Biomedical subjects

Andrew Mahar

Publications and source records attributed to Andrew Mahar.

21 records · Page 2Linked to original sources

PubMedDate not supplied

Biomechanical stability of single-screw versus two-screw fixation of an unstable slipped capital femoral epiphysis model: effect of screw position in the femoral neck.

PURPOSE: To biomechanically evaluate single screw and varying 2 screw fixations for an unstable slipped capital femoral epiphysis (SCFE) model using physiologically relevant loading. STUDY DESIGN: In vitro biomechanical study. METHODS: Twenty-four immature porcine proximal femurs were prepared to simulate a mild-to-moderate unstable SCFE. The femurs were randomized into 4 fixation groups: single screw, 2 screws horizontally placed, 2 screws vertically placed, and 2 oblique screws. Biomechanical testing determined maximum load to failure (N), load (N) at 2, 4, 6, and 8 mm of femoral head displacement, and stiffness (newtons per millimeter) for each group. RESULTS: No significant differences were found among the 3 different 2 screw configurations. The 2 screw constructs were 66% stiffer and 66% stronger than the single screw construct. In addition, whereas there was no difference at 2 mm of femoral head displacement, each subsequent displacement (4, 6, and 8 mm) demonstrated significantly higher failure loads when 2 screws were used for stabilization. CONCLUSIONS: Slipped capital femoral epiphysis stabilization with 2 screws leads to increased stability over single screw fixation; however, none of the 3 configurations/placement patterns of the 2 screw constructs seemed to be superior in fixation stability. CLINICAL RELEVANCE: These data support the use of a 2 screw construct in acute/unstable SCFE fixation. The biomechanical benefit of 2 screws needs to be considered in the face of greater potential for inadvertent penetration into the joint with an increased number of screws.

Animals↗

PubMedDate not supplied

Intramedullary flexible nail fixation of unstable pediatric tibial diaphyseal fractures.

Flexible intramedullary nail fixation provides excellent fixation in children with unstable tibial shaft fractures, but few published series demonstrate the results and complications with this technique in children. A retrospective review of 19 patients was performed, as well as a biomechanical analysis of two implant configurations. Outcome measures included union rates, residual deformity, and complications. Union occurred in all cases. Five patients (26%) had complications. None required repeat operation. Two (11%) angular deformities (>/=10 degrees) occurred with the medial C and S construct, versus none with the double C. The C and S construct was more stable to mechanical testing with axial and torsional loading. Flexible intramedullary nail fixation is a straightforward technique that reliably produces good results. While the C and S construct was superior in biomechanical testing, the double C construct is more reliable and straightforward and remains by far the authors' preferred technique.

Adolescent↗

PubMedDate not supplied

Biomechanical evaluation of a new technique for rotator cuff repair.

BACKGROUND: In recent studies, investigators have used a cyclic loading model to investigate the efficacy of rotator cuff fixation modalities. HYPOTHESIS: A bioabsorbable poly-D-lactic acid screw and toothed washer implant will provide more stable fixation of rotator cuff repairs than standard suture anchor techniques. STUDY DESIGN: Controlled laboratory study. METHODS: Forty bovine shoulders (ages 3 to 6 months) had 1 x 2 cm defects created in the infraspinatus tendon. There were five repair groups (eight specimens per group) consisting of either two screw and washer implants or two suture anchors. Four suture techniques were tested: single-loaded anchors with simple sutures, double-loaded anchors with simple sutures, single-loaded anchors with horizontal mattress sutures, or single-loaded anchors with modified Mason-Allen sutures. Repairs were loaded at 5-second cycles from 10 to 180 N with use of a hydraulic testing machine. The number of cycles to gap formation of 5 and 10 mm was recorded. RESULTS: Gap formation of 5 and 10 mm occurred significantly later for the screw repair group than for any of the suture anchor groups. There was no significant difference between suture groups. CONCLUSIONS: The bioabsorbable screw and washer provided more stable fixation than suture anchor techniques under isometric cyclic loading conditions. CLINICAL RELEVANCE: This is a time-zero study of implant performance. The results indicate that the implant may decrease clinical failures in the early postoperative period under standard rehabilitation protocols.

Analysis of Variance↗