Can handheld dynamometry predict rotator cuff tear size? A study in 2100 consecutive patients

Abstract

Background: This study aimed to determine whether handheld dynamometry measurements could predict rotator cuff tear size in patients who required surgical treatment of their shoulder pathology.

Methods: Handheld dynamometer readings were collected prior to surgery and analyzed retrospectively for 2100 consecutive patients. Post hoc, the cohort was divided into patients with rotator cuff tears (n = 1747) and those without rotator cuff tears (n = 353). The tear group was stratified into partial- vs. full-thickness tears and into 4 groups based on tear size area.

Results: Patients with partial-thickness tears had greater internal rotation (P = .03), external rotation (P < .001), and supraspinatus (P < .001) strength than patients with full-thickness tears. Patients with tears had lower supraspinatus strength than patients without tears (r = -0.82, P < .001). Patients with a larger tear size had lower values of external rotation (r = -1.46, P < .001) and supraspinatus (r = -1.18, P < .001) strength. A model involving internal rotation and supraspinatus strength could predict the presence of a tear with a sensitivity of 82% and specificity of 29%. The correct prediction rate was 73% overall (82% in tear group and 29% in no-tear group). The following formula was found to predict rotator cuff tear size, showing modest correlation with our raw data (r = 0.25, P < .001): Tear size = 482.8 + (3.9 × Internal rotation strength) + (1.6 × Adduction strength) - (7.2 × External rotation strength) - (2.0 × Supraspinatus strength).

Conclusions: Handheld dynamometer readings could not reliably predict rotator cuff tear size, showing only modest correlation with our raw data. Handheld dynamometry readings could predict the presence of a tear, although tears in the intact cohort were overestimated (a specificity of 29% and negative predictive value of 25%).

Keywords: Handheld dynamometry; arthroscopic rotator cuff repair; rotator cuff tear; rotator cuff tear size; supraspinatus tear; supraspinatus tear size.