DEFINITION

Shortening of the first metatarsal may occur after first metatarsal osteotomies for hallux valgus correction.1,2,3

If the first metatarsal is considerably shortened, the patient may develop painful transfer metatarsalgia of the lesser toes.7

 

 

ANATOMY

 

The physiologically normal first metatarsal is generally of similar length to or slightly shorter than the neighboring second metatarsal.

 

This length relationship between the first metatarsal and the lesser metatarsals allows for a smooth, progressive weight transfer and optimizes the windlass mechanism during gait.

 

The relative plantar position of the first metatarsal head (and sesamoids) also makes the windlass mechanism more effective in transferring weight to the lesser toes and may compensate for a physiologically shorter first metatarsal.

 

PATHOGENESIS

 

Some metatarsal shortening occurs with the majority of all first metatarsal osteotomies performed during hallux valgus correction.6

 

An iatrogenically shortened first metatarsal can disrupt the normal forefoot weight transfer mechanism and cause a pathologic overload of the adjacent metatarsals.

 

Relative dorsiflexion of the metatarsal head can also occur after hallux valgus correction with metatarsal osteotomy, exacerbating the mechanical disadvantage of the shortened metatarsal and further contributing to transfer metatarsalgia.

 

NATURAL HISTORY

 

Transfer metatarsalgia generally does not resolve spontaneously, particularly if coupled with a concomitant forefoot fat pad atrophy.

 

Mild transfer metatarsalgia is generally well tolerated, as the patient is able to modify gait, stance, and activity to compensate.

 

However, the problem may progress, with painful callus formation developing under the lesser metatarsal heads. Severe, recalcitrant transfer metatarsalgia may cause debilitating forefoot pain that often persists until normal forefoot biomechanics are restored or reasonable footwear accommodation is used.

PATIENT HISTORY AND PHYSICAL FINDINGS

 

The great toe usually, but not always, appears shorter than the adjacent metatarsal, especially when compared to the contralateral foot (FIG 1).

 

The plantar surface of the forefoot usually, but not always, has calluses under the lesser metatarsal heads.

 

 

 

 

FIG 1 • Foot with relatively short first metatarsal after distal first metatarsal osteotomy.

 

 

The lesser metatarsal heads are tender.

 

When examined simultaneously, the first metatarsal head (and sesamoids) may appear elevated and more proximal relative to the second metatarsal head, particularly when compared to the contralateral foot.

 

The medial forefoot incisions from prior forefoot surgery must be noted in anticipation of potential revision surgery.

 

Hallux metatarsophalangeal (MTP) joint alignment must be examined. A recurrence of hallux valgus deformity after prior surgery will need to be corrected in conjunction with metatarsal lengthening.

 

Hallux MTP joint motion must be determined. Stiffness and crepitance may suggest arthrosis that may favor

first MTP joint arthrodesis over first metatarsal lengthening (FIG 2).

 

 

 

 

FIG 2 • Assessing range of motion of hallux MTP joint before metatarsal lengthening.

 

 

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IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Weight-bearing plain radiographs are mandatory; we recommend bilateral radiographs to include the contralateral foot for comparison.

 

Anteroposterior (AP) radiographs of the symptomatic foot indicate the amount of first metatarsal shortening, the presence of residual deformity (particularly the first metatarsal head-sesamoid relationship), the nature of the prior hallux valgus surgery, and the integrity of the first MTP joint (FIG 3A).

 

Lateral radiographs suggest the degree of concomitant elevation of the first metatarsal (FIG 3B).

 

Contralateral foot radiographs provide some indication of the required lengthening, which is useful in surgical planning.

 

DIFFERENTIAL DIAGNOSIS

Recurrence of hallux valgus

First metatarsal head avascular necrosis Dorsiflexed malunion of first metatarsal

 

 

 

 

FIG 3 • Preoperative radiographs of foot before hardware removal, application of external fixator, and metatarsal corticotomy. A. AP view. B. Lateral view.

 

NONOPERATIVE MANAGEMENT

 

Oral anti-inflammatory medication

 

 

Shoe wear modification (ie, greater stiffness in combination with a rocker sole to unload the forefoot) Orthotics with medial posting for the first metatarsal and metatarsal support for the lesser metatarsals

SURGICAL MANAGEMENT

 

Surgical management is indicated when nonoperative treatments have failed and other causes are not responsible for the forefoot pain and transfer metatarsalgia.

