Structured oral examination question 4: Cavus foot

Structured oral examination question 4: Cavus foot

EXAMINER: These are pictures of the left foot of a 20- year-old man. Describe them. (Figure 4.4.)

CANDIDATE: These photographs show the anterior, medial and posterior views of a left foot with a cavus deformity. The hindfoot is in varus and there is a high arch. There doesn’t appear to be any significant clawing or abnormality of the toes.

EXAMINER: What is the likely underlying cause?

CANDIDATE: A cavus foot develops a high arch as the result of imbalance in the musculature of the foot. It can be caused by a plantar flexion deformity of the forefoot or by a dorsiflexion deformity of the hindfoot known as calcaneocavus. The causes of a cavus foot may be broken down into congenital or acquired. The most common causes of congenital deformities are idiopathic, a sequela of clubfoot or due to arthrogryposis. The acquired deformities may be due to trauma or neuromuscular conditions. The neuromuscular causes may be grouped into central nervous system disease such as cerebral palsy or Friedrich’s ataxia, spinal cord lesions such as spina bifida or spinal dysraphism, peripheral nervous system lesions such as an HSMN or muscular causes such as muscular dystrophy.

EXAMINER: HSMN?

CANDIDATE: Hereditary motor–sensory neuropathy. These are a group of inherited neurological conditions.

Charcot–Marie–Tooth (CMT) is the most common group of these conditions.

EXAMINER: Can you go into more detail? How do these conditions lead to a cavus foot deformity?

CANDIDATE: The hereditary motor sensory neuropathies are a group of related conditions that may lead to cavus foot deformity due to muscle imbalance. The conditions are generally diagnosed by the pattern of deformity and a positive family history. The most commonly recognized is the Charcot–Marie–Tooth disease group which affects approximately 1 in 2500 people. These patients commonly have weakness of the intrinsic muscles, tibialis anterior and peroneus brevis. Type I will tend to present in the second decade, it is an autosomal dominant inheritance and patients have peroneal weakness, slow nerve conduction and absent reflexes. Type II presents later, in the third or

Figure 4.4 Cavus foot deformity.

fourth decade, and reflexes and nerve conduction are normal, however the foot signs may be more pronounced. Genetic analysis is able to diagnose and group these conditions more accurately and at least 17 types of CMT have been described.

EXAMINER: How would you assess this foot?

CANDIDATE: My assessment would have two components. I need to determine any underlying cause of the cavus and also evaluate the deformity itself. I would establish whether this is a unilateral or bilateral deformity and then I would begin by taking a thorough patient history. A cavus deformity is often secondary to a neurological cause so I would ask whether the foot had always been this shape and whether the deformity was progressive. I would ask what symptoms the foot causes and how it affects their function. I would also ask about any previous medical or surgical history, family history, and any previous surgical or non-surgical treatment the patient had received.

EXAMINER: What symptoms is this patient likely to complain about?

CANDIDATE: Common complaints in cavus feet are of pain, particularly forefoot pain, lateral foot pain under the metatarsal heads, or arch pain, instability of the ankle with a history of frequent ankle sprains. They may also have problems with fitting of footwear or alteration of gait.

EXAMINER: What are the main findings you would look for in the examination of a cavus foot?

CANDIDATE: On first, general inspection I would be looking to see if the deformity was bilateral and whether there were stigmata of a generalized condition such as wasting within the hands. With the patient standing I would look to see whether the heel was in varus, neutral or valgus alignment, assess the height of the longitudinal arch by inspection and also see whether I could pass more than two fingers underneath. I would look to see the posture of the toes. This would be to assess the degree of deformity. While the patient was standing I would also look at the spine for any stigmata of an underlying abnormality such as a hairy patch or scoliosis.

With the patient sitting I would inspect the soles of the feet for callosities or areas of ulceration. I would look to see whether the cavus was due to plantarflexion of the first ray or the whole forefoot. I would assess sensation, deep tendon reflexes and power of the major muscle groups, particularly the tibialis anterior and posterior and the peroneal tendons. I would assess lateral ankle ligament competence with an anterior drawer and talar tilt test and look at the active and passive range of movement and see whether the deformities were flexible or fixed.

EXAMINER: What is shown in the following two diagrams?

CANDIDATE: These diagrams show the Coleman block test.

(Figure 4.5.)

Figure 4.5 Coleman block test.

EXAMINER: And what is that?

CANDIDATE: The Coleman block test looks for flexibility of the hindfoot deformity by eliminating the deforming drive of the forefoot. In a cavus foot the first ray is plantarflexed so to place the foot stably on the ground the hindfoot has to move into varus. In the Coleman block test the foot is positioned so that the lateral border of the foot and the heel are placed on a block and the medial forefoot is allowed to hang off the edge of the block. If the heel then assumes a physiological alignment of neutral to 5 valgus when viewed from behind the hindfoot deformity is both flexible and driven by the

forefoot.¹

EXAMINER: What investigations would you use to evaluate this foot further?

CANDIDATE: In terms of evaluating the foot itself I would first obtain a series of weightbearing radiographs, a lateral of the foot and ankle, a hindfoot alignment view and an AP of the foot. If the patient had any signs or history suggesting an underlying spinal cause then radiographs or MRI scan of the spine should be considered.

EXAMINER: What information does the lateral X-ray tell you?

CANDIDATE: The magnitude of the cavus deformity can be quantified using Meary’s angle, the angle between the long axis of the talus and the first metatarsal shaft. Normally this lies between þ5 and 5. Hibb’s angle is the angle between the long axis of the first metatarsal shaft and the long axis of the calcaneum. This angle is normally 150 but decreases as the cavus worsens. The calcaneal pitch angle, the angle between the floor and the undersurface of the calcaneum, should be less than 30 but may be elevated in a cavus foot. The radiographs can also be used to look for signs of degenerative changes and the bones themselves may be abnormal in shape in a deformity that began early in childhood.

EXAMINER: What are the principles of managing this condition?

CANDIDATE: Firstly it is important to identify and if necessary address the underlying cause of the cavus. The patient should be examined for neuromuscular causes and investigated and referred for a neurological opinion if appropriate. The patient’s current symptoms need to be understood as well as the likelihood of progression. Management can be nonoperative with the use of orthotics to try and offload pressure areas and improve stability. Surgical treatment needs to be tailored to the individual patient’s underlying pathology, risk of progression, level of deformity and muscular imbalance. Correction of deformity without addressing the muscular imbalance will not be successful.

EXAMINER: Thank you.

1. Coleman S, Chestnut W. A simple test for hindfoot flexibility in the cavovarus foot. Clin Orthop Relat Res 1977;123:60–62.