Gastrocnemius Muscle
Overview
| Muscle | Origin | Insertion | Innervation | Action |
|---|---|---|---|---|
| Gastrocnemius | Superior-posterior aspect of Medial Femoral Condyle Lateral surface of Lateral Femoral Condyle |
Calcaneal tuberosity via Achilles' Tendon | Tibial n. S1 - S2 |
TCJ: PF Knee: Flexion |
Overview
The gastrocnemius is the only muscle that crosses the posterior knee that does not have the ability to flex and to internally or externally rotate the knee2
“The gastrocnemius originates from above the knee by two heads, each head connected to a femoral condyle and to the joint capsule (Fig. 20-4). Approximately halfway down the leg, the gastrocnemius muscles merge to form an aponeurosis. As the aponeurosis gradually contracts, it accepts the tendon of the soleus, a flat, broad muscle deep to the gastrocnemius. The aponeurosis and the soleus tendon end in a flat tendon called the Achilles tendon, which attaches to the posterior aspect of the calcaneus. The two heads of the gastrocnemius and the soleus are collectively known as the triceps surae (see Chapter 21)”3
“Although the primary function of the gastrocnemiussoleus complex is to plantar flex the ankle and to supinate the subtalar joint, the gastrocnemius also functions to flex or extend the knee, depending on whether the lower extremity is WB or not. It has been proposed that weakness of the gastrocnemius may cause knee hyperextension.”3
Origin
Insertion
Calcaneal tuberosity via the Achilles’ tendon1
Innervation
Action
Biomechanics
The Triceps Surae inserts onto the calcaneal tuberosity via the achilles tendon. The fulcrum is technically the distal foot and the external load acting upon this muscle, joint, tendon complex is at the tibia. Thus, this is a second class lever and as a result, the triceps surae create more torque relative to their force compared to most other muscles in the body.
Muscle Length Test
Gastroc: knee extended + DF
- self assess at wall
Strength Test
SL calf raise >25reps
“Plantar flexion strength can be tested initially in non–weight-bearing (Fig. 21-22). However, unless there is significant weakness, clinician strength is usually insufficient to overcome ankle plantar flexor force, which necessitates a weight-bearing assessment of ankle plantar flexor strength. If no plantar flexion weakness is apparent in non–weight-bearing, a heel raise test is performed in the functional position, standing with the knee extended and the opposite foot off the floor Technically, one heel raise through full ROM, while standing with support on one leg, scores a 3/5 (fair) with manual muscle testing, with five single-limb heel raises scoring a 4/5 (good) and 10 single-limb heel raises scoring a 5/5 (normal). From a functional viewpoint, a wider range of scoring can sometimes prove more useful. Table 21-9 outlines an alternative scoring method. An alternative test, which is frequently used to assess talocrural and overall ankle function and is ften prescribed as an exercise, is the heel rise task. The task is performed using a block or a step, and the patient is positioned in standing with the balls of both feet on the block/step edge and the remaining parts of the feet over the edge. The patient may use a solid object for balance only. The patient is then asked to rise and lower his or herself on the balls of their feet as far as possible in each direction. The test can be also applied having the patient stand on only one leg. It is interesting to note that one study75 that measured both the ankle plantar flexion angle and the ankle dorsiflexion angle during this task found that the angles achieved were 23.7 degrees and 30.4 degrees respectively. The apparently large dorsiflexion angle compared to what is typically measured using a goniometer is likely the result that the motion combines both talocrural movement and forefoot movement.11 Although the task of raising up on the toes is generally thought to be predominantly performed by the triceps surae, a study by Kulig et al.76 reported significant contributions of the fibularis muscles and tibialis posterior during this task.”3
Function
“In addition, it has been theorized that the gastrocnemius acts as an antagonist to the ACL, exerting an anteriorly directed pull on the tibia throughout the range of knee flexion–extension motion, particularly when the knee is near extension.”3
Pails & Rails
P.A.I.L.’s
- Plantarflexion
- Knee flexion
R.A.I.L.’s
- Dorsiflexion
- Knee extension