Predictors of dislocations after reverse shoulder arthroplasty: a study by the ASES complications of RSA multicenter research group.

BACKGROUND: Instability after reverse shoulder arthroplasty (RSA) is one of the most frequent complications and remains a clinical challenge. Current evidence is limited by small sample size, single-center, or single-implant methodologies that limit generalizability. We sought to determine the incidence and patient-related risk factors for dislocation after RSA, using a large, multicenter cohort with varying implants. METHODS: A retrospective, multicenter study was performed involving 15 institutions and 24 American Shoulder and Elbow Surgeons members across the United States. Inclusion criteria consisted of patients undergoing primary or revision RSA between January 2013 and June 2019 with minimum 3-month follow-up. All definitions, inclusion criteria, and collected variables were determined using the Delphi method, an iterative survey process involving all primary investigators requiring at least 75% consensus to be considered a final component of the methodology for each study element. Dislocations were defined as complete loss of articulation between the humeral component and the glenosphere and required radiographic confirmation. Binary logistic regression was performed to determine patient predictors of postoperative dislocation after RSA. RESULTS: We identified 6621 patients who met inclusion criteria with a mean follow-up of 19.4 months (range: 3-84 months). The study population was 40% male with an average age of 71.0 years (range: 23-101 years). The rate of dislocation was 2.1% (n = 138) for the whole cohort, 1.6% (n = 99) for primary RSAs, and 6.5% (n = 39) for revision RSAs (P < .001). Dislocations occurred at a median of 7.0 weeks (interquartile range: 3.0-36.0 weeks) after surgery with 23.0% (n = 32) after a trauma. Patients with a primary diagnosis of glenohumeral osteoarthritis with an intact rotator cuff had an overall lower rate of dislocation than patients with other diagnoses (0.8% vs. 2.5%; P < .001). Patient-related factors independently predictive of dislocation, in order of the magnitude of effect, were a history of postoperative subluxations before radiographically confirmed dislocation (odds ratio [OR]: 19.52, P < .001), primary diagnosis of fracture nonunion (OR: 6.53, P < .001), revision arthroplasty (OR: 5.61, P < .001), primary diagnosis of rotator cuff disease (OR: 2.64, P < .001), male sex (OR: 2.21, P < .001), and no subscapularis repair at surgery (OR: 1.95, P = .001). CONCLUSION: The strongest patient-related factors associated with dislocation were a history of postoperative subluxations and having a primary diagnosis of fracture nonunion. Notably, RSAs for osteoarthritis showed lower rates of dislocations than RSAs for rotator cuff disease. These data can be used to optimize patient counseling before RSA, particularly in male patients undergoing revision RSA.

Risk factors of acromial and scapular spine stress fractures differ by indication: a study by the ASES Complications of Reverse Shoulder Arthroplasty Multicenter Research Group.

BACKGROUND: Both patient and implant related variables have been implicated in the incidence of acromial (ASF) and scapular spine fractures (SSF) following reverse shoulder arthroplasty (RSA); however, previous studies have not characterized nor differentiated risk profiles for varying indications including primary glenohumeral arthritis with intact rotator cuff (GHOA), rotator cuff arthropathy (CTA), and massive irreparable rotator cuff tear (MCT). The purpose of this study was to determine patient factors predictive of cumulative ASF/SSF risk for varying preoperative diagnosis and rotator cuff status. METHODS: Patients consecutively receiving RSA between January 2013 and June 2019 from 15 institutions comprising 24 members of the American Shoulder and Elbow Surgeons (ASES) with primary, preoperative diagnoses of GHOA, CTA and MCT were included for study. Inclusion criteria, definitions, and inclusion of patient factors in a multivariate model to predict cumulative risk of ASF/SSF were determined through an iterative Delphi process. The CTA and MCT groups were combined for analysis. Consensus was defined as greater than 75% agreement amongst contributors. Only ASF/SSF confirmed by clinical and radiographic correlation were included for analysis. RESULTS: Our study cohort included 4764 patients with preoperative diagnoses of GHOA, CTA, or MCT with minimum follow-up of 3 months (range: 3-84). The incidence of cumulative stress fracture was 4.1% (n = 196). The incidence of stress fracture in the GHOA cohort was 2.1% (n = 34/1637) compared to 5.2% (n = 162/3127) (P < .001) in the CTA/MCT cohort. Presence of inflammatory arthritis (odds ratio [OR] 2.90, 95% confidence interval [CI] 1.08-7.78; P = .035) was the sole predictive factor of stress fractures in GHOA, compared with inflammatory arthritis (OR 1.86, 95% CI 1.19-2.89; P = .016), female sex (OR 1.81, 95% CI 1.20-2.72; P = .007), and osteoporosis (OR 1.56, 95% CI 1.02-2.37; P = .003) in the CTA/MCT cohort. CONCLUSION: Preoperative diagnosis of GHOA has a different risk profile for developing stress fractures after RSA than patients with CTA/MCT. Though rotator cuff integrity is likely protective against ASF/SSF, approximately 1/46 patients receiving RSA with primary GHOA will have this complication, primarily influenced by a history of inflammatory arthritis. Understanding risk profiles of patients undergoing RSA by varying diagnosis is important in counseling, expectation management, and treatment by surgeons.

