HOW SHOULD THE SUBSCAPULARIS BE REPAIRED FOLLOWING OPEN ANTERIOR APPROACH TO THE SHOULDER? A BIOMECHANICAL ANALYSIS.

Abstract

Introduction: A secure repair of the subscapularis represents an integral part of any surgery involving the anterior approach to the shoulder. Dysfunction of the subscapularis leads not only to poor functional results but also to anterior joint instability which is potentially untreatable. We have devised a new technique of double row fixation of the subscapularis using two suture anchors.

Aim: To evaluate the biomechanical strength of this double row technique against the established methods of simple suturing and transosseous repair techniques.

Method: Twenty matched pairs of human cadaveric shoulders were allocated into 3 groups. Group 1 consisted of 10 shoulders repaired with the double row technique. This involved incising the subscapularis along the bicipital groove and a lesser tuberosity osteotomy carried out leaving the subscapularis attached to a thin island of bone. A suture anchor (Twinfix) was then inserted just medial to the osteotomy site and the tendon repaired to bone using two horizontal mattress sutures. A second anchor was inserted laterally to supplement the repair with two simple suture knots. The remaining 10 contralateral shoulders were allocated equally between groups 2 and 3. In group 2, the subscapularis was divided longitudinally 1cm medial to the bicipital groove and repaired with simple interrupted suture knots. In group 3, the subscapularis was incised at its insertion to lesser tuberosity and the tendon repaired to the osteotomy site by multiple transosseous sutures through drill holes in the anterior humeral cortex.

The suture material used in all three groups was identical and consisted of an ultra high molecular weight poly-ethylene suture (Ultrabraid). To simulate the direction of pull of the subscapularis, the testing block was tilted 45 degrees while a vertically applied distraction force was applied. A custom made jig was used to measure the amount of displacement in response to a gradually applied load. All specimens were tested to failure. The mode of failure of each fixational construct was recorded.

Results: The load to failure was found to be significantly higher in the double row repair technique compared to simple suturing and transosseous methods. Simple suturing failed by suture cutting out of soft tissue and tranosseous repair failed by a combination of the suture cutting out through bone and soft tissue.

Conclusion: This new double row technique is simple to perform and preliminary biomechanical testing has shown this to be superior in terms of fixational strength compared to established methods. Additional advantages of this technique which have not been taken into account in this in vitro study include non violation of the subscapularis tendon with bone to bone healing.