In vitro Evaluation of Labral Seal after Labrum Reconstruction

OBJECTIVES: The objective of this study was to quantify labral seal in labrum reconstructed joints by measuring the suction force, and compare them to the same joints with intact labrum and torn labrum. METHODS: Six cadaveric specimens of hemi-pelvis with proximal femur were obtained for the study from musculoskeletally normal donors (mean age: 54.5 yrs, range 46-61 yrs). Full pelvis specimens were first skeletonized and potted onto a custom mounting jig secured at the iliac wings using bolts and dental cement. The mounting jigs consisted of a metal bracket system which allowed the hemipelvis to rotate anteriorly and posteriorly. A pullout handle with a 6-axis load cell (AMTI, Watertown, MA) on board was fixed in the lateral aspect of the femur, 1-inch below the greater trochanter. Manual pullout was performed along the axis of femoral neck, while suction force induced by the negative pressured measured by the load cell was recorded at a rate of 100 Hz. The width of the intact labrum was measured with a ruler at the 12 o’clock position. Each specimen was tested under three labrum conditions: intact, torn, and reconstructed. The intact specimen was tested first. The labrum was then released directly off of the bony acetabular rim from the 11 o’clock position to the 2 o’clock position using a scalpel. The pull out strength was tested again. Finally, labral reconstruction was performed using five suture anchors evenly spaced within the span of the tear, and secured with a single simple suture per anchor. Pull out test was performed the third time using the same protocols. Prior to each of three pull out tests, light mineral oil (Johnson & Johnson baby oil) was applied to the surfaces of the femoral head and acetabulum to simulate the lubricating effect of synovial fluid. The peak suction forces from the three stages were derived from the load cell measurement based on the handle orientation. Peak suction force from the torn and reconstruction stages were also normalized with respect to the native stage and repeated measure ANOVA was used to test the differences. RESULTS: Large variations in labral morphology were observed among the six specimens. The width of the labrum at 12 o’clock ranged from 3 mm to 15 mm (mean 6.3 mm). Two of the six labrums showed signs of ossification. Correspondingly, the peak suction force measured from the six-axis load cell also exhibited wide inter-specimen ranges. On average, the peak suction force was 45.1±45.5 N in the native stage, 7.4±5.9 N in the torn stage, and 27.2±22.6 N in reconstruction stage. However, after normalization with respect to the intact stage, all specimens demonstrated a consistent trend of significant 74%±26% reduction for the labral torn stage (p<0.01), and a substantial 77%±25% restoration for the labral reconstruction stage compared to its native stage. The difference in peak suction force between the reconstructed stage and the native stage was not statistically significant (p=0.19). CONCLUSION: We produced a cadaver model to quantify labral seal in its intact, torn, and reconstructed stages. Results from this study demonstrated a consistent trend across various labral morphologic conditions, that is labral tear had significant impact on labral seal, and labral reconstruction can restore 77% of sealing function as the intact.