Results
Of the 20 rotator cuff tears evaluated (Table 1), 13 were crescent-shaped, 5 were U-shaped, and 2 were L-shaped. Mean (SD) A-P tear size was 17.7 (5.8) mm, and mean (SD) M-L tear size was 19.1 (8.6) mm. Mean age of the 20 patients (15 men, 5 women) was 57.9 years (range, 44-72 years). Mean (SD) length of symptoms was 12.9 (12.4) months (range, 3-48 months). Mean (SD) modified Goutallier score was 1.4 (0.7; range, 0-3).
Mean (SD) rotator cuff tension for all tears approximated to the medial footprint was 0.41 (0.33) pound, and mean (SD) cuff tension for all tears approximated to the lateral footprint was 2.21 (1.20) pounds—representing a 5.4-fold difference (P < .0001).
No statistically significant differences were detected in the ANOVA comparing tensions at medial and lateral positions among tear morphologic subtypes (all Ps >.05).
Subgroup analysis (Table 2) was performed for smaller (≤20 mm A-P) and larger (>20 mm A-P) tears. For smaller tears, mean (SD) tension was 0.27 (0.24) pound applied with the cuff tendon pulled to the medial footprint and 2.06 (1.06) pounds applied with the tendon pulled to the lateral footprint—a 7.6-fold difference (P < .0018). For larger tears, mean (SD) tension was 0.58 (0.37) pound applied with the tendon pulled to the medial footprint and 2.38 (1.4) pounds applied with the tendon pulled to the lateral footprint—a 4.1-fold difference (P < .005).
A statistically significant difference in tensions was found between small and large cuff tears positioned at the medial footprint (0.27 vs 0.58 lb; P = .0367); no difference was found between groups with the tendon at the lateral footprint (2.06 vs 2.38 lb; P = .284).
Univariate and multivariate analyses were performed using linear regression analysis (Table 3). During univariate analysis for medial footprint position, A-P tear size and Goutallier score both positively correlated with increasing tension; for lateral footprint position, no factors statistically correlated with lateral tension, though there was a positive trend for medial tension and female sex. During multivariate analysis for medial footprint position, only A-P tear size positively correlated with increasing tension; for lateral footprint position, both age (in nonlinear fashion as function of age + age2) and medial tension positively correlated with increasing tension.
Discussion
Our results indicated that significantly more tension is placed on the torn rotator cuff tendon when it is reduced across the footprint from a medial to a more lateral position in vivo. More tension was required for all tears to be reduced to the lateral footprint compared with the medial footprint. As expected, compared with smaller tears, larger tears required significantly more tension in order to be reduced to the medial footprint. Interestingly, no statistical difference was found between tensions required to reduce either small or large tears to the lateral footprint, which suggests that, regardless of tear size, more force must be applied to reduce the torn tendon to the lateral footprint compared with the medial footprint.
Hersche and Gerber34 were the first to report rotator cuff tension measurements in vivo. Although their study did not specifically compare cuff tensions reducing the tear to the medial versus lateral footprint, it did examine tension at displacement of 10 and 20 mm. Tension increased from 27 N to 60 N, correlating with a 2.2-fold difference between the 2 distances. Domb and colleagues35 also compared in vivo rotator cuff tension differences between the medial footprint and the lateral footprint in 4 patients. Mean tension applied to the cuff during reduction to the articular margin was 27 N, or 6 pounds. Mean tension needed to reduce the cuff to the lateral tuberosity was 76 N, or 17 pounds, for a 2.8-fold difference. Tears were not measured but were described as massive and retracted.
Although repair tension has long been recognized as a crucial factor in RCR healing, little clinical research has focused on the effects of excess tension. Davidson and Rivenburgh11 prospectively followed the clinical outcomes of 67 consecutive cuff repairs after intraoperative tension measurement and found that high-tension repairs (>8 lb) had significantly lower clinical outcome measures. However, the authors did not report on correlations with radiologic healing and stated, “Functional outcome is inversely proportional to rotator cuff repair tension.” Further study of the in vivo effects of increased tension on clinical and radiologic outcomes is needed.
Several animal studies have been conducted on the effects of tension on RCRs. Gerber and colleagues36 reported that the force needed to produce 1 cm of sheep supraspinatus tendon excursion increased 7-fold, from 6.8 N to 47.8 N, after 40 weeks of tendon tear. Coleman and colleagues37 compared the modulus of elasticity in sheep supraspinatus tendon after 6 weeks and 18 weeks of detachment and reported increases of 60% and 70%, respectively. Gimbel and colleagues38 showed that, in a rat model, “repair tension rapidly increased initially after injury followed by a progressive, but less dramatic, increase with additional time.” Of note, we did not identify any correlation between chronicity of symptoms and the tension needed to reduce the tendon medially or to a more lateral position on the footprint.