Orthopaedics - Foot and ankle

Question 1

What is the shape of the tibia?

Answer 1

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.

Question 2

How many muscle compartments are present in the leg?

Answer 2

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.

Question 3

What nerves supply the muscles of the leg and ankle?

Answer 3

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.

Question 4

Describe the course of the common peroneal nerve?

Answer 4

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.

Question 5

Describe the course of the tibial nerve?

Answer 5

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.

Question 6

What type of joint is the ankle joint?

Answer 6

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.

Question 7

What ligaments help to stabilise the ankle joint?

Answer 7

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.

Question 8

What bones form the foot?

Answer 8

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.

Question 9

Where do the tendons of tibialis posterior and peroneus brevis insert?

Answer 9

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.

Question 10

What are the symptoms of OA of the foot?

Answer 10

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.

Question 11

How is OA of the foot treated?

Answer 11

Analgesia
Activity modification
Orthotics - insoles and stiff soled shoes
Surgery

Question 12

What surgical therapies can be used to treat ankle OA?

Answer 12

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.

Question 13

What are the features of RA affecting the foot and ankle? What joints are affected first?

Answer 13

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.

Question 14

How is foot RA treated?

Answer 14

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.

Question 15

What is tibialis posterior insufficiency?

Answer 15

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.

Question 16

What is the classic sign in tibialis posterior insufficiency?

Answer 16

Classically patients are unable to stand on tiptoes (heel raise) and the abducted position of the forefoot leads to the ‘too many toes’ sign when viewed from behind.

Question 17

How is tibialis posterior insufficiency staged?

Answer 17

Tibialis posterior insufficiency is split into 4 stages, which determine treatment:

Stage 1:

• no deformity
• pain/swelling behind medial malleolus
• heel rise present
• no arthritis
• Rx: insole, debridement of tendon

Stage 2:
- flexible planovalgus deformity
- heel rise absent
- no arthritis
- because the planovalgus is flexible and correctable, the
torn tibialis posterior tendon can be reconstructed by transferring flexor digitorum longus tendon into the navicular

Stage 3:

• rigid planovalgus deformity
• heel rise absent
• subtalar arthritis
• Rx: fusion of the subtalar, calcaneocuboid and talonavicular joints (‘triple fusion’)

Stage 4:

• rigid planovalgus deformity
• heel rise absent subtalar and ankle arthritis
• Rx: triple fusion plus ankle fusion (‘pantalar fusion’) – which severely limits mobility

Question 18

What is hallux valgus?

Answer 18

Hallux valgus is medial deviation of the first metatarsal and lateral deviation of the proximal phalanx of the first toe. The prominent metatarsal head may form a painful bunion. It is more common in women and may be related to footwear.

Most cases can be treated simply with accommodative, wide‐ fitting shoes. If this fails and pain is present, surgical correction may be considered.

Question 19

What surgical approaches can be used to treat hallux valgus?

Answer 19

The objective of surgery is to realign the first metatarsal with the long axis of the foot. This may be achieved in a number of ways, depending on the severity of the deformity, but generally a corrective osteotomy of the first metatarsal is performed. This may be augmented with fusion of the first tarsometatarsal joint if it is hypermobile, and corrective osteotomy of the proximal phalanx if it is contributing to the deformity.

Question 20

What is hallux rigidus?

Answer 20

Arthritis of the first metatarsophalangeal joint is known as hallux rigidus. It may occur along with hallux valgus and is important to recognise. Patients complain of a painful arc of movement, and OA changes will be seen on X‐ray. A fusion of the first metatarsophangeal joint is considered if there is signifi- cant arthritis here.

Question 21

What causes diabetic foot ulcers?

Answer 21

Diabetic foot ulcers occur due to a combination of peripheral neuropathy resulting in unnoticed trauma, poor healing due to microvascular disease, and a susceptibility to infection caused by hyperglycaemia. Infections can be very difficult to control and osteomyelitis is common. Treatment is primary prevention with regular foot care, aggressive debridement of infected ulcers and offloading ulcerated areas with plaster casts. Amputation is performed in recalcitrant cases.

Question 22

What is Charcot arthropathy?

Answer 22

Charcot arthropathy is bone and joint destruction in the presence of peripheral neuropathy due to persistent loading of damaged joints combined with poor proprioception. The commonest cause is diabetes, but it is seen in other causes of neuropathy. First‐line treatment is to cast the affected limb to allow bone healing to occur.

Question 23

What is congenital talipes equinovarus (CTEV)?

Answer 23

Also known as ‘club foot’, CTEV has an incidence in the UK of around 2/1000, with three‐quarters of cases occurring in males. Twenty‐five percent of cases have a positive family history and 50% of cases are bilateral.

Question 24

What conditions are associated with CTEV?

