Acromial fractures following reverse shoulder arthroplasty: the role of the acromial morphology and a comparison of clinical outcomes

Analysis and optimization of plate fixation fitness in acromion fracture reduction by calculating dry scapulae and x-rays acromion curvature

BACKGROUND

The acromion projects laterally in a curving orientation. When a fracture of the acromion occurs, despite being rare, matching the best-fit fixation plate is challenging due to few options and limited availability of fixation plate types. Alternative fixation methods can carry risk of nonunion complications.

PURPOSE

The objective of this study was to investigate the morphological curvature pattern of the acromion to assess the level of the fixation plates fitness and provide the suitable imaging modalities for evaluating the acromion curvature.

BASIC PROCEDURES

The correlation between the acromion curvature and five fixation plates were calculated and their fitness level was evaluated statistically. The curvature of acromion and the five available fixation plates were photographed and assessed digitally by software (FIJI ImageJ and Microsoft Excel). The method entails plotting seven points along the curving surface and margins of the acromion, while the Excel Solver function calculates the regression, ultimately giving curvature values. First, the acromion parameters were studied on 180 paired healthy dry scapulae. Then, the acromion curvature values were compared to the fixation plates curvatures. Likewise, the acromion curvature was assessed as applicable on 153 (100 AP- views, 50 Y- views, and 3 superior-views) retrospective plain X-rays and 40 3D-CT scapula reconstructions of healthy acromia.

MAIN FINDINGS

The mean length of the acromion was 48.70 ± 5.29 mm, mean thickness was 8.51 ± 1.67 mm, and mean width was 25.97 ± 5.97 mm. The calculated values of the mean curvatures were 0.050 ± 0.015 mm-1 for the mean acromion surface, 0.042 ± 0.027 mm-1 for the internal margin, and 0.055 ± 0.010 mm-1 for the external margin. The curved geometry of the acromion was plotted on a graph giving a spectrum of curvature patterns with distribution values revealing fixation plates fitness represented by area under the curve with frequencies of 4.32 % for the acromion-specific fixation plate, 14.28 % for the large clavicle fixation plate, 0.26 % for the small clavicle fixation plate, 53.38 % for the flexible universal fixation plate, and none for the rigid universal fixation plate.

PRINCIPAL CONCLUSIONS

Approximately 27.76 % of the acromion surface curvatures distribution does not overlap with any of our measured fixation plates. Evaluating the acromion surface curvature was possible on plain X-rays in the Y-view only.

Clinical outcomes following surgical fixation of acromion fractures

Background

Acromial fractures are rare in the traumatic setting; however, they have recently gained attention due to the increase in incidence as a result of a postoperative complication of reverse total shoulder arthroplasty. While historically these fractures were routinely treated nonoperatively, there is evidence that surgery can improve outcomes. The study aims to evaluate clinical outcomes following surgical treatment of acromion fractures and compare outcomes among patients with an intact rotator cuff against those with a deficient rotator cuff or reverse shoulder arthroplasty.

Methods

This is a retrospective review of patients with acromion fractures that were treated with open reduction internal fixation between January 2014 and March 2023. Patients were stratified into three cohorts as follows: 1) rotator cuff intact; 2) rotator cuff impaired; and 3) presence of reverse total shoulder arthroplasty.

Results

Thirty-seven patients were included in the study with a mean follow-up of 9 months (range 0.5-77). The mechanism of injury was stress fracture (46%), high-energy trauma (32%), or low-energy falls (22%). The mean time to surgery was 6 months (0-24). Older age and female sex were associated with stress fractures (P < .05). The odds of having a stress fracture were higher in patients with an impaired rotator cuff (OR 6.5, P = .04) or reverse total shoulder arthroplasty (OR 2.8, P = .02) compared to those with an intact rotator cuff. The mean shoulder flexion improved from 81 degrees preoperatively to 113 degrees at the time of the last visit (P = .02). The mean shoulder external rotation improved from 24 degrees preoperatively to 48 degrees at the time of the last visit (P = .04). The nonunion rate was 19% (7 of 37) and the reoperation rate was 11% (4 of 37) for removal of broken hardware or nonunion revision. Two patients went on to have reverse total shoulder arthroplasty. There were no differences in nonunion or reoperation rates among patients with an intact cuff, an impaired cuff, or the presence of shoulder arthroplasty.

