Jeffrey E. Johnson
DEFINITION
Forefoot varus is a component of the multiplanar pes planovalgus deformity that occurs as a result of posterior tibial tendon insufficiency.
In addition to being a component of adult acquired flatfoot deformity, forefoot varus is also present in some cases of congenital pes planus and posttraumatic deformities of the first tarsometatarsal joint.
In 1936, F. J. Cotton described an adjunctive procedure for the operative treatment of flatfoot deformity using an opening wedge plantarflexion medial cuneiform osteotomy to restore what he termed the “triangle of support” of the static foot.3
ANATOMY
Forefoot varus deformity may occur through a dorsiflexion angulation or rotation at the talonavicular, naviculocuneiform, or tarsometatarsal joints.
These joints are supported by the spring ligament and the plantar intertarsal ligaments, including the long plantar ligament.
In addition, the naviculocuneiform and tarsometatarsal joints are supported by their relatively constrained joint architecture, which in the normal state allows only a few degrees of motion in the sagittal plane.
Medial displacement calcaneal osteotomy, lateral column lengthening, and subtalar fusion all provide correction of heel valgus; lateral column lengthening will correct forefoot abduction, but none of these procedures adequately addresses the fixed forefoot varus component of the pes planovalgus deformity.
PATHOGENESIS
The pathogenesis of forefoot varus in association with an adult acquired flatfoot deformity secondary to posterior tibial tendon insufficiency is not well understood.
Forefoot varus is presumed to develop when the posterior tibialis tendon can no longer provide dynamic support to the medial column of the midfoot. In the absence of the posterior tibialis tendon acting as a dynamic stabilizer, the static ligamentous stabilizers (spring ligament complex and the plantar supporting intertarsal ligaments) stretch out due to the repetitive dorsally directed weight-bearing forces on the medial column of the foot.
Several patterns of medial column “sag” have been described, although the understanding of why some patients have dorsal instability at the first tarsometatarsal joint, the naviculocuneiform joint, or the talonavicular joint is not well understood. The differences in the magnitude and location of the dorsal “sag” may be related to bony anatomy, generalized ligamentous laxity, the presence or absence of gastroc–soleus contracture, and the existence of an underlying congenital pes planovalgus deformity.
NATURAL HISTORY
The natural history of forefoot varus associated with an acquired adult flatfoot deformity has not been studied. It is presumed that the severity of the forefoot varus deformity progresses as the underlying pes planovalgus deformity progresses. Longstanding instability and subluxation at the first tarsometatarsal joint or naviculocuneiform joint may result in localized osteoarthritis of these joints.
Some acquired adult flatfeet develop a fixed forefoot varus without osteoarthritis when the deformity has been longstanding and capsular stiffness holds the joint in the deformed position.
PATIENT HISTORY AND PHYSICAL FINDINGS
Forefoot varus is one of the components of a pes planovalgus deformity that is determined primarily by radiographic and physical examination findings.
In the patient history, there may be complaints of localized pain to the dorsal medial column of the midfoot, either the tarsometarsal joint or the naviculocuneiform joint.
Patients may complain of pressure-related discomfort beneath the base of the first metatarsal or cuneiform due to excessive weight bearing at the apex of the plantar medial column sag.
The presence and the magnitude of forefoot varus are determined on physical examination by placing the hindfoot into the “subtalar neutral” position with the patient seated (FIG 1). With the hindfoot held in neutral, with the talonavicular joint congruent, a dorsally directed force is applied to the fourth and fifth metatarsal heads until the ankle is dorsiflexed to the neutral position. If the first metatarsal head rests above the transverse plane of the fifth metatarsal, then forefoot varus is present. Forefoot varus is quantified clinically by the degree to which the first metatarsal rests above the transverse plane of the forefoot as a mild, moderate, or severe deformity.
The deformity is also qualified by whether the forefoot varus deformity is passively correctable by manual pressure to bring the first ray back down to the level of the other metatarsals or whether it is fixed in this position.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Standing, AP, and lateral radiographs with a medial oblique view of the involved foot will determine the presence of subluxation or osteoarthritis at the first tarsometatarsal or naviculocuneiform joint.
