The contribution of the acetabular labrum to hip joint stability: a quantitative analysis using a dynamic three-dimensional robot model.

The acetabular labrum provides mechanical stability to the hip joint in extreme positions where the femoral head is disposed to subluxation. We aimed to quantify the isolated labrum's stabilizing value. Five human cadaveric hips were mounted to a robotic manipulator, and subluxation potential tests were run with and without labrum. Three-dimensional (3D) kinematic data were quantified using the stability index (Colbrunn et al., 2013, "Impingement and Stability of Total Hip Arthroplasty Versus Femoral Head Resurfacing Using a Cadaveric Robotics Model," J. Orthop. Res., 31(7), pp. 1108-1115). Global and regional stability indices were significantly greater with labrum intact than after total labrectomy for both anterior and posterior provocative positions. In extreme positions, the labrum imparts significant overall mechanical resistance to hip subluxation. Regional stability contributions vary with joint orientation.

Effect of pretension and suture needle type on mechanical properties of acellular human dermis patches for rotator cuff repair.

BACKGROUND: Dermal grafts are used for rotator cuff repair and augmentation. Although the in vitro biomechanical properties of dermal grafts have been reported previously, clinical questions related to their biomechanical performance as a surgical construct and the effect of surgical variables that could potentially improve repair outcomes have not been studied. METHODS: This study evaluated the failure and fatigue biomechanics of acellular dermis constructs tested in a clinically relevant size (4 × 4 cm patches) and manner (loaded via sutures) for rotator cuff repair. Also investigated were the effect of 2 surgical variables: (1) the fixation of grafts under varying magnitudes of pretension (0, 10, 20N), and (2) the use of reverse-cutting vs tapered needles for suturing grafts. RESULTS: Dermis constructs stretched ∼25% before bearing significant loads in the high stiffness region. Although 91% of the patches withstood 2500 cycles of loading to 150 N, the constructs stretched 13 to 19 mm after fatigue loading. This elongation could be reduced by 20% to 32% when reverse-cutting needles were used to prepare constructs or by applying 20 N of in situ circumferential pretension to the constructs before loading. CONCLUSIONS: Although dermis patches demonstrated robustness for use in rotator cuff repair, the patches underwent significant, substantial, and presumably nonrecoverable elongation, even at low physiologic loads. This study indicates that use of reverse-cutting needles for suture passage, preconditioning (cyclically stretching several times), and/or surgical fixation under at least 20 N of circumferential pretension could be developed as strategies to reduce compliance of dermis for its use for rotator cuff repair.

Locking and nonlocking plate fixation pubic symphysis diastasis management.

We evaluated the stability of locking and nonlocking plate fixation of the pubic symphysis in a cadaveric model of an unstable pelvic injury. Five fresh cadaver pelves--intact and with an unfixed simulated Tile B injury--were tested under compressive load simulating a 2-legged stance. On each pelvis, 3 pubic symphysis fixation constructs were tested: a 4-hole unicortical locking plate, a 4-hole bicortical locking plate, and a 4-hole bicortical compression plate. There were no significant differences in displacement among the 3 fixation methods tested on Tile B pelvic simulations. Symphysis pubis fixation alone reduced the anterior superior pubic symphysis mean gap displacement by 95% and the anterior inferior pubic symphysis by 78%, compared with the noninstrumented Tile B injury. There is no evidence that anteriorly placed locking constructs confer an advantage, in terms of pubic symphysis stability, over standard anterior compression plates for Tile B injuries.