Femoral head ostectomy and medial patellar ligament desmotomy to treat a pregnant miniature horse with coxofemoral joint luxation and upward fixation of the patella

Abstract

A 2-year-old, 8-weeks pregnant, non-weight bearing miniature horse mare was treated for a 6-day-old left coxofemoral joint luxation with a femoral head ostectomy. The procedure had no negative effects on pregnancy or parturition and 23 months following surgery the horse had minimal lameness.

Case description

A 2-year-old, 113 kg, miniature horse mare that was approximately 8 wk pregnant was referred to the large animal hospital at the Virginia-Maryland College of Veterinary Medicine (VMCVM) Veterinary Teaching Hospital (VTH) because of non-weight bearing left hind limb lameness. The owners found the mare non-weight bearing on that limb in a paddock 6 d before presentation at the VMCVM hospital. Initially, the mare had been admitted to another large animal hospital, where the horse was diagnosed with a luxated left coxofemoral joint. Four days before the mare arrived at the VMCVM hospital, 5 unsuccessful attempts at closed reduction of the left coxofemoral joint under general anesthesia had been performed at the other large animal hospital. The mare’s lameness did not improve following attempted closed reduction of the coxofemoral joint, and the owners elected to bring the horse to the VMCVM hospital for further assessment.

Physical examination at the time of arrival at the VMCVM VTH revealed that the mare had a non-weight bearing lameness of the left hind limb with upward fixation of the patella in that limb. The mare would not place the foot down when ambulating, and would toe-touch when non-ambulatory. The mechanical lameness caused by the upward fixation of the patella made assignment of the lameness grade difficult, but it was estimated at AAEP grade 4/5 (1). The left hind limb was rotated externally and there was moderate edematous swelling of the hock and mild distal limb edema. The cause of the moderate limb swelling was unknown, but could have been attributed to prior limb manipulation or dependent edema secondary to the coxofemoral joint luxation. The right and left hip joint regions were asymmetric in appearance and the greater trochanter of the left femur was displaced proximally (as determined via palpation). No crepitus was palpated when the left coxofemoral joint was manipulated. The remainder of the physical examination was unremarkable. A transabdominal ultrasound examination revealed no abnormalities of the pregnancy. Standing radiographs of the pelvis (laterolateral and lateral-oblique projections) were obtained with the mare unsedated and a diagnosis of craniodorsal luxation of the left coxofemoral joint was made (Figure 1).

Figure 1.

Perioperative standing lateral-oblique radiograph of a luxated left coxofemoral joint in a 2-year-old female miniature horse. The left femoral head is luxated craniodorsally.

Due to the 6-day duration of the coxofemoral joint luxation and previous failure at closed reduction, the owners elected to have a femoral head ostectomy procedure performed for the mare. Financial limitations of the owners dictated the need for a surgical procedure that could be performed relatively rapidly and did not require extensive follow-up care. Additionally, left medial patellar ligament desmotomy was planned for the correction of upward fixation of the patella. Perioperative and postoperative antimicrobial and anti-inflammatory medications were administered. Potassium penicillin G (Pfizerpen; Pfizer, New York, New York, USA), 22 000 IU/kg body weight (BW), IV, q6h, and gentamicin (Sparhawk Laboratories, Lenexa, Kansas, USA), 6.6 mg/kg BW, IV, q24h were administered for 3 d, followed by sulfamethoxazole-trimethoprim (Aurobindo Pharma USA, Cranbury, New Jersey, USA), 30 mg/kg BW, PO, q12h for 14 d. Phenylbutazone liquid (MWI/VetOne, Boise, Idaho, USA), 4.4 mg/kg BW, IV, q12h was also administered for 5 d, then phenylbutazone 1-g tablets (First Priority, Elgin, Illinois, USA), 2.2 mg/kg BW, PO, q12h for 5 d.

After sedation with acepromazine (MWI/VetOne), 0.02 mg/kg BW, IV and xylazine (MWI/VetOne), 0.5 mg/kg BW, IV, general anesthesia was induced with tiletamine/zolazapam (Telazol; Zoetis, Exton, Pennsylvania, USA), 2.0 mg/kg BW, IV and propofol (Zoetis), 0.4 mg/kg BW, IV, and maintained with balanced inhalation anesthesia using isoflurane (Isoflo; Zoetis) in oxygen in a semiclosed circle system. The mare was positioned in right lateral recumbency and the surgical sites were clipped, aseptically prepared, and surgically draped.