 

Two broad categories may be considered in the surgical management of transfer metatarsalgia secondary to a

short first metatarsal: shortening of the lesser metatarsals and lengthening of the first metatarsal.4,5,8,9

 

 

With severe first metatarsal shortening, a combination of these two approaches may need to be considered.

 

First metatarsal lengthening affords the advantage of correcting the problem at its source in lieu of performing surgery on lesser metatarsals that are physiologically normal but subject to an overload phenomenon.

 

Preoperative Planning

 

Weight-bearing plain radiographs are essential to plan the desired lengthening and potential realignment of the metatarsal and MTP joint, determine the need for hardware removal from previous surgery, and identify potential arthritis in the MTP joint.

 

 

The contralateral first metatarsal, if not previously operated, serves as an ideal template to determine how a more physiologic first metatarsal anatomy may be restored.

 

To account for magnification, relative lengths of the first and second metatarsals may be used as a reference.

 

Once the patient is deemed appropriate for metatarsal lengthening, the appropriate position for the external fixator half-pins and corticotomy should be planned radiographically.

 

Positioning

 

The patient should be placed in the supine position on the operating table.

 

A bump should not be placed under the ipsilateral hip to allow external rotation of the leg and better access to the medial side of the foot.

 

Approach

 

A four-pin single-plane external fixator will be placed along the medial border of the first metatarsal, and a short, longitudinal dorsal approach to the metatarsal is needed to perform the metatarsal osteotomy (FIG 4).

 

 

The incision may need to incorporate or be within previous surgical scars to minimize the risk of soft tissue complications.

 

The four drill holes for the external fixator pins are created percutaneously, under fluoroscopic guidance, using a 1.5-mm Kirschner wire or the small-diameter drill corresponding to the particular external fixator set.

 

 

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FIG 4 • External fixator is held against metatarsal to determine appropriate adjustment of fixator.

 

 

After percutaneous placement of the four external fixator pins, a longitudinal dorsal approach to the metatarsal is used to perform the metatarsal corticotomy.

 

 

Occasionally, a distal soft tissue procedure is necessary, and surgical incisions must be planned carefully. In our experience, this procedure is most effective for a shortened first metatarsal and satisfactory alignment of the first MTP joint.

 

TECHNIQUES

• Placement of the External Fixator Pins

Using a surgical marker, plan the incision for the corticotomy by drawing a 2-cm line along the middle third of the dorsal border of the first metatarsal (see FIG 4).

Using the closed external fixator as a drill guide, create four drill holes (two proximal and two distal) percutaneously along the medial side of the metatarsal using a 1.5-mm Kirschner wire. The external fixator must not be fully distracted when using it as a drill guide; however, it should be slightly distracted in order to apply initial compression after performing the corticotomy.

With respect to sequence of drill holes, we recommend creating the most distal drill hole first and the most proximal one second, after which these half-pins are secured and the external fixator is attached. This sequence ensures that a monorail external fixator is parallel to the first metatarsal.

Alternatively, a hinged external fixator may be employed that can be adjusted to accommodate the pins while still creating longitudinal distraction (TECH FIGS 1, 2, 3 and 4).

Place all four pins into the drill holes in a similar percutaneous fashion, and check their position using fluoroscopy (TECH FIG 5).

Some external fixator half-pins are tapered (eg, 2.5-mm tapered threads with 3.0-mm shafts) and thus should not be advanced beyond the lateral cortex of the first metatarsal and then reversed, as they will

then lose their stability.

 

 

 

TECH FIG 1 • Determining proper location for external fixator, using a needle as a reference. A. Clinical view. B. Fluoroscopic view.

 

 

 

TECH FIG 2 • First pin placed in distal first metatarsal. A. Clinical view. B. AP fluoroscopic view. C. Lateral fluoroscopic view.

 

 

31

 

 

 

 

TECH FIG 3 • Determining optimal proximal pin position. A. Clinical view. B. Fluoroscopic view.

 

 

 

TECH FIG 4 • Placing second pin in proximal first metatarsal. A. Clinical view. B. AP fluoroscopic view. C.

Lateral fluoroscopic view.

