What structural and physiologic changes occur in the feet as people age, and how do these changes relate to foot problems encountered in elderly patients?
It is difficult to isolate foot problems of the elderly caused solely by aging, such as delayed effects of trauma, repetitive microtrauma, and metabolic disturbances. An intra-articular fracture of the great toe may reappear as painful arthrosis many years later. Premature arthrosis of the great toe, midfoot, or hindfoot may develop in recreational athletes. Chondrocalcinosis is a causative factor in degenerative arthrosis of the ankle or foot.
Evidence suggests that age-related changes in type I collagen do change the mechanical properties of ligaments, tendons, and bones. The structural changes that occur in ligaments lead to progressive stiffening of joints and decreased excursion of tendons. Structural weakness of the posterior tibial tendon may lead to an acquired flatfoot deformity, which is often painful in women older than 50 years.
Collagen changes lower the fracture threshold of bones. This is compounded by osteoporosis, another possible effect of increasing age. The metatarsal and calcaneus are most susceptible to fatigue and insufficiency fractures. Painful pressure distribution on the plantar surface may result.
Weakening of intermetatarsal ligaments is associated with splaying of the metatarsals, which, in turn, predisposes to bunion/hallux valgus and bunionette formation. Contracture of the triceps surae complex leads to progressive loss of ankle dorsiflexion and is associated with increased pressure beneath the toes and metatarsal heads.
The peripheral nerves of the foot have the longest axons in the body and deteriorate with time. The loss of innervation of the intrinsic muscles of the foot leads to muscle imbalance of the toe and possibly to claw-toe deformity. Loss of intrinsic muscle mass decreases the energy-absorbing padding of the foot; plantar foot pain or painful keratosis forms beneath bony prominences.
The fibrofatty padding that cushions the metatarsal heads and the posterior calcaneus lose fat content over time. The resulting fibrosis leads to increased pressure on the skin and the bone. The skin itself ages and becomes more likely to produce keratotic lesions over bony prominences.
The geriatric patient is likely to develop painful keratoses (calluses), toe deformity, forefoot splaying,bunion, decreased motion, and arthrosis because of physiologic changes associated with aging. Problems may be compounded by a decrease in function of the neuromuscular system and the cardiovascular system. Weakness, spasticity, dysequilibrium, arterial insufficiency, and venous congestion all lead to more problems in the foot.