Total Hip Arthroplasty in the Horse: Overview, Technical Considerations and Case Report N

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

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.

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. the biceps femoris and caudal border of the superficial gluteal muscle; incising the deep and superficial lamina of the tensor fascia lata muscle distally. The incision underlying pubis to allow unrestricted weightbearing post was deepened using blunt dissection along the cranial operatively. A 36 mm inside diameter polyethylene liner border of the biceps femoris muscle and caudal border was snapped into the shell, of a design that would of the abductor (gluteal) muscles down to the surface constrain or ‘capture’ the femoral head and prevent post of the greater trochanter where the insertion of the operative luxation. middle and accessory gluteal muscles were identified. The femoral canal was prepared with graduated An oblique osteotomy of the greater trochanter was conical reamers until it was judged that sound fixation completed with an oscillating bone saw at 30° to the against endosteal cortical bone could be achieved and long axis of the femur in the sagittal plane while a 24 mm diameter conical titanium stem was inserted preserving the attachments of the middle and deep in neutral varus/valgus alignment, with 20° anteversion. gluteal muscles on the greater trochanter. This was Finally, a 36 mm chrome-cobalt femoral head was elevated and reflected to expose the underlying impacted onto the stem (Fig 4), the hip joint reduced, and redundant capsule of the hip and proximally displaced the constraint-locking ring engaged (Fig 5). Satisfactory femoral head. The femoral head was flattened and joint range of motion and stability were confirmed the femoral neck excessively anteverted, as the before closure was commenced. The greater trochanter radiographs had suggested. The femoral head was was rigidly secured, after advancing it distally 2 cm to exposed using a combination of straight and curved add dynamic stability to the reconstruction, using a Hohmann retractors. Femoral ostectomy with an combination of two 6.5 mm AO/ASIF screws and figure-8 oscillating bone saw divided the femoral neck at its wire fixation. The deep and superficial fascial layers were base, which was subsequently removed. The normal closed using 0 Vicryl placed in a simple continuous pattern, location of the acetabulum was identified and and the subcutaneous layer was closed with 2-0 Vicryl in graduated reamers were used to create a cavity of a similar manner. The skin incision was closed with 0 Prolene 62 mm diameter, with sufficient depth to cover and in a horizontal mattress pattern and a stent bandage support an acetabular shell without perforating the was sutured over the wound. acetabular floor. A nominal 62 mm modular trabecular The surgical time was3h50minwith a total metal shell (real outside diameter 64 mm) was implanted anaesthesia time of5h10min. Intraoperative radiographs with an orientation of 45° lateral opening and 20° revealed satisfactory location, orientation and fixation of retroversion, in relation to the normal orientation of the the femoral stem and acetabular shell (Fig 6). The patient equine pelvis during quadruped gait (Fig 3). Titanium underwent a sling recovery and was fully weightbearing screws were placed through the acetabular shell into the 24 h post operatively.

Fig 4: Intraoperative image demonstrating the new femoral head on the stem (black arrow) that is inserted in the femoral canal (white arrow). The retracted greater trochanter and attached Fig 6: Intraoperative radiograph demonstrating satisfactory gluteal muscles are to the right of the head. The asterisk is located location and orientation of the femoral stem and head within the at the caudoventral aspect of the left hindlimb. acetabular cup.

butorphanol tartrate (10 mg i.m. q. 8 h). The patient was maintained in a sling during the post operative period. The incision had a moderate amount of serosanginous discharge during the 5 day post operative period. On post operative Day 3 the patient was taken for a walk and was fully ambulating on the left hindlimb (Figs 7a,b). On the fourth post operative day the patient became mildly febrile, anaemic and leucopenic with a moderate neutropenia. On post operative Day 5 the patient deteriorated rapidly, showing signs of weakness after collapsing in the sling. This was accompanied by deteriorating haematology results indicating a worsening of the anaemia, leucopenia and severe neutropenia. The foal was subjected to euthanasia due to its deteriorating condition. A post mortem examination revealed multiple pulmonary thromboemboli and an infarcted section of mid-jejunum.

Discussion

Cases of equine hip dysplasia are uncommon in the Fig 5: Intraoperative image of the femoral head reduced into the veterinary literature. Early reports have described new socket (the black arrow illustrates the femoral neck with the attached 36 mm chrome-cobalt femoral head). The hip joint degenerative arthritis of the coxofemoral joints, which is reduced with the constraint-locking ring engaged. To the right eventually resulted in luxation as an inheritable condition is the retracted greater trochanter (white arrow). The asterisk is in Norwegian Dole horses (Jogi and Norberg 1962; Speirs located at the caudoventral aspect of the left hindlimb. and Wrigley 1979). In young horses, there are 2 reports of unilateral degenerative coxofemoral arthritis and Treatment and aftercare subluxation (Jogi and Norberg 1962; Davison 1967). More recently, there have been 2 reports of bilateral Following surgery, the patient continued to receive ceftiofur coxofemoral joint disease in foals leading to subluxation (2.2 mg/kg bwt i.v. q. 12 h), amikacin (6.6 mg/kg bwt i.v. q. and complete luxation of the femoral head (Speirs and 24 h) and phenylbutazone (1.1 mg/kg bwt Wrigley 1979; Trent and Krook 1985). Our patient had a i.v. q. 12 h). Additional pain management consisted of flattened femoral head, anteverted femoral neck and a

