Femoral diaphyseal stress injury

Femoral diaphyseal stress injuries comprise different grades of a stress response and/or a stress fracture of the femoral diaphysis.

Epidemiology

Femoral diaphyseal stress injuries are seen in middle and long-distance runners and military recruits ^1-5 with a reported incidence of up to 199/100000 person-years in military recruits ². The femoral diaphysis is affected in about 20-22% of all stress injuries affecting the femur ^2,3. Of those most (>80%) are located proximally ^2,5 and the medial side seems more commonly affected ^4,5.

Risk factors

Typical activities increasing the risk of femoral diaphyseal stress fractures include marching or running long distances ^1-3.

Clinical presentation

Symptoms can be vague and include hip pain, hip-related groin pain, or pain in the thigh related to exercise ^1,2, knee pain can occur from a distal stress injury.

Complications

Complications of stress injuries include the following ²:

• progression to fracture (in early stages)
• displacement
• delayed union
• nonunion

Pathology

Stress injuries develop from repetitive loading forces, which lead to morphological alterations of the bony structure and ultimately result in a stress fracture if the causative loading forces are not withheld ^6,7. During weight-bearing, the medial aspect of the femoral shaft is exposed to compressive forces, whereas the lateral aspect is subject to tensile forces ^1,4,5.

Etiology

The typical etiology of a stress injury is overuse causing micro-damage to the weight-bearing parts of the bone exceeding its repair capacity ^6,7.

Location

Possible locations for diaphyseal stress injuries are sites of increased compressive load and include the weight-bearing parts and involve most frequently the proximal femoral diaphysis with the medial part being more susceptible ^1,2,4 and less commonly the middle, distal or entire shaft area ^2,5.

Radiographic features

General radiographic features include periosteal reaction, endosteal bone marrow edema, and a linear osseous discontinuity. Plain radiographs are recommended as an initial imaging modality, whereas MRI is the modality of choice if advanced imaging is indicated ⁸.

Plain radiograph

Plain radiographs will not show anything in the very early stages, later it may show subtle cortical lucencies followed by thickening or periosteal alterations ⁷. A stress fracture will be visible as linear diaphyseal lucency with periosteal reaction. Signs of callus formation may occur in later stages.

CT

Like in radiographs a stress fracture will be apparent as linear diaphyseal lucency with associated periosteal reaction and/or cortical thickening at the fracture site. There might be density changes in the adjacent endosteal bone marrow, better visible on dual-energy CT.

MRI

Images should be acquired in all three planes with a combination of water-sensitive sequences and T1 weighted sequences.

On MRI a stress injury is characterized by periosteal edema and endosteal bone marrow edema like signals in different stages. Linear or globular cortical signal changes are seen in case of a stress fracture ^1,4,8. Bone marrow edema like signal in the setting of a stress injury should show a gradual signal intensity transition with indistinct margins and interspersed fatty marrow ⁷.

Signal characteristics

• T1: mildly hypointense, with effacement but not a replacement of the fatty marrow
• T2FS/PDFS: hyperintense

An MRI grading scheme for stress injuries ⁴ originally proposed for the tibia ⁵:

• grade 1: periosteal edema without bone marrow changes
• grade 2: bone marrow edema like signal seen on fat-saturated T2 weighted images
• grade 3: bone marrow edema like signal also clearly seen on T1 weighted images
• grade 4: fracture line present on T1 weighted and/or T2 weighted images

Nuclear medicine

Bone scintigraphy (^99mTc-MDP) is sensitive but less specific than radiography and leads to increased focal or linear tracer uptake ^5,8.

Radiology report

The radiological report should include a description of the following:

• the exact location and orientation
• periosteal changes
• endosteal bone marrow changes
• fracture line (if present) with the extent
• surrounding muscular tissue
• rating whether it is a stress response or a stress fracture, which can comprise the above grading scheme

Treatment and prognosis

Management is typically conservative if there is no complete cortical break or displacement evident. Treatment typically includes activity modification, restricted impact activities e.g. weight-bearing. The patient can start with normal weight-bearing activities and a gradual return to sports and athletic activity once the pain has resolved ^5,8. A treatment algorithm based on four different phases has been developed ⁹.

Non-steroidal anti-inflammatory drugs should be avoided as these may impair bone healing ⁸.

An intramedullary rod may be considered in cases with delayed union or nonunion.

Differential diagnosis

Differential diagnoses of medial stress injuries include the following ⁷:

• atypical femoral fracture
  • associated with biphosphonates
  • usually laterally located
  • focal lateral cortical thickening
  • ‘medial spike appearance’
• pathological fracture
  • might be challenging
  • more likely in elderly patients without repetitive activities
  • homogeneously T1-hypointense signal with well-defined margins
  • infiltration of the fracture space in cancellous bone
  • aggressive periosteal reaction
• primary lymphoma
• Ewing sarcoma

See also

• stress response
• stress fracture