Measurement of lower limb alignment: there are within-person differences between weight-bearing and non-weight-bearing measurement modalities

Daphne A L Schoenmakers,Nanne P Kort,Peter Z Feczko,Martijn G M Schotanus,Bert Boonen,Pieter J Emans

doi:10.1007/s00167-017-4636-1

Abstract

Purpose Previous studies have compared weight-bearing mechanical leg axis (MLA) measurements to non-weight-bearing measurement modalities. Most of these studies compared mean or median values and did not analyse within-person differences between measurements. This study evaluates the within-person agreement of MLA measurements between weight-bearing full-length radiographs (FLR) and non-weight-bearing measurement modalities (computer-assisted surgery (CAS) navigation or MRI).Materials and methodsTwo independent observers measured the MLA on pre- and postoperative weight-bearing FLR in 168 patients. These measurements were compared to non-weight-bearing measurements obtained by CAS navigation or MRI. Absolute differences in individual subjects were calculated to determine the agreement between measurement modalities. Linear regression was used to evaluate the possibility that other independent variables impact the differences in measurements.ResultsA difference was found in preoperative measurements between FLR and CAS navigation (mean of 2.5° with limit of agreement (1.96 SD) of 6.4°), as well as between FLR and MRI measurements (mean of 2.4° with limit of agreement (1.96 SD) of 6.9°). Postoperatively, the mean difference between MLA measured on FLR compared to CAS navigation was 1.5° (limit of agreement (1.96 SD) of 4.6°). Linear regression analysis showed that weight-bearing MLA measurements vary significantly from non-weight-bearing MLA measurements. Differences were more severe in patients with mediolateral instability (p = 0.010), age (p = 0.049) and ≥3° varus or valgus alignment (p = 0.008).ConclusionThe clinical importance of this study lies in the finding that there are within-person differences between weight-bearing and non-weight-bearing measurement modalities. This has implications for preoperative planning, performing total knee arthroplasty (TKA), and clinical follow-up after TKA surgery using CAS navigation or patient-specific instrumentation.Level of evidenceIII.

Highlights

Accurate lower limb alignment in total knee arthroplasty (TKA) is important to improve clinical results and prosthesis survival [8, 18, 20]
mechanical leg axis (MLA) measured on Full-length weight-bearing anteroposterior radiographs (FLR) versus measurements by computer-assisted surgery (CAS) navigation showed differences >3° in 27.9% of the patients preoperatively and in 8.4% of patients postoperatively
MLA on preoperative FLR compared to preoperative measurements obtained by magnetic resonance imaging (MRI) showed differences >3° in 22.9% of the persons

Summary

Introduction

Accurate lower limb alignment in total knee arthroplasty (TKA) is important to improve clinical results and prosthesis survival [8, 18, 20]. Full-length weight-bearing anteroposterior radiographs (FLR) are regarded as the gold standard for determining knee joint alignment [19]. Several studies have found differences between these measurement modalities [1, 6, 11, 13, 24, 28, 30,31,32] Most of these studies compared mean or median values of. Knee Surg Sports Traumatol Arthrosc (2017) 25:3569–3575 the measurement modalities and did not analyse within-person measurement differences. Comparing different measurements within individuals might be of greater value, as this shows the agreement between measurement modalities themselves. Neither correlation coefficients nor regression analysis are appropriate in the analysis of measurement method comparison data [2]

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Results

Conclusion