Discussion and conclusion

Patients with rotator cuff dysfunction or presence of reverse total shoulder arthroplasty are more likely to have acromion stress fractures compared to those with an intact rotator cuff. Surgical fixation of acromion fractures can improve the shoulder range of motion and pain scores. The nonunion rate is lower for surgical fixation compared to existing literature on nonoperative treatment of acromion fractures.

The acetabularization index: a novel measure of acromial bone loss prior to reverse shoulder arthroplasty

BACKGROUND

Acromial stress fractures following reverse shoulder arthroplasty (RSA) have gained attention among specialized surgeons over the past decades craving answers regarding predisposing factors and technical aspects as how to avoid the complication. This study introduces the acetabularization index (AI) for the preoperative estimation of acromial bone loss attributed to acetabularization in cases of cuff tear arthropathy (CTA).

METHODS

The acromiohumeral interval (AHI), extent of acromial acetabularization (AA), acromial height (AH), and width of acetabularization (r) were measured on preoperative radiographs and two-dimensional computed tomography scans (2D CT) of patients who underwent RSA within the timeline 2019-2023 for CTA. The AI calculatedAI % = AA mm ÷ AH mm . The CTA grade was determined according to the Hamada classification. The AI values on radiographs and 2D CT were compared by a Student's t-test. Possible correlation between the AI and AHI was investigated via Pearson's coefficient. The intraclass correlation coefficient (ICC) was employed to test the interobserver reliability among two independent testers.

RESULTS

The radiographs and 2D CT scans of thirty-three patients who underwent RSA were analyzed. The mean AHI, AH, AA, r, and AI values on radiographs were 5.5 ± 2 mm, 10 ± 2 mm, 2 ± 2 mm, 30 ± 4 mm, 16 ± 16%, respectively. On 2D CT, the corresponding mean values were 4.7 ± 2.5 mm, 10.8 ± 2.65 mm, 2.45 ± 2.35 mm, and 30 ± 4.5, and 22.3 ± 22%, respectively. There was a statistically significant difference between the AI values on radiographs and 2D CT (P = .000). The Pearson's correlation coefficient demonstrated a negative correlation between AI and AHI (r = - 0.33). Excellent reliability was observed by the ICC values for all parameters in both groups among two testers.

CONCLUSION

The AI is a reliably measurable tool on radiographs and 2D CT scans; however, the measurements derived from radiographs vary significantly from CT based measurements due to projection restrictions. Grade IVB of the Hamada/Fukuda classification is associated with the highest AI values. Further research is warranted to assess the clinical utility of this index as a predictive tool for postoperative acromial stress fractures.

Robert H. Cofield, MD, Award for Best Oral Presentation 2023: Up to 8 mm of glenoid-sided lateralization does not increase the risk of acromial or scapular spine stress fracture following reverse shoulder arthroplasty with a 135° inlay humeral component

BACKGROUND

Glenoid-sided lateralization in reverse shoulder arthroplasty (RSA) decreases bony impingement and improves rotational range of motion, but has been theorized to increase the risk of acromial or scapular spine fractures (ASFs). The purpose of this study was to assess if glenoid-sided lateralization even up to 8 mm increases the risk for stress fracture following RSA with a 135° inlay humeral component.

METHODS

A retrospective review was performed from a multicenter prospectively collected database on patients who underwent primary RSA from 2015 to 2021. All RSAs were performed with a 135° inlay humeral component. Varying amounts of glenoid lateralization were used from 0 to 8 mm. Preoperative radiographs were reviewed for the presence of acromial thinning, acromiohumeral distance (AHD), and inclination. Postoperative implant position (distalization, lateralization, and inclination) as well as the presence of ASF was evaluated on minimum 1-year postoperative radiographs. Regression analyses were performed on component and clinical variables to assess for factors predictive of ASF.

