Humeral offset as a predictor of outcomes after reverse shoulder arthroplasty.

INTRODUCTION: The Grammont-style reverse shoulder arthroplasty (RSA) relies on medialization and distalization of the shoulder center of rotation. Lateralized designs have recently gained popularity. The amount of lateralization, however, remains a controversial topic. The purpose of this study was to correlate the change in humeral offset (HO) with outcomes and complications following RSA. We hypothesized that a lateralized HO following RSA would be associated with improved range of motion (ROM), better patient-reported outcomes (PROs), and fewer complications. MATERIALS AND METHODS: A consecutive series of 104 patients (109 shoulders) was retrospectively evaluated. All patients underwent primary RSA by 2 shoulder and elbow fellowship-trained orthopedic surgeons at 2 different centers. Inclusion criteria was a primary RSA with at least 1-year follow-up. All patients had the HO measured on a preoperative and a postoperative Grashey radiograph, and the change in HO was calculated (ΔHO = PostHO-PreHO). A negative value was defined as a medialized HO and a positive value as a lateralized HO. ROM and primary outcomes, including forward elevation (FE), external rotation (ER), internal rotation (IR), Subjective Shoulder Value (SSV), and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) score, were collected. Complications and revisions were also reported. RESULTS: The mean age was 72 years with a mean follow-up of 22.3 months. The average FE (92° vs. 148°), ER (34° vs. 44°), SSV (35% vs. 87%), and ASES score (37.2 vs. 81.2) increased significantly (all P < .01) compared with preoperative values. The HO was medialized postoperatively in 63 shoulders and lateralized in 46 shoulders. No statistically significant differences in the mean values for postoperative FE (147° vs. 146°, P = .892), ER (43° vs. 45°, P = .582), IR (L3 vs. L3, P = .852), SSV (88% vs. 85%, P = .476), and ASES score (81.3 vs. 81.1, P = .961) were found between the groups. However, there was significantly more improvement in ER in the lateralized HO cohort than the medialized cohort (16° vs. 7°, P = .033). Six shoulders, 5 medialized and 1 lateralized HO, demonstrated scapular notching and remained asymptomatic. Five shoulders, 4 medialized and 1 lateralized HO, experienced at least 1 instability incident, and 2 shoulders with medialized HO had an acromion/scapular spine fracture. Overall, 2 shoulders with medialized HO underwent revision surgery because of instability. CONCLUSIONS: Although RSA provides significant improvement in ROM and PROs regardless of postoperative HO, restoring baseline HO or lateralization beyond baseline may be favorable for improving ER and decreasing complications following RSA.

Locating the rotator cable during subacromial arthroscopy: bursal- and articular-sided anatomy.

BACKGROUND: The rotator cable (RCa) is an important articular-sided structure of the cuff capsular complex that helps prevent suture pull out during rotator cuff repairs (RCRs) and plays a role in force transmission. Yet, the RCa cannot be located during bursal-sided RCRs. The purpose of this study is to develop a method to locate the RCa in the subacromial space and compare its bursal- and articular-sided dimensions. METHODS: In 20 fresh-frozen cadaveric specimens, the RCa was found from the articular side, outlined with stitches, and then evaluated from the bursal side using an easily identifiable reference point, the intersection of a line bisecting the supraspinatus (SS) tendon and posterior SS myotendinous junction (MTJ). Four bursal-sided lengths were measured on the SS-bisecting line as well as the RCa's outside anteroposterior base. For the articular-sided measurements, the rotator cuff capsular complex was detached from bone and optically scanned creating 3D solid models. Using the 3D models, 4 articular-sided lengths were made, including the RCa's inside and outside anteroposterior base. RESULTS: The RCa's medial arch was located 9.9 ± 5.6 mm from the reference point in 10 intact specimens and 4.1 ± 2.4 mm in 10 torn specimens (P = .007). The RCa's width was 10.9 ± 2.1 mm, and the distance from the lateral edge of the RCa to the lateral SS insertion was 13.9 ± 4.8 mm. The bursal- and articular-sided outside anteroposterior base measured 48.1 ± 6.4 mm and 49.6 ± 6.5 mm, respectively (P = .268). The average inside anteroposterior base measurement was 37.3 ± 5.9 mm. DISCUSSION: The medial arch of the RCa can be reliably located during subacromial arthroscopy using the reference point, analogous to the posterior SS MTJ. The RCa is located 10 mm in intact and 4 mm in torn tendons (P = .007) from the posterior SS MTJ. If the above 6-mm shift in location of the RCa is not taken into consideration during rotator cuff suture placement, it could negatively affect time zero repair strength. The inside anteroposterior base of the RCa measures on average 37 mm; therefore, rotator cuff tears measuring >37 mm are at risk of rupturing part or all of the RCa's 2 humeral attachments, which if not recognized and addressed could impact postoperative function.

The Rotator Cable Does Not Stress Shield the Crescent Area During Shoulder Abduction.

BACKGROUND: It is accepted by the orthopaedic community that the rotator cable (RCa) acts as a suspension bridge that stress shields the crescent area (CA). The goal of this study was to determine if the RCa does stress shield the CA during shoulder abduction. METHODS: The principal strain magnitude and direction in the RCa and CA and shoulder abduction force were measured in 20 cadaveric specimens. Ten specimens underwent a release of the anterior cable insertion followed by a posterior release. In the other 10, a release of the posterior cable insertion was followed by an anterior release. Testing was performed for the native, single-release, and full-release conditions. The thicknesses of the RCa and CA were measured. RESULTS: Neither the principal strain magnitude nor the strain direction in either the RCa or the CA changed with single or full RCa release (p ≥ 0.493). There were no changes in abduction force after single or full RCa release (p ≥ 0.180). The RCa and CA thicknesses did not differ from one another at any location (p ≥ 0.195). CONCLUSIONS: The RCa does not act as a suspension bridge and does not stress shield the CA. The CA primarily transfers shoulder abduction force to the greater tuberosity. CLINICAL RELEVANCE: The CA is important in force transmission during shoulder abduction, and efforts should be made to restore its continuity with a repair or reconstruction.