REVISION HIP REPLACEMENT SURGERY
Why is revision hip replacement surgery needed?
Joint replacements can fail for various reasons. The most typical cause of failure within the first year of implantation is an infection of the joint. Late failure of the joint replacement is due to loosening of the parts, the joint starting to feel unstable or wear of the sections related to use. Revision joint replacement surgery is generally more complicated than the first operation. The duration of revision joint replacement surgery tends to be longer, and the parts implanted typically tend to be more extended versions of components used in first-time operations. Bone graft (from a bone bank) may also be used to restore bone stock in instances where there has been extensive bone loss. Be prepared for an extended hospital stay. The surgery is more comprehensive, and you are older than at the time of the first operation. The rehabilitation process is similar, but you may be required to use walking aids for a more extended period to avoid putting your full weight through the operated leg.
Revision surgery for the infected joint replacement
If an infection is recognised within the first month, there is a high likelihood that it can be cleared by surgical removal of infected tissue without removing the entire replacement. An extended course of antibiotics would follow this process. Established infection can only be cured by surgical removal of infected tissue and all parts. Revision joint replacement for infection is complicated and is typically carried out as two separate procedures. In the first procedure, infected tissue and all parts are removed, and an antibiotic laden temporary space filler is implanted. Surgery is followed by an extended course of antibiotic treatment as an inpatient. Only once the infection is cleared would we consider the second procedure, which involves implantation of revision joint replacement parts. The period between the two processes is typically two to three months.
Metal on Metal Hip Replacement
Metal on metal hip replacement refers to hip replacements where both the ball and the articulating part of the socket are made of metallic alloy. The hip replacement may be of a conventional type (total hip replacement), or it may be "hip resurfacing". Hip resurfacing is a type of hip replacement that was introduced in the late '90s as a high-performance replacement for the younger and more active patient. Only a small part of the head is removed in this procedure, and a metallic "cap" is then attached to the remaining head to create the ball of the hip joint. The socket consists of a single part made entirely of metallic alloy. The movement of the ball within the cavity results in friction and shedding of the metallic particles into the hip joint. The shed particles find their way into the bloodstream and are partly excreted by the kidneys. The particles can potentially overwhelm the body resulting in the formation of cysts around the hip and allergic reactions. There are also theoretical concerns about cancer formation and toxicity of these metals. However, to date, there has not been any evidence directly implicating the shed metallic particles of cancer. Moreover, the Orthopaedic community is yet to agree on metal levels in the blood circulation that would be deemed acceptable following this type of surgery. Toxic levels are of a much higher magnitude.
The popularity of all types of metal on metal hips reached a peak in the middle of the last decade but has since waned because of reports of higher failure rates compared to conventional hip replacements. The vast majority of metal on metal hip replacements and hip resurfacings put into patients function well, and patients are satisfied with their hips. However, in a small number of patients, the replaced hips fail earlier than expected and can be problematic. Design flaws have been identified in metal on metal products offered by some companies, and the defective products have primarily been withdrawn from the market.
The South African Orthopaedic Association has taken cognisance of issues related to the metal on metal hips and aligned itself with a medical device alert released by the Medicines and Healthcare products Regulatory Agency (MHRA) in the United Kingdom. The warning was first issued in 2010 and has been updated regularly as our understanding of metal on metal hips improves. There has been a complete ban on large-diameter total hip replacements in the context of a first time joint replacement (primary operation) other than in ethically conducted clinical trials. Extensive diameter hip replacements are those with head diameters more than 36mm. There has also been a ban on particular metal on metal hip resurfacing products. Problems peculiar to the metal on metal hips are currently the subject of intensive scientific study.
All patients with metal on metal hip implants have to attend follow-up visits with their Orthopaedic surgeon at least once a year. In general, there is no concern in hips that continue to function well. Your surgeon may order specialised tests including, ultrasound and Magnetic Resonance Imaging (MRI) of the hipbone if there are concerns. He may also order blood tests to monitor levels of metals in the blood circulation.
Picture illustrating the difference in size between first-time hip replacement prosthesis (right) and repeat surgery prosthesis.