Currently available fracture fixation devices that were originally developed for healthy bone are often not effective for patients with osteoporosis. Resulting outcomes are unsatisfactory, with longer recovery times, often requiring re-surgery for failed cases. One major issue is the design of bone screws, which can loosen or pull-out from osteoporotic bone. Design improvements are possible, but the development of new screws is a lengthy and expensive process due to the manufacture of the complex geometry involved. The aim of this research was to validate our currently available 3D printing technology in the design, manufacture and testing of screws.

Three standard wood screw designs were reverse-engineered using computational modelling and then fabricated in polymeric resin using 3D rapid prototyping on a Stereolithography (SLA) machine. The original metal screws and the 3D screws (n=5 of each) were then inserted into a synthetic bone block (Sawbones, PCF5) representing the mechanical properties of severely osteoporotic cancellous bone. Pull-out tests were conducted in accordance with ASTM 543-13.

The three metal screws exhibited pull-out strengths of 125, 74 and 118 N respectively. The 3D printed screws by comparison showed pull-out strengths approximately 15–20 % lower than their metal counterparts. However, when the results were normalised to the material tested, showing the relative changes to the first design, the pattern of results in the metal and 3D printed groups were almost identical (within 3 % of each other), showing excellent correlation.

This study is the first to show that 3D Rapid Prototyping can be used in the pre-clinical testing of orthopaedic screws. The methodology provides a cheaper, faster development process for screws, allowing huge scope for development and improvement. Future work will include expanding the study to include more screw configurations as well as testing in higher density foams to compare performance in healthier bone.

Introduction

Patellofemoral pain and instability can be quantified by using the tibial tuberosity to trochlea groove (TT-TG) distance with more than or equal to 20mm considered pathological requiring surgical correction. Aim of this study is to determine if knee joint rotation angle is predictive of a pathological TT-TG.

Introduction: Hip resurfacing has gained popularity for treating young and active patients with arthritis. Recent literature has reported increase revision rate amongst females as compared to males undergoing resurfacing. The aim of this study is to identify any differences in survival or functional outcome between male and female patients treated with metal-on-metal hip resurfacing.

Methods: All procedures performed between July 1997 to July 2003 were extracted from the database and grouped based on gender. 1266 patients (1441 hips, 582 female and 859 male patients) were identified. The preoperative diagnosis, Oxford hip score, component size, post operative complications and revisions were recorded. Failures included revision of either the femoral or acetabular components.

Results: The mean follow up was 5.5 years. There were 52 revisions in total (30 in female and 22 in male group). The 8 year survival in the male and female groups were 96.1% and 91.5% respectively which is significantly different (p=0.0006). The size of the femoral component was significantly associated with revision (p=0.0008). Cox proportional hazard modelling including gender, aetiology and femoral component size identified a diagnosis of osteoarthritis reduced the risk of revision of 0.2 times (p=0.0004). However, SUFE was significantly associated 5.57 times increased risk of revision (p=0.0019). With every millimetre increase in head size there was a reduction in risk of revision of 0.89 (p=0.0098). By inclusion of all variables in this model gender was found not to be significantly associated with failure.

Conclusion: This study demonstrates that although females may initially appear to have a greater risk of revision this is related to differences in the femoral size and pre-operative diagnosis between the genders. Patient selection for resurfacing is best made on size and diagnosis rather than gender.