Effect of Biceps Tenodesis Using PEEK Screw on the Torsional Strength of Humerus: Biomechanical Study

OBJECTIVES: Biceps tendoesis is a commonly accepted surgical option for long head biceps related pathology. Sub-pectoral tenodesis with interference screw offers reproducible outcomes with high biomechanical strength allowing for accelerated rehabilitiation. However, there is concern regarding potential fracture risk associate with a diaphyseal humeral tunnel particularly in an athletic population. The purpose of this study was to determine the amount of torsional strength reduction in the humerus resulting from an unicortically drilled hole, and to evaluate the effect of inserting a tenodesis screw into the drilled defect. We hypothesized that unicortical drilling would weaken the humerus and that the use of tenodesis screws would restore strength to the humerus. METHODS: Twenty (10 matched pairs) of fresh frozen full length humeri (mean age 55.3 years, range 37-70 years) were used to perform this study. All humeral specimens were stripped of all soft tissue, except for the pectoralis major tendon, which was used to determine location of the tenodesis. Specimens were allocated to either Screw (n=5) or Empty Ream Group (n=5) and the matching contralateral pairs remained intact. In the Empty Ream specimens, an 8 mm unicortical hole was placed into the bicipital groove 1 cm proximal to the inferior border of the pectoralis major tendon. The humeri in the Screw Group were prepared in the same manner and filled with a 8mm x 12 mm polyetheretherketone (PEEK) screw. All specimens were tested until failure under torsional loading at a rate of 1 degree/second. Peak torque, angular deformation at peak, and total energy to failure were recorded. A paired t-test was used to compare data from left and right humeri for each of the two groups. Data were also evaluated as the ratio of the intervention humerus to its contralateral intact humerus in order to compare Tenodesis Screw and Empty Ream groups via a 2-tailed, unpaired t-test. Statistical significance was assumed for P <0.05. RESULTS: When compared with intact group, both Screw and Empty Ream groups showed a significant reduction in peak torque, energy and angular displacement (P < 0.05). No statistical differences were noted between Screw and Empty Ream group for all measured values (Table 1). CONCLUSION: Drilling an 8mm unicortical hole for subpectoral biceps tenodesis reduces the torsional load to failure of the proximal humerus at time zero. Placing a PEEK tenodesis screw alone does not appear to increase the strength of the humerus.