Early fixation of the humeral component in stemless total shoulder arthroplasty : a radiostereometric and clinical study with 24-month follow-up

Developing and Validating a Model of Humeral Stem Primary Stability, Intended for In Silico Clinical Trials

In silico clinical trials (ISCT) can contribute to demonstrating a device's performance via credible computational models applied on virtual cohorts. Our purpose was to establish the credibility of a model for assessing the risk of humeral stem loosening in total shoulder arthroplasty, based on a twofold validation scheme involving both benchtop and clinical validation activities, for ISCT applications. A finite element model computing bone-implant micromotion (benchtop model) was quantitatively compared to a bone foam micromotion test (benchtop comparator) to ensure that the physics of the system was captured correctly. The model was expanded to a population-based approach (clinical model) and qualitatively evaluated based on its ability to replicate findings from a published clinical study (clinical comparator), namely that grit-blasted stems are at a significantly higher risk of loosening than porous-coated stems, to ensure that clinical performance of the stem can be predicted appropriately. Model form sensitivities pertaining to surgical variation and implant design were evaluated. The model replicated benchtop micromotion measurements (52.1 ± 4.3 µm), without a significant impact of the press-fit ("Press-fit": 54.0 ± 8.5 µm, "No press-fit": 56.0 ± 12.0 µm). Applied to a virtual population, the grit-blasted stems (227 ± 78µm) experienced significantly larger micromotions than porous-coated stems (162 ± 69µm), in accordance with the findings of the clinical comparator. This work provides a concrete example for evaluating the credibility of an ISCT study. By validating the modeling approach against both benchtop and clinical data, model credibility is established for an ISCT application aiming to enrich clinical data in a regulatory submission.

Is stemless total shoulder arthroplasty indicated in elderly patients?

BACKGROUND AND HYPOTHESIS

Stemmed anatomic total shoulder arthroplasty has represented the gold standard for the treatment of glenohumeral osteoarthritis with an intact rotator cuff for decades. To the author's knowledge, no study has specifically examined the outcomes of stemless, modular total shoulder arthroplasty in elderly patients. The hypothesis of this study was that stemless anatomic total shoulder arthroplasty in elderly patients (age ≥70 years) would have equivalent clinical and radiographic outcomes compared with a younger population (age <70 years).

MATERIALS AND METHODS

A prospectively collected database of patients undergoing primary, modular, stemless anatomic total shoulder arthroplasty for osteoarthritis was retrospectively reviewed. Patient-determined outcomes including the Western Ontario Osteoarthritis Index (WOOS) score, American Shoulder and Elbow Surgeons (ASES) score, Single Assessment Numeric Evaluation (SANE) score, Simple Shoulder Test score, and Shoulder Activity Level score were recorded preoperatively and postoperatively at 1 year and 2 years. Preoperative and 1-year postoperative range of motion was recorded. Postoperative radiographs were examined to assess for radiographic evidence of complications.

RESULTS

Stemless arthroplasty was planned in 116 patients. Seven patients underwent conversion intraoperatively to a stemmed prosthesis. There was no difference between patients aged <70 yr and those aged ≥70 years who required intraoperative deviation from the preoperative plan to a stemmed prosthesis (5.8% vs 6.4%, P = .90). At the time of stemless arthroplasty, 64 patients were aged <70 yr and 44 patients were aged ≥70 years. Between the 2 groups, there were no clinically or statistically significant differences in WOOS, ASES, and SANE scores at baseline, 1-year follow-up, or 2-year follow-up. The changes in all scores from baseline to 2 years were similar between the group aged <70 yr and the group aged ≥70 years. There was no difference in the percentage of patients achieving the minimal clinically important difference or substantial clinical benefit in either group after shoulder arthroplasty at 2-year follow-up. There was no difference between the 2 groups in terms of final postoperative range of motion or change in range of motion for any metric examined. There was no evidence of radiographic complications in either group.

CONCLUSIONS

Age ≥70 years does not appear to be a contraindication to stemless anatomic total shoulder arthroplasty. Postoperative improvements in patient-determined outcome scores, the percentage of patients achieving clinically important outcomes for the ASES, SANE, and WOOS scores, and postoperative range of motion were similar between patients aged <70 yr and those aged ≥70 years. There was no difference between the groups regarding the patients who required intraoperative deviation from the preoperatively planned stemless prosthesis to a stemmed prosthesis. Neither age group demonstrated a radiographically apparent complication.