Summary

Improved functional and gait parameters in kinematic alignment when compared to mechanical alignment in bilateral total knee arthropplasty

Abstract

Background

Neutral mechanical alignment (MA) has been traditionally used in total knee arthroplasty (TKA) aims to position femoral and tibial components perpendicular to the mechanical axis of the limb. However, many authors have researched the wide individual and racial variation in anatomy of arthritic knees. It is a subject of debate that if mechanical alignment is used in all knees, it may require extensive soft tissue balancing which in turn may lead to higher rates of dissatisfaction and suboptimal functional outcomes. In contrast to MA-TKA, Kinematic Alignment (KA) aims to match the post operative implant position to the highly variable pre-arthritic anatomy of the individual patient in accordance with the three kinematic axes of the knee. Quality research and comparative data between the two techniques are lacking, especially in Indian population.
QUESTIONS/PURPOSE: The purpose of this randomized controlled trial is to determine and compare the functional and radiological outcomes, joint awareness and complications in TKA with Mechanical alignment (MA) and Kinematic alignment (KA).

Methods

We performed a prospective randomized controlled trial in 27 patients(54 knees). All recruited patients meeting the inclusion criteria underwent Bilateral simultaneous total knee replacement by highly experienced senior arthroplasty surgeons. One knee was randomized to Kinematic Alignment group and the second knee in the same patient simultaneously underwent Mechanically Aligned TKA to overcome bias associated with patient related factors. Pre operative, Intraoperative and post operative data was recorded meticulously. Primary outcome was assessed by the Forgotten Joint Score (FJS) with a minimum of 6 month follow up. Secondary Outcomes were assessed using intra operative parameters, limb preference, Knee Society Score, and radiographic parameters in long leg X -ray films.

Results

Clinical, Radiological and Gait Parameters were compared in the RCT. The mean Forgotten Joint score( FJS) at 6 month follow-up was 70.9 for the KA group and 66.88 for the MA group (p<0.04). A significantly more number of patients preferred the KA knee as compared to the the MA knee on the preference questionnaire for better appearance and ease of rehabilitation. KA technique resulted in significant net varus of the proximal tibia (MPTA 86.4 SD=2) and valgus of the distal femur (LDFA= 87.2 SD=2.2).The KSS scores and Overall Limb alignment (femoral-tibial alignment ) showed no significant difference. Intra-operative parameters such as surgical time and blood loss showed similar outcomes. The KA technique resulted in a fewer number of soft tissue releases required for balancing, and the total bone resected in the KA group was lesser than the MA group. Gait Parameters showed significantly less Knee Adduction moment in the KA group as compared to the MA group.

Conclusion

We found that KA and MA techniques achieved similar and comparable functional and radiological outcomes, with more people preferring the KA technique at early follow up. Kinematic alignment was not associated with increased complication rate or catastrophic failure at early (at 6 months) follow up. This RCT suggests that KA is an acceptable and alternative alignment to MA, Since KA inserts the tibial component in varus, aseptic loosening might be a potential long term concern. Multi-centre trials with a larger cohort and a longer follow-up should be done to rule out long term survivorship concerns