A Guide To Lower Extremity Muscle Testing
The flexor hallucis longus tendon runs posterior to the ankle joint so it can plantarflex the ankle joint. The muscle belly is much smaller than the gastroc and soleus, and the flexor hallucis longus has a shorter lever arm so it is a much weaker plantarflexor of the ankle joint than the muscles attached to the Achilles tendon. The flexor hallucis longus tendon runs more medial than the flexor digitorum longus tendon and posterior tibial tendon, and therefore it has less leverage to affect the subtalar joint. The flexor hallucis longus tendon runs plantar to the midtarsal joint and can plantarflex that joint. Finally, the tendon inserts into the first distal phalanx and is the only muscle that can plantarflex that joint.
When testing the strength of the flexor hallucis longus tendon, one must be aware of its effect at the ankle joint. This muscle is similar to the long flexors of the hand in that the muscle cannot shorten enough to plantarflex both the ankle and hallux interphalangeal joint. So one needs to test the muscle with the ankle joint dorsiflexed.
What To Look For In Testing The Peroneus Brevis Muscle And The Peroneus Longus Tendon
Peroneus brevis. The course of the tendon of the peroneus brevis muscle runs very close to the ankle joint axis and therefore has little effect on ankle joint motion. The tendon runs the farthest lateral to the subtalar joint and therefore is the best pronator of the subtalar joint. The tendon also runs lateral to the midtarsal joint and is an abductor of that joint. The peroneus brevis is a direct antagonist of the posterior tibial tendon at both the subtalar joint and metatarsal joints.
To test the strength of the peroneus brevis, one should pronate the subtalar joint and abduct the forefoot on the rearfoot. Ask the patient to hold the foot in this position while you place one hand on the lateral side of the forefoot and the other hand on the medial side of the leg, and push both hands together.
Peroneus longus tendon. The peroneus longus tendon has a very similar course to the peroneus brevis tendon so it will have a similar effect to the peroneus brevis tendon in the joints they both cross. It will have minimal effect at the ankle joint, a strong pronation effect at the subtalar joint and an abduction effect at the midtarsal joint. Additionally, the tendon courses through the notch in the cuboid and inserts into the base of the proximal phalanx. The pulley effect at the cuboid will tend to create a dorsiflexion moment at the midtarsal joint. The attachment at the base of the proximal phalanx will cause a plantarflexion moment of the first ray.
The peroneus longus muscle is difficult to isolate as it has a similar action to the peroneus brevis and extensor hallucis longus muscles. The extensor hallucis longus muscle can plantarflex the first ray through the windlass mechanism. Being aware of the extensor hallucis longus effect can avoid this problem. To test the muscle, have the patient sitting relaxed and dorsiflex the first ray with the palm of the hand. While dorsiflexing the ray, note the range of motion of the first ray. Activation of the peroneus longus will plantarflex the ray and create the appearance of a higher arch.