A Guide To Lower Extremity Muscle Testing
In testing the posterior tibial muscle, it is best to eliminate the effects of other muscles that might contribute to the moment at the joints of concern. The anterior tibial muscle can contribute some supination moment so the foot should be plantarflexed when one is attempting to test the posterior tibial muscle.
The examiner asks the patient to relax the foot and then places the foot in a plantarflexed and adducted position. Place a hand on the medial side of the first metatarsal and place the other hand on the lateral leg. Then push the hands toward each other.
Use this principle for testing all other muscles of the foot. Place the foot in the position where the maximum pull of the tendon would place it. Then ask the patient to prevent you from moving the tendon. I have found these instructions to be the easiest for patients to understand. Also, in this position, when the forces exerted by the examiner are strong enough to overcome the muscle strength, then you will see motion. If the joints were at the opposite end of the range of motion, the resistance to the examiner’s forces may just be the physical end of range of motion of the joint and not the strength of the muscle.
Flexor digitorum longus tendon. The flexor digitorum longus tendon runs in a very similar course to the posterior tibial tendon. Instead of inserting into the navicular tuberosity, the tendon travels laterally and plantarly deep in the foot to insert, after splitting into four slips on to the base of the distal phalanx of the toes. Since its path is similar to the posterior tibial tendon, the flexor digitorum longus will have a similar effect at the subtalar joint. It will also have a similar lack of effect at the ankle joint. Distally, it runs inferior to the midtarsal joint and will create a plantarflexion moment there.
To test the flexor digitorum longus muscle, you want to eliminate the effects of other muscles and this is fortunately easy to do as it is the only muscle that plantarflexes the distal phalanges of the toes. Just ask the patient to curl the toes. All the lesser toes should curl at the same time because the one muscle belly pulls on the tendon that splits to all of the lesser digits.
The similarity between the path of flexor digitorum longus tendon and the posterior tibial tendon means that the flexor digitorum longus tendon is a good supinator of the subtalar joint. This fact explains the phenomenon of flexor stabilization. When a patient subconsciously chooses to get an extra subtalar joint supination moment from the flexor digitorum longus muscle, there will be a flexion contracture of the toes that can be visible in gait.
Flexor hallucis longus tendon. The flexor hallucis longus tendon differs from the other medial ankle tendons in that it passes posterior to the talus before traveling distally inferior to the midtarsal joint before finally inserting into the base of the proximal phalanx of the first toe. A certain percentage of the time, the flexor hallucis longus tendon sends slips to the distal slips of the flexor digitorum longus tendon. This arrangement is called the master knot of Henry. When the tendon of the flexor hallucis longus slides proximally, it will also plantarflex the second toe and, in some feet, the third toe as well.