Background: Graft reconstructions of the lateral collateral
ligament, popliteus tendon, and popliteofibular ligament are frequently
performed in conjunction with a reconstruction of the posterior cruciate
ligament to restore knee stability. The purpose of this study was to determine
the femoral fixation sites resulting in the optimum isometry of popliteus
tendon, popliteofibular ligament, and lateral collateral ligament grafts in a
knee with a reconstruction of the posterior cruciate ligament.
Methods: Relative length changes (isometry measurements) were
recorded between sutures fixed at femoral grid points and appropriate fibular
or tibial graft tunnel sites; sites resulting in the least change in suture
length as the knee was moved from 0° to 90° of flexion were identified
as optimum isometric points. Bone blocks of Achilles tendon grafts were fixed
with the midpoint of the tissue's leading edge adjacent to the optimum
isometric point (optimum placement). Isometry measurements were repeated with
a lateral collateral ligament graft placed in a fibular tunnel and with
popliteus tendon and popliteofibular ligament grafts alternately placed in
appropriate tibial and fibular tunnels. The graft isometry measurements were
then repeated with the bone block centered over the femoral footprint of the
lateral collateral ligament or popliteus tendon.
Results: For all reconstructions, there was no difference between
the relative length changes of the suture placed at the optimum isometric
point and the relative length changes of the graft with an optimally placed
bone block. The mean location of the optimally placed bone-block center of the
lateral collateral ligament graft was within 1.85 mm of the mean center of the
footprint of the lateral collateral ligament; the mean graft isometry
measurements with the optimally placed bone block were not significantly
different from those with the bone block centered over the lateral collateral
ligament footprint. The mean optimally placed bone-block center of the
popliteus tendon and popliteofibular ligament reconstructions was 11 mm
anterior and 2.7 mm proximal to the center of the popliteus tendon footprint.
The mean relative length changes of the popliteus tendon and popliteofibular
ligament grafts with the bone block optimally placed were <0.9 mm and
<1.2 mm, respectively; the means with the popliteus tendon and
popliteofibular ligament bone blocks centered over the popliteus tendon
footprint were 3.7 mm and 5.0 mm, respectively.
Conclusions: A popliteus tendon or popliteofibular ligament
reconstruction with the bone block centered over the femoral footprint of the
popliteus tendon was highly non-isometric. If the graft were fixed at 30°
of flexion, it would elongate approximately 4 mm when the knee was extended to
0° and possibly stretch out.
Clinical Relevance: We found suture isometry to be a good indication
of graft isometry. In situ measurements of relative suture-length changes at
the time of surgery may be helpful in determining a femoral fixation site that
will result in graft isometry.