Abstract
It is unusual to require the use of a total knee implant with more constraint than a posterior-stabilised post in primary knee arthroplasty. The most common indication is a knee with a severe deformity, usually fixed valgus with an incompetent medial collateral ligament, and an inability to correctly balance the knee in both flexion and extension. The pre-operative deformity is usually greater than 15–20 degrees fixed valgus and may be associated with a severe flexion contracture. This is usually seen in an elderly female patient with advanced osteoarthritis. Those pre-operative diagnoses more likely to require a constrained design include advanced rheumatoid arthritis, true neuropathic joint, and the “Charcot-like” joint due to bone loss or crystalline arthritis. Rarely, patients with periarticular knee Paget's disease of bone may require more constraint following correction of a severe deformity through the knee joint. Beware those patients with a staple or screw at the medial epicondyle or those with severe heterotopic ossification at the medial joint line, as this may signify a serious prior injury to the medial collateral ligament. Finally, there is a possibility of inadvertent division of the medial collateral ligament intra-operatively. Although this situation may be treated with suture repair and bracing, my choice is to switch to more constraint and early unbraced motion.
There are over 20 designs of varus-valgus constrained components, with a variety of tibial post designs with specific rotary and angular biomechanics, and many have the option of adding modular stems. Our experience with constrained, non-linked designs has been favorable with both the use of nonmodular and modular stem extensions. Longer-term survival analysis has shown a 96% survival at 10 years with these constrained components. However, the older designs frequently required a lateral retinacular release for proper patella tracking, and there were patella complications (fracture and osteonecrosis) in 16%. With a more modern design, over the past 12 years, the need for a lateral retinacular release and patella complications have been notably decreased. Varus-valgus constrained components have a small but important role in primary total knee arthroplasty for patients with severe deformity or an incompetent medial collateral ligament.
