Proximal opening wedge osteotomy
This procedure was originally described by Trethowan in 1925, but was rarely performed or reported until recently, when the introduction of new implants incorporating a wedge block made the procedure more reliable and stable. The strategy is to combine the corrective power of a proximal osteotomy with an opening wedge to maintain or increase metatarsal length.
Approach
Access to the 1st MTP joint and to the osteotomy site can be obtained from two medial longitudinal incisions on the first ray centred on the relevant sites. It is often convenient to combine these into a single incision. A lateral release of the first MTPJ may be done across the 1st MTP joint or through a separate longitudinal incision in the first intermetatarsal space.
Procedure
We normally do the lateral release first through a 1st space incision. Dissection is deepened bluntly with scissors until the adductor hallucis tendon and the lateral capsule of the 1st MTPJ are exposed. The deep peroneal nerve and its branches are protected with retractors. A partial lateral capsulotomy is performed and the sesamoid-metatarsal ligament released. A Macdonald elevator in the 1st MTPJ is useful to identify and tense the sesamoid-metatarsal ligament for incision. The adductor tendon does not always have to be released (Schneider 2007), but if the contractures is very tight it can be released from the proximal phalanx taking care not to damage the flexor hallucis brevis.
A medial longitudinal incision is deepened to the capsule of the 1st MTPJ obtaining any necessary haemostasis. The plantar part of the capsule is partially exposed to facilitate later double-breasting. The capsule is opened longitudinally and the medial eminence exposed. The eminence is excised with a power saw in line with the medial surface of the metatarsal shaft (not according to the groove in the metatarsal head, which will usually result in excessive excision). The joint is inspected and its alignment relative to the metatarsal shaft (DMAA) assessed.
The osteotomy site is 1cm distal to the 1st tarsometatarsal joint, which can usually be palpated transcutaneously. A longitudinal incision is made exposing enough MT shaft to allow plate fixation. We use a transverse osteotomy; angling it proximally (but keeping it at least 5mm distal to the TMTJ) allows placement of proximal plate screws across the osteotomy site (Shurnas 2009). The orientation of the osteotomy does not affect the amount of correction of length or intermetatarsal angle that can be obtained (Budny 2009). The osteotomy is made initially with a power saw taking care not to cut the lateral cortex. It is then opened gradually using the osteotomes on the Arthrex set, or equivalents. The amount of opening required can be calculated pre-operatively from Xrays, using a chart or by using Shurnas (2009) finding that 2-3degrees of IMA will be corrected per 1mm of wedge. Alternatively, it can be assessed intra-operatively with fluoroscopy.
The wedge plate is then inserted and fixed with cortical (Arthrex) or locking (Darco) screws. The Darco BOW plate is more stable in cadaver studies (Hofstaetter 2007) but no comparative studies are available in vivo. If the lateral cortex breaks (about 10% of published cases) a locking plate may be advisable for stability. Wukich (2009), Saragas (2009), Shurnas (2009) and Randhawa (2009) all grafted their osteotomy spaces, usually from the medial eminence, but Shah (2009) did not without apparent ill-effects on healing.
If the articular surface of the 1st MTPJ is in significant valgus relative to the metatarsal shaft axis, a medial closing wedge distal osteotomy can be carried out; we use a biplanar chevron osteotomy. Hallux valgus interphalangeus can be corrected with an Akin osteotomy of the proximal phalanx.
The medial capsule of the 1st MTPJ is now repaired. Many different techniques have been reported; we use a double-breasting technique aiming to take up the slack in the transverse tie-bar of the forefoot. Skin closure is according to normal practice.
Aftercare
Published series have used dressings rather than plaster, with heel walking for up to 6 weeks. Post-operative splintage of the hallux may be used. There are no comparative series of post-operative protocols.
The osteotomy usually takes 6-8 weeks to unite. Most surgeons take check Xrays early and then around the expected date of union to document initial correction and position of union. However, Murphy (2007) found that only one of 412 post-operative Xrays was noted to be abnormal, and no change in management was made.
Holt (2008) found that braking reaction time had returned to normal 6 weeks after a chevron, scarf or basal first metatarsal osteotomy. Although they did not measure braking response between 2 weeks (when most patients were unable to do the test due to pain) and 6 weeks, it is probably advisable to recommend that patient wait till 6 weeks before driving until further evidence is available.
Results
There are no RCTs or other comparative series. There are four published case series: Wukich (2009), Saragas (2009), Shurnas (2009) and Randhawa (2009), and Shah (2009) reported a fifth series at BOFAS. This amounts to 231 feet in 169 patients. Randhawa and Shah mainly used the procedure for more severe deformities. The results are similar to those for other proximal osteotomies, with average correction of IMA of about 9deg and HVA of about 15 deg. The series that reported metatarsal length change found an average lengthening of about 2mm. Four non-unions, 9 recurrences, 7 over-corrections and no cases of transfer metatarsalgia were noted, though Randhawa did not detail complications. Wukich, Saragas and Shah reported AOFAS scores with means of 85, 87, 81/100.
It appears the proximal opening wedge osteotomy has similar results to other proximal osteotomies and does not change metatarsal length by much. Good comparative studies are required to define whether it has a distinct place in the repertoire or is simply a fashion driven by a new and interesting fixation device.
Proximal closing wedge osteotomy
Resch compared the DCO and proximal closing wedge osteotomy (PCWO). Although the PCWO gave better correction of deformity this was at the cost of more complications, especially metatarsalgia. Overall, the clinical results were similar. The simplicity and good healing potential of the DCO may outweigh the theoretical advantages of a proximal osteotomy.
A study with 10-22 year follow-up found that although 85% of patients were clinically satisfied, 25% had dorsal malunion and 23% had metatarsalgia.
The PCWO appears to have a significant risk of malunion and metatarsalgia, probably greater than the crescentic and proximal chevron osteotomies. There seems no good reason to use it in preference to these osteotomies which seem to have lower complication rates and have been examined in a prospective randomised trial. However, a trial of the PCWO versus the crescentic or PCO would be ethical.
Some authors have described modifications to the technique to improve the stability of the osteotomy, but no clinical results have been presented. Validation of these modified techniques would preferably be in a prospective randomised trial against the PCO and/or proximal crescentic procedure.