one of the most predominant features in dwarf Friesians (Back et al. 2008). At the time of surgery, our patient had probably reached maximal limb growth, thereby allowing surgical intervention. Surgical repair of the coxofemoral joint requires an understanding of the magnitude and direction of forces generated by the muscles and kinetics of the limb in weightbearing positions. Therefore, the use of human prosthetic implants in animals requires comparative knowledge of joint biomechanics between bipeds and quadrupeds. Specifically, surgical replacement of the coxofemoral joint requires an understanding of the magnitude and direction of the physiological resultant hip joint reaction force during weightbearing. Man is unique with a fully upright posture and during walking the ground reaction force vector aligns closely with the knee and hip joints (Biewener 1989). However, data from instrumented hip prostheses implanted in sheep, dogs and man demonstrated similarity in the direction of the resultant hip joint reaction force among bipeds (man) and quadrupeds (sheep and dogs), despite differences in femoral kinematics (Bergmann et al. 1984, 1999). In man, the maximum hip joint reaction forces during walking ranges from 280–480% bwt (Bergmann et al. 1993), while in sheep the forces during walking ranges from 65–140% bwt (Bergmann et al. 1999). In sheep, there is minimal influence of walking speed on hip joint forces. The forces during fast walking are only about 20% higher than during slow walking (Bergmann et al. 1984, 1999). Comparison of these Fig 7: Post operative Day 4 images obtained from a video of the patient walking (a). A stent bandage covers the incision (b). data indicates that the force magnitudes during walking in man are approximately 3 times higher than in sheep weighing 58–71 kg. Although it is tenuous to extrapolate, reduced acetabular diameter. The chronic duration of a small horse weighing 2–3 times the bodyweight of a the patient’s condition resulted in a grossly distended sheep may experience hip joint loads approximating coxofemoral joint capsule. The findings are consistent with those in man. Consequently, because the direction and chronic traumatic coxofemoral subluxation, resulting in magnitude of the hip joint reaction force are estimated to secondary flattening and excessive anteversion of the be similar in man and small horses, it is reasonable to use a femoral head with severe degenerative changes to the human hip implant in small horses until equine specific acetabulum and femoral head. Histopathology would be implants are developed. Other considerations would required to determine if secondary osteonecrosis of the include implant geometry relative to femoral and capital epiphysis caused the degenerative changes. acetabular geometries and stresses at the bone implant Coxofemoral luxation is most commonly reported in interface. Future complications such as bone resorption, foals and ponies (Garcia-Lopez et al. 2001) and it has been femoral fracture and implant failure, could not be proposed that the deep acetabular rim in mature horses determined due to the short-term outcome of this case. leads to ileal fractures before luxation could occur Currently, there is no information available to assess the (Field et al. 1992). In addition to the deep acetabular degree of acetabular retroversion, femoral conical stem configuration, the equine coxofemoral joint also consists anteversion and femoral varus/valgus alignment for THA of a strong round and accessory ligament and abundant implants in horses. Measurements taken from the pelvis soft tissue support, which makes luxations of this joint and femur of adult horses at Washington State University rare (Nyack et al. 1982; Malark et al. 1992; Garcia-Lopez Veterinary College by the senior authors (B.G. and C.D.) et al. 2001). The decreased size in the majority of patients indicated the correct orientation of femoral stem and presenting with coxofemoral luxation lends itself to a larger acetabular cup alignment. The authors chose the pelvic variety of surgical stabilisation techniques. The patient in acetabular cup angles with a 45° lateral opening and 20° this report was 9 months old and weighed 145 kg. Dwarfism of retroversion. Additionally, the femoral stem was set in a in Friesians has a reported incidence of 0.25% with the neutral varus/valgus alignment with 20° anteversion. These recorded weight of a mature dwarf Friesian being 231 kg orientations of the femoral stem and acetabular cup were (Back et al. 2008). Physeal growth retardation in the limbs is based on the assumption that form follows function and