The left medial patellar ligament desmotomy was performed first, as previously described (2). Following the left medial patellar ligament desmotomy, the left femoral head ostectomy was performed by use of a craniolateral approach to the coxofemoral joint. A 30-cm curvilinear skin incision was made over the craniolateral aspect of the left coxofemoral joint, extending over the cranial aspect of the greater trochanter and continuing parallel to the long axis of the femur. The superficial gluteal muscle over the greater trochanter was incised and retracted caudodorsally. The tensor fascia latae and vastus lateralis muscle were separated via blunt and sharp dissection and retracted caudally. The caudal part of the greater trochanter was palpated and used as a guide for the approach to the femoral head in its craniodorsally displaced location. The middle and deep gluteal muscles were partially transected and retracted cranially and caudally to obtain access to the femoral head. The ilium was palpated axial to the head of the femur. Hohmann bone elevators were used to rotate and elevate the femoral head from the surrounding tissue. Femoral head ostectomy was performed using an oscillating bone saw to establish a cutting plane along the neck of the femoral head, and an osteotome was used to complete the femoral head transection. The transected surface of the femur was smoothed with a bone rasp and the surgical site was copiously lavaged with sterile saline (0.9% NaCl) solution. No. 0 polygalactin 910 (Vicryl; Ethicon, Somerville, New Jersey, USA) was used to close the muscle layers in an interrupted cruciate pattern. The subcutaneous tissue was closed using No. 0 polygalactin 910 in a simple continuous pattern. The skin was closed using No. 2-0 polypropylene suture (Prolene; Ethicon, San Lorenzo, Puerto Rico) in an interrupted cruciate pattern. A stent bandage was applied over the closed incision. Total surgical time was 135 min. The horse’s recovery from anesthesia was hand-assisted and without complications. Immediately following recovery, the horse received a dose of butorphanol (Turbogesic; Zoetis), 0.04 mg/kg BW, IM, once. The mare bore full weight on the left hind limb and ambulated with minimal discomfort.

The mare was hospitalized for 4 d following surgery, during which time she seemed comfortable and was able to bear full weight on the left hind limb. The stent bandage was removed 3 d after surgery, and the incision appeared to be healing appropriately. The mare walked with a moderate lameness (AAEP grade 4/5) (1) that gradually improved during hospitalization. Transrectal ultrasonography was performed prior to the mare’s discharge from the hospital; a moving fetus was visualized and a fetal heartbeat was detected. Due to the owners’ financial limitations, post-operative radiographs were not taken. At the time of discharge the mare weighed 116 kg.

Clinicians recommended to the owners that they house the mare in a small paddock for a minimum of 2 mo, allowing the mare to ambulate in a quiet environment. The mare was rechecked by the referring veterinarian and the skin sutures were removed 14 d after surgery. Passive range of motion exercises of the left hind limb were performed by the owners for 10 min several times each day.

The mare returned to the VMCVM VTH 10 wk after surgery for examination of the fetus and assessment of surgical site healing. The mare was housed in a pasture at this time and the owners were continuing left hind limb passive range of motion exercises. The owners reported that the patient was fully weight bearing on the affected limb and seemed comfortable, but they had not observed the horse to lie down. The mare had a moderate hip hike when ambulating (AAEP lameness grade 4/5) (1) and a shorter stride of the left hind limb compared with the right hind stride. The left hind limb seemed to be mildly shorter than the right hind limb and there was moderate muscle atrophy of the left gluteal muscles. The surgical sites had healed appropriately without complications. Transabdominal ultrasonography was performed and a viable fetus with a heartbeat was detected.

Approximately 6 mo after surgery, the mare was re-evaluated at the VMCVM hospital. At that time, the mare weighed 121 kg and was housed in a stall at night and on pasture during the day. The horse was reported to ambulate with ease, but still had not been observed to lie down. The owners continued to perform passive range of motion exercises of the affected limb. The left hind limb remained slightly shorter than the right hind limb. Lameness examination at the walk revealed a mild hip hike of the left hind limb and shorter stride compared with the right hind limb, which was improved from the previous assessment. A hoof pad was conformed to the shape of the horse’s left hind hoof and applied to the sole with elastic tape to elevate the limb to the same height as the right hind. Following application of the hoof pad, the mare immediately walked with a longer left hind stride, matching the stride length of the right hind limb. The owners were advised to continue with the passive range of motion exercises and keep the left hind hoof pad in place.

