Strain behavior of native and reconstructed medial patellofemoral ligaments during dynamic knee flexion - a cadaveric study

Landmarks Used in Medial Patellofemoral Ligament Reconstruction Have Variable Topography

Purpose

To describe the morphology of the adductor tubercle (AT), medial epicondyle (ME), and gastrocnemius tubercle (GT); to quantify their relationships to the medial patellofemoral ligament (MPFL) footprint location; and to classify the reliability of each landmark based on measurement variability.

Methods

Eight cadaveric specimens were dissected to expose the following landmarks on the femur: MPFL footprint, AT, ME, and GT. Using the MicroScribe 3D digitizer, each landmark was projected into a 3-dimensional coordinate system and reconstructed into a complex, closed polygon. For each specimen tubercle, the base surface area, volume, height, base:height ratio, sulcus point, and distance from the MPFL footprint center were calculated. Levene's test was performed to evaluate differences in variance of the morphologic parameters between the three osseous structures.

Results

The ME had significantly greater variance in volume than the GT (P = .032), and the AT (17.5 ± 3.9) and GT (19.5 ± 3.6) were significantly less variable in base:height ratio than the ME (95.3 ± 19.2; P < .001). The GT was the closest to the MPFL footprint center (7.1 ± 3.1 mm) compared with the AT (13.4 ± 3.6 mm, P = .002) and ME (13.2 ± 2.7 mm, P = .003). However, the tubercles were equally variable in terms of distance to the MPFL footprint center (P = .86). Lastly, the sulcus point was estimated to be on average 1.9 ± 2.9 mm distal and 2.0 ± 2.0 mm posterior to the MPFL center point.

Conclusions

The 3 major osseous landmarks of the medial femur have significantly different variances in volume and base:height ratio. Specifically, the variability and elongated morphology of the ME differentiated this landmark from the AT and GT, which demonstrated the most consistent morphology.

Clinical Relevance

The results of this study may be useful to accurately locate landmarks for femoral tunnel placement and determine the isometric MPFL point during reconstruction.

Biomechanical comparison of two medial patellofemoral ligament reconstruction techniques: Quadriceps tendon fixation versus single-tunnel patella fixation with gracilis autograft did not differ in load to failure and stiffness

BACKGROUND

The purpose of this study was to evaluate the ultimate failure load and stiffness of two patellar fixation techniques for medial patellofemoral ligament (MPFL) reconstruction: (1) quadriceps tendon fixation (QT), (2) single tunnel (STG) patella fixation with gracilis autograft.

METHODS

A total of 16 fresh-frozen cadaveric knees (eight matched pairs) were randomized into two groups (QT vs. STG). The MPFL reconstructions were subjected to cyclic loading for 10 cycles to 30 N and then tested to failure at a constant displacement rate of 15 mm/min using a materials-testing machine (MTS 810 Universal Testing System). Failure mode, ultimate failure load and stiffness were recorded for each cadaveric specimen.

RESULTS

There was no significant difference in mean ultimate failure load among groups (P = 0.35). The STG group failed at a mean ultimate load of 190.04 N [standard deviation (SD) 23.18] and the QT group failed at 206.24 N (SD 37.99). The STG group had a mean stiffness of 21.38 N/mm (SD 1.44). This was not significantly higher than the mean stiffness value achieved for the QT group at 20.36 N/mm (SD 1.3) (P = 0.19). In the QT group all reconstructions failed due to tendon rupture at the patella attachment. The reason for failure in the STG group was the graft-suture connection.

CONCLUSIONS

This cadaver study showed no statistically significant difference in biomechanical performance of the evaluated patella fixation techniques, in terms of maximum load to failure and stiffness. Both techniques are reliable in terms of biomechanical properties and could offer additional surgical solutions.