Medical grade polyurethanes have been widely promoted for biomedical applications. In particular, the use of polycarbonate-urethanes (PCU) has drawn considerable attention in the orthopaedic device industry as a result of their excellent mechanical properties, biostability and biocompatibility. PCUs have been extensively utilized in vascular grafts, stents and artificial heart valves. Specifically, bionate thermoplastic PCU, commercially produced by DSM PTG (Berkeley, California), has been of great interest in the field of orthopaedics because of its outstanding load-bearing properties and excellent wear resistance. Also, it is characterized by its long-term durability and resistance to hydrolytic degradation making it a good candidate for in-vivo orthopaedic applications. PCUs have been considered for meniscal replacement because of its unique weight-bearing capabilities, ability to withstand intense forces within the knee joint and ease of lubrication due to its hydrophilic nature. In addition, the low frictional properties essential for a meniscal replacement is obtainable with PCUs.

Materials used for this study were a commercial polycarbonate-urethanes, Bionate PCU 80A (B8) and 90A (B9) pellets, and polyethylene continuous strands fibres (PE) obtained from DSM Polymer Technology Group, USA. Some quantity of the B8 and B9 pellets were dried separately in a vacuum oven at 100°C for 14 hours. A custom mould was designed for the production of the mechanical test samples. The quantity of the constituent materials was determined using composite theory known as the Rule of Mixtures.

$E_c=E_m{V}_m+E_f{E}_f$

where V_m and V_f are the volume fraction of the matrix and fibre respectively. Three specimens each of the prepared composites were tested for tensile and compression strength and at a crosshead speed of 12 mm/min using a Zwick/Roell 1484 Material Testing Machine.

The PCUs were not as stiff as their fibre-reinforced composites, which indicate that the stiffness of the PCU composite materials is a function of both the stiffness of the PCU matrix and the interspersed fibres. The tensile moduli of composites of B8 and B9 increased appreciably with PE. An increase of 227% was obtained for the B8 with the incorporation of PE fibres while percentage increase in stiffness for B9 was 148% for PE reinforcement fibres. The compressive modulus dropped with the inclusion of the PE fibres in the B9, a reduction of 55% was recorded while an increment of 4% was obtained with PE added to the B8.

The results from this study demonstrate that the tensile and compressive properties of PCU can be custom-tailored to that of the meniscal tissue by systematically embedding reinforcement fibres into the PCU matrix such that a composite with desirable mechanical properties is obtained. The results of both tensile and compressive results visibly revealed the reinforcing effect of the fibres used in this study. However, additional studies are required to completely describe the PCU composite as a candidate meniscal substitute capable of gaining its full functionality.

The morphology of the proximal part of the humerus varies largely. Morphometric features characterizing the three-dimensional geometry of the proximal humerus have revealed a wide difference within individuals. These parameters include head size, radius of curvature, inclination angle, retroversion angle, offsets and neck-shaft angle. Different implant designs have been adapted so as to make provision for these anatomical variations. However, the optimal design criteria are yet to be established. Implant design is one of the main factors determining the success of Total Shoulder Arthroplasty (TSA) since slight modifications in the implant anatomy could have significant biomechanical effects. Therefore, this study investigates the three-dimensional morphometric parameters of the South African proximal humerus which will serve as a basis for designing a new Total Shoulder Prosthesis for the South African population.

Sixteen South African (SA) fresh cadaveric humeri (8 left, 8 right; 8 paired) were used in this study. The data consisted of 6 men and 2 women with ages ranging from 32 to 55 years (43.13 ±8.51). The humeri were scanned using a Computer Tomography (CT) scanner. The Digital Imaging and Communications in Medicine (DICOM) files from the CT data were imported into medical modelling software, MIMICS for reconstruction. The 3D reconstructed model of the humeri as an STL file was used for further processing.

The STL data were generated as a cloud of points in a CAD software, SolidWorks. These were then remodeled by defining the detailed Referential Geometric Entities (RGEs) describing the anatomical characteristics. Anatomical reference points were defined for the anatomical neck plane, the epiphyseal sphere and the metaphyseal cylinder. Also, axes were defined which comprises of the humeral head axis and the metaphyseal axis. Thereafter, the posterior offsets medial offsets and the inclination angles were measured based on the RGEs.

The posterior offset varied from 0.07 mm to 2.87 mm (mean 1.20 mm), the medial offset varied from 4.40 mm to 8.45 mm (mean 6.50 mm) while the inclination angle varied from 114.00º to 133.87º (mean 121.05º)

The outcome of the study showed that the shape and dimensions of the proximal humerus varies distinctively. The articular surface is not a perfect sphere and differs independently with respect to the inclination angles. In addition, variations were noticeable in the medial and lateral offsets.

The morphometric data on the African shoulder is very limited and this study will significantly contribute to the shoulder data repository for the SA population. The morphometric parameters measured in this study will be useful in designing a South African shoulder prosthesis that mimics the native shoulder hence eliminating post-surgical complications.