Orthopaedics - Foot and ankle Flashcards
What is the shape of the tibia?
The tibia is triangular in cross section with a prominent anteromedial border just beneath the skin. Fracture of the tibia may result in the bone penetrating the skin, called an open fracture.
The fibula is located posterolaterally to the tibia and is largely for muscle attachment.
How many muscle compartments are present in the leg?
Similar to the thigh, the leg has 3 compartments.
The anterior compartment contains the dorsiflexors of the ankle, foot and big toe. These include tibialis anterior, extensor hallucis longus and extensor digitorum longus
The lateral compartment contains the everters of the foot. These muscles include peroneus longus and peroneus brevis.
The posterior compartment contains muscles that are largely plantarflexors of the foot at the ankle, flexors of the toes, and invertors of the foot. This is the largest group of muscles and includes:
- tibialis posterior
- flexor digitorum longus
- flexor hallucis longus
- soleus
- gastrocnemius
Much like the upper limb and thigh, these muscles are arranged in distinct oseofascial compartments making compartment syndrome a risk following trauma.
What nerves supply the muscles of the leg and ankle?
2 nerves that are a direct extension of the sciatic nerve (derived from the lumbar plexus) supply all the muscles below the knee.
These are the (i) common peroneal nerve and the (ii) tibial nerve.
Describe the course of the common peroneal nerve?
The common peroneal (or fibular nerve) is a direct extension of the sciatic nerve. It wraps superficially around the head of the fibula and divides into a superficial branch and a deep branch.
The superficial peroneal nerve innervates the muscles in the lateral compartment of the leg, which are essentially involved in eversion of the foot. It then courses down the lateral aspect of the leg and over the extensor retinaculum to end as dorsal cutaneous nerves (a medial and intermediate branch) that give off digital nerves. The deep fibular nerve innervates muscles of the anterior compartment of the leg and muscles on the dorsum of the foot. These muscles are essentially dorsiflexors of the foot at the ankle and extensors of the toes.
Describe the course of the tibial nerve?
The tibial nerve is a direct extension of the sciatic nerve. It innervates muscles of the posterior compartment of the leg and the intrinsic muscles on the plantar surface of the foot. The muscles of the posterior compartment of the leg are essentially plantarflexors at the ankle and flexors of the toes. These muscles also can participate in inversion.
A lesion to the tibial nerve may result in loss of plantarflexion and weakened inversion of the foot, leading to a shuffling gait.
Lacerations on the sole of the foot may damage the terminal branches of the tibial nerve, the medial and lateral plantar nerves, which innervate the intrinsic muscles of the foot.
What type of joint is the ankle joint?
The ankle is a hinge joint between the talus and tibia. The talus acts as fulcrum and is stabilised by the medial malleolus of the tibia and the lateral malleolus of the fibula. This configuration is known as a mortise. Fractures of either the medial or lateral malleoli may result in disruption of the mortise.
What ligaments help to stabilise the ankle joint?
Medially is the tough deltoid ligament. Laterally there are three main ligaments: the anterior talofibular ligament, the calcaneofib- ular ligament and the posterior talofibular ligament. Inversion injuries can tear or stretch the lateral ligament complex, resulting in an ankle sprain.
What bones form the foot?
The foot is composed of the talus, calcaneum, navicular, cuboid, three cuneiforms, five metatarsals and 14 phalanges. On the sole of the foot flexor tendons flex the toes. Dorsally lie extensor tendons.
Where do the tendons of tibialis posterior and peroneus brevis insert?
Medially the tibialis posterior tendon inserts into the navicular and supports the arch as well as providing inversion. Laterally the peroneus brevis inserts into the base of the fifth metatarsal to evert the foot. Fracture of this bony insertion occurs after inversion injury and is prone to non‐union.
What are the symptoms of OA of the foot?
Osteoarthritis (OA) may affect any joint in the foot or ankle. It may be idiopathic or secondary to trauma. The symptoms vary accord- ing to which joint is affected:
Ankle arthritis limits dorsiflexion and plantarflexion. In maximal dorsiflexion, osteophytes on the anterior margin of the joint get trapped between the talus and the tibia, known as anterior impingement.
Subtalar arthritis results in pain when walking on uneven ground as the hindfoot tries to accommodate in varus/valgus.
Midfoot arthritis includes many joints – pain is commonly felt dorsally, exacerbated by walking. Patients may notice prominent osteophytes and collapse of the arch.
First metatarsophalangeal joint arthritis, also known as hallux rigidus, may be associated with a bunion. Pain is worse when standing on tiptoe and walking barefoot, as this is when movement of the joint is greatest.
How is OA of the foot treated?
Analgesia
Activity modification
Orthotics - insoles and stiff soled shoes
Surgery
What surgical therapies can be used to treat ankle OA?
1) Target injection - it is often hard to decide which joint is arthritic, especially in the midfoot. Injections of local anaesthetic and steroid, placed under X‐ray guidance, offer short‐term relief, and also guide the surgeon as to which joints are the most painful.
2) Arthroscopic debridement – an option for the ankle and subtalar joint; removal of osteophytes and debridement of damaged cartilage may alleviate symptoms to some extent.
3) Arthrodesis (fusion) – eliminating movement by removing any residual cartilage from the bone ends before rigidly fixing the joint with screws and/or plates to allow the joint to fuse. Non‐union may occur in smokers or diabetics.
4) Joint replacement – prosthetic ankle replacement allows movement to remain but complication rates are high. In very physically active patients, early failure of the implant may result.
What are the features of RA affecting the foot and ankle? What joints are affected first?
In contrast to OA, soft‐tissue attenuation is the main problem in rheu- matoid arthritis (RA). Joints may become unstable, and in combina- tion with bone erosion, may sublux or dislocate. The forefoot is often affected first, with dislocated metatarsophalangeal (MTP) joints and overlapping toes. The midfoot and hindfoot may also be involved.
How is foot RA treated?
Treatment starts with systemic disease control, anti‐inflamma- tories and orthotics. Surgical intervention is usually in the form of fusion, as this will treat both instability and pain. Periarticular bone erosion and steroid‐related osteoporosis can make this technically challenging. If significant deformity exists, the more proximal joints should be corrected first.
What is tibialis posterior insufficiency?
The tibialis posterior tendon runs round the posterior aspect of the medial malleolus and has insertions into all of the bones of the midfoot. The main insertion is into the navicular. It acts an inverter of the hindfoot and adductor of the forefoot. It also maintains the medial longitudinal arch of the foot.
The tendon has an area of relatively poor blood supply as it passes behind the medial malleolus. In middle age this section of the ten- don may become degenerate and stretched or eventually rupture.
The result is pain and swelling behind the medial malleolus and eventually loss of the medial longitudinal arch, abduction of the forefoot and eversion (valgus) of the hindfoot. This is known as a planovalgus deformity.