Distal Minimally Invasive Metatarsal Osteotomy

Olivier Laffenêtre

♦ INTRODUCTION

Lesser ray osteotomies are an effective treatment for metatarsalgia when conservative management fails. They potentially allow three-dimensional displacement of the distal capital fragment, thus modifying the weight bearing on the metatarsal head. Stephen Isham, DPM, designed this distal, extra-articular, and unfixed osteotomy in the 1980s. It was subsequently introduced to European surgeons by Mariano De Prado in Spain in 1994 who established, along with anatomist Pau Golanó, the surgical and anatomical bases essential for a safe and reproducible practice.² This technique was further developed in France from 2002, under the aegis of the Research Group and Study in Minimally Invasive Surgery of the Foot (GRECMIP),³ now MIFAS by Grecmip.

A thorough understanding of forefoot anatomy and proper osteotomy technique depending on the deformity is mandatory as each osteotomy may have a functional impact on the adjacent metatarsals. When performing one or more lateral metatarsal osteotomies, the surgeon must aim to obtain sufficient stability to maintain the desired correction and to respect the anterior arch of the metatarsal heads in the coronal and sagittal planes. In general, the more proximal a procedure is, the less stable it is. In addition, osteotomies oriented from dorsal-distal to plantar-proximal are more stable than those that are vertical or perpendicular to the metatarsal axis or those oriented from plantar-proximal to dorsal-distal. Many surgeons have adopted percutaneous techniques to treat lesser metatarsal pathology even with a relative lack of literature on the subject. With lesser ray osteotomies, the main challenge remains the ability to sufficiently balance the correction of the plantar hyperpressure while at the same time preserving a harmonious metatarsal arch in the anteroposterior and frontal planes, by avoiding a transfer metatarsalgia.¹

Principles

This technique is performed through a working 1- to 3-mm incision, guided by intraoperative fluoroscopy. The absence of osteosynthesis is the main asset of this procedure, providing the ability to allow “self-adjustment” of the metatarsal heads according to ground reaction forces. However, this does require some control, and the osteotomies are maintained first by a postoperative dressing, which is removed generally after 2 weeks and replaced by cohesive strips for a few more weeks. During this time, walking and thus loading of the metatarsal heads is encouraged as this facilitates normalization of the pressure under the metatarsal heads. The developments of this technique discussed later also demonstrate the importance of the direction of the cut line to orient the displacement.

♦ INDICATIONS AND CONTRAINDICATIONS

Indications

De Prado and separately members of GRECMIP have described this procedure to treat metatarsalgia.⁴,⁵ A nonpropulsive or static metatarsalgia, which appears during the second rocker of gait, when the entire foot contacts the ground under the gastrocnemius eccentric contraction control, is the best indication for 2/3/4 distal metatarsal metaphyseal osteotomies (DMMOs). However, when the second metatarsal (M2) and the third metatarsal (M3) are long relative to first metatarsal, it is possible to perform only two DMMOs even if other associated lesser ray deformities and/or a bunion are present (Figure 8.1).

Furthermore, another excellent indication is a propulsive metatarsalgia, which appears during the third rocker, the last part of the stance phase, when only the forefoot contacts the ground just before the swing phase. In this case, the metatarsalgia is considered secondary to excessive of lesser metatarsal length.

DMMO and variations of percutaneous metatarsal osteotomies are useful for recurrence of metatarsalgia after classical open surgery (Figure 8.2).

Figure 8.1 A 45-year-old female suffering from a bunion associated to static metatarsalgia and crossover toes. A-D. Preoperative aspect and AP, lateral, and sesamoid Guntz incidence radiographs. E. AP view after 6 weeks (percutaneous chevron, distal metatarsal metaphyseal osteotomy M2-M3, percutaneous lesser toes M2-M3 procedures). F-I. Postoperative aspect and radiographs at 6 months.

Figure 8.1 (Continued)

Contraindications

Because of the anatomical connection of the metatarsal heads by the intermetatarsal transverse ligaments, they tend to move together. Thus, an isolated osteotomy will not move back very much but may on the contrary significantly elevate the head and cause a load transfer. The main rule is never to perform an isolated DMMO and to be very careful by performing only two. Transfer metatarsalgia is a great risk after a single metatarsal shortening, and transfer pain to the fourth metatarsal may be experienced after M2 and M3 DMMOs performed in isolation. The DMMO allows a maximum shortening of only 5 mm; therefore, if the toe is subluxated or dislocated completely, sufficient shortening and/or joint reduction may not be possible.