Follow-up telephone communication with the owners was regularly obtained weekly and multiple visits of one author (EKL) were performed to the horse’s farm. The mare’s comfort improved dramatically following the application of the left hind hoof pad. The horse was noted to trot in the pasture, and get up and down from recumbency with ease. Nine months after surgery, the mare successfully foaled, after which the left hind hoof pad was no longer applied and passive range of motion exercises were discontinued. Immediately post-parturition, the mare became substantially more active in the pasture, trotting and cantering with minimal lameness (Figure 2). The mare was successfully re-bred via live cover and foaled with no complications. Lameness examination performed by one author (EKL) 17 mo after surgery revealed the mare’s hind limbs to be similar lengths, with the left hind limb very mildly shorter than the right hind limb, and there was no atrophy of muscles of the left hind limb. There was minimal lameness (AAEP grade 1/5) (1) observed at the walk, trot, and canter, and the left hind limb flexed and extended normally. At the time of most recent follow-up, 23 mo following surgery, the owners were extremely satisfied with the mare’s comfort level and minimal lameness.

Figure 2.

Photograph of the mare trotting with her foal 10 months after surgery.

Discussion

We treated a coxofemoral joint luxation in a large, pregnant miniature horse with a femoral head ostectomy. The mare recovered from the procedure with relative ease, successfully foaled, and has remained comfortable with minimal lameness after surgery. Coxofemoral joint luxation is an uncommon injury in horses (3–7). The heavy musculature, round ligament, and accessory ligament of the femoral head, and transverse acetabular ligament that surrounds the acetabulum provide strength and stability to the hip (3,5,7–9). Equine coxofemoral joint luxations, therefore, are frequently caused by a traumatic event, such as a kick or fall (3–8,10–12). Coxofemoral joint luxation is typically unilateral with the femoral head oriented craniodorsal to the acetabulum; foals, ponies, and miniature horses are most commonly reported (4,5,7,8,12). In full sized horses, however, the ileum is more likely to fracture than the coxofemoral joint luxating as a result of trauma (6). Additionally, coxofemoral luxations can occur during recovery from anesthesia, due to a hind limb cast or previous injury, or secondary to upward fixation of the patella (5–7,13–15). Some authors have speculated that upward fixation of the patella can cause a strong contraction of the quadriceps femoris muscle as the horse attempts to flex the locked stifle, resulting in coxofemoral joint luxation (3,6,9,16). Alternatively, a luxated coxofemoral joint may cause external rotation of the hind limb: the rectus femoris muscle is unable to release the patella and the mechanics of the femoropatellar joint are altered, resulting in upward fixation of the patella (5,7,9,11). The inciting cause of coxofemoral joint luxation in the horse of this report was unknown, as the mare was found lame in the paddock. After the horse was diagnosed with the luxation and the upward fixation of the patella, the owners reported the mare might have had previous episodes of a locked left stifle. Therefore, it is possible that upward fixation of the patella may have resulted in the coxofemoral joint luxation in this mare. Alternatively, the mare could have suffered an unseen trauma which resulted in the coxofemoral joint luxation.

Horses affected with coxofemoral joint luxation have severe lameness, with the affected limb rotated externally (the toe and stifle point away from the horse) (3,6–11). The pelvis may appear asymmetric and the affected limb may be shorter than the contralateral limb (8,10,16). The shortened limb length can result in a decreased cranial stride length of the affected limb when ambulating (3,7). Manipulation of the affected hind limb may result in detection of crepitus or signs of pain (3,7,10,16). The mare in this report had external rotation of the left hind limb and asymmetry of the pelvis, but no crepitus when the limb was manipulated. Diagnosis of coxofemoral joint luxation can be made on the basis of patient history, clinical signs, and diagnostic imaging. Radiography can be performed for a standing or anesthetized patient to confirm the diagnosis and rule out other potential injuries (3,9). Ventrodorsal radiographic views of the pelvis are typically obtained for patients during general anesthesia; however, ventrodorsal radiographic views have been obtained in standing animals (9,11,15,17,18). The use of general anesthesia to facilitate radiographic imaging is an added expense, and carries risks associated with anesthetic use and patient recovery (9,19). Laterolateral and lateral-oblique radiographic views performed for standing horses are adequate for diagnostic imaging of coxofemoral joint luxation and were performed on the horse in this report (6,9,16,20,21). Ultrasonography can also be used to diagnose coxofemoral joint luxation and subluxation for standing horses (3,10,18,19).

