66. Osteomalacia
Definition
Osteomalacia is a bone disease producing increasingly soft, brittle, flexible, and deformed bones because of a loss or shortage of calcium salts, or inadequate or delayed mineralization of osteoid in mature and spongy bone. Osteomalacia is often referred to as the adult form of rickets.
Incidence
The incidence of osteomalacia is reported to be less than 0.1% in developed countries. In areas with high vegetarian populations, it has been reported to be as high as 15%.
Etiology
Osteomalacia is produced by a metabolic disorder for which the underlying disease needs to be diagnosed.
Causes of Rickets/Osteomalacia
• Acidosis
• Chronic renal failure
• Defective matrix synthesis
• Gastrointestinal tract inadequacy
• Generalized renal tube disorders
• Miscellaneous
• Phosphate depletion
• Primary mineralization disorders
• States of rapid bone formation with or without defect in bone resorption
• Vitamin D deficiency
• Vitamin D metabolism disorders
Signs and Symptoms
• Bowed limbs
• Craniotabes (abnormal softness of skull bone, particularly along the lambdoidal sutures)
• Genu valgum
• Joint laxity
• Mild to more pronounced scoliosis
• Muscle weakness
• Pectus carinatum
• Poor dentition
• Rachitic rosary
• Triradiate pelvis configuration (the pelvis radiates in three directions)
Medical Management
Vitamin D supplementation is particularly important for infants exclusively breastfed by mothers who are also deficient in vitamin D. The infant’s supplementation should be at the rate of 400 International Units (IU) per day after the child has reached 2 months of age. Adults should receive vitamin D supplements daily and are strongly encouraged to increase (within reason) exposure to direct sunlight to aid the natural, in vivo, conversion process.
Complications
• Fractures
• Kyphosis
• Muscle cramps
• Paresthesias
• Pseudofracture
• Renal dysfunction
• Scoliosis
• Tetany
Anesthesia Implications
The anesthetist should pay particular attention to the degree of dysfunction of the patient’s kidneys. Renal dysfunction may be a significant contributing factor in the development of osteomalacia. In addition, abnormal liver function may be a major contributing factor as well. Complete metabolic profiles should be obtained preoperatively and closely reviewed for indications of either kidney or liver dysfunction. Where possible, electrolyte imbalances should be corrected preoperatively.
The patient with osteomalacia is prone to develop scoliosis and/or kyphosis. A patient with either of these maladies should undergo complete pulmonary function testing preoperatively to indicate the degree of pulmonary dysfunction that may have been produced. Frequently pulmonary dysfunction develops in a restrictive form. During general anesthesia, the anesthetist should strive to reduce the peak inspiratory pressure, either by selecting lower peak pressure in the pressure-controlled volume/ventilation setting on the anesthesia ventilator or by manually ventilating the patient using the reservoir bag. The expiratory phase should also be prolonged in the patient with any restrictive lung disease to reduce the possible degree of air trapping and barotrauma. The prolonged inspiratory:expiratory (I:E) phase should be 1:2.5, 1:3—or possibly 1:3.5—depending on the severity of the restrictive pulmonary disease.
The anesthetist must be particularly attentive to the patient’s positioning during surgery. Padding is extremely important for the patient with osteomalacia. Gel pads are greatly preferred to simple foam padding to prevent injury. The anesthetist must remember that the patient who is untreated or undertreated is much more susceptible to bone injury (see also Osteogenesis Imperfecta, p. 251).
