Summary

It was a common phenomenon that the shortened supraspinatus tendon appeared to be lengthened after rotator cuff repair, and the tendon lengthening did not affect postoperative outcomes such as shoulder motion, clinical scores and postoperative pain; however, the amount of the lengthening had negative weak correlation with abduction strength index.

Abstract

Introduction

There is a phenomenon in which the tendon appears to be extended after rotator cuff repair. However, it is unclear in which cases tendon extension occurs and how the degree of extension affects the surgical outcome. This study aimed to evaluate pre- and postoperative musculotendinous junction (MTJ) and tendon length on magnetic resonance imaging (MRI) and to assess the postoperative tendon lengthening and its impact on postoperative outcomes.

Methods

We reviewed 109 patients with good repair integrity (Sugaya type I and II) after arthroscopic rotator cuff repair. Patients whose supraspinatus tendons were simply pulled out laterally without any additional procedures were included. They underwent serial MRI before surgery and at 3, 6, and 24 months after surgery. The location of the MTJ and the supraspinatus tendon length were measured. Clinical evaluation was conducted 2 years after surgery, including the range of shoulder motion, shoulder strength index (affected/unaffected strength), Constant score, University of California, Los Angeles (UCLA) score, and pain numeric rating scale (NRS). The characteristics of the preoperative tendon, change in tendon length over time, amount of the lateral shift of MTJ location and tendon length, and impact of tendon lengthening on postoperative clinical outcomes were analyzed.

Results

The preoperative tendon retraction significantly correlated with the MTJ location (r = -0.75; p < 0.0001) and preoperative tendon length (r = -0.46; p < 0.0001). Tendon length at 3, 6, and 24 months after surgery was significantly longer than those before surgery (26.7 ± 5.8 mm, 27.9 ± 6.6 mm, 28.5 ± 5.6 mm, and 21.5 ± 5.1 mm, respectively). From before surgery to 24 months after surgery, the MTJ location moved 8.4 ± 8.6 mm laterally and the tendon extended 7.0 ± 6.1 mm. A significant and weak negative correlation was found between tendon lengthening and the abduction strength index (r = -0.22; p = 0.03); however, no significant correlation with pain, range of shoulder motion, external rotation strength index, Constant score, and UCLA score was found. Multiple linear regression analysis also showed that tendon lengthening was only associated with the abduction strength index (standardized coefficient = -0.20, p = 0.03).

Conclusions

In this study, preoperative MRI showed that the more retracted the cuff tear, the more medially retracted the MTJ and the shorter the tendon length. With successful tendon repair, the shortened tendons appeared to be lengthened over time after surgery, extending an average of 7.0 mm at 2 years after surgery, and larger preoperative cuff tears appeared to have more postoperative tendon lengthening and lateral shift of MTJ location. The tendon lengthening did not affect postoperative pain, range of motion, or clinical scores; however, the amount of tendon lengthening had a weak negative correlation with the abduction strength index. Tendon elongation may decrease the tension of the supraspinatus muscle belly, resulting insufficient recovery of strength.