Examination of the patient with a cavus foot should aim to answer several questions, which will guide management:
What is the extent of the deformity?
- is there just forefoot plantarflexion or is the hindfoot involved?
- is the whole forefoot plantarflexed or (more commonly) is the first ray most plantarflexed?
- is the hindfoot neutral or varus in the coronal plane
- is the hindfoot dorsiflexed (commonest), neutral or plantarflexed in the sagittal plane?
- is there significant toe clawing?
- are there proximal limb problems such as length discrepancy, or deformity at hip or knee?
What other effects is the deformity creating?
- calluses or skin breakdown over toe deformities
- calluses under metatarsal heads
- calluses along the lateral foot border, especially under the base of the fifth metatarsal - this is usually due to hindfoot varus
- ankle instability - do the draw and tilt tests to distinguish functional instability from actual ligamentous insufficiency
- shoe problems - inspect shoes and orthoses
Is the deformity flexible or fixed?
The Coleman block test. Varus of the right hindfoot corrects when the first ray hangs free.
- does the arch correct at all on stretching or weightbearing?
- can the first ray be brought level with the other rays?
- if the hindfoot is in varus on standing, does it correct passively or on the Coleman block test?
- It is often easier to appreciate passive correctability from behind with the patient kneeling or prone.
- The Coleman block test distinguishes hindfoot varus due to the tripod effect from fixed varus. The patient stands on a wooden block thick enough to let the first ray hang freely over the edge. The hindfoot position is measured with the first ray on the block. The first ray is then moved to hang freely over the edge of the block and the hindfoot position measured. If it corrects to a normal position the varus is purely driven by the first ray plantarflexion and can be treated by correcting or accommodatng the first ray; if it does not, the hindfoot varus is fixed and should be managed on its own merits. Standing hindfoot alignment radiographs can be used to confirm the findings of the clinical test.
- if the hindfoot is in equinus, does it correct passively? Do the Silferskjold test to distinguish between gastrocnemius and soleus tightness.
- is any hip or knee deformity fixed or flexible?
Is there an underlying neurological abnormality?
- a full neurological examination (not just the foot) is required
- light touch, pain, protective sensation, vibration and position sensation
- look for upper limb weakness, ataxia or muscle wasting (especially in the intrinsic muscles of the hand)
- spinal deformity or external abnormalities such as a hairy patch
- proximal limb weakness
- gait abnormalities
- specific comparison of strength in the main muscle groups which may be in imbalance in cavus:
- tibialis anterior vs peroneus longus
- tibialis anterior, EHL and FHL
- peroneus brevis vs tibialis posterior
- look for intrinsic wasting
- check for protective sensation