Interphalangeal joints of the foot
Interphalangeal joints are the articulations between consecutive phalanges of the foot. Each foot has nine interphalangeal joints: two on each of the four lateral toes and one on the big toe. They can be often categorized as:
- Proximal interphalangeal joints: between the heads of the proximal phalanges and the base of the middle phalanges
- Distal interphalangeal joints: between the heads of the middle phalanges and bases of the distal phalanges
Since the big toe does not have a middle phalanx, it has only one interphalangeal joint between the proximal and distal phalanges.
The interphalangeal joints of the foot are classified as uniaxial hinge joints, which are a type of synovial joint that permit movement along one axis, in this case flexion (plantarflexion) and extension (dorsiflexion) of the middle and distal phalanges.
|Type||Hinge joints; uniaxial|
Proximal interphalangeal joints: head of proximal phalanx, base of middle phalanx;
Distal interphalangeal joints: head of middle phalanx, base of distal phalanx;
Interphalangeal joint of big toe: head of proximal phalanx, base of distal phalanx;
|Ligaments||Collateral ligaments, plantar ligament|
|Innervation||Dorsal digital and proper plantar nerves (of medial and lateral plantar nerve)|
|Blood supply||Digital branches of plantar arch|
This article will discuss the anatomy and function of the interphalangeal joints.
- Articular surfaces
- Joint capsule
- Blood supply
- Muscles acting on the interphalangeal joints
The interphalangeal joints of the foot are articulations between the phalanges of the toes. In toes 2-5, a proximal and distal set of interphalangeal joints is present. A proximal interphalangeal joint is formed between the convex trochlear surface on the head of a proximal phalanx and the corresponding concave articular surface on the adjacent base of a middle phalanx. The distal interphalangeal joints of toes 2-5 are formed in a similar manner; between the trochlear surfaces on the heads of a middle phalanx and the corresponding concave articular surface on the adjacent bases of a distal phalanx.
As mentioned previously, the big toe has only one interphalangeal joint, formed between the trochlear surface on the head of the proximal phalanx and the concave articular surface of the base of the distal phalanx.
Each interphalangeal joint is completely enclosed by a joint capsule, lined by synovial membrane. The joint capsule is attached along the articular margins and reinforced by the collateral ligaments, plantar ligament, and the extensor expansions of the extrinsic and intrinsic muscles of the foot.
There are two types of ligaments that support and stabilize both the proximal and distal interphalangeal joints:
- Collateral interphalangeal ligaments: strong ligaments found on the medial and lateral sides of each joint, extending proximally and medially from small tubercles present on each side the head of the proximal phalanx to the base of the next phalanx.
- Plantar interphalangeal ligament: is not a true ligament but a dense fibrocartilaginous plate found on the plantar surface of phalangeal heads in the interphalangeal joints.
The interphalangeal joints receive nervous supply from proper plantar branches of the medial and lateral plantar nerves, that arise from the tibial nerve.
Minor contributions to the innervation of the interphalangeal joints of the lateral toes are received from dorsal digital branches, which stem from the deep fibular (peroneal), intermediate dorsal cutaneous and sural nerves. The interphalangeal joint of the big toe receives additional innervation from the medial dorsal cutaneous branch of the superficial fibular nerve.
Interphalangeal joints of the foot receive arterial blood supply from digital branches of the plantar arch, an anastomosis formed by the lateral plantar artery and deep plantar artery.
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Being uniaxial hinge joints, the only movements permitted in the interphalangeal joints are flexion (plantarflexion) and extension (dorsiflexion), which occur in the sagittal plane around a frontal axis. A considerable amount of flexion is possible, while extension is limited by the collateral and plantar ligaments. The movements are also significantly more pronounced in the proximal interphalangeal joints than in the distal.
In the close packed position, the interphalangeal joints are completely extended, while their loose packed (or resting) position is that of slight flexion. The capsular pattern (or loss of passive range of motion during inflammation) of these joints is flexion more limited than extension.
Muscles acting on the interphalangeal joints
|Flexion||Flexor hallucis longus, flexor digitorum longus, flexor digitorum brevis|
|Extension||Extensor hallucis longus, extensor digitorum longus, extensor digitorum brevis, lumbrical and interossei muscles of the foot|
The primary flexor of the proximal interphalangeal joint is flexor digitorum longus, while the main flexor of the distal interphalangeal joint is flexor digitorum brevis. The interphalangeal joint of the big toe is flexed by flexor hallucis longus.