a healthy foal, would be an indicator of infectious arthritis in adult [21]. Another difference is the irregularity in subchondral bone that can be seen in foals, and is a physiological finding [20], while similar appearance in adult horses is pathological [22]. 11 Dynamic ultrasonography is the assessment of the moving articulation, compared to static ultrasonography for which the horse is standing still. It can be very useful to diagnose coxofemoral subluxation in adult horses [10]. In some horses, coxofemoral subluxation is not visible on images when the horse is resting the limb, but appear as the limb becomes fully weightbearing [10]. 2.4.3 Radiography Radiography of the coxofemoral joint is challenging in adult horses, mostly because of the thick soft tissue covering limiting image quality [16]. Traditionally, ventrodorsal projections were obtained in dorsal recumbency under general anaesthesia [23]. To acquire the greatest possible details of a lesion on one side of the pelvis, a slightly oblique, lesion-oriented ventrodorsal radiograph is required [10]. To avoid general anaesthesia, a standing radiographic technique was developed, positioning the generator under the horse’s abdomen and directing the beam dorsally to obtain ventrodorsal radiographs [24]. The method is limited by the horse’s height but provides superior visualization, compared to the traditional dorsal recumbency view, of the cranial acetabular rim and joint space. Imaging the joint under weightbearing conditions aids in differentiating between coxofemoral luxation and subluxation [24]. A latero-lateral projection can be acquired in a standing position with light or no sedation. However, superimposition of the contralateral coxofemoral joint decreases image quality. The acetabulum and the proximal femur are less visible and the image usually cannot be used for diagnosis of coxofemoral luxation [24]. A lateral oblique radiographic technique has been developed as an improved alternative to standard views for evaluating the coxofemoral joint [25]. The standing lateral oblique projection, described as a lateral 30° dorsal – lateral ventral oblique view, has proven to be a valuable diagnostic tool for assessing this region [14, 25] 12 With this technique, useful information can be gained of the iliac shaft, the greater trochanter of the femur, the femoral head and the acetabulum, and the overall the integrity of the coxofemoral joint [25]. However, the ventral and dorsal aspects of the acetabular rim cannot be seen, which can be a major limitation in horses with certain fracture configurations [14]). For good quality radiographs, the rectum should be evacuated, some air inflated to avoid artefacts caused by rectum content and to increase contrast, and the horse should stand as squarely as possible [14, 25]. 2.4.4 Computed tomography Computed tomography can be used to obtain clear and useful images of the osseous structures of the pelvis [26]. Coxofemoral luxation was successfully diagnosed using computed tomography in two Shetland ponies, and in two adult horses with concurrent acetabular rim fracture [26]. Limitations are associated with the size of the pelvis of mature horses. Large and dense pelvic bones create beam artefacts and larger horses with thick musculature have more image noise. Only minimal information on soft tissues can be gained [26]. Although a wide range of abnormalities can be detected with computed tomography, there is a lack of clinical correlation between the symptoms and imaging findings [26]. 2.4.5 Scintigraphy Scintigraphy can be a useful tool for identifying pelvic injuries in horses. By detecting areas of increased radiopharmaceutical uptake, it can identify regions of increased bone turnover, inflammation, or injury in structures including the coxofemoral joint, tuber coxae, and tuber [27]. This makes scintigraphy useful for localizing potential sources of lameness or poor performance in the pelvis that might otherwise go undetected [27]. However, increased radiopharmaceutical uptake is not always specific to the cause of lameness; scintigraphic findings must be interpreted alongside clinical examination and other diagnostic imaging modalities [27]. 2.5 Treatment options and prognosis of coxofemoral luxation Multiple treatment options have been successfully reported in ponies, ranging from minimally invasive techniques to salvage procedures [13]. While some ponies achieve full recovery and even return to previous levels of activity, others have less favourable outcomes. 