Hypermobility concerning the first ray has been a hot topic of discussion over the last three to five years. Hypermobility is obviously a clinical finding and, other than studies by Meyerson, has never been measured quantitatively. Given the mechanics of hallux abducto valgus development (with subtalar joint pronation, inability of (peroneus longus) to stabilize the first ray, elevation of the first metatarsal and an opening of the intermetatarsal space), it is easy to conceptualize the proper type of procedure needed to stabilize this deformity.
Those patients who also present with an inter-cuneiform separation have maximized their metatarsus primus elevatus and the first intermetatarsal, and now the excessive motion has begun to separate at the inter-cuneiform joint. Failure to address this inter-cuneiform joint separation by choosing the incorrect procedure will result in recurrence of the deformity in many patients.
Let’s also look at where the apex of the deformity lies in these patients with hallux abducto valgus deformity. Anatomical studies for years have said 90 percent of the motion within the first ray generally takes place at the navicular cuneiform joint while only 10 percent of the motion is in the area of the metatarsal cuneiform joint. Likewise, it has been reported that very little motion at all takes place in either of the three plains at the metatarsal cuneiform joint.
People fail to realize the foot that presents with the hallux abducto valgus deformity also presents with altered mechanics in that the axis of motion has changed and motion does now develop at the first metatarsal cuneiform joint. In the hallux abducto valgus foot type, motion at the navicular cuneiform joint and metatarsal cuneiform joint now approaches 50 percent. Understanding this helps you to address the apex of the deformity and the hypermobility by fusing the first metatarsal cuneiform joint and limiting motion. As an orthopedist repairs tibial varus with a proximal tibial osteotomy, so should we begin to stabilize deformities at their apexes.
Hallux abducto valgus procedure selection in patients with a metatarsus adductus component has also been a hotly debated controversy over the years.
Proximal osteotomies have been advocated along with closing the intermetatarsal space in these patients based on a calculated intermetatarsal angle associated with metatarsal abductitis deformities. Unfortunately, the proximal osteotomy has not provided long-term optimal results because of the mechanics of this deformity. Arguing whether head osteotomy or base wedge osteotomy is needed depending on this calculated intermetatarsal angle really makes no clinical sense.
With metatarsus adductus deformity, surgically you can only move the first metatarsal over laterally until it abuts the second metatarsal. It is important to stabilize the first ray. By performing arthrodesis of the first metatarsal cuneiform joint in these patients as opposed to a closing base wedge osteotomy, you can maintain stability of the forefoot and practically eliminate the risk of recurrence.