This page explains the basic ankle joint anatomy. I think this is enough details for most amateur runners and just gives an insight into the complexities of the joint and structures which are commonly injured in runners.
Ankle Joint Anatomy: The Bones
The ankle joint is made up of three bones – The Tibia; Fibula and Talus. The Tibia and Fibula are the bones found in the lower leg which together form a kind of socket, or bracket for the Talus to fit in to. The Fibula is positioned on the outer ankle (the bony lump on the outside is the lateral malleolus of the Fibula) and the Tibia on the inside (the bony lump on the inside is the medial malleolus of the Tibia). The Talus bone is a smaller bone which has a head and neck at the front and two tubercles at the back and has a dome shape on the top part which articulates with the two shin bones.
The ankle joint allows the up and down movement of the foot – known as dorsiflexion (pulling the foot up) and plantarflexion (pointing the foot away).
There are another two joints in close proximity to the ankle joint which allows it to function. The Subtalar joint is formed between the Talus and the Calcaneus (heel bone) underneath. Whilst not technically the ankle joint, gliding movements at this joint allow the movements of inversion (turning the foot inwards) and eversion (turning the foot outwards) at the ankle.
Above the ankle, the inferior Tibio-Fibular joint is the joint between the two lower leg bones, which holds them together and provides a stable socket for the Talus to sit in. This joint is not synovial (free moving) and is held together by a strong ligamentous structure called the Syndesmosis. This is worth knowing as can occasionally be injured during a severe ankle sprain.
In terms of injuries, fractures do occasionally occur in runners, usually as a result of twisting the ankle, when an avulsion fracture may occur. This is where a small piece of bone is pulled off by a ligament or tendon when a strong force or contraction is passed through it. Stress fractures are rare in the ankle – they tend to be either higher up the lower leg, or in the Calcaneus (heel bone) or smaller bones of the foot.
Ankle Joint Anatomy: The Joint
As with all synovial joints, the ends of the bones within the joint are covered with hyaline cartilage and the joint itself is surrounded by a capsule.
There are seven main ligaments of the ankle including the lateral ligaments:
- Anterior TaloFibular Ligament (ATFL)
- Posterior TaloFibular Ligament
- Calcaneofibular Ligament
And the Medial ligaments of which there are four, collectively known as the Deltoid ligaments.
Ankle ligament injuries are the most common form of ankle injury and more commonly known as a sprained or ‘twisted’ ankle. These injuries only occur in runners if they fall or twist the ankle off a curb or more likely during off-road running.
Ankle Joint Anatomy: The Muscles
Muscles which affect the ankle joint tend to be found in the lower leg and pass a tendon across the ankle joint to attach to one or more of the many foot bones.
I will separate them into three groups:
The Plantarflexors or calf muscles
These are found in the back of the lower leg. The most well known in the Gastrocnemius. This is the largest and most superficial of the calf muscles which originates above the knee joint on both sides. Underneath this is the Soleus muscle. Soleus is a little smaller and less well known but still very important in ankle function. It originates lower down on the Tibia bone. These two muscles together converge to form the Achilles tendon – the biggest tendon in the body.
Also in this group is the smaller Tibialis Posterior muscle. This muscle is found even deeper than Soleus, but passes a long tendon down and to the inside of the ankle, running underneath the medial malleolus and attaching on to the Navicular and Medial Cuneiform bones. As well as assisting the other two muscles with plantarflexion, Tibialis Posterior also acts to invert the foot – turning the sole of the foot inwards.
Also working with these three muscles are the less significant (in terms of ankle movement) Flexor Digitorum Longus and Flexor Hallucis Longus. Their main roles are that of flexing (or curling) the toes.
The Dorsiflexors or shin muscles
The largest of the Dorsiflexors is the Tibialis Anterior muscle. This muscle is found at the front of the lower leg, with a tendon which passes across the front of the ankle, attaching on to the top of the Medial Cuneiform and 1st Metatarsal bones. Its function is to Dorsiflex the foot and tp assist Tibialis Posterior in inverting it.
Extensor Digitorum Longus and Extensor Hallucis Longus assist Tibialis Anterior in Dorsiflexing the ankle, but also work together to extend the toes.
The Peroneal muscles (sometimes called Fibularis muscles) are found on the outside of the lower leg. Their function is to evert the ankle (turn it so the sole faces outwards). The Peroneus Longus and Peroneus Brevis both have their attachment points on the Fibula (the longus is higher up – hence the name meaning long!) and both tendons pass behind and underneath the lateral malleolus. The Peroneaus Brevis attaches to the base of the 5th Metatarsal on the outside of the foot, whilst the Peroneus Longus crosses underneath the sole of the foot to insert into the base of the 1st Metatarsal and the Medial Cuneiform.
Muscle and tendon injuries of the lower leg and ankle are frequent in runners. Achilles tendinopathy; Calf muscle tightness; Peroneal tendinopathy; Tibialis posterior tendinopathy and compartment syndromes name just a few.