13 Unfortunately, in adult horses, no treatment has been reported to be consistently successful, even in cases involving lightly worked animals [7, 13]. Closed reduction is adviced to be attempted within 12 hours of injury, involving traction and limb rotation, but carries a high risk of reluxation, particularly if performed late or in cases with acetabular fractures [16]. Open reduction may be attempted when closed reduction is not feasible, often combined with stabilizing methods, though success remains limited [16]. Surgical techniques, including femoral head osteotomy, trans-articular pinning, prosthetic capsule stabilization, and total hip arthroplasty, have been described in ponies and miniature horses with varying degrees of success [13, 28–30] However, these procedures are not recommended in full- sized horses, generally those weighing over 150 kg, due to the considerable biomechanical forces acting on the coxofemoral joint and the limited capacity for postoperative stabilization and functional recovery [7, 16] 2.6 Conclusion Coxofemoral subluxation and luxation in full-sized horses can be challenging to diagnose and prognosis is poor. Treatment options have consistently shown no success in the literature, with luxation inevitably re-occurring and athletic careers always ending. The challenge does not only lie in accurately identifying the clinical signs but also in establishing a correct diagnosis. Multiple diagnostic imaging tools can be employed, with ultrasound and radiography used as first-line imaging. Most of the literature on coxofemoral luxation focuses on ponies, with very few reports describing adult horses. As a result, there is limited information on the clinical signs, gait abnormalities, diagnosis, and management of this condition in full-sized horses. To provide evidence-based information on the clinical features of coxofemoral subluxation and luxation in horses, my study will focus on detailed description of the history, clinical signs, including clinical examination and gait assessment, in horses with coxofemoral subluxation or luxation. 14 3 Objectives The main objective of the study was to provide a descriptive analysis of clinical features of coxofemoral luxation in adult horses. Specifically, we aimed to document the signalment, history, clinical presentation, and gait characteristics of affected cases based on information collected from equine veterinarians. 4 Material and methods A convenience sample was used. A questionnaire was sent by email between April 2025 and May 2025 to veterinarians known by my supervisor to have diagnosed horses with coxofemoral luxation. A structured questionnaire was created using Microsoft Excel and included eight main sections: signalment, history, clinical signs, gait analysis, diagnostic imaging, diagnosis, treatment and outcome and postmortem findings (Table 1). In total there were 48 questions, combining open-ended and closed-ended formats. Table 1. Questionnaire items and answer choices: The form included open- and closed-ended questions addressing signalment, history, clinical findings, diagnostic methods, treatment, and outcome. Body condition was assessed using the 9-point body condition scoring system (1 =poor to 9= extremely fat) [31], “Outward rotation of the affected limb” refers to external rotation of the hindlimb. “Proximal location of the tuber calcanei” indicates that the point of the hock was positioned higher on the affected limb compared to the contralateral side. Muscle atrophy severity was graded as mild, moderate, or severe based on visual assessment of hindquarter musculature. “Restricted range of passive motion” refers to reduced mobility of the coxofemoral joint upon manipulation. Lameness grades were scored on a 0–8 scale as described by Dyson [32], with 0 = sound, 2 = mild, 4 = moderate, 6 = severe, and 8 = non–weightbearing lameness. Signalment Institute / country Open ended question Horse name / identifying number Open ended question Breed Open ended question Sex Stallion, Mare, Gelding Age (years) Open ended question Weight (kg) Open ended question Discipline Open ended question Body condition score (1 to 9) 1,2,3,4,5,6,7,8,9 15 Recent exercise history Unbroken, In light work, In strenuous/ competitive work, Out of work or retired, Unknown If out of work or retired, please specify the reason if known Open ended question History History of lameness in the affected limb with no identifiable cause Yes, No, Unknown Traumatic incident Yes, No, Unknown Comments about cause of injury Open ended question Duration / onset of the lameness Open ended question Clinical signs Outward rotation of the affected limb Yes, No, Unknown More proximal location of the tuber calcanei of the affected limb Yes, No, Unknown Muscle atrophy of hindquarters of the affected limb None, Mild, Moderate, Severe, Unknown Muscle group involved Open ended question Soft tissue swelling in the region of the coxofemoral joint Yes, No, Unknown Audible or palpable crepitus Audible, Palpable, Both, None, Unknown Pain on palpation or manipulation Pain during palpation, Pain during manipulation, Pain during both, No pain, Unknown Restricted range of passive motion Yes, No, Unknown Photos available Yes, No If injury less than 7 days, any additional clinical signs Open ended question Any other clinical signs (e.g. distress, sweating), please specify Open ended question Gait analysis Lameness grade at walk (0 to 8) 0,1,2,3,4,5,6,7,8, Not applicable Description of the gate at walk Open ended question 