Scapular fractures after reverse shoulder arthroplasty: evaluation of risk factors and the reliability of a proposed classification.

BACKGROUND: The aims were to determine the sensitivity of plain radiographs to detect scapular fractures after reverse shoulder arthroplasty (RSA), to test the reliability of a proposed classification, and to evaluate risk factors. MATERIALS AND METHODS: We matched 53 patients with scapular fractures after RSA to 212 control patients. Clinical risk factors were assessed by correlating comorbidities. Independent observers reviewed radiographs to assess fracture detection accuracy and test the reliability of a proposed classification. Radiographic risks were evaluated by measuring acromial thickness, acromial tilt, glenoid-to-tuberosity distance, and acromion-to-tuberosity (AT) distance. RESULTS: Independent reviewers accurately diagnosed 78.8% of fractures and 97.4% of controls with good inter-rater reliability (κ = 0.782) and excellent intrarater reliability (κ = 0.862). Inter-rater reliability of the classification was moderate (κ = 0.422). Osteoporosis significantly increased the risk of fracture (odds ratio, 1.97; 95% confidence interval, 1.00-3.91); however, no difference was found for other comorbidities or between preoperative and postoperative radiographic parameters. A significant difference occurred between groups from the postoperative radiographs to the most recent radiographs for AT distance (0.4 ± 5.5 mm for control group and 8.3 ± 7.6 mm for fracture group, P < .001) and acromial tilt (1.8° ± 6.3° for control group and 14° ± 15° for fracture group, P < .001). Of 16 scapular spine fractures, 14 occurred from a screw tip; however, screw orientation and length were not different between groups. CONCLUSION: Osteoporosis is a significant risk factor for scapular fractures after RSA. The current classification has only moderate reliability, suggesting that an alternative classification method is needed. Decreasing AT distance and increasing acromial tilt on consecutive radiographs may improve fracture detection. Advanced imaging may be needed to confirm the diagnosis. Whereas most scapular spine fractures occurred from a screw, the surgical technique did not increase the relative risk.

Improving glenoid-side load sharing in a virtual reverse shoulder arthroplasty model.

BACKGROUND: The goal of glenoid fixation in reverse shoulder arthroplasty (RSA) is to provide a stable environment to allow bony ingrowth into the baseplate. When this does not occur, eventual baseplate failure is likely. This study aims to determine the additional implant-bone contact achieved when the glenosphere undersurface is in contact with the glenoid and if this increase in implant-bone contact improves stability through load sharing with respect to baseplate fixation. We hypothesize that substantial increases in contact area are possible and that this increased contact area will improve baseplate stability through load sharing. METHODS: A computer-assisted design program was used to create 3-dimensional models of 7 currently available RSA devices. Total implant-bone contact area was compared in 2 conditions: (1) baseplate flush with bone and no additional glenosphere contact, or (2) baseplate and glenosphere undersurface in contact with bone. Next, finite element models were created from a commercially available system. Micromotion and stress were computed for each size of implant in the 2 conditions. RESULTS: All devices tested can achieve increased total contact area when the glenosphere is in contact with bone. Stress and micromotion were reduced when comparing condition 2 with condition 1 in all sizes of one commercially available system. The average micromotion decreased 37%, from 98.04 to 61.97 µm. Larger glenospheres experienced a greater reduction in micromotion. Likewise, average von Mises stress decreased 26%, from 3.29 to 2.42 MPa. CONCLUSION: Increasing glenosphere size and allowing glenosphere undersurface contact increased overall implant-bone contact area and baseplate stability.

Prognosis for recovery of posterior interosseous nerve palsy after distal biceps repair.

BACKGROUND: There is very little information on the incidence of and usual recovery period for posterior interosseous nerve (PIN) palsies after distal biceps repair. This study examined the incidence and the time to resolution of PIN palsies in a large consecutive series of primary distal biceps repairs. MATERIALS AND METHODS: A retrospective review was performed of a consecutive series of patients treated by 34 fellowship-trained upper extremity surgeons with primary distal biceps repair through a single anterior incision technique. Patients' records were reviewed to determine how many experienced a postoperative PIN palsy, defined as postoperative digital extension weakness on clinical examination. Demographic information, surgical fixation used, and clinical resolution was collect for these patients. All patients had clinical follow-up until complete resolution of PIN palsy symptoms. RESULTS: We found 280 patients who were treated with a single-incision technique and 1 of 2 methods of biceps tendon fixation. Of these, 9 (3.2%) developed a postoperative PIN palsy after primary distal biceps repair. These 9 patients had complete lack of finger and thumb extension at the first postoperative visit and had complete resolution of symptoms at an average of 86 days (range, 41-145 days). CONCLUSIONS: The incidence of PIN palsy after a single-incision distal biceps repair was 3.2% in our series. These injuries typically resolve within 3 months, and at the latest, 5 months after surgery.