gms | German Medical Science

Objectives: Several anatomic characteristics have been suggested as potential risk factors for anterior cruciate ligament (ACL) rupture. Decreased femoral notch width; decreased depth of concavity of the medial tibial plateau; and an increase in the posterior-inferior-directed slope of the tibial plateau, have been shown to synergistically increase the risk of ACL injury. Other possible anatomic risk factors include: body mass; generalized joint laxity; Q-angle; and foot pronation. Femoral anteversion has also been mentioned as a potential risk factor for ACL injury, possibly through an increased Q angle. However, there is insufficient evidence available to determine whether femoral anteversion is associated with ACL injury. In a cadaveric experiment designed to study the effect of femoral torsion on knee kinematics during flexion, Sobczak et al. showed that medial femoral torsion decreased medial tibiofemoral translation, while lateral femoral torsion increased medial translation. In the current study, we hypothesized that external or internal rotation of the distal femur in an ACL-deficient specimen, achieved through a femoral osteotomy, would affect the magnitude of tibiofemoral translation during the anterior drawer, Lachman and pivot shift tests.

Methods: Six fresh-frozen whole lower limb specimens (hip-to-toes) were used. Instrumented stability testing consisted of the anterior drawer test; the Lachman test; and the pivot shift test. A mechanized pivot shifter was used to perform the pivot shift maneuvers, in order to reduce test-retest variability and ensure more accurate examinations. All tests were performed for each of four conditions: native knee; ACL deficient knee (ACL-); ACL deficient knee and 20-degree internal rotation of the distal femur (ACL-/IR); ACL deficient knee and 20-degree external rotation of the distal femur (ACL-/ER).

Results and Conclusion: Tibial Translation: Increased femoral anteversion, achieved through internal rotation of the distal femur, significantly reduced anterior tibial translation in the ACL deficient knee during the anterior drawer, Lachman and pivot shift tests (P < 0.05). Conversely, decreasing femoral anteversion through external rotation of the distal femur resulted in an increase in anterior tibial translation in the anterior drawer (n.s.), Lachman (P < 0.05) and pivot shift (P < 0.05) tests.

Tibial Rotation: Internally rotating the distal femur significantly reduced the magnitude of tibial rotation during the pivot shift in the ACL deficient knee (P < 0.05), while external rotation of the distal femur significantly increased tibial rotation (P < 0.05).

These changes in tibiofemoral translation may have been due to changes in the resting position of the tibia or increased or decreased tension of the IT band. Further research is warranted to fully determine how femoral version may affect knee kinematics in the setting of an ACL injury.