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Dr Lipalo Mokete, Specialist Arthroplasty Surgeon

Revision Hip Replacement Surgery

Joint replacements can fail for various reasons. The commonest cause of failure within the first year of implantation is 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 parts related to use. Revision joint replacement surgery is generally more complicated than the first operation. The duration of surgery tends to be longer and the parts implanted generally tend to be longer versions of parts 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. Prepare for a longer hospital stay! The surgery is more extensive 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 longer period to avoid putting your full weight through the operated leg.

Revision surgery for the infected joint replacement

If infection is recognized within the first month, it can be cleared by surgical removal of infected tissue and limited replacement of the parts without removing the entire replacement. This process would be followed by an extended course of antibiotics. Established infection can only be cured by surgical removal of infected tissue and all parts. The surgery is complex and is normally carried out as two separate procedures. In the first procedure, infected tissue and all parts are removed and antibiotic laden temporary space filler is implanted. This 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 time period between the two procedures is 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 90's 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 socket results in friction and shedding of the metallic particles into the hip joint. The shed particles find their way into the blood stream and are partly excreted by the kidneys. The particles can potentially overwhelm the body resulting in 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 in formation 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 largely been withdrawn from the market.

The South African Orthopaedic Association has taken cognizance of issues related to 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 alert 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. Large diameter hip replacements are those with head diameters more than 36mm. There has also been a ban on certain specific metal on metal hip resurfacing products. Problems peculiar to 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 specialized tests including, ultrasound and Magnetic Resonance Imaging (MRI) of the hip if there are concerns. He may also order blood tests to monitor levels of metals in the blood circulation.

Hip Revision

Picture illustrating the difference in size between first time hip replacement prosthesis (right) and repeat surgery prosthesis.