Biomechanical Evaluation of Two Arthroscopic Biceps Tenodesis Techniques: Proximal Interference Screw and Modified Percutaneous Intra-Articular Transtendon
The percutaneous intra-articular transtendon (PITT) technique has recently been shown to have results comparable to those of more accepted techniques. Its mode of failure was secondary to the suture pulling through the tendon substance. A modification was made whereby the tendon is locked within the suture configuration in an attempt to avoid pullout. We compared this new technique with a well-accepted technique of all-arthroscopic interference screw.
In each of 8 pairs of cadaveric shoulders (mean age, 55 years; range, 51-59 years), one shoulder was randomized to be treated with either modified PITT or interference screw (Biceptor; Smith & Nephew) biceps tenodesis, and the other shoulder was treated with the other technique. The tendons were preloaded at 10 N and then cycled at 0 to 50 N for 100 cycles at 1 Hz. Load to failure was calculated at a rate of 1.0 mm per second until peak load was observed.
Mean (SD) ultimate load to failure was 157 (41) N for the modified PITT technique and 107 (29) N for the interference screw technique (P = .003). In 7 of 8 specimens, the interference screw technique failed at the junction of the tendon, the screw, and the bone interface. In 7 of 8 specimens, the PITT technique failed by the tendon slipping through the suture or pulling through transverse ligament/rotator interval tissue.
Study results showed the modified PITT technique was a biomechanically superior construct.
This article provides the first description of the modified PITT technique. Our mean (SD) load to failure of the modified PITT technique was 157 (41) N, slightly higher than that reported for the classic PITT technique, albeit under a different setup.20 There was more variation in ultimate load to failure in our study than in previous studies, which could be secondary to tissue quality. As the modified PITT technique relies on surrounding tissue holding the biceps in place, this tissue would need to be of good quality and strength to obtain strong fixation. A possible concern is that placing stitches in the rotator interval could increase the risk of shoulder stiffness, but this has not been encountered clinically.
A more variable mechanism of failure was also found in the present study. Although half the specimens failed by suture pullout through the tendon, similar to what Lopez-Vidriero and colleagues20 described, 3 of our 8 specimens failed with the entire biceps tendon–suture construct pulling through the transverse ligament tissue, and 1 specimen failed by suture breakage. Although these numbers are too small for making definitive statements, our modified PITT technique may add some security to the tendon–suture construct. Such added security may be of particular value in the setting of poor-quality, diseased tendon tissue, and the construct may be more limited by the strength of surrounding tissues. In addition, if failure occurs at the suture transverse humeral ligament–rotator interval interface, more surrounding rotator interval tissue can be incorporated into the tenodesis to decrease the likelihood of failure through this mechanism.
This study had several limitations. First, it was a time zero study in a cadaveric model with simulated biomechanical loading. As such, it provided information only on initial fixation strength and could not prove any superior clinical outcomes or account for any biological changes with healing that occurred over time. Second, the study may have been underpowered, though sample size was chosen in accordance with other cadaveric biomechanical studies. Third, all procedures were performed in an open manner, simulating the arthroscopic approach. Particularly in the setting of the modified PITT technique, this represented a best case scenario. Spinal needles and subsequent sutures were easily passed under direct visualization through the transverse humeral ligament, rotator interval, and biceps tendon. There is likely marked variability in this step during arthroscopy in which visualization is more limited, as in the setting of concomitant procedures, such as subacromial decompression or rotator cuff repair. In addition, all tendons tested were normal in appearance and gave no indication of chronic degenerative changes.
Another study limitation is that we did not quantify bone mineral density, which if poor would have affected interference screw strength. However, mean specimen age was 55 years, minimizing chances of poor bone quality. In addition, 7 of the 8 failures in the interference screw group occurred not with pullout but at the screw–tendon junction, suggesting poor bone quality was not a significant factor. As tendon diameter was not measured before the procedures were performed, there is the possibility it could have been better in the modified PITT group and worse in the interference screw group because of tunnel crowding, as noted.
