I personally feel that the flexibility (or lack thereof) of the first ray and metatarsophalangeal joint (MPJ) is the most important element that one needs to evaluate when selecting a procedure. Unfortunately, this is often an intraoperative finding that arises after performing the modified McBride procedure. Therefore, intraoperative decisions have to happen. I teach my residents that you cannot just go through the technical aspect of an Austin bunionectomy without performing range of motion of the great toe joint and/or evaluating where the proximal phalanx aligns to the metatarsal head.
I generally think of two types of bunion deformities. There is a functional bunion, which tends to be very flexible. You can manually reduce the functional deformity by taping the foot (squeezing the metatarsal heads together) or increase the deformity by sticking your thumb in the interspace, causing splay. A structural bunion deformity is typically a rigid deformity that one cannot easily manipulate. A radiographic clue may be an intermetatarsal joint between the first and second metatarsals, or a patient with metatarsus adductus.
As a general rule, surgeons can correct functional bunions with distal metatarsal osteotomies and structural ones need proximal osteotomies or fusion of the first tarsometatarsal joint (i.e. Lapidus). Certainly, there are exceptions to the rules and surgeons may base decisions on other factors such as first metatarsal length, quality of the cartilage and the amount of intermetatarsal correction that will be necessary to get the first metatarsal head over the sesamoids, thereby obtaining a congruent joint.
Why Bunion Surgeries Fail And How To Avoid The Pitfalls
My personal feeling is that the number one reason that a bunion “comes back” is that one never completely corrected it. This may in part be due to choosing a procedure that was inadequate to correct the deformity. Surgeon error is not the only cause for failure. Patient non-adherence and other tangibles most definitely play a role.
So what does it take to “correct the deformity”? Most will say reduction of the intermetatarsal angle. I do feel that is important but not as critical as having the metatarsal head over the sesamoids and having a congruent first metatarsophalangeal joint.
If you do not have a congruent joint, you will be doomed to having a recurrent deformity over time. The buckling effect on the first metatarsal will eventually cause splay and an increase in the intermetatarsal angle. Even if the surgeon performs a Lapidus bunionectomy and the great toe joint is not congruent, splaying will occur at the intercuneiform joint. Now we are seeing more surgeons employ an intermetatarsal “spot weld” technique in addition to fusing the first tarsometatarsal joint by fusing the base of the first and second metatarsal to eliminate the potential intercuneiform splay.
Remember, the sesamoids and the base of the proximal phalanx of the great toe are fixed in space. The sesamoids are anatomic but the metatarsal is not. When the sesamoids are visible under the first metatarsal head, we know the periarticular soft tissues are all in alignment. For example, the extensor tendon apparatus is going to be located directly over the long flexor tendons. If the metatarsal head is not sitting over the sesamoids, the flexor and extensor tendons are going to be lateral to the the long axis of the great toe joint, leading to buckling of the joint. The opposite effect occurs with over-correction of a bunion in which the tibial sesamoid is medial to the metatarsal head, causing buckling of the toe (in the opposite direction) and leading to hallux varus.