Intercondylar Notch Impingement of the Anterior Cruciate Ligament: A Cadaveric In Vitro Study Using Robots

Background. Research has indicated that a smaller intercondylar notch could cause contact between the anterior cruciate ligament and the femoral notch, which may predispose individuals to an increased rate of anterior cruciate ligament injury. Hypothesis. Contact between the lateral notch wall and the anterior cruciate ligament does increase the strain past the structural integrity of the ligament. Study Design. A descriptive laboratory study. Methods. A biomechanical study using robotic manipulators was conducted to investigate the occurrence of impingement in human cadaver specimens. Six cadaveric knees from six donors (three male and three female) were instrumented with a thin force sensor, placed on the lateral wall of the femoral condyle, and a differential variable reluctance transducer (DVRT) was attached to the middle section of the anterior medial bundle of the ACL. The knees were then moved through a series of flexion (5 degrees to 90 degrees), valgus (0 to 7.5 degrees), and external rotation (0 to 7.5 degrees) movements using two interacting robots. Results. The results revealed that impingement occurred in both male and female specimens with a maximum impingement force of 28 N. Impingement occurred more prominently in female knees and in the combination loading of valgus and external rotation for both genders. The corresponding strain due to impingement was small or compressive, with the male knee maximum strain less than 1.28% and the female knee strain less than 7.1% in the worse case conditions. Conclusion. The lack of increased force or strain when impingement occurred indicates that impingement may not affect the healthy function of the knee with a nonstenotic notch. Additionally, the analysis shows that impingement may not be a major contributing factor to anterior cruciate ligament injury, but rather a common occurrence in healthy knees. Clinical Relevance. Impingement within the femoral notch does not appear to be a major contributory factor to ACL injury. Other more severe injuries to the knee would occur before ACL impingement with the femoral notch becoming a contributing factor to ACL injury. The small sample size limits the conclusivity of the results presented in this research; thus, additional large sample size studies are warranted.