The lateral standing radiograph will quantify the amount of dorsiflexion based on the measurement of the lateral talo–first metatarsal angle.
FIG 1 • Placing the hindfoot into the “subtalar neutral” position allows the examiner to determine the presence and the magnitude of a forefoot varus deformity that may accompany pes planovalgus. A,B. The forefoot is in varus alignment relative to the neutral heel as evidenced by the examiner visualizing and palpating the first metatarsal head dorsally translated relative to the fifth metatarsal head. C,D. The forefoot and hindfoot alignment are both in neutral with the first and fifth metatarsal heads in the same plane. This is the position desired after the appropriate-sized bone wedge has been placed into the first cuneiform osteotomy.
The apex of the deformity may be at the talonavicular joint, the naviculocuneiform joint, or the first tarsometarsal joint.
In the case of an acquired flatfoot deformity superimposed on a congenital pes planovalgus deformity, comparison measurements of the opposite-foot standing radiograph may help determine what amount of deformity is a result of posterior tibial tendon insufficiency.
A weight-bearing AP radiograph of the involved ankle will determine the presence of a valgus tilt of the talus within the ankle joint mortise secondary to deltoid insufficiency.
Additional procedures to address medial ankle instability due to deltoid ligament insufficiency may be needed to fully correct the valgus hindfoot deformity.
DIFFERENTIAL DIAGNOSIS
Forefoot varus secondary to instability or osteoarthritis at the first tarsometatarsal joint
Global forefoot varus associated with supination of the first, second, and third metatarsals
NONOPERATIVE MANAGEMENT
If the deformity is passively correctable, a custom-molded total contact foot orthosis is fabricated with posting under the medial aspect of the hindfoot and midfoot to correct heel valgus and additional posting placed under the lateral aspect of the forefoot to promote plantarflexion of the first ray with weight bearing.
If the forefoot varus is fixed, an accommodative total contact foot orthosis would be fabricated with medial posting under the entire hindfoot and midfoot, or a medial wedge could be added to the sole of the shoe.
If pain symptoms are not controlled with foot orthoses alone, a custom-made leather and polypropylene molded gauntlet-style brace or a polypropylene custom-molded short articulated ankle–foot orthosis would be indicated.1,2
Since forefoot varus is only one component of a complex multiplanar pes planovalgus deformity, decision making about conservative versus operative treatment will most likely depend on the characteristics of the hindfoot valgus deformity rather than solely on the forefoot varus component alone.
SURGICAL MANAGEMENT
The plantarflexion opening wedge medial cuneiform osteotomy for correction of fixed forefoot varus associated with a flatfoot deformity is rarely performed in isolation and typically is performed as a component of multiple procedures to correct a given flatfoot deformity.
Typically, the surgeon begins with bony correction of the foot, followed by soft tissue reconstruction and tendon transfers.
The reconstructive procedure begins in the proximal aspect of the foot and ankle and proceeds distally since each level of correction is determined by aligning it to the next-most-proximal segment. Therefore, the forefoot varus is often the last portion of the bony deformity to be corrected during the realignment portion of the procedure.
Occasionally, once the hindfoot deformity correction has been performed, the apparent forefoot varus that was present preoperatively has been improved sufficiently that osteotomy of the first cuneiform is not required.
Preoperative Planning
This opening wedge osteotomy requires interposition of some type of bone graft material. Therefore, the surgeon should be prepared to harvest a bone graft or have allograft or synthetic bone graft material available.
We have used exclusively frozen tricortical iliac crest allograft bone for this interposition osteotomy without complication.
Positioning
The patient is positioned supine with a small pad placed under the ipsilateral buttock to internally rotate the foot to the neutral position.
Approach
The osteotomy opens dorsally; therefore, the approach is over the dorsal aspect of the first cuneiform.