Figure 8.2 Weil revision using distal metatarsal metaphyseal osteotomy M2-M4; (A) pre- and postoperative (3 years) and (B) AP views.

♦ PREOPERATIVE PLANNING AND PREPARATION

Planning for DMMO requires careful understanding of the concepts and power of each osteotomy. Generally, it is necessary to perform osteotomies on the M2, M3, and fourth metatarsal (M4), even if the M4 is less overloaded and thus usually asymptomatic. The addition of the M4 osteotomy does appear to permit a more harmonious alignment of the metatarsal heads in relation to one another.

The patient is in supine position, with the surgeon facing the end of the table (Figure 8.3).

The use of a tourniquet is not recommended for an exclusive percutaneous procedure as natural blood flow helps to cool the bone during the osteotomy.

Figure 8.3 Setup.

SURGICAL TECHNIQUE

Note: Described for DMMO surgery on the left foot by a righthanded surgeon.

This is an extra-articular osteotomy where the correction occurs slightly more proximally than the Weil osteotomy and begins 2 to 3 mm from the articular surface at the metatarsal neck.

The use of dedicated instrumentation, and particularly of a high torque low-speed drill, lower than 8,000 rpm, is fundamental. A 2 × 12 mm Shannon burr is required for the osteotomy. For surgery on a left foot by a right-handed operator, the precise top of the metatarsal head must first be palpated with the left thumb (Figure 8.4). Then, at this level in the interspace, on the right side from top of the head (ie, lateral side for the left foot), the surgeon makes a 2-mm incision, parallel to the extensor tendons, preparing a path for the burr using a periosteal elevator to move along the flare on the proximal part of the head onto the neck. A thin curved mosquito clamp may also be used to create space for the burr (Figure 8.5). The burr is positioned obliquely at a 45° angle to the metatarsal axis, against the neck.

Figure 8.4 High torque low-speed drill and Shannon 2 × 12 burr.

A 1-cm area at the osteotomy site is carefully dissected, peeling, and therefore preserving, the integrity of the soft tissue. This allows a precise location of the distal point on the neck corresponding to the beginning of the head. Once the surgeon reaches it, they angle the burr 45° to the metatarsal axis.

Before cutting, the head is held firmly between the left thumb and the forefinger.

The correct positioning of the burr may be checked with a C-arm at the beginning, but with experience, this will
not be necessary (Figure 8.6A). Identification of the transition from the flare of the head to the narrower neck may be achieved by feel alone.

Figure 8.5 Mosquito clamp preparing the path for the burr.

Figure 8.6 Distal metatarsal metaphyseal osteotomy M2-M3. A. Location of the burr in the neck area under preoperative fluoroscopic control. B. Axial mobilization allowing the expected postoperative displacement.

The osteotomy begins at the lateral cortex, and the burr is moved plantar and medial, completing the cut at the dorsal cortex. This is done by pivoting the hand with the burr in a rotational movement from the point of skin entry, supinating the wrist through a 90° arc. The burr thus comes to almost lie flat on the foot at 90° to the metatarsal axis in the AP plane (Figure 8.7).

To avoid a lateral translation, it is necessary, depending on the side, right or left of the foot, to finish the cut with an angle of 135° or 45°, respectively, with respect to the metatarsal axis, again for a right-handed operator (Figure 8.8). By producing a somewhat oblique cut in the dorsoplantar projection, the lateral cortex is slightly longer than the medial cortex, thus producing a buttress to lateral displacement as this is the natural direction for drift.

Figure 8.7 Distal metatarsal metaphyseal osteotomy M4: Position of the burr at a 90° angle from the metatarsal axis at the end of the cut.

Figure 8.8 Direction of the final cut by 135° (right foot) and 45° (left foot) to avoid a lateral displacement.

It is very important to mobilize the toe in the metatarsal axis to make sure that the metatarsal heads can move together with full weight bearing by mobilizing periosteal adhesions that could prevent the shortening and elevation of the distal fragment (Figure 8.6B). This is performed using the straight elevator through the incision to release the soft tissues.

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