Origin: Postenor surfaces of the head of the fíbula and proximal h of its body, soleal line and middle 73 of the medial border of the tibia, and tendinous arch between the tibia and fibula.

Insertion: With the tendon of the gastrocnemius, into the posterior surface of the calcaneus.

Action: Plantar flexes the ankle joint.

Patient: Prone, with the knee flexed at least 90°.

Fixation: The examiner supports the leg, proximal to the ankle.

Test: Plantar flexion of the ankle joint, without inversion or eversión of the foot.

Pressure: Against the calcaneus (as illustrated), pulling the heel in a caudal direction (i.e., in the direction of dorsiflexing the ankle). When weakness is marked, the patient may not be able to hold against pressure at the heel. When weakness is not marked, more leverage is necessary and is obtained by applying pressure simultaneously against the sole of the foot. (See p. 413.)

Note: Inversion of the foot shows substitution by the tibialis posterior and toe flexors. Eversion shows substitution by the peroneals. Extension of the knee is evidence of attempting to assist with the gastrocnemius. That is, the gastrocnemius is at a disadvantage with the knee flexed 90° or more, and to bring it into a stronger action, the patient will attempt to extend the knee.

Weakness: Permits a calcaneus position of the foot, and predisposes to a cavus. Results in inability to rise on the toes. In standing, the insertion of the soleus muscle on the calcaneus becomes the fixed point for action of this muscle in maintaining normal alignment of the leg in relation to the foot. The deviation that results from weakness of the soleus may appear as a slight knee flexion fault in posture, but it more often results in an anteno displacement of the body weight from the normal plumb line distribution, as seen when the plumb line is hung slightly anterior to the outer malleolus.

A nonparalytic type of weakness may result from sudden trauma to the muscle, as in landing from a jump in a position of ankle dorsiflexion and knee flexion, or from gradual trauma, as in repeated deep knee bending in which the ankle is fully dorsiflexed. The gastrocne-mius escapes the stretch because of the knee flexion-Contracture: Equinus position of the foot, both m weight bearing and in nonweight bearing. Shortness: A tendency toward hyperextension of the knee in the standing position. When walking barefoot, the shortness is compensated for by toeing out, thereby transferring the weight from posterolateral heel to the anteromedial forefoot. In shoes with heels, the shortness may go unnoticed.

Note: This test is important in the examination oj the cases with deviation of the body forward from plumb line. It is also advisable to test this must in cases with an increase in height of the longM' dinal arch.

Post. sup. view



Origin of Medial Head: Proximal and posterior part of the medial condyle and adjacent part of the femur, capsule of the knee joint.

Origin of Lateral Head: Lateral condyle and posterior surface of the femur, capsule of the knee joint.

Insertion: Middle part of the posterior surface of the calcaneus.


Origin: Distal part of the lateral supracondylar line of the femur, adjacent part of its popliteal surface and oblique popliteal ligament of knee joint.

Insertion: Posterior part of the calcaneus.

Action: The gastrocnemius and the plantaris plantar flex the ankle joint and assist in flexion of the knee joint.

Patient: Standing. (Patients may steady themselves with a hand on the table, but they should not take any weight on the hand.)

Test Movement: Rising on toes, pushing the body weight directly upward.

Resistance: Body weight.

Note: Inclining the body forward and flexing the knee is evidence of weakness. The patient dorsi-flexes the ankle joint, attempting to clear the heel from the floor by tension of the plantar flexors, as the body weight is thrown forward.

Shortness: Shortness of the gastrocnemius and soleus muscles tends to develop among women who constantly wear high-heeled shoes.

Muscles that Act in Plantar Flexion:


Gastrocnemius Plantaris

Tibialis posterior Peroneus longus Peroneus brevis

Ankle joint plantar flexors (tendo calcaneus group)

Forefoot and ankle joint plantar flexors

Flexor hallucis longus ] Toe, forefoot, and ankle Flexor digitorum longus J joint plantar flexors

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