A Detailed Anatomical Description of the Gastrocnemius Muscle—Is It Anatomically Positioned to Function as an Antagonist to the Anterior Cruciate Ligament?

Abstract

Objective: The purpose of this cadaveric investigation was to provide a detailed morphologic description of the proximal gastrocnemius within the popliteal region of the knee and test the hypothesis that the gastrocnemius is anatomically positioned to function as an antagonist to the anterior cruciate ligament (ACL) of the knee. Methods: Twenty-two lower limbs from 11 embalmed cadavers underwent detailed dissection and anatomical analysis. Results: The results indicate that 63.3 ± 5.8% of the popliteal region is comprised of the hamstrings and the gastrocnemius, whereas 36.8 ± 5.7% is occupied by free space (fossa). Within the popliteal region, the gastrocnemius had a length crossing above the knee joint line of 5.4 ± 1.2 cm, which would likely result in a posterior pull on the femur during muscular contraction. Data provide an in-depth description of length and width morphology of the gastrocnemius and provide a detailed comparison between the medial and lateral heads of the muscle. Our results agree with earlier reports in the literature which suggest that the medial head is significantly longer and wider than the lateral head of the gastrocnemius. The medial head length was 23 ± 3.4 cm, compared to a lateral head length of 20.5 ± 2.9 cm. The medial head maximum width was 5.5 ± 1.6 cm, compared to a lateral head maximum width of 4.2 ± 1.1 cm. Conclusion: This research expands on past descriptions of the femoral origin of the gastrocnemius muscle’s medial head and confirms past descriptions of the lateral head origin on the femur. Our data clearly illustrate that the femoral attachment of the medial head of the gastrocnemius was much different (or more complex) than previously described and that it wraps around the posterior side of the medial femoral condyle and attaches more anteriorly. Further research should be directed at exploring the functional significance (if any) of these differences and examining the effect they may have on ACL function and knee joint kinematics.