Age / Sex : 17 / M

Chief complaint: Right lower leg pain and swelling, 5 months ago.


What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).


Courtesy : 김동현 (Dong Hyun Kim), 보라매병원 (SMG-SNU Boramae Medical Center)

Stress fracture (Medial tibial stress syndrome, shin splints)

Discussion

Findings: 

Localized periosteal reaction is appreciated along the anterior surface of the mid tibial shaft.

MRI findings: MR images show focal cortical hypertrophy with segmental periosteal reaction at anterior tibia mid-diaphysis, with linear dark intensity line at tibial cortex, adjacent T2 hyperintensity.

Bone scan : There is focal increased uptake in the right tibia cortical area, anterolateral aspect

Differential Diagnosis:

Osteoid osteoma.

Osteomyelitis

Discussion:

Stress fractures refer to fractures occurring in bone due to a mismatch of bone strength and chronic mechanical stress placed upon the bone. Fractures can either be:

• fatigue fracture: abnormal stresses on normal bone


• insufficiency fracture: normal stresses on abnormal bone

Radiographs have limited sensitivity for an acute stress fracture, although repeat delayed radiographs may show changes of healing. MRI is the most sensitive modality for diagnosis of stress fracture and is an important tool to distinguish high and low-risk fractures to help clinicians for management plans.

Clinical presentation

Stress fractures normally present with worsening pain with a history of minimal or no trauma. In the lower (weight-bearing) limb, there is often a history of a recent increase of physical activity or significant alteration in the type or duration of normal athletic activity.

Location

Stress fractures are far more common in the lower limb (~95%) than the upper limb.

High-risk sites of stress fractures are locations at greatest risk of a progression to complete fracture, displacement or non-union. These sites are under tensile stresses and have poor vascularity. These include:

• superolateral femoral neck


• anterior tibial cortex


• 5th metatarsal base


• great toe sesamoids (hallux sesamoids)


• talar neck


• posterior cortex of tarsal navicular


• 2nd to 4th metatarsal necks - e,g. March fracture


• medial malleolus


• femoral head


• patella


• pars interarticularis of the lumbar spine

Low-risk sites of stress fracture are at low risk of complications and are under compressive stresses. They include:

• calcaneus


• pubic rami


• sacrum


• ribs


• proximal humerus/humeral shaft


• posterior medial tibial shaft


• lateral malleolus


• 2nd to 4th metatarsal shafts

Radiographic features

Plain radiographs have poor sensitivity (15-35%) in early-stage injuries, which increases in late-stage injuries (30-70%). MRI is the modality of choice with a sensitivity reported to reach close to 100%.

Plain radiograph

Plain radiographs have poor sensitivity in detecting stress fractures, as positive findings may take months to appear. During the first few weeks after the onset of symptoms, x-rays of the affected area may look normal.

Positive findings can include:

• grey cortex sign: subtle loss of cortical density in early-stage stress injury


• increasing sclerosis or cortical thickening along the fracture site


• periosteal reaction/elevation


• may take up to 2 weeks to be detectable


• fracture line

Nuclear medicine

Bone scans can show evidence of stress fracture within a few days upon the onset of symptoms. As a modality, it is considered less sensitive than MRI .

Stress fractures on bone scintigraphy appear as foci of increased radioisotope activity ('hot spot') due to increased bone turnover at the site of new bone formation. However, as with all bone scintigraphy, this is non-specific; the increased uptake can also be due to osteomyelitis, bone tumors or avascular necrosis.

CT

The findings are similar to plain radiography, including sclerosis, new bone formation, periosteal reaction, and fracture lines in long bones.

CT may be useful in differentiating stress fractures from bone tumor or osteomyelitis if the plain radiographs are negative and bone scans are positive.

MRI

MRI is the most sensitive modality for detecting stress fracture, and may also be useful for differentiating ligamentous/cartilaginous injury from bone injury.

Typical MRI appearance of stress fracture includes:

• periosteal or adjacent soft tissue edema


• band-like bone marrow edema


• T1 hypointense fracture line evident in high-grade injury

The use of MRI grading system for bone stress injuries is helpful for predicting recovery time (important especially for athletes).

References:

1. Berger FH, de Jonge MC, Maas M. Stress fractures in the lower extremity. The importance of increasing awareness amongst radiologists. (2007) European journal of radiology. 62 (1): 16-26. doi:10.1016/j.ejrad.2007.01.014 - Pubmed


2. Marshall RA, Mandell JC, Weaver MJ, Ferrone M, Sodickson A, Khurana B. Imaging Features and Management of Stress, Atypical, and Pathologic Fractures. (2018) Radiographics : a review publication of the Radiological Society of North America, Inc. 38 (7): 2173-2192. doi:10.1148/rg.2018180073 - Pubmed

     3. Radiopaedia, https://radiopaedia.org/articles/stress-fractures