In vivo Investigation of Patellofemoral Cartilage Contact Mechanisms- Impact of Mechanical Loading and Patellofemoral Geometry

Abstract

Aims and Objectives:Today the selection of the procedures for treatment of focal cartilage lesions is standardized to the defect size. Subject specific parameters like individual cartilage contact mechanisms are not taken into account. Aim of the present study therefore was to investigate inter-individual differences in the patellofemoral cartilage contact mechanisms of healthy subjects and to correlate them to the individual patellar joint surface area and patellar and femoral dimensions.Materials and Methods:10 knees of 10 healthy subjects with regular shaped patella and trochlea underwent magnetic resonance imaging at rest and during mechanical loading for simulated weight bearing. Imaging was performed at 30° knee flexion. A custom made pneumatic loading device was used to apply 0 and 200 N axial loading to the leg. Manual segmentation of the patella, the trochlear and the patellofemoral cartilage was performed. Patellar volume, joint surface area and cartilage contact areas were calculated for each loading condition. Moreover patellar height, diameter and femoral epicondylar width were determined. Prospective motion correction was performed to reduce motion artifacts during load application.Results:Mean size of the patellar surface area was 16,08 cm2 (range 13,11-18,07 cm2). Mean patellofemoral contact area (PCA) without loading was 6,15 cm2 (range 5,12-7,33 cm2). During axial loading of the leg with 200N PCA significantly increased to 6,77 cm2 (range 6,05-7,55 cm2) (p<0,05). Patellar surface area and PCA were not correlated (r=0,01; p<0,05). Mean Patella width was 5,4 cm (Range 4,8-6,2 cm) and mean femoral width at the epicondyles was 8,5 cm (Range 7,9-9 cm). The mean patellofemoral cartilage contact area showed poor correlation to patellar geometry (patellar width (r=0,48, p<0,05; patellar cartilage surface r=0,06, p<0,05) but moderate correlation to the femoral width (r=0,75, p<0,05).Conclusion:Main finding of the presented study is that patellofemoral cartilage contact mechanisms are responsive to loading and show relevant inter individual differences. A second important finding is that cartilage contact mechanisms cannot be concluded directly by geometric parameters such as joint surface area or patellofemoral dimensions. Further investigation is needed to identify parameters influencing size of patellofemoral contact area at rest and during loading in order to include them into diagnostics and treatment of the cartilage defects in clinical routine.