The objective of this study was to evaluate the effectiveness of
reconstructions of the anterior cruciate ligament to resist anterior
tibial and rotational loads. We hypothesized that current reconstruction
techniques, which are designed mainly to provide resistance to anterior
tibial loads, are less effective in limiting knee instability in
response to combined rotational loads.
Twelve fresh-frozen young human cadaveric knees (from individuals
with a mean age [and standard deviation] of 37 ± 13 years
at the time of death) were tested with use of a robotic/universal
force-moment sensor testing system. The loading conditions included
(1) a 134-N anterior tibial load with the knee at full extension
and at 15°, 30°, and 90° of flexion, and
(2) a combined rotational load of 10 N-m of valgus torque and 10
N-m of internal tibial torque with the knee at 15° and 30°
of flexion. The kinematics of the knees with an intact and a deficient
anterior cruciate ligament, as well as the in situ force in the
intact anterior cruciate ligament, were determined in response to
both loads. Each knee then underwent reconstruction of the anterior
cruciate ligament with use of a quadruple semitendinosus-gracilis
tendon graft and was tested. A second reconstruction was performed
with a bone-patellar tendon-bone graft, and the same knee was tested
again. The kinematics of the reconstructed knees and the in situ
forces in both grafts were determined.
The results demonstrated that both reconstructions were successful
in limiting anterior tibial translation under anterior tibial loads.
Furthermore, the mean in situ forces in the grafts under a 134-N
anterior tibial load were restored to within 78% to 100% of that
in the intact knee. However, in response to a combined rotational
load, reconstruction with either of the two grafts was not as effective
in reducing anterior tibial translation. This insufficiency was
further revealed by the lower in situ forces in the grafts, which
ranged from 45% to 65% of that in the intact knee.
In current reconstruction procedures, the graft is placed close to
the central axis of the tibia and femur, which makes it inadequate
for resisting rotational loads. Our findings suggest that improved
reconstruction procedures that restore the anatomy of the anterior
cruciate ligament may be needed.