Topic four covers a very key area within orthopaedics; the failure of implants. Failed implants help surgeons and biomechanics engineers alike understand why implants fail and what can be done to try and prevent this.
SIP factors - Surgeon, implant and patient factors all influence the lifespan of an orthopaedic implant. It is important to understand that any three of these factors can lead to the failure of implants.
Surgeon factors - The positioning of an implant will effect how it performs and how long it lasts within the patient. For example, if a knee replacement is implanted in the wrong orientation, it will increase the amount of polyethylene wear produced by the implant. It is known that polyethylene wear particles can cause an inflammatory reaction, and this can lead to osteolytic loosening of the implant.
Implant factors - The implant itself makes up the biggest list of reasons for failure. Bearing surfaces, material of the implant, shape of the implant, size of the implant components, fixation method etc. can all affect how the implant will survive when it is within the human body.
Patient factors - The patient themselves can affect the longevity of their implant. High mechanical loading and increased activity can increase the rate of wear of the bearing surfaces on the implant increasing the risk of failure.
When implants fail it can be very hard to determine which of the three factors has caused the failure. Normally more than one factor influences implant failure, so you need to collect information regarding all three before you can decide why the implant has failed.
Understanding implant failure is vital to improving implant design and orthopaedic surgery for the future. The LIRC works closely with orthopaedic surgeons and biomechanics engineers all across the world to ensure lessons are learnt from failed implants. Check out their website - http://www.lirc.co.uk
EXAMPLE CASES - Click on the image to load the case
A case of osteolysis secondary to an adverse reaction to metal debris. A and B were taken 8-years apart. The change in bone stock is huge.
This case pre-operative radiograph shows an intra-operative pseudotumour secondary to taper corrosion between a cobalt chromium head and a titanium stem.
Look at the acetabular liner of the right hip. This radiograph evidences a ceramic liner fracture. A rare complication.
Osteolysis of the left acetabular component due to polyethylene wear.