Comparison of Contact Pressure Change Following Medial and Lateral Osteochondral Graft Harvest (SS-58)

Article Outline

• Introduction
• Methods
• Results
• Conclusions
• Copyright

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Introduction 

Given the limited healing potential of cartilage, treatment of focal cartilaginous defects in the weight bearing portion of the knee is a difficult problem for orthopedic surgeons. Studies have shown autologous osteochondral transfer (OATS) to be a valid option, with good results, for the treatment of such lesions. While OATS repair yields a desirable hyaline-like cartilage, there continues to be concern over graft site morbidity. It has been proposed that grafts harvested from sites that see significant contact pressure are more likely to be associated with crepitous, pain, and possibly early degeneration morbidity. Simonian and others have shown that all harvest sites along the lateral condular ridge and in the femoral notch see significant contact pressure. However, they have failed to report on contact pressures along the medial condular ridge following osteochondral harvest. We propose that donor sites on the medial femoral condyle will see decreased or zero contact pressure, and should lead to a lower risk of graft site morbidity.

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Methods 

Six fresh frozen cadaver knees were dynamically tested in a deep knee bend simulator from ten to 105 degrees while physiologic tendon loads were applied to the quadriceps and hamstrings. Loading was based on reported flexion moment data of Nagura et al. Testing was done at 10% and 30% load, which resulted in a maximum of 535 N of quadriceps force and 54 N on the hamstrings. A Tekscan pressure sensor was affixed to the medial and lateral portions of the trochlear notch of the femur. Data was collected in the intact case, after two medial and two lateral 6 mm cartilage cores were removed, after a 4 mm core removed from the lateral side between the 6 mm cores and following a 6 mm core removed from over the 4mm core. The pressure data was integrated to determine the total force on each femoral condyle, the peak pressure on each condyle and the amount of area of each condyle being loaded during the motion. The peak and average pressure in the region surrounding each core, before and after coring, was also examined. Repeated measures ANOVA paired t tests were used to compare the results.

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Results 

Contact area was significantly greater in the area of the lateral donor sites beyond 43 degrees. Furthermore, ten of the 12 medial harvest sites had no contact from the patella, while only three of 18 lateral sites saw no contact. (p<0.05) Additionally, the lateral condyle received significantly greater force than the medial condyle, with the greatest differences noted beyond 60 degrees of knee flexion. (p<0.05) Less significance was appreciated in the peak contact pressure until after 75 degrees of knee flexion. (p<0.05).

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Conclusions 

Given that the medial side is in fact non-articulating in most cases, we conclude that harvesting from these sites should lower the risk of graft site morbidity. This is additionally supported by our results, which showed that the articulating areas of the medial condyle saw significantly less force than the lateral side.