The effect of oblique femoral tunnel placement on rotational constraint of the knee reconstructed using patellar tendon autografts

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Abstract

Purpose

Despite the high long-term success rates of anterior cruciate ligament (ACL) reconstructions, 8% of patients undergoing this primary procedure have recurrent disability and graft failure. Nonanatomic tunnel positioning (primarily of the femoral tunnel) accounts for most of all technical failures. We hypothesized that reconstructions that closely recreate the oblique femoral attachment of the ACL would result in more normal knee rotational stability than more vertical reconstruction. The purpose of this study was to determine whether obliquity of the femoral tunnel in the coronal (frontal) plane has an effect on rotational constraint after ACL reconstruction, as measured by anterior tibial translation, external rotation, and internal rotation.

Type of study

Ex vivo biomechanical study.

Methods

Ten matched pairs of fresh-frozen cadaver knees were alternately assigned to a standard or an oblique tunnel position reconstruction. Each knee was tested at 30° and 90° of flexion on a materials testing machine in ACL-intact, ACL-sectioned, and ACL-reconstructed states. A 100-N load was applied at a rate of 10 N/second, and anterior tibial translation was measured. Then 6.5 Nm of torque were applied, and external tibial rotation and internal tibial rotation were measured. The effects of tunnel placement and ligament condition were analyzed with a repeated measures analysis of variance. Significance was set at P ≤ .05 (Tukey’s test).

Results

At 30° of flexion, internal tibial rotation in oblique reconstruction was restored to intact values and was significantly less than the internal tibial rotation values in standard reconstruction. Internal tibial rotation in standard reconstruction was significantly greater than intact values. No significant differences were found between standard and oblique tunnel reconstructions and the respective intact values for the remaining internal tibial rotation and all external tibial rotation tests, regardless of flexion angle.

Conclusions

In our biomechanical model, ACL reconstructions using oblique femoral tunnels restored normal knee kinematics.

Section snippets

Methods

Ten matched pairs of adult human fresh cadaver knees (age range at death, 51 to 86 years; specimens from 7 men, 3 women) were obtained from the Maryland State Anatomy Board. No specimen had evidence of previous surgery or ligamentous injury. In each specimen, the femur and tibia-fibula were transected 15 cm from the lateral joint line and denuded of soft tissue to within 7 cm of the joint line. The knees were placed in plastic bags and stored at −20°C. The knees were allowed to thaw in the

Anterior tibial translation

Knees reconstructed with an oblique femoral tunnel showed no significant differences in anterior tibial translation compared with knees reconstructed with a standard femoral tunnel, regardless of knee flexion angle (Beta = 0.95 for 30° of flexion; Beta = 0.95 for 90° of flexion). All sectioned specimens showed significantly increased anterior tibial translation compared with intact and reconstructed specimens.

External tibial rotation

Knees reconstructed with an oblique femoral tunnel showed no significant difference in

Discussion

The anatomic origin of the ACL is posterior in the sagittal plane and oblique in the coronal plane. Reconstructions that place the femoral attachment in a nonanatomic position have a high incidence of failure.2 In the current study, increasing the coronal plane obliquity of the femoral tunnel to the anatomic origin of the ACL restored rotational stability to the knee. The oblique femoral tunnels (60° from vertical) resulted in internal tibial rotation similar to that measured in the intact

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