Clinical significance of intraoperative glenohumeral joint load evaluation using a novel humeral sensor in navigated reverse total shoulder arthroplasty

Background

Advances in preoperative planning and technology have assisted the surgeon in appropriate placement of implants during reverse total shoulder arthroplasty (RTSA). However, assessment of soft tissue tension, balance, and stability remains subjective and dependent on surgeon experience. The aims of this study are to measure intraoperative joint loads with a novel trial humeral load sensor during RTSA, to evaluate the utility of this device in the operative setting, and to determine the association between recorded joint loads and postoperative patient-reported outcomes.

Methods

A pilot study of 15 patients with the diagnosis of osteoarthritis, rotator cuff arthropathy, or massive cuff tear were scheduled for computer-navigated RTSA and intraoperative joint load measurements. Following appropriate soft tissue releases, load recordings were made in standardized arm positions: neutral, across the chest, behind the back, and overhead. Participants were clinically and radiographically reviewed at 3 and 12 months post-surgery for evidence of joint instability, bony stress reaction or fracture, and American Shoulder and Elbow Surgeons (ASES) score.

Results

Intraoperative joint load measurements vary between participants, but there were no significant associations with age or body mass index (P > .05). Mean joint load in the neutral position was recorded as 6.1 lbf (standard deviation [SD] 7.4 range 0-25). In each of the three testing positions, mean joint load was recorded in the range of 30-40 lbf. Maximum joint loads above 70 lbf were observed in individual participants. There were no postoperative complications including joint instability or bony stress reactions. At 3 months, no statistically significant correlations were observed between clinical scores and load measures. At 12 months, the mean ASES score was 83.1 (SD 11.6, range 63.3-98.3), and demonstrated a large and significant association with load magnitude in the behind back position (r = 0.66, P = .008). The mean ASES pain subscale score was 45.3 (SD 6.4, range 30.0-50.0) and demonstrated a significant association with load magnitude in the behind back position (r = 0.69, P = .004) and with load magnitude in the across chest position (r = 0.55, P = .034). No other significant associations were observed.

Discussion

This pilot study indicates a novel humeral trial load sensor can be used safely and effectively during RTSA. This trial reports a range of intraoperative joint load measurements in neutral and commonly performed arm positions, which at 12 months post-surgery are associated with satisfactory shoulder function. Further clinical studies are required to define an upper limit for intraoperative joint load, which may potentially compromise clinical outcome.