Abstract
There are multiple proximal prosthetic geometries available for a surgeon to select when humeral head replacement is indicated for four-part proximal humerus fractures. We compared different proximal prosthetic geometries in stable and unstable fracture patterns, with a standard tuberosity fixation method.
Simulated four-part fractures were created with an oscillating saw in six synthetic shoulder models. Three different proximal prosthetic geometries used polymetylmethacrelate (PMMA) – a smooth circular shape (SCS), a diamond shape (DS) and an irregular multiple fin shape (IMFS) prostheses. A standardised fixation method using vertical, and horizontal straps along with a medial based cerclage strap was performed. Passive motion was then carried out using a robotic articulator. Interfragmentary displacement was measured from tuberosity to tuberosity as well as tuberosity to shaft using mercury strain gauges.
The least amount of interfragmentary motion occurred when an IMFS was used in a stable fracture pattern. This geometry provided more interfragmentary stability even with the unstable fracture pattern than the DS or SCS. The least stable construct was the SCS prosthesis with an unstable fracture pattern.
Prosthetic geometry does affect stability of tuberosity reconstruction in proximal humerus fractures. An irregular shaped prosthesis augments the fixation construct. When using a smooth prosthetic design a stable fracture pattern must be achieved to prevent excessive interfragmentary motion. A smooth prosthetic design for tuberosity reconstruction is not recommended.
The abstracts were prepared by Nico Verdoschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, Universitair Medisch Centrum, Orthopaedie / CSS1, Huispost 800, Postbus 9101, 6500 HB Nijmegen, Th. Craanenlaan 7, 6525 GH Nijmegen, The Netherlands.
