The trochlear isometric point is different in patients with recurrent patellar instability compared to controls: a radiographical study

Campos, Tulio, Soogumbur, Akash, McNamara, Iain R. and Donell, Simon T. (2018) The trochlear isometric point is different in patients with recurrent patellar instability compared to controls: a radiographical study. Knee Surgery, Sports Traumatology, Arthroscopy, 26 (9). 2797–2803. ISSN 0942-2056

[thumbnail of Published manuscript]
PDF (Published manuscript) - Published Version
Available under License Creative Commons Attribution.

Download (1MB) | Preview


Purpose: The purpose of the study was to investigate the theoretical isometric point based of the curve of the femoral groove and relating it to the origin of the MPFL femoral tunnel on lateral radiograph by comparing a patellar instability cohort with a control cohort. Methods: From a Patellar Instability database the radiographs of 40 consecutive patients were analysed to define Schöttle’s point, and the arc of the circle of the trochlear groove. A comparison population of 20 radiographs from comparable patients with tibiofemoral joint disorders was used as a control. The distance from Schöttle’s point to the most anterior part of the groove (extension) was also compared to the distance to the distal end of the roof of the notch (flexion). Results: The trochlea was circular in the controls but not the Patellofemoral Instability cohort where trochlear dysplasia is usually present. The difference between the extension and flexion length was a mean of − 2.0 ± 0.5 mm in the controls and + 6.0 ± 0.5 mm in the patellofemoral cohort. In neither cohort did the centre of the circle correspond to Schöttle’s point. The extension distance correlated with the boss height. Conclusions: The dysplastic trochlea is not circular and the centre of the best matched circle was different to the control trochleae which were circular. The circle centres did not correlate with Schöttle’s point for either cohort, and was more proximal in the Patellofemoral Instability cohort. Clinical relevance: For the MPFL to have equal tension throughout flexion within the groove, the length should not change. In normal knees the MPFL does not behave isometrically. The change in length, as measured from Schöttle’s point to the trochlea, was greater for patellofemoral instability patients explaining why an isolated MPFL reconstruction in the presence of severe trochlear dysplasia risks poor outcomes.

Item Type: Article
Uncontrolled Keywords: medial patellofemoral ligament,femoral tunnel,isometry,schöttle’s point,trochlear dysplasia
Faculty \ School: Faculty of Medicine and Health Sciences > Norwich Medical School
Related URLs:
Depositing User: Pure Connector
Date Deposited: 20 Dec 2017 16:23
Last Modified: 22 Oct 2022 03:26
DOI: 10.1007/s00167-017-4740-2


Downloads per month over past year

Actions (login required)

View Item View Item