Comparison of pull out strength of resorbable screws in human cadaveric laryngeal cartilage using different drill diameters.

BACKGROUND: In a previous study at our institution, it was determined that resorbable screws with untapped drill holes resulted in the highest resistance forces to linear load when compared with titanium screws. The 1.1-mm drill diameter/2.0-mm screw diameter and 1.5/2.0 drill/screw combinations were superior to the 1.1/1.5 combinations; however, there was no conclusion as to the best screw size to drill bit diameter. The aim of this prospective study was to compare the pull out strength of resorbable screws in fresh frozen cadaveric laryngeal cartilage. The importance of drill hole diameter will also be determined. METHODS: After debridement of connective tissue and perichondrium, 12 cartilage specimens were tested. Linear pull out strength of screws was measured using a load cell. Resorbable screws of size 2.0 mm were tested using drill hole diameters of 0.0 mm, 0.8 mm, and 1.5 mm. All tested screws were 6 mm in length or greater. RESULTS: We found no strong evidence that the means for the 0.8/2.0 and 1.5/2.0 differ or that the 0.0/2.0 and 0.8/2.0 means differ. There is evidence that the 0.0/2.0 and 1.5/2.0 means differ (adjusted p value .0108), with the 0.0/2.0 combination having a smaller mean. CONCLUSIONS: Resorbable screws without pre drilled holes result in less resistance to linear loads than either the resorbable screws with the 0.8/2.0 or the 1.5/2.0 drill/screw combinations. The 1.5/2.0 drill/screw combination had the strongest pull out force, though this was not statistically significant.

Comparison of pullout strength of resorbable screws and titanium screws in human cadaveric laryngeal cartilage.

OBJECTIVES: To compare the pullout strength of titanium screws and resorbable screws from human fresh-frozen cadaveric laryngeal cartilage. The importance of drill hole diameter, screw diameter, and whether the drill hole was tapped (resorbable screws only) was also determined. STUDY DESIGN: Prospective. METHODS: Sixteen cartilage specimens were tested after debridement of connective tissue and perichondrium. Linear pullout strength of screws was measured using a load cell. Titanium and resorbable screw sizes of 1.5 and 2.0 mm were tested using drill hole diameters of 1.1 and 1.5 mm. For the resorbable-tapped group, screw diameters of 1.5 and 2.0 mm were tapped with 1.5 and 2.0 mm taps, respectively. All tested screws were 6 mm in length. RESULTS: We found a uniformly constant difference between the three screw types (P < .001). Post hoc analysis indicated a significant difference between the resorbable-untapped screw and both the resorbable-tapped screw and the titanium screw. We failed to find a significant difference, however, between the resorbable-tapped screw and the titanium screw. We also found a significant effect in regard to screw size (P = .0133), with post hoc analysis demonstrating the 1.1/1.5 mm combination to be inferior to the 1.1/2.0 and 1.5/2.0 mm combinations. There was no significant difference between the 1.1/2.0- and 1.5/2.0-mm combinations. CONCLUSIONS: Resorbable screws with untapped drill holes result in higher resistance to linear loads than both titanium screws and resorbable screws with tapped drill holes. The 1.1/2.0- and 1.5/2.0-mm drill/screw combinations are superior to the 1.1/1.5-mm combination when considering untapped resorbable screws.