Surgical Technique for Percutaneous Transverse Distal First Metatarsal Osteotomy and Akin Bunionectomy

Oliver N. Schipper

♦ INTRODUCTION

The percutaneous extra-articular transverse distal first metatarsal osteotomy and Akin osteotomy technique (PETA) offers several potential benefits over the percutaneous distal first metatarsal chevron osteotomy and Akin osteotomy technique. First, a transverse osteotomy allows for easier rotational correction of the pronation component of a hallux valgus deformity. Second, more bone is preserved at the first metatarsal head, allowing for increased bony screw purchase, as opposed to a chevron osteotomy where the screws may be placed within the central apex of the chevron with less bony purchase at the first metatarsal head. Third, the transverse osteotomy is quicker to perform. Finally, the transverse osteotomy allows for a medial midaxial incision rather than a dorsomedial incision for the chevron osteotomy, which reduces the risk of iatrogenic dorsomedial sensory nerve branch injury. A prior biomechanical study attempted to compare the biomechanical strength of the percutaneous chevron osteotomy versus the percutaneous transverse osteotomy but found no significant difference in ultimate load, yield load, and ultimate stiffness between the two osteotomies.¹ The study was limited by poor screw placement, and therefore, further studies are needed to determine if the transverse osteotomy is biomechanically and clinically superior to the chevron osteotomy.

♦ PREOPERATIVE PLANNING

Consider patient bone quality
- Younger patients may have better bone quality, which increases the risk of bone and skin thermal injury with use of the Shannon and wedge burrs. The surgeon should pause every 10 seconds to clean the burr flutes and allow the burr to cool.
- Patients should be counseled that foot swelling is normal for 6 months postoperatively.
- If clear first tarsometatarsal joint radiographic instability or symptomatic first tarsometatarsal joint arthritis is present, lapidus bunionectomy is the preferred procedure over PETA.

♦ PREPARATION AND PATIENT POSITIONING

The surgical technician should have all equipment on the Mayo stand prior to starting the case (Figure 2.1). The Mayo stand is placed to the right of the surgeon, and the surgeon typically stands to the left of the patient’s foot if right handed (opposite if left handed).
The patient is positioned supine with the operative foot off of the bed distally and externally rotated slightly away from the
body to facilitate AP and lateral fluoroscopy views of the forefoot with minimal adjustment of the mini C-arm (Figure 2.2).

Figure 2.1 Equipment setup on Mayo stand for percutaneous extra-articular transverse distal first metatarsal osteotomy and Akin osteotomy (PETA) technique prior to starting procedure.

Figure 2.2 The operative leg is elevated on a bump and the entire foot is off the end of the operative table.
The operative leg is elevated on a bump or blankets. The nonoperative leg may be frog-legged proximally away from the field and taped in order to avoid interfering with the C-arm.

Figure 2.3 The mini C-arm is positioned to the right of the patient and the surgeon typically sits or stands to the left of the foot if right handed. The opposite is true for left-handed surgeons.
The mini C-arm is typically positioned to the right of the patient for right-handed surgeons and to the left of the patient for left-handed surgeons, although this may be altered based on surgeon preference (Figure 2.3).

SURGICAL TECHNIQUE

Distal First Metatarsal Osteotomy

Tips
- Copious refrigerated (37 °F) bulb syringe irrigation is used at all times with the burr, during guidewire insertion, and when overdrilling the guidewire to prevent skin and bone thermal injury.
- Burring is paused every 5 to 10 seconds in order to reduce heat generation, especially in younger patients with good bone quality.
The 4:1 reducer is attached to the handpiece, and the core console is set to 4:1 reducer attachment at 5,000 rpm once the handpiece has been attached to the power cord.
The procedure is performed without a tourniquet.
- Use of tourniquet may increase the chance of thermal bone necrosis and therefore nonunion/delayed union.
- The patient may be placed in 10° to 20° of Trendelenburg to reduce bony bleeding during the procedure.
A medial ankle peripheral nerve block or first ray field block is performed using a combination of lidocaine 1% and ropivacaine 0.5%.
The central longitudinal axis of the first metatarsal shaft (midaxial) is marked out on a lateral fluoroscopy view of the foot (Figure 2.4).
Using fluoroscopic guidance, a 3- to 4-mm medial, midaxial, percutaneous, longitudinal incision is made at the distal metaphyseal-diaphyseal junction of the first metatarsal at the base of the first metatarsal head flare (Figure 2.5).
- No periosteal stripping is necessary.
- The incision is midaxial in order to avoid the dorsomedial sensory nerve.

(Optional) The first metatarsal head medial eminence may be resected prior to the osteotomy or after fixation of the osteotomy and removal of the residual distal medial shaft bone spike. Preservation of the medial eminence allows for greater shift of the first metatarsal head during hallux valgus correction, and therefore, the author recommends waiting to perform the medial eminence resection until after fixation of the osteotomy and removal of the residual distal medial shaft bone spike (Figure 2.6).

Figure 2.4 The central longitudinal axis of the first metatarsal shaft (midaxial) is marked out using a lateral fluoroscopy view of the foot.

Figure 2.5 A 3- to 4-mm medial, midaxial, percutaneous, longitudinal incision is made at the distal metaphyseal-diaphyseal junction of the distal first metatarsal at the base of the first metatarsal head flare.

Figure 2.6 AP fluoroscopy view of the foot showing first metatarsal head medial eminence resection.

Figure 2.7 The 2.2 × 22 mm Shannon burr is inserted through the same incision used for medial eminence resection under AP fluoroscopic guidance into the base of the medial first metatarsal head flare and angled 10° distally relative to the second metatarsal shaft.