Biomechanical model of distal articular humeral fractures-influence of bone density on the fracture threshold.

INTRODUCTION: Working hypothesis: The distal humeral bone density influences supracondylar fracture threshold. The aim of this study was first to develop a reproducible model of intra-articular distal humeral fractures and second to establish a relationship between bone mineral density (BMD) and the fracture threshold of the humerus. MATERIALS AND METHODS: An original model of the fracture was developed using ten sawbones. After obtaining a reproducible and clinically relevant fracture model, we tested 21 cadaveric distal humeri for which the BMD was known with a stainless-steel custom-made proximal ulna jig. Fractures were created using a servo hydraulic-testing machine in axial compression to simulate a fall onto an outstretched hand. Fracture lines, load to failure, and rigidity of the bone were recorded based on the stress-strain curves. RESULTS: The fracture generation was reliable, reproducible, and clinically relevant (type B2). A significant correlation between the BMD and the fracture threshold was found. Mean threshold was 901.86 N/m2. Mean distal humerus BMD was 0.9097 g/cm2 (r = 0.7321). CONCLUSIONS: We developed a reproducible articular fracture of the distal humerus model and found a correlation between the fracture threshold and bone mineral density.

The precision of patient-specific instrumentation guides for the positioning of the glenoid component in total reverse shoulder arthroplasty: an in vivo scanographic study.

OBJECTIVE: Optimal position and fixation of the baseplate is essential for the longevity of the reverse shoulder arthroplasty (RSA) and the patient-specific instrumentation (PSI) can help the surgeon to achieve that purpose. The aim of this study was to assess the reliability of the PSI guides for the positioning of the baseplate and the fixation's screws. METHOD: Prospective study involving 35 patients operated for RSA. The PSI guides were planned and used by the senior surgeon in all cases. We compared the planned orientation (frontal and axial) of the baseplate and the screws with the post-operative CT scan. RESULTS: The mean difference between the planned measures and the post-op measures was inferior to 2.5°. The screw's length corresponded with the pre-op plan in 70% of the cases. CONCLUSION: The use of a PSI guide to position the glenoid implant in total reverse shoulder arthroplasty is reliable, reduces the risk of positioning errors and improves the quality of fixation with the screws.

Geometric modification of the humeral position after total reverse shoulder arthroplasty: what is the optimal lowering of the humerus?

BACKGROUND: The main mechanical effect after reverse shoulder arthroplasty (RSA) is the lowering of the glenohumeral rotation center. The optimal value of the humeral lowering after RSA is still debated. The main objective of our study was to determine the lowering and medialization of the humerus and to correlate these parameters with short-term functional results. MATERIALS AND METHODS: The study included 70 patients with complete radiographic and clinical data. A multivariate analysis was used to compare the clinical and radiographic outcomes with the humeral lowering. RESULTS: The mean humeral lowering was 25.4 mm (range, 6-38 mm), and the mean medialization was 9.2 mm (range, 0-20 mm). Humeral lowering significantly influenced active forward elevation and the rate of scapular notching. DISCUSSION: The best clinical results and the lowest incidence of scapular notching were found after a lowering of more than 24 mm in our series. We recommend humeral lengthening of at least 24 mm after implanting a total reverse shoulder prosthesis.

Reproducibility of a new method for measuring lowering and medialisation of the humerus after reverse shoulder arthroplasty.

BACKGROUND: Reverse shoulder arthroplasty (RSA) requires lowering the humerus and medialisation of the centre of rotation. Several techniques based on standard X-rays are available in the literature. The aim of this study was to expose and validate a new technique for measuring these parameters. MATERIALS AND METHODS: Radiographic data of 20 patients were included. Three observers examined each X-rays three times to establish the inter- and intra-reproducibility of each technique (Jobin, Renaud and our method). RESULTS: Intra-observer reproducibility was between 0.10 and 0.94. The best intra-observer intraclass correlation coefficient (ICC) was obtained using Renaud's and our techniques. The inter-observer reproducibility was between 0.37 and 0.74. The best inter-observer ICC was obtained with our technique. DISCUSSION: We describe a reliable and reproducible method to evaluate lowering and medialisation of the humerus after RSA. This technique may allow determine the optimal threshold of lengthening after RSA.