This author has not observed any increased rate of complications from undertaking bilateral simultaneous MICA hallux valgus corrections in patients with normal bone density. In younger patients with bilateral symptomatic deformities, it is preferable to undertake correction of both feet at the single sitting.

General anesthetic and/or regional (ankle) anesthetic block is administered. The patient should be positioned supine with their feet overhanging the end of the operating table. Use of a tourniquet is not required but may be used based on surgeon preference. If a tourniquet is used, then it is vital that adequate cooling irrigation of the burr is employed during use, so as to avoid thermal injury. The burr driver system should be able to deliver saline irrigation and capable of delivering high torque at low speeds. Fluoroscopy is required and preferably mini C-arm for its lower dose of radiation to both patient and surgeon and better maneuverability for switching easily from anteroposterior to lateral and oblique views during the surgery (Table 1.1). For a right-handed surgeon, the C-arm is positioned to the right of the patient and the surgeon to the left (independent of which foot is to be operated on). The scrub nurse should be to the left or tangential to the surgeon and the trolley positioned to allow the surgeon to access the instruments easily. The surgeon requires a working arc of 90° (Figure 1.1A). The patient’s preoperative weight-bearing radiographs should be displayed in theatre for reference during surgery (Figure 1.1B).

After preparation of the skin and sterile draping, the surgeon will begin by making a portal through which the distal chevron osteotomy is created. The incision is dorsolateral at the level of the distal metaphyseal-diaphyseal junction of the first metatarsal (Figures 1.1C and 1.2A). A small working space is created using a straight elevator ensuring that the dorsomedial cutaneous nerve is not damaged. A 2 mm × 20 mm Shannon burr is then “shown” to the bone through this portal at the base of the flare of the distal first metatarsal metaphysis, and fluoroscopy is used to ensure that the plane of entry of the burr is correct (Figure 1.2A). In order to maintain the length and sagittal plane profile of the first metatarsal, the burr should be directed approximately 10° to 20° (distal) beyond perpendicular and 10° to 20° (plantar) beyond parallel to the first metatarsal. If the burr is directed perpendicular to the first metatarsal, it will result in slight shortening of the metatarsal due to the 2-mm kerf of the burr. Similarly, without plantar direction of the burr, slight elevation of the distal metatarsal will occur due to the 2-mm kerf.

The initial insertion site of the burr through both near and far cortices becomes the apex of the chevron osteotomy, and it is therefore vital that the plane is correct (Figure 1.2B). The chevron is then cut in two stages. First, the dorsal limb is cut in a plane perpendicular to the axis of the metatarsal. The plantar limb cut is parallel to the floor (as if foot on floor), and should be shorter than the dorsal limb cut (Figure 1.2C). It is also important to avoid inadvertent “reverse” cuts (creating an “X” cut rather than “V”/chevron) due to the center of burr rotation lying within the bone—the center of rotation should lie medial to the first metatarsal. The burr hand movements when creating the osteotomies are a combination of translation with modest rotation. It is essential that the surgeon has experience with using the burr and such technique concepts before attempting to learn the MICA hallux valgus correction.

Once the osteotomy has been created, then the proximal screw guidewire is inserted via the proximal metaphyseal flare via an additional skin portal and advanced so as to pick up the lateral metatarsal cortex approximately 12 mm proximal to the osteotomy site (Figure 1.2D). Once the wire has penetrated the lateral cortex, it is not advanced any further until the osteotomy has been displaced.

The osteotomy is then displaced using a combination of levers and elevators (Figure 1.3A and B). The displacement maneuver internally rotates the proximal metatarsal fragment and laterally translates the head fragment. It is important to avoid external rotation of the head fragment by adding varus force to the hallux during the displacement maneuver. At this point, the coronal plane rotation of the first metatarsal can also be corrected. Both anteroposterior and lateral view fluoroscopy should be used to ensure correct plane of displacement.

The obtuse chevron osteotomy shape with short plantar tail serves to protect against inadvertent elevation of the head fragment and improve stability of the osteotomy without
compromising the ability to correct rotation and without compromising the bicortical fix of the proximal screw (as long as the point of traversing the lateral wall is greater than 12 mm from the osteotomy). The guidewire is then advanced into the head fragment and the appropriate screw length measured. A 4-mm chamfered head screw is preferred. The wire is then driven through the foot and clipped with a hemostat. This gives the surgeon control of both ends of the wire should this break during drilling and also avoids inadvertent removal of the wire during drilling. Drilling and screw insertion then follow.

Once the proximal screw has been inserted, then the distal antirotation screw guidewire and screw insertion follows. The second distal screw is important to avoid rotational
instability in larger displacements (>50% of the metatarsal width). A narrower (3-mm) MICA screw is preferred for this role—unless a larger bone patient. It is often easier to use a larger guidewire (2 mm diameter) initially, which is stiffer and less able to skive, to obtain the desired plane and then exchange this for the fine 0.9-mm guidewire required for the 3-mm MICA screw insertion (Figures 1.3C and 1.4). In male or larger feet with large displacements, a 4-mm MICA screw may be more appropriate for the distal screw.