Abstract
Introduction
Acromial and scapular fractures are a rare but difficult complication with reverse total shoulder arthroplasty (rTSA), with an incidence rate reported from 1–10%. The risk factors associated with these fractures types is largely unknown. The goal of this study is to analyze the clinical outcomes, demographic and comorbidity data, and implant sizing and surgical technique information from 4125 patients who received a primary rTSA with one specific prosthesis (Equinoxe, Exactech, Inc) and were sorted based on the radiographic documentation of an acromial and/or scapula fracture (ASF) to identify factors associated with this complication.
Methods
4125 patients (2652F/1441M/32 unspecified; mean age: 72.5yrs) were treated with primary rTSA by 23 orthopaedic surgeons. Revision and fracture reverse arthroplasty cases were excluded. The radiographic presence of each fracture was documented and classified using the Levy classification method. 61 patients were identified as having ASF, 10 patients had fractures of the Type 1, 32 patients had Type 2, and 18 patients had Type 3 fractures according to Levy's classification. One fracture was not classifiable. Pre-op and post-op outcome scoring, ROM as well as demographic, comorbidity, implant, and surgical technique information were evaluated for these 61 patients and compared to the larger cohort of patients to identify any associations. A two-tailed, unpaired t-test identified differences (p<0.05).
Results
The overall rate of ASF was 1.48% with the average time after surgery occurring at 12.9 ± 17.9 months (range 1 day to 78 months). Men had an ASF rate of 0.69% (10 of 1441); whereas women had a rate of 1.92% (51 of 2652). Patients with ASF were observed to be significantly shorter than patients without ASF (65.1 in vs 63.3 in, p=0.0004). ASF were more common in females (p=0.0019), have Rheumatoid Arthritis (p=0.0051), Cuff Tear Arthropathy (p=0.0093), or previous shoulder surgery (p=0.0189). Patient's weight did not correlate, nor did BMI. No difference was observed in humeral stem size, glenosphere diameter, or the humeral tray offset, humeral liner offset, or combined humeral tray+liner offset. The average number of screws used in the fracture group was significantly more than in the non-fracture group (p=0.0327), and 93% of patients in the fracture group had a screw in the superior hole of the baseplate. Pre-operatively, patients who developed ASF had significantly worse ASES (p=0.0104) and SPADI (p=0.0136) scores and also had significantly worse forward elevation (p=0.0237) and internal rotation (p=0.0054) than those who did not develop ASF. At latest follow-up, patients with ASF had significantly worse SST, UCLA, ASES, Constant, and SPADI scores (all p<0.0001); significantly worse abduction, forward elevation, internal rotation, strength (all p<0.0001); and significantly less preop-to-postop improvement in all measured outcomes, except for external rotation (all p<0.0001). Finally, 24% of fractures were identified as being caused by a traumatic event, 28% of patients with fractures had a previous acromioplasty, and 53% of fractures were Levy type 2.
Discussion
Acromial and scapular fractures after rTSA are a rare complication, with an incidence of 1.48% in this analysis of 4125 patients with a single rTSA prosthesis. These fractures were observed to occur at an average of 12.9 months after surgery, but were observed as early as 1 day and as late as 6.5 years. Female patients, Rheumatoid Arthritis, Cuff Tear Arthropathy, previous shoulder surgery, relatively worse pre-operative ASES or SPADI scores, relatively decreased pre-operative forward elevation and internal rotation as well as a larger number of screws placed in the baseplate all were significantly associated with the occurrence of ASF. Although 93% of patients with ASF had a screw placed in the superior hole of the baseplate, we cannot conclude that this is a driving factor at this time, as the superior screw number for the non-fracture group was not recorded. Future work should evaluate if usage of a superior glenoid baseplate screw and previous acromioplasty are also risk factors for these fracture types after rTSA. This study is the largest ever performed analysis of this rare complication and provides news insight into the predisposing risk factors to consider when evaluating patients for rTSA.
