Summary

When comparing full kinematic, "conservative kinematic" and mechanical alignment for TKR patients, patients with the conservative kinematic approach had worse outcomes with regard to postoperative pain

Abstract

Introduction

& aims

Kinematic alignment has emerged as an alignment philosophy to challenge mechanical alignment, with a focus on restoring native anatomy. Conservative kinematic alignment approaches are emerging as a means of finding a compromise between these techniques(1). This study sought to investigate retrospectively if achieved TKA alignment technique correlated with short term patient outcomes.

Method

A database of TKR patients operated on by six surgeons from 1-Jan-2014 was accessed. All patients had a pre-operative CT scan segmented as part of routine surgical planning and a post-operative CT scan attained. Each patient had a mechanical and a kinematic surgical plan generated from the preoperative CT scan. A conservative kinematic alignment plan was also generated according to the technique described by Almaawi et al.(1), restricitng coronal component alignments to within 5° and combined coronal alignment to within 3° of neutral.

The achieved alignment was categorised as one of these three approaches from the post-operative CT scan and the relationship between these groupings and a 12-month postoperative Knee Osteoarthritis & Outcome Score (KOOS) was determined. All TKR’s used Omni Apex implants.

Results

A total of 369 TKR knees were identified in the database. 60% (221) were female and the average age was 70.1 years (+/- 8.2). 21% (76) of the knees were classified as kinematically aligned, with 10% of the total (37) being conservative rather than fully kinematically aligned.

When binarising patients into those with a KOOS Pain score less than or greater than 70, a trend was found, with 76% (28/37) of the conservative kinematic alignment group, 88% (257/293) of the mechanically aligned group and 95% (37/39) of the full kinematically aligned group reaching the threshold low pain. When grouping the mechanically aligned group with the fully kinematically aligned group, this difference was statistically significant (p = 0.0258), with the conservatively kinematically aligned group having a 2.1x greater risk of failing to reach the 70-point threshold. This relationship remained significant when considering only patients whose anatomy was extreme enough to be modified by conservative kinematic alignment rules.

Conclusions

This study showed an increase in pain when the achieved alignment formed a compromise between a restorative and a reconstructive approach. This suggests that conservative approaches to kinematic alignment, whilst not going beyond "acceptable boundaries" may actually result in worse outcomes, such that it may be preferable for surgeons to select either a traditional mechanical alignment or a "full kinematic" approach, depending on the patient and surgeon preference.