Cavus foot (pes cavus) is an orthopedic condition defined by an abnormally high arch that persists even when bearing weight. This deformity alters the foot’s biomechanics, concentrating pressure on the heel and the ball of the foot. The rigid structure of a cavus foot often causes pain, instability, and recurrent ankle sprains. The condition can develop in one or both feet and frequently progresses over time. Determining the specific etiology is important because it dictates whether the deformity is likely to worsen and guides the appropriate medical or surgical management.
The Dominance of Neurological Disorders
Neurological conditions represent the majority of cases where cavus foot is severe and progressive, accounting for approximately 70% of all diagnoses. The high arch is not a primary bone defect but a secondary result of muscle imbalance caused by nerve damage. This imbalance leads to disproportionate muscle weakness, allowing stronger muscle groups to overpower weaker ones and pull the foot into the characteristic high-arched position.
Charcot-Marie-Tooth (CMT) disease is the most common single cause of neurogenic cavus foot, often present in over two-thirds of cases with an identifiable neurological origin. CMT is a hereditary peripheral neuropathy that progressively damages the peripheral nerves, leading to weakness in the smaller intrinsic muscles of the foot and the muscles responsible for lifting the foot, such as the tibialis anterior and peroneus brevis. The relatively stronger opposing muscles, like the peroneus longus, then pull the first metatarsal bone downward, creating the forefoot-driven cavus deformity. This process is progressive, meaning the foot deformity tends to worsen as the underlying nerve condition advances.
Other neurological disorders can also lead to cavus foot through similar mechanisms of muscle imbalance. Conditions affecting the spinal cord or brain are known culprits.
Common Neurological Causes
- Spina bifida
- Cerebral palsy
- Spinal cord tumors
- Friedreich’s ataxia
- Poliomyelitis
- Stroke
A unilateral cavus foot, affecting only one foot, often prompts physicians to investigate for a localized spinal issue, such as a spinal cord tumor or tethered cord syndrome, especially if there is no history of trauma.
Structural Inheritance and Genetic Predisposition
Some instances of cavus foot are familial, passed down through generations, but are not clearly linked to a major, named neurological syndrome like CMT. This is sometimes referred to as “pure hereditary cavus foot” or subtle cavus foot, which often presents as a bilateral and less severe high arch. Current understanding suggests that even without a formal neuropathy diagnosis, subtle genetic variations can influence the structural components of the foot, predisposing an individual to a muscle imbalance that is not pathologically progressive. This non-progressive nature distinguishes it from the deformities caused by severe neurological diseases.
Acquired Injuries and Idiopathic Cases
Cavus foot can also develop as a result of localized injury or trauma, falling into the category of acquired causes. Severe physical trauma to the lower leg or foot, such as crush injuries or fractures, can result in muscle contracture and subsequent imbalance. For example, the scarring of deep muscle compartments following compartment syndrome can lead to a fixed deformity. Malunion of fractures in the talus or calcaneus, or chronic instability of the ankle and subtalar joint, can also mechanically drive the development of a high arch. Localized nerve damage, such as injury to the peroneal nerve, also creates a muscle imbalance similar to a progressive neuropathy but confined to the site of the injury.
A significant portion of cavus foot cases, estimated to be around 20% to 30%, are classified as idiopathic, meaning the cause remains unknown after a thorough medical investigation. These cases are typically non-progressive and less severe than those with a neurological origin. The diagnosis of idiopathic cavus foot is made only after ruling out all known neurological, traumatic, and systemic causes.