Effects of experimental excision arthroplasty of the hip joint

Feline hip dysplasia

Practical relevance:

The reported incidence of hip dysplasia (HD) in cats varies dramatically between studies, but the condition is likely more common than we realise. There is little doubt that cats with HD and associated osteoarthritis (OA) suffer pain, and this warrants appropriate therapy.

Diagnostic challenges:

Clinical signs of HD in cats are often gradual in onset, making them difficult to appreciate, but may include inactivity, pelvic limb lameness, difficulty jumping and climbing stairs, and reluctance to squat to defecate. Often lameness is bilateral, and can be particularly difficult to recognise. The most common radiographic finding is an abnormally shallow acetabulum. Subluxation, however, is not consistently associated with OA in cats and therefore the role that joint laxity plays in disease progression remains uncertain. Degenerative changes of the femoral head and neck seem to develop later than in the dog, and are less marked.

Therapeutic challenges:

The majority of cats respond to non-surgical management with environmental modulation, physical therapy, dietary modulation, weight loss, nutraceuticals and drug therapy. Should non-surgical management not provide sufficient relief, two salvage surgical options are available: femoral head and neck excision (FHNE) and total hip replacement (THR). While there is a risk of complications with micro-THR, the positive outcomes that have been reported indicate that it should be considered in the treatment of coxofemoral pathology in cats in the same way that THR is considered for larger dogs, especially given the inconsistent results associated with FHNE. Monitoring the effect of treatment is challenging as the assessment of pain in cats is complex and there is no validated scoring system or owner-completed questionnaire yet available for cats.

Evidence base:

There is a paucity of clinical reports focusing solely on HD in cats. The author draws on a combination of published studies, in cats, dogs and humans, as well as personal clinical experience.

Simultaneous Bilateral Femoral Head and Neck Ostectomy for the Treatment of Canine Hip Dysplasia

Simultaneous bilateral femoral head and neck ostectomy (FHO) was performed on 15 dogs for severe bilateral hip dysplasia. A follow-up survey was performed 6 to 48 months after surgery to assess the postoperative recovery and activity levels of the operated dogs. All dogs had normal activity levels and were pain free according to their owners. Owner satisfaction regarding the outcome of the surgery was high. Simultaneous bilateral FHO was a viable surgical option for the treatment of painful bilateral hip disease in dogs, especially when other surgical options were not indicated or were cost prohibitive.

Effect of two muscle sling techniques on early morbidity after femoral head and neck excision in dogs

Femoral head and neck excision was performed on the left coxofemoral joint of 18 dogs. The osteotomy site was padded with a partial-thickness biceps femoris muscle sling in one group of six dogs, and with a deep gluteal muscle flap in another group of six dogs. In a third group of six dogs, a partial-thickness biceps flap was created and sutured back in its original location. The dogs were monitored daily for 3 weeks for degree of lameness, range of motion, fever, and postoperative complications. Dogs with intra-articular muscle pads were less lame and had a greater range of motion in the treated hip than dogs without intra-articular muscle pads. Dogs with biceps slings showed more improvement in limb function and range of motion than did dogs with deep gluteal flaps. There were no significant differences in mean temperature elevations and no clinically significant postoperative complications. Use of a partial-thickness biceps muscle sling or a deep gluteal muscle flap decreased the chances of early postoperative morbidity and provided an earlier return to function. The partial-thickness biceps sling appeared to be more beneficial than the deep gluteal flap.

A comparison of standard femoral head and neck excision and femoral head and neck excision using a biceps femoris muscle flap in the dog

Sixteen normal 20 to 30 kg dogs had standard femoral head and neck excision (8 dogs) or femoral head and neck excision with interposition of a biceps muscle flap (8 dogs). Lameness lessened at week 6, and did not differ between groups; neither group returned to a completely normal gait. Weightbearing decreased on the operated pelvic limb compared to controls (forceplate analysis). Weightbearing force of the muscle flap dogs was significantly less at weeks 6 and 16 than that of the standard femoral head and neck excision dogs. The operated limb of both groups was shortened; shortening was significantly greater for the muscle flap group. Hip extension was limited in both groups. Both groups had decreased (more acute) hip, stifle, and hock angles measured in standing position. Thigh muscle atrophy was more pronounced in the muscle flap group at week 6. More soft tissue was interposed in the muscle flap group at necropsy compared to the group with standard femoral head and neck excision, but the difference was not statistically significant. Skeletal muscle fibers were present in the interposed fibrous connective tissue of the muscle flap group, and the healed surfaces were smoother than those of the standard femoral head and neck excision group.

Morphological and radiological findings in induced abnormal bone growth in lambs

Unilateral hip excision arthroplasty in skeletally immature lambs resulted in altered load bearing and posture in the contralateral limb. Derangement of endochondral bone growth occurred in distal tibiae and metatarsi and both angular and torsional deformities developed. There was no absolute correlation between torsional and angular deformities. Although femoral torsion was variable, the unoperated pelvic limbs frequently developed exaggerated internal torsion of tibiae and metatarsi. Tibiae of operated limbs developed less torsion than was seen in control animals. These findings suggest that functional limb loading can modify developing bone torsion and that torsional deformities in lambs may be a consequence of increased functional torque.

Histopathology of growth plate changes in induced abnormal bone growth in lambs

Unilateral hip excision arthroplasty in lambs resulted in osteochondrosis developing in distal tibiae and metatarsi of the contralateral pelvic limb. The physeal cartilage of distal tibiae and metatarsi developed clefts which probably represent shear failure. The histopathology of the meataphyseal defects differed between the medial and lateral growth plate sectors. Medially, the lesions were typical of physeal osteochondrosis in other mammals, with disorganized chondrocyte columns, cell death and matrix necrosis. Laterally, metaphyseal defects were predominantly fibrous, and islands of bone formed in physeal cartilage from re-established endochondral ossification. Both medial and lateral metaphyseal defects were associated with disturbed primary spongiosa formation. It is suggested that, in some instances at least, traumatic physeal clefts, resulting from shear failure in previously normal growth cartilage, may interfere with endochondral ossification and produce osteochondrosis.