Lateral view of right ankle at time of injury
Lateral view 12 weeks postinjury
A 27-year-old woman presents for follow-up of a nondisplaced right talar neck fracture. She was treated with a nonweight-bearing boot for the past 12 weeks. Figure 1 shows a lateral radiograph of the right ankle at the time of injury, and Figure 2 shows a lateral radiograph at 12 weeks from injury. The 12-week radiograph shows loss of bone mineral density (BMD), most notably at the calcaneus, due to her nonweight bearing.
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Treatment of fractures of the lower extremity often requires cast immobilization with nonweight bearing. Nonweight bearing for an extended period of time is known to decrease BMD in the affected extremity. BMD both proximal and distal to the fracture site in the affected extremity decreases over time with nonweight bearing. Inactivity, or a lack of mechanical loading, causes accelerated bone turnover as bone resorption outpaces bone formation. One example of this: astronauts can lose 1% to 2% of their BMD every month in space due to nonweight bearing. Injured soldiers in World War II on bed rest were found to have a decrease in BMD associated with increased bone resorption and hypercalciuria. Bone mineral density loss of up to 50% in the affected extremity can occur with nonweight bearing past 6 to 12 months. A decrease in BMD after nonweight bearing can persist long after the fracture is healed and may to some degree persist permanently in adults. Children and adolescents reverse BMD loss within 3 to 6 months after weight bearing is resumed, and adults generally take 6 to 12 months to regain baseline BMD scores. Weight bearing increases BMD as forces placed across bone accelerate bone formation.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
- Ceroni D, Martin XE, Delhumeau C, et al. Recovery of decreased bone mineral mass after lower-limb fractures in adolescents. J Bone Joint Surg Am. 2013;95:1037-1043.
- Bloomfield SA. Disuse osteopenia. Curr Osteoporos Rep. 2010;8:91-97.