[Options and limits of stemless shoulder prostheses]

Mid-term results of a stemless ceramic on polyethylene shoulder prosthesis - A prospective multicentre study

INTRODUCTION

Early reports of stemless shoulder arthroplasty have shown promising clinical and radiological outcomes. The purpose of this study was to report on the mid-term results of an implant that utilises a ceramic humeral head.

METHODS

A prospective, consecutive, multicentre study of stemless shoulder prosthesis with a minimum of four years of follow-up was conducted between August 2009 and May 2012. The adjusted Constant-Murley Score (CMS), revision rate and presence of radiolucent lines were recorded at intervals.

RESULTS

A total of 207 patients were eligible for study inclusion; 62.8% were female and mean age was 64.8 years (range 30-86). Mean follow-up was 70.7 months (range 48-100), 73% underwent TSA and 27% hemiarthroplasty. The mean CMS improvement was 42.6 (p < 0.0001) at 48 months. Radiolucencies were present in 2.7% of humeral zones and 14% of glenoid zones at 48-month follow-up. The revision rate was 6.3% with rotator cuff failure (2.9%) the most common indication.

CONCLUSIONS

Mid-term results demonstrate that the studied stemless implant with a ceramic humeral head had clinical and radiological outcomes that are comparable to other reported studies.

[Shoulder endoprosthesis in the elderly : Hemiarthroplasty or total shoulder arthroplasty? Anatomic or reverse?]

Implantation of reverse shoulder endoprostheses is becoming more popular for elderly patients besides the well-established standard anatomic endoprostheses. The reasons for this are the increased life expectancy, age-dependent degeneration of the rotator cuff leading to cuff tear arthropathy, posttraumatic disability after failed osteosynthesis and primary reverse fracture arthroplasty. Stemless implants are more frequently used for primary osteoarthritis with the bone quality being the limiting factor. Modern implant systems allow the stepwise extension from bone preserving primary implants to modular and convertible revision implants that allow a partial exchange of components. Revision surgery, especially that of reverse arthroplasty, has limited potential for secondary treatment options and therefore implantation and revision should be performed in specialized treatment facilities.

Comparison of proximal humeral bone stresses between stemless, short stem, and standard stem length: a finite element analysis

BACKGROUND

The stem lengths of humeral components used in shoulder arthroplasty vary; however, the literature on these devices is limited. This finite element study investigates the effect of humeral component length on stresses in the proximal humerus.

METHODS

Intact and 3 reconstructed (standard length, short, and stemless implants) finite element models were created from shoulder computed tomography scan data (N = 5). Loading was simulated at varying abduction angles (15°, 45°, and 75°). The average bone stress (represented as a percentage of intact values) was reported at 8 transverse slices. In addition, the overall average change in cortical and trabecular bone stresses was quantified.

RESULTS

Cortical bone stresses in the most proximal slice for the standard (58% ± 12%) and short (78% ± 10%) stem models were significantly reduced compared with the intact (100%) and stemless (101% ± 6%) models (P = .005). These reductions persisted in the second cortical slice for the standard stem compared with the intact, stemless, and short models (P = .025). Interestingly, stresses in the trabecular bone within these proximal slices were significantly elevated when stemless implants were used compared with all other implants (P < .001), regardless of abduction angle.

CONCLUSION

Reducing stem length produced humeral stresses that more closely matched the intact stress distribution in proximal cortical bone. Opposing trends presented in the proximal trabecular bone, probably because of differences in load transfer when shorter stems are used. Accordingly, the results suggest that implant stem length is 1 variable that can be modified in an attempt to better mimic intact bone stresses during humeral component insertion, provided stem fixation is adequate.

Total shoulder arthroplasty: are the humeral components getting shorter?

Each generation of total shoulder arthroplasy has improved on the previous. The newest humeral component innovation is shortening the humeral component or eliminating the stem entirely to rely on stemless fixation in the humeral metaphysis. This offers theoretical advantages of preserved bone stock, less stress shielding, eliminating the diaphyseal stress riser, ease of stem removal at revision, and humeral head placement independent from the humeral shaft axis. There are a number of short term cohorts that have shown low complication rates and outcomes similar to previous generations of stemmed humeral components. Longer term and better designed studies are needed in order for short stems and stemless components to become the standard of care.