By: Robert H. Sheinberg, D.P.M., D.A.B.F.A.S., F.A.C.F.A.S.
The soleus muscle originates on the backside of the tibia and fibula and runs deep to the inner and outer heads of the calf muscle (gastrocnemius). The soleus extends down beyond the gastroc muscle and joins the covering of the gastrocnemius called the aponeurosis to form the Achilles tendon.
The function of the soleus muscle is to assist the gastrocnemius and other muscles in the posterior leg to lift the heel off the ground during propulsion. It also stabilizes the ankle by preventing it from flexing as it decelerates forward momentum of the tibia. The muscle also has a very strong force in turning the foot in (supination), which stabilizes the outside of the foot to the ground. Its action also helps the knee. When the tibia is moving forward it stops excessive movement so that the knee joint can be extended.
Injuries to the soleus are relatively rare. Because of its attachment to the tibia, the soleus is most often implicated in shin splints (medial tibial stress syndrome). As the foot rolls in during shock absorption, the soleus helps to prevent the foot from excessively pronating. The muscle may pull excessively on the bone causing inflammation at the muscle periosteal bone junction.
Accessory soleal muscles have also been implicated in tarsal tunnel syndrome. The muscle can extend more distally into the inner portion of the ankle. It would take up space into the tarsal tunnel and during activity and fill with blood, causing compression of the posterior tibial nerve. MRIs are definitive in diagnosing accessory soleal muscles. If symptoms persist, removal of the accessory muscle will eliminate the underlying problem to the tarsal tunnel.
Diagnosis of soleal injuries is relatively straightforward. When the knee is flexed and the foot is moved up to its maximum position (dorsiflexion) pain is usually elicited in the soleus. Swelling may be seen on the lower one-third of the lower leg. An ultrasound examination may reveal fluid (hematoma) around the muscular injury. MRI scanning may also be helpful in evaluating injuries to the soleus.
Treatment for acute injuries of the soleus include rest by placing the foot in a plantarflexed or pointing down posture. Ice can be applied over a sock or a towel on the back part of the leg to lessen the pain and swelling. Compression in the form of an ace bandage will also help to lessen some of the swelling in the region. If there is an inability to weightbear, crutches for a period of 3-7 days may be very helpful. Early range of motion to minimize scar tissue formation would also benefit restoring the muscle. Physical therapy to return flexibility and strength to the area is helpful in almost all cases. Any shoe that has a small wedge that keeps the heel higher than the ball of the foot will also minimize stress to the region.
Chronic cases of problems with the soleus are usually associated with medial tibial stress syndrome (shin splints). Treatment protocol includes activity modification and changes in the running surfaces. Shoes with more support and a lift to lessen the stress to the soleus and prevent the foot from pronating. Orthotics to prevent excess pronation and excessive stress to the soleus. Anti-inflammatories to reduce inflammation and physical therapy to improve flexibility and strength to the muscle. In cases that are unresponsive to conservative care of if pain precludes normal weightbearing, a boot (Cam Walker) would be very helpful to take away stress from the soleus. In rare cases a hard fiberglass cast may be necessary to completely rest the area. Shockwave therapy has been shown to be beneficial for these injuries that become chronic. Rarely is surgery needed to return the patient back to full activity.