Biomechanical analysis of articular-sided partial-thickness rotator cuff tear and repair.

BACKGROUND: Articular-sided partial-thickness rotator cuff tears are common injuries in throwing athletes. The superior shoulder capsule beneath the supraspinatus and infraspinatus tendons works as a stabilizer of the glenohumeral joint. PURPOSE: To assess the effect of articular-sided partial-thickness rotator cuff tear and repair on shoulder biomechanics. The hypothesis was that shoulder laxity might be changed because of superior capsular plication in transtendon repair of articular-sided partial-thickness rotator cuff tears. STUDY DESIGN: Controlled laboratory study. METHODS: Nine fresh-frozen cadaveric shoulders were tested by using a custom shoulder-testing system at the simulated late-cocking phase and acceleration phase of throwing motion. Maximum glenohumeral external rotation angle, anterior translation, position of the humeral head apex with respect to the glenoid, internal impingement area, and glenohumeral and subacromial contact pressures were measured. Each specimen underwent 3 stages of testing: stage 1, with the intact shoulder; stage 2, after creation of articular-sided partial-thickness tears of the supraspinatus and infraspinatus tendons; and stage 3, after transtendon repair of the torn tendons by using 2 suture anchors. RESULTS: Articular-sided partial-thickness tears did not significantly change any of the shoulder biomechanical measurements. In the simulated late-cocking phase, transtendon rotator cuff repair resulted in decreased maximum external rotation angle by 4.2° (P = .03), posterior shift of the humeral head (1.1-mm shift; P = .02), decreased glenohumeral contact pressure by 1.7 MPa (56%; P = .004), and decreased internal impingement area by 26.4 mm(2) (65%; P < .001) compared with values in the torn shoulder. In the acceleration phase, the humeral head shifted inferiorly (1.2-mm shift; P = .03 vs torn shoulder), and glenohumeral anterior translation (1.5-mm decrease; P = .03 vs torn shoulder) and subacromial contact pressure (32% decrease; P = .004 vs intact shoulder) decreased significantly after transtendon repair. CONCLUSION: Transtendon repair of articular-sided partial-thickness supraspinatus and infraspinatus tears decreased glenohumeral and subacromial contact pressures at time zero; these changes might lead to reduced secondary subacromial and internal impingements and consequently progression to full-thickness rotator cuff tear. However, repair of the tendons decreased anterior translation and external rotation and changed the positional relationship between the humeral head and the glenoid. CLINICAL RELEVANCE: Careful attention should be paid to shoulder laxity and range of motion when transtendon repair is chosen to treat articular-sided partial-thickness rotator cuff tears, specifically in throwing athletes.

The relation between knee flexion angle and anterior cruciate ligament femoral tunnel characteristics: a cadaveric study comparing a standard and a far anteromedial portal.

PURPOSE: The purpose of this study was to compare the anterior cruciate ligament (ACL) femoral tunnel characteristics between 2 common arthroscopic portals used for ACL reconstruction, a standard anteromedial portal and a far anteromedial portal. METHODS: Seven cadaveric knees were used. A 1.25-mm Kirschner wire was drilled through the center of the ACL femoral footprint and through the distal femur from the standard anteromedial and far anteromedial portals at knee flexion angles of 100°, 120°, and 140°. No formal tunnels were drilled. Each tunnel exit point was marked with a colored pin. After all tunnels were created, the specimens were digitized with a MicroScribe device (Revware, Raleigh, NC) to measure the tunnel length; distance to the posterior femoral cortical wall (posterior cortical margin); and tunnel orientation in the sagittal, coronal, and axial planes. RESULTS: The standard anteromedial portal resulted in a longer tunnel length, a less horizontal tunnel in the coronal plane, and a greater posterior cortical margin compared with the far anteromedial portal at all knee flexion angles. For both portal locations, the tunnel length and posterior cortical margin increased, and the tunnel position became more horizontal in the coronal plane, more anterior in the sagittal plane, and less horizontal in the transverse plane as knee flexion increased. CONCLUSIONS: Portal position affects femoral tunnel characteristics, with results favoring the more laterally positioned standard anteromedial portal at all flexion angles. Increasing the knee flexion angle leads to a longer femoral tunnel length and posterior femoral cortical margin with either portal position. CLINICAL RELEVANCE: Understanding how portal positioning and knee flexion angle affect femoral tunnel orientation and characteristics may lead to improved surgical outcomes after ACL reconstruction.

Longitudinal analysis of effects of operator experience on accuracy for ultrasound detection of supraspinatus tears.

BACKGROUND: Magnetic resonance imaging (MRI) is highly accurate in diagnosing full-thickness rotator cuff tears but has the limitations of high cost and patient-based inconveniences. Diagnostic ultrasound of the rotator cuff has become popular, but its accuracy is operator dependent. We hypothesized that the incremental learning associated with initiation of shoulder ultrasonography in the orthopedic office setting could be quantified. MATERIALS AND METHODS: Ultrasound was performed by 2 surgeons in different patient populations each consisting of 200 patients within the clinical setting. Analysis of the operator learning curves based on sensitivity, specificity, positive predictive value, negative predictive value, and κ agreement scores was performed with MRI used as the reference standard. RESULTS: Surgeon 1 detected 67 (ultrasound) of 72 (MRI) full-thickness supraspinatus tears, and surgeon 2 detected 92 (ultrasound) of 95 (MRI) full-thickness tears. Agreement between ultrasound and MRI improved with increasing number of ultrasounds performed. The maximal rate of increase in sensitivity occurred by the 50th ultrasound for both surgeons. The maximal rate of increase in specificity occurred by the 75th ultrasound for both surgeons. Overall accuracy to detect full-thickness supraspinatus tears plateaued after 100 ultrasounds. CONCLUSIONS: The majority of learning to detect full-thickness supraspinatus tears by ultrasound occurred in the surgeons' first 50 cases. The ability to accurately distinguish a normal supraspinatus tendon by ultrasound took longer, occurring within the first 75 cases. The majority of learning before accuracy plateaued occurred within the first 100 ultrasounds. The recommended operator experience necessary to evaluate the supraspinatus tendon before clinical application was 100 ultrasounds. LEVEL OF EVIDENCE: Level I, Diagnostic Study.