The effect of posterior knee capsulotomy on posterior tibial translation during posterior cruciate ligament tibial inlay reconstruction.

PURPOSE

To measure the biomechanical effect of the surgical capsulotomy made during a posterior cruciate ligament reconstruction using the tibial inlay technique.

HYPOTHESIS

The posterior capsule contributes to posterior tibial stability.

STUDY DESIGN

Controlled laboratory experiment.

METHODS

Six knee specimens were tested on a robotic testing system from 0 degrees to 120 degrees of flexion with the posterior cruciate ligament intact and resected and with a posterior capsulotomy identical to that performed during tibial inlay reconstruction (sham surgery). A longitudinal incision with medial and lateral soft tissue stripping sufficient to mount an inlay bone block and pass an Achilles tendon graft into the knee was made in the oblique popliteal ligament, muscle belly of the popliteus, and posterior capsule. The posterior tibial translation was measured under a posterior tibial load of 130 N at multiple flexion angles.

RESULTS

Capsulotomy increased the posterior laxity compared with the posterior cruciate ligament-resected knee at every flexion angle. An additional 0.97 +/- 0.48 mm, 0.65 +/- 0.47 mm, 0.56 +/- 0.33 mm, 0.48 +/- 0.38 mm, and 0.94 +/- 0.60 mm of posterior laxity was recorded at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion, respectively. These values were all statistically significant (P < .001).

CONCLUSIONS

A posterior capsulotomy alone, without associated posteromedial or posterolateral disruption, produces additional posterior tibial translation in vitro compared with posterior cruciate ligament-deficient knee with intact capsule.

CLINICAL RELEVANCE

Damage to the posterior capsule may contribute to the residual posterior laxity noted clinically after posterior cruciate ligament reconstruction.