Acetabular labral tears are associated with hip osteoarthritis. A current surgical treatment strategy for a torn labrum, labral resection, has recently shown poor patient outcomes with radiographic signs of osteoarthritis two-years post-operation. Since mechanical factors play a role in the etiology of osteoarthritis, identifying the mechanical role of the labrum may enhance current surgical treatment strategies.
In this pilot study, we assessed the relationship between mean cartilage strain, maximum cartilage strain and the three-dimensional cartilage strain distribution in six human cadaver hips with various pathologic conditions of the labrum. We developed a novel technique of mapping cartilage strain using quantitative magnetic resonance imaging (qMRl). qMRl provides a non-invasive means of quantifying the cartilage strain distribution in the hip in threedimensions. Each specimen was assessed first with an intact labrum, then after surgically simulating a longitudinal peripheral labral tear, then after arthroscopically repairing the tear, and after labral resection. We validated the precision of the technique through use of an additional specimen which served as a control.
To minimize motion artifact in the high-resolution MR images, we determined that 225 minutes was required for cartilage to reach a steady-state thickness under load. We also determined 16.5 hours was required for cartilage to recover to a steady-state unloaded thickness.
The difference in mean and maximum cartilage strain when the labrum was repaired and resected was assessed using a paired t-test. We found that the resected group had an increased mean and maximum cartilage strain of 4% and 6%, respectively and the 3D cartilage strain distribution was elevated throughout the region of interest. When the condition of the intact labrum was compared to the torn labrum, we found no change in mean and maximum cartilage strain, and little obvious change in the 3D pattern of cartilage strain distribution.
Based on our findings of increased cartilage strain after labral resection when compared to labral repair, we hypothesize that the labrum’s contribution of additional surface area assists in load distribution, which spares cartilage from excessive loads. We therefore recommend that the longitudinal peripheral torn labrum should not be resected if it is possible to be repaired, because in vivo, labral resection may create an environment with increased articular cartilage strain, which is thought to be associated with cartilage degeneration.
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