16 Lameness grade at trot if possible (0 to 8) 0,1,2,3,4,5,6,7,8, Not applicable Video available Yes, No, Unknown Ability to lie down Yes with difficulty, Yes with no difficulty, No, Unknown Ability to stand up Yes with difficulty, Yes with no difficulty, No, Unknown Diagnostic imaging Diagnostic imaging tools used Radiography, Ultrasonography, CT, Scintigraphy, Not applicable If multiple imaging tools were used please specify here Radiography, Ultrasonography, CT, Scintigraphy, Not applicable If multiple imaging tools were used please specify here Radiography, Ultrasonography, CT, Scintigraphy, Not applicable If multiple imaging tools were used please specify here Radiography, Ultrasonography, CT, Scintigraphy, Not applicable Comment on diagnosis Open ended question Diagnosis Was there a concurrent pelvic fracture? Yes, No, Unknown If yes, how was it confirmed? Open ended question If no, how was it excluded? Open ended question Confirmation of the diagnosis Imaging, Clinical signs, Both Treatment and outcome Treatment attempted Yes, No, Unknown Specify the treatment Open ended question Outcome Retired, Euthanized, Other Further information about the outcome Open ended question Post mortem examination Post mortem examination Yes, No, Not applicable Post mortem findings Open ended question Any additional comment Open ended question 17 Case details and accompanying photographs and video footages were thoroughly reviewed. Only cases in which the submitted information included comprehensive documentation of clinical signs and detailed descriptions of gait were considered for inclusion. Following the selection process, descriptive data analysis was performed on the included cases to summarise clinical presentation, gait abnormalities, and associated findings that could be helpful in characterizing the condition. 5 Results Case details of 18 horses were submitted; six were excluded due to unclear history, insufficient description of clinical signs, or lack of detailed gait evaluation. Twelve horses diagnosed with coxofemoral joint luxation were included in the study. Cases originated from multiple institutions: the University of Bristol (n=1), the University of Veterinary Medicine in Budapest (n=4), the University of California Davis, United States of America (n=4), The Animal Health Trust, United Kingdom (n=2), and the Equine Clinic of the Freie Universität Berlin, Germany (n=1). Details on signalment and clinical findings are shown in Table 2. 5.1 Signalment The horses’ age ranged 1–32 years (median: 11 years); most horses (9/12, 75%) were adults (≥ 3 years old). Regarding the younger horses, there was one yearling and two 2-year-olds. The cohort consisted of five geldings (41%), four stallions (33%) and three mares (25%). Horses represented several breeds: three Friesians, two Quarter Horses, two Warmbloods, one Haflinger, one Appaloosa, one Arabian, one Mustang and one Thoroughbred. Half of the cohort (6/12) had a BCS of 5, classified as moderate. A further 2/12 (16%) were scored 6, considered moderately fat, while 2/12 (16%) presented with a BCS of 7, categorized as fleshy. One horse was assigned a body condition score (BCS) of 4, corresponding to a moderately thin condition. For one individual, the BCS was not recorded. With respect to workload, three horses were under two years of age and therefore not in active use. Among the remainder, three were used for show jumping, two for driving, and two as general-purpose horses. Of the nine horses of riding age, those in strenuous work, light work, and retirement each accounted for 3/9 (33%). 18 5.2 History Horses could be divided into three groups based on the duration of lameness: five horses presented with chronic lameness of ≥4 months to 4 years’ duration, two had a subacute onset ranging from 1 week to 3 months, and five experienced an acute episode with an onset of a few hours to a few days. Six horses (50%) had a history of previous undiagnosed lameness on the affected limb. In five of these cases, lameness had persisted for four months to four years before progressively worsening and ultimately leading to diagnosis of coxofemoral joint luxation. The remaining horse in this group developed lameness following a traumatic incident during recovery from anaesthesia. Among the six horses without a prior history of lameness in the affected limb, none experienced a traumatic incident. Two sustained injuries while being ridden, one following a bucking episode and the other after landing from a jump. Two others were found lame in the field, while no identifiable inciting event was reported in the final two cases. For the last two cases no specific notes on the onset of lameness were recorded. 