Background
Stemless total shoulder arthroplasty is a well-established and reliable surgical treatment option for glenohumeral osteoarthritis resulting in loss of pain and improvement of shoulder function. Currently the two methods for the fixation of the humeral component are either screw fixation or impaction. The purpose of this study is the clinical and radiological comparison of two different stemless designs (screw fixation vs impaction) for total shoulder arthroplasties in patients suffering from primary glenohumeral osteoarthritis.
Methods
A retrospective cohort study including 39 patients with a mean age of 67 years and a minimum follow-up of 2 years was performed. Patients were separated into two groups based on the selected implant. In group A (n = 18) a screw fixation design and in group B (n = 21) an impaction type design was used. For clinical examination the Constant-Murley-Score (CS) and Subjective-Shoulder-Value (SSV) were evaluated. Radiological examination was performed on true-AP, axial and Y-view radiographs.
Results
In group A the CS increased from 27.1 to 65.2 points and SSV from 27.3 to 76.7% (p < 0.05). No osteolysis of the medial calcar or subsidence of the humeral implant were found in this group. In group B the CS increased from 29.0 to 72.6 points and SSV from 33.1 to 85% (p < 0.05). Osteolysis of the medial calcar was present in seven patients in this group. No signs for humeral loosening were found in both groups.
Conclusion
Impaction and screw fixation total shoulder arthroplasty for primary glenohumeral osteoarthritis using a stemless device provide reliable clinical results. The screw fixation seems to prevent osteolysis of the medial calcar.
Background
Prosthetic replacement of the proximal humerus with reverse shoulder arthroplasty (RSA) is an established means of treatment. Due to its unique biomechanical characteristics, RSA can restore shoulder function to a satisfying level in the case of cuff tear arthropathy, arthritis, and fractures. However, complications are frequent in RSA, one of the more common being implant instability with dislocation. The present study investigated the influence of glenosphere diameter and metaglene lateralization using a unique test setup.
Methods
Seven fresh-frozen cadaveric specimens of the shoulder were thawed and dissected. The subscapularis muscle, the infraspinatus, and the three heads of the deltoid muscle were fixed to a pulley system. After implanting an RSA in different configurations (38/42 mm glenosphere with lateralization of +0 mm, +5 mm, or +10 mm), the implants were dislocated using selective muscle pull. The frequency of dislocations depending on the prosthesis configuration was documented.
Results
The larger glenosphere diameter of 42 mm showed less dislocations than the diameter of 38 mm (39 vs. 46). Lateralization of +0, +5 mm, and +10 mm showed 26, 29, and 30, dislocations, respectively. Dislocation via pull on the infraspinatus muscle was most frequent. None of the results reached statistical significance.
Conclusion
The current investigation used a novel technique for investigating the effect of lateralization and glenosphere diameter on RSA instability. Despite indicating tendencies, the present test setup could not prove the hypothesis that a larger glenosphere diameter and increased lateralization add to stability. The lack of statistical significance could be attributable to the low specimen number. The clinical significance of lateralization and glenosphere diameter should be further assessed in future biomechanical investigations.
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