Sagittal Patellar Offset Ratio Can Be a Predictor of Anterior Knee Pain after Primary Total Knee Arthroplasty without Patella Resurfacing

Abstract

Background Anterior knee pain (AKP) is an issue that persists even after successful total knee arthroplasty (TKA). In some patients, reasons for AKP occurrence are known, but it is unexplained in some others despite the patellofemoral joint being thought to be the main focus of pain. We investigated the relationship between unexplained AKP and the patellofemoral joint in the sagittal plane after primary TKA.

Methods We evaluated 372 knees of 317 patients retrospectively, who had completed a minimum 24-month follow-up. We divided them into two groups according to the presence of AKP. Sagittal patellar offset ratio (SPOR), anterior femoral offset ratio (AFOR), and Insall-Salvati ratio (ISR) were measured on lateral X-rays. Clinical outcomes were evaluated using the Oxford knee score (OKS) and WOMAC pre-and postoperatively, and AKP was evaluated using a visual analog scale (VAS) postoperatively.

Results Between non-AKP and AKP groups, SPOR (p < 0.001) and AFOR (p = 0.03) were significantly different but not ISR (p = 0.89). SPOR and AFOR were found to be two independent risk factors that may predict the likelihood of AKP. Receiver operating characteristic (ROC) analysis revealed that AFOR is a poor value, whereas SPOR is a reasonable predictive value. No correlation between SPOR and postoperative OKS (p = 0.92) and WOMAC (p = 0.25) and no correlation between AFOR and postoperative OKS (p = 0.44) and WOMAC (p = 0.58) were found.

Conclusion We found that SPOR is a good predictive tool with a cutoff value of 46.4% and 91.5% sensitivity for AKP and its increased ratio increases the probability of AKP following TKA. Considering that the patellar offset will not change, especially in patients without patella resurfacing, care should be taken not to increase the anterior femoral offset.

Zusammenfassung

Hintergrund Auch nach erfolgreicher Totalen Knie-Arthroplastik (TKA) klagen Patienten häufig über die Persistenz von vorderen Knieschmerzen (AKP). Während bei einigen Patienten die Gründe für das Auftreten von AKP bekannt sind, ist AKP bei anderen noch ungeklärt, obwohl das Patellofemoralgelenk als Hauptaugenmerk der Schmerzen angesehen wird. In dieser Studie untersuchten wir die Beziehung zwischen ungeklärter AKP und Patellofemoralgelenk in der Sagittalebene nach primärer TKA.

Methoden Wir evaluierten retrospektiv 372 Knie von 317 Patienten, die eine mindestens 24-monatige Nachbeobachtung abgeschlossen hatten. Die Patienten wurden entsprechend dem Vorhandensein von AKP in zwei Gruppen eingeteilt. Das sagittale Patellar-Offset-Verhältnis (SPOR), das anteriore Femur-Offset-Verhältnis (AFOR) und das Insall-Salvati-Verhältnis (ISR) wurden auf seitlichen Röntgenaufnahmen gemessen. Die klinischen Ergebnisse wurden prä- und postoperativ anhand des Oxford Knee Score (OKS) und WOMAC beurteilt. AKP wurde postoperativ anhand einer visuellen Analogskala (VAS) bewertet.

Ergebnisse Zwischen Nicht-AKP- und AKP-Gruppen waren SPOR (p < 0,001) und AFOR (p = 0,03) signifikant unterschiedlich, nicht jedoch ISR (p = 0,89). Es wurde festgestellt, dass SPOR und AFOR zwei unabhängige Risikofaktoren sind, die die Wahrscheinlichkeit des Auftretens von AKP vorhersagen können. Die ROC-Analyse ergab, dass AFOR, im Vergleich zur angemessenen Vorhersagbarkeit von SPOR, einen schlechten Vorhersagewert aufweist. Es gab keine signifikante Korrelation zwischen SPOR und postoperativem OKS (p = 0,92) und WOMAC (p = 0,25). Ebenso wurde keine signifikante Korrelation zwischen AFOR und postoperativem OKS (p = 0,44) und WOMAC (p = 0,58) gefunden.

Schlussfolgerung Wir fanden heraus, dass SPOR ein gutes Vorhersageinstrument mit einem Cutoff-Wert von 46,4 % und einer Sensitivität von 91,5 % für die AKP ist, wobei ein erhöhtes SPOR die Wahrscheinlichkeit einer AKP nach TKA erhöht. Da sich das Patella-Offset insbesondere bei Patienten ohne Patella-Resurfacing nicht verändert, sollte darauf geachtet werden, den anterioren Femur-Offset nicht zu erhöhen.

Keywords

knee - arthroplasty - anterior knee pain - sagittal patellar offset ratio - anterior femoral offset

Schlüsselwörter

Knie - Endoprothetik - vorderer Knieschmerz - sagittales Patella-Offset-Verhältnis - anteriorer Femur-Offset

Publication History

Received: 15 July 2021

Accepted after revision: 11 April 2022

Article published online:
02 June 2022

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