Do preoperative factors and implant design features influence humeral stem extraction efforts?

BACKGROUND: Variations in humeral component designs in hemiarthroplasty and anatomic total shoulder arthroplasty cases can impact the degree of difficulty during a revision surgery that necessitates the removal of the humeral stem. However, no metric exists to define stem extraction effort nor to identify associated factors that contribute to extraction difficulty. The purpose of this study is to describe a method to quantify stem extraction difficulty and to define features that will impact the effort during stem removal. METHODS: This was a retrospective review of 58 patients undergoing revision of hemiarthroplasty or anatomic total shoulder arthroplasty requiring stem extraction. Each included patient had existing preoperative radiographic examination, an intraoperative video of the stem removal process, and explants available for analysis by 3 surgeons. The following factors were assessed for the impact on extraction difficulty: (1) preoperative features such as cement use, fill of proximal humerus, and stem design features; (2) intraoperative data on extraction time and bone removal; and (3) postoperative findings related to extraction artifacts (EAs). A scoring system was established to distinguish easy (Easy group) and difficult (Difficult group) stem removal cases and further used to identify the features that may affect intraoperative difficulty of stem removal. RESULTS: The Difficult group accounted for 26% (15/58) of the study population with an 18-minute average stem extraction time, average EA count of 69, and 35 mm of bone removed. The Easy group accounted for 74% (43/58) of patients, with a 4-minute average extraction time, average EA count of 23, and 10 mm of bone removed. Logistic regression model was able to correctly classify 82% of the cases, explaining 26.7% of the variance in humeral stem removal with cement and proximal coating variables. The likelihood of cemented stem removal being difficult is 5 times greater compared to an uncemented stem, and having proximal coating doubles the likelihood of a difficult stem removal compared to cases with no coating. CONCLUSIONS: Quantifying stem extraction difficulty is possible with intraoperative video as well as explant analysis. Preoperative features of the fixation type and specific features of stem design such as proximal coating will impact difficulty of stem extraction.

Improved mechanical fixation of an all-polyethylene glenoid reduces postoperative radiolucent lines.

BACKGROUND: The rationale for advances in implant design is to improve performance in comparison to their predecessors. The purpose of this study was to compare a newer, self-pressurizing peripheral peg glenoid to a traditional polyethylene pegged glenoid through biomechanical evaluation and a retrospective radiographic and clinical review. METHODS: Three testing conditions (uncemented, partially cemented, and fully cemented) were chosen to assess the 2 component designs in a foam block model. The number of hammer hits to seat the component, amount of time to seat the component, and resistance-to-seat were collected. The implants were then cyclically loaded following ASTM F2028-17 testing standard. Clinically, postoperative radiographs of patients with a self-pressurized glenoid component (n = 225 patients) and traditional glenoid component (n = 206 patients) were evaluated for radiolucent lines and glenoid seating at various timepoints. Clinical outcomes (American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, Simple Shoulder Test, and visual analog scale pain scores) and complications were recorded. The presence of radiolucent lines at the bone-cement interface was evaluated using the Modified Franklin Grade and the Lazarus grade. RESULTS: The self-pressurizing glenoid design required significantly more hammer hits than traditional glenoid designs in all groups tested (P < .029). Moreover, the self-pressurizing design had significantly more resistance-to-seat than traditional components in both the uncemented and partially cemented group (P < .002). No difference in resistance-to-seat was found between designs in the fully cemented group. The uncemented and partially cemented groups did not survive the full 50,000 cycles; however the self-pressurizing design had significantly less motion than the traditional design (P < .001). No differences between component designs were found in the fully cemented group at 50,000 cycles. The self-pressurizing glenoid component had 0.005% radiographic radiolucent lines, and the traditional glenoid component had 45% radiographic radiolucent lines, with 38% of the radiolucencies in the traditional glenoid component group being defined as grade E. There were no progressive radiolucencies, differences in clinical outcomes, or complications at 2 years postoperatively. CONCLUSION: In the fully cemented condition, the 2 component designs had comparable performance; however, the differences in designs could be better observed in the uncemented group. The self-pressurizing all-polyethylene design studied has superior biomechanical stability. Clinically, the improved stability of the glenoid component correlated with a reduction of radiolucent lines and will likely lead to a reduction in glenoid component loosening.

Optimizing humeral stem fixation in revision reverse shoulder arthroplasty with the cement-within-cement technique.

BACKGROUND: The purpose of this study was to report on the clinical outcomes of patients undergoing revision reverse shoulder arthroplasty (RSA) by the cement-within-cement technique, as well as to identify whether surgical technique can affect subsequent humeral loosening. METHODS: In 98 patients, cemented humeral components that were revised to RSA using the cement-within-cement technique were identified and included in this study. We compared 8 patients in whom humeral stem loosening developed with 90 patients whose stem remained fixed. Preoperative and postoperative radiographs of each patient were downloaded in DICOM (Digital Imaging and Communications in Medicine) format and analyzed in Mimics. The total area of the cement mantle (in square millimeters) and of the stem (in square millimeters), as visualized on 2-dimensional plain films, was measured in each subject on both preoperative and postoperative radiographs. Outcomes at a minimum of 2 years of follow-up were analyzed. RESULTS: Clinical outcomes were available in 57 patients, with a mean follow-up period of 54 months (range, 21-156 months). Patients demonstrated significantly improved functional outcome scores and shoulder range of motion. In the group without loosening, the mean increase in the cement mantle area was 4380 ± 12701 mm2 (P < .0001). In the group with loosening, the mean increase in the cement mantle area was only 811 ± 4014 mm2 (P = .484). CONCLUSIONS: Use of the cement-within-cement technique for fixation of the humeral component in revision RSA is effective in improving functional outcome scores and shoulder range of motion. Furthermore, these findings suggest that efforts to maximize the cement volume during reimplantation may lessen the chance of humeral stem loosening requiring additional revision.