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Open Access Research article

Prosthesis alignment affects axial rotation motion after total knee replacement: a prospective in vivo study combining computed tomography and fluoroscopic evaluations

Melinda K Harman12*, Scott A Banks3, Stephan Kirschner4 and Jörg Lützner4

Author Affiliations

1 Department of Bioengineering, Clemson University, 301 Rhodes Engineering Research Center, SC, Clemson, 29634-0905, USA

2 Medical Technology Laboratory, Rizzoli Orthopaedic Institute, Via di Barbiano 1/10, Bologna, 40136, Italy

3 Department of Mechanical & Aerospace Engineering, University of Florida, P.O. Box 116250, Gainesville, FL, 32611-6250, USA

4 Orthopaedic Department, University Hospital Carl Gustav Carus Dresden, Fetscherstrasse 74, Dresden, 01307, Germany

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BMC Musculoskeletal Disorders 2012, 13:206  doi:10.1186/1471-2474-13-206

Published: 23 October 2012

Abstract

Background

Clinical consequences of alignment errors in total knee replacement (TKR) have led to the rigorous evaluation of surgical alignment techniques. Rotational alignment in the transverse plane has proven particularly problematic, with errors due to component malalignment relative to bone anatomic landmarks and an overall mismatch between the femoral and tibial components’ relative positions. Ranges of nominal rotational alignment are not well defined, especially for the tibial component and for relative rotational mismatch, and some studies advocate the use of mobile-bearing TKR to accommodate the resulting small rotation errors. However, the relationships between prosthesis rotational alignment and mobile-bearing polyethylene insert motion are poorly understood. This prospective, in vivo study evaluates whether component malalignment and mismatch affect axial rotation motions during passive knee flexion after TKR.

Methods

Eighty patients were implanted with mobile-bearing TKR. Rotational alignment of the femoral and tibial components was measured from postoperative CT scans. All TKR were categorized into nominal or outlier groups based on defined norms for surgical rotational alignment relative to bone anatomic landmarks and relative rotational mismatch between the femoral and tibial components. Axial rotation motion of the femoral, tibial and polyethylene bearing components was measured from fluoroscopic images acquired during passive knee flexion.

Results

Axial rotation motion was generally accomplished in two phases, dominated by polyethylene bearing rotation on the tibial component in early to mid-flexion and then femoral component rotation on the polyethylene articular surface in later flexion. Opposite rotations of the femur-bearing and bearing-baseplate articulations were evident at flexion greater than 80°. Knees with outlier alignment had lower magnitudes of axial rotation and distinct transitions from external to internal rotation during mid-flexion. Knees with femoral-tibial rotational mismatch had significantly lower total axial rotation compared to knees with nominal alignment.

Conclusions

Maintaining relative rotational mismatch within ±5° during TKR provided for controlled knee axial rotation during flexion. TKR with rotational alignment outside of defined surgical norms, with either positive or negative mismatch, experienced measurable kinematic differences and presented different patterns of axial rotation motions during passive knee flexion compared to TKR with nominal mismatch. These findings support previous studies linking prosthesis rotational alignment with inferior clinical and functional outcomes.

Trial Registration

Clinical Trials NCT01022099

Keywords:
Total knee replacement; Mobile-bearing prosthesis; Implant alignment; Surgical alignment; Knee kinematics; Axial rotation; Knee biomechanics; Knee arthroplasty