4 Advanced Imaging

Laura M. Fayad and Jonathan Samet

Abstract

This chapter will explain when and why certain radiologic tests should be ordered for orthopaedic conditions of the wrist. Examples of multiple common orthopedic wrist entities will be discussed and shown.

Wrist MRI – CT – scaphoid fracture – ganglion cyst – arthritis

4 Advanced Imaging

I. Computed Tomography (CT)

Advantages:
- Excellent for bone detail.
- Identifies small bone fragments better than MRI.
- Identify fracture lines.
- Can identify bone matrix of lesions better than MRI.
- Can identify sclerosis and calcification better than MRI.
- Very fast (seconds), much faster than MRI (wrist MRI25-30 minutes).
- Can image with metal hardware in place.
Disadvantages:
- Radiation exposure: Lower dose in extremities however.
- Cannot see bone marrow edema.
- Tendon evaluation limited.
- Ligament evaluation poor.
- Soft tissue evaluation limited.

II. MRI

Advantages:
- Excellent soft tissue detail.
- Excellent for tendon and ligament evaluation.
- Very sensitive for fluid (bone marrow edema, effusion, tenosynovitis).
- Very sensitive for occult fracture (useful after negative X-ray).
- Excellent to characterize soft tissue masses (fat, cyst, solid mass etc.).
Disadvantages:
- Images can be degraded by motion artifact.
- Difficult to image with orthopedic metal hardware due to MRI artifact.
- Much longer scanner times than CT.
- Calcification and small bone fragments are hard to visualize.

III. Wrist Trauma

Bone marrow edema
- T2 hyperintense.
- T2 hyperintensity is accentuated with T2 fat suppression (T2 fat suppression, short tau inversion recovery [STIR]).
- T1 hypointensity.
Fracture
- Acute
  - Fracture lines are linear and T1 hypointense.
  - On T2, fracture lines can be T2 hypointense or T2 hyperintense depending on if there is fluid in the fracture cleft or not.
- Chronic (unhealed)
  - Fracture lines persist.
  - Sclerotic margins are hypointense on T1 and T2.
  - Persistent bone marrow edema.
  - Small cyst formation along fracture margin.
- Scaphoid waist fracture (► Fig. 4.1)
  - Acute or chronic fracture line as above.
  - Significant bone marrow edema around the fracture line.
Overuse injury and others
- Physeal stress injuries in skeletally immature.
- Physis is T2 slightly hyperintense and T1 hypointense.
- Can request optional three-dimensional cartilage sequence for better evaluation.
- Physis becomes thickened and irregular.
- Classic example is “gymnast’s wrist” (► Fig. 4.2).
Extensor carpi ulnaris (ECU) tendinopathy
- Common cause of ulnar sided pain.
- Tendinosis is T2 hyperintense (grayish), unlike normal black tendon signal (► Fig. 4.3).
- Partial tears will have T2 hyperintense (white) fluid clefts.
- Can have associated tenosynovitis—T2 hyperintense fluid rim around ECU.
Triangular fibrocartilage complex tear
- Cause of ulnar sided pain.
- Triangular fibrocartilage disc is T2 hypointense (black).
- Two distal attachments to ulna—fovial and styloid; can have some T2 grayish signal normally due to fibrovascularity.
- T2 hyperintense fluid signal to diagnose tear (► Fig. 4.4).
Scapholunate ligament tear
- On X-ray and CT, can be seen as widening of scapholunate interval (► Fig. 4.5).
- On MRI, T2 hyperintense (fluid bright) gap instead of expected T2 hypointense ligament.