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Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 287 - 287
1 Dec 2013
Puthumanapully PK Shearwood-Porter N Stewart M Kowalski R Browne M Dickinson A
Full Access

Introduction

Implant-cement debonding at the knee has been reported previously [1]. The strength of the mechanical interlock of bone cement on to an implant surface can be associated with both bone cement and implant related factors. In addition to implant surface profile, sub-optimal mixing temperatures and waiting times prior to cement application may weaken the strength of the interlock.

Aims

The study aimed to investigate the influence of bone cement related factors such as mixing temperature, viscosity, and the mixing and waiting times prior to application, in combination with implant surface roughness, on the tensile strength at the interface.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 288 - 288
1 Dec 2013
Puthumanapully PK Stewart M Browne M Dickinson A
Full Access

Introduction

Fatigue and wear at the head/stem modular junction of large diameter total hip replacements can be exacerbated as a result of the increase in frictional torque. In vivo, a “toggling,” anterior-posterior (A-P) movement of the head taper on the trunnion may facilitate corrosion in the presence of physiological fluids, leading to increased metal ion release. Clinically, metal ion release has been linked to the formation of pseudo tumours and tissue necrosis [1].

Aims

In this investigation, a large diameter metal on metal THR was tested on a rig designed to recreate the toggling motion at the head/stem junction. Post-test analyses are conducted to look for evidence of mechanical and corrosive damage.


Orthopaedic Proceedings
Vol. 95-B, Issue SUPP_34 | Pages 89 - 89
1 Dec 2013
Puthumanapully PK Amis A Harris S Cobb J Jeffers J
Full Access

Introduction:

Varus alignment of the knee is common in patients undergoing unicondylar knee replacement. To measure the geometry and morphology of these knees is to know whether a single unicondylar knee implant design is suitable for all patients, i.e. for patients with varus deformity and those without. The aim of this study was to identify any significant differences between normal and varus knees that may influence unicondylar implant design for the latter group.

Methodology:

56 patients (31 varus, 25 normal) were evaluated through CT imaging. Images were segmented to create 3D models and aligned to a tri-spherical plane (centres of spheres fitted to the femoral head and the medial and lateral flexion facets). 30 key co-ordinates were recorded per specimen to define the important axes, angles and shapes (e.g. spheres to define flexion and extension facet surfaces) that describe the femoral condylar geometry using in-house software. The points were then projected in sagittal, coronal and transverse planes. Standardised distance and angular measurements were then carried out between the points and the differences between the morphology of normal and varus knee summarised. For the varus knee group, trends were investigated that could be related to the magnitude of varus deformity.