Influence of sagittal plane component alignment on kinematics after total knee arthroplasty

Knee kinematics is pivotal to patient satisfaction and functional ability after total knee arthroplasty (TKA). The aim of this study is to examine the influence of sagittal plane component alignment as defined by femoral component angle (FCA), tibial slope (TS) and posterior condylar offset (PCO) on knee kinematics as defined by maximum extension angle (MEA), maximum flexion angle (MFA) and range of motion (ROM) after TKA.

This is a prospective, cross-sectional study of 105 osteoarthritic knees that underwent primary cruciate retaining TKA using a single implant design at a single tertiary institution. The sagittal plane component alignment was measured on weight-bearing true lateral radiographs taken day one post-operation and knee kinematics measured using a goniometer 1 year after TKA by the primary investigator.

Although the MFA was influenced by gender (P = 0.04); age, gender and pre-operative kinematics did not otherwise influence post-operative knee kinematics. The prediction model for MFA was statistically significant (P = 0.03) and accounted for 8.4 % of the variance. FCA (r = 0.3, P = 0.01) and PCO (r = 0.2, P = 0.05) demonstrated a statistically significant correlation with MFA. However, the prediction models for ROM and MEA did not achieve statistical significance. FCA (r = 0.2, P = 0.02) demonstrated a statistically significant correlation with ROM.

The most important findings of this study are that the FCA demonstrates weak positive correlation with MFA and ROM and that PCO demonstrates weak positive correlation with MFA. However, TS does not contribute significantly to knee kinematics after TKA. This is clinically relevant as orthopaedic surgeons can increase the PCO in cruciate retaining TKA and the FCA within therapeutic limits to improve knee kinematics.

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