The New Zealand Orthopaedic Associations National Joint Registry has recently released their eight year report, outlining the current state of play of joint replacement surgery in New Zealand. With its arrival in the mail, I thought it timely that we update our current thoughts about Total Hip Joint Replacement.
Total hip joint replacement is one of the most common elective operations performed. Nearly 6,500 in New Zealand last year, 685 of these in the Wellington region. The number has increased on a yearly basis, especially since 2004 when the Government allocated extra funds ‘The Joint Initiative’ specifically for increased joint surgery. Some might say at the expense of surgery for other Orthopaedic conditions.
From a patients point of view, total hip replacement offers the potential for pain relief, improved mobility and function. For the vast majority, these expectations are met.
From a surgeons point of view, seeing the change in these patients is very satisfying. There will always be a small number who unfortunately have a complication associated with this sort of major surgery, and on a daily basis we strive to decrease the occurrence of such events.
The whole topic of hip replacement surgery can be very confusing for some patients, often dependent on how much research they have done into the subject. Indeed it is an ever evolving area full of controversies for the orthopaedic surgeon.
At any orthopaedic meeting there is debate as to what is the best surgical approach to access the hip joint to perform the surgery. Most replacements are done via a posterior approach, involving detachment of the short external rotator muscles of the hip or via a lateral approach with detachment of part of the abductor muscles. There are pros and cons for either approach with the posterior surgeons adamant that patients limp more after surgery done through a lateral approach and in response the lateral approach surgeons will bemoan the higher dislocation rate in patients operated via the posterior approach. In the joint registry, dislocation is the commonest reason for early revision surgery. Within the world literature there is evidence that with repair of the posterior structures (not routinely done in the past) the dislocation rate for the two approaches are similar. Newer minimally invasive approaches and computer assisted surgeries have not taken off in New Zealand and as yet have no long term results comparable to our standard approaches.
Although we would like to think that a hip joint replacement will last forever they don’t. A number will wear out or fail with time. We commonly tell patients they have a 90-95% chance that their replacement will still be functioning fine at 10 years. The National Joint Registries figures show Revision-free survival for all hips of 95.3% at eight years. This number is comaparable with overseas results.
The longevity of a hip replacment in a large part is dependent on the bearing surface (the ball and cup articulation) remaining functional and the prosthesis remaining solidly fixed within the bone. These two are intimately linked as the debris or wear particles that are formed from the constant movement at the articulating surfaces contribute to osteolysis (bone loss around the hip replacement) and implant loosening.
When performing a hip replacement the components can be cemented into the femur and acetabulum or press fit into the pre-prepared bone. A hip replacement can have both components cemented in place, both press-fit (uncemented) or one component cemented and one uncemented (a hybrid hip replacement).
The ‘Gold Standard’ for bearing surfaces is a metal ball on the femoral component articulating with a poyethylene (plastic) cup. Probably the biggest changes of recent have been in the development of alternatives to this. Alternatives are a ceramic ball in a plastic cup, a metal ball in a metal cup or a ceramic ball in a ceramic cup. All designed and marketed as the way to decrease the volume of wear at the joint surface in the hope that this will prolong the life of the hip replacement.
A more recent development has been the resurgence of hip resurfacing, essentially a variation of a hip replacement. It is the fastest growing joint replacement surgery worldwide. Advocates propose it as an alternative that will result in superior function and quicker recovery after surgery. At present we view it as an alternative in younger patients in the hope that they may last longer than a conventional replacement in this high demand group and if revision surgery is needed it may be easier because less femoral bone is removed during the first surgery.
At present, revision hip replacement surgery accounts for about 13% of all hip surgeries performed. Because of the number of joint replacements being performed the demand for revision surgery in the future will increase significantly and for some surgeons become a major part of their surgical practice. Revision surgery comes with its own quota of controversies and challenges.
When to perform a hip replacement, what approach to use, which implants to use, which bearing surface to use are all decisions that we as orthopaedic surgeons spend some time thinking about and tailoring for the individual patient. As patients become better informed, these are also decisions that in the future we may be asked to justify on a more regular basis.