Hallux Valgus Correction: Modified Mcbride and Chevron Osteotomy

Hallux valgus is a radiographic diagnosis in which the
angle between the first metatarsal shaft and the proximal phalanx is
greater than 15 degrees. The condition represents a statistical range
of normality rather than a pathologic entity in and of itself. When a
patient presents complaining of a “bunion.” the clinician must first
determine the source of the symptoms, such as whether the chief
complaint is cosmetic or there is a localized pain due to poor shoe
fit, arthritis, tendonitis, neuroma, or progressive deformity of
adjacent toes. The treatment should be tailored to treat the chief
complaint and the inherent pathomechanics of hallux valgus.
Radiographs, although useful for determining corrective procedures and
their respective known limitations, are no substitute for a good
history and a problem-oriented clinical examination.

The first metatarsophalangeal (MTP) joint is held
statically in place by medial and lateral collateral ligaments, the
volar plate and the sesamoid complex on the plantar aspect, and the
dorsal capsule on the dorsum of the MTP joint ( Fig. 34-1 ).
The dynamic stabilizers are the abductor hallucis medially, the
adductor hallucis laterally (two heads indicate a conjoint tendon), the
extensor hallucis longus (EHL) and brevis dorsally, and the flexor
hallucis longus and brevis on the plantar aspect. The sesamoids sit on
either side of a crista. They are also held in place by the sesamoid
metatarsal retinaculum, with the lateral sesamoid tethered to the
second metatarsal head by the deep transverse metatarsal ligament. As
the HVA angle increases, the abductors become mechanically
disadvantaged and the extensors and flexors progressively fall lateral
to their neutral position and secondarily become adductors. The
abductor itself can be displaced plantarward, causing pronation of the
toe. Because every action has an equal and opposite reaction, the
result is increasing medialization of the metatarsal head and an
increase in the intermetatarsal angle. Ultimately, the static medial
ligaments stretch out, and the proximal phalanx subluxates laterally,
leading to an incongruous joint. Because the sesamoids are tethered by
the intermetatarsal ligament, they remain in place as the head moves
medially, making them appear to have dislocated laterally.

Infrequently, there is a pure exostosis with no increase
in the hallux valgus angle (HVA) or an associated bursa that thickens
the area. The degenerative exostosis of hallux rigidus can be
dorsomedial in location and mimic a hallux valgus but requires a
different treatment.

Hallux valgus grading systems are devised to guide surgical decision making. The
most common cause of failure or recurrence (barring the patient
returning to shoes that just do not fit) is stretching the indications
for surgery. Surgical treatment is most appropriate when it
addresses the symptoms and concerns of the patient. Hence, the surgical
decision-making process is “guided” by the HVA and the intermetatarsal
angle (IMA) rather than being dogmatically determined by them ( Fig. 34-2 and Table 34-1 ).

FIGURE 34-2.
Weight-bearing radiograph with the hallux valgus angle (HVA),
intermetatarsal angle (IMA), and distal metatarsal articular angle
(DMAA) drawn.

Younger patients tend to have ligamentous laxity or a
genetic predisposition, or both—hence the need for bony corrections and
a subgroup of patients who have increased distal metatarsal articular
angle (DMAA). For elderly patients, the surgeon should consider a
simple exostectomy, Keller procedure, or a fusion. For neuromuscular
conditions, the surgeon should first lean toward an MTP arthrodesis,
particularly if the condition is progressive. For patients with
metatarsocuneiform joint pathology (i.e., instability or degenerative
arthritis), an arthrodesis of the first metatarsocuneiform joint (i.e.,
Lapidus procedure) should be considered. For patients with MTP
arthritis (especially inflammatory joint disease), an arthrodesis
should be considered. An Aiken osteotomy of the proximal phalanx is
used for hallux valgus interphalangeus or to augment a procedure that
does not correct the hallux valgus angle or IMA satisfactorily. It may
be used in patients with asymptomatic hallux valgus associated with
hammering of the second toe to make space for the second toe to be
brought down into. Clinicians should beware of
younger patients with a hallux valgus and a congruent joint. They may
have an increased DMAA and require a distal bony procedure that
addresses this angular deformity. In an elderly patient,
remember the adage that “the punishment should fit the crime,” meaning
that the surgeon should perform a simple exostectomy or a Keller
procedure so the foot may fit in a shoe rather than performing a
complex distal soft tissue procedure with a proximal osteotomy. For
patients with neuromuscular problems, arthritis, or failed hallux
valgus surgery, an MTP fusion should be considered.