If procedures are performed on the medial side of the midfoot, the incisions should be kept at least 3 cm apart to minimize undermining.
Performing this osteotomy through a medial approach would significantly increase the difficulty, would require significant additional soft tissue dissection, and would require retraction of the anterior tibialis tendon near its insertion.
TECHNIQUES
PLANTARFLEXION OPENING WEDGE MEDIAL CUNEIFORM OSTEOTOMY FOR CORRECTION OF FIXED FOREFOOT VARUS (COTTON OSTEOTOMY)
Under tourniquet control, make a dorsal longitudinal skin incision over the medial cuneiform and the base of the first metatarsal.
Carry dissection through the skin and subcutaneous tissue to develop the interval between the extensor hallucis longus tendon (retracted medially) and the extensor hallucis brevis tendon (retracted laterally).
Free up and retract any crossing cutaneous branches of the superficial peroneal nerve.
Expose the dorsal portion of the medial cuneiform with identification of the first tarsometatarsal joint and the joint between the medial and middle cuneiform. It is not necessary to open the joint capsule of the first tarsometatarsal joint.
With fluoroscopic guidance, identify the midportion of the cuneiform and draw a saw cut line on the bone. Usually this line is at or just proximal to the plane of the second tarsometatarsal joint (TECH FIG 1).
TECH FIG 1 • Location of first cuneiform osteotomy.
With a small microsagittal saw, make a transverse osteotomy in the dorsal-to-plantar direction through the midportion of the medial cuneiform by cutting down to, but not through, the plantar cortex (TECH FIG 2).
Use a thin osteotome to complete the osteotomy, leaving the plantar periosteum intact.
Pull the osteotome distally to lever open the medial cuneiform osteotomy and plantarflex the first ray (TECH FIG 3).
Using a ruler, measure the amount of opening of the cuneiform osteotomy needed to achieve the desired plantarflexion of the first ray.
On average, a 4to 6-mm wedge of bone graft is needed to plantar-displace the first metatarsal to the desired level of the other metatarsal heads (especially the fifth metatarsal) in order to restore Cotton's normal “tripod” configuration.
A wedge of iliac crest bone graft is either harvested from the patient or obtained from the bone bank.
Use a microsagittal saw to shape this bone into a wedge, with the dorsal cortex of the iliac crest wedge cut to the width of the dorsal opening gap that was measured
TECH FIG 2 • The osteotomy is made dorsal to plantar across the midportion of the first cuneiform. A narrow elevator or retractor is placed into the 1, 2 intercuneiform joint to prevent inadvertent osteotomy of the second cuneiform. previously and oriented so that the exposed cancellous bone surfaces of the iliac wedge will be adjacent to the exposed cancellous surfaces of the osteotomized cuneiform.
TECH FIG 3 • An assistant levers the osteotomy open to depress the first metatarsal head while the surgeon determines when the forefoot varus deformity has been adequately corrected.
Use a narrow osteotome to lever open the cuneiform osteotomy while an assistant places plantar-directed pressure on the first metatarsal to help open the osteotomy maximally while the bone graft wedge is impacted from dorsal to plantar into the medial cuneiform osteotomy using a bone tamp (TECH FIG 4).
Place small amounts of morselized cancellous bone graft, either as autograft from adjacent osteotomies of the hindfoot or from the piece of allograft, medially and laterally around the bone wedge to fill whatever gap remains in the cuneiform.
TECH FIG 4 • The interposition bone graft wedge is placed into the dorsal opening in the first cuneiform to depress the first metatarsal and correct the forefoot varus deformity.
TECH FIG 5 • Fixation of the osteotomy with a 0.62-inch Kirschner wire placed from the distal portion of the first cuneiform obliquely into the second cuneiform.
The osteotomy is stable due to the surrounding ligamentous support and the compression across the bone wedge created by tamping the bone wedge into the osteotomy. Use percutaneous fixation across the osteotomy to prevent dorsal displacement of the bone block until early healing has occurred (TECH FIG 5).