Answer 24

A number of aetiological theories exist, including abnormali- ties in muscles or nerves and intrauterine moulding. It is associ- ated with ‘packaging deformities’, including developmental dysplasia of the hip (DDH) and torticollis, which occur when intrauterine space is restricted due to twins or oligohydramnios. CTEV may also be associated with arthrogryposis (multiple joint contractures), spina bifida or other syndromes.

Question 25

What are the features of the deformity in CTEV?

Answer 25

The deformity affects the foot and calf. The foot has four deformities (an aide‐memoire is the acronym CAVE):

• Cavus – a high arch and plantar‐flexed first ray.
• Adductus of the midfoot – the foot turns inwards.
• Varus of the hindfoot – together this comprises supination.
• Equinus – a tight Achilles tendon.

In addition to these deformities, the calf muscles are hypo- trophic and the foot is smaller, requiring different shoe sizes in later life.

Question 26

How is CTEV treated?

Answer 26

Treatment is cast correction using the “Ponseti technique”. The deformity can be gradually corrected over several weeks with serial casts. The treatment regimen is started immediately from birth. Moulded plaster casts are applied at weekly intervals for around 3 months.

The foot deformities are corrected sequentially, starting with correction of cavus by raising the first ray. Then the hindfoot adductus and varus are corrected simultaneously. Finally, the equinus deformity is addressed by applying dorsiflexion at the ankle. In most hospitals, the casts are applied by specialist physiotherapists.

Around 90% of cases have a very tight Achilles tendon, which prevents correction of the equinus. The tendon is therefore released surgically. This minor procedure can be done under local anaes- thetic in clinic. A small blade is inserted through a tiny incision to divide the tendon beneath the skin.

Question 27

What are “Denis Browne boots”?

Answer 27

Once the foot is in an acceptable position, it is put into a final cast for 3 weeks. Once this cast is removed, there is a natural tendency for recurrence, so the foot must be held corrected for some time. This is achieved with ‘Denis Browne boots’. Two soft boots connected by a bar hold the feet adducted at shoulder width. The child wears the boots full‐time for 3 months, and then at night‐time and nap‐time for 3 years. Although this sounds like an ordeal, most children and their parents manage well.

Question 28

What is resistant CTEV?

Answer 28

Failure to respond to Ponseti casting is known as resistant CTEV. This is commoner in syndromic conditions such as arthrogrypo- sis. In these cases, surgical correction may be required. Tight ligaments are divided, tendons lengthened and the bones aligned and held with wires. Risk of wound breakdown, neurovascular injury, growth arrest and overcorrection exist.

Question 29

What is tarsal coalition?

Answer 29

The tarsal bones comprise the talus, navicular, cuboid and three cuneiforms. Movement between them maintains a flexible arch and is important for normal function of the midfoot. Failure of the bones to separate during development results in abnormal rigid connec- tions between the tarsal bones. This is known as tarsal coalition.

Question 30

What is the main type of tarsal coaliation?

Answer 30

There are two main types of coalition, which account for 90% of cases: calcaneonavicular coalition (CNC) and talocalcaneal coalition (TCC), although coalitions may occur between any of the tarsal bones.

Question 31

What are the symptoms and signs of tarsal coalition?

Answer 31

Although the coalition will be present from birth, it is flexible cartilage until ossification begins. Coalitions therefore do not present until around the second decade (earlier for CNC). The child may complain of frequent ankle sprains or pain following sports. Pain may be medial or lateral. As the condition progresses, restricted movement may be noted and progressive flattening of the foot will develop.

Question 32

How should tarsal coalition be investigated?

Answer 32

Imaging should initially be in the form of plain X‐rays. In CNC, oblique images of the foot may show an osseous bar between the calcaneum and the navicular. This is known as the anteater sign as it is said to resemble the nose of an aardvark. In TCC, irregularity of the posterior facet of the calcaneum may be seen on the lateral view, along with the ‘C‐sign’.

CT or MRI is the next step. The latter is perhaps more useful because it shows the full extent of a fibrous coalition as well as the presence of any other coalitions.

Question 33

How should tarsal coalition be treated?

Answer 33

In the first instance the foot should be rested for 6 weeks in a below‐ knee cast or fixed‐angle walker boot. In mild cases this resolves the pain and with activity modification no further treatment is required.
If this fails to settle symptoms, or restriction of sporting activity is unacceptable to the patient, resection of the coalition can be per- formed. This may be open or arthroscopic. Recurrence is frequent and the surgeon may try interposing fat or muscle between the bones to prevent this. In recurrent cases, or if the majority of the joint surface is involved, subtalar fusion can be performed. Although this will not restore movement, the aim is to achieve a painless fusion in a position which maintains the arch.

Question 34

What is idiopathic flat foot?

Answer 34

This is very common, especially in Afro‐Caribbean people. The arch usually restores when standing on tiptoes or when the big toe is pushed into dorsiflexion (Jack’s test). Pain or rigidity should prompt investiga- tion for coalition. Insoles and orthotics do not improve function and are not recommended. Reassurance is normally all that is needed.