Flexion Contracture Deformities

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Introduction: Flexion contracture deformities are one of the most common biomechanical pathologies affecting the lesser digits. There are three forms of flexion contracture deformity: hammer toe, claw toe, and mallet toe. A hammer toe is characterized by extension at the metatarsophalangeal joint (MTPJ) and flexion at the proximal interphalangeal joint (PIPJ). A claw toe is characterized by extension at the MTPJ and flexion at the PIPJ and distal interphalangeal joint (DIPJ). A mallet toe is characterized by flexion at the DIPJ.¹

Patient Impact: Flexion contracture deformities can cause both physical and psychological harm to patients. Patients may develop corns and calluses due to the excess pressure on the skin resulting from the deformity, leading to pain, redness, and swelling. Additionally, patients may feel self-conscious when displaying their feet with the deformity.

Clinical Outline:

Expert Opinion with Marie Williams, DPM, DABPS, DHLS:

On the initial encounter of a patient with painful hammertoes…
 

The initial discussion focuses on understanding the patient’s symptoms and concerns. I ask questions such as: How and when does the pain occur? What type of shoes do you typically wear? Are there any lesions on your toes that are painful? Where exactly on the toes does it hurt? Finally, I discuss their goals to tailor my approach to treatment.

On the physical examination of a patient with painful hammertoes…

During the physical examination, I perform a thorough biomechanical assessment of the affected joints and conduct a gait analysis to identify the underlying etiology of the hammer toe deformity: flexor stabilization, flexor substitution, or extensor substitution. Additionally, I evaluate their shoe gear, examining the wear patterns to detect areas of excess pressure. In some cases, something as simple as adjusting or changing footwear can provide significant relief!

On conservative treatment strategies for painful hammertoes…

Effective conservative treatments for painful hammertoes include Kinesio tape (K-tape) strapping, orthoses, and shoe gear modifications. I use K-tape strapping to reduce swelling, improve function, reposition the toes, and alleviate pressure on the affected joints. Additionally, I recommend over-the-counter or custom orthoses to address abnormal foot mechanics contributing to the deformity. I also evaluate and adjust the patient’s footwear to ensure proper fit and comfort. This involves recommending shoes with a wide toe box, breathable materials, and adequate cushioning to minimize pressure on the toes. Proper footwear can significantly reduce pain and help prevent the progression of hammer toe deformities.

Anatomy: The anatomy of the forefoot is complex and when functioning properly, contributes to stability and proper alignment of the toes. The proper metatarsophalangeal ligaments, accessory collateral ligaments, and the plantar plate aid in the static stabilization of the lesser digits. The proper metatarsophalangeal ligaments connect the tubercles on the dorsal-lateral and dorsal-medial aspect of the metatarsal head to the plantar aspect of the respective sides of the proximal phalanx. The accessory collateral ligaments connect the tubercles of the dorsal-lateral and dorsal-medial aspect of the metatarsal head to the respective sides of the plantar plate. The plantar plate is attached to the deep transverse metatarsal ligament, the accessory collateral ligaments, the plantar fascia, and the base of the proximal phalanx. More importantly, the plantar plate provides a socket for the metatarsal head which resists dorsiflexion at the MTPJ.⁴

The extensor digitorum longus (EDL), extensor digitorum brevis (EDB), flexor digitorum longus (FDL), flexor digitorum brevis (FDB), interossei, and lumbricals contribute to the dynamic stabilization of the lessor digits. The extensor expansion is the fibrous sheath of the EDL that separates into the extensor hood and the extensor sling. The extensor hood inserts on the plantar aspect of the proximal phalanx and the extensor sling inserts directly onto the plantar plate. The EDL tendon divided into three slips over the proximal phalanx to which the central slip inserts on the base of the middle phalanx and the lateral/medial slips inserts at the base of the distal phalanx. The EDB tendon inserts onto the lateral aspect of the EDL tendon on digits 2,3,4 just distal to the MTPJ. Although there is dorsal insertion of the EDL and EDB on the dorsal aspect of the phalanges, primary insertion is on plantar aspect of the phalanx through the extensor sling apparatus. As the extensors contract, primary force is dorsally directed from the plantar aspect of the extensor sling causing extension of the MTPJ.⁴

The FDL tendon inserts on the plantar aspect of the distal phalanx allowing flexion at the distal interphalangeal joint and proximal interphalangeal joint. The FDB splits at the level of the proximal interphalangeal joint allowing passage of the FDL to its insertion. The medial/lateral splits then insert onto the base of the middle phalanx. The FDB induce flexion at the proximal interphalangeal joint.⁴

