INTRODUCTION AND BIOMECHANICAL RATIONALE

The surgical management of hallux valgus requires a nuanced understanding of forefoot biomechanics, angular deformity, and soft tissue balancing. While isolated distal metatarsal osteotomies are frequently sufficient for mild deformities, they often fail to address concurrent phalangeal deformities or an abnormal distal articular set angle (DASA). To achieve greater correction and optimize functional outcomes in mild-to-moderate hallux valgus deformities, Mitchell and Baxter described a powerful combination: the Chevron-Akin double osteotomy.

This dual-osteotomy approach synergistically combines the translational corrective power of the distal metatarsal chevron osteotomy with the angular corrective capability of the Akin proximal phalangeal closing wedge osteotomy. In their seminal review, Mitchell and Baxter reported highly satisfactory results in 95% of 24 feet across 16 patients utilizing this combined procedure. By addressing both the intermetatarsal angle (IMA) and the hallux valgus interphalangeus (HVIP) angle simultaneously, the surgeon can achieve a rectus alignment of the first ray without over-translating the metatarsal head, thereby preserving the biomechanical integrity of the first metatarsophalangeal (MTP) joint.

Clinical Pearl: The Chevron-Akin double osteotomy is particularly valuable when a standard chevron osteotomy corrects the intermetatarsal angle but leaves residual clinical valgus of the great toe due to intrinsic phalangeal deformity or articular cartilage orientation.

INDICATIONS AND PATIENT SELECTION

Proper patient selection is the cornerstone of success in forefoot reconstruction. The Chevron-Akin double osteotomy is not a panacea for all bunion deformities; its application must be strictly guided by clinical and radiographic parameters.

Primary Indications

• Mild-to-Moderate Hallux Valgus: Typically defined as a Hallux Valgus Angle (HVA) between 15° and 30°, and an Intermetatarsal Angle (IMA) between 10° and 13°.
• Hallux Valgus Interphalangeus (HVIP): An intrinsic valgus deformity of the proximal phalanx exceeding 10°.
• Abnormal Distal Articular Set Angle (DASA): Where the articular surface of the proximal phalanx is not orthogonal to its diaphyseal axis.
• Congruent First MTP Joint: Deformities where the joint remains relatively congruent despite the valgus deviation, necessitating an extra-articular correction to prevent iatrogenic joint subluxation.

CONTRAINDICATIONS

Mitchell and Baxter explicitly cautioned against the indiscriminate use of this procedure in severe deformities.

Absolute Contraindications

• Advanced Sesamoid Subluxation: If the tibial sesamoid is laterally displaced beyond 50% of the crista (Grade III or IV), a distal osteotomy alone will fail to restore the sesamoid apparatus.
• Wide Intermetatarsal Angles: An IMA greater than 15° to 20° exceeds the translational capacity of a chevron osteotomy (which is limited to approximately 3 to 5 mm of lateral shift). Attempting to correct a severe IMA with a chevron osteotomy risks metatarsal head instability or "troughing."
• First MTP Joint Degenerative Joint Disease (Hallux Rigidus): Osteotomies are contraindicated in the presence of advanced osteoarthritis; arthrodesis or arthroplasty is preferred.
• Hypermobility of the First Ray: Tarsometatarsal (TMT) instability requires a proximal fusion (Lapidus procedure) rather than a distal osteotomy.

Surgical Warning: Performing a Chevron-Akin procedure on a patient with a wide IMA (>15°) and severe sesamoid subluxation will inevitably lead to undercorrection, high recurrence rates, and patient dissatisfaction.

PREOPERATIVE PLANNING AND RADIOGRAPHIC EVALUATION

A meticulous preoperative radiographic evaluation is mandatory. Standard weight-bearing anteroposterior (AP), lateral, and sesamoid axial views of the foot must be obtained.

1. Hallux Valgus Angle (HVA): Normal is <15°.
2. Intermetatarsal Angle (IMA): Normal is <9°.
3. Distal Metatarsal Articular Angle (DMAA): Evaluates the orientation of the metatarsal articular cartilage.
4. Proximal Articular Set Angle (PASA) and DASA: Crucial for determining the need for the Akin component.
5. Sesamoid Position: Evaluated on the AP and axial views using the Hardy and Clapham classification.

Templating should be performed to calculate the exact millimeter translation required at the metatarsal head and the precise wedge size (typically 1 to 3 mm) to be resected from the proximal phalanx.

SURGICAL ANATOMY AND VASCULAR CONSIDERATIONS

A profound understanding of the vascular supply to the first metatarsal head is critical when performing distal osteotomies. The primary blood supply to the metatarsal head arrives via the first dorsal metatarsal artery, the first plantar metatarsal artery, and the superficial branch of the medial plantar artery. These vessels form an intricate capsular network.

Pitfall: Extensive lateral soft tissue stripping combined with a distal metatarsal osteotomy significantly increases the risk of avascular necrosis (AVN) of the metatarsal head.

For this reason, in the specific technique described by Mitchell and Baxter for the Chevron-Akin double osteotomy, an adductor tenotomy (lateral release) is strictly avoided. Preserving the lateral soft tissue attachments ensures robust perfusion to the capital fragment following the chevron cut.

SURGICAL TECHNIQUE: STEP-BY-STEP

The following technique details the Mitchell and Baxter modification of the Chevron-Akin double osteotomy.

Patient Positioning and Anesthesia

1. The patient is placed in the supine position on the operating table.
2. A bump is placed under the ipsilateral hip to internally rotate the leg to a neutral position, ensuring the foot rests directly upward.
3. The procedure is typically performed under a regional ankle block or popliteal sciatic nerve block, supplemented with monitored anesthesia care (MAC) or general anesthesia.
4. A calf or thigh tourniquet is applied and inflated following exsanguination of the limb to provide a bloodless surgical field.

Incision and Soft Tissue Dissection

1. Skin Incision: Make a longitudinal medial skin incision extending from the mid-diaphysis of the first metatarsal to the interphalangeal (IP) joint of the great toe. This single, extensile incision provides excellent exposure for both the metatarsal and phalangeal osteotomies.
2. Neuroma Prevention: Carefully identify and retract the dorsal and plantar branches of the medial dorsal cutaneous nerve.
3. Capsulotomy: Perform a longitudinal or inverted L-shaped medial capsulotomy. Elevate the capsule to expose the medial eminence of the first metatarsal head and the base of the proximal phalanx.
4. Exostectomy: Resect the medial eminence (bunion) using an oscillating saw. The cut should be made parallel to the medial border of the foot, starting at the sagittal groove. Do not resect past the sagittal groove, as this may destabilize the tibial sesamoid.

The Chevron Distal Metatarsal Osteotomy

1. Apex Placement: Identify the center of the metatarsal head. The apex of the chevron cut should be placed centrally, approximately 1 cm proximal to the articular cartilage.
2. Osteotomy Execution: Using a fine-blade oscillating saw, create a V-shaped osteotomy with an apex-distal orientation. The angle between the dorsal and plantar arms should be approximately 60 degrees. Ensure the saw blade is held perpendicular to the plantar aspect of the foot to prevent unwanted dorsal or plantar elevation of the metatarsal head.
3. Translation: Translate the capital fragment laterally. In the Mitchell and Baxter technique, the lateral displacement of the metatarsal head is typically limited to approximately 3 mm.
4. Fixation: Secure the distal metatarsal osteotomy by placing a single 0.045-inch smooth Kirschner wire (K-wire). Drive the pin percutaneously from dorsal to plantar, positioning it in a slightly more proximal location to ensure adequate purchase in both the proximal shaft and the translated capital fragment.
5. Resection of Overhang: Once fixed, use the oscillating saw to resect the overhanging medial cortical prominence of the proximal metatarsal shaft, creating a flush medial border.
6. Crucial Step: As emphasized by Mitchell and Baxter, do not perform an adductor tenotomy. The lateral soft tissues must remain intact to preserve the vascularity of the metatarsal head.

The Akin Proximal Phalangeal Osteotomy

1. Exposure: Extend the dissection distally to expose the proximal phalanx subperiosteally.
2. Osteotomy Design: Perform a medially based closing wedge osteotomy. The cut must be directed away from the articular surface, running parallel to the concavity of the base of the proximal phalanx.
3. Wedge Resection: Remove a conservative 1-mm to 2-mm wedge of bone.
4. Hinge Preservation: It is imperative to leave the lateral cortex intact to act as a stabilizing hinge. Do not attempt to remove the contiguous lip of the proximal phalanx.
5. Closure and Fixation: Close the osteotomy by applying gentle lateral pressure to the distal phalanx. To maintain the osteotomy closure, place a 3-0 polyglactin 910 (Vicryl) suture from the periosteum on the distal side of the cut, passing it through the proximal undisturbed capsular tissues. Alternatively, modern techniques may utilize a single headless compression screw or a staple, though the Mitchell/Baxter technique relies on robust suture fixation.

Capsulorrhaphy and Closure

1. Capsular Imbrication: The medial capsule is carefully imbricated (tightened) using interrupted absorbable sutures (e.g., 2-0 or 3-0 Vicryl). This step is critical for holding the toe in the corrected, rectus position and restoring tension to the medial soft tissue envelope.
2. Skin Closure: Close the skin with interrupted 4-0 nylon or silk sutures.
3. Dressing: Apply a meticulous, bulky compressive dressing. The dressing itself acts as a splint; gauze should be woven between the first and second toes to hold the hallux in slight plantarflexion and neutral alignment.

POSTOPERATIVE REHABILITATION PROTOCOL

The postoperative protocol is designed to protect the osteotomies while preventing stiffness of the first MTP joint.

• Day 0 to Week 2:
  • Ambulation is permitted on the day of surgery in a rigid-soled postoperative sandal, weight-bearing as tolerated on the heel and lateral border of the foot.
  • The limb should be elevated strictly to minimize edema.
  • The bulky gauze wrap dressing is changed weekly for the first 2 weeks to monitor the incision and maintain alignment.
• Week 2:
  • Sutures are removed.
  • The 0.045-inch smooth K-wire securing the chevron osteotomy is removed in the clinic.
  • An elastic bandage or specialized bunion splint is applied to hold the corrected toe position.
  • Physical Therapy: Passive and active plantarflexion and dorsiflexion exercises of the great toe are initiated and strongly encouraged to prevent capsular adhesions and joint stiffness.
• Week 4 to Week 6:
  • Radiographs are obtained to confirm early callus formation and maintenance of alignment.
  • The patient is gradually transitioned into a wide-toebox, supportive athletic shoe.
• Week 8 and Beyond:
  • Return to higher-impact activities and normal footwear is permitted based on radiographic union and clinical resolution of swelling.

COMPLICATIONS AND PITFALLS

While the Chevron-Akin double osteotomy is highly successful when indicated, surgeons must be vigilant regarding potential complications.

1. Avascular Necrosis (AVN) of the Metatarsal Head: The most devastating complication. Risk is minimized by avoiding the lateral release (adductor tenotomy) and ensuring the chevron cuts are not made too far distally into the capsular attachments.
2. Undercorrection / Recurrence: Often results from poor patient selection (e.g., performing the procedure on a patient with an IMA > 15° or severe sesamoid subluxation).
3. Overcorrection (Hallux Varus): Can occur if the medial capsule is over-imbricated or if the metatarsal head is translated too far laterally. Hallux varus is notoriously difficult to treat and often requires soft tissue reconstruction or arthrodesis.
4. Intra-articular Fracture: If the Akin osteotomy is not directed parallel to the concavity of the phalangeal base, the saw blade may breach the MTP joint, leading to early osteoarthritis.
5. Pin Tract Infection: The percutaneous K-wire requires meticulous care. Superficial infections usually resolve rapidly upon pin removal at the 2-week mark and a short course of oral antibiotics.
6. Loss of Fixation / Malunion: If the lateral cortical hinge of the Akin osteotomy is breached, the proximal phalanx becomes highly unstable. If this occurs intraoperatively, the surgeon must abandon suture fixation and utilize rigid internal fixation (e.g., crossed K-wires or a micro-plate) to prevent malunion.

By adhering strictly to the biomechanical principles, precise surgical steps, and postoperative protocols outlined by Mitchell and Baxter, the orthopedic surgeon can utilize the Chevron-Akin double osteotomy to deliver profound, lasting relief for patients suffering from mild-to-moderate hallux valgus deformities.