Stem height in reverse total shoulder arthroplasty for fracture: deltoid and pectoralis major tendon distances from an inlay tray

Background

Reverse total shoulder arthroplasty (RTSA) has emerged as a favorable treatment for comminuted proximal humerus fractures, however, can be challenging due to the need to restore humeral height. Minimal research has been done investigating distances from anatomic landmarks to inlay tray designs in RTSA. This study evaluated anatomic references for use in RTSA and investigated how inlay stem designs impact distances from anatomic landmarks.

Methods

Twelve fresh frozen cadaver shoulders were dissected via a standard deltopectoral approach. Zimmer Trabecular Metal and DonJoy Orthopedics Altivate inlay stems were utilized in each cadaver, placed with the prosthesis tray flush with the cut. Measurements were taken from the top of the deltoid insertion to the most medial and lateral edges of the prosthesis tray (distance between deltoid tendon insertion and medial tray and distance between deltoid tendon insertion and lateral tray, respectively). Measurements were also taken from the transverse fibers at the top pectoralis major tendon (PMT) insertion to the most medial and lateral prosthesis tray (distance between PMT and medial tray and distance between pecotralis major tendon and lateral tray, respectively).

Results

Using the Zimmer system, the average distance from the deltoid insertion to the medial tray edge was 64.8 ± 13.1 mm, and the average distance from the deltoid insertion to the lateral tray edge was 84.9 ± 10.7 mm. The average distance from the pectoralis insertion to the medial tray edge was 30 ± 4.3 mm, and the average distance from the pectoralis insertion to the lateral tray edge was 49.4 ± 4.3 mm. Using the DonJoy Orthopedics system, the average distance from the deltoid insertion to the medial tray edge was 64.6 ± 11.9 mm, and the average distance from the deltoid insertion to the lateral tray edge was 86.4 ± 10.7 mm. The average distance from the pectoralis insertion to the medial tray edge was 29.8 ± 4.2 mm, and the average distance from the pectoralis insertion to the lateral tray edge was 51.2 ± 3.1 mm. The overall mean distance between PMT and medial tray and distance between pecotralis major tendon and lateral tray was 29.9 ± 4.2 mm and 50.3 ± 3.7 mm, respectively, and the overall mean distance between deltoid tendon insertion and medial tray and distance between deltoid tendon insertion and lateral tray was 64.7 ± 12.2 mm and 85.7 ± 10.5 mm, respectively.

Conclusion

More precise and accurate ratios were found using the PMT insertion compared to the deltoid tendon insertion. Measurements using two different inlay tray system manufacturers were comparable. These findings aid surgeons intraoperatively in the attempt of proper prosthesis placement during RTSA.