Summary

The Relationship Between Humeral Head Size and Infraspinatus Tendon Length

Abstract

Purpose

Hill-Sachs lesions (HSLs) are noted to be common among patients suffering anterior shoulder dislocation. The remplissage procedure consists of surgical tenodesis of the infraspinatus (IS) tendon into a HSL in order to create an extra-articular boney defect that can no longer engage the anterior glenoid. If the IS tendon medial-lateral (M-L) length is less than the M-L length of the HSL, in particular the superior portion of the IS tendon, then replissage would require suture capture of less robust capsule and muscle tissues rather than a true tenodesis. Anatomic studies regarding the amount of available IS tendon relative to the humeral head size have not been described in the literature. The aim of this study was to compare the bony anatomy of the humeral head (HH) in relation to the amount of available IS tendon.

Methods

15 fresh frozen human cadaveric shoulders with intact rotator cuff tendons were included in this study. The interval between the teres minor and the infraspinatus was identified and divided. The IS tendon was measured along its superior-inferior width and M-L length. Given the variability in the morphology of the IS tendon the superior and inferior aspects of the tendon M-L length were measured independently. Each HH was measured in three planes: anterior to posterior (A-P), mid-sagital humeral neck from superior to inferior (HN) and medial to lateral (M-L) from the lateral portion of the proximal humerus to the most medial portion of the HH articular surface. Pearson correlation coefficients (r) of the of tendon measurements relative to their corresponding HH measurements were calculated.

Results

The mean HH measurements were 44.3mm ± 3.3mm for A-P, 49.3mm ± 3.4mm at the HN and 52.2mm ± 3.4mm (M-L). The mean value for the M-L length of the superior portion of the IS tendon was 42.4mm ± 5.5mm, while the mean for the inferior length was 31.0mm ± 4.7mm. The mean width of the IS tendon was 19.4mm ± 3.0mm. There was a statistically significant correlation (r = 0.58) found between the M-L length of the superior aspect of the IS tendon relative to the M-L HH length (p < 0.05) and the A-P HH diameter (p < 0.05). Based on these data, the approximate amount of IS tendon available for remplissage tenodesis can be calculated by the following formula:
Superior IS length = 0.969*(A-P HH measurement) – 0.503.

Conclusion

To our knowledge, this is the first study to define the relationship between the size of the HH and the amount of available IS tendon. There was a direct correlation between both the M-L HH length and A-P HH diameter with length of the superior aspect of the IS tendon. This information may help guide the future management of HSLs in the setting of subcritical glenoid bone loss. These data indicate that pre-operative HH measurements on advanced imaging may help define a “critical” amount of HH bone loss where the M-L length of the HSL is greater than the M-L length of the IS tendon.