Total Hip Replacements: Indications for Problems Other Than Hip Dysplasia
William D. Liska, DVM, DACVS
Canine total hip replacement (THR) is a common surgical procedure. It was originally developed to treat pain associated with osteoarthritis secondary to hip dysplasia. The goals are to provide a pain-free joint and restore biomechanical function for the life of the animal. Hip dysplasia remains the most common indication for THR, but there are multiple other indications as well.
Several new generations of implants and instrumentation have been developed during the last two decades. New technology improves the surgeon’s ability to consistently deliver excellent results with minimal risk. THR surgery success led to demands from veterinary surgeons and the public to expand prosthesis size availability for both larger and smaller dogs and recently for cats. The scope of indications also expanded well beyond animals with uncomplicated hip dysplasia concurrent with the decline of other salvage procedures such as femoral head ostectomy (FHO).
The registry of 1900 consecutive THRs performed by one surgeon between October 1990 and December 2016 was reviewed to compile information about indications for the surgery. The indication for surgery was documented preoperatively based on patient history, physical examination and radiographic appearance. The categories are discussed. The periodic interjection of new technology and implant size availability skews the relative incidence of each indication beginning at their respective introduction dates. Following those dates, hip dysplasia became relatively less prevalent as the new indications were adopted as routine.
Coxofemoral luxation (Figure 1)
Coxofemoral luxation can be treated with THR if closed or open reduction is not feasible or is unsuccessful. THR is the first option if a hip luxation with pre-existing osteoarthritis (OA) is present. Treatment of dogs with traumatic hip luxation by THR is reported in the literature. Gait analysis documented successful treatment. Hip luxation was the indication for 17 (25.7%) of the 66 Micro THR cases in one report. 140 (9.3%) of the 1500 consecutive THRs in this report were performed with hip luxation as the indication.
Capital physeal fracture (Figure 2)
Capital physeal fracture (CPF) treated with THR in 21 dogs and 4 cats has been reported. No statistically significant difference was present at a minimum of 6 months after surgery involving thigh circumference and ground reaction forces using force plate analysis compared to the normal contralateral limb. In another report, CPF was the indication for THR in 16.6% of the 66 cases of Micro THR. 68 (4.5%) of the 1500 consecutive THRs in this report were performed with CPF as the indication.
Avascular necrosis of the femoral head (Figure 3 and 4)
The contemporary treatment for AVN for decades has been femoral head ostectomy. The advent of Micro THR provides a better option. AVN was the indication for 22.4% of the dogs receiving the Micro THR in dogs in the initial report of 66 Micro THR cases. No significant difference in ground reaction forces of the Micro THR side compared to the normal contralateral side in 7 dogs is reported. AVN was the indication for 27 of the 1500 dogs in this report receiving a THR. 4.6% of all THRs in the study have been performed due to AVN since the initial THR was performed with AVN as the indication.
Malunion of the pelvis, acetabulum, or femur and TPO revision
Malunion of pelvis, acetabulum, femoral head/neck, or femoral diaphysis can lead to OA to abnormal articulation angles and weight distribution. Bone stock voids, altered bone density and proximal femoral medullary canal sclerosis can create technical challenges during THR surgery. Fourteen malunion fractures (0.1%) (1 ilium, 6 acetabular, and 7 femoral) led to secondary OA and ultimately a THR indication in the series of 1500 procedures. (Figure 5)
Femoral head ostectomy (FHO) revision (Figure 6)
Revision of a FHO with unacceptable function to a THR is reported. Although FHO revision to THR is more technically challenging than primary THR, increased complication rates have not been observed or reported and client satisfaction is achieved. Even though FHO revision to a THR is entirely feasible, animal owners should never be advised that an FHO can be performed first and if function is unsatisfactory later, the FHO can be revised to a THR. Six FHOs were revised to a THR in the series of 1500 cases. The frequency of primary FHO procedures declined precipitously during the same time period. This coincides with literature reports that based on objective data, FHO does not produce nearly as good results as previously thought. In this study of 81 dogs and cats, limb function was rated as good in only 38%, satisfactory in 20%, and unsatisfactory in 42% at a mean of four years postoperatively. These results seem poor compared to other studies, however all other studies were based on subjective data by the owners.
Nonunion of a femoral head or neck fracture (Figure 7)
Nonunion of a femoral head or neck fracture will occasionally be presented for a THR. The incidence is low (3 of the 1500) for several reasons including the presence of chronic pain that can be treated with excision similar to a FHO. When THR is requested, the procedure is the same as revision of a FHO to a THR once the femoral head has been removed.
Injury Leading to Osteoarthritis (Figure 8)
Nondescript hip injuries of normal joints occur in both companion and athletic animals. Abnormal radiographic evidence of an injury may not be present initially, but pain and dysfunction may persist followed by osteoarthritis later. Examples may include capital physeal Salter V injury, femoral head or neck compression fracture, articular cartilage damage, acetabular rim cartilaginous labrum tears, femoroacetabular impingement, and round ligament tears.
Revision of a previous THR
As THR surgery becomes more prevalent, revision of complications is occasionally necessary. Revision of human hip replacements has become a super-specialty with some orthopedic surgeons dedicating a majority of their time performing revisions compared to primary THR. This seemingly unattractive role provides new challenging and stimulating operating room time for the high-volume surgeon with thousands of primary THRs completed. Seven THRs were successfully revised during the 1500 study group time interval. It is advisable that veterinary surgeons understand and be capable of THR revision before attempting primary THR surgery.
Osteopathy (Figure 9)
Coxofemoral periarticular neoplasia can be managed in some rare scenarios with a custom designed and manufactured prosthesis. Minimally invasive preoperative differentiation between neoplasia, low grade osteomyelitis, septic arthritis, and benign non-neoplastic osteopathy require advanced diagnostics such as scintigraphy, cross sectional imaging, arthroscopically obtained or ultrasound-guided tissue cultures, and a histopathological diagnosis for surgical planning. Well contained circumscribed benign lesions near the acetabular surface or within the femoral head and neck can be treated during a one-stage excision and prosthesis implantation.
Acetabular Fractures (Figure 10)
Acetabular fractures can be reconstructed with plates and screws, can be reconstructed only to have OA anyway, can be highly comminuted and not be amenable to open reduction internal fixation, and can be healed by second intention as a malunion with secondary OA in animals with an unknown past history. Some of the painful acetabular fractures can be converted to a THR.
Osteoarthritis Secondary to Hip Dysplasia (Figure 11)
Osteoarthritis secondary to hip dysplasia (or suspected hip dysplasia when OA is end-stage with no other etiological evidence) is still by far the most common indication for THR. 1221 (81.4%) of the 1500 THRs were performed with the presumptive diagnosis (or lack of more definitive diagnosis – particularly with end-stage OA present) of hip dysplasia. Conversely, the acceptance of new indications has increased the incidence of THR for non-dysplastic hips from 18.6% to 22.4% of the last 1000 THRs and to 26.6% of the last 500 THRs in the original study group of 1500.