Lesser tuberosity osteotomy repair in stemless anatomic shoulder arthroplasty: a biomechanical analysis of repair techniques.

BACKGROUND

Lesser tuberosity osteotomy (LTO) repair in total stemless shoulder arthroplasty has a high nonunion rate and thus presents a challenge to shoulder surgeons. Improved repair techniques may mitigate nonunion from excessive fragment motion or inadequate compression. The purpose of this study was to evaluate the biomechanical properties of 3 LTO repair techniques in the setting of stemless shoulder arthroplasty. Tensionable cortical button (Button) and suture anchor (Anchor) constructs were compared to a reference suture with a lateral plate construct (Suture).

METHODS

Forty human cadaveric shoulders from 20 matched pairs were dissected and the lesser tuberosity osteotomized. In each pair, the LTO was repaired with a Suture and lateral plate construct on one side and on the other side, either a tensionable cortical Button or suture Anchor construct was used. Sutures were passed through the humeral components of a stemless arthroplasty system during the procedures. All specimens were cycled 1,000 times from 10 to 100 N at 1 Hz using a custom subscapularis cryoclamp. Cyclic construct gapping was recorded at regular intervals with a digital video system. All specimens were then loaded to failure, and failure load, displacement, mode, and construct stiffness were recorded. Statistical analyses compared the Suture constructs to their paired Button or Anchor constructs.

RESULTS

Compared to their Suture pairs, the Button group displayed no differences in construct gapping (P ≥ .138), but the Anchor group displayed up to 50% increased gapping from cycles 1-400 (P ≤ .049). The Suture construct supported approximately 25% higher loads prior to failure when compared to their paired Button and Anchor group (P ≤ .014). There were no differences in failure stiffness between the Sutures and their paired Buttons or Anchors.

CONCLUSION

In this controlled laboratory study, the decreased rate of initial construct gap formation and greater failure load of the suture construct suggests an environment for superior in vivo healing of the LTO as a result of decreased micromotion, with clinical implications still to be determined. Furthermore, the greater failure load in the suture construct could prevent catastrophic failure of the LTO in the delicate postoperative period. In the setting of total shoulder arthroplasty, an LTO subscapularis repair using a suture with a lateral plate construct provides a biomechanically superior repair to either a tensionable cortical button or suture anchor repair.