The effects of tibial rotation on the patellofemoral joint: assessment of the changes in in situ strain in the peripatellar retinaculum and the patellofemoral contact pressures and areas.

The objective of this study was to determine the effects of tibial rotation on in situ strain in the peripatellar retinaculum and patellofemoral contact pressures and areas. Patellofemoral joint biomechanics demonstrate a strong correlation with the etiology of patellofemoral disorders, such as chondromalacia, and are significantly influenced by tibial rotation. Six human cadaveric knees were used along with a patellofemoral joint testing jig that permits physiological loading of the knee extensor muscles. Patellofemoral contact pressures and areas were measured with a Fuji pressure-sensitive film, and the changes in in situ strain in the peripatellar retinaculum were measured with four differential variable reluctance transducers. Tibial rotation had a significant effect on patellofemoral joint biomechanics. The data showed an inverse relationship between increasing knee flexion angles and the change in patellofemoral contact pressures and in situ strain with tibial rotation. At higher knee flexion angles, the patella is well-seated in the trochlear groove and the function of the peripatellar retinaculum is minimized and less affected by tibial rotations.

The anterior band of the inferior glenohumeral ligament. Assessment of its permanent deformation and the anatomy of its glenoid attachment.

Surgical treatment for traumatic, anterior glenohumeral instability requires repair of the anterior band of the inferior glenohumeral ligament, usually at the site of glenoid insertion, often combined with capsuloligamentous plication. In this study, we determined the mechanical properties of this ligament and the precise anatomy of its insertion into the glenoid in fresh-frozen glenohumeral joints of cadavers. Strength was measured by tensile testing of the glenoid-soft-tissue-humerus (G-ST-H) complex. Two other specimens of the complex were frozen in the position of apprehension, serially sectioned perpendicular to the plane containing the anterior and posterior rims of the glenoid, and stained with Toluidine Blue. On tensile testing, eight G-ST-H complexes failed at the site of the glenoid insertion, representing a Bankart lesion, two at the insertion into the humerus, and two at the midsubstance. For those which failed at the glenoid attachment the mean yield load was 491.0 N and the mean ultimate load, 585.0 N. At the glenoid region, stress at yield was 7.8 +/- 1.3 MPa and stress at failure, 9.2 +/- 1.5 MPa. The permanent deformation, defined as the difference between yield and ultimate deformation, was only 2.3 +/- 0.8 mm. The strain at yield was 13.0 +/- 0.7% and at failure, 15.4 +/- 1.2%; therefore permanent strain was only 2.4 +/- 1.1%. Histological examination showed that there were two attachments of the anterior band of the inferior glenohumeral ligament at the site of the glenoid insertion. In one, poorly organised collagen fibres inserted into the labrum. In the other, dense collagen fibres were attached to the front of the neck of the glenoid.