 

 

 

TECH FIG 5 • Final two pins placed. A. Second most proximal pin being placed. B. External fixator tightened. C. Fluoroscopic view of all four pins secured. (Note that the external fixator was removed; no further adjustments are made so that the external fixator may be repositioned on the pins so that the metatarsal maintains its anatomic alignment.)

 

 

 

• Creating the Corticotomy

  32

   

  Make a 2-cm incision along the dorsal border of the metatarsal between the central two fixator pins (TECH FIG 6A).

   

  Dissect sharply to bone, and incise the periosteum transversely at the site of the planned corticotomy. Avoid unnecessary periosteal stripping; the periosteum only needs to be elevated directly at the corticotomy site.

   

   

   

  TECH FIG 6 • A. Minimally invasive incision for metatarsal corticotomy with minimal periosteal stripping.

  B. Corticotomy being performed (irrigation is being performed to diminish the risk of bone necrosis from the saw). C. Before making the corticotomy, the ideal location is confirmed fluoroscopically (the external fixator has been removed to allow for better access during corticotomy).

   

   

  Make a transverse osteotomy using a mini-sagittal saw while simultaneously cooling the blade with iced saline irrigation (TECH FIG 6B).

• Applying the External Fixator

   

  After creating the corticotomy, confirm adequacy and distractibility of the distal and proximal first metatarsal segments with careful distraction through the external fixator and fluoroscopic confirmation (TECH FIG 7A,B).

   

  Add dummy pins to increase stability of the fixator (TECH FIG 7C,D).

   

   

   

  TECH FIG 7 • A,B. The external fixator is replaced with the metatarsal in its preoperative position, and the corticotomy is distracted to confirm that it is complete. Additional “dummy” pins are added to the external fixator to afford greater fixator stability. (continued)

   

   

  Compress the corticotomy using the external fixator; little compression is required—essentially the width of the saw blade (TECH FIG 7E,F).

   

  Using fluoroscopic imaging, verify adequate bone-on-bone contact of the two first metatarsal segments and secure the fixator set screws.

   

  Occasionally, there is slight subluxation of the two first metatarsal segments, and this should be adjusted so that the bony apposition is anatomic.

   

  33

   

   

   

  TECH FIG 7 • (continued) C. Adding the pin. D. Trimming the pin. E,F. The corticotomy is compressed to its anatomic, preoperative position, and the external fixator is tightened.

• Wound Closure

   

  We approximate the periosteum with 4-0 absorbable polyglactin suture and close the skin with 4-0 nylon suture.

   

  Apply a soft dressing. The patient can be discharged to home, non-weight bearing the same day of the procedure.

   

  PEARLS AND PITFALLS
  	Placement of ▪ Use the external fixator as a drill guide. the external ▪ Be sure to place the distal two pins in the plantar half of the distal fragment.

   

  fixator pins This helps impart relative plantarflexion of the distal fragment and metatarsal head, thus limiting the potential for first metatarsal elevation.

   

  Creating the corticotomy

  • Cool the saw blade to limit thermal necrosis of the bone edges.

     

    Applying the external fixator

  • The wound may be reapproximated before placing the fixator, but be sure to verify good bony contact clinically and using fluoroscopic imaging.

     

    Sequence of external fixator pins

  • Placing the distal- and proximalmost pins first ensures that the external fixator is parallel to the first metatarsal and that no pin will violate the MTP or tarsometatarsal joints.

     

    Stiffness of the first MTP joint

  • In our experience, with gradual distraction, preoperative motion of the first MTP joint is not compromised.

     

    Formation of bone (“regenerate”)

• Bone or callus does not form immediately with distraction at the corticotomy site; it may lag several weeks behind.

   

  Failure of the regenerate to form

• Occasionally, the regenerate will not form despite appropriate distraction technique. Once the full desired distraction has been achieved, alternating quarter-turn distraction and compression may stimulate formation of the regenerate. Use of an external bone stimulator may be considered. As a last resort, the intercalary segment may be bone grafted, and internal fixation may be substituted for the external fixator, albeit only with a history of clean and healthy pin sites (the risk of infection with internal fixation is increased after previous external fixation in close proximity).

   

  Duration of the external fixator

  • Generally, the regenerate becomes adequately stable for external fixator removal by 8-10 weeks, but occasionally, 12-14 weeks is required. We routinely remove the external fixator in the office setting.

