Measurement of the End-to-End Distances Between the Femoral and Tibial Insertion Sites of the Anterior Cruciate Ligament During Knee Flexion and With Rotational Torque
ABSTRACT The aim of this study was to determine the end-to-end distance changes in anterior cruciate ligament (ACL) fibers during flexion/extension and internal/external rotation of the knee.
The positional relation between the femur and tibia of 10 knees was digitized on a robotic system during flexion/extension and with an internal/external rotational torque (5 Nm). The ACL insertion site data, acquired by 3-dimensional scanning, were superimposed on the positional data. The end-to-end distances of 5 representative points on the femoral and tibial insertion sites of the ACL were calculated.
The end-to-end distances of all representative points except the most anterior points were longest at full extension and shortest at 90°. The distances of the anteromedial (AM) and posterolateral (PL) bundles were 37.2 ± 2.1 mm and 27.5 ± 2.8 mm, respectively, at full extension and 34.7 ± 2.4 mm and 20.7 ± 2.3 mm, respectively, at 90°. Only 4 knees had an isometric point, which was 1 of the 3 anterior points. Under an internal torque, both bundles became longer with statistical meaning at all flexion angles (P = .005). The end-to-end distances of all points became longest with internal torque at full extension and shortest with an external torque at 90°.
Only 4 of 10 specimens had an isometric point at a variable anterior point. The end-to-end distances of the AM and PL bundles were longer in extension and shorter in flexion.
The nonisometric tendency of the ACL and the end-to-end distance change during knee flexion/extension and internal/external rotation should be considered during ACL reconstruction to avoid overconstraint of the graft.
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ABSTRACT: The purpose of this study was to determine the effect of physiological axial loading during knee flexion on changes in anterior cruciate ligament (ACL) end-to-end distance for normal and ACL-deficient knees. Biomechanical tests were conducted on ten cadaveric knees using an Instron machine. We gathered positional data of the tibia and femur at low to middle flexion angles (0°, 15°, 30°, 45° and 60°) with/without axial loading. First, no external load was applied to the specimens at each angle, and then, a 1000-N axial load was applied to the knees. The same test protocols were repeated after transection of the ACL. Using computer software (Geomagic Studio 10), we regenerated positional data and calculated the end-to-end distances of the anteromedial, posterolateral and the entire ACL bundle at each angle. Compared with ACL-intact knees without axial loading, knees under axial loading did not show significant increases in end-to-end distance. Under axial loading, we found no significant differences in end-to-end distances between bundles in ACL-intact knees according to the increase in knee flexion angle. After ACL transection, axial loading significantly increased end-to-end distances of all three bundles (P < 0.001), and the distances increased significantly with flexion angle (P < 0.05 at all angles in all bundles). The changing patterns of the ACL end-to-end distance in ACL-deficient knees were different from those in healthy knees after applying physiological axial loading, and the ACL end-to-end distances in ACL-deficient knees increased remarkably as knee flexion angles increased.Knee Surgery Sports Traumatology Arthroscopy 03/2014; DOI:10.1007/s00167-014-2935-3 · 2.84 Impact Factor
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ABSTRACT: Because distance between the knee ACL femoral and tibial footprint centrums changes during knee range-of-motion, surgeons must understand the effect of ACL socket position on graft length, in order to avoid graft rupture which may occur when tensioning and fixation is performed at the incorrect knee flexion angle. The purpose of this study is to evaluate change in intra-articular length of a reconstructed ACL during knee range-of-motion comparing anatomic versus transtibial techniques. After power analysis, seven matched pair cadaveric knees were tested. The ACL was debrided, and femoral and tibial footprint centrums for anatomic versus transtibial techniques were identified and marked. A suture anchor was placed at the femoral centrum and a custom, cannulated suture-centring device at the tibial centrum, and excursion of the suture, representing length change of an ACL graft during knee range-of-motion, was measured in millimeters and recorded using a digital transducer. Mean increase in length as the knee was ranged 120°-0° (full extension) was 4.5 mm (±2.0 mm) for transtibial versus 6.7 mm (±0.9 mm) for anatomic ACL technique. A significant difference in length change occurs during knee range-of-motion both within groups and between the two groups. Change in length of the ACL intra-articular distance during knee range-of-motion is greater for anatomic socket position compared to transtibial position. Surgeons performing anatomic single-bundle ACL reconstruction may tension and fix grafts with the knee in full extension to minimize risk of graft stretch or rupture or knee capture during full extension. This technique may also result in knee anterior-posterior laxity in knee flexion.Knee Surgery Sports Traumatology Arthroscopy 09/2013; DOI:10.1007/s00167-013-2694-6 · 2.84 Impact Factor