Background:
The tibial inlay technique of reconstruction of the posterior cruciate
ligament offers potential advantages over the conventional transtibial
tunnel technique, particularly with regard to the graft force levels
that develop over a functional range of knee flexion. Abnormally
high graft forces generated during rehabilitation activities could
lead to stretch-out of the graft during the critical early healing
period. The purpose of this study was to compare graft forces between
these two techniques and with forces in the native posterior cruciate
ligament.
Methods:
A load cell was installed at the femoral origin of the posterior cruciate
ligament in twelve fresh-frozen cadaveric knees to measure resultant
forces in the ligament during a series of knee loading tests. The
posterior cruciate ligament was then excised, and the femoral ends
of 10-mm-wide bone-patellar tendon-bone grafts were attached to
the load cell to measure resultant forces in the grafts. For the
tunnel reconstruction, the distal bone block of the graft was placed
into a tibial tunnel and thin stainless-steel cables interwoven
into the bone block were gripped in a split clamp attached to the
anterior tibial cortex. With the inlay technique, the distal bone
block was fixed in a tibial trough with use of a cortical bone screw
with a washer and nut. The proximal ends of all grafts were pretensioned
to a level of force that restored intact knee laxity at 90°
of flexion, and loading tests were repeated.
Results:
There were no significant differences in mean graft forces between
the two techniques under tibial loads consisting of 100 N of posterior
tibial force, 5 N-m of varus and valgus moment, and 5 N-m of internal
and external tibial torque. Mean graft forces with the tibial tunnel
technique were approximately 10 to 20 N higher than those with the
inlay technique with passive knee flexion beyond 95°. Mean graft
forces with both reconstruction techniques were significantly higher
than forces in the native posterior cruciate ligament with the knee
flexed beyond approximately 90° for all but one mode of
loading.
Conclusions:
In this cadaveric testing model, neither technique for reconstruction
of the posterior cruciate ligament had a substantial advantage over
the other with respect to generation of graft forces.
Clinical Relevance:
The relatively high graft forces (compared with the forces in the
native posterior cruciate ligament) observed beyond 90°
of knee flexion after reconstruction of the posterior cruciate ligament
with either the tunnel or the inlay technique suggest that rehabilitation
activities that involve loading of the knee while it is flexed beyond
90° (such as kneeling, squatting, or climbing high stairs)
should be avoided in the early postoperative period.