Posterior condylar offset is an independent predictor of functional outcome after revision total knee arthroplasty

Abstract

Objectives: Preservation of posterior condylar offset (PCO) has been shown to correlate with improved functional results after primary total knee arthroplasty (TKA). Whether this is also the case for revision TKA, remains unknown. The aim of this study was to assess the independent effect of PCO on early functional outcome after revision TKA.

Methods: A total of 107 consecutive aseptic revision TKAs were performed by a single surgeon during an eight-year period. The mean age was 69.4 years (39 to 85) and there were 59 female patients and 48 male patients. The Oxford Knee Score (OKS) and Short-form (SF)-12 score were assessed pre-operatively and one year post-operatively. Patient satisfaction was also assessed at one year. Joint line and PCO were assessed radiographically at one year.

Results: There was a significant improvement in the OKS (10.6 points, 95% confidence interval (CI) 8.8 to 12.3) and the SF-12 physical component score (5.9, 95% CI 4.1 to 7.8). PCO directly correlated with change in OKS (p < 0.001). Linear regression analysis confirmed the independent effect of PCO on the OKS (p < 0.001) and the SF-12 physical score (p = 0.02). The overall rate of satisfaction was 85% and on logistic regression analysis improvement in the OKS (p = 0.002) was a significant predictor of patient satisfaction, which is related to PCO; although this was not independently associated with satisfaction.

Conclusion: Preservation of PCO should be a major consideration when undertaking revision TKA. The option of increasing PCO to balance the flexion gap while maintaining the joint line should be assessed intra-operatively.Cite this article: N. D. Clement, D. J. MacDonald, D. F. Hamilton, R. Burnett. Posterior condylar offset is an independent predictor of functional outcome after revision total knee arthroplasty. Bone Joint Res 2017;6:172-178. DOI: 10.1302/2046-3758.63.BJR-2015-0021.R1.

Keywords: Arthroplasty; Condylar offset; Knee; Outcome; Revision.

Fig. 1

Anterior and lateral views of the Kinemax TS (to the left) and Triathlon TS (to the right) revision TS TKA systems.

Fig. 2

Measurement of posterior condylar offset (PCO) and anterior condylar offset (ACO) on a true lateral radiograph to the distal femur. PCO was measured (A) relative to the tangent of the posterior cortex of the femur and ACO was measured (C) relative to the tangent of the anterior cortex of the femur. The PCO ratio was calculated by dividing PCO by the width of the femoral diaphysis at the level of the condylar flare (A/B). The ACO ratio was calculated by dividing ACO by the width of the femoral diaphysis at the level of the condylar flare (C/B).

Fig. 3

Graph showing the correlation between posterior condylar offset (PCO) ratio and improvement in Oxford Knee Score (OKS) one year after revision total knee arthroplasty (r = 0.45, p < 0.001 Pearson’s correlation).