5.3 Clinical signs Eight horses exhibited outward rotation of the affected limb (Figures 1 and 2), whereas one demonstrated inward rotation during weight bearing. More than half of the cohort, 7/12 (58%), presented with a proximally positioned tuber calcanei in the affected limb. These clinical signs were seen in horses with acute, subacute and chronic lameness. The six horses with muscle atrophy (Figure 1) had a longer duration of lameness (at least several weeks) prior to diagnosis than those without muscle atrophy. In all cases the gluteal muscles were affected; in two horses the quadriceps were also involved, and in another two the biceps femoris. Four (33%) horses presented with luxation of the left coxofemoral joint, and six (50%) with luxation of the right. In two cases, the side of the luxation was not specified. None of the horses exhibited bilateral involvement. 19 Figure 1. Photograph of Horse 4: Showing outward rotation of the right hindlimb and severe atrophy of the gluteal and biceps femoris muscles. Soft tissue swelling over the coxofemoral joint was observed in only two horses, both were acute cases. One was associated with traumatic recovery, while the other followed an unspecified incident in a field. 20 Crepitus was present in the majority of cases: five horses exhibited both audible and palpable crepitus, two showed only audible crepitus, and one only palpable crepitus. Only one horse showed no pain on palpation or manipulation; three were painful during both, and five experienced pain exclusively on manipulation. Restriction in passive range of motion was recorded in 8/12 horses, only one of these horse had no reduced range of motion. At the time of diagnosis, two acute cases displayed signs of distress. 5.4 Gait evaluation Lameness grades among horses at walk ranged from moderate to non-weightbearing, with the following distribution: 3/8 (n = 1), 5/8 (n = 1), 6/8 (n = 4), 7/8 (n = 4), and 8/8 (n = 2). At the walk, five horses exhibited outward limb rotation, which was also evident while standing. Four horses demonstrated a shortened caudal phase of the stride. Only one horse was able to trot; the severity of lameness increased from grade 5/8 at the walk to grade 6/8 at trot. 5.5 Diagnostic imaging Diagnosis was confirmed using ultrasound and/or radiography in all cases (Figures 2 and 3). Ultrasonography was used in 58% (7/12), radiography in 75% (9/12) of cases. Computed tomography and scintigraphy were both used in one case each, as complementary tool for the diagnosis. Of the twelve horses, two were diagnosed with subluxation of the coxofemoral joint. The remaining cases had complete luxation of the coxofemoral joint, with an additional diagnosis including acetabular rim fractures (3/12), femoral head fracture (1/12) and coxofemoral joint dysplasia (1/12). In 66% (8/12) of cases, the presence of a pelvic fracture could neither be confirmed nor excluded. In 41% (5/12) of cases, imaging alone was sufficient to confirm the diagnosis, whereas in 59% (7/12) the diagnosis was established through a combination of clinical signs and imaging findings. No cases were confirmed on the basis of clinical signs alone. In acute cases, diagnostic imaging revealed cranio-dorsal luxation (6/12); in one horse associated with acetabular rim fractures. In the six horses with a longer duration of lameness, additional pathologies, including synovitis and osteoarthritis were diagnosed. 21 Figure 2. Photograph of Horse 2 undergoing radiographic examination of the right coxofemoral joint (lateral oblique projection). Outward rotation and proximal displacement of the tuber calcanei are visible on the right hindlimb. Figure 3. Lateral dorsal - lateral ventral radiographs of luxated (a) and contralateral healthy (b) coxofemoral joints of Horse 2. (a) The head of the femur is displaced craniodorsally (arrow). 22 5.6 Treatment and outcome Treatment was attempted in 50% (6/12) of cases. Of these, 50% (3/6) underwent closed reduction, 33% (2/6) received pharmacological therapy, and 16% (1/6) were managed conservatively without medication. Pharmacological therapy included either non-steroidal anti-inflammatory therapy combined with stall confinement, or intra-articular administration of a corticosteroid and an aminoglycoside antimicrobial. The conservative approach consisted of box rest and restricted exercise. Seven horses (59%) were euthanised. Among these horses, five were euthanized immediately, one after a year and a half due to progressive worsening of clinical signs, and another three years post-diagnosis. One horse was retired and four were lost to follow up. 5.7 Post-mortem examination Post-mortem examination was performed in 4/7 horses that had been euthanised. In all, the diagnosis of coxofemoral joint luxation was confirmed. For two of them the expected diagnosis seen upon clinical signs were confirmed. Further pathology was diagnosed in two others. In one case, the horse had been lame for approximately four months prior to presentation, consistent with the chronic pathological changes observed post-mortem. Examination revealed severe osteoarthrosis and pseudoarthrosis of the coxofemoral joint, with the femoral head dorsally displaced and encased in proliferative new bone arising from the dorsal acetabular rim. Extensive remodeling of the femoral head and acetabulum, along