FATIGUE FRACTURE - TIBIA• MERCURY IMAGING INSTITUTE • SCO 172-173 SEC 9C

CHANDIGARH• MERCURY IMAGING CENTRE • SCO 16-17 SEC 20D

CHANDIGARH

18 YR OLD FEMALE WITH H/O TIBIAL PAIN. RECENT HISTORY

OF INCREASED PHYSICAL ACTIVITY IN THE TRAINING

CAMP.

MR imaging -Single best technique in assessment of patients with

suspected tibial stress injuries in some patients with negative MR imaging findings, CT can depict

osteopenia, which is the earliest finding of fatigue cortical bone injury.

OVERVIEW OF THE CT , MR FINDINGS IN FATIGUE FRACTURES.

PATHOGENESIS

Pathogenesis of stress fracture is poorly understood. Stresses related to daily activities stimulate the remodeling process. Increased osteoclastic resorption is the initial response to abnormal stress. If increased stress persists, imbalance between bone resorption and bone replacement leads to weakening of the bone. Weight bearing, muscle actions, and muscle fatigue may play a role in increasing stress on bone. In the tibia, tensile forces are produced along its anterior convex side, while compressive forces occur along its posterior concave margin . Accelerated intracortical remodeling causes microscopic cracks, osteopenia, and formation of resorption cavities that may join in larger lesions. Stresses in cancellous bone may initially result in microfractures. If the inciting activity is not decreased, the accumulation of microdamages may result in stress fracture of cortical or trabecular bone .

POINTS TO PONDER UPON IN STRESS RELATED INJURIES

• Define the epicentre of injury

1. Cortical bone2. Cancellous bone

( Fractures in the cancellous bone appear earlier than the cortical bone).

Define the Prefracture lesions Periosteal edema Marrow edema./ marrow

bruise. Resorption cavities in the cortex. Osteopenia . Striations Gray cortical sign ( Subtle

illdefinition of the cortex) Simultaneous involvement of

the anterior and posterior tibial cortex / periosteum– explained by simultaneous involvement of the compressive and tensile forces ( important point to differentiate mitotic / infective lesions from stress related injuries)

( FRACTURE OF THE CANCELLOUS BONE WITH ASSOCIATED CHANGES IN THE MEDULLARY CAVITY , PERIOSTEUM ) Linear hypointense lines with associated Hypointense haze in the medullary cavity ( Marrow edema , bruise )Cortical thickening with hypointense haze in the soft tissue abuting the periosteum

MEDULLARY EDEMA , BRUISE , CONTUSION, MICROTRABECULAR FRACTURES.

FAT SATURATION SEQUENCE - BETTER DEPICTION OF MEDULLARY EDEMA , BRUISE , CONTUSION, PERIOSTEAL EDEMA .

PERIOSTEAL EDEMA

RESOPTION CAVITIESFocal ill-defined areas of edema / hyperintense haze on STIR / T2w sequences

SIMULTANEOUS INVOLVEMENT OF THE ANTERIOR AND

POSTERIOR PERIOSTEUM ( THIS IS AN IMPORTANT POINT

TO DIFFERENTIATE STRESS/ FATIGUE RELATED MR FINDINGS

FROM THE MITOTIC / INFECTIVE LESIONS

TI W

T2 WSTIR