Radiolucency in stemless shoulder arthroplasty is associated with an imaging phenomenon

Stemless humeral implants show comparable midterm clinical results compared to stemmed components. Recently, radiolucencies around the metaphyseal seating of humeral stemless implants were reported on postoperative radiographs. It is controversial whether they are attributable to bone resorption. We hypothesized these radiolucencies result from imaging artifacts. Seven cadaveric specimens (three male and four female) were first radiographed and then scanned with CT. A stemless humeral component of current design was implanted in each specimen. After implantation, all specimens were radiographed with different exposure settings. The implant was removed, and the specimens were scanned with CT again. Pre‐ and post‐implantation radiographs and CT scans were compared. The mean Hounsfield units (HU) at the humeral resection plane from the pre‐implantation CT were correlated with the diameter of the radiolucent halo on the post‐implantation radiographs. A symmetric radiolucent halo of variable diameters occurred on all radiographs after implantation when an automatic exposure control was used. The halo disappeared in all specimens when the tube voltage was reduced. Lower CT‐values (HU) before the implantation resulted in greater halos on the radiograph after implantation. Symmetric radiolucent halos can result from imaging artifacts, which is most likely due to radiation scatter. The halos can be minimized by reducing the tube voltage. The halo effect appears to be pronounced in bones with decreased density. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2040–2050, 2017.

     

Failure rates and outcomes after anatomic total shoulder arthroplasty are equivalent irrespective of subscapularis repair technique

BackgroundSubscapularis management during total shoulder arthroplasty (TSA) remains an area of debate. Although subscapularis-sparing techniques exist, most TSAs are performed through a deltopectoral interval with the subscapularis released and repaired. A paucity of literature exists comparing transosseous repair (TOR) with direct primary tendon repair (PTR) of a subscapularis tenotomy. Our study compared outcomes after TOR and PTR in patients undergoing anatomic TSA.MethodsThis retrospective study included patients who underwent primary anatomic TSA through a deltopectoral approach with subscapularis tenotomy using either PTR or TOR for repair. Outcome measures included subscapularis failure rates, visual analog scale (VAS) scores, American Shoulder and Elbow Surgeons (ASES) survey scores, internal rotation range of motion and strength, complications, and reoperation rates at 3 months, 1 year, and 2 years.ResultsInstitutional database query identified 306 patients who had primary anatomic TSA, 114 of whom had PTR and 192 TOR. Postoperative ASES and VAS scores were significantly improved at all time points in both groups compared with the preoperative scores (P < .001). Average active internal rotation was significantly improved at all time points in the PTR group (P < .001). In the TOR group, significant improvement was noted at 1 and 2 years but not at 3 months. Overall, subscapularis failure occurred in 13 patients, and complications that did not require surgery were noted in 28 patients. Reoperation was performed in 18 patients. However, subscapularis failures, complications not requiring surgery, and reoperations were not significantly different between the two groups. The difference in average internal rotation range of motion between the TOR and PTR groups was statistically significant at 3 months (P = .015) but not at 1 year (P = .265), although the difference trended toward significance again at the 2-year mark (P = .080). No significant differences were noted between the two groups in internal rotation strength, VAS scores, and ASES averages.ConclusionBoth transosseous and primary soft-tissue repair techniques after subscapularis tenotomy result in good outcomes after primary anatomic TSA. No differences were found between groups regarding clinical subscapularis failure rate, internal rotation range of motion or strength, VAS, or ASES scores at 2-year follow-up.Level of evidenceLevel III, Retrospective Comparative Study     

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     

The biomechanics of subscapularis repair in reverse shoulder arthroplasty: The effect of lateralization and insertion site

Functional outcomes of subscapularis (SSc) repair following reverse shoulder arthroplasty (RSA) remains controversial. SSc repair in combination with glenosphere lateralization was reported to yield worse clinical outcomes compared with the non-lateralized glenosphere. The aim of this biomechanical study was to investigate how glenosphere lateralization and different re-insertion sites can affect the biomechanics of the SSc after RSA. Nine patient-specific RSA shoulder models were created from patients' computed tomography scans. Moment arms and SSc length were calculated for abduction, forward flexion, and internal rotation in 20° and 90° abduction for three configurations of glenosphere lateralization (standard/+0, +5, and +10 mm) and three SSc repair sites (native, superior, and inferior) and compared with the native shoulder. When compared with the native shoulder, RSA resulted in large adducting SSc moment arms that were antagonistic to the deltoid. Glenosphere lateralization had no effect on SSc moment arms in any motion. However, lateralization increased SSc tension beyond its anatomic length for +5 and +10 mm of lateralization when attached to its native insertion. A superior SSc repair site created the least adductive moment arm as well as the least amount of SSc lengthening. Increased glenosphere lateralization showed a significant increase in the SSc length, which in combination with its adductive moment arm can be antagonistic to deltoid function. However, a superior SSc repair site may help reduce the adductive SSc moment arm and allow for reduced tension on the repair as its length in that location is less than that of the native SSc. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:888-894, 2020