with thickening of the joint capsule and fibrinous effusion, reflected a long-standing and unstable luxation. The round ligament was thin, elongated, and frayed, suggesting chronic strain rather than acute rupture. Table 2: Summary of history and clinical findings in horses with coxofemoral joint luxation Lameness grade at walk was assessed on a scale from 0 (sound) to 8 (non-weight bearing) [32]. History of undiagnosed lameness in the affected limb Duration/ onset of the lameness Outward rotation of the affected limb More proximal location of the tuber calcanei of the affected limb Muscle atrophy of hindquarters of the affected limb (severity) Lameness grade at walk (0 to 8) Description of the gate at walk Horse 1 No 2.5 weeks No No Moderate 3 23 Horse 2 No Few hours Yes Yes None 7 Stifle rotated outwards, needs support when walking. Horse 3 No Several days Yes Yes None 7 Drifting to the left, limb rotated outwards, shortened caudal phase Horse 4 No 3 months Yes Yes Severe 7 Instability on weightbearing Horse 5 Yes 6 months, insidious onset, progressive deterioration No No Moderate 6 Shortened caudal phase, mild abduction during protraction. Horse 6 Yes ~4 months Yes Unknown Unknown 5 Left hip lower than right hip and he holds the left hind leg toed out when standing or walking. Horse 7 Yes ~18 months No Unknown Severe 6 Horse 8 Yes 48 months Yes Yes Moderate 6 Horse 9 Yes 4 months to first presentation and diagnosis. Followed up by ~1.5 before euthanasia Unknown Unknown Severe 7 Severe grade 4/5 lameness at the walk with aubdible crepitus. Horse 10 Yes 2 days Yes Yes None 8 Stiff limb flight; foot rotated outwards; shortened caudal phase of step. Horse 11 No 1 day Yes Yes None 8 Stiff limb flight; foot rotated outwards; 24 6 Discussion This is the first study providing detailed description of the clinical presentation in full-sized horses with coxofemoral luxation. Information on 12 horses is presented, which makes it the largest case series on coxofemoral joint luxation in horses. Previously, a series on 17 cases had been reported, but 10 of these were ponies, miniature horse, or less than a year old [13]. The population was heterogenous regarding the sports discipline and recent exercise history. Most horses exhibited a body condition score (4-7/9) with half (6/12) of the population having a 5/9, in that instance no link can be made regarding weight being a predisposing factor to coxofemoral luxation. The relatively large proportion of geldings (41%) is likely not due to biological causes; the sample size is not large enough to draw conclusions. It is interesting that 3/12 horses were Friesians, which is a larger percentage than the typical presentation of this breed in the general riding or sports horse population presented to any of the contributing hospitals. Friesian horses are known to have multiple predispositions to developmental abnormalities, including coxofemoral dysplasia which can facilitate the luxation of the coxofemoral joint [11]. In one of the horses from this study, computed tomography confirmed coxofemoral joint dysplasia. Another Friesian had a postmortem examination performed, which did not confirm any signs degenerative or developmental diseases. In the third Friesian horse in the study no postmortem nor CT examination were performed to rule out potential underlying disease. shortened caudal phase of step. Horse 12 No Acute - same day Yes Yes None 6 Toe touching with outward rotation of the limb - no positive response to flexion tests. 25 All but one horses that had suffered from an undiagnosed prior lameness on the affected limb, presented with a long duration of lameness, up to four years. Three of these horses also exhibited deterioration of their condition which triggered their diagnosis. This suggests that chronic or low-grade lameness, particularly when the cause remains unidentified, may mask an underlying luxation or subluxation that evolves over time. This slow evolution of the pathology may allow the horse to adapt, often delaying recognition until a marked decline in clinical status occurs. One horse that had a history of undiagnosed lameness but presented with an acute onset of lameness developed coxofemoral luxation following a traumatic incident during recovery. It is therefore unlikely that the previous lameness was related to the luxation. A post-mortem examination was performed on this horse, revealing no evidence of pre-existing changes in the coxofemoral joint. One horse from the subacute group was diagnosed a few weeks after the onset of lameness and exhibited moderate lameness at walk (3/8), which was less severe than seen in most other horses (5–8/8). This horse became lame after bucking and showed moderate gluteal atrophy. The two-week duration of lameness likely explains the development of atrophy. It is possible that the joint had only been subluxated, explaining the milder lameness than in horses with complete luxation. The distinction between the clinical presentations of coxofemoral luxation and subluxation remains unclear, as no comparative studies have been published. The duration of lameness ranged from a few hours to several years, this indicates that coxofemoral joint luxation does not always present as an acute, severe lameness after traumatic incident, as seen mostly in the literature [7]. Moderate or gradually developing cases also occur, and diagnosis appeared more straightforward in acute cases, whereas pre- existing or unresolved lameness on the affected limb can make the diagnosis more challenging. 