Biomechanics in an Incomplete Versus Complete Supraspinatus Tear: A Cadaveric Study

Abstract

Background: Degenerative and traumatic changes to the rotator cuff can result in massive and irreparable rotator cuff tears (RCTs). Purpose/Hypothesis: The study objective was to conduct a biomechanical comparison between a small, incomplete RCT and a large, complete RCT. We hypothesized that the incomplete supraspinatus (SS) tear would lead to an incremental loss of abduction force and preserve vertical position of the humeral head, while a complete SS tear would cause superior humeral migration, decrease functional deltoid abduction force, and increase passive range of motion (ROM). Study Design: Controlled laboratory study. Methods: Six cadaveric shoulders were evaluated using a custom testing apparatus. Each shoulder was subjected to 3 conditions: (1) intact/control, (2) 50%, full-thickness, incomplete SS tear, and (3) 100%, complete SS tear. Deltoid abduction force, superior humeral head migration, and passive ROM were measured in static conditions at 0°, 30°, and 60° of glenohumeral abduction, respectively. Results: The intact SS resulted in a mean deltoid abduction force of 2.5, 3.3, and 3.8 N at 0°, 30°, and 60° of abduction, respectively. Compared with the intact shoulder, there was no significant difference in mean abduction force seen in the incomplete tear, while the force was significantly decreased by 52% at 30° of abduction in the complete tear ( P = .009). Compared with the incomplete tear, there were significant decreases in abduction force seen in the complete tear, by 33% and 48% (0.9 N and 1.1 N) at 0° and 30° of abduction, respectively ( P = .04 and .004). The intact configuration experienced a mean superior humeral head migration of 1.5, 1.4, and 1.1 mm at 0°, 30°, and 60° of abduction, respectively. The complete tear resulted in a superior migration of 3.0 and 4.4 mm greater than the intact configuration at 0° and 30° of abduction, respectively ( P = .001). There was a 5° and 10° increase in abduction ROM with 50% and 100% tears, respectively ( P = .003 and .03). Conclusion: An incomplete SS tear does not significantly alter the biomechanics of the shoulder, while a large, complete SS tear leads to a significant superior humeral migration, a decreased deltoid abduction force, and a mild increase in passive ROM. Clinical Relevance: Our findings demonstrate the effects of large SS tears on key biomechanical parameters, as they progress from partial tears.

Isolated traumatic full-thickness supraspinatus tear with intact glenohumeral capsule: a case report

“… 12 Due to superior rotator cuff anatomy, full-thickness traumatic supraspinatus lesions are strongly associated to glenohumeral capsule lesions. 24 Fetal anatomical studies showed that, since 10th week of gestation, the fibers of the deep layer of supraspinatus tendon and superior glenohumeral capsule are intimately intertwined and cannot be separate at their insertion point on greater tuberosity. 6 So, in case of traumatic supraspinatus tear, superior glenohumeral capsule tears with supraspinatus tendon deep layer, explaining why it is so unusual to find an isolated full-thickness supraspinatus tear with intact glenohumeral capsule.…”

Infraspinatus Muscle Fiber Moment Arms During Abduction: A Biomechanical Comparison of Values for Intact Rotator Cuff, Supraspinatus Tear, Superior Capsular Reconstruction, and Reverse Total Shoulder Arthroplasty

“…The machine device was designed and weighted according to the protocol described by Mihata et al 14 , 17 and as used in other similar cadaveric studies. 6 , 21 , 22 This experimental frame allowed the glenohumeral joint to be stabilized through force applied to the insertion sites of the muscles. The tendon attachments were connected to a pulley system and attached to free-hanging weights exerting the force vectors depicted in Figure 1 .…”

Effect of different loads on the shoulder in abduction postures: a finite element analysis

“…Christopher et al 12 used a dynamic shoulder simulator to test the maximum abduction force of the deltoid muscle during the abduction process. Danil et al 13 analyzed the stress of the shoulder joint in normal patients with rotator cuff tears during abduction through biomechanical experiments. However, due to the limitations of the experimental environment and conditions, the results of many indicators are difficult to predict.…”

“…Christopher et al 12 used a dynamic shoulder simulator to test the maximum abduction force of the deltoid muscle during the abduction process. Danil et al 13 analyzed the stress of the shoulder joint in normal patients with rotator cuff tears during abduction through biomechanical experiments. However, due to the limitations of the experimental environment and conditions, the results of many indicators are difficult to predict.The finite element analysis method can simulate working conditions that are difficult to carry out in biomechanics and obtain the corresponding mechanical results; it has been widely used in research on the shoulder joints.…”