Foot Strain and the Pronated Foot

Warning: The terms used are very technical which may [or may not] be difficult for a non-medical professional to understand.

The musculoskeltal system is a collection of bones, joints, ligaments, tendons and muscles considered as a whole unit. While it is studies by region or segment, abnormality in one region can cause ripple effect on other parts. If a patient comes with a painful lower back or hip or knee, the joints above and below it are also studied. An abnormality on the foot can cause mechanical distortion on the knee as well, and in turn might affect the hips, pelvis and even the lower back.

Foot Functional Anatomy:

The foot is an intricate structure composed of 26 articulating bones, constructed to bear full body weight and to transport the human body over various type of terrain. The foot can be divided into three functional units: anterior, middle and posterior. It is beyond the scope of this article to discuss the anatomical structure of each region.

Foot Strain and the Pronated Foot:

Pronated Supinated Foot

Foot strain can be acute, subacute, or chronic. As in so many painful musculoskeletal conditions, the cause maybe classified as: (1) abnormal stress upon a normal structure, (2) normal stress upon an abnormal structure, or (3) normal stress upon a normal structure but the structure is not prepared to receive the stress at that moment in time.

Acute foot strain may result from activity to which the patient is unaccustomed, like when a person jogs for exercise after a long period of inactivity. Patient may spontaneously recover after some rest and gradual return to activity without any medical help.

Chronic stress may occur when excessive stress is repeated, or when there is mechanical abnormality that predisposes the patient to pain and disability.

The initial stress causes ligamentous inflammation with resultant pain. Persistent strain can cause ligamentous elongation and some degeneration. Support to the joint is compromised and the joint goes into excessive motion or malalignment. The stress can also inflame the joint capsule, another cause of pain. Persistence of irritation in the joint or malalignment causes structural damage to the artucular surfaces, and degenerative arthritis results. The body’s natural response to irritation and its sequelae is bony overgrowth [osteophyte formation], which further deforms the joint with arthrosis. Early intervention can reverse the sequence… Irreversible damage may occur if this sequence is allowed to proceed.

Pathomechanics:

pronation

The weight-bearing foot is a complex structure with all component parts interdependent. The body weight is transmitted through the tibia upon the talus. The talus is in turn supported by the calcaneus. The calcaneus is oblique with respect to the ground surface and therefore encourages the forward and medial gliding of the talus. This further everts the calcaneus and depresses its anterior portion. Because of these changes, the plantar fascia becomes involved in supporting the longitudinal arch and becomes tender.

The increased obliquity of the calcaneus places stress on the deltoid [medial longitudinal] ligament, producing another site of pain. The forward gliding of the calcaneus puts stress upon the calcaneunavicular ligament, depressing the navicular bone with further decrease of the longitudinal arch.

As the calcaneus everts [valgus], the forefoot abducts, an action that decreases the two anterior transverse arch. The anterior metatarsal arch, when depressed, splays the foot and causes the arch to disappear. Pain results because the weight is borne in all metatarsal heads although wight bearing is not their functions.

As the calcaneus goes into valgus, the Achilles tendon undergoes adaptive shortening, thus causing further valgus and equinus and further strain on the anterior segment of the foot.

The talocalcaneal ligament is normally taut in the supinated foot and slack in the pronated foot. As the foot pronates, the tarsal canal deforms. This deformation subjects the talocalcaneal ligament to abnormal stress and becomes inflamed.

The plantar fascia becomes elongated as the longitudinal arch flattens. Tender ares maybe palpable.

The calcaneocuboid and the talonavicular joints develop more “play” and sustain capsular and irritation with possible pain. Pain originating at these joints can be verified by manually and forcefully everting [pronating] the forefoot while simultaneously stabilizing the heel. Tenderness can be elicited by pressure upon the plantar surface of the calcaneonavicular joint and its ligament.

Muscles Involvement:

The pronated foot is supported by muscular activity. When this protective muscular action is overwhelmed, the stress is transferred to the ligaments, the joint capsules, and ultimately the joint itself.

As the foot assumes a more pronated foot, the tibialis anterior muscle, an invertor, acts to oppose further pronation. Under stress, the muscle becomes tender.

In the pronated foot, the foot evertors, consisting of peroneal muscles,  shortens to take up the slack. With further forefoot pronation, the toe extensors change theor position and become evertors of the foot as well. In prolonged stress, the evertors may become inflamed and tender.

The toe flexors also contribute to the maintenance of the longitudinal and transverse arches. Normally, the long extensors extends the DIP joints thus allowing the toe flexors to press the straightened toes against the floor. This action elevates the anterior transverse metatarsal arch simultaneously. But int he pronated foot, the everted forefoot causes malalignment of the toe extensors, which may hyperextend the MTP joint causing the flexors to claw the toe. The big toe extensor muslce imposes traction on the longitudinal arch. In this position, the MTT heads become more prominent. and bear more wight.

Treatment:

  • Proper and thorough assessment of the foot as well the whole body is always important as with any other musculoskeletal conditions.
  • Replacing shoes with proper footwear is valuable. Shoe inserts after assessing the weight bearing foot, both static and dynamic function, can alter areas of pressure upon the foot or can alter the weight-bearing or ambulatory foot.
  • Metatarsal pads placed behind the 2nd, 3rd, and 4th metatarsal heads can elevate the forefoot and restore the transverse arch.  A longitudinal pad insert can restore the longitudinal arch and simultaneously inverts the foot to supination.
  • The invertors, posterior tibialis, as well as the calf muscles are helpful in preventing pronation.
  • A tight heel cord aggravates pronation, and therefore should be stretched.
  • Your physical therapist will perform thorough assessment and prescribe exercises to attain these goals.
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