26 Only one case was associated with a clear traumatic incident at recovery from general anaesthesia, which contrasts with reports in the literature where cases secondary to trauma are considered as the main cause [8]. Episodes arising from routine activity appear to be more common than those associated with overt trauma. Almost half of the cohort presented lame after routine activities such as bucking, landing from a jump or playing, which suggest that coxofemoral luxation may occur more frequently than currently recognized. These cases likely reflect an underlying predisposition or preexisting weakness in the joint rather than the result of major trauma. Clinical signs, other than lameness, presented by the horses were not always overt. An outward rotation and shortening of the affected limb have been described as pathognomic clinical signs in literature [7]. In our study, more than half of the cohort (7/12) presented the pathognomic signs. Even if most horses presented these signs which could lead to a quicker diagnosis, it was in the cases posing a diagnostic challenge with longer duration of lameness that the rotation and shortening of the limb could not be detected. Subacute (2/2) and chronic (4/5) groups of duration of lameness also suffered from muscle atrophy from moderate to severe, affecting several different muscle groups (quadriceps and biceps femoris) but always including the gluteal muscles. Only two horses with pathognomic signs exhibited muscle atrophy as well, one involving the gluteal and biceps femoris muscles, and the other affecting the gluteal and quadriceps muscles, suggesting that the presence of one does not always mean the absence of the other. Also, there appears to be no clear relationship between the clinical history or other presenting signs and the selective involvement of specific muscle groups in atrophy, however it is clear that gluteal muscles are always involved as they are major actors in the coxofemoral joint movement. Upward fixation of the patella is the only clinical sign described in ponies that has not been reported in horses with coxofemoral luxation or subluxation [33]. In our study, this finding was confirmed, as none of the horses had concurrent upward fixation of the patella, suggesting a size-related predisposition. The duration of lameness before diagnosis in horses presenting muscle atrophy was of at least a few weeks. Muscle atrophy is an indicator of a lack of utilization which is usually due to pain [7, 32]. However, this process takes time (over weeks) and can only be a clinical sign seen during chronic and subacute process rather than acute. 27 Audible and palpable crepitus were noticed in most but not all cases. Whilst crepitus itself in a joint is not sufficient for a diagnosis, it can be an indicator of change in the joint positioning arising from bones moving against each other. The majority of horses exhibited pain during palpation or manipulation. Pain response to manipulation of the limb would be expected; however, one horse exhibited no pain upon manipulation and palpation of the limb. It was noted that the horse was in distress, this lack of response is thought to be linked with severe pain. One horse presented with an abnormal bony projection between tuber ischia and tuber coxae, this additional clinical sign was not described by any other case. This horse also exhibited other clinical signs: audible crepitus, severe gluteal atrophy and painful manipulation of the limb. Crepitus and pain on palpation or manipulation, while not sufficient for a definitive diagnosis, can serve as important clinical indicators of coxofemoral luxation. Interestingly, these signs were observed more frequently than the classic pathognomonic features, with an equal number of horses also exhibiting muscle atrophy. Moreover, they were present across all categories of lameness onset, acute, subacute, and chronic suggesting that their occurrence is not limited to a specific stage of the condition. As expected from the literature, most horses presented with a gait characterised by an outward rotated limb, however only a few with a shortened caudal phase of the stride and a stiff limb. One horse presented with an inward rotation of the toe upon weight placement, which is the opposite of the typical outward rotation described in all other cases and has not been previously reported in the literature. The only notable different abnormality identified in this horse, compared with the others (also seen in one