Motion, and Patient-Reported Outcomes

Objectives: Patients with irreparable rotator cuff tears (RCT) exhibit functional limitations believed to be caused by superior migration of the humerus1,2. One viable treatment is superior capsule reconstruction (SCR). SCR has been shown to restore stability of the glenohumeral (GH) joint in cadavers1, but its effectiveness at controlling in vivo humeral motion is unknown. Outcomes are typically evaluated through standard clinical radiographs to assess acromial-humeral distance (AHD), and patient-reported outcomes (PROs) such as ASES and Visual Analog Scale3. Reported changes in AHD are inconsistent, with some studies reporting an increase in AHD of 2.6 to 3.2 mm4,5, while other studies reported no significant change in AHD after SCR6,7. Additionally, AHD does not account for anterior-posterior translations of the humeral head and clinical radiographs cannot assess dynamic translation of the humerus during arm abduction. The aim of this study was to determine the in vivo effect of SCR on in vivo glenohumeral arthrokinematics during scapular abduction, and to compare these results to PROs. We hypothesized that static and dynamic AHD would increase, humeral head location on the glenoid would be more inferior at corresponding abduction angles after SCR, and changes in humeral head translation or AHD would correlate with increased GH abduction range of motion and improved PROs. Methods: Ten patients (8M, 2F, age 63 ± 7 years) with irreparable RCT provided informed consent to participate in this prospective IRB-approved study. ASES, DASH, and WORC surveys were completed before (PRE) and 1-year (1YR-POST) after SCR. Synchronized biplane radiographs of the shoulder were collected PRE and 1YR-POST at 50 images/s while patients performed 3 trials of scapular plane arm abduction. Biplane radiographs were also collected during a static neutral trial where the participants placed their hand on their lap. Six degree of freedom GH and scapular kinematics were determined with sub-millimeter accuracy by matching subject-specific CT-based bone models of the humerus and scapula to radiographs using a validated volumetric tracking technique8. AHD was calculated as the minimum distance between the acromion and the humerus at 10° increments of GH abduction and averaged throughout the motion. Humeral head translation, defined as the relative translation of the center of the humeral head compared to the center of the glenoid, was calculated at 10° increments of GH abduction and expressed as averages in the superior/inferior (SI) and anterior/posterior (AP) directions. Differences between PRE and 1YR-POST static AHD, average dynamic humeral head location, PROs, and maximum GH abduction were evaluated using a paired t-test. A Pearson correlation was used to determine associations between static AHD and average humeral head location, and both PROs and maximum GH abduction. Significance was set at p < 0.05 for all tests. Results: There was no difference in static AHD from PRE (5.3±1.6mm) to 1YR-POST (4.6±1.6mm) while the average dynamic AHD during GH abduction decreased from 2.7±1.2mm PRE to 2.3±1.0mm 1YR-POST (Figure 1). Static AHD was larger than the average dynamic AHD both PRE and 1YR-POST (Figure 1). The average position of the humeral head during abduction moved 1.5% of the glenoid height superior from PRE to 1YR-POST and 1.7% of the glenoid width anterior from PRE to 1YR-POST (Figure 2). ASES, WORC, and DASH scores significantly improved from PRE to 1YR-POST and maximum GH abduction significantly increased from PRE (78.1±23.1°) to 1YR-POST (93.9±12.3°) (Table 1). Interestingly, there was a positive correlation between the AP humeral head location and DASH score PRE such that a higher DASH score was associated with the humeral head being more anterior (R = 0.767). No other associations were found between either average humeral head locations or AHD and either PROs or maximum GH abduction at both time points as well as the changes in those measures between time points (all R < 0.67). Conclusions: Static AHD, as measured clinically, may not be a good representation of dynamic AHD during scapular abduction given the differences between the static and dynamic AHD measurements at similar abduction angles. Additionally, our in vivo kinematics findings are not consistent with prior results of a cadaver-based biomechanical study of SCR as we found were minute changes in the SI humeral head position, with a 0.4mm more superior humeral head position following SCR. Regardless, patient-reported qualitative outcomes and maximum GH abduction all improved significantly. This suggests clinical outcomes after SCR may be influenced by mechanisms other than restoration of humeral head translation. Future in vivo studies are needed to evaluate the kinematic mechanisms behind improved PROs after SCR. [Table: see text]