INTRODUCTION TO EXTENSOR HALLUCIS BREVIS TENODESIS

Iatrogenic hallux varus is a notoriously challenging complication following hallux valgus corrective surgery, characterized by medial deviation of the great toe at the metatarsophalangeal (MTP) joint. This deformity is often accompanied by an extension contracture of the MTP joint and flexion of the interphalangeal (IP) joint, leading to significant pain, shoe-wear difficulty, and cosmetic dissatisfaction.

The extensor hallucis brevis (EHB) tenodesis, popularized by Myerson and Komenda, as well as Juliano et al., has emerged as a highly reliable, joint-sparing reconstructive option for flexible hallux varus. Unlike arthrodesis, which sacrifices joint motion, or simple soft-tissue releases, which suffer from high recurrence rates, the EHB tenodesis provides a robust static and dynamic tether. By rerouting the EHB tendon to replicate the function of the sacrificed or incompetent lateral structures (specifically the adductor hallucis and the lateral collateral ligament complex), this procedure restores the delicate biomechanical balance of the first ray.

This comprehensive guide details the pathoanatomy, preoperative evaluation, and step-by-step surgical execution of the EHB tenodesis, providing orthopedic surgeons with the nuanced understanding required to achieve optimal outcomes.

PATHOANATOMY AND BIOMECHANICS OF HALLUX VARUS

To appreciate the mechanics of the EHB tenodesis, the surgeon must first understand the pathoanatomy of the hallux varus deformity. Iatrogenic hallux varus typically results from a combination of factors during the index bunionectomy:
* Over-resection of the medial eminence: Removing the medial sagittal groove destabilizes the medial collateral ligament and the tibial sesamoid.
* Aggressive lateral release: Complete transection of the adductor hallucis, lateral collateral ligament, and lateral capsule removes the primary lateral stabilizing forces.
* Over-plication of the medial capsule: Excessive tightening pulls the proximal phalanx into varus.
* Excessive lateral translation of the metatarsal head: Seen in aggressive osteotomies, altering the mechanical axis.

Once the hallux deviates medially, the extensor hallucis longus (EHL) and flexor hallucis longus (FHL) tendons subluxate medially, transforming from stabilizing forces into deforming forces that exacerbate the varus and extension moments.

The Biomechanical Rationale of EHB Tenodesis

The EHB tenodesis directly counteracts these deforming forces. By detaching the EHB proximally, leaving its distal insertion on the extensor hood intact, and routing it plantar to the deep transverse metatarsal ligament (DTML), the tendon is converted into a lateral and plantar tether.
1. Correction of Varus: The tendon acts as a substitute for the adductor hallucis and lateral collateral ligament, pulling the proximal phalanx laterally.
2. Correction of Extension: By passing plantar to the MTP joint's axis of rotation, the tenodesis exerts a plantarflexion moment, correcting the dorsal contracture.

PREOPERATIVE EVALUATION AND INDICATIONS

Clinical Assessment

A meticulous clinical examination is paramount. The surgeon must assess the flexibility of the MTP and IP joints. The EHB tenodesis is strictly indicated for flexible deformities. If the MTP joint is rigidly fixed in varus or extension, or if there is significant degenerative joint disease (hallux rigidus), a joint-sparing soft-tissue procedure will fail, and an MTP joint arthrodesis is indicated.

Assess the resting posture of the hallux and the degree of active and passive correction. Evaluate the medial soft tissues for severe scarring or contracture, which will require extensive release.

Radiographic Evaluation

Weight-bearing anteroposterior (AP), lateral, and sesamoid axial radiographs are required.
* AP View: Assess the hallux valgus angle (HVA), which will be negative (varus). Evaluate the intermetatarsal angle (IMA) to ensure it is not excessively narrow or negative, which might necessitate a reverse corrective osteotomy.
* Lateral View: Evaluate the MTP joint for dorsal subluxation and the IP joint for flexion (clawing).
* Sesamoid Axial: Assess the position of the tibial sesamoid. In hallux varus, it is often subluxated medially.

Indications

• Flexible, symptomatic iatrogenic hallux varus.
• Congenital hallux varus (less common, but applicable).
• Traumatic loss of lateral MTP joint stabilizers.

Contraindications

• Rigid, fixed hallux varus deformity.
• Advanced osteoarthritis of the first MTP joint.
• Severe osseous deformity requiring osteotomy (unless performed concomitantly).
• Incompetent or previously resected EHB tendon.

💡 Clinical Pearl: Managing Patient Expectations

Preoperative counseling is critical. Patients must be explicitly informed that the EHB transfer functions primarily as a tenodesis (a static tether) rather than a dynamic tendon transfer. Consequently, they should expect a mild, permanent loss of passive and active MTP joint flexion. The goal is stability and alignment, not the restoration of normal kinematics.

SURGICAL ANATOMY

A precise understanding of the first web space anatomy is required to execute this procedure safely:
* Extensor Hallucis Brevis (EHB): Originates from the superolateral surface of the calcaneus and inserts into the dorsal aspect of the proximal phalanx base and the extensor hood. Its muscle belly lies over the lateral tarsal bones.
* Deep Peroneal Nerve: The terminal medial branch courses through the first web space, providing sensation to the adjacent sides of the first and second toes. It lies in close proximity to the EHB tendon and must be protected during harvest.
* Deep Transverse Metatarsal Ligament (DTML): A strong, fibrous band connecting the plantar plates of the metatarsal heads. Routing the EHB plantar to this structure is the crux of the procedure, providing the necessary plantar and lateral vector.

SURGICAL TECHNIQUE: STEP-BY-STEP

1. Positioning and Anesthesia

The patient is placed supine on the operating table. The procedure can be performed under general anesthesia, regional anesthesia (popliteal block), or a comprehensive ankle block. A calf or thigh tourniquet is applied to ensure a bloodless surgical field.

2. Incision and Exposure

• Make a dorsal longitudinal incision centered over the first web space, extending proximally for approximately 2 inches (5 cm) from the level of the MTP joint.
• Carefully deepen the incision through the subcutaneous tissue.
• Identify and gently retract the terminal branch of the deep peroneal nerve. This nerve is highly susceptible to traction injury or accidental transection during the EHB harvest.

3. Tendon Harvest and Preparation

• Identify the extensor hallucis brevis tendon. It lies lateral and deep to the extensor hallucis longus (EHL) tendon.
• Trace the EHB proximally to its musculotendinous junction.
• Transect the EHB at the musculotendinous junction to maximize tendon length.
• Insert a 4-0 monofilament locking suture (e.g., Prolene or nylon) into the proximal stump of the EHB tendon to maintain control.
• Dissect the EHB tendon free of surrounding soft tissues, tracing it distally to its attachment into the extensor hood and the base of the proximal phalanx.
• CRITICAL STEP: Do not interrupt or detach this distal attachment. The integrity of the distal insertion is the foundation of the tenodesis.
• Carefully free the proximal end of the EHB from any fascial attachments to the EHL tendon to ensure smooth excursion.

4. Soft Tissue Release (Capsulotomy and Abductor Release)

Before the tenodesis can be performed, the medial and dorsal contractures must be completely eradicated.
* Perform a thorough dorsal and medial capsulotomy of the first MTP joint. If the capsule is severely contracted and fibrotic, a formal capsulectomy may be required to correct the extension and varus deformity.
* Identify the abductor hallucis tendon, which is often contracted and acting as a primary deforming force pulling the toe into varus.
* Release the abductor hallucis tendon in conjunction with the medial capsulotomy.
* Assessment: After these releases, assess the resting position of the hallux. The deformity must be passively correctable to a neutral or slightly valgus position without resistance.
* If the hallux remains resistant, extend the capsulotomy plantarly, completing a release from the tibial sesamoid to the fibular sesamoid. Failure to achieve a fully passive correction at this stage will result in failure of the tenodesis.

🔪 Surgical Warning: Inadequate Release

The most common cause of early recurrence or failure in EHB tenodesis is an inadequate medial release. The tenodesis is not designed to overcome a rigid contracture; it is designed to hold a passively corrected toe in proper alignment.

5. Tendon Routing

• Identify the deep transverse metatarsal ligament (DTML) in the first web space.
• Using a curved hemostat or tendon passer, create a pathway plantar to the DTML.
• Pass the proximally tagged stump of the EHB tendon plantar to the DTML, routing it from distal to proximal.
• This specific routing creates a pulley effect, redirecting the line of pull to mimic the native adductor hallucis and providing a plantarflexion force to counteract the extension deformity.

6. Tensioning and Biomechanical Assessment

• Apply proximal tension to the EHB tendon stump and carefully assess the alignment and rotation of the hallux.
• The Supination Pitfall: Because the EHB inserts dorsally into the extensor hood, pulling it proximally and laterally under the DTML creates a tendency to supinate (internally rotate) the hallux.
• If supination is observed during tensioning, partially release the most dorsal fibers of the EHB's distal insertion. This shifts the effective attachment point more laterally and plantarly, neutralizing the rotational moment.

7. Fixation to the First Metatarsal

• The goal is to attach the EHB tendon to the lateral aspect of the first metatarsal shaft under appropriate tension.
• Target Alignment: The desired position of the hallux after correction and fixation is approximately 5 degrees of valgus.
• Tensioning Strategy: With the tendon pulled proximally, assess the range of motion of the MTP joint. Compare this motion to the baseline motion with no tension. The objective is to apply the maximal tension on the tendon that interferes the least with MTP joint range of motion.
• Fixation Methods:
  • Bone Tunnel: Drill a transverse or oblique bone tunnel in the first metatarsal neck, approximately 1.5 cm proximal to the MTP joint line. Pass the tendon through the tunnel and suture it back onto itself.
  • Suture Anchor: Alternatively, place a biocomposite or metallic suture anchor into the lateral cortex of the first metatarsal, 1.5 cm proximal to the joint. Secure the tendon to the anchor using a Krackow or locking whipstitch technique.

8. Adjunctive Stabilization

• If the soft tissue balance feels tenuous, or if the surgeon wishes to protect the tenodesis during the initial healing phase, temporary pin fixation is highly recommended.
• Drive a 0.062-inch Kirschner wire (K-wire) longitudinally across the MTP joint, holding the hallux in the desired 5 degrees of valgus and neutral dorsiflexion/plantarflexion.

POSTOPERATIVE CARE AND REHABILITATION

A strict and well-monitored postoperative protocol is essential to protect the tenodesis while preventing excessive stiffness.

• Immediate Postoperative Phase (Weeks 0-4):
  • The patient is permitted to weight-bear as tolerated on the heel and lateral border of the foot in a rigid, wooden-soled surgical shoe immediately after surgery.
  • Dressings are kept clean and dry.
  • If a K-wire was utilized across the MTP joint for stability, it is typically removed in the clinic at 7 to 10 days postoperatively.
• Intermediate Phase (Weeks 4-8):
  • At 4 weeks, the patient may transition from the wooden-soled shoe to a comfortable, stiff-soled athletic shoe with a wide toe box.
  • The hallux must be continuously taped into a slight valgus position for a total of 2 months postoperatively to protect the lateral repair and prevent medial capsule contracture.
  • Range of Motion: Active and passive ROM exercises of the MTP joint are initiated as soon as the wound is healed and the K-wire (if used) is removed. Early motion is critical to prevent severe arthrofibrosis, keeping in mind the preoperative warning regarding a mild permanent loss of passive flexion.
• Late Phase (8+ Weeks):
  • Taping is discontinued.
  • The patient is permitted to progressively return to all desired activities, including high-impact sports, as tolerated.

COMPLICATIONS AND MANAGEMENT

While highly effective, the EHB tenodesis carries specific risks that the surgeon must be prepared to manage:

1. Recurrence of Hallux Varus

Recurrence is almost exclusively due to inadequate medial soft tissue release (failure to completely release the abductor hallucis or medial capsule) or insufficient tensioning of the EHB tendon during fixation. If recurrence is symptomatic and flexible, revision tenodesis or alternative soft tissue transfers (e.g., split EHL transfer) may be attempted. If the joint becomes rigid, MTP arthrodesis is the salvage procedure of choice.

2. Overcorrection (Return to Hallux Valgus)

Over-tensioning the EHB tendon, or aggressively over-releasing the medial structures without repairing the medial capsule, can drive the toe back into a valgus deformity. Careful intraoperative assessment of the resting posture (aiming for exactly 5 degrees of valgus) mitigates this risk.

3. MTP Joint Stiffness

Because the procedure relies on a static tether, some loss of plantarflexion is expected and biomechanically necessary. However, severe arthrofibrosis can occur if postoperative ROM exercises are delayed. Aggressive physical therapy is the first line of treatment. In refractory cases, a dorsal capsulotomy may be required, though this risks destabilizing the joint.

4. Supination Deformity

As discussed in the surgical technique, failure to recognize and address the supinating vector of the EHB tendon during tensioning will result in a cosmetically and functionally unacceptable rotated digit. Intraoperative partial release of the dorsal insertion is the definitive preventative measure.

5. Nerve Injury

The terminal branch of the deep peroneal nerve is highly vulnerable during the dorsal first web space approach. Retraction must be gentle. Neuroma formation in this area is exquisitely painful and may require subsequent surgical excision and nerve burying if conservative measures (e.g., gabapentinoids, targeted injections) fail.

CONCLUSION

The extensor hallucis brevis tenodesis remains a cornerstone technique in the armamentarium of the foot and ankle surgeon for the management of flexible iatrogenic hallux varus. By adhering strictly to the principles of complete medial release, precise tendon routing plantar to the deep transverse metatarsal ligament, and meticulous tensioning, surgeons can reliably restore the alignment and functional stability of the first ray. Thorough preoperative patient education regarding expected postoperative stiffness, combined with a rigorous rehabilitation protocol, ensures high rates of patient satisfaction and long-term success.