Management of feline slipped femoral capital epiphysis with a Biomedtrix nano total hip replacement

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Subedited by Dr Phil Tucak

feline slipped femoral capital epiphysis

Mischa is a 18-month-old female spayed domestic long hair cat, who presented to Queensland Veterinary Specialists (QVS) after a four week period of left pelvic limb lameness. Prior to referral, Mischa had been managed with confinement and opioid analgesia. During this time the owners reported decreased activity levels, decreased appetite and depressed demeanour. Radiographs were performed and Mischa was referred for concerns regarding a capital physeal fracture. 

Mischa was initially seen by QVS surgery registrar Dr Guy Bird. Significant findings included reduced weight bearing on the left pelvic limb, reduction in range of motion, pain and crepitus on left hip extension, and marked left pelvic limb muscle atrophy. Further radiographs confirmed a left slipped femoral capital epiphysis (SCFE) with resorption of the femoral neck and muscle atrophy.  Slipped capital femoral epiphysis is a degenerative progressive condition separate from primary fractures of the physis. The spontaneous nature of SCFE injuries in the absence of trauma is a key component in differentiating them from a Salter Harris type 1 fracture of the femoral capital physis. 

Slipped femoral capital epiphyseal fractures should be high on the differential list in a skeletally mature cat with acute presenting signs of pathology. The aetiopathogenesis of SCFE is incompletely understood and believed to be multifactorial. Specific risk factors in cats over one year of age include: sex (males have an increased risk); reproductive status (neutering is a predisposing factor); biomechanical (delayed physeal closure from presumptive hypotestosteronism secondary to gonadectomy); and mechanical (increased body weight). 

feline slipped femoral capital epiphysis
Radiographs show a left slipped femoral capital epiphysis with resorption of the femoral neck and muscle atrophy. 

While reduction and fixation have a good prognosis for the management of traumatic femoral capital physeal fractures (Salter Harris), this method of fixation is not appropriate in cases of SCFE. Options for SCFE are limited to salvage procedures consisting of total hip replacement (THR) or femoral head and neck excision (FHNE). Where salvage procedures of the coxofemoral joint are indicated, restoration of the normal hip joint function via total hip replacement is the preferred outcome to FHNE. The Biomedtrix THR system has implants suited to all sizes of pets and should be considered for not only hip dysplasia but in coxofemoral luxations, femoral head and neck factures, developmental disorders, avascular necrosis of the femoral head and failed FHNE procedures. 

Overall success rates following total hip replacement are reported to exceed 90%. In a study evaluating clinical outcomes in small breed dogs and cats, 92% of cases had a lameness score of 1 or 2 indicating good to excellent limb function three months after surgery.

Conversely a high proportion of femoral head and neck excisions have suboptimal clinical outcomes. While subjective improvements are reported, force plate data demonstrates persistent functional deficits after FHNE and intense physiotherapy intervention is required for functional outcomes. Total hip replacement is the only treatment that fully restores lifelong mobility providing better range of motion, improved function and pain-free joints. Mischa’s owners elected to proceed with a Biomedtrix nano total hip replacement and Mischa’s care was transferred to orthopaedic surgeons Dr Lucas Beierer and Dr Tim Pearson. 

Prior to surgery, Mischa had calibrated radiographs (ventrodorsal pelvis with limbs extended, lateral pelvis, cranio-caudal femur and mediolateral femur) for surgical planning and to guide implant sizing. A craniolateral approach to the left coxofemoral joint was performed to allow disarticulation of the femoral head. On gross examination the femoral head had collapsed, was friable and easily displaced cartilage. The remaining femoral neck was removed with an oscillating saw. 

feline slipped femoral capital epiphysis
Above and below right: Post-operative radiographs demonstrate appropriate implant positioning.

Acetabular exposure was achieved using Gelpi and Senn Miller retractors to allow for acetabular preparation with a pneumatic burr. Once an appropriate acetabular depth was reached a trial cup was placed to assess appropriate sizing, positioning and depth. 

The acetabular prosthesis (CFX size 10 – 6mm I.D.) was secured with antibiotic (tobramicin) impregnated simplex poly methyl methacrylate (PMMA) bone cement placed in the dough phase. Orientation (angle of lateral opening, retroversion and inclination) of the implant is important and assessed intra-operatively before allowing the cement to harden. Elevation of the femur for reaming was achieved using a skid elevator and crab-claw bone holding forceps placed on the proximal femur. The medullary canal of the femoral canal was reamed sequentially with a 1.6 K-wire, 2.0mm drill bit and then specially designed #1-2 femoral reamer. A trial implant was placed to confirm appropriate implant sizing and anatomic alignment of the femoral stem. Bone cement was inserted in the liquid phase into the reamed portion of the femoral medullary cavity and the femoral stem inserted. Mischa received a monoblock Biomedtrix stem implant (CFX #2+4) which is a feature of the nano hip implants in which the acetabular head is fixed to the femoral stem. 

