The cavus foot has limited motion and absorbs shock poorly. Although it is often only a minor problem in multidirectional sports or sprinting, it can be a severe problem for long distance runners, especially on unyielding surfaces.
With all types of cavus feet, stretching exercises are indicated. A good one has the runner standing on the 35 deg incline board with the toes facing downhill and the heel facing uphill. They then rock back on the heels, strengthening those muscles in the front of the leg and stretching the muscles in the back of the leg. By inverting and everting the foot, muscles about the ankles are stretched and strengthened. After completing this exercise, the runner than reverses the position and allows the heels to sag, with helps to stretch the posterior muscle groups and plantar fascia.
The treatment of choice is functional biomechanical orthotics. Simple alterations to the shoes or addition of heel lifts may help. But for long term care, orthotics work the best. However, the three categories of cavus feet require different types of orthotics…
Flexible Cavus Feet
The flexible cavus foot will often have a callus underneath the second metatarsal. This is usually due to a hypermobile plantarflexed first metatarsal which doesn’t bear weight effectively. A biomechanical semi-rigid orthotic posted with a rearfoot varus post will increase the vector of the peroneus longus tendon, thereby increasing plantarflexion of the first metatarsal. In additional, soft tissue supplement extensions, added to the orthotics, can alleviate this problem.
Semiflexible Cavus Feet
A semiflexible cavus foot has more advanced contracture or clawing of the toes and probably more serious callus and/or complaints of pain underneath the metatarsal heads. There is an obvious forefoot drop when compared to the rearfoot. This foot has a talipes equinus and often has a more rigid forefoot valgus. This type of foot may be prone to plantar fascial strains and Achilles tendon problems. Overuse injuries can include those normally seen when the foot pronates too much, but will also include those associated with a foot that does not absorb shock well. It may be prone to shin splints and stress fractures.
Orthotics for this foot should be more flexible than for the flexible cavus foot. A slight decrease in the calcaneal inclination angle of the orthotic should be prescribed to allow for shock absorption. The forefoot should be balanced and the reafoot should be perpendicular. A 1/8″ heel raise can be used, and should be made out of a shock absorbing material. Having orthotics does not guarantee that the flexible cavus foot will not turn into a semiflexible or even rigid cavus foot. Often the cavus foot is due to some form of neuromuscular imbalance which is not diagnosed.
Rigid Cavus Feet
The rigid cavus foot is the most difficult foot to work with. It always has a tight plantar fascia and responds poorly to semiflexible orthotics. The forefoot is usually dropped and there is often a callus under the first and/or fifth metatarsal head. The toes are clawed with or without weight bearing. Achilles tendon problems often occur. Patients with this type of foot absorb shock very poorly and are more prone to stress fractures as well as overuse injuries from increased stress. The patient is best suited to an orthotic mold that is very soft. A more radical decrease in the calcaneal inclination angle is needed as well as perpendicular rearfoot posts. Soft tissue supplements are needed both as a forefoot extension and as a 1/8″- 3/16″ heel lift.
The cavus foot is a complex deformity which is classified in three different groups. Treatment requires specialized orthotics and stretching exercises.