Restricted kinematic alignment: The ideal compromise?

Human lower limb anatomy varies widely, and a systematic approach, using right-angled femoral and tibial bone cuts (Mechanical Alignment) leads to important anatomic alterations for many subjects. The restoration and preservation of pre-arthritic knee anatomy and ligament laxities during TKA has gained interest in recent years. The kinematic alignment (KA) technique represents a resurfacing of articular surfaces, removing equivalent amounts of bone and cartilage to match implant thickness. Concerns remain about restoring extreme anatomies, which may not be compatible with current TKA prostheses and fixation methods. Some knee anatomies may be inherently biomechanically inferior, or may have been altered by trauma, tumors, childhood deformity, or previous surgery. Keeping in mind these uncertainties, the senior author (PAV) developed a restricted KA (rKA) protocol. rKA aims to perform KA bone resections for most cases, but performing adjustments for patients outside a “safe range” defined by the following criteria: independent tibial and femoral cuts must be within 5° of the mechanical axis of the respective bone and the overall resulting Hip-Knee-Ankle angle (HKA) must fall within 3° of neutral. rKA may be the best compromise, by helping the surgeon to preserve native knee ligament balance during TKA and avoid residual instability, whilst keeping the lower limb alignment within a safe range.