# Clinical Cases: Medical Imaging - Musculoskeletal

## Case 1: Distal Radius Fracture with Appropriate Imaging Selection

### Clinical Image
![Colles Fracture](case_01_image.jpg)
*Source: [Wikimedia Commons - Colles Fracture](https://commons.wikimedia.org/wiki/File:Colles_fracture.jpg) - CC BY-SA 3.0*

### Case Presentation
A 68-year-old woman presents to the emergency department after slipping on ice and landing on her outstretched right hand. She reports immediate pain and visible deformity of her right wrist. Physical examination reveals a "dinner fork" deformity with dorsal angulation at the distal wrist. There is significant swelling, tenderness, and limited range of motion. Neurovascular examination reveals intact sensation in the median, ulnar, and radial nerve distributions with palpable radial pulse. Standard PA and lateral radiographs of the wrist are obtained, which demonstrate a distal radius fracture with dorsal angulation (Colles fracture), dorsal comminution, and shortening of 5 mm. The fracture extends into the radiocarpal joint (intra-articular). Given the intra-articular nature and comminution, CT scan is obtained to better characterize the articular surface and surgical planning. CT confirms a two-part intra-articular fracture with 2 mm step-off at the articular surface. She undergoes open reduction and internal fixation with a volar locking plate. Post-operative radiographs confirm anatomic restoration of radial length, inclination, and volar tilt.

### Key Learning Points
- Radiographs (X-rays) are the first-line imaging modality for suspected fractures - fast, inexpensive, low radiation
- Standard orthogonal views (two views 90 degrees apart) are essential; special views may be needed for specific injuries
- CT provides superior bony detail and is indicated for complex fractures, articular involvement, and preoperative planning
- Key parameters for distal radius: radial inclination (22 degrees), radial length (11 mm), volar tilt (11 degrees)
- Intra-articular step-off >2 mm and radial shortening >5 mm are indications for operative fixation

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## Case 2: Occult Hip Fracture on MRI

### Clinical Image
![Hip MRI](case_02_image.jpg)
*Source: [Wikimedia Commons - Hip MRI](https://commons.wikimedia.org/wiki/File:MRI_of_knee.jpg) - CC BY-SA 4.0*

### Case Presentation
A 75-year-old woman with osteoporosis presents with left hip pain after a fall in her home 2 days ago. She reports difficulty bearing weight since the fall and has had persistent groin pain. She has no obvious deformity, and initial emergency department radiographs were read as "no acute fracture." She was discharged with a diagnosis of hip contusion. She now presents to her primary care physician with ongoing pain. Physical examination reveals tenderness with palpation over the left groin and pain with internal rotation of the hip. She is unable to perform a straight leg raise on the left. Given high clinical suspicion despite negative X-rays, MRI of the left hip is obtained. MRI demonstrates a non-displaced subcapital femoral neck fracture with linear hypointensity on T1 and corresponding hyperintensity on T2/STIR images representing the fracture line and surrounding bone marrow edema. There is no evidence of avascular necrosis. She is taken to the operating room for percutaneous screw fixation of the non-displaced fracture to prevent displacement.

### Key Learning Points
- Up to 10% of hip fractures are not visible on initial radiographs (occult fractures)
- MRI is the gold standard for detecting occult hip fractures with near 100% sensitivity and specificity
- MRI shows fracture as a hypointense line on T1 with surrounding bone marrow edema (bright on T2/STIR)
- CT has lower sensitivity than MRI for non-displaced fractures but may be used if MRI is unavailable
- Clinical suspicion should override negative X-rays; delayed diagnosis leads to fracture displacement and worse outcomes

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## Case 3: Stress Fracture Evaluation with Multi-Modality Imaging

### Clinical Image
![Bone Scan](case_03_image.jpg)
*Source: [Wikimedia Commons - Bone Scan](https://commons.wikimedia.org/wiki/File:Bone_scan.jpg) - Public Domain*

### Case Presentation
A 22-year-old female cross-country runner presents with 3 weeks of progressive left anterior shin pain. The pain started after she increased her weekly mileage for an upcoming race. It initially occurred only during running but now hurts with walking and at rest. She reports her menstrual periods have been irregular. Physical examination reveals point tenderness over the anterior tibia at the junction of the middle and distal thirds. There is no swelling, warmth, or erythema. Single-leg hop test reproduces her pain. Initial radiographs of the tibia are normal with no visible fracture line or periosteal reaction. Given the high clinical suspicion, MRI is obtained which demonstrates bone marrow edema in the anterior tibial cortex with a focal linear hypointensity consistent with a stress fracture. There is no evidence of a complete fracture. She is diagnosed with a tibial stress fracture, placed in a walking boot, and her training is modified. Laboratory evaluation reveals low vitamin D and relative energy deficiency (RED-S) is suspected. She is counseled on proper nutrition and referred to sports medicine for comprehensive management.

### Key Learning Points
- Stress fractures occur from repetitive loading; radiographs are often negative early (2-4 weeks to show changes)
- MRI is most sensitive for early stress fractures, showing bone marrow edema before cortical changes are visible
- Bone scintigraphy (bone scan) is highly sensitive but less specific; shows increased uptake at sites of bone remodeling
- Female athlete triad/RED-S (relative energy deficiency in sport) predisposes to stress fractures
- Radiograph findings of stress fracture (when visible): periosteal reaction, cortical thickening, fracture line