Kinematics of the Metatarsophalangeal Joints, Deformities of the First Metatarsophalangeal Joint, Treatment Approaches

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The metatarsophalangeal (MTP) joints exhibit two degrees of freedom, making them essential for functional human movement. The primary movements include:
  • Extension (dorsiflexion) and flexion (plantarflexion), which occur in the sagittal plane around a mediolateral axis.
  • Abduction and adduction, which occur in the transverse plane around a vertical axis.
These complex movement patterns are crucial for gait and postural control. The second toe serves as the reference point for naming abduction and adduction movements, in contrast to the hand, where the third finger serves as the reference.
The axes of rotation for all voluntary movements at the MTP joints pass precisely through the center of each metatarsal head, enabling efficient and stable joint motion. However, abduction and adduction are significantly restricted, an anatomical characteristic that enhances foot stability.
In a neutral position, the toes can passively extend up to approximately 65° and flex between 30° and 40°. Notably, the first toe (hallux) typically has the largest range of motion, with extension reaching up to 85°. This extensive extension range is essential for functions such as tiptoeing and plays a critical role in generating propulsion during the terminal stance phase of gait.

Deformities of the First Metatarsophalangeal Joint

Hallux limitus and its more severe form, hallux rigidus, are progressive disorders affecting the first MTP joint, characterized by:

  • Severe restriction of joint motion
  • Progressive joint degeneration
  • Chronic pain

These conditions can arise from various causes, with trauma or sprain of the first toe being a common factor. A significant mechanism of injury involves forceful hyperextension of the first MTP joint, which can lead to structural damage.

In more severe cases, complications may include:

  • Fractures of the sesamoid bones
  • Partial or complete rupture of the plantar ligaments, joint capsule, or associated tendons

A particularly noteworthy condition associated with hyperextension injuries of the first MTP joint is known as "turf toe." This injury is common among American football players, occurring due to excessive dorsiflexion of the hallux. The term “turf toe” originated with the transition from natural grass fields to artificial turf, along with the widespread use of lightweight athletic footwear, which increased the frequency of such injuries.

From a diagnostic perspective, hallux limitus is generally diagnosed when:

  • Extension is limited to 55° or less
  • Persistent pain is present

If the condition progresses to osteoarthritis, excessive osteophyte formation can occur, further restricting joint movement in all directions. This can have a significant impact on gait, particularly in the late stance phase, where approximately 65° of first MTP joint extension is required for normal heel lift-off. As a result, patients often develop compensatory gait patterns, such as:

  • Shifting weight laterally to avoid pain
  • Externally rotating the foot while walking

Treatment Approaches

  • Footwear modification: Patients are advised to wear shoes with stiff soles to limit excessive toe extension and avoid walking on inclined surfaces.
  • Physical therapy: Therapy aims to improve joint mobility and reduce pain through specific interventions.
  • Surgical intervention: In cases that do not respond to conservative treatment, surgical options may be considered to restore joint function.