Biomechanical comparison of primer and post-fusionstability of long head of biceps tenodesis fixation methods

Since there is no bone-like structure that prevents movement in the shoulder joint, the wide range of motion is achieved almost exclusively by soft tissues, making some compromise in stability in this joint. This causes the shoulder tissue to be exposed to trauma more frequently. Today, the incidence of biceps tendon pathologies is increasing day by day and this situation increases the importance of treatment. Failure of the treatment results in severe pain in the shoulder area and limitation of movement, which significantly reduces the quality of life of the patients. In this study, primer and post fusion biomechanical features of fixation with frequently used techniques which are tenodesis with interference screw and tenodesis with suture-anchor for pathologies of the long head of the biceps brachii were compared. The effect of different cortical layer thickness and bone densities also investigated. To mimic the bone structure, bone simulating Polyurethane foam blocks with different cortical bone thickness and trabecular bone density was prepared according to ASTM F 1839-08 standards. The screws and artificial tendons were embedded into artificial bone blocks to determine the ex-situ pull-out strength of primer fixation. Besides, to investigate the post fusion effect on the in situ biomechanical performance, the screw and artificial tendon were embedded into the blocks. The fixation strength performance of these methods for long head of biceps brachii was evaluated in terms of patient treatment. Pullout test were conducted to both fixation methods. During the static tests, load and displacement values were recorded. In dynamic loading tests 50 N was applied cyclically after preloading 10 N. The load ratio was 10, the waveform was sinusoidal, the frequency was 1 Hz. Runout endurance limit cycle accepted as 1,000 cycles without failure. Axial pullout tests were performed after the cyclic loading. Results showed that tenodesis with suture anchor was significantly superior in terms of pullout strength both primer and post-fusion tests. The mechanical performance of the suture anchor tenodesis method was not affected by the level of trabecular bone density, cortical bone thickness or cyclic loading regardless of pre-fusion or post-fusion models. Our findings suggest that interference screw fixation pull-out strength is radically decreased with decreasing the degree of trabecular bone density in primer and post-fusion period in both static and cyclic loading tests. It was determined that biomechanical performance of the fixation technique with interference screw was affected by cortical thickness primer and post-fusion period. The pull-out strength of the post-fusion period was significantly greater than primer strength of interference screw fixation method. While the pull-out strength of the fixation technique with interference screw was not affected by cyclical loading in the primer fusion period, it was observed that the pull-out strength decreased after cyclic loading in advanced osteoporotic and osteoporotic groups in the post-fusion period. These results have led to a scientific review for treatment protocols. The data obtained from this study suggest that for interference screw fixation method, it would be appropriate to wait for the post-fusion period for rehabilitation. However, considering all the data obtained primer and post fusion, we strongly recommend the use of suture anchor tenodesis fixation method. Even in advanced osteoporotic patients, the suture anchor tenodesis method performed superior to the interference screw in all aspects in order to start the rehabilitation process immediately after surgery.