Bend to 90 degrees the percutaneous pin protruding from the dorsal medial aspect of the first cuneiform and apply a pin cap.
Irrigate the wound and close it in layers.
POSTOPERATIVE CARE
The pin site is dressed along with the other wounds and a compressive, bulky Robert Jones type of dressing is applied with medial lateral and posterior plaster slab splints covered with an elastic wrap.
If a tendon transfer has been performed as part of the reconstructive procedure, the foot is positioned as needed for proper soft tissue healing.
At 10 to 14 days after surgery, the splint, dressings, and sutures are removed.
A dressing is placed around the pin site, which is then padded with a small felt doughnut, and a short-leg fiberglass cast is applied in neutral or whatever position is needed for proper soft tissue healing if a tendon transfer has been performed.
The cast is removed at 6 weeks after surgery.
Radiographs are obtained to ensure early incorporation of the graft without displacement.
The percutaneous pin is removed and full weight bearing as tolerated is allowed in a removable walker boot (FIG 2). Joint and muscle rehabilitation, as indicated by the other operative procedures performed in addition to cuneiform osteotomy, is begun.
OUTCOMES
Outcomes of this procedure have shown predictable healing. In review of 16 feet (15 patients) by Hirose and Johnson4 there were no malunions or nonunions. All patients at follow-up described mild to no pain with ambulation.
Average improvement in the first metatarsal–medial cuneiform angle as measured on the lateral radiograph was 9 degrees.4
Because of the variety of hindfoot procedures performed in patients undergoing the cuneiform osteotomy, the degree of hindfoot correction contributed by the cuneiform osteotomy alone is difficult to determine.4
This procedure combined with hindfoot reconstruction for flatfoot provides superior correction of the flatfoot deformity (as evidenced by the lateral talo–first metatarsal angle and the medial-cuneiform-to-floor distance) compared to flexor digitorum longus tendon transfer with subtalar joint arthrodesis or medial displacement calcaneal osteotomy.4
COMPLICATIONS
No complications have been described in the few reports on this procedure except for the need for hardware removal due to a prominent screw head.
Structures at risk during the exposure include the extensor hallucis longus or the extensor digitorum brevis tendon and the deep peroneal nerve.
Although predictable healing has been noted, nonunion, overcorrection, and undercorrection could occur.
When a dorsal screw is used for fixation, removal of the hardware is often required due to dorsal shoe pressure or irritation of the overlying nerve or tendon.
FIG 2 • Lateral (A) and AP (B) radiographs at 10 weeks after acquired flatfoot deformity correction with first cuneiform osteotomy. The allograft bone wedge has healed.
REFERENCES
1. Alvarez RG, Marini A, Schmitt C, et al. Stage 1 and II posterior tibial tendon dysfunction treated by a structured nonoperative management protocol: an orthosis and exercise program. Foot Ankle Int 2006:27:2–8.
2. Augustin JF, Sheldon SL, Berberian WS, et al. Nonoperative treatment of adult acquired flatfoot with the Arizona brace. Foot Ankle Clin North Am 2003;8:491–502.
3. Cotton FJ. Foot statics and surgery. N Engl J Med 1936;214:24–27.
4. Hirose CG, Johnson JE. Plantarflexion opening wedge medial cuneiform osteotomy for correction of fixed forefoot varus associated with flatfoot deformity. Foot Ankle Int 2004;25:568–574.
5. Johnson JE, Cohen BE, DiGiovanni BF, et al. Subtalar arthrodesis with flexor digitorum longus transfer and spring ligament repair for treatment of posterior tibial tendon insufficiency. Foot Ankle Int 2000;21:722–729.
6. Johnson JE. Plantarflexion opening wedge cuneiform osteotomy for correction of fixed forefoot varus. Tech Foot Ankle Surg 2004; 3:2–8.
7. Myerson MS, Corrigan J, Thompson FM, et al. Tendon transfer with calcaneal osteotomy for treatment of posterior tibial tendon insufficiency: a radiological investigation. Foot Ankle Int 1995; 16:712–718.