Abstract
Introduction
Reverse total shoulder arthroplasty (RTSA) is a commonly performed operation for a variety of pathologies. Despite excellent short-term outcomes, complications are commonly encountered. Recurrent instability occurs in up to 31% of cases, often due to components placed with too little tension. Acromial stress fractures can occur in up to 7% of cases, often due to components placed in too much tension. Despite these concerns, there is little evidence evaluating the intraoperative tension and glenohumeral contact forces (GHCF) during RTSA. The purpose of this study was to measure the intraoperative GHCF during RTSA.
Methods
26 patients were enrolled after obtaining IRB approval. Inclusion criteria were patients undergoing primary RTSA. An instrumented strain gauge implant was designed to attach to an Exactech Equinoxe (Gainesville, FL) baseplate during RTSA. A specially designed trial glenosphere was then attached to the instrumented baseplate. Wires from the strain gauges were connected to a 24-bit analog input and placed outside the operative field to a computer that measure the forces. After joint reduction, GHCF were measured in neutral, passive flexion, passive abduction, passive scaption and passive external rotation (ER). Five patients were excluded due to wire calibration issues.
Results
21 patients were enrolled. The average age was 70 (range 54–84). The average height was 169.5cm (range 154.9–182.9), and average weight was 82.7 kg (range 45.4–129.3) There were 11 females and 10 males. There were thirteen 42mm glenospheres and eight 38mm glenospheres used. The mean GHCF values were 135N at neutral, 123N at ER, 165N in flexion, 110N in scaption, and 205N in abduction. The mean force values were significantly affected by joint position (p=0.002). The mean force at terminal abduction is significantly greater than the mean force at terminal ER and terminal scaption (p<0.05).
Conclusion
This study demonstrates that an intraoperative measurement of GHCF can be successfully performed during RTSA using strain gauges. GHCF during RTSA are at their lowest in scaption and ER. They are at their maximum in abduction. Surgeons should keep these findings in mind during trialing to potentially reduce complications associated with inappropriate intraoperative tensioning.
