Bunions: Are Proximal Osteotomies Necessary?

Thursday, December 01, 2011

Addressing The Altered Mechanics Of Hallux Abducto Valgus Deformity

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.

Author(s):

By John McCord, DPM, and Mark Hofbauer, DPM

Yes, if the procedure is done correctly, it is a valuable adjunct to bunion correction, says John McCord, DPM.

Who will ever forget the memorable autistic man played by Dustin Hoffman in the film Rain Man? My favorite scene was when he refused to fly on any airline but Quantas because that carrier had no history of accidents. I reflect on that scene when I talk with colleagues in podiatry who refuse to consider performing proximal osteotomies while correcting bunion deformities. Their logic makes as much sense as the Rain Man in that they will choose a head osteotomy even though it won’t correct the deformity.
Proximal osteotomies were the gold standard in podiatry until metatarsal head osteotomies became popular in the mid-‘70s. Mostly, we performed transverse closing wedge procedures to correct high IM angles. We secured these with stainless steel wire and, in most cases, they worked well. Then the hinge/axis concept was introduced and it helped to prevent elevatus of the first metatarsal. Screw fixation was also introduced and this required an oblique Juvara osteotomy.

Why Distal Osteotomies Aren’t The Answer With Severe IM Angles
Metatarsal head or distal osteotomies were easy to perform and became the favored procedures. You could think two dimension and achieve a relative correction of a high IM angle without much danger of a surgical complication. Proximal osteotomies demand that you think three dimensions and work with templates preoperatively. A poorly executed proximal osteotomy could result in severe elevatus of the first metatarsal and subsequent hallux limitus. A poorly executed head osteotomy just kind of takes care of itself in time.
The problem with distal osteotomies is that they don’t really correct the deformity. They are okay when the IM angle isn’t severe but anything over 16 degrees will fail unless you correct the deformity at its source, the proximal aspect of the first metatarsal. There have been variations of the metatarsal head osteotomies with long legs that stretch back to the proximal shaft. If the deformity approaches 18 degrees, these are unstable because of troughing.
The solution is that we should all be capable of performing proximal first metatarsal head osteotomies or willing to refer cases with high IM angles to colleagues who can do the job right.
I don’t look forward to the patients who come in with high IM angles. These patients tend to be young people who have had juvenile hallux abducto valgus. The best solution is to select a procedure which corrects the hallux valgus plus an appropriate osteotomy to correct the metatarsus primus varus. In these cases, I go by the patient’s apparent needs rather than my limitations or desire for an easy trouble free operation. It is best to correct the deformity and its underlying cause so the patient doesn’t have to face a series of operations.
I went for a long period of time in the ‘80s in which I avoided performing the dreaded closing wedged osteotomy. I had created a few elevated metatarsals and had encountered a few non-compliant patients who liked to bear weight before things had healed. I reasoned that it was better to err on the side of caution and risk a recurrence than to do what was needed at a higher risk. Then I looked back at 10 years of my easy metatarsal head osteotomies and was appalled at the numbers of recurrence and unsatisfactory results. The worst results occurred with patients who had IM angles of around 18 degrees.