RESULTS

Acromial or scapular spine fractures were identified in 26 of 470 shoulders (5.5%). Glenoid-sided lateralization was not associated with ASF risk (P = .890). Furthermore, the incidence of fracture did not vary based on glenoid-sided lateralization (0-2 mm, 7.4%; 4 mm, 5.6%; 6 mm, 4.4%; 8 mm, 6.0%; P > .05 for all comparisons). RSA on the dominant extremity was predictive of fracture (odds ratio [OR] 2.21, 95% confidence interval [CI] 1.20-5.75; P = .037), but there was no relationship between patient age, sex, preoperative acromial thinning, or diagnosis and risk of fracture. Although there was no difference in mean postoperative AHD between groups (P = .443), the pre- to postoperative delta AHD was higher in the stress fracture group (2.0 ± 0.7 cm vs. 1.7 ± 0.7 cm; P = .015). For every centimeter increase in delta AHD, there was a 121% increased risk for fracture (OR 2.21, 95% CI 1.33-3.68; P = .012). Additionally, for every 1-mm increase in inferior glenosphere overhang, there was a 19% increase in fracture risk (P = .025).

CONCLUSION

Up to 8 mm of glenoid-sided metallic lateralization does not appear to increase the risk of ASF when combined with a 135° inlay humeral implant. Humeral distalization increases the risk of ASF, particularly when there is a larger change between pre- and postoperative AHD or higher inferior glenosphere overhang. In cases of pronounced preoperative superior humeral migration, it may be a consideration to avoid excessive postoperative distalization, but minimizing bony impingement via glenoid-sided lateralization appears to be safe.

Do preoperative scapular fractures affect long-term outcomes after reverse shoulder arthroplasty?

BACKGROUND

Postoperative scapular stress fractures (SSFs) are a formidable problem after reverse shoulder arthroplasty (RSA). Less is known about patients who have these fractures preoperatively. The primary aim of this study was to examine postoperative satisfaction in patients undergoing primary RSA who have preoperative SSF and compared to a matched cohort without preoperative fracture. The secondary aim was to examine the differences in patient-reported outcomes between and within study cohorts.

METHODS

A retrospective chart review of primary RSAs performed by a single surgeon from 2000 to 2020 was conducted. Patients diagnosed with cuff tear arthropathy (CTA), massive cuff tear (MCT), or rheumatoid arthritis (RA) were included. Five hundred twenty-five shoulders met inclusion criteria. Fractures identified on preoperative computed tomography scans were divided into 3 groups: (1) os acromiale, (2) multifragments (MFs), and (3) Levy types. Seventy-two shoulders had an occurrence of SSF. The remaining 453 shoulders were separated into a nonfractured cohort. American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) and visual analog scale (VAS) scores were compared pre- and postoperatively in the total fracture group and the nonfractured group cohort. The multifragment subgroup was also compared to the pooled Os/Levy subgroup.

RESULTS

The total incidence of SSF in all shoulders was 13.7%. There was a difference in satisfaction scores at all time points between the nonfracture (7.9 ± 2.8) and total fracture group (5.4 ± 3.6, P < .001, at last visit). There was also a greater ASES total score in the nonfractured group vs the total fracture group at the final visit (69.4 ± 23.4 and 62.1 ± 24.2; P = .02). The MF group had worse ASES functional or VAS functional scores than the Os/Levy group at all time points: at 1 year, ASES function: MF 24.2 ± 14.5 and Os/Levy 30.7 ± 14.2 (P = .045); at 2 years, ASES function: MF 21.4 ± 14.4 and Os/Levy 35.5 ± 10.6 (P < .001); and at last follow-up, VAS function: MF 4.8 ± 2.8 and Os/Levy 6.4 ± 3.2 (P = .023).

DISCUSSION

Scapular fractures were proportionally most common in patients diagnosed with CTA (16.3%) compared with a 9.2% and 8.6% incidence in patients diagnosed with MCT and RA, respectively. Patients with preoperative SSF still see an improvement in ASES scores after RSA but do have lower satisfaction scores compared with the nonfractured cohort. The multifragment fracture group has lower functional and satisfaction scores at all postoperative time points compared with both the nonfracture and the Os/Levy fracture group.

