Navigated functional alignment total knee arthroplasty achieves reliable, reproducible and accurate results with high patient satisfaction

Abstract

Purpose: The decision on which technique to perform a total knee arthroplasty (TKA) has become more complicated over the last decade. Perceived limitations of mechanical alignment (MA) and kinematic alignment (KA) have led to the development of the functional alignment (FA) philosophy. This study aims to report the 2-year results of an initial patient cohort in terms of revision rate, PROMs and complications for Computer Aided Surgery (CAS) Navigated FA TKA.

Methods: This paper reports a single surgeon's outcomes of 165 consecutive CAS FA TKAs. The final follow-up was 24 months. Pre-operative and post-operative patient-reported outcome measures, WOMAC and KSS, and intra-operative CAS data, including alignment, kinematic curves, and gaps, are reported. Stress kinematic curves were analysed for correlation with CAS final alignment and CAS final alignment with radiographic long-leg alignment. Pre- and post-operative CPAK and knee phenotypes were recorded. Three different types of prostheses from two manufacturers were used, and outcomes were compared. Soft tissue releases, revision and complication data are also reported.

Results: Mean pre-operative WOMAC was 48.8 and 1.2 at the time of the final follow-up. KSS was 48.8 and 93.7, respectively. Pre- and post-operative range of motion was 118.6° and 120.1°, respectively. Pre-operative and final kinematic curve prediction had an accuracy of 91.8%. CAS data pre-operative stress alignment and final alignment strongly correlate in extension and flexion, r = 0.926 and 0.856, p < 0.001. No statistical outcome difference was detected between the types of prostheses. 14.5% of patients required soft tissue release, with the lateral release (50%) and posterior capsule (29%) being the most common.

Conclusion: CAS FA TKA in this cohort proved to be a predictable, reliable, and reproducible technique with acceptable short-term revision rates and high PROMs. FA can account for extremes in individual patient bony morphology and achieve desired gap and kinematic targets with soft tissue releases required in only 14.5% of patients.

Level of evidence: IV (retrospective case series review).

Keywords: Functional alignment; Kinematic alignment; Mechanical alignment; Total knee arthroplasty; Total knee replacement.

Fig. 1

Radiographic parameters demonstrating measurement of the; mechanical Lateral Distal Femoral Angle (mLDFA), mechanical Proximal Tibial Angle (mPTA) and Posterior Tibial Slope (PTS)

Fig. 2

Differential Posterior Tibial Slopes; Lateral Posterior Tibial Slope (LPTS) and Medial Posterior Tibial Slope (MPTS)

Fig. 3

PFJ Radiographic parameters; Trochlea Angle to Distal Femoral Angle (TA-DFA) and Trochlea Angle to Posterior Condylar (TA-PCA)

Fig. 4

Pre- and post-operative functional phenotypes. a The twelve most frequent functional knee phenotypes measured pre-operatively. b The eight most frequent functional knee phenotypes measure post-operatively

Fig. 5

Scatterplot of Pre-op vs post-op alignment in extension

Fig. 6

Scatterplot of Pre-op vs post-op alignment in flexion

Fig. 7

Mean WOMAC pre-op, at 12 months and at 24 months post-op. WOMAC pre-op, 12 months, 24 months, mean scores of 48.8 (SD ± 3.8), 1.4 (SD ± 3.9) and 1.2 (SD ± 5.2), power 24 months ß = 0.146, p = 0.003

Fig. 8

Mean KSS pre-op, at 12 months and at 24 months post-op and regards to KSS, 48.8 (SD ± 8.0), 92.5 (SD ± 7.2) and 93.7 (SD ± 5.8) respectively