ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

that muscle imbalance associated with PFPS did not cause shifting in the contact
pressure. Furtherfmore, a recent study by Draper et.al. (2012) [14] found an increased
bone metabolic activity in medial side for few subjects and Gorniak (2009) [13] found
higher cartilage wear in the medial side compare to the lateral side of PF joints of the
cadaveric specimen. These findings support our results demonstrating that higher
stresses occur in the medial side of the PF joint in PFPS subjects. PD estimation using
alternate geometric method also gives similar trends with the FEA results.
Other previous studies have found that octahedral shear stress was higher in patellar
cartilage surface compared to the femur cartilage surface [17,18], and higher bone
metabolic activity in the patella compared to femur [14]. In the present study we also
found higher stresses in the patellar cartilage surface in both healthy and PFPS subjects.
PD estimated by using method PD2, PD4, and PD5 is greater in PFPS subjects. Finite
element models also show higher stresses in the PFPS subjects which corresponds to the
quantification of the PD using alternate geometric method. In both FEA and alternate
geometric method, we found that the PFPS subjects experienced higher stresses
compared to the healthy subject which are consistent with the current literature [17].
Our results reveal that contact stress is related to penetration depth. Both FEA and
alternate geometric method show similar trend in both the healthy and PFPS subjects.
Therefore, alternate geometric method could be a robust useful tool for almost accurate
assessment of PFPS.
Current study using both FEA and alternate geometric method show that PFPS subjects
experience higher stress in the medial side of the PF joint which is completely against
the main clinical idea that the greatest load occurs through the lateral facet causing
higher stress in the lateral side, not the medial side. According to clinician study as the
PF joint reaction force is directed laterally, it will create higher pressure in the lateral
facet. In the current study we are focusing on the stress not the force. However,
additional subjects will be investigated in future to confirm these findings.
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