The patient is placed supine, with or without the use of an Esmarch tourniquet. Sometimes,
the EHL is tight and acts as a deforming force and must be lengthened.
An Esmarch tourniquet may noticeably tighten the EHL tendon. If this
occurs, the tourniquet is taken down so that the EHL is not
Z-lengthened erroneously. The leg can be placed on a wellpadded stand to facilitate access. A hip roll can prevent external rotation of the foot.

An incision that is approximately 6 to 8 cm long is made
from the center of the middle one third of the proximal phalanx to the
center of the head to the center of the first metatarsal shaft ( Fig. 34-3 ).

With a longitudinal incision centered over the medial
eminence, the surgeon should take care to spread down to the capsule,
using blunt dissection with a Stevens or Littler scissors. Often,
the dorsal digital nerve may have been displaced from its dorsomedial
position to a more medial central position on the exostosis and can be
inadvertently injured. A plane should be developed over the capsule that allows a V-Y capsulotomy.

The V-Y capsulotomy is performed with the arms distal and tail proximal ( Fig. 34-4 ). The capsule is elevated off the medial eminence with sharp dissection, and the exostosis is exposed ( Fig. 34-5 ). An exostectomy is performed with a sharp osteotome or a sagittal saw at the level of the sulcus ( Fig. 34-6 ). The cut should be made parallel to the medial margin of the foot and perpendicular to the dorsum of the foot. The center of the head is then determined at approximately

1 cm from the articular margin.
A 60-degree angled cut is marked at the center of the head in such a
manner that the limbs extend proximal to the joint capsule ( Fig. 34-7 ).
Whether the dorsal limb is equal to the plantar limb depends on the
surgeon, especially if fixation with a screw is contemplated. A
0.62-inch Kirschner wire (K-wire) is inserted at the center of the head
to help in orienting the two cuts in the same plane and to help prevent
cutting beyond the center of the head. Divergent
cuts in the mediolateral plane should be avoided, because with these
type of cuts, the head may jam on the proximal shaft that then acts
like a wedge and splits the head. The wire is cut short ( Fig. 34-8 ), and a sagittal saw blade is used to make the osteotomy ( Fig. 34-9 ).
Soft tissue is gently elevated with a Freer elevator and retracted with
a narrow baby Hohmann retractor, taking care not to overstrip the
lateral tissue and devascularize the head. After cuts are made, the
blade can be removed and used as a probe to ensure a full lateral cut
and further clear the soft tissue that may prevent lateralization of
the head. The head is displaced approximately 4 mm laterally and impacted ( Fig. 34-10 ).
In general, the osteotomy is stable in this position, because the
normal tissue tension (e.g., tendons) provides constant impaction at
the osteotomy site.
If the osteotomy appears to be unstable, a 0.45-inch K-wire can be
placed under direct visualization and left out through the skin ( Fig. 34-11 ) ;
the wire can be removed at 3 weeks after surgery . The medial eminence
of the proximal shaft is shaved off and made smooth with a sagittal
saw. The V-Y capsulotomy is advanced and closed first with a 0- Vicryl corner stitch while the toe is held in varus ( Fig. 34-12 ). The
capsulotomy is then closed with 0-Vicryl, taking care to identify the
dorsal digital nerve that is invariably trying to be incorporated into
the capsulorrhaphy. The skin is closed with 4-0 nylon vertical mattress sutures.

FIGURE 34-3.
Incision landmarks from the center of the proximal phalanx to the
center of the head to the center of the first metatarsal shaft. The
incision is 6 to 8 cm long.