 

 

34

 

 

 

FIG 5 • A. Distraction at 3 weeks (regenerate is not yet evident). B. Distraction at 10 weeks, regenerate is present but not mature. C,D. Radiographic appearance at final 12-month follow-up. First metatarsal consolidation is complete, and adequate lengthening has been obtained.

 

POSTOPERATIVE CARE

 

The patient is kept non-weight bearing. The first metatarsal needs to be protected until the regenerate has formed at the lengthening site. Weight bearing may compromise the stability of the corticotomy and the external fixator; moreover, weight bearing is not axial at the corticotomy site.

 

We routinely see the patient in the clinic about 7 days postoperatively for wound inspection, patient education on distraction, and initiation of first metatarsal lengthening.

 

We typically set the distraction rate for 1 mm per day (a quarter-turn of the external fixator every 6 hours).

 

The patient should be given instructions in pin care and the number of days to distract the device to yield the desired length.

 

We encourage daily first MTP joint range of motion to prevent joint contracture.

 

The patient should return to the clinic regularly for radiographs to verify adequate distraction, appropriate position of the distal segment, and passive range of motion of the first MTP joint (FIG 5A).

 

The lengthening phase is complete once the first metatarsal has reached the desired length, typically the physiologic length based on the first-second metatarsal length ratio from the physiologically normal contralateral foot.

 

Partial weight bearing is allowed when there is radiographic evidence of consolidation within the distracted segment so long as it does not impinge on the external fixator. Boot or brace modifications typically allow for weight bearing even with the external fixator in place (FIG 5B).

 

The fixator is removed once there is satisfactory radiographic consolidation of the regenerate. The patient can resume full weight bearing once the fixator is removed, but we recommend several weeks of protected weight bearing in a surgical shoe or boot to avoid fracture through the half-pin holes, which are potential stress risers

(FIG 5C,D).

 

FIG 3 shows the radiographic clinical progression throughout the lengthening treatment.

OUTCOMES

See the 2007 study by Hurst and Nunley.2

 

 

COMPLICATIONS

Pin tract infection (inadequate pin care)

First MTP joint stiffness (failure to perform intermittent first MTP joint range of motion) Early consolidation of distracted segment (distraction schedule too slow)

Loss of hallux valgus correction (rare, with routine distraction schedule)

Dorsiflexion of the metatarsal head (poor pin placement or premature removal of external fixator) Nonunion (poor fixation or stability of external fixator or premature removal of external fixator)

 

 

REFERENCES

1. Holden D, Siff S, Butler J, et al. Shortening of the first metatarsal as a complication of metatarsal osteotomies. J Bone Joint Surg Am 1984;66(4): 582-588.

    

    

2. Hurst JM, Nunley JA II. Distraction osteogenesis for the shortened metatarsal after hallux valgus surgery. Foot Ankle Int 2007;28:194-198.

    

    

3. Jones RO, Harkless LB, Baer MS, et al. Retrospective statistical analysis of factors influencing the formation of long-term complications following hallux abducto valgus surgery. J Foot Surg 1991;30:344-349.

    

    

4. Mather R, Hurst J, Easley M, et al. First metatarsal lengthening. Tech Foot Ankle Surg 2008;7:25-30.

    

    

5. Nunley JA. The short first metatarsal after hallux valgus surgery. In: Nunley JA, Pfeffer GB, Sanders RW, et al, eds. Advanced Reconstruction: Foot and Ankle. Rosemont, IL: American Academy of Orthopaedic Surgeons, 2004:31-33.

    

    

6. Nyska M, Trnka H, Parks BG, et al. Proximal metatarsal osteotomies: a comparative geometric analysis conducted on sawbone models. Foot Ankle Int 2002;23:938-945.

    

    

7. Sammarco GJ, Idusuyi OB. Complications after surgery of the hallux. Clin Orthop Relat Res 2001; (391):59-71.

    

    

8. Saxby T, Nunley JA. Metatarsal lengthening by distraction osteogenesis: a report of two cases. Foot Ankle 1992;13:536-539.

    

    

9. Urbaniak JR, Richardson WJ. Diaphyseal lengthening for shortness of the toe. Foot Ankle 198