There are both plantar and dorsal interossei. The plantar interossei insert on the medial side of the base of the proximal phalanx, MTPJ capsule, and extensor expansion of digits 3 through 5. The dorsal interossei insert onto the bases of the proximal phalanx. The first dorsal interossei inserts medically on the 2nd digit while the rest attach laterally. The lumbricals originate from the FDL tendon and pass medial to the MTPJ and under the deep transverse metatarsal ligament to insert onto the medial aspect of the extensor expansion. The interossei and lumbricals act to plantar flex at the MTPJ and extend at the PIPJ and DIPJ. Moreover, the plantar interossei adduct digits 3 through 5. The dorsal interossei abduct digits 2 through 5, noting that the first dorsal interossei pull medially on the 2nd digit while the second, third, and fourth dorsal interossei pull laterally on digits 2 through 4. The lumbricals adduct digits 2 through 5.⁴

A combination of static and dynamic support is required to keep the lesser digits in straight alignment. The extensor expansion dorsiflexion moment at the MTPJ is balanced by the lumbricals/interossei and the static stabilizers. The primary stabilizers are the plantar plate. The lumbricals/interossei dorsiflexion moment at the PIPJ is balanced by the FDL and FDB. And the lumbricals/interossei dorsiflexion moment at the DIPJ is balanced by the FDL alone.^4,5

Pathomechanics: There are three theorized biomechanical etiologies of flexion contracture deformities.

Flexor Stabilization: This etiology occurs when the FDB and FDL overpower the interossei. In patients where the tibialis posterior is weak, the FDL compensates for this muscle during gait. The interossei are unable to balance the flexion moment at the DIPJ and PIPJ. Additionally, the new flexion moment at the PIPJ and DIPJ results in an extension of the MTPJ. Flexion at the PIPJ dorsiflexes the proximal phalanx causing a retrograde force on the dorsal aspect of the metatarsal head, pushing it plantarward, ultimately creating an extension moment at the MTPJ.⁵ 

Flexor Substitution: This etiology occurs when there is weakness of the calf musculature or injury to Achilles tendon. In such patients, the FDL, FHL, PT compensate for the plantarflexion moment of the ankle joint during terminal stance which overpowers the interossei. Again, the interossei is unable to balance the flexion moment at the DIPJ and PIPJ, and therefore, progress to reverse bucking and causing an extension moment at the MTPJ.⁵ 

Extensor Substitution: This etiology occurs where there is overactivity of the EDL secondary to weakness of the anterior muscle groups of the leg which overpower the lumbricals during the swing phase of gait. When the tibialis anterior is weakened, the EDL compensates for the lack of ankle dorsiflexion during swing phase. The resulting extension moment at the MTPJ alters the placement of the force of the lumbricals. The lumbricals now create a force closer to and dorsal to the axis of rotation of the MTPJs. This results in the lumbricals inability to flex at the MTPJ and stabilize the PIPJ/DIPJ.⁵ 

Evaluation: Diagnosis of flexion contracture deformities is primarily based on physical examination. A static and dynamic biomechanical evaluation of the patient will aid in both diagnosis and treatment of the pathology.^2,3

Static Evaluation: By assessing the flexion and extension appearance of the MTPJ, PIPJ, and DIPJ, the flexion contracture deformity can be characterized as a hammer toe, claw toe or mallet toe. Additionally, flexion contracture deformities are categorized into flexible, semi-rigid, or rigid based on the Kelikian push up test. This is where a dorsal force is applied on the plantar aspect of the MTPJ. If the deformity reduces, it is flexible. If slightly reduces, semi-rigid. If it does not reduce, it is rigid.⁶ 

Dynamic Evaluation: The point in the gait cycle where the flexion contracture occurs allows for further characterization of the deformity. When the flexion contracture occurs in midstance, the deformity is based on a flexor stabilization etiology. When the flexion contracture occurs in terminal stance, the deformity is based on a flexor substitution etiology. And when the flexion contracture occurs during swing phase, the deformity is based on extensor substitutions etiology.⁵ 

Treatment: Flexion contracture deformities can be treated either conservatively or surgically.

Shoe Gear: Patients can wear shoe gear with a wider and higher toe box to accommodate the deformities and prevent painful shear forces on the affected skin.

Paring: A podiatrist can pare the corns and calloses that develop secondary to the deformity to relieve excess skin pressure. However, this is a palliative measure and not a true treatment option, as without further intervention, the patient will continue development of hyperkeratotic lesions.

Padding: A crest pad can also be fabricated. This padding technique decreases the reverse bucking presenting during gait and relieves pressure on the distal tips of the digits.⁷ 

Surgical: Patients may opt for surgical correction of flexion contracture deformity. This will be discussed in a later article.

Conclusion: Flexion contracture deformities are categorized into hammer toes, claw toes, and mallet toes. There are three biomechanical etiological origins of flexion contracture deformities including flexor stabilization, flexor substitution, and extensor substitution. The deformities are evaluated by both a static and dynamic evaluation which aids the physician in both diagnosis and treatment of the deformity. Treatment options for these deformities include shoe gear changes, paring of corns and callus lesions, padding, and surgical intervention.