Mr Ian McDermott, Consultant Knee Surgeon at London Sports Orthopaedics, believes 3D technology is well and truly already here in the field of orthopaedics, and it looks set to evolve and expand significantly in years to come
My first encounter with 3D technology was several years ago, when I did hips as well as knees (for a number of years now I’ve been purely a dedicated specialist knee surgeon). Everyone with any sense of 3D awareness knows that it’s impossible to judge femoral neck angles and offset from just plain x-rays, where rotation cannot be controlled properly. Therefore, when Symbios came out with 3D CT planning software that was able to measure every hip angle and distance with millimetre precision, this was a big step forward. From CT data it was then apparent that hip angles and distances vary enormously between individuals, and that most of the angles and distances can vary independently of each other. Thus, to replicate hip biomechanics accurately, one has to be able to account for each of these variables accurately and independently. Symbios therefore developed a modular stemmed prosthesis with a large number of different options covering the majority of hip anatomies encountered. For the roughly 5 per cent of people whose hip geometry falls outside of the range that can accurately be replicated with a modular stem, Symbios are able to provide a custom-made prosthesis that matches the patient perfectly.
But does any of this really matter?
Yes. If the femoral offset is altered by as little as 15 per cent (which is just a few millimetres) then this significantly weakens the hip abductors. At best, this can lead to early muscle fatigue with walking; at worst, this can leave the patient with weakness and a Trendelenberg gait.
But does it actually make a difference?
My personal experience of doing Symbios hips was that they were a joy. Every hip had precise pre-op planning and there were never any nasty unexpected intra-operative surprises. No eyeballing. No guessing. Proper pre-op planning led to excellent patient outcomes, and for those patients with badly deformed hips, it transformed what could have been a really difficult operation into a really easy straight forward procedure: something that’s good for the surgeon and the patient alike.
However, I’m no longer a hip surgeon. I’m a specialist knee surgeon. So, I’ll leave it up to others to debate the pros and cons of 3D planning and custom-made prostheses in hip surgery. However, I can happily talk as an expert about knees.
Several years ago I was struggling to find an acceptable solution for that small cohort of patients with isolated lateral unicompartmental osteoarthritis who might benefit from a partial knee replacement, as none of the prostheses on the market were particularly easy to implant or gave predictably good results for the lateral compartment. However, in 2012, Conformis entered the UK market with its custom-made knee prostheses. The process of Conformis knee replacement surgery involves the patient having a CT scan, with a scannogram including the hip and the ankle and with fine-cut imaging of the knee itself. From this, the engineers over in Boston design and manufacture a patient-specific prosthesis that exactly matches the precise size and shape of the patient’s own knee.
By Ian McDermott, MD | Orthopaedic Product News
Image Credit: The New York Times
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