other horse), was modeling of the femoral head. This finding may suggest that chronic modeling or altered joint conformation could modify the biomechanics of the limb, leading to atypical gait patterns. It also highlights that variations in joint pathology can influence how coxofemoral luxation manifests clinically, and that not all cases follow the classical outward rotation presentation. Only one horse could be trotted for lameness assessment, which was graded as 6/8. In contrast, some horses were unable to walk without assistance. No other study reports of a horse being able to have a lameness assessment performed at the trot. The gait evaluation performed in this study confirmed that most affected horses presented with severe, sometimes even non–weight-bearing lameness. 28 As reported in the literature [10, 25], ultrasonography and radiography proved to be valuable diagnostic tools. The limited use of scintigraphy may reflect restricted access and its relative impracticality for rapid diagnosis. Similarly, computed tomography was only used once, in horses with chronic, progressive hindlimb lameness to investigate any potential underlying pathology. In acute cases, diagnostic imaging readily revealed craniodorsal luxation; additional articular pathologies were seen in subacute and chronic changes. These additional changes should be expected in horses suffering from lameness lasting for a prolonged period of time prior to diagnosis of coxofemoral joint luxation [8, 20]. Pelvic fractures are commonly described in association with coxofemoral luxation [8, 23, 26]. The joint is well secured within the acetabulum, a fracture of the acetabular rim compromising the stability of the joint is often a predisposing factor for luxation [10]. In the present study, a pelvic fracture was confirmed in one third of the horses, the presence of a fracture was excluded by postmortem examination in only one case. In the horse, where coxofemoral joint dysplasia was diagnosed, a pelvic fracture was definitively excluded using computed tomography. Pelvic fracture seems to be an additional finding along coxofemoral joint luxation, if not found it is rare for veterinarians to exclude it once luxation has been confirmed. This is due to the poor prognosis of a coxofemoral luxation diagnosis, the presence or absence of a concurrent pelvic fracture in adult horses would not change the overall prognosis, which is already grave. However, an acute fracture may necessitate prompt euthanasia due to even more severe pain and distress. In this cases series, diagnosis of coxofemoral luxation was never based solely on clinical signs; confirmation was most commonly achieved through a combination of clinical examination and diagnostic imaging. In five cases, luxation could only be identified using diagnostic imaging, and four of these lacked the pathognomonic signs of outward limb rotation and limb shortening. 29 With regards to the outcome, almost all cases experienced a negative outcome, indicating a generally poor prognosis. Only one horse was retired, and more than half of the cohort euthanised. A third of the cohort was lost at follow up, it is assumed that the horses were euthanized as their grade of lameness would not allow them to live comfortably. Regarding the retired horse, because it presented with a moderate lameness at the walk, this horse was more comfortable than all the others and therefore it was possible to avoid euthanasia, of course prognosis for any athletic activity was hopeless. In this case, welfare considerations remain significant, as the horse continued to be lame at a walk, demonstrating a very poor quality of life. Postmortem examination was performed in four horses. Findings indicated progressive degenerative and adaptive changes that can occur in chronic coxofemoral luxation and highlight the difficulty of achieving an early diagnosis in such cases. In the case with an acute onset, the short duration of the lameness corresponded with the traumatic nature lesions observed post-mortem. Examination revealed complete rupture of the ligamentum capitis femoris, comminution of the acetabulum, and extensive soft tissue trauma findings consistent with a high-impact, acute injury leading to coxofemoral luxation. The extent of structural damage supports the traumatic origin and explains the severity of clinical signs and poor prognosis associated with such cases. Comparing the two cases, one with a chronic lameness and the other with an acute onset. In the chronic case, post-mortem findings reflected gradual degenerative changes that could have led to coxofemoral luxation, with anatomical adaptations allowing the horse to function for four months before diagnosis and 1.5 years before euthanasia. In contrast, the acute case showed no secondary changes, and rupture of the ligamentum capitis femoris prevented any compensatory adaptation of the anatomy. This study was limited by the small number of cases fitting the criteria, which restricts the generalizability of the