Incidence, risk factors, and complications of acromial stress fractures after reverse total shoulder arthroplasty

BACKGROUND

An acromial stress fracture (ASF) is an uncommon complication after reverse total shoulder arthroplasty (RTSA) that can have severe clinical consequences on shoulder function. Although patient-specific factors have been identified to influence the risk of ASF, it is unclear whether modifying these factors can minimize risk. Moreover, there is limited information on the treatment outcomes of these fractures. Therefore, the purpose of this study was to determine modifiable risk factors for ASFs and the complication and revision rates of conservatively and operatively managed ASFs.

METHODS

The PearlDiver database was queried to identify a cohort of patients who underwent RTSA with minimum 2-year follow-up. Current Procedural Terminology and International Classification of Diseases codes were used to compare the demographic characteristics, comorbidities, and medication use of patients with and without ASFs. Surgical complication and revision rates were compared between operatively and conservatively treated fractures.

RESULTS

The overall incidence of ASFs was 1.4%. Patient-specific factors that were independently associated with the occurrence of an ASF included osteoporosis, rheumatologic disease, shoulder corticosteroid injection within 3 months before surgery, and chronic oral corticosteroid use. Among patients with osteoporosis, the initiation of physical therapy within 6 weeks after surgery also increased the risk of ASF. Patients who underwent surgical treatment of ASFs had a revision arthroplasty rate of 7.0% compared to a rate of 3.2% among those with conservatively managed fractures.

CONCLUSION

ASFs are infrequent complications that can occur after RTSA. Preoperative factors that affect the quality of bone independently increase the fracture risk. Moreover, this risk can be minimized by avoiding shoulder corticosteroid injections 3 months before surgery and delaying physical therapy exercises among patients with osteoporosis. Surgical fixation of these fractures should be reserved for instances when conservative management has failed given high rates of infection, instability, and revision shoulder arthroplasty.

Predictive factors of acromial fractures following reverse total shoulder arthroplasty: a subgroup analysis of 860 shoulders

Background

Acromion stress fractures (ASF) or scapular spine fractures (SSF) following reverse total shoulder arthroplasty (RTSA) are common complications with impaired clinical outcome. The underlying biomechanical factors remain unclear. The aim of this study was to evaluate basic demographic and radiographic parameters predicting occurrence of different types of ASF/SSF in a large single-center study cohort.

Methods

A total of 860 RTSA (805 patients) with available minimum follow-up of 2 years were implanted between 2005 and 2018 at a tertiary academic center. All RTSA with subsequent ASF/SSF (n = 45 in 43 shoulders [42 patients, 5%]) were identified and classified as Levy I to III. Predictive demographic, surgical, and radiographic factors were evaluated for each subtype and compared to the control group (817 RTSA, 763 patients). The radiographic analysis included critical shoulder angle, lateralization shoulder angle (LSA), distalization shoulder angle (DSA), acromio-humeral distance (ACHD), acromial thickness, deltoid tuberosity index, deltoid length, and center of rotation.

Results

Of the 45 ASF/SSF in 42 patients, 8 were classified as Levy I, 21 as Levy II, and 16 as Levy III. Demographic analysis revealed indication as risk factor for Levy I fractures, higher American Society of Anesthesiologists score as risk for Levy type II fractures and higher age as risk factor for Levy type III fractures. None of the measured radiographic parameters were predictive for occurrence of Levy type I and Levy type II ASF. However, analysis of Levy III SSF revealed a higher postoperative LSA (89° ± 10° vs. 83° ± 9°, P = .015), a lower postoperative DSA (45° ± 8° vs. 53° ± 12°, P = .002), less distalization (ACHD of 33 ± 8 mm vs. 38 ± 10 mm, P = .049), and a more medial center of rotation preoperatively (COR-LA 16 ± 8 mm vs. 12 ± 7 mm, P = .048) as predictive radiographic factors.

Conclusion

The present analysis showed a significant association of higher postoperative LSA, lower DSA, a lower ACHD, and higher age as predictive factor only for Levy type III fractures. Some of these factors can be surgically influenced and this knowledge can be of value for preoperative planning and surgical execution to avoid these complications.