Hammertoes - Types - Flexor Stabilization, Flexor/Extensor Substitution - Origins - Etiology

Описание: Hammertoes - Types - Flexor Stabilization, Flexor/Extensor Substitution - Origins - Etiology

Hammertoes are among the most common deformities of the forefoot.[1] It results from an imbalance between the weak intrinsic muscles and the stronger extrinsic muscles surrounding the metatarsophalangeal joints (MTPJ) of the lesser digits. Hammertoe is a deformity that involves flexion at the interphalangeal joints (IPJ) and can be distinguished into categories including the classic hammertoe, mallet toe or claw toe. With the lesser digits being an important component in the balance of the foot, as well as in pressure distribution, deformities may lead to compensatory gait changes, distortions in cosmetics, callous formations, and pain. It is, therefore, important to know that there is a multitude of viable treatment options to consider. Treatments should first and foremost be centered around conservative measures such as wearing shoes with a wider toe box, toe pads, and the proper utilization of orthotics. If conservative management fails and pain persists with worsening deformity, the patient may benefit from surgical intervention. There are different types of characteristics of the deformities, and depending on its rigidity, the surgical approach will differ. A proper clinical evaluation of the patient is, therefore, of the utmost importance when aiming for long-term reduction of the deformity.

Anatomy

Deformities of the lesser digits result from an imbalance between the weak intrinsic muscles and the stronger extrinsic muscles. Any imbalance in these forces will favor the stronger extrinsic muscles and thus will result in an extended proximal phalanx and possible MTPJ hyperextension, as well as with a PIPJ and/or DIPJ flexion due to the long unopposed flexor.[2]

Extensor digitorum longus (EDL) primary function is in the swing phase of gait and functions to dorsiflex the foot. EDL tendon splits into four separate tendon slips as it courses across the ankle, with each one going to each of the lesser digits. Over the proximal phalanx, the tendon again divides into 3 slips, with the middle slip inserting into base of the middle phalanx, and the 2 lateral slips converting into a terminal tendon and inserting into the base of the distal phalanx.

Extensor digitorum brevis (EDB) only has three slips and inserts into the fibrous expansion of EDL at the level of MTPJ of digits 2, 3, 4 forming what is called the extensor hood apparatus. Because of this unique anatomical construct, the pull of the EDL and EDB creates significant dorsiflexion of the MTPJ and minimal dorsiflexion power at the IPJ.

Flexor digitorum longus (FDL) divides into 4 separate slips that insert onto the lesser digits distal phalanx and flex at the DIPJ, while FDB inserts onto the middle phalanx and flexes the PIPJ. With no flexor inserting into the proximal phalanx and working as an antagonist to the MPJ in an extended position, the force results in flexion in the PIP and DIP joints.