findings. Signalment, history, and lameness grades were assessed by multiple veterinarians, and not all clinicians evaluated the same set of clinical signs, resulting in some data being recorded as “unknown.” Detailed gait descriptions were not consistently documented according to a standardized protocol, and pelvic fractures were not ruled out in all cases. Finally, post-mortem examinations, which could have provided valuable insights into anatomical changes and their correlation with clinical history, was not performed in all 30 euthanized horses. These limitations reflect the nature of retrospective clinical case series and highlight the importance of standardized, systematic assessment and clinical record keeping. To conclude, coxofemoral luxation was rarely linked to an obvious traumatic event, and the onset of lameness ranged from just a few hours to several months. Coxofemoral luxation may occur under a broader range of circumstances than previously recognized. The seemingly high representation of the Friesian breed deserves more attention and requires further investigation. Common clinical signs included outward limb rotation, a proximal position of the tuber calcanei, and muscle atrophy affecting the gluteal, biceps femoris, and quadriceps muscles. The absence of certain signs, such as outward rotation or a proximal position of the tuber calcanei in some chronic cases is also noteworthy. This could reflect the horse’s ability to adapt over time or perhaps a slow progression from a subluxation to a full luxation. Future studies comparing the clinical signs with each horse’s history could help clarify these patterns. 7 Summary Coxofemoral joint luxation is uncommon in horses and the limited literature on clinical findings make diagnosis challenging. Most publications focus on ponies; minimal information is available on full-sized horses. The aim of the study was to aid recognition of coxofemoral luxation in horses, by providing detailed description of history, clinical presentation and gait patterns in cases with confirmed diagnosis (by diagnostic imaging and/or postmortem examination) of coxofemoral luxation. Data were collected through a structured questionnaire distributed to veterinarians who had diagnosed coxofemoral luxation. Data included details on signalment, history, clinical examination, gait assessment, diagnostic imaging, outcome and postmortem evaluation. Descriptive data analysis was performed. Twelve cases with sufficient information were included in the study. Five horses presented with chronic lameness of ≥ 4 months’ – 4 years’ duration (mean 16 months). Subacute presentation consisted of two horses, ranging from 1 week to 3 months (mean 7 weeks). Five horses presented within a few hours to a few days after the onset of the lameness. One horse developed luxation during a traumatic recovery 31 from general anaesthesia. Five horses presented lame after routine activities such as bucking or jumping, and for six horses no events were noted. Atrophy of the gluteal, biceps and quadriceps muscles on the affected side was observed in six horses, all had subacute or chronic lameness. Soft tissue swelling over the coxofemoral region was noted in two cases with an acute onset of lameness. Eight horses exhibited outward rotation of the affected limb, proximal position of the tuber calcanei compared to the contralateral limb, and reduced range of passive motion of the coxofemoral joint. Six of these eight horses also exhibited a shortened caudal phase of the stride. Palpable and/or audible crepitus was detected in eight horses. Horses with acute and subacute onset of lameness showed severe to non-weight bearing lameness (7-8/8), while in horses with chronic lameness severity varied between 3- 7/8. Diagnosis was confirmed using ultrasound and/or radiography in all cases. Seven horses were euthanized due to hopeless prognosis, one was retired and four were lost to follow-up. Post-mortem examination was performed in four horses. 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Equine Vet J 15:371–372. https://doi.org/10.1111/j.2042-3306.1983.tb01826.x 32. Dyson S (2011) Can lameness be graded reliably?: Can lameness be graded reliably? Equine Vet J 43:379–382. https://doi.org/10.1111/j.2042-3306.2011.00391.x 33. Sprick M, Koch C (2020) Successful Treatment of a Coxofemoral Luxation in a Shetland Pony by Closed Reduction and Prolonged Immobilization Using a Full-Body Animal Rescue Sling. Case Rep Vet Med 2020:1–5. https://doi.org/10.1155/2020/2424653 34 9 Acknowledgements I would like to thank my supervisor, Dr. Nagy Annamária, for her guidance and support throughout this research. I am grateful to the clinicians and staff who provided cases for this study: Dr. Whitcomb and Dr. Pige at UC Davis Veterinary Hospital, Dr. Sue Dyson at the Animal Health Trust, United Kingdom, Dr. Ehrle at the Equine Clinic of the Freie Universität Berlin, and the teams at the Equine Clinics of the University of Veterinary Medicine Budapest and the University of Bristol.