A new method for evaluation of patellar height and the position of the joint line before and after total knee arthroplasty

Hua Han,Xiaohui Zhang

doi:10.1186/s12891-020-03794-1

Hua Han, Xiaohui Zhang

Open Access

https://doi.org/10.1186/s12891-020-03794-1

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Abstract

BackgroundThe measurement of patellar height and restoration of the natural position of the joint line are crucial to total knee arthroplasty (TKA). However, there remains a lack of consensus on an optimal measurement method to associate the patellar height with the joint line position. The objective of this study was to introduce a new method and validate the application in TKA both preoperatively and postoperatively.MethodsInstead of taking marginal landmarks as the tibial references, the tibial shaft axis was used to construct the new measurement method, which comprises the axis-patella (AP), joint axis-patella (jAP) indices and joint line height (JLH). Patellar heights were measured using the Insall-Salvati (IS), modified Insall-Salvati (mIS), Blackburne-Peel (BP), Caton-Deschamps (CD) indices, and the new method in 175 knees both preoperatively and postoperatively. Intraclass correlation coefficients and Pearson’s correlation analyses were respectively used to evaluate the reliabilities and correlations.ResultsThere were good correlations between the proposed method and the mIS, CD, and BP indices. High inter-observer reproducibility was found for AP (preoperative and postoperative 0.83), jAP (preoperative 0.82; postoperative 0.86) indices and JLH (preoperative 0.88; postoperative 0.95). High intra-observer repeatability was also found for AP (preoperative 0.85; postoperative 0.87), jAP (preoperative 0.83; postoperative 0.87) indices and JLH (preoperative 0.80; postoperative 0.92).ConclusionsThe new method is reliable for measuring patellar height before and after TKA, providing an alternative to distinguish between true and pseudo patella baja. Furthermore, JLH can be applied to assess and restore the joint line position in TKA.

Highlights

The measurement of patellar height and restoration of the natural position of the joint line are crucial to total knee arthroplasty (TKA)
An elevated joint line is responsible for the pseudo patella baja, whereas a shortened patellar tendon is the main cause of the true patella baja [11, 12]
In view of the fact that the following factors may have an impact on the measurement of patellar height, the exclusion criteria were determined: (1) patients who presented preoperative or postoperative radiographs with the knee in less than 30° of flexion; (2) patients who had undergone a unicompartmental knee arthroplasty (UKA), high tibial osteotomy (HTO) or a revision procedure; (3) patients with an excessively rotated knee radiographs due to poor technique, impairing an accurate identification for bone landmarks during measurement of patellar height

Summary

Introduction

The measurement of patellar height and restoration of the natural position of the joint line are crucial to total knee arthroplasty (TKA). Among the postoperative complications of TKA, patellofemoral pain, knee instability, and reduction of movement range are still common, which resulted from abnormal patellar height to some extent [3, 4]. Patella alta or patella baja is considered to be one of the indicators of poor clinical outcomes after TKA. The former is associated with patellofemoral instability [5], and the latter is associated with the reduction of movement range and anterior knee pain [6, 7]. An elevated joint line is responsible for the pseudo patella baja, whereas a shortened patellar tendon is the main cause of the true patella baja [11, 12]

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