Bone Stress Injuries

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Original Editor - Puja Gaikwad

Top Contributors - Puja Gaikwad, Kim Jackson, Vidya Acharya, Rucha Gadgil and Lucinda hampton  

Introduction

Bone Stress Injuries (BSI) are overuse injuries associated with repeated loading of bone by strenuous weight-bearing activities (such as running, jogging, marching) and inadequate recovery periods. BSI’s represent the failure of skeleton bone to withstand repetitive loading, leading to structural fatigue, localized bone pain, and tenderness around the area. Bone Stress Injuries (BSI) are commonly seen in avid runners, track and field athletes, endurance athletes, military recruits, gymnasts, dancers, but also among otherwise healthy people who have recently started the new or intensive physical activity accounting for 10% of all sports-related injuries. BSI differs in severity, with initial findings of periosteal edema and marrow edema. In more severe conditions, stress fractures with distinct fracture lines are present. Stress fractures account for > 10% of total sports-related injuries and it could be as high as 30% in running.

Pathophysiology

When the bone is subjected to mechanical forces the forces cause adaptive changes in the trabecular (i.e internal architecture of bone), followed by secondary adaptive changes in the bone cortex (i.e external architecture of bone). In trabecular bone, the initial response to mechanical forces is the microdamage of the trabecular which is repaired by a microcallus. In cortical bone, the initial response to an increase in mechanical forces is osteoclastic activity (bone break down) which leads to resorption of bone. Osteoblastic cellular activity fills the resorption cavities with a lamellar bone. However, bone formation is slower than bone resorption.

Bone Stress Continuum

There is a continuum of bone stress injury varying from "normal to bone strain to stress reaction to the ultimate progression of a stress fracture. These injuries sit on a continuum whereby they start with a stress reaction (often called a ‘hot spot) which can progress towards a stress fracture and finally towards a complete bone fracture. Essentially, as the BSI progresses along the continuum, the longer it takes to recover. Therefore, an understanding and early recognition of these injuries are critical to any athlete and their sports-specific goals.

On the continuum, bone is accruing microdamage following mechanical forces from loading, for example from running. Microdamage accrues proportionate to the number of loading cycles, rate of loading, and strain magnitude of the skeleton bone. When the bone is given adequate time between loading cycles to recover the rate of bone resorption is met by the rate of bone repair and remodeling. However, when insufficient time is given for the bone to adapt to external mechanical forces, an imbalance may occur between bone remodeling and microdamage to the bone resulting in structural deformation of bone and fatigue This accumulative microdamage can continue to progress and result in further pathology. It can progress from the bone being in a state of stress reaction through to stress fracture and at times even frank cortical fracture.