Why hip replacement?
One of the largest joints in the human body is the hip. A healthy hip joint will be surrounded by cartilage to support the joints and stop the bones from rubbing against each other.
The ‘ball and socket joint’ is connected by ligaments and lubricated to help prevent friction.
A hip replacement is necessary when the joint becomes damaged and causes persistent pain or mobility problems. Osteoarthritis is the main cause for hip joint operations. Severe hip fractures and rheumatoid arthritis may also lead to surgery to replace the hip joint.
Degenerative osteoarthritis of the hip joint, also known as coxarthriosis, is the most common cause of hip problems in adults. Hip joints are most frequently prone to osteoarthritis and the destruction of the articular cartilage. Often, the existing damage is not discovered until very late in the progression of the disease. This is usually at the stage where the patient is already experiencing restricted movement and/or pain.
If osteoarthritis is not treated, it inevitably leads to the failure of the hip joint. The destruction of articular cartilage as the bone surfaces rub against each other causes extreme pain and inflammation.
Hip joint surgery
There are two different operational strategies to treat coxarthrosis depending on the degree of damage. If there’s still enough cartilage present at the hip joint, it may be possible to preserve the joint.
However, in the absence of sufficient cartilage, the joint socket and joint head may need replacing with metal prostheses.
Joint-preserving surgery is less common compared with hip replacement surgery. This is usually because the symptoms of coxarthrosis frequently go unnoticed until there isn’t enough cartilage remaining to perform this preservation procedure.
Often joint-preserving surgery is performed following an injury, such a motor vehicle accident for example. The surgery realigns joint surfaces and prevents joint abrasion to protect remaining cartilage. This procedure is more commonly performed on younger adults with a strong bone structure.
In elderly patients with advanced osteoarthritis, a hip replacement is typically the only option. Tens of thousands of people have hip replacement surgery every year in the UK. During the procedure, all joint surfaces must be replaced with metal implants. Generally, 90% of these artificial joints last for 10 years, with 80% lasting for up to 20 years.
However, hip replacement surgery won’t restore full mobility. Patients generally have the same level of mobility as they had prior to the surgery, although their discomfort should be significantly reduced. In addition to the physical shortcomings associated with hip replacement surgery, there are also the risks that may arise from the metal alloys themselves.
In the case of knee joint arthroscopy, a tourniquet is often applied above the knee and around the thigh. This is used to temporarily interrupt local circulation in order to properly investigate the joint.
For several decades metal prostheses have been used to replace joints, particularly the hip joint. Nevertheless, relatively little is known about the effects these metal implants have on the body and the possible problems with metal prosthesis of the Hip.
More recently, increasing concerns have being raised about metal prostheses and their ability to trigger metal sensitivity and metal toxicity within the body.
Several studies have shown that sensitivity associated with metal prostheses is particularly common in women. Research has found the development of soft tissue masses around hip joints containing necrotic tissue1, 2. These pseudotumors affect more women than men and are associated with a high level of iron in the blood.
The exact cause is unknown and may be the result of a range of factors. Researchers believe that these pseudotumors are most likely caused by a toxic reaction or hypersensitivity to excessive metal debris. These metal particulates are released into the blood stream from the mechanical grinding of the prostheses.
A London based study published in 2012 found that rubbing the metal surfaces together leads to the release of metal ions. These metal irons are suspected to be pro-inflammatory and the cause of hip failures within the first five years following hip replacement surgery3. In particular, cobalt and chromium from alloys within the implants appear to play a major role in these processes.
Most recently, an American research group found a link between metal prostheses and neurological disease. A pilot with a hip replacement had high levels of cobalt and chromium in his blood stream after a receiving a metal prostheses. These excessive metal ion concentrations are believed to have lead to the development of a neurological condition4.
The results of a decade-long American based study into the link between elevated metal ion concentrations and metal prostheses were published in 2013. This research revealed that all study participants exhibited elevated levels of cobalt, chromium and/or titanium5.
Cobalt concentrations measured three times higher, chromium levels almost four time higher, and titanium concentrations eighteen times higher following hip replacement surgery. The most plausible explanation for these elevated mental concentrations is the mechanical wear and tear of the metal surfaces of the joint.
At this stage, it’s unclear what the effect these concentrations of metal ions will have on the body over time. More research is needed to investigate the release and effect of metal ions from joint prostheses.
- Pandit H, Glyn-Jones S, McLardy-Smith P, et al. 2008. “Pseudotumours associated with metal-on-metal hip resurfacings”. J Bone Joint Surg Br. 90(7): 847–51
- Boardman DR, Middleton FR, Kavanagh TG. 2006. “A benign psoas mass following metal-on-metal resurfacing of the hip”. J Bone Joint Surg Br. 88(3): 402–4
- Hart et al. 2012. “Cobalt from metal-on-metal hip replacements may be the clinically relevant active agent responsible for periprosthetic tissue reactions”. Acta Biomater. 8(10): 3865-73
- Soto JG and Tower SS. 2013. “Systemic disease after hip replacement: Aeromedical implications of arthroprosthetic cobaltism.” Aviat Space Environ Med. 84(3): 242-5
- Levine et al. 2013. “Ten-year outcome of serum metal ion levels after primary total hip arthroplasty: a concise follow-up of a previous report.” J Bone Joint Surg Am. 95(6): 512-8