Stemless versus stemmed anatomic total shoulder arthroplasty: a meta-analysis of randomized clinical studies at short term follow-up

BackgroundStemless total shoulder arthroplasty (TSA) implants were developed to counteract many of the complications and challenges associated with the stemmed humeral component. The purpose of this study was to evaluate the clinical efficacy, radiographic outcomes, and incidence of major complications of stemless implants relative to stemmed implants in the context of anatomic TSA using pooled data from randomized clinical studies.MethodsEight databases were queried in October 2021 for randomized clinical studies directly comparing the outcomes between patients treated with stemless anatomic TSA, and conventional anatomic TSA with a stemmed humeral component. Clinical outcomes between groups were compared using a random effects model and a pooled weighted mean difference, a pooled standardized mean difference, or a pooled odds ratio.ResultsFive randomized clinical studies were identified with a total of 584 patients at final follow-up (range: 24.0-32.7 months) and an average age of 64.9 years (range: 62.1-69.0 years) at the time of surgery. There was no significant difference between the 2 groups for adjusted Constant–Murley Scores (P = .20), pooled patient reported functional outcomes (P = .41), forward flexion range of motion (P = .92), external rotation range of motion (P = .05), radiographic migration/subluxation of the humeral component (P = .52), infection risk (P = .89), odds of a revision surgery (P = .86), or odds of a subsequent reverse TSA (P = .68). For odds of a periprosthetic fracture (P = .07) and odds of developing radiolucency related to the humeral component (P = .06), there was a potential clinical benefit for the stemless component; however, this difference was not statistically significant for the current data set.ConclusionThis meta-analysis directly compared stemless and stemmed anatomic TSA implants and demonstrated no significant difference in the pooled results for any of the included clinical outcomes, radiographic outcomes, major complication outcomes, or revision surgery related outcomes between the 2 groups at early follow-up, although the small sample size may preclude in finding significance. These findings suggest that there are equivalent clinical outcomes of stemless anatomic TSA components and that these implants are safe, efficacious, and non-inferior relative to the current gold standard stemmed humeral implant. The data suggest that this is true for relatively younger anatomic TSA patients sampled from a population that is similar to those included in this meta-analysis.     

Stemless and stemmed total shoulder arthroplasty: a comparison of short-term clinical and radiographic outcomes

BackgroundStemless total shoulder arthroplasty could provide benefits over stemmed arthroplasty which has represented the gold standard for decades. Proposed benefits of stemless arthroplasty include better reproduction of anatomy and reduction in stress shielding; however, this does not appear to be confirmed by any study. The hypothesis was there would be no clinical differences between the stemless and the short-stem prosthesis, but the stemless prosthesis would better reproduce coronal radiographic anatomy and have less radiographic evidence of stress shielding.Materials and MethodsA prospectively collected data of patients undergoing primary, anatomic total shoulder arthroplasty for osteoarthritis were retrospectively reviewed. Patient-determined outcomes including the Western Ontario Osteoarthritis Index, American Shoulder and Elbow Surgeons score, Single Assessment Numeric Evaluation, Simple Shoulder Test, and Shoulder Activity Level were recorded preoperatively, at 1 year, and at 2 years. Preoperative and 1-year postoperative range of motion was recorded. Radiographic parameters to assess restoration of proximal humeral anatomy included humeral head height, humeral neck angle, humeral centering on the glenoid, and postoperative restoration of the anatomic center of rotation. Final postoperative radiographs were assessed for evidence of stress shielding.ResultsForty-eight patients had a stemmed humeral prosthesis, and 109 patients had a stemless prosthesis. Patient-determined outcomes were available from 2 years postoperatively in 99.4%. Both groups had significant improvements in all patient-reported outcomes and range-of-motion metrics, but there were no differences between the stemless and stemmed groups in these outcomes. The prosthetic humeral head of the stemmed components was more likely to extend further superior to the humeral osseous margin than that of the stemless group (2.0 ± 2.4 vs. 0.8 ± 1.4 mm; P = .0004). The stemless group had a smaller postoperative deviation from the anatomic center of rotation than the stemmed group (2.5 ± 1.9 vs. 3.2 ± 2.1 mm; P = .04). The humeral neck angle was comparable between the stemmed group and the stemless group (133 ± 7° vs. 131 ± 8°; P = .06). There was similar mean deviation of humeral head centering on the glenoid prosthesis between the stemmed and stemless groups (1.9 ± 1.8 vs. 1.6 ± 1.7 mm; P = .20). There was evidence of stress shielding in 10 patients (21%) with a stemmed prosthesis and in no patients with a stemless prosthesis at 1-year follow-up (P < .0001).ConclusionsThere were no differences in patient-determined outcomes between the groups at 2-year follow-up. Restoration of proximal humeral anatomy was either better or equivalent with the stemless prosthesis compared to the stemmed one. Radiographic evidence of stress shielding was found in the stemmed prosthesis but not in the stemless prosthesis at 1-year follow-up.     

Biomechanical comparison of stemless humeral components in total shoulder arthroplasty

BackgroundThe purpose of this study was to compare initial fixation strength between various stemless and stemmed humeral components and to correlate implant fixation strength with bone mineral density (BMD).MethodsFive humeral stem designs were investigated: Stemless-A (four hollow fins), Stemless-B (central body, three solid fins), Stemless-C (central screw, peripheral rim-fit), Short stem (50 mm), and Standard stem (130 mm). Fifty cadaveric human humerii were obtained and divided into five groups. BMD within the humeral head was determined for all samples. The mean BMD was similar between groups. The 25 samples with the lowest and highest BMDs were categorized as “Low” and “High,” respectively, with a BMD threshold of 0.35 g/cm², creating BMD subgroups. After implantation, each sample underwent a standardized biomechanical testing protocol, with axial loading followed by torsional loading. Sensors attached to the specimen recorded micromotion throughout testing. Axial loading consisted of cyclic loading for 100 cycles at 3 peak forces (220, 520, and 820 N). Torsional loading consisted of 100 cycles of internal/external rotation at 0.1 Hz at 6 peak torques, or until failure (±2.5, 5, 7.5, 10, 12.5, and 15 Nm). Failure was defined as the torque at which any bone fracture, implant detachment from anchor/stem, or an excess of 50° internal/external rotation occurred. Groups and BMD subgroups were compared.ResultsAt maximal axial loading, Stemless-B demonstrated greater micromotion (540 μm) than Stemless-C (192 μm) (P = .003). Stemless-B and Stemless-A (387 μm) also had greater micromotion than Short stem (118 μm, P < .001, P = .03) and Standard stem (85 μm, P < .001, P = .01). When comparing low-BMD samples at maximal axial loading, these differences were accentuated, but comparison of high-BMD samples showed no significant differences between groups. Torsional testing demonstrated that Standard stem failed at greater torque (7.2 Nm) than Stemless-B (2.3 Nm, P < .001), Stemless-A (1.9 Nm, P < .001), and Stemless-C (3.9 Nm, P = .01). When comparing torsional testing results of low-BMD samples, both Standard stem and Short stem failed at greater torque than Stemless-B (P = .02, P = .003) and Stemless-A (P = .03, P = .004) but failed at a similar torque to Stemless-C. Torsional testing of high-BMD samples showed that Standard stem failed at a greater torque than all stemless designs.ConclusionStemless humeral implants should be used with caution in low-BMD settings (<0.35 g/cm²). A central screw and peripheral rim-fit stemless anchor design demonstrated greater fixation strength at low BMD when compared with other designs, while all stemless designs performed similarly at high BMD.Level of evidenceBasic Science Study; Cadaveric Study