Scaphoid Radiography

Introduction

The fall onto an outstretched hand (FOOSH) is a common mechanism of bony injury and the scaphod fracture is a common result. This page considers all aspects of scaphoid radiography.

Anatomy

The carpal bones can be thought of as being arranged in two rows- a proximal row and a distal row. The lunate and scaphoid occupy the proximal row and articulate with the radius. The row theory is based on the fact that the proximal and distal rows work as 2 separate functional units. This model has been challenged/modified by the proposition that the two rows are stabilized by the scaphoid which could be considered to be part of both rows. There is also an alternate column theory.

Surface Anatomy

<a class="external" href="http://www.aafp.org/afp/20040901/879.html" rel="nofollow" target="_blank"></a> adapted from <a class="external" href="http://www.flickr.com/photos/data_op/2211821511/" rel="nofollow" target="_blank">http://www.flickr.com/photos/data_op/2211821511/</a>

The scaphoid position centrepoint is most easily determined by locating the surface anatomy feature known as the anatomical snuff box. This is a void at the base of the thumb best demonstrated when the thumb is abducted (hitch-hiking position). This triangular depression is defined by the extensor and abductors of the thumb, and is easily visible when the wrist is partially ulnar deviated and the thumb abducted and extended.<a class="external" href="http://www.aafp.org/afp/20040901/879.html" rel="nofollow" target="_blank"> http://www.aafp.org/afp/20040901/879.html</a>

"- scaphoid receives majority of its blood supply via dorsal vessels at or just distal to waist area; - these vessels perfuse the proximal pole in a retrograde fashion; - most important vascular branches of radial artery enter scaphoid thru foraminae along its dorsal ridge; - it supplies 70-80% of bone, including entire proximal pole; - second group of vessels, arise from palmar & superficial palmar branches of radial artery & enter carpal scaphoid in region of its distal tubercle; - it perfuses distal 20-30 % of bone, including tuberosity" quoted from <a class="external" href="http://www.wheelessonline.com/ortho/vascular_anatomy_of_scaphoid" rel="nofollow" target="_blank">http://www.wheelessonline.com/ortho/vascular_anatomy_of_scaphoid</a>

Mechanism of Injury

adapted from source: unknown

Scaphoid fractures are almost invariably caused by a fall onto an outstretched hand. This is useful for the radiographer to know. It is good practice to ask the patient about their mechanism of injury in cases of acute injury to help assess the likelihood that the patient may have sustained a scaphoid fracture. A history of a fall onto an outstretched hand and acute localised pain in the anatomical snuff box suggests a high probability of a scaphoid fracture (base of thumb fractures - Bennett, Rolando, other- are common clinical misdiagnoses). Scaphoid fractures are most common in males 15 to 30 years of age and are rare in young children and infants.<a class="external" href="http://www.aafp.org/afp/20040901/879.html" rel="nofollow" target="_blank"> http://www.aafp.org/afp/20040901/879.html</a>

The Scaphoid View (PA with Ulnar Deviation and Tube angulation)

This is the commonly performed "scaphoid view" that is an essential inclusion in any scaphoid series. This view provides an often elongated image of the scaphoid that can reveal a fracture that is not evident in any of the other views. The scaphoid fat pad is also demonstrated best with the wrist in ulnar deviation.

Radiographic Technique

The hand and wrist are placed on the IR with the palmar/volar aspects of the hand and wrist in contact with the IR. The wrist is ulnar deviated and the tube angled 20 - 30 degrees towards the patient's elbow. In an acute injury case, collimate to include the proximal metacarpals and the distal radius- this will potentially demonstrate base of thumb fractures and distal radius fractures which are sometimes clinically misdiagnosed as scaphoid fractures. In a follow-up of a previously diagnosed scaphoid fracture, inclusion of the metacarpals and distal radius is not essential.

Zero Degree Tube Angle modified from <a class="external" href="http://www.aafp.org/afp/20040901/879.html" rel="nofollow" target="_blank">http://www.aafp.org/afp/20040901/879.html</a>	20 Degrees Tube Angle modified from <a class="external" href="http://www.aafp.org/afp/20040901/879.html" rel="nofollow" target="_blank">http://www.aafp.org/afp/20040901/879.html</a>	30 Degrees Tube Angle modified from <a class="external" href="http://www.aafp.org/afp/20040901/879.html" rel="nofollow" target="_blank">http://www.aafp.org/afp/20040901/879.html</a>
This demonstrates the positioning for a scaphoid view with no tube angle. The wrist is positioned for a PA wrist view then moved into an ulnar deviated position. Note that the wrist position is not sufficiently ulnar deviated in this photograph- a good guide is when the first metacarpal lines up with the longaxis of the radius. Centre the X-ray beam immediately medial to the anatomical snuff-box.	A tube angle of 20 degrees is applied as shown above. The tube angle is an approximation of the angle of the scaphoid to achieve an en face image of the scaphoid. The perfect angle will vary between patients and with the degree of ulnar deviation.	Some centres employ a 30 degree tube angle which tends to elongate the scaphoid, often to good effect.

Why Angle the Beam?

The scaphoid view can be performed with no beam angulation. This will almost invariably produce a foreshortened image of the scaphoid. It is preferable to produce an image of the scaphoid that is either en face or elongated slightly. The reason for using beam angulation is clear when you consider the orientation of the scaphoid in the wrist as shown below

	If the positioning objective is to image the scaphoid en face, the beam should in theory be angled at 90 degrees to the long axis of the scaphoid.
	The scaphoid long axis shows considerable variability in the angle of its long axis. This suggests that the scaphoid angle will always be an approximation of the scaphoid angle.

Why Ulnar Deviation?

Ulnar deviation of the patient's wrist is important for the following reasons

1. Ulnar Deviation rotates the scaphoid parallel to the long axis of the forearm and moves it away from the radius
   
2. Ulnar deviation rotates the scaphoid marginally in a palmar direction reducing the angle required to achieve an en face image.

1. Ulnar Deviation rotates the scaphoid parallel to the long axis of the forearm

Radial Deviation

Ulnar Deviation

The radial deviation wrist position (left image) positions the scaphoid in closer proximity to the radius (undesirable in terms of superimposition). Conversely, the ulnar deviated position pulls the scaphoid away from the radius. In doing so, ulnar deviation also orientates the long axis of the scaphoid such that a tube angled towards the patent's elbow will not be angled across the scaphoid.

2. Ulnar deviation rotates the scaphoid marginally in a palmar direction reducing the angle required to achieve an en face image.

Ulnar Deviation	Radial Deviation	The difference in appearance of the carpal bones between the two images, particularly evident in the change in appearance of the scaphoid, suggests that there is a flexion/extension movement of the carpal bones associated with radial/ulnar deviation. During radial deviation, the proximal carpal row rotates in a palmar direction/flexes. Conversely, during ulnar deviation the proximal carpal row (including the scaphoid) rotates in a dorsal direction.
Ulnar Deviation <a class="external" href="http://books.google.com.au/books?id=67UjC6sFy04C&pg=PA120&lpg=PA120&dq=meniscus+homologue&source=bl&ots=LbhEMWnz-M&sig=yf1l2Js5wqLx8XAzBncGuRnz6Ds&hl=en&ei=D8ETSp6pKtGUkAW0p4T9Dg&sa=X&oi=book_result&ct=result&resnum=11#PPA129,M1" rel="nofollow