Hallux Varus

Etiology

Rarely is hallux varus congenital, with no apparent genetic component identified.[3] Often, the condition is associated with a combination of structural or biomechanical abnormalities such as a short first metatarsal, accessory bones, or a fibrous band along the first MTP joint.[3] Flexible hallux varus may be found in newborns and reflects their intrauterine positioning. It corrects to valgus in early childhood when walking begins.[4]

More frequently, this deformity develops after a surgical procedure for hallux valgus because of overcorrection, excessive lateral release, over-resection of the medial eminence, over-plication of the medial capsule, a 0° or negative intermetatarsal angle, or immobilization of the toe in excessive varus after surgery. Iatrogenic hallux varus from hallux valgus correction has been reported to have an incidence of 2% to 13%.[5]  Other causes include trauma and certain systemic inflammatory diseases such as psoriasis and rheumatoid arthritis.[6]

Noniatrogenic causes of hallux varus include the following:

• Congenital hallux varus which is divided into 3 classifications as follows:
  • Primary hallux varus is rare and related to an overactive abductor hallucis.
  • Secondary hallux varus is associated with congenital abnormalities such as great toe polydactyly, a delta phalanx longitudinal epiphyseal bracket syndrome, and metatarsus adductus.
  • Tertiary hallux varus is associated with severe anomalies such as dwarfism.[7][8]   
• Medial insertion of the abductor tendon causes primary dynamic infantile hallux varus.                                 
• Acquired adult hallux varus is an inflammatory arthropathy that includes psoriatic and rheumatoid arthritis. The mechanism of arthropathies combines destruction of the articular surfaces by distention of the joint capsule with subsequent laxity of the collateral ligaments, intrinsic muscular contracture, and pannus. 
• Traumatic hallux varus occurs with sports injuries secondary to rupture of the lateral collateral ligament and conjoined tendon.

Congenital hallux varus may be due to connective tissue disorders (ie, Marfan syndrome and Ehlers-Danlos syndrome) or is associated with Down syndrome and neuromuscular disorders (ie, cerebral palsy).[9] Spontaneous idiopathic hallux varus is noted incidentally, and the cause is not usually demonstrable.

Epidemiology

The incidence of iatrogenic postoperative hallux varus varies from 2% to 14% after corrective surgery for hallux valgus deformity. Crescentic osteotomies have an overall varus rate of 10%. The incidence of idiopathic, congenital/infantile, traumatic, and otherwise acquired hallux varus is unknown.[10]

Pathophysiology

Hallux varus occurs due to musculotendinous and bony imbalances. The first MTP joint is stabilized by the flexor halluces brevis (FHB), extensor halluces brevis (EHB), abductor hallucis brevis, adductor hallucis, flexor hallucis longus (FHL), and extensor hallucis longus (EHL).[11] In a typical anatomic foot, the average position of the first MTP joint is 15° valgus.[12] Muscular imbalances may result from the overcorrection of a hallux valgus deformity.[11]

Juliano et al evaluated the tendinous restraints acting on the first MTP joint that influence the acquisition of a hallux varus deformity. Their study identified that the release of the lateral capsule decreased the load across the first MTP by 42.2% to displace the hallux 4 mm. Transection of the adductor tendon further reduced the force by 67.4%, and the addition of the FHB reduced the force by 81.6%.[13]

With a chevron osteotomy, a hallux varus deformity can develop if the capital fragment is excessively displaced laterally. Likewise, with a proximal osteotomy, the distal segment can be translated too far laterally. For the classical McBride procedure, the fibular sesamoid is excised, which causes MTP joint hyperextension, interphalangeal (IP) joint flexion, and medial deviation of the hallux.[11] The incidence of hallux varus following a classical McBride procedure has been reported between 5.1% and 15.4%.[14]

With time, the deformity becomes fixed, making it difficult for the patient to obtain comfortable footwear. The deformity typically manifests as a medial deviation of the great toe, supination of the phalanx, and claw toe deformity.[5]

