The Pivot-shift test is a clinical test for knee instability for patinets with Anterior cruciate ligament (ACL), however the test has low inter-observer reliability. Dynamic radiostereometry (dRSA) imaging is a highly precise method for objective evaluation of joint kinematics. The purpose of the study was to quantify precise knee kinematics during Pivot-shift test by use of the non-invasive dynamic RSA imaging. Eight human donor legs with hemipelvis were evaluated. Ligament lesion intervention of the ACL was performed during arthroscopy and anterolateral ligament (ALL) section was performed as a capsular incision. Pivot-shift test examination was recorded with dRSA on ligament intact knees, ACL-deficient knees and ACL+ALL-deficient knees. A Pivot-shift pattern was identifyable after ligament lesion as a change in tibial posterior drawer velocity from 7.8 mm/s in ligament intact knees, to 30.4 mm/s after ACL lesion, to 35.1 mm/s after combined ACL-ALL lesion. The anterior-posterior drawer excursion increased from 2.8 mm in ligament intact knees, to 7.2 mm after ACL lesion, to 7.6 mm after combined lesion. Furthermore a change in tibial rotation was found, with increasing external rotation at the end of the pivot-shift motion going from intact to ACL+ALL-deficient knees. This experimental study demonstrates the feasibility of RSA to objectively quantify the kinematic instability patterns of the knee during the Pivot-shift test. The dynamic parameters found through RSA displayed the kinematic changes from ACL to combined ACL-ALL ligament lesion

The anterolateral ligament (ALL) has been recently recognized as a distinct stabilizer for internal rotation in the ACL-deficient knee and it has been hypothesized that ALL reconstruction may play an important role in improving anterolateral instability following ACL reconstruction. Both the gracilis tendon (GT) and a portion of the iliotibial band (ITB) have been suggested as graft materials for ALL reconstruction, however, there is an ongoing debate concerning whether GT or ITB are appropriate grafting materials. Furthermore, there is limited knowledge in how the mechanical properties of these potential grafts compare to the native ALL. Consequently, the aim of this study was to characterize the elastic (Young's modulus and failure load) and viscoelastic (dynamic and static creep) mechanical properties of the ALL and compare these results with the characteristics of the grafting materials (GT and ITB), in order to provide guidance to clinicians with respect to graft material choice. Fourteen fresh-frozen cadaveric knees (85.2±12.2 yr) were obtained. The ALL, ITB, and the distal (GTD) and proximal gracilis tendons (GTP) (bisected at mid portion) were harvested from each donor and tested with a dynamic material testing frame. Prior to testing, the cross-sectional area of each tissue was measured using a casting method and the force required to achieve a min-max stress (1.2–12 MPa) for the testing protocol was calculated (preconditioning (20 cycles, 3–6 MPa), sinusoidal cycle (200 cycles, 1.2–12 MPa), dwell at constant load (100 s, 12 MPa), and load to failure (3%/s)). Kruskall-Wallis tests were used to compare all tissue groups (p<0.05). The Young's modulus of both ALL (181.3±63.9 MPa) and ITB (357.6±94.4 MPa) are significantly lower than GTD (835.4±146.5 MPa) and GTP (725.6±227.1 MPa). In contrast, the failure load of ALL (124.5±40.9 N) was comparable with GTD (452.7±119.3 N) and GTP (433±133.7 N), however, significantly lower than ITB (909.6±194.7 N). Dynamic creep of the ALL (0.5±0.3 mm) and ITB (0.7±0.2 mm) were similar (p>0.05) whereas the GTD (0.26±0.06 mm) and GTP (0.28±0.1 mm) were significantly lower. Static creep progression of the ALL (1.09±0.4 %) was highest across all tissues, while GTD (0.24±0.05 %) and GTP (0.25±0.0.04 %) were lowest and comparable with ITB (0.3±0.07 %) creep progression. Since grafts from the ITB, GTD and GTP were comparable to the ALL only for certain mechanical properties, there was no clear preference for using one over another for ALL reconstruction. Therefore, further studies should be performed in order to evaluate which parameters play a vital role to determine the optimum grafting choice