Total knee replacement (TKR) is a well-recognized surgical procedure in humans, with approximately 500,000 procedures performed annually in the United States. Implants are typically made of metal-on-plastic or ultrahigh-molecular-weight polyethylene, and cementless or cemented techniques are described. The most common causes of implant failure reported in humans are aseptic loosening, infection, and implant wear. Much of what is known about TKR in dogs has come from preclinical research for human TKRs. However, studies have reported data and design on canine TKR for the past 30 years.

This prospective study examined the biological response to and the mechanical stability of cemented TKR surgery in 24 laboratory-reared, healthy, medium-sized hound dogs. Radiography ruled out preexisting joint pathology and routine blood analysis ruled out concurrent disease. The surgical technique for cemented TKR is well described in the article. Immediately after surgery, caudocranial and mediolateral radiographs were obtained to confirm implant positioning and again at 1, 6, 12, 26, 39, and 52 weeks. Radiographs were also used to assess implant migration, osteolysis, aseptic loosening, and formation of radiolucent lines greater than 1 mm thick at the cement–bone or cement–implant interface. Lameness was scored and stifle joint range of motion (in degrees) was measured. Bone density in the proximal tibia was measured by using dual-energy x-ray absorptiometry using a clinical scanner.

The stifle joint was opened upon necropsy at each study end point, and tissue was collected. The joint was examined for evidence of implant loosening, device impingement, and gross wear of the polyethylene or metallic components. Finally, specimens of the implant–cement–bone interface were mounted in a screw-driven mechanical test frame to calculate peak strength. The implants did not cause significant adverse response in adjacent hard or soft tissues, and the changes observed within the joint at time points up to 12 months revealed patterns of soft and hard tissue remodeling around the device similar to that seen after total hip replacement. Stable fixation was confirmed after 52 weeks; only 1 of 24 femoral components was loose at necropsy. The authors concluded that cemented TKR creates adequate function and joint excursion in the canine joint.

COMMENTARY:
This study is the largest to date of cemented TKRs in dogs. It suggests that this technique works within the dog knee; however, these dogs were clinically healthy and without arthritis before surgery. We hope that this information can be applied to a population of patients with severe, end-stage osteoarthritis of the knee. Self-proclaimed limitations of the study include the absence of a postoperative rehabilitation schedule and the lack of objective gait assessment, such as force-plate analysis. However, a study on laboratory hounds may be the only way to acquire necropsy data on the affected knees. —Heather Troyer, DVM, Diplomate ABVP (Canine & Feline Practice)

Cemented total knee replacement in 24 dogs: Surgical technique, clinical results, and complications. Allen MJ, Leone KA, Lamonte K, et al. VET SURG 38:555-567, 2009.