Patella-height analysis and correlation with clinical outcome after primary total knee arthroplasty

Christian Konrads; Jesin Rejaibia; Lucia C Grosse; Fabian Springer; Anna J Schreiner; Florian Schmidutz; Felix Erne

doi:10.1016/j.jor.2021.01.001

Patella-height analysis and correlation with clinical outcome after primary total knee arthroplasty

J Orthop. 2021 Jan 8:23:169-174. doi: 10.1016/j.jor.2021.01.001. eCollection 2021 Jan-Feb.

Authors

Christian Konrads¹, Jesin Rejaibia¹, Lucia C Grosse¹, Fabian Springer², Anna J Schreiner¹, Florian Schmidutz^{1

3}, Felix Erne¹

Affiliations

¹ Department for Trauma and Reconstructive Surgery, BG Klinik, University of Tübingen, Tübingen, Germany.
² Department of Radiology, BG Klinik, University of Tübingen, Tübingen, Germany.
³ Department of Orthopaedics, University of Munich (LMU), Munich, Germany.

Abstract

Background: It is the aim of this study to conceptualize a scheme for patellar-height analysis suitable for knees without and with implanted endoprosthesis. Furthermore, patellar-height and change of patellar-height by total-knee-arthroplasty (TKA) should be studied and correlated with clinical outcomes. We hypothesize that not only True-Patella-Infera (TPI) but also Pseudo-Patella-Infera (PPI) might be correlated with elevated anterior-knee-pain and reduced range-of-motion.

Methods: Several patellar-height indices were measured by three independent raters in two passes. Indices were analyzed and intra- and interobserver agreements were determined. For radiographic and clinical evaluation of 92 knee arthroplasties, the Insall-Salvati Index (ISI) and the Caton-Deschamps Index (CDI) were used to determine patellar-height and especially the amounts of TPI and PPI. Patellar-height was correlated with clinical outcome parameters: pain, ROM, Oxford Knee Score, Knee Society Score, Kujala Score, SF-36, Tegner and Lysholm.

Results: All used patellar-height indices demonstrated good intra- and interobserver agreement. Low preoperative ROM was correlated with low postoperative ROM after primary TKA. Postoperatively, 2.2% of the patients had a TPI and 9.8% had a PPI. Patella infera was not correlated with reduced subjective or objective clinical outcome parameters.

Conclusions: Preoperative ROM is a good predictor of postoperative ROM after primary TKA. Patellar-height analysis can be sufficiently performed using the ISI and the CDI, respectively the derived CDI (dCDI) in cases with implanted endoprosthesis. As an alternative to the CDI/dCDI, the BPI/mBPI can be used. There seems to be a certain threshold of acceptable patellar-height reduction, in which clinical outcome is not deteriorated.

Keywords: Anterior knee pain; Caton-deschamps; Insall-salvati; Patella baja; Patella infera; TKA.