Many dogs and cats will sustain good quality of life with appropriate and judicious plan for exercise, bodyweight management, supplementation, oral medication and rehabilitation modalities. However, there are instances where partial or complete joint replacement can be a good option for individual patients. Total hip replacement is now commonplace and commonly sought by families of both large and small dogs of all ages and also cats. Total knee replacement and total or partial elbow replacement are more recently commercially available. Implants are now emerging for partial or complete replacement of many joints. The emergence of new technologies in 3D printing and bone, tendon or skin on-growth metals has ushered a new era of personalised implants for joint replacement. Attitudes are changing within the veterinary profession regarding offering these options to clients for canine and feline patients and clients are very much aware of these options from digital and other visual media. Increasingly clients ask for options when faced with conditions for their dogs and cats that may have traditionally been treated by excision arthroplasty, arthrodesis or full limb amputation. Most dogs and cats can have an excellent quality of life on three legs or with selected arthrodeses, but there are circumstances where joint preservation may yield superior quality of life.
We must place special emphasis on the moral and ethical implications of the application of new technologies in clinical patients and explain all other options as well. The procedure must be in the welfare interests of the patient if other options are suboptimal but conversely, we have an increasing responsibility as a profession to offer clients all of the options to enable fully informed consent. Evidence of efficacy for personalised implants is emerging for veterinary and human patients, and when conventional options are limited, increasingly clients seek alternatives. Outcomes of surgical intervention using new implants of any kind, for routine or advanced procedures, should be subject to consistent vigilant scrutiny. It should also be noted that the development and implementation of many of the implants discussed in this lecture require significant resource in terms of engineers and machinists and this may limit availability.
Focal Resurfacing
When focal bone and cartilage loss is a cause of lameness, pain and debilitation, focal resurfacing implants can be employed. These can include commercially available biphasic polyurethane fillers on a trabecular metal base (SynACART™), custom devices made of poly ether ether ketone (PEEK), and custom devices made of titanium and cobalt chrome. These devices can be employed for treatment of focal joint lesions of developmental (osteochondritis dissecans) or traumatic origin in multiple joints. More recently personalised biphasic implants of trabecular metal and polylactide seeded with stem cells aim to recapitulate endogenous joint surfaces.
Coxofemoral Joint
Total hip replacement (THR) is now a routine opt ion for the treatment of end stage arthrosis of the coxofemoral joint in dogs and cats. Potential patients historically precluded by virtue of age or size are no longer excluded from this intervention if deemed clinically appropriate. Juvenile dogs under a year of age and small dogs under 5 kg are now routinely operated, as are cats. Both cemented and biologic ingrowth implants are available, the procedure is standardised and reproducible and with a low complication rate.
Reported complications after femoral head and neck excision (FHNE) include ongoing lameness associated with limb shortening, patellar luxation, sciatic neuropraxia and fibrous adhesions, and limitation in range of hip motion accompanied by severe muscle atrophy and pain associated with fibrous adhesions. It has been shown that dogs never achieve full peek vertical impulse following FHNE by comparison with THR. Revision of FHNE to THR has been reported in dogs and cats with positive outcomes but should not be a first choice. In such cases and also in cases of revision of previously failed THR, there can be notable deficits of the proximomedial aspect of the femur. This can be compensated using a reinforcing stem collar foundation linked to the greater trochanter for added resistance to fracture.
Bone deficits of the acetabulum or femur can present significant surgical challenges. The simplest options for managing dorsal acetabular rim (DAR) insufficiency du ring total hip replacement include implantation of a relatively small diameter cup, recessing a non-cemented cup into the medial acetabulum, leaving a portion of the cup exposed laterally, and moving the acetabular component further cranially into the caudal ilium and app lying a longer neck length. Plates and cement in conjunction with a cemented cup may also be used to augment a paucity of dorsal acetabular rim. However, these methods may be susceptible to complications including luxation or aseptic loosening. Custom metallic rim augmentation prostheses coated in hydroxyapatite or trabecular metal for bone on-growth have been employed with success. Cemented acetabular components are placed within these augmentation shells.