that replication of normal orientation would be the best Biewener, A.A. (1989) Mammalian terrestrial locomotion and size. way to simulate normal biomechanics and minimise the Bioscience 39, 776-783. risk of post operative luxation. There is limited information Clegg, P.D. (1995) Idiopathic infective arthritis of the coxofemoral joint in a mature horse. Vet. Rec. 137, 460-464. in previous reports of large animal THA to support the Clegg, P.D. and Butson, R.J. (1996) Treatment of a coxofemoral luxation orientation of the prosthetic devices. We recommend the secondary to upward fixation of the patella in a Shetland pony. Vet. aforementioned pelvic and femoral prosthetic angulations Rec. 138, 134-137. based on the immediate post operative loading of the Clegg, P.D. and Comerford, E.J. (2007) Coxofemoral luxation-how does prosthetic leg, functional ability of the patient outside of our knowledge of treatment in other species help us in the horse? the sling and lack of functional complications in the Equine vet. Educ. 19, 482-483. immediate post operative period. Cook, J.L. (2007) Future trends in joint replacement and tissue engineering in small animal orthopedics. Vet. Surg. 36, 287-288. Serious complications of this procedure involved the Davison, P.J. (1967) A case of coxo-femoral subluxation in a Welsh pony. unfortunate, sudden death of the patient caused by Vet. Rec. 80, 441. multiple pulmonary emboli in the lungs and an infarcted Dyson, S.J. (2003) Pelvic injuries in the non-racehorse. In: Diagnosis and segment of jejunum. Histopathology was not performed to Management of Lameness in the Horse, Eds: M.W. Ross and S.J. further classify the damage to these affected regions. Dyson, W.B. Saunders, Philadelphia. pp 499-500. Fat embolisation syndrome (FES) is a rare complication Embertson, R.M., Bramlage, L.R., Herring, D.S. and Gabel, A.A. (1986) described in man as a possible sequela to femoral canal Physeal fractures in the horse: I. classification and incidence. Vet. Surg. 15, 223-229. medullary reaming and interlocking nail fixation and Field, J.R., McLaughlin, R. and Davies, M. (1992) Surgical repair after cemented and uncemented THA (Apostolou et al. of coxofemoral luxation in a Miniature horse. Can. vet. J. 33, 404- 2002; Giannoudis et al. 2006). FES is most commonly 405. reported following the cemented technique (Apostolou Garcia-Lopez, J.M., Boudrieau, R.J. and Provost, P.J. (2001) Surgical et al. 2002); however, the pathomechanics involved repair of coxofemoral luxation in a horse. J. Am. vet. med. Ass. 219, appear multifactorial and controversial. No pulmonary 1254-1258. complications were recorded in the 7 ponies that had Giannoudis, P.V., Tzioupis, C. and Pape, H.C. (2006) Fat embolism: The reaming controversy. Injury 37, 50-58. partial hip replacements using a cemented implant (Recum et al. 1980) or in sheep fitted with telemeterised Hance, R.H. (1998) Hematogenous infections of the musculoskeletal system in foals. Proc. Am. Ass. equine Practnrs. 44, 159-166. cemented titanium femoral stems (Bergmann et al. 1984, Hendrickson, D.A. (2002) The coxofemoral joint. Adams’ Lameness 1999). The patient had a heart murmur and it is possible in Horses, 5th edn., Ed: T.S. Stashak, Lippincott Williams & Wilkins, that unidentified heart pathology increased the patient’s Philadelphia. pp 1037-1043. risk to FES. Therefore, more controlled information is Hunt, D.A., Snyder, J.R., Morgan, J. and Pascoe, J.R. (1990a) Femoral required regarding reaming of the femoral neck and capital physeal fractures in 25 foals. Vet. Surg. 19, 41-49. associated emboli risks in horses. Hunt, D.A., Snyder, J.R., Morgan, J., Stover, S.M., Pool, R. and Pascoe, Overall, the short-term comfort of the patient post J.R. (1990b) Evaluation of an interfragmentary compression system for the repair of equine femoral capital physeal fractures. Vet. Surg. operatively and its ability to bear weight successfully on the 19, 107-116. THA limb, leads us to believe that this procedure is an Jogi, P. and Norberg, I. (1962) Malformation of the hip joint in a effective treatment option for coxofemoral disease in small standard-bred horse. Vet. Rec. 74, 421. breed horses. Lamb, C.R. and Morris, E.A. (1987) Coxofemoral arthrosis in an aged mare. Equine vet. J. 19, 350-352. Loesch, D.A., Bryant, J.E. and Lopez-Martinez, A. (2003) Septic Manufacturers’ addresses coxofemoral arthritis with extension into the abdominal cavity in a foal. Equine vet. Educ. 15, 15-18. 1CDA Products, Potter Valley, California, USA. Malark, J.A., Nixon, A.J., Haughland, M.A. and Brown, M.P. (1992) 2 3M, Maplewood, Minnesota, USA. Equine coxofemoral luxations: 17 cases (1975-1990). Cornell Vet. 82, 79-90. References Miller, C.L. and Todhunter, R. (1987) Acetabular osteochondrosis dissecans in a foal. Cornell Vet. 77, 75-83.

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