Treatment options for coxofemoral joint luxations include closed reduction, open reduction, greater trochanter transposition, augmentation of the lateral joint capsule, toggle pinning, total hip arthroplasty, or femoral head ostectomy (3,4,6–8,10,11,15,16,20,22,23). Closed reduction is often not successful or re-luxation can occur quickly (3 8). Failure of closed coxofemoral joint luxation reduction is often attributable to blood clots, granulation tissue, joint capsule, tissue, or ligamentous debris in the acetabulum and the contraction of surrounding musculature (3–5,8,11,21,22). Results of 1 study reported 4 of 5 horses with coxofemoral luxation treated via closed reduction re-luxated (7) and for patients in which closed reduction was successful, osteoarthritis, and persistent lameness developed (6). Greater trochanter osteotomy provides good exposure of the coxofemoral joint and increases ease of manipulation (21,24). Also, a greater trochanter transposition procedure provides further support to the reduced luxation (4). Joint capsule augmentation and toggle pinning have been used successfully in combination or alone in several cases (4,10,11). Total hip arthroplasty has been attempted for 3 patients, but these animals did not survive to hospital discharge (22,23).

Femoral head ostectomy is generally considered to be a salvage procedure for horses with coxofemoral joint luxation (4,8,22,24). During this procedure, the head of the femur is excised; after surgery, a pseudoarthrosis forms that provides pain relief to the horse (15,16,20). Rasping the transected end of the femur smoothes the bone, helping to prevent osteochondral fragmentation and postoperative lameness (16,24). Authors of previous studies have concluded that patient prognosis following femoral head ostectomy is mainly dependent on patient weight, with a favorable prognosis for patients weighing less than 100 kg (21,24,25). In a report on femoral head ostectomies in 9 horses, 6 horses weighed 100 kg or greater (range: 100 to 225 kg) at the time of surgery, and 4 of these 6 horses were euthanized after surgery (24). Overall, the prognosis following treatment of coxofemoral joint luxations is guarded, with 50% or fewer of horses surviving (7,8,10,17,24). If reduction of the femoral head in the acetabulum is maintained, most horses are sound enough for breeding, with a small number of horses returning to complete soundness (3).

The 6-day duration of the coxofemoral joint luxation and failures at closed reduction resulted in the decision to perform femoral head ostectomy for the mare of this report. Our treatment goal was to improve the mare’s comfort to a level that would allow breeding and a high quality of life during pasture activity. This horse was pregnant; to our knowledge, this surgical technique has not been reported for a pregnant mare. Other mares have been reported to successfully foal following femoral head ostectomy, but the surgical procedure was performed for these mares when they were foals (1-week-old, 1-month-old, and 4-months-old), allowing for prolonged postoperative healing prior to maturation, pregnancy, and parturition (17,24). Additionally, this horse weighed 113 kg at the time of surgery, which was heavier than most horses for which femoral head ostectomy procedures had been previously reported, and the mare was gaining weight due to pregnancy (15–17,20,21,24). We were uncertain as to whether the mare in this study would be able to carry a fetus to term, support the additional weight of the foal, and foal successfully following the femoral head ostectomy. The mare was able to foal with no complications, was rebred via live-cover, showing no signs of discomfort from the weight of the stallion during breeding, and was able to foal a second time successfully.

While there are other published reports on successful femoral head ostectomies in equines, few have the detailed follow-up of this report (15–17,20,21,24). The comfort level and lameness for the patient of this report were improved immediately following surgery and continued to improve during the following 23 mo. Previously published reports described a range of post-operative lameness, with the AAEP lameness scale used in only 2 cases, and these cases involved AAEP grades 2/5 and 3/5 (15–17,20,21,24). The mare in this report was AAEP grade 1/5 at the last examination. Left hind limb passive range of motion exercises and the addition of a hoof pad to the left hind hoof may have contributed to the horse’s minimal lameness. The gradual postoperative recovery resulted in the horse having similar hind limb lengths and no obvious atrophy of the left gluteal muscles.

Femoral head ostectomy for the treatment of a chronic coxofemoral joint luxation was successful in this large, pregnant miniature horse, with no negative effects on postoperative parturition and re-breeding. Additionally, the mare was able to return to near-baseline soundness (AAEP grade 1/5 lame), an improvement over previous reports of femoral head ostectomy in horses (1,16,17,21,24). Femoral head ostectomy can result in an excellent outcome for treatment of coxofemoral joint luxations in large miniature horses and ponies. CVJ