Stifle Joint
Total knee replacement (TKR) has to date been limited to canine patients for the treatment of severe osteoarthritis or juxta-articular bone loss using a commercially available unconstrained femoral metal component on a cemented polyethylene tibial component with or without a metallic base-plate. Thus far a commercial system is yet to be marketed for the feline patient. Current salvage options for multi-ligamentous disruption of the canine or feline stifle include multiple ligament reconstruction with or without ancillary trans-articular support which is fraught by challenges in attaining concomitant isometricity of all support structures. Extra-articular support without ligamentous reconstruction has been reported with a paucity of objective data and is contingent upon periarticular fibrosis.
Semi-constrained TKR devices have been commercially offered as custom made units for selected patients. Both uniaxial hinged and rotating hinged TKR akin to the human semi-constrained total knee replacement prostheses have been custom made by the author and used in salvage arthroplasty procedures for both cats and dogs. Additionally, these implants can be extended proximally or distally with appropriate fixation to provide articulating prostheses for replacement of tumours of the distal femur and proximal tibia. Generally dual element fixation using a cemented stem for immediate stability and an abutment collar plus a plate for bone on-growth is employed.
Custom medial compartment replacement which consists of a metallic femoral and tibial bearing surface with an interposed mobile-bearing polyethylene liner is now also available for dogs with unicompartmental stifle disease associated with end stage cartilage erosion meniscal pathology.
Tibia-tarsal Joint
Both partial and total hock replacement is a promising technology being investigated by the author and others but limited case numbers and short duration of follow-up preclude conclusions on efficacy at this time. This allows potentially effective treatment of pain and disability arising from developmental or trauma tic conditions of the tibiotarsal joint as an alternative to pantarsal arthrodesis.
Shoulder Joint
Orthopaedic conditions of the shoulder joint are an important cause of thoracic limb lameness in the dog. Articular and comminuted fractures of the proximal aspect of the humerus or distal aspect of the scapula have a guarded prognosis after surgical repair, with a high rate of articular scapular fractures resulting in long-term lameness. Arthrodesis is the most commonly described technique for management of dogs with severe traumatic, degenerative or congenital shoulder pathology unresponsive to medical management and where long-term joint stability could not be otherwise achieved. Very satisfactory clinical functio n can be achieved. By contrast, in people, total shoulder replacement has become the standard of care for many clinical conditions affecting the shoulder joint although anatomic, biomechanical and functional differences between species preclude direct comparison.
The author has recently used a custom made semi constrained total shoulder prosthesis to treat end-stage glenohumeral arthrosis and bone loss, using both cemented and uncemented prostheses. The technique has allowed the operated dogs to return to satisfactory levels of activity. The semi-constrained prosthesis provides a stable scapula-humeral joint and can facilitate recovery of severely atrophic shoulder musculature. The procedure has potential as an alternative to shoulder arthrodesis in selected cases.
Elbow Joint
For end-stage medial compartment disease of the canine elbow, a custom focal partial joint replacement is now commercially available consisting of a metallic humeral insert and a polyethylene ulnar insert in the region of the medial coronoid process. Joint access had been developed via a medial epicondylar osteotomy, but more recently a caudo-medial approach is advocated. Custom medial compartment replacement is also now possible for resurfacing larger areas and for specific indications in dogs which are deemed too large or too small for the commercially available devices.
Replacement of the elbow joint (TER) has been possible for several years and three implant systems have been introduced commercially, The Iowa, The TATE and The Sirius. Whilst complication rates have reduced over time, TER remains challenging and the complication rate bot h immediately postoperatively and in the longer term remains high. Earnest efforts are continually being expended by various groups to improve outcomes. Custom total elbow replacement is also now possible with 30 printed customised implants for specific indications such as end stage traumatic disruption and congenital deformity.