Basic science
Biomechanical analysis of the modified Bristow procedure for anterior shoulder instability: is the bone block necessary?

https://doi.org/10.1016/j.jse.2014.03.003Get rights and content

Background

Anterior shoulder instability with bone loss can be treated successfully with the modified Bristow procedure. Opinions vary regarding the role of the soft-tissue sling created by the conjoined tendon after transfer. Therefore, the aim of this study was to determine the effect of the modified Bristow procedure and conjoined tendon transfer on glenohumeral translation and kinematics after creating anterior instability.

Methods

Eight cadaveric shoulders were tested with a custom shoulder testing system. Range-of-motion, translation, and kinematic testing was performed in 60° of glenohumeral abduction in the scapular and coronal planes under the following conditions: intact joint, Bankart lesion with 20% glenoid bone loss, modified Bristow procedure, and soft tissue–only conjoined tendon transfer.

Results

A Bankart lesion with 20% bone loss resulted in significantly increased external rotation and translation compared with the intact condition (P < .05), as well as an anterior shift of the humeral head apex at all points of external rotation. Both the modified Bristow procedure and soft-tissue Bristow procedure maintained the increase in external rotation but resulted in significantly decreased translation (P < .05). There was no difference in translation between the 2 reconstructions.

Conclusions

The increase in external rotation suggests that the modified Bristow procedure does not initially restrict joint motion. Translational stability can be restored in a 20% bone loss model without a bone block, suggesting the importance of the soft-tissue sling.

Section snippets

Materials and methods

Eight cadaveric shoulders (4 left and 4 right shoulders from 6 male and 2 female cadavers with a mean age of 60 years) were prepared by removing the clavicle and major shoulder muscles, leaving the rotator cuff, capsule, coracoacromial ligament, and conjoined tendon intact. Three small reference screws were placed on the anterolateral edge of the acromion and the proximal humerus for measuring glenohumeral kinematics.

The scapula was secured to a mounting bracket, and the humerus was secured to

Rotational range of motion

After creation of a bony Bankart lesion, internal, external, and total range of motion increased significantly from the intact condition in both the scapular and coronal planes (P < .005 for all comparisons) (Table I). The increase in motion remained significantly increased from the intact condition after modified and soft tissue–only Bristow procedures in both planes (P < .01). There was no significant difference in range of motion between the modified and soft-tissue Bristow groups.

Discussion

In this biomechanical model, a Bankart lesion with 20% glenoid bone loss resulted in a significant increase in external rotation and overall range of motion. The modified Bristow procedure resulted in motion that was not statistically different from the intact condition in the scapular plane but was significantly increased in the modified Bristow condition in the coronal plane. The soft-tissue transfer condition resulted in significantly increased external rotation and total range of motion

Conclusions

The increase in external rotation observed in our instability model remained significantly increased from the intact condition in each repair condition. This suggests that nonanatomic reconstruction does not initially restrict joint motion. The data also show that translational stability can be restored in a 20% bone loss model without a bone block, suggesting the importance of the soft-tissue sling created by the conjoined tendon and subscapularis in the position of abduction and external

Disclaimer

Partial funding was provided by VA Rehabilitation Research and Development Merit Review and the John C. Griswold Foundation. The funding source did not play a role in the investigation.

The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

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    All investigations were performed at the Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA.

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