Purpose

The presence of a Hill-Sachs lesion is a major contributor to failure of surgical intervention following anterior shoulder dislocation. The relationship between lesion size, measured on pre-operative MRI, and risk of recurrent instability after surgery has not previously been defined.

Hypothesis: We hypothesized that the size of Hill-Sachs lesions on pre-op MRI would be greater among patients who failed soft tissue stabilization when compared to patients who did not fail. We also hypothesized that the existence of a glenoid lesion would lead to failure with smaller Hill-Sachs lesions.

Purpose: Osteochondral allograft transplantation for the treatment of osseous defects to the humeral head has recently grown in popularity. Because only a portion of the articulating surface of the humeral head is replaced, conformity of the allograft to the native surface is imperative to restore the natural geometry of the joint. To achieve proper conformity, it is essential that the curvature of the humeral head of the allograft tissue match that of the native tissue. Curvature determination is also important for shoulder replacement procedures. Curvature of the humeral head is difficult to directly measure in allograft specimens. As a result, predictive measurements, such as the maximum length of the humerus are used to predict this curvature. The purpose of this study was to investigate the value of various anthropometric measurements for predicting humeral head curvature. We hypothesized that the maximum length of the humerus would be the most predictive of humeral curvature.

Method: 60 (28 female, 32 male) cadaveric humeri were obtained from the Hamann-Todd Human Osteological Collection. Specimens ranged from 20 to 35 years of age at the time of death (27.9 ± 4.5, mean ± SD). Specimens from this collection include height and weight as collected at the time of death. All specimens were scanned with a 3-dimensional laser scanner (NextEngine, Santa Monica, California, USA). This scanner has been shown to be accurate to within 0.005 inches. Linear measurements (maximum humeral length, epicondylar breadth) were made according to the recording standards for skeletal remains. Both measurements were made by choosing points on the 3-dimensional scan, rather than the traditional osteometric board. Humeral head curvature was determined by a custom computational code to fit a sphere to the articulating surface of the humerus. Data analysis was performed in Minitab (version 13, State College, PA, USA). A linear regression was performed for each predictive measurement. A stepwise linear regression with forward and backward substitution was performed for the most predictive variables from the initial linear regression.

Results: The most predictive factors (R^2 > 0.5) were epicondylar breadth, height, maximum humeral length, and gender. Based on the linear regression coefficients, these four factors (all normalized) were included in a forward and backward stepwise regression (alpha to enter and remove = 0.15). The resulting equation (shown below) had an R^2 values of 0.807. Humeral Diameter = 0.894 + 0.048*(epicondylar breadth) + 0.043*height – 0.020*gender

Conclusion: Of the predicted measurements evaluated, patient height, epicondylar breadth, and gender were most correlated with humeral head curvature. Including these three factors in a linear regression model increased the R2 value to 0.807. If only a single measurement can be used to size the humeral curvature, patient height will give approximately the same accuracy as epicondylar breadth, and can more easily be obtained.

Purpose: Tibial slope is an important contributor to sagittal plane stability. Anterior opening wedge high tibial osteotomy (HTO) has received increased attention for sagittal plane correction. A previous study demonstrated that anterior opening wedge HTO induced no increased strain in the ACL [1]. The goal of this present study was to determine the effect of increasing tibial slope on the strains of the major ligamentous restraints of the knee and on the change in position of the tibia in relation to the femur.

Method: Six cadaveric knee specimens were mounted at 15 degrees of flexion in a testing apparatus providing both compressive and anterior loading. Strains were measured in the ACL, PCL, MCL, and LCL for six randomized loading combinations and 3 conditions: intact, after anterior opening wedge HTO with 5mm plate, and 10mm plate. Tibial translation, rotation measurements and tibial slopes were obtained for each test.

Results: ACL strain was significantly associated with the plating intervention (p< 0.001). ACL strain decreased from −0.66 +/− 1.48 at baseline to −7.44 +/− 6.60 with a 5mm anterior opening wedge HTO and −7.99 +/− 6.45 with a 10mm osteotomy. Stepwise regressions yielded no significant effect of compression, anterior loading or osteotomy or combination thereof on PCL, MCL or LCL strain. Tibial slope and external rotation were significantly correlated with the plating intervention (p< 0.001 for both).

Conclusion: Increasing posterior slope via HTO did not increase strain in any of the major ligamentous restraints of the knee. Increasing tibial slope in the setting of a ligamentous deficient knee can be performed to increase stability without fear of submitting ligaments to increased strain.