Foot Strain - Types, mechanism and sequence

Foot strain may be acute, subacute, or chronic. It may occur in the normal foot from normal walking or standing if the patient has been unaccustomed to a great deal of activity. Since foot strain has a mechanical effect on the soft tissues, if it is allowed to persist, deformity may result.

A foot, considered mechanically abnormal may be strained by essentially normal activity. Stress on a pre-existing deformity will cause earlier and more intense pain and the foot will resist correction and palliation. The general rule that applies to all musculoskeletal dysfunctions applies here; that is, pain and dysfunction can occur from

1. abnormal stress on a normal structure,
2. normal stress on an abnormal structure,or
3. normal stress on a normal structure when the structure is not prepared for the stress.

The static foot is supported by ligamentous tissues. There is no muscular activity in the foot or leg muscles during standing, even when large weights are superimposed upon the body. The muscular activity during locomotion prevents excessive strain upon the supportive ligaments and ' joint tissues. Therefore, pain in the static foot must result from faulty mechanics or an overwhelming stress upon the ligaments.

In the moving foot, pain results when muscular incompetence due to disuse, imbalance, or abuse places an excessive burden upon the ligaments. In either case, the stress upon the soft tissues causes inflammation, elongation, and ultimately degeneration of the ligaments.

Acute painful ligamentous strain is usually self-limited, subsides with rest, and rarely presents a therapeutic problem. The acute situation is exemplified in the person paying an unaccustomed visit to a museum, the weekend athlete, or the doctor visiting the many booths at an annual convention. Rest followed by a gradual return to normal activities leads to recovery.

If excessive stress is repeated or if normal stress is imposed upon a mechanical abnormality, the symptoms may become chronic. Symptoms may vary from those of ligamentous strain to those caused by joint misalignment resulting from the stress. Ultimately degenerative arthritic changes may be the source of pain.

The “breakdown” process follows a sequence. Ligaments exposed to chronic strain elongate and undergo inflammatory changes which result in pain. If the condition persists, the ligaments elongate and degenerate, lose their supporting function, and permit excessive motion of the joints. This excessive “play” and misalignment of the joints will inflame the joint capsules and surfaces, and articular inflammation becomes the source of pain.

If irritation to the joints continues, structural damage to the articular surfaces results, and degenerative arthritis is present. Nature responds to these irritations by attempting reconstruction or forming a bulwark against the irritation with an overgrowth of bone that results in a deformed joint called an “arthrosis.” If early changes are recognized, this cycle is reversible, but if it is allowed to proceed too far, the joint may be beyond repair.

The initial symptom of acute stress from activity such as prolonged walking is muscular fatigue, usually described as an “aching” in the sole of the foot, calf muscles, or occasionally the anterior leg. Deep tenderness of the plantar tissues of the foot or the leg muscles is found.

The foot, now symptomatic, may be normal but is more likely to be a pronated foot which flattens its longitudinal arch upon weight bearing. Muscular fatigue from activity permits stress to be imposed upon the ligaments resulting in ligamentous pain.

The foot and ankle must be considered as a complex structure with each of its component parts dependent upon the others. Body weight is borne upon the talus through its articulation with the tibia. In turn, the talus is supported by the calcaneus and is held in an oblique manner. The oblique seating of the talus upon the calcaneus gives the talus a tendency to glide forward and medially upon the calcaneus. The resultant force of this movement forces the calcaneus into eversion and depresses its anterior portion. This pronation depresses the longitudinal arch and stretches the plantar ligament and fascia.

The valgus position of the heel places a torque stress upon the forefoot, which responds by becoming everted. The foot now bears the weight on its inner border, which forces the foot into more pronation thus placing strain on the medial ankle ligaments and upon the tendon of the posterior tibial muscle. Due to the valgus heel position, the Achilles tendon deviates laterally and shortens. The shortened tendon places more strain upon the anterior segments of the foot.