OTSR - 2026-05-01 - Journal Article
Total shoulder arthroplasty preoperative planning: Does the patient's arm position in the CT-scan affect posterior humeral head subluxation?
Caubère A, Vervaecke AJ, Jung A, Werthel JD, Gauci MO, Boux de Casson F
Topics
Key Takeaway
In 21,863 TSA preoperative CT scans, arm position significantly affects PHHS measurement, but the effect is clinically small: a 10° change in flexion or internal rotation shifts subluxation by only ~2%, and abduction by ~1%.
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Summary
This study quantified how scapulohumeral arm position at CT acquisition affects PHHS measurement in patients planned for TSA using a single 3D planning platform (Equinoxe GPS). Across 21,863 patients, arm position varied substantially (internal rotation range: −41.4° to +48.9°), and regression analysis showed flexion (β=−0.249) and internal rotation (β=−0.157) negatively correlated with PHHS while abduction correlated positively (β=0.130), all p<0.0001. Despite statistical significance driven by cohort size, the absolute effect was small: ±10° of motion produced only ±1–2% change in PHHS.
Key Limitation
The study cannot determine whether the statistically significant but small positional effects on PHHS translate into any difference in surgical decision-making or implant selection outcomes, as no clinical or intraoperative correlation was performed.
Original Abstract
BACKGROUND
Posterior Humeral Head Subluxation (PHHS) is a critical aspect to consider during the preoperative planning for Total Shoulder Arthroplasty (TSA). This study aims to investigate how variations in the initial arm position affect PHHS measurements obtained from CT scans.
METHODS
A prospective analysis was conducted involving patients diagnosed with primary osteoarthritis (OA) or rotator cuff tear arthropathy (CTA) from February 2021 to February 2025. The focus was on cases planned for TSA, utilizing data sourced from a single shoulder arthroplasty planning platform (Equinoxe, Exactech GPS, Blue Ortho). Validated three-dimensional (3D) bone models were employed to compute scapular and humeral landmarks automatically. The positioning of the humerus relative to the scapula was calculated, allowing assessment of abduction, flexion, and internal rotation angles at the scapulohumeral joint. HHS was measured as the ratio between the distance from the posterior border of the head to the Friedman axis and the diameter of a best-fit circle aligned with the humeral head.
RESULTS
The study encompassed 21,863 patients. Preoperative measurements indicated a median abduction of 10.3 ± 12.4° (percentile range: -14.0°; 36.6°), median flexion of 3.5 ± 8.9° (percentile range: -16.0°; 26.1°), and median internal rotation of 7 ± 18.9° (percentile range: -41.4°; 48.9°). The median PHHS recorded was 57.9 ± 10.8% (percentile range: 23.7%; 81.2%). A correlation between preoperative humeral positioning and subluxation was identified-positive for abduction (β = 0.1302, p < 0.0001) and negative for flexion (β = -0.2490, p < 0.0001) as well as internal rotation (β = -0.1570, p < 0.0001). This correlation is weak but highly significant, probably due to the large cohort size. Thus, a change of 10° in abduction corresponded to a shift of approximately +1% in subluxation values while similar adjustments in flexion or internal rotation resulted in roughly -2%.
CONCLUSION
Posterior humeral head subluxation is significantly influenced by patient posture during scanning, particularly sensitive to changes in flexion and internal rotation which tend to decrease subluxation more than abduction does; however, these alterations remain minimal at about ±1-2%.
LEVEL OF EVIDENCE
IV; Case series with no comparison group.