Comparatively the modular femoral stem implant (also available in micro, nano and universal THRs) allows modularity in choice of the acetabular head implant size. The femur was then reduced and adequate positioning, stability and range of motion were demonstrated intra-operatively. The soft tissues were closed routinely. Post-operative radiographs (Figure 2,3) demonstrate appropriate implant positioning. 

feline slipped femoral capital epiphysis

A fentanyl constant rate infusion (2-5mcg/kg/hr) was used peri-operatively and a fentanyl patch (12mcg/hr) was used for analgesia after discharge. Non-steroidal anti-inflammatory (meloxicam, 0.05mg/kg PO SID) was continued for four weeks and a short course of prophylactic antibiotics (amoxicillin-clavulanic acid, 20mg/kg, PO, BID) was prescribed for five days.

The day following surgery Mischa was starting to put small amounts of weight on the operated limb. She was discharged two days post-operatively at which time she was weight bearing well on her operated limb. She was discharged with instructions to be sensibly confined in an environment with non-slip matting that did not allow jumping on/off objects for six weeks. Gabapentin (100mg, PO, BID) was dispensed to assist with confinement.

Mischa was reviewed two weeks post operatively at which point her owner described absent lameness, increasing affection and a much improved appetite. 

Orthopaedic examination revealed mild ongoing lameness consistent with her stage of recovery. At the six-week recheck, physical examination revealed consistent weight bearing, no bone or joint pain, marked improvement in muscle mass and some non-painful muscular restriction on hip extension. 

Radiographs were obtained which demonstrated an uncomplicated recovery post THR. An additional four weeks’ confinement was recommended (10 weeks total) and a final review 12 weeks post operatively scheduled. 

Mischa’s case demonstrates an excellent outcome following total hip replacement for management of a slipped femoral capital epiphysis. It highlights restoration of coxofemoral joint function, an outcome a FHNE cannot provide.


References:

Borak, D., Wunderlin, N., Brückner, M., Schwarz, G., & Klang, A. (2017). Slipped capital femoral epiphysis in 17 Maine Coon cats. Journal of feline medicine and surgery, 19(1), 13-20.

Liska, W. D. (2010). Micro total hip replacement for dogs and cats: surgical technique and outcomes. Veterinary surgery, 39(7), 797-810.

Marino, D. J., Ireifej, S. J., & Loughin, C. A. (2012). Micro total hip replacement in dogs and cats. Veterinary Surgery, 41(1), 121-129.

McNicholas Jr, W. T., Wilkens, B. E., Blevins, W. E., Snyder, P. W., McCabe, G. P., Applewhite, A. A., … & Breur, G. J. (2002). Spontaneous femoral capital physeal fractures in adult cats: 26 cases (1996–2001). Journal of the American Veterinary Medical Association, 221(12), 1731-1736.

Witte, P. G., Scott, H. W., & Tonzing, M. A. (2010). Preliminary results of five feline total hip replacements. Journal of Small Animal Practice, 51(7), 397-402.


Dr Lucas Beierer BVSC GradDipEd MVetSurg DACVS-SA 

feline slipped femoral capital epiphysis

Registered specialist in small animal surgery, Queensland Veterinary Specialists

Dr Beierer graduated as a veterinarian from the University of Queensland and immediately undertook a rotating internship at QVS. Surgical internships then followed in Adelaide and Perth, part of which involved a tertiary qualification in adult education.

Dr Beierer undertook a residency in small animal surgery at Murdoch University while also completing a masters of veterinary surgery specialising in the biomechanics of locking plates.

He was accepted by examination as a Member of the Australian and New Zealand College of Veterinary Scientists (Surgery chapter) in 2011. He became a Diplomate of the American College of Veterinary Surgeons – Small Animal in 2015 and an RCVS Recognised Specialist in Small Animal Orthopaedics in 2016. 

Dr Sean Wood BSc BVSc 

feline slipped femoral capital epiphysis

Small animal surgery intern, Queensland Veterinary Specialists

Dr Wood completed his veterinary science degree at Massey University in New Zealand in 2018. As a new graduate he completed a rotating internship at Queensland Veterinary Specialists and Pet Emergency. Dr Wood has since stayed on with QVS as a surgery intern. There he enjoys the varied surgical caseload.

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