Knee sagittal alignment and ACL injury.

Sagittal Alignment of the Knee and Its Relationship to Noncontact Anterior Cruciate Ligament Injuries. 
Terauchi, M., Hatayama, K., Yanagisawa, S., Saito, K. and Takagishi, K. American Journal of Sports Medicine, 2011; 39, 1090 – 1094. 
http://www.ncbi.nlm.nih.gov/pubmed/21285443

Non – contact ACL injuries accounts for majority of all ACL ruptures. Research suggests that injury mechanism is multifactorial. Sagittal alignment of the knee is one of the intrinsic risk factors that have been studied; however results seem to be unclear. Terauchi et al conducted this study to determine if there is a difference in sagittal alignment of the knee between an ACL-deficient group and a control group.

Patient group consisted of 73 ACL-deficient patients who sustained a noncontact injury to the ACL which was verified by arthroscopy. A negative control group consisted of 58 patients who underwent MRI examinations for knee joint pain during the same period. T2-weighted sagittal MRI scans of the knee in full extension were acquired. The following angles were measured: the femoral plateau angle, the extension angle and the tibial posterior slope angle. Results showed that the femoral plateau angle and tibial posterior slope angle were significantly larger in the ACL-deficient group than in the negative control group; however it was only seen among female subjects. Moreover, in the female subjects, a negative correlation between the extension angle and the tibial posterior slope angle was seen in the ACL-deficient group.

This study confirms the relationship between knee sagittal alignment and ACL injuries. However it does not provide information whether ACL deficient group sustained rupture due to differences observed. Nevertheless, most likely, results indicate knee sagittal kinematics as one of the potential ACL injury risk factors. Different proposals how does it contributes to higher ACL injury risk, has been developed.  It is usually observed that athletes who suffered ACL tear had their knees at position close to full extension. Some authors point out the, so called, position of no return, where the back is straight without lumbar lordosis, and the trunk is in a relatively upright position with little flexion of the hip and knee. When there is a change in the sequence of movement to regain control, there is an excessive eccentric contraction of the quadriceps muscle leading to hyperextension of the knee with increased anterior translation of the tibia and subsequent ACL tear. It has also been reported that at full extension, the proximal attachment of the patellar tendon is situated above and mostly anterior to its distal attachment at the tibial tuberosity. Hence, the horizontal force vector of the quadriceps muscle at the tibial tuberosity is largest at full extension which leads to an increase in the anterior shear force applied to the tibia and increased ACL stress. Finally, one study has also found that the posterior tibial slope may also contribute to stability in the sagittal plane and might be an ACL risk factor. The other study available which researched the association between posterior tibial slope and ACL injury risk, obtained contrary results.

Despite conflicting reports in the literature regarding the relation between knee sagittal plane kinematics and ACL injury risk, one has to admit its impact. Most likely, ACL injury mechanism is multifactorial and multiplanar.
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