PDF《Management and Prevention of Bone》

journal of orthopaedic &

sports physical therapy?|?volume 44?|?number 10?|?october 2014?|?749 H umans are structurally and physiologically developed for long-distance running, which likely evolved during our time as hunters and gatherers.

Althoughtheabilitytohuntandgatherisnolonger an evolutionary requirement, many people continue to run long distances today to take advantage of the well-known health and wellness benefits of endurance exercise. Unfortunately, distance running also carries the risk of developing overuse injuries, which in bone consist of bone stress injury (BSI). A BSI represents the inability of bone to withstand repeti- tive mechanical loading, which results in structural fatigue and localized bone pain and tenderness. Bone stress inju- ries occur along a pathology continuum beginning with stress reactions, which can progress to stress fractures and, ul- timately, complete bone fractures. The purpose of this commentary is to discuss management and prevention options for BSIs in runners. In doing so, information is provided on the pathophysiology, epi- demiology, risk factors, clinical diagnosis, and classification of BSIs. PATHOPHYSIOLOGY OF BSI T he pathophysiology underlying BSI remains somewhat speculative;

however, there is growing consensus that it involves an imbalance between load-induced microdamage formation and its removal. A theoretical model is presented in FIGURE 1. The skeleton is ex- posed to mechanical loading during run- ning, which causes bones to deform. The amount of deformation depends on the load magnitude and ability of bone to re- sist deformation, and is often expressed as strain. Strain refers to the change in length per unit length of a bone. It is a unitless value;

however, because it is small for bone, it is often expressed as microstrain (?ε). Attachment of strain gauges to the tibia in select individuals has demonstrated compressive and ten- sile bone strains of

417 to

2456 ?ε during running.1 While the safety factor between these strains and those required to break cortical bone in tension is large (7300 ?ε),6 strains below the level required for fracture are capable of generating micro- scopic damage (termed microdamage) (FIGURE 2A). Microdamage formation is thresh- old dependent, with the threshold for its formation depending on the interac- T TSYNOPSIS: Bone stress injury (BSI) repre- sents the inability of bone to withstand repetitive loading, which results in structural fatigue and localized bone pain and tenderness. A BSI occurs along a pathology continuum that begins with a stress reaction, which can progress to a stress fracture and, ultimately, a complete bone fracture. Bone stress injuries are a source of concern in long-distance runners, not only because of their frequency and the morbidity they cause but also because of their tendency to recur. While most BSIs readily heal following a period of modified loading and a progressive return to running activi- ties, the high recurrence rate of BSIs signals a need to address their underlying causative factors. A BSI results from disruption of the homeostasis between microdamage formation and its removal. Microdamage accumulation and subsequent risk for development of a BSI are related both to the load applied to a bone and to the ability of the bone to resist load. The former is more amenable to intervention and may be modified by interventions aimed at training-program design, reducing impact-related forces (eg, instructing an athlete to run softer or with a higher stride rate), and increasing the strength and/or endur- ance of local musculature (eg, strengthening the calf for tibial BSIs and the foot intrinsics for BSIs of the metatarsals). Similarly, malalignments and abnormal movement patterns should be explored and addressed. The current commentary discusses management and prevention of BSIs in runners. In doing so, information is provided on the pathophysiology, epidemiology, risk factors, clini- cal diagnosis, and classification of BSIs. T TLEVEL OF EVIDENCE: Therapy, level 5. J Orthop Sports Phys Ther 2014;