EQUINE VETERINARY EDUCATION / AE / November 2010 547 Case Reporteve_118 547..553 Total hip arthroplasty in the horse: Overview, technical considerations and case report N. Huggons*, R. Andrea†, B. Grant‡ and C. Duncan§ WR Pritchard Veterinary Medical Teaching Hospital, University of California Davis; †Chaparral Veterinary Medical Center, Arizona; ‡31624 Wrightwood, California, USA; §Gordon & Leslie Diamond Health Care Centre, Vancouver, Canada. Keywords: horse; total hip arthroplasty; hip replacement; coxofemoral joint; acetabulum Summary Hance 1998; Loesch et al. 2003; Smith et al. 2004), disruption of intra-articular ligaments (Trotter et al. 1986; A total hip arthroplasty was performed in a small Nixon 1994), fractures (Turner et al. 1979; Embertson equine patient with a history of traumatic subluxation of et al. 1986; Hunt et al. 1990a) and dysplasia (Jogi and the coxofemoral joint during infancy resulting in severe Norberg 1962; Speirs and Wrigley 1979) have also been degenerative changes to the femoral head and described. acetabulum. The transtrochanteric surgical approach Few treatment options exist for hip disease, with used to expose the joint, as well as the technique and limitations primarily due to the large muscle mass technology to replace the joint, is described. The patient covering the joint, difficulty with surgical access to the was weightbearing within 24 h of surgery and walking joint and implant failure associated with post operative successfully without sling support 4 days post operatively. weightbearing. Surgical fixation of femoral capital On the fifth post operative day, the patient abruptly epiphyseal fractures in foals has included excision deteriorated and succumbed to multiple pulmonary arthroplasty, Steinmann or Knowles pin fixation, multiple thromboemboli and a jejunal infarction. Despite the intramedullary pins, femoral head ostectomy and an systemic complications in this case, the initial short-term interfragmentary compression system (Hunt et al. success of this treatment option indicate its potential to be 1990a,b; Squire et al. 1991). Conservative therapy considered in the management of equine coxofemoral carries a poor to guarded prognosis (Hunt et al. 1990a). joint disease/lesions. Closed reduction under general anaesthesia is indicated in acute cases of coxofemoral luxation Introduction (Clegg and Comerford 2007) and closed reduction in combination with an Ehmer sling has resulted in short-term success in a miniature pony (Clegg and Coxofemoral disease in the equine species is infrequently Butson 1996). Chronic coxofemoral luxation has been reported and rarely a primary source of pain causing treated with open reduction and a variety of surgical lameness (Hendrickson 2002; Dyson 2003). Diagnosis is stabilisation techniques. Excision arthroplasty of the based on physical examination, ultrasound and/or femoral head, joint capsule imbrication, open surgical radiographs of the coxofemoral region. Various aetiologies reduction, transarticular Steinmann pin, an ischio-ilial of coxofemoral disease have been reported including (DeVita) pin, total hip arthroplasty and toggle-pin coxofemoral luxation (Rothenbacher and Hokanson technique with capsullorrhaphy have all been reported 1965; Nyack et al. 1982; Field et al. 1992; Malark et al. 1992; with variable success rates (Trotter et al. 1986; Platt et al. Clegg and Butson 1996; Garcia-Lopez et al. 2001; Portier 1990; Malark et al. 1992; Garcia-Lopez et al. 2001; Toth and Walsh 2006), acetabular osteochondrosis dissecans et al. 2007). (Rose et al. 1981; Miller and Todhunter 1987; Nixon 1994), In human hip disease, total hip arthroplasty (THA) has femoral head osteochondrosis (Nixon et al. 1988; Nixon become one of the most effective and reliable surgical 1994) and degenerative joint disease (Trent and Krook interventions for improving quality of life. It has been 1985; Lamb and Morris 1987; Nixon 1994; Clegg and Butson found to provide considerable improvement in functional 1996). Pathologies such as septic arthritis (Clegg 1995; mobility and range of motion and permanently relieves *Corresponding author email: [email protected] pain in the majority of patients (Roder et al. 2003). The © 2010 EVJ Ltd 548 EQUINE VETERINARY EDUCATION / AE / November 2010 success in man has resulted in total hip arthroplasty being a routinely performed treatment measure in small animal orthopaedics (Cook 2007). To date, there are only 3 reports of THA for use in large animals. Two successful case reports of total hip replacements in alpacas have been recently published (Ortved et al. 2009; Schulz et al. 2009). In the horse, a single case is reported in the literature and was performed in a 9-year-old miniature horse with early complications due to implant failure following discharge from the hospital (Malark et al. 1992). Recum et al. (1980) reported the results of experimental coxofemoral hemiarthroplasty in 7 ponies, concluding that coxofemoral surgery can be performed in the adult pony and a total artificial hip joint may provide better results than a partial hip replacement. The purpose of this paper is to describe the transtrochanteric surgical technique employed to fit a small equid with a total hip arthroplasty, along with the post operative management and outcome of a single case. Clinical report An 8-week-old Dwarf Friesian filly presented with a history of trauma at age 6 weeks sustained by falling into a hole at pasture. At that time, a severe left hindlimb lameness (grade 4/5) was present. Diagnostic work-up localised the injury to the pelvic region. Neutral and stressed Fig 1: Ventral-dorsal radiographs including a neutral view on the left (a) and a stressed view on the right with the left hip subluxated radiographic views were obtained, demonstrating left (b). coxofemoral subluxation (Fig 1). Diagnostic arthroscopy of the left coxofemoral joint was performed and showed rupture of the round ligament. Conservative treatment was attempted and the patient re-presented with difficulty weightbearing of 3 months’ duration. Examination of the limb revealed muscle atrophy around the hip and proximal displacement of the greater trochanter. A ventral-dorsal radiograph revealed subluxation of the left coxofemoral joint, flattening and excessive anteversion of the femoral head, and severe degenerative changes to the acetabulum and femoral head (Fig 2). The diagnosis was traumatic coxofemoral subluxation at infancy with secondary femoral head flattening and severe osteoarthritis. Arthrocentesis and laboratory evaluation ruled out infection. The foal was again managed conservatively with stall rest for a period of 4 months. During this time the left hindlimb suffered severe disuse atrophy Fig 2: Ventral-dorsal radiograph 4 months after Figure 1 and the foal developed external rotation demonstrating a normal right hip joint, while on the left there is of the left hindlimb with intermittent weightbearing on subluxation of the coxofemoral joint, severe degenerative the dorsum of the fetlock. The patient also displayed a changes to the acetabulum and femoral head, excessive femoral number of congenital abnormalities, including phenotypic neck anteversion and a flattened femoral head. dwarfism, scoliosis and a heart murmur. The long-term prognosis for this foal was considered to be guarded due Preoperative planning for a total hip arthroplasty to the chronic duration and associated degenerative included consulting with a human orthopaedic specialist changes to the left hindlimb. (C.D.). Measurements of the opposite normal Case management included analgesics and anti- coxofemoral size suggested that total hip replacement inflammatory medication in addition to sling training would be feasible, using components similar in size and (Anderson Pony Sling)1, while the surgical choices were shape to those used in man, but at the larger end of considered. the scale. © 2010 EVJ Ltd EQUINE VETERINARY EDUCATION / AE / November 2010 549 Surgical technique A 14 gauge catheter was placed in the left jugular vein and ceftiofur (2.2 mg/kg bwt i.v.), amikacin (6.6 mg/kg bwt i.v.) and phenylbutazone (1.1 mg/kg bwt i.v.) were administered. The patient was premedicated with xylazine (0.5 mg/kg bwt i.v.) and induced with diazepam (0.1 mg/kg bwt i.v.) and ketamine (2.2 mg/kg bwt i.v.). Anaesthesia was maintained with isoflurane in oxygen delivered by a semiclosed rebreathing circuit. The foal was placed in right lateral recumbency with the left limb suspended in partial extension. The hair was clipped and proximal limb and hip aseptically prepared. An antimicrobial surgical incise drape (Ioban)2 was placed over the proposed surgical site, centred over the greater trochanter. An impervious sterile abdominal drape (Steri-Drape)2 was placed over the left hindlimb centred over the greater trochanter and the remaining areas covered with sterile half drapes (Steri-Drape). A 25 cm curvilinear skin incision was made, centred Fig 3: Intraoperative image demonstrating the reflected greater trochanter (white arrow) and attached gluteal muscles on the right, over the greater trochanter, extending 10 cm proximally the wide surgical exposure that this afforded and the implanted towards dorsal midline and 15 cm distally towards acetabular shell (black arrow) within the newly reamed acetabular mid-diaphysis of the femur. A combination of sharp and cavity in the centre. The asterisk is located over the caudal pelvis blunt dissection was used along the cranial border of and semitendinosus musculature.