The Lapidus procedure is a corrective fusion of the 1st TMT joint with a distal soft-tissue correction. It is designed to stabilise a hypermobile first ray, although this rationale has been challenged by several pieces of evidence in the last 5 years. It can also be useful when a severe deformity is associated with 1st TMT OA or an adult acquired flatfoot deformity.
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.
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 1st TMTJ is exposed either through a continuation of the medial approach or through a separate medial or dorsomedial approach, protecting the dorsomedial cutaneous nerve. The joint is opened. Laminar spreaders are useful in gaining access. Joint surfaces are removed with curette, burr, osteotome or gouge, taking care not to remove subchondral bone unless this is necessary for deformity correction. If approaching dorsomedially it is easy to fail to clear the lower third of the joint. Multiple drill holes are then made in the subcortical bone. Sangeorzan (1989) also made a small dorsal trough across the joint for local bone graft. Deformity in both transverse and sagittal planes can normally be corrected by sliding and rotating the joint surfaces; removing wedges is only necessary in very severe deformities.
Most series have reported stabilisation with two or three lag screws. Klos (2010) compared two screws with a medial locking plate and screw in a cadaver model and found less movement and fewer cycles to failure with the locking plate, especially in more porotic specimens. Scranton (2009) also found that a (different) locking plate including a lag screw had a higher bending moment and higher ultimate load to failure that two crossed screws. However, Kazzaz (2009) found no malunions or non-unions in 27 Lapidus procedures fixed with standard crossed screws and allowed to weight-bear immediately, so the additional stability of the locking plate may not be necessary.
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.
Once the correction is completed, or earlier if more convenient, the degree of residual hallux valgus in the phalanx can be assessed and, if necessary, and Akin osteotomy can be added. Some surgeons use an Akin osteotomy on almost every patient while others are selective; there is no evidence that routine Akin is necessary to obtain good results after scarf (Malviya 2007) or chevron (Lechler 2012) osteotomy . Skin closure is as standard for the surgeon.
Most series restrict weightbearing for 6-8 weeks and several use a below-knee or slipper cast. However. Kazzaz reported 27 Lapidus procedures allowed to bear weight immediately in a heel wedge shoe and bandage, without any non-union or displacement.
It would seem reasonable to Xray at about 8 weeks and thereafter until fusion is confirmed.
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 at least 6 weeks before driving until further evidence is available; many surgeons will wish to wait till radiographic union is demonstrated.
Morton and then Lapidus proposed that hallux valgus was caused by a short, unstable first ray and the TMT fusion was designed to stabilise such a ray to prevent recurrent hallux valgus. There is certainly an association between hallux valgus and increased first ray dorsiflexion using a number of measurement techniques (Wanivenhaus 1989, Klaue 1994, Faber 1999). However, association does not prove causality, and studies from a number of perspectives (Rush 2000, Coughlin 2004 + 2007, Kim 2008), and summarised by Smith (2008), suggest that in fact hallux valgus causes first ray hypermobility rather than the other way round. Coughlin (2007) and Kim (2008) demonstrated that hypermobility was reduced by simply correcting the hallux valgus with a basal osteotomy and soft tissue reconstruction. Coughlin found that 23/122 feet had >9mm mobility pre-op compared with 2/122 post-op, and mean mobility diminished from 7.2mm to 4.5mm. In Kim's study mean mobility was reduced from 6.8 to 3.2mm, and the improvement was greater in the hypermobile group. Most importantly, Faber et al (2004) reported a study in which 87 patients, about half of whom had instability according to a recognised method, were randomised to a Lapidus procedure or a distal metatarsal osteotomy. There were no differences in clinical outcome even in the unstable groups.
Of clinical series of the Lapidus procedure, Sangeorzan and Hansen (1989) reported clinical success in 75% of 40 Lapidus procedures, with a non-union rate of 10%. Myerson (1992) also reported 10% non-unions in a series of 67 procedures, with 77% unqualified satisfaction. Coetzee (2004) reported 105 Lapidus procedures followed for an average of 3.7y. Hypermobility was not a specific inclusion criterion. The mean AOFAS hallux score improved from 52 to 87/100 and the VAS pain score from 5.3 to 1.3/10. Mean HVA improved from 37 to 16deg and IMA from 18 to 8deg. The non-union rate was 6.7% and there were five recurrent deformities and four patients with metatarsalgia. The same group (Coetzee 2003) reported 26 Lapidus procedres for previous failed hallux valgus surgery. Clinical and radiological results were almost identical to primary procedures, but the non-union rate was 11.5%. Kopp (2005) reported 35 Lapidus procedures in patients defined as having first ray instability. The mean AOFAS hallux score improved from 45 to 87/100 and mean VAS pain score from 7.5 to 2.3/10. Mean HVA improved from 34 to 11 deg, with 3 hallux varus, and mean IMA from 16 to 6 deg. Kopp had no non-unions or transfer lesions. 34% of patients noted forefoot stiffness, although this was not troublesome. Thompson (2005) reported union rates but not clinical results in 180 Lapidus procedures (plus 21 having 1st TMT fusions as part of a flatfoot correction). In 155 primary Lapidus procedures the non-union rate was 1.5%, while in 25 procedures for failed hallux valgus surgery the rate was 20%.
The Lapidus procedure is capable of correcting significant deformities, including failed previous reconstructions. In primary procedures the non-union rate is probably about 5%, but in revision procedures 10-20%. Dorsal malunion can produce transfer lesions.
However, the procedure is based on a theoretical model of hallux valgus that does not accord well with current evidence – it is designed to address a biomechanical problem that probably does not exist. Moreover, there is no evidence that it gives better correction of the symptoms of hallux valgus than other procedures which are simple and lack some of its complications. Therefore the procedure should probably be reserved for:
- very severe deformities
- hallux valgus with symptomatic TMT joint OA
- as part of a flatfoot correction with forefoot supination and hallux valgus
- as a revision or salvage procedure