Introduction

Over the past 3 decades, total hip replacement has become a routine salvage procedure use mainly for the treatment of intractable coxofemoral osteoarthritis (OA). More recently, the veterinary orthopedic community has attempted to address end-stage OA of the elbow and knee using total (and/or hemi) joint prostheses. This presentation will be an overview of total joint replacement using BioMedtrix's elbow and knee prostheses in dogs.

Total Elbow Replacement - Tate Prosthesis

In recent years, new total and hemi elbow replacement prostheses (TER & HER) have been designed (Conzemius, Acker -Van Der Muellen and Innes [TER]/Wendelburg - Tepic [HER]) for the treatment of intractable end-stage canine elbow OA as well as early so called "medial compartment disease." While most systems remain cemented, unlinked, semi-constrained, stemmed designs, a novel TER system (TATE Elbow^TM) was recently devised by Acker and Van Der Meulen.

The TATE is a cementless implant designed to use a novel resurfacing concept, as well as minimally invasive surgery. These features may explain the improved, time-matched, clinical outcomes seen with the TATE prosthesis in particular with regards to lateral luxation and humeral/ulnar fractures, complications seen with cemented stemmed designs.

From a surgical standpoint, the elbow is approached via an osteotomy of the medial humeral epicondyle. The articular surfaces of the humerus, radius and ulna are simultaneously removed without luxating the elbow using a precision milling tool. As a cementless system, the TATE prosthesis is initially stabilized through a "press-fit" mechanism. Long-term stability relies on bone ingrowth into the porous structure of the implants. Both TATE components are impacted simultaneously as a pre-assembled cartridge.

While clinical and experimental studies are ongoing at Michigan State University, no objective data is available on the clinical outcome of the TATE Elbow system. The following is a compilation of subjective and objective data obtained from 2 clinical centers (Sun Valley Animal Center [Acker - 65 cases] and MSU [Dejardin - 20 cases]). We emphasize that this information is mostly subjective in nature and therefore should be assessed cautiously. The TATE prosthesis has been implanted in approximately 200 cases worldwide since July 2007 (~8 years ago).

Subjective clinical evaluation and owners' feedback suggest that limb function improves up to 1 year after surgery following a typical aggravation of the lameness between 6 and 12 weeks. Although dogs appear pain free and show improved range of motion, mainly in extension, subtle to mild lameness may persist.

Severe complications consisting of two ulnar fractures and one implant loosening were recorded, all within 8 weeks post-operatively. These complications were addressed via amputation or primary fracture repair. The rate of severe complications, up to 6 years after surgery, was ~7.7% prior to revision and ~5.5% following successful revision.

Objective force plate analysis was conducted on 9 patients at Michigan State University up to 32 months after implantation of a TATE (ongoing prospective clinical study). In all cases, pre-operative peak vertical force of the affected limb was significantly lower than normal.

By 6 to 12 months after surgery, the peak vertical force of the operated limb was greater than that of the contralateral side. Continued improvement was seen at 2 years, as the peak vertical force of the operated limbs had returned to a normal reported value of ~115% BW. One dog underwent bilateral elbow replacement. That dog received a 2nd generation TATE prosthesis 2 years after successful implantation of a 1st generation implant.

Regardless of design, a major limitation of TER is the absence of effective revision options in case of failure. Unfortunately, because end-stage elbow OA is often a bilateral condition, amputation is not a valid option in most cases and arthrodesis remains the main alternative. Although some fractures or luxations may successfully be revised, others may require explantation and arthrodesis because of the limited bone stock available for implant fixation. Infection is and will likely continue to be the most challenging complication as antibiotherapy alone is unlikely to be effective as long as the prosthesis is implanted. Because of these limitations, owner education is critical and must be thorough and objective.

Total Knee Replacement - BioMedtrix Prosthesis

Total knee replacement (TKR) is a common and extremely successful clinical procedure in humans, with improved quality of life in around 90% of patients. In the veterinary field, TKR is a more recent development, with the earliest reports of the procedure coming from preclinical studies on implant fixation in orthopedic research literature. The BioMedtrix implant, which has now been used in more than 250 cases worldwide, consists of a cobalt-chromium (Co-Cr) femoral component with a stem, and either a Co-Cr tibial tray with an ultra-high molecular weight polyethylene (UHMWPE) insert or a monobloc tibial component with a keel for rotational and translational stability. Recently, an all-cementless implant system has been developed (GenuSys; Innovet, Hamburg, Germany). This system uses a Co-Cr femoral component and a Co-Cr tibial baseplate that holds an UHMWPE insert. The femoral component is secured to the distal femur with a bone screw, while the tibial component is implanted in press-fit fashion.

The most common indication for canine TKR is end-stage intractable degenerative joint disease (DJD), usually secondary to rupture of the cranial cruciate ligament (CCL) or to other intra-articular pathologies such as osteochondrosis or chronic fractures. As surgeons have become more confident with the procedure, indications have started to expand, and animals with severe but not end-stage DJD are now being treated with TKR.

The surgical technique for TKR has been described in the literature and will not be repeated here. Briefly however, the major steps of the procedure include 1) ostectomy of the tibial plateau leaving a residual slope of 6°, 2) femoral ostectomies using a dedicated cutting block, 3) trial prostheses to ascertain adequate, balanced tension of the collateral ligaments, 4) sequential prosthetic impaction (cementless design) and 5) layered closure after ROM assessment.

Recovery following TKR is typically slower than is seen after total hip replacement, with most animals taking around 10–12 weeks to return to optimal joint function. Dogs are assessed at 6 weeks and 12 weeks post surgery. If the knee is stable, pain-free and able to move through a satisfactory range of motion (approximately 100°), the owners are allowed to reintroduce off-leash exercise. Dogs are seen again at 6 and 12 months, then annually thereafter.

There has only been a single report of clinical results following canine TKR in dogs with end-stage stifle DJD. In that series of 6 dogs, limb function (as assessed by range of motion and force plate analysis) was significantly improved one year following surgery. Additional, larger case series are now needed. Only when they are presented will it be possible to determine the true efficacy of this procedure.

In the last couple of years, there has been renewed interest in the development of revision solutions for canine TKR, as well as in the development of custom implants that can be used to manage animals with significant knee joint instability (e.g., following stifle joint derangement, or recurrent medial collateral rupture) or dogs with malignant lesions in the distal femur or proximal tibial. Although case series are not available, the isolated case reports indicate that the use of hinged implants is a viable option for these complex cases.

However, data on the long-term survival of these implants must be collected before any conclusions can be drawn regarding the potential utility of these revision implants.