X-Wrist

Indication/Technique

Indication

X-rays of the wrist joint are requested frequently, particularly at the Emergency Assistance department. They are used primarily to confirm/exclude a fracture in the diagnostics of (rheumatoid) arthritis, and in functional hand and wrist symptoms.

Technique

By way of repetition of anatomical terminology: volar/palmar (palm of hand), dorsal (back of hand), ulnar (side of little finger) and radial (side of thumb). See also figure 1.

Figure 1. Palmar flexion / volar flexion vs. dorsal flexion (dorsiflexion) & radial abduction vs. ulnar abduction.

When asked to confirm or exclude a fracture, the wrist should be imaged in at least two directions, as in any conventional image.

A standard examination frequently consists of a posterior-anterior (PA) image and a lateral image.  In a PA image, the shoulder is abducted to 90° and the elbow flexed to 90° (fig. 2). The wrist is placed flat on the X-ray plate.

Figure 2. Technique for PA image of the wrist.

A lateral image is obtained by turning the wrist with the thumb upwards (fig. 3).

Figure 3. Technique for lateral image of the wrist.

To assess whether an image is purely lateral, consider the relationship between the capitate, pisiform and the scaphoid bones.  The palmar cortex of the pisiform should be located centrally between the palmar cortex of the capitate and the scaphoid (fig. 4).
Note: additional anatomy is discussed in the Normal Anatomy section.

Figure 4. Technique for purely lateral image of the wrist. Ideally, the palmar cortex of the pisiform is located exactly between the palmar cortex of the capitate and the scaphoid (see top left). In the lower two positions, the image is not purely lateral.

Due to the complex shape of the scaphoid and the overlap of other carpal bones, a standard examination will not suffice. A so-called ‘scaphoid series’ can be obtained when a scaphoid fracture is suspected. Up to the present, there is no consensus in the literature what this series should include: both positions and number differ among hospitals/specialists. In most cases, the scaphoid is imaged in at least three directions. 
Some common images include the PA image in ulnar deviation (fig. 5), 60° oblique image in ulnar deviation (fig. 6), fist image (fig. 7), lateral image (fig. 8).

Figure 5. Technique for PA image in ulnar deviation (left wrist).

Figure 6. Technique 60° oblique image in ulnar deviation (left wrist).

Figure 7. Technique for fist image (left wrist).

Figure 8. Technique for lateral image (left wrist).

Normal anatomy

The wrist is made up of a number of complex joints. 
Some key structures:

  • Radiocarpal joints; articulation between the radius and the first row of carpal bones (carpalia). 
  • Distal radioulnar joint (DRU joint); articulation between the distal radius and the distal ulna. 
  • The triangular fibrocartilaginous complex (TFC complex), comprising the articular disc. This structure separates the radiocarpal joint from the DRU joint.

Via the lunate fossa and the scaphoid fossa, the radius connects to both the lunate and scaphoid bones (fig. 9).
The DRU joint (together with the proximal radioulnar joint) facilitates the pronation and supination movement of the arm. The convex joint surface at the lateral side of the ulna communicates with the concave sigmoid notch on the radius (fig. 9).

Figure 9. The distal radioulnar joint and the radiocarpal joint.  The distal radius has three concave articulating surfaces; sigmoid notch (green), lunate fossa (blue) and scaphoid fossa (yellow).

The TFC complex connects the radius, the ulna and the carpal bones and is a key stabilizer of the distal radioulnar joint.  It also acts as a shock absorber for axial forces and is an extension of the articulating radiocarpal surface. It is located between the ulnar styloid process (= projection at the distal part of the ulna) and the distal radius (immediately next to the sigmoid notch).
The TFC complex consists of a central triangular fibrocartilaginous disc (=TFC) which is surrounded by two ligamentary structures; the dorsal and palmar radioulnar ligament (fig. 10). Additionally, the complex includes the tendon shaft of the extensor carpi ulnaris muscle and the ulnocarpal ligaments (ulnolunate ligament & ulnotriquetral ligament).

 Figure 10. The TFC complex (TFCC) RUL's = radioulnar ligaments. UCL's = ulnocarpal ligaments, where UL = ulnolunate ligament and UT = ulnotriquetral ligament.

The carpal bones can be subdivided into a proximal row (scaphoid, lunate, triquetrum) and a distal row (hamate, capitate, trapezium, trapezoid), see figure 11/12. 
On the palmar side of the triquetrum is the pisiform, this is a sesamoid bone in the flexor carpi ulnaris tendon. The pisiform plays no role in the kinetic movement of the proximal row.

♦ Figure 11. Carpal bones. Normal anatomy.

♦ Figure 12. Normal anatomy of the hand. PIP = Proximal interphalangeal joint, DIP = distal interphalangeal joint, MCP = metacarpophalangeal joint, S= scaphoid, L = lunate, Tri = triquetrum, P = pisiform, Tm = trapezium, T = trapezoid, C = capitate, H = hamate.

A few rules of thumb:

  1. So Long To Pinky, Here Comes The Thumb
  2. Some Lovers Try Positions That They Can Not Handle
  3. She Looks Too Pretty, Try To Catch Here

Scaphoid bone (proximal).
Lunate bone (proximal).
Triquetral bone (proximal).
Pisiform bone (proximal).
Trapezium bone (distal).
Trapezoid bone (distal).
Capitate bone (distal).
Hamate bone (distal).

PA Image:

Characteristics of a normal PA image:

  • The joint spaces between the carpal bones are the same everywhere; in adults 1-2 mm. Broadening of a joint space suggests traumatic injury (ligamentary or ossal). If the space is narrow, think of degenerative disorders.
  • Three arcs can be drawn on a normal PA image (fig. 13). These Gilula's arcs are the proximal rim of the first carpal row (I), the distal rim of the first carpal row (II) and the proximal rim of the second carpal row (III). The arcs should curve smoothly. When one of the arcs is interrupted at any place (‘step-off'), be alert for a fracture/ligamentary damage. 

♦ Figure 13. Gilula carpal arches.

  • In normal situations, the joint surface of the distal radius angulates somewhat towards the ulna (fig. 14). The radial inclination is the angle between the radial styloid and the vertical mechanical axis of the distal radius (normal values 21 - 25°). The radial length is the vertical distance between the radial styloid and radial rim of the distal ulna (normal values 10 - 13 mm).

Figure 14. Radial inclination & radial length.

Lateral Image:

The overprojecting carpal bones complicate the assessment of lateral images. Tip: first try to identify the moonshaped configuration of the lunate and then look for the contours of the scaphoid and capitate (fig. 15).

♦ Figure 15. Lateral image of the wrist; normal anatomy. MC III = metacarpal III.

Characteristics of a normal lateral image:

  • Importantly, the radius, lunate, capitate and MC III should be aligned. The lunate can be recognized by its moonshaped configuration.
     
  • All contours are smooth. Particularly on the dorsal side of the radius, there should be no visible irregularities (caveat: fracture!).
     
  • The joint surface of the radius normally angulates somewhat towards palmar. If not, be alert for a fracture. The palmar tilt (inclination) could be determined (fig. 16). It usually has an angle of 10° (range 2 - 20°).

Figure 16. Palmar tilt: the angle between the longitudinal axis of the radial shaft and the joint surface of the distal radius.

Movement of the Carpal Bones

In a healthy wrist, there is a balanced interaction between the proximal and distal rows of the carpal bones. The carpal bones can move in the flexion/extension plane and in the ulnar/radial plane. Relative movements are complex and are not addressed in this course.  
Key points:

  • In ulnar movement of the wrist, the scaphoid will reach its full length (see also the scaphoid series in the Technique section).
     
  • Be aware of the fact that the lunate and scaphoid on PA images may assume different configurations with flexion/extension of the wrist (fig. 17). Under wrist flexion and radial deviation, the scaphoid will angulate towards palmar and therefore shorten. This gives the scaphoid the configuration of a signet ring, the so-called signet ring sign / scaphoid cortical ring sign. The signet ring configuration occurs in a normal wrist, but can also be seen in pathologic scaphoid rotation, as in scafolunar dissociation (see Pathology section).

Figure 17. Positions of the lunate and scaphoid in flexion and extension. Signet ring sign (scaphoid) under wrist flexion.

Checklist

The following points may be used as a guide to assess wrist X-rays.

  1. Has everything been imaged? Clinical suspicion of scaphoid fracture? (scaphoid series!).
  2. Is there soft tissue swelling?
  3. General impression of the bone; osteoporosis? Ossal lesions? 
  4. Is there an incongruence of the radiocarpal joint or the DRU joint?
  5. Check the full length of the cortex. Is there an interruption or asymmetry anywhere?
  6. Position of the carpal bone; is there an interruption of one of Gilula's arcs? Are the joint spaces evenly distributed between the carpal bones? Are the radius - lunate - capitate - MC III in alignment?
  7. In the event of fracture: orientation of the fracture line, intra- or extra-articular, extension and position (dislocation/angulation/rotation/shortening)? Classification?
  8. As needed, calculate radial inclination, radial length and palmar tilt.
  9. Changes versus previous examinations?

Pathology

Distal Radial Fracture

A distal radial fracture is a common fracture of the wrist and is seen frequently in the elderly with osteoporosis. 
In terms of treatment, it is important to know whether the fracture continues into the joint (= intra-articular). Additionally, extension and position (dislocation/angulation/rotation/shortening) should be carefully observed.

There are various classifications for a distal radial fracture. A commonly used classification is the Fernandez classification (fig. 18):

  • Bowing fractures (Colles, Smith).
  • Shear fractures (dorsal/volar Barton).
  • Intra-articular compression fractures (die-punch).
  • Avulsion fractures of ligament insertions.
  • Combined/complex high-energy fractures.

Figure 18. Fernandez classification.

Irrespective of the classification used, the extent and position (dislocation/angulation/rotation/shortening) should be carefully identified.

Some commonly used terms in the workplace are Colles’ fracture, Smith's fracture and Barton's fracture. 
Colles’ fracture is a transversal fracture (bowing fracture) and also the most common distal radial fracture. It usually occurs as a result of a fall on an extended hand with the wrist in dorsiflexion. Dorsal angulation/dislocation of the distal fragment is characteristic (fig. 19/20).

Figure 19. Colles’ fracture (bowing fracture).

♦ Figure 20. PA and lateral image of a Colles’ fracture.

Frequent concomitant abnormalities are shortening of the radius, fracture of the ulnar styloid process and extension of the fracture line into the radiocarpal and distal radioulnar joint.

Smith's fracture is the opposite of a Colles’ fracture and is relatively less common. It can develop from high-energy traumas and a fall on an extended hand with the wrist in palmar flexion. Volar angulation/dislocation of the distal fragment is characteristic (fig. 21).

Figure 21. Smith's fracture (bowing fracture). 

Barton's fracture is a shear fracture of the distal radius. The oblique oriented fracture line arises from an axial force with a shearing component (fig. 22).
Depending on location, dorsal Barton's fracture and volar Barton's fracture may be distinguished.

Figure 22. Barton's fracture (shear fracture).

Chauffeur Fracture

A chauffeur fracture is an intra-articular fracture of the radial styloid process (fig. 23). From a classical perspective, this involved a direct trauma at the dorsal side of the wrist.
Background: historically, most chauffeur fractures were seen in people starting their car with an old-fashioned hand crank. The person turning the crank may lose control over the crank, with the crank slamming into the back of the wrist at high speed. 

♦ Figure 23. PA image. Intra-articular fracture of the radial styloid process; chauffeur fracture.

Greenstick/Torus Fracture

Wrist fractures are common in playing children. Specific fractures at a young age include the greenstick and torus fractures (fig. 24).
A greenstick fracture (= breaking twig) is an incomplete fracture where the bone bends (cortical interruption at one side, always the convex side). 
A torus fracture (= buckle fracture) is an incomplete fracture creating a 'buckle’ of the cortex, always at the concave side. The picture resembles the bottom of a Greek pillar.
The torus fracture heals quicker than a greenstick fracture.

♦ Figure 24. Lateral image (a) and PA image (b) of a radial greenstick fracture and ulnar torus fracture.

Scaphoid Fracture

Of all carpal bones fractures, the scaphoid fracture is the most common. 
The complex shape and overlap of the other carpal bones always necessitate imaging the scaphoid from different directions. Despite the scaphoid series, many scaphoid fractures are not visible in the acute setting.  When a scaphoid fracture is clinically suspected without radiologic abnormalities, options include repeating the X-rays after about 10 days (bone resorption will occur after a few days improving fracture visibility), or additional imaging (particularly MRI) after the first X-ray series.  Note: the specific diagnostic protocol (options for X-ray/MRI/CT/bone scan) for scaphoid fractures may vary among hospitals.
Don't be surprised that many scaphoid fractures have poor visibility on a scaphoid series. 
The exact mechanism is unclear. The literature describes an axial force in hyperextended position of the wrist (fall on outstretched hand). Scaphoid fractures are seen commonly in high-energy traumas also. When assessing an X-ray, vascularization should always be accounted for. Vascularization of the scaphoid takes place particularly through branches of the radial artery at the level of the distal pole (fig. 5). The branches at the dorsal side account for 70-80% of scaphoid blood supply. Blood supply to the proximal pole is mainly retrograde through the above-described distal dorsal branch.

Figure 25. Vascularization of the scaphoid.

Retrograde vascularization increases the risk of complications of delayed union, nonunion and avascular necrosis as compared to proximal scaphoid fractures.  Other notorious complications include instability and secondary osteoarthritis.

There are various classifications for scaphoid fractures. They can be subdivided by location; proximal, middle (= waist), distal, tubercle (fig. 26/27).
It is frequently a waist/middle fracture (80%).

Figure 26. Classification of scaphoid fractures based on location.

♦ Figure 27. Tubercle scaphoid fracture.

Additionally, the fracture lines may be described versus the long axis of the scaphoid (fig. 28).

Figure 28. Classification of scaphoid fractures based on fracture line orientation.

Characteristics suggesting instability include cortical interruption of more than 1 mm, fracture angulation, movement in ulnar/radial deviation and ligamentary damage (fig. 29). The scapholunate ligament is frequently involved in ligamentary damage (expansion of SL interval, see also Scapholunate Dissociation section).

♦ Figure 29. Transversal scaphoid fracture with cortical interruption > 1mm. Note also marked soft tissue swelling.

Triquetral Fracture

A triquetral fracture is the most common carpal bone fracture after the scaphoid fracture. It can occur in isolation or in combination with complex carpal fractures.  In most cases, it is a (chip) fracture at the dorsal side; there is an avulsion fracture of the dorsal radiotriquetral ligament (fig. 30). The fracture cannot be seen on a PA image.
Usually a fall on an extended arm is reported. There may be impingement of the ulnar styloid process, a shear trauma or an avulsion of the dorsal radiotriquetral ligament.

♦ Figure 30. Avulsion fracture of the triquetral bone (not visible on a PA image).  

Lunate Dislocation

A dislocation of the lunate bone is rare and requires quick (surgical) intervention. In the event of dislocation, the lunate has shifted in the palmar direction.

Characteristics (fig. 31): 

  • Palmar angulation of the lunate bone (spilled teacup) on the lateral image.
  • The lunate shows no articulation with the radius and the capitate (lateral image).
  • Triangular configuration (piece of pie sign) rather than normal square configuration on the PA image.

♦ Figure 31. Lunate dislocation; piece of pie sign (PA image) and spilled teacup (lateral image).

The lateral image is the key image to demonstrate/exclude lunate dislocation; this diagnosis can be easily missed on a PA image.

By its concave shape, the lunate has a moonshaped configuration. When the wrist flexes, shape changes on the PA image (fig.  32). Important: do not interpret each triangular shape of the lunate on a PA image as a lunate dislocation. The lateral image is more reliable in this respect.

Figure 32. Positions of the lunate in flexion and extension of the wrist.

Perilunate Dislocation

Perilunate dislocation can be confused with lunate dislocation.  The dislocation is seen particularly after high-energy traumas (like falling from a height with the wrist in dorsiflexion). 
In perilunate dislocation, articulation between the lunate and the radius is preserved. 
Characteristics of perilunate dislocation (fig. 33):

  • The capitate does not articulate with the lunate and is dislocated in the dorsal direction. 
  • The radius and lunate remain aligned.

Figure 33. Lunate dislocation (with spilled cup) versus perilunate dislocation.  

A perilunate dislocation is strongly associated with fractures of the other carpal bones (particularly scaphoid) and ligamentary damage.

Carpal Instability

As a result of ligamentary damage, carpal bones may no longer move as a fixed chain relative to each other in their original direction.  Causes: trauma, arthritis.
The instability may be dynamic (visible when exerting stress) or static (visible on X-ray WITHOUT stress).
Untreated carpal instability symptoms may lead to chronic pain, deformations, osteoarthritis and loss of joint function. 

Scapholunate Dissociation
Scapholunate dissociation is the most common form of carpal instability. It occurs after damage to the scapholunate ligament.
A PA image shows the increased space between the scaphoid and lunate (fig. 34). Normally, the joint space between the intercarpal joints does not exceed 2 mm. A difference of > 4 mm between the scaphoid and lunate is considered pathognomonic for scapholunate dissociation (SL dissociation).
Widening on X-ray is also termed the Terry Thomas sign. 
When in doubt about clinical/X-ray findings, imaging the other wrist by way of comparison can be considered 

♦ Figure 34. Scapholunate dissociation; widening of the scaphoid-lunate space. Also note the signet ring configuration of the scaphoid (signet ring sign).

SLAC stands for Scapholunate Advanced Collapse and describes a certain pattern of osteoarthritis and subluxation in the wrist.  The most common cause is a scapholunate dissociation with rotatory subluxation of the scaphoid.
Other causes: scaphoid nonunion advanced collapse (SNAC), avascular necrosis of the scaphoid bone, inflammatory arthritis, Kienböck's disease. 
When the scaphoid bone is in chronic subluxation, the forces of the wrist movements are transferred abnormally to the wrist joints.  The first consequence is the degeneration between the radial styloid process and the scaphoid. Degenerative abnormalities will then spread between the capitate and lunate (fig. 35).

 Figure 35. Pattern of Scapholunate Advanced Collapse (SLAC).

Sources

  • B.J. Manaster et al. The Requisites – Musculoskeletal Imaging. 2007.
  • N. Raby et al. Accident & Emergency Radiology – A Survival Guide. 2005.
  • R.W.Bucholz Rockwood & Green’s Fracturen in Adults. 2006.
  • Prof.dr. J.A.N. Verhaar, dr. J.B.A. van Mourik. Orthopedie. 2008.
  • Malik A.K. et al; Scaphoid views: a need for standardisation. Ann R Coll Surg Engl 2004.
  • Goldfarb C.A., MD et al; Wrist Fractures: What the Clinician Wants to Know. Radiology 2001.

Author

  • Annelies van der Plas, resident radiology LUMC

  • Prof. dr. J.L. Bloem, radiologist LUMC

09/07/2016

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