Experience with Metal on Metal (MoM) hip resurfacing devices has shown adequate cementation of the femoral head is critical for implant survival. Bone necrosis can be caused by the temperature change in the peri-prosthetic bone whilst the cement cures during implantation. This can lead to implant loosening, head/neck fracture and implant failure. During the implantation it is known that implants change shape potentially altering joint clearance and causing loosening. Given the history of Metal on Metal implant failure due adverse tissue reactions from Cobalt and Chromium particles we sought to test a novel Ceramic on Ceramic (CoC) bearing which may mitigate such problems. We set out to compare the behaviour of a novel ceramic femoral head component to a standard metal component in a hip resurfacing system after cemented implantation in a physiological warmed cadaveric model. Our first aim was to perform heat transfer analysis: To document time to, and extent of, maximum temperature change on the metal/ceramic surface and inside the resurfaced femoral head bone. Our second aim was to perform a dimensional analysis: To document any resulting deformation in the metal/ceramic femoral head bearing diameter during cementation.INTRODUCTION
AIM
The cup component of modern resurfacing systems are often coated creating a cementless press-fit fixation in the acetabulum based on surgical under-reaming, also enabling osseoconduction/integration. Due to the higher density of cortical bone along the antero-superior and postero-inferior regions of the acetabulum, the greatest forces occur between the anterior and posterior columns of the pelvis. This produces pinching of the implant that can result in deformation of the cup. Metal shell/modularpress-fit acetabular cups are susceptible to substantial deformation immediately after implantation. This deformation may affect the lubrication, producing point loading and high friction torques between the head and the cup that increase wear and may lead to head clamping and subsequent cup loosening. We sought to test a novel ceramic on ceramic (CoC) hip resurfacing system that should allay any concerns with the Adverse Reaction to Metal Debris associated with metal on metal (MoM) resurfacing devices. We sought to quantify the deformation of a novel CoC hip-resurfacing cup after implantation, using a standard surgical technique in a cadaveric model, and compare to the MoM standard. We also assessed if the design clearances proposed for this CoC hip resurfacing implant are compatible with the measured deformations, allowing for an adequate motion of the joint.INTRODUCTION
AIM
Unlike current acetabular cups, this novel ceramic cup has a Ti/HA coating which removes the requirement for assembly into a metal shell which avoiding potential chipping/misalignment and reducing wall thickness [Figure 1]. This study examines the resistance of novel thin-walled, direct to bone fixation ceramic cups to critical impact loads. Samples of the smallest (Ø46mm) and largest (Ø70mm) diameter ReCerfTM acetabular cups and corresponding femoral head implants were implanted into Sawbones foam blocks considered representative of pelvic cancellous bone. Two different positional configurations were tested and were considered worst case and the extremes of surgical compromise; P1 simulates the cup fully supported by the acetabulum with a high inclination angle (70°) and a vertical impaction axis (worst case loading near the cup rim) and. P2 simulates the cup implanted with a lower inclination (55°) but with the superior section unsupported by acetabulum bone [Figure 2]. For each size, three acetabular cups were tested in each position. The impact fixture was positioned within a drop weight rig above a bed of sand and ≈22mm of pork belly representative of soft tissues damping effect and the implant components aligned to achieve the defined impact point on the cup [Figure 2]. Lateral falls were tested on all available samples applying impact energy of 140J [1] and 3m/s impact velocity [2]. After the lateral fall test, each sample was tested under impact conditions equivalent to a frontal car crash considering a peak impact force of 5.7kN occurring 40ms from initial contact (able to produce acetabular fracture)[3].INTRODUCTION
METHODS
