Original Research

Biomechanical Evaluation of Two Arthroscopic Biceps Tenodesis Techniques: Proximal Interference Screw and Modified Percutaneous Intra-Articular Transtendon

Am J Orthop. 2016 July;45(5):E261-E267

References

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Discussion

This study was the first to directly compare a bony interference screw technique with a soft-tissue technique (modified PITT). Fixation strength is crucial. A load of 112 N is applied to the long head of the biceps tendon when a person holds 1 kg of weight in the hand with the elbow at 90° flexion.²² As mean (SD) ultimate load to failure was 157 (41) N with the modified PITT technique and 107 (29) N with the interference screw technique in this study, the interference screw can be recommended only with some hesitation.

The interference screw was stiffer with cyclic loading—an expected outcome, as it was secured to rigid bone—vs soft tissue, as in the modified PITT technique. Although the clinical implications for the modified PITT technique are unknown, more than likely, with the tendon being secured to soft tissue, there will be scarring over time.

In laboratory testing of biceps tenodesis constructs, interference screw fixation has had superior load-to-failure characteristics in comparisons with other fixation methods. Golish and colleagues¹³ found significantly higher load to failure with a biotenodesis screw than with a double-loaded suture anchor for subpectoral tenodesis. Testing similar implants, in a location more proximal in the bicipital groove, Richards and Burkhart¹⁴ likewise found superior fixation strength with an interference screw. Ozalay and colleagues¹⁶ found superior strength in an interference screw compared with suture anchor, keyhole, and bone tunnel in sheep. In a pig model, the highest ultimate load to failure was found in an interference screw—vs keyhole, bone tunnel, suture anchor, and ligament washer.¹⁹ Load to failure for the interference screw in these studies ranged from 170 N to over 400 N.^13,14,16,19

A few other investigators have studied the Biceptor interference screw. Slabaugh and colleagues¹⁵ found a mean (SD) load to failure of 173.9 (27.2) N for all specimens tested. Patzer and colleagues^9,17 found that the mean (SD) ultimate load to failure with the Biceptor proximal interference screw, 173.9 (27.2) N, was superior to that of a suture anchor.

The mean (SD) ultimate load to failure reported for the Biceptor interference screw in the present study, 107 (29) N, is lower than the values reported in the other studies—not only for the Biceptor screw but for interference screws in general. Nevertheless, we performed the technique as the manufacturer recommended.²² Our results were consistent across all specimens studied. Interestingly, in the study by Slabaugh and colleagues,¹⁵ 7 specimens failed at the tendon–screw interface during cyclic testing and were not included in the analysis of ultimate load to failure. As these specimens failed at a load between 5 N and 70 N, including their data would have significantly lowered the mean load to failure.

Concern over the Biceptor interference screw’s lower failure load relative to that of other interference screws has been raised before.^9,17 A major issue is possible overstuffing of the humeral tunnel, as the hole is reamed the same size as the screw. With the Biceptor, the proximal and distal portions of the tendon are placed in the tunnel in a U-shaped configuration with the screw between these limbs. The idea is that the 2 biceps tendon limbs might become abraded and consecutively weaken as the screw is inserted between the tendon limbs, more so than with a single loop. This idea was suggested by the typical longitudinal tendon splitting that occurs at the screw–tendon interface at the distal aspect of the tunnel.²³ In the present study, consistent failure (Figures 5A-5C) at the distal aspect of the screw–tendon junction supported the idea that the tendon is abraded during placement of the interference screw or during the friction-causing 90° turn the tendon takes into the bone on loading. There is no way to quantitatively examine tendon quality before interference screw placement, but on gross inspection all the tendons were of good quality. Slabaugh and colleagues¹⁵ also found consistent failure at the screw–tunnel interface.

The PITT technique has been described as a simple all-arthroscopic soft-tissue technique for biceps tenodesis.^23,24 Subsequently developed soft-tissue techniques have demonstrated clinical benefits.^25-27 Proposed advantages of these techniques are lower cost associated with decreased implant needs, no reliance on quality of bone for fixation, suturing while biceps tendon is still attached to anchor (anatomical tension is closely reproduced), and less interference with any subsequent use of magnetic resonance imaging for diagnostic purposes in the shoulder.

There have been only 2 biomechanical studies of the PITT technique. Lopez-Vidriero and colleagues²⁰ compared the biomechanical properties of the PITT and suture anchor techniques in a human cadaveric laboratory study and found that the PITT technique had mean (SD) ultimate load to failure of 142.7 (30.9) N and mean (SD) stiffness of 13.3 (3) N/mm. They observed consistent suture pullout through the tendon substance during failure, which suggests the most important factor for strength is the quality of the biceps tendon. Su and colleagues²¹found biomechanically inferior results of the classic PITT technique as compared with the interference screw technique.