Hip dysplasia is the most common cause of chronic intermittent hind limb lameness in dogs. Genetic predisposition towards the development of hip dysplasia is the most important cause. Laxity predisposes to malformation and malformation predisposes to laxity. Osteoarthritis (OA) or Degenerative Joint Disease (DJD) develops secondarily.
Contrary to popular belief the femoral head and neck ostectomy (FHO) does not have a good functional outcome when compared to Total Hip Replacement. New data has revealed that after an FHO patients remain significantly lame based on force plate analysis with reduced range of motion, significant muscle atrophy and in some cases persistent pain. A total hip replacement (THR) is the only procedure that can re-establish normal coxofemoral kinematics and function as well as completely eliminate pain. Many surgeons have become reluctant to recommend a THR due to unfamiliarity with the technique as well as previous complication rates from older cemented and cementless hip replacement systems. The overall complications rates with the various THR systems typically range from 5-25%. However, an experienced surgeon and surgical team can have success rates of approximately 90% to 95%.
The new THR systems have excellent success rates and low complication rates compared to the older systems. Some of the current cementless systems available include the Kyon, Biometrix (BFX), and Helica THR systems. The cemented THR is no longer being used by most surgeons. Most cementless THR systems rely on a press fit method for the initial stability of the implants followed by bone ingrowth into the implants for long term stability. The Kyon THR system (fig 1a and 1b.) is the only cementless system that combines a press fit application with screws to lock the implant in place which adds to the initial stability of the implants and reduces the complications of premature implant loosening. The Kyon titanium implants are also now coated with hydroxyappetite which also enhances bone ingrowth into the implants. This is the only system that allows for immediate and permanent proprietary locking-screw fixation and near-physiolological loading of the proximal femur with full range of impingement free motion. The all titanium Kyon system is more resistant to infections when compared to the Biometrix BFX system. The Kyon Total Hip Replacement is also the only system that has been successfully revised after an infection. In a retrospective study in 60 dogs with the Kyon THR system they had a 97% success rate with only 11% overall complications and only one explantation (Guerrero TG, Montavon PM. Vet Surg 2009).
Total hip replacements can also be used to treat other conditions other than hip dysplasia such as femoral head and neck fractures, coxofemoral luxations, Legg Calves Perth's (aseptic necrosis of the femoral head and neck), poorly healed acetabular fractures and capital physeal fractures. Patient selection is extremely important and a THR can now be performed in patients as early as 10 months of age. There are also Nano/Micro THR systems now available for small dogs and cats (91% success rate small dogs and cats, Liska W. Vet Surg 2010). Only 20% of patients require bilateral THR for a good functional outcome in patients with severe bilateral hip dysplasia. If bilateral procedures are required, they should be spaced apart by 3-6 months. Patients must also be free of neurologic disease, other orthopedic hind limb problems and infection. A THR must be done before severe degeneration results in loss of bone or marked muscle atrophy.
The post-operative recovery includes 12 weeks of strict activity restrictions. It typically requires a total of 16 weeks until they can be gradually returned to normal activity. Recheck radiographs are typically performed at 2 weeks, 8 weeks and 16 weeks post operatively. A THR is designed to last the entire life of the patient; however, in rare cases an implant may need to be revised.
A THR is a lifelong treatment and client communication is extremely important. Careful patient selection is necessary in order to determine when a THR is appropriate. Only 20% of patients require bilateral THR for a good functional outcome. Patients must be free of neurologic disease, other orthopedic hind limb problems and infections. A THR must be done before severe degeneration results in loss of bone or marked muscle atrophy. The Kyon THR system has the highest success rate and the lowest complication rates when compared to the other available systems. At LEADER Animal Specialty Hospital we are now offering the Kyon THR. Please feel free to contact us for more information.
Figure 1a. Kyon THR system.