Postoperative infraspinatus contractility is independently associated with objective outcomes after arthroscopic...

Tendon integrity alone cannot fully explain recovery after arthroscopic rotator cuff repair (ARCR). Because the infraspinatus stabilizes the glenohumeral joint, we investigated whether postoperative infraspinatus contractility, measured using real-time tissue elastography (RTE), is related to objective recovery.

One hundred fifty-one patients with full-thickness supraspinatus tears with variable posterior extension underwent ARCR between November 2021 and June 2023. Analyses excluded subscapularis tears and postoperative retears and included only intact repairs confirmed on magnetic resonance imaging at 1 and 2 years. Inclusion required pre- and postoperative RTE and functional testing with ≥2 years follow-up. Forty-six shoulders met criteria. The RTE-derived activity value (difference in strain ratio at rest and isometric contraction) was obtained preoperatively and 6 months, 1 year, and 2 years postoperatively. Additional measures included acromiohumeral distance, Goutallier stage, shoulder range of motion, isometric strength (abductor at 90° and 45° abduction, external rotator), and Constant-Murley score (CMS). Longitudinal changes were assessed with Friedman's test. Associations were analyzed with Spearman's correlation. Multivariable linear regression modeled 2-year CMS using predictors from univariable results and risk factors.

Mean age was 66.3 (46-79) ± 7.8 years; and 48% were female. Mean anteroposterior and medio-lateral tear sizes were 18.2 (4-36) ± 7.4 mm and 20.7 (10-40) ± 6.9 mm, respectively. Infraspinatus activity value, CMS, shoulder strength, range of motion, and acromiohumeral distance improved over 2 years (all P < .001), while supraspinatus activity value did not. At 2 years, infraspinatus activity value correlated with abduction strength at 90° (r = 0.405, P = .005) and 45° (r = 0.519, P < .001), and with external rotation strength (r = 0.345, P = .019). It also correlated with CMS (r = 0.480, P = .001). Neither infraspinatus nor supraspinatus activity values correlated with range of motion. CMS showed a weak negative correlation with the supraspinatus Goutallier stage (r = -0.301, P = .042) and no correlation with infraspinatus Goutallier stage, acromiohumeral distance, or age. No association with sex or Cofield classification was detected. In multivariable analysis, infraspinatus activity value remained independently associated with 2-years CMS (standardized β = 0.583, P < .001).

Postoperative infraspinatus contractility improved after ARCR and was independently associated with shoulder strength and CMS at 2 years. These associations support integrating RTE-based muscle assessment with anatomic evaluation in postoperative care.