Choosing on the evidence
Evidence-based advice on the choice of procedure for hallux valgus is very difficult to produce. The Cochrane database considered that the quantity and quality of the evidence base was not good enough to draw firm conclusions. There have been few RCTs and most of those have significant methodological flaws. Some of the commonest procedures, such as the Mitchell and scarf procedures, have never been prospectively compared to other candidate operations.
Textbooks and review articles often contain guidelines for procedure selection based on clinical and radiological features. Clinical findings may be quite reproducible (Menz 2003), but the standard radiological measurements are subject to significant error. Nor is there any evidence that selecting a procedure on the basis of radiological findings produces better clinical outcomes than applying the same procedure to everyone. Indeed, the studies of Resch (no difference between distal chevron and proximal closing wedge osteotomy) and Faber (no difference between Hohmann distal osteotomy and Lapidus procedure, even in hypermobile first rays) could be interpreted in favour of distal osteotomies for all.
In the longer run we need many more good-quality RCTs which ask clinically worthwhile questions answered in a way that matters to patients. But how shall we make decisions in the meantime?
A pragmatic choice
Accepting that there is no right answer to procedure selection, East Lancs Foot and Ankle Service takes a fairly pragmatic approach.
Our main surgical aim is to reposition the first metatarsal head over the sesamoids using the simplest method possible. If this can be achieved with a distal osteotomy, with the 5-6mm lateral translation that can usually be achieved, we use a distal chevron osteotomy.
If more lateral translation is required, we normally use a scarf procedure. These two operations make up over 90% of our hallux valgus procdures. We choose them not because they have been shown to be better than others, but because they are good enough and allow immediate weightbearing without casts. This is less inconvenient for patients and readily allows bilateral surgery.
We correct hallux valgus interphalangeus with an Akin osteotomy when the great toe touches the second after a standard procedure. We correct DMAA, with a modified chevron or scarf procedure, where this is the main cause of MTP angulation, and it is confirmed at surgery.
We use the Silver, isolated Akin, Keller and Lapidus procedures occasionally.
Choosing in the exam
For the FRCS (T+O) it is probably best to stick to conventional advice. Obviously, non-surgical management should be advised if applicable.
Where surgery is required, measure the hallux valgus, intermetatarsal, DMAA and hallux valgus interphalangeus angles, accepting in discussion if necessary that these are subject to significant measurement errors.
In general you should be safe to offer a distal osteotomy for an intermetatarsal angle of up to 12 deg and a proximal or scarf osteotomy above this.
If the joint is congruent and the DMAA is over 10deg you could suggest modifying your main osteotomy to correct IMA and DMAA together. Similarly if the interphalangeus angle is over 10deg you could add an Akin procedure.
If the joint is mildly arthritic the normal procedure is probably OK. If there is severe OA it's probably best to suggest a fusion or Keller arthroplasty. In a rheumatoid patient a fusion may be best even if the 1st MTP joint is still good.