History and Physical

The hallux varus deformity is often asymptomatic. Some patients complain of deformity and have difficulty in wearing shoes, instability, and weakness with push-off. Other patients may present with chronic pain, difficulty walking and standing for extended time periods, foot weakness, ingrown toenails, limited MTP joint range of motion, foot swelling, and occasionally redness or ulceration of the big toe. The symptoms become worse when patients wear closed-toe shoes that crowd the toes. The most common cause of pain in hallux varus is irritation of the deformed toe due to a poorly fitting shoe. Pain indicates an underlying arthritic process. 

Information regarding previous surgery is a crucial aspect of the patient's history that should be obtained. Primary procedure selection, fixation, and time since the initial surgery will influence prognostic and treatment options.

A thorough physical exam focuses on bone and joint deformity, joint flexibility and integrity, and soft-tissue balance. Assessment may demonstrate the following:

• Bone deformity: Varus orientation of the great toe and/or medial displacement of the medial sesamoid.
• Joint flexibility and integrity: Dorsal contracture of the MTP joint with or without IP joint contracture. The degree of extension of the first MTP joint should be analyzed, considering whether it is weight-bearing and whether the dynamics of ambulation increase the deformity or not.                                                                
• Soft tissue balance: Medial displacement of the EHL with a bowstring deformity. The plantar surface should be examined for any callosities.[11]

Evaluation

Evaluation with weight-bearing radiographs can provide significant insight into the degree of deformity and potential treatment options. Useful radiographic measurements to assess a structural deformity include the metatarsal protrusion distance, first intermetatarsal angle, and hallux valgus angle.[15] Specifically, a hallux varus deformity of 16° to 24° was found to be clinically significant and defined as a higher degree of deformity.[16] Additional evaluation of the IP joint can assess for rotational deformity, arthritic changes, or osseous deformities.

Understanding the type of deformity aids in treatment selection. Hallux varus deformities are classified into 3 types according to Akhtar et al as follows:

• Type 1: bone deformity
• Type 2: myoligamentous deformity
• Type 3: combined deformity [17]

Blood tests are only needed if an infectious or inflammatory process is considered.

Treatment / Management

Nonoperative treatment includes shoe stretching and modification. Shoes with wide toe boxes and padding over bony prominences should be recommended. Tapping or splinting the toes can be effective for early postoperative varus deformities after hallux valgus correction surgery. This should be continued for 12 weeks until soft tissue healing. If there is persistent pain or inability to wear shoes, surgery is indicated.[18][19][20][21](A1)

The aims of surgery include maintaining and/or restoring a normal gait pattern and weight-bearing mechanism, realigning the sesamoids, correcting deformity in the sagittal and transverse plane, and preserving the first MTP joint range of motion, if possible.

Operative treatment

Operative treatment may involve soft tissues and/or bones. Surgical planning should consider the following:

• Type of deformity- flexible or rigid
• Degree of deformity
• Presence of arthritis in the first MTP joint

As a rule, a flexible deformity can be corrected with a soft tissue procedure. Lengthening the medial capsular structures may be sufficient if the deformity is not too advanced. For advanced but flexible deformities,  procedures have been described either alone or in combination as follows:

• Adductor hallucis tendon reattachment with medial release                                                                             
• Abductor hallucis tendon transfer on the base of the lateral base of the proximal phalanx in combination with reattachment or reefing of the conjoined tendon in the webspace or transfer of a part of EHB or EHL under the transverse intermetatarsal ligament to the distal metatarsal neck                                                      
• Abductor hallucis tendon transfer to the lateral aspect of the proximal phalanx in combination with medial capsule release and medial sesamoid mobilization [14]                                                                                          
• Medial release without or with IP joint arthrodesis                                                                                            
• Split EHB transfer and reverse Akin procedure                                                                                                      
• Tenodesis of the EHB tendon in combination with the release of the medial soft tissues [22][13]
• EHL transfer to the proximal phalanx to act as a dynamic stabilizer.[23] This is done in combination with IP arthrodesis.
• Keller resection arthroplasty                                                                                                                           
• Implant arthroplasty

Contraindications for tendon transfer procedures include the following:

• Arthropathies (degenerative and inflammatory)
• Active infection
• Neurovascular compromise (eg, peripheral neuropathy, peripheral vascular diseases)
• Excessive resection of the medial eminence
• Fixed deformity of the MTP joint

In cases with rigid deformity, deformity with limited first MTP joint motion, or arthritic changes in the first MTP joint, arthrodesis of the first MTP joint is considered. Lateral closing wedge osteotomy with or without repair of the lateral ligaments can be offered in cases of iatrogenic hallux varus due to overcorrection of a hallux valgus deformity with either metatarsal or proximal phalangeal osteotomy.[24]  A reverse scarf osteotomy has also shown improvement in the hallux valgus angle and clinical outcomes following the treatment of iatrogenic hallux varus.[25]

Differential Diagnosis

The presentation of hallux varus may be clear clinically and radiographically (see Image. Iatrogenic Hallux Varus). However, underlying disease processes contributing to the deformity are essential to consider and include the following:

• Osteoarthritis: Cortical degeneration with subchondral changes may result in medial deviation of the hallux in individuals affected by osteoarthritis. Radiographic evaluation will differentiate osteoarthritis from iatrogenic or congenital hallux varus. 
• Rheumatoid arthritis: Rheumatoid arthritis causes dysregulation of chondrocytes and synovial fibroblasts in the musculoskeletal system,  manifesting in articular and non-articular presentations. This often depreciates the capsular integrity of the first MTP joint, shifting the hallux in valgus; however, hallux varus has been reported in 0.2% to 10% of cases. Laboratory evaluation can confirm the diagnosis of rheumatoid arthritis.[26]                                                                                                     
• Charcot-Marie-Tooth (CMT) disease: CMT is a neuromuscular disorder that initially presents motor and sensory dysfunction in the foot. The disease progresses proximally and gradually affects the lower extremity.[27] The musculotendinous imbalances often present as hallux malleus.[28]                                             
• Avascular necrosis (AVN) of the metatarsal head: Historically, AVN following a distal chevron osteotomy for hallux valgus correction has been cited as a 20% occurrence. More recent literature has shown a 0% occurrence. However, the clinical presentation of AVN can range from asymptomatic to significant pain, deformity, and bone collapse.[29]

Prognosis

Surgery improves the overall position of the hallux but not necessarily its motion. In cases of flexible iatrogenic hallux varus, tendon transfer with soft tissue release has been reported to result in sustainable correction.[30] Patient satisfaction rates of 94% following an arthrodesis procedure for fixed deformity have also been reported.[5]

Complications

Patients undergoing conservative treatments may experience limited efficacy or adverse reactions to orthotic devices or splints, necessitating adjustments or alternative approaches. Moreover, any delay in seeking treatment or failure to adhere to postoperative rehabilitation protocols can compromise treatment outcomes and exacerbate existing complications. 

Complications of surgical treatment in hallux varus can arise despite meticulous preoperative planning and execution. Potential complications of hallux varus surgery include the following:

• Soft tissue complications, including infection, impaired wound healing, and nerve damage or irritation
• MTP joint instability
• Recurrence of hallux varus
• Under-correction or over-correction
• Avascular necrosis of the metatarsal head
• Stiffness
• Hardware failure
• Progression of degenerative changes in the MTP joint
• Shortening of the medial column
• Transfer metatarsalgia

Comprehensive preoperative assessment, patient counseling, and vigilant post-treatment monitoring are crucial to minimize the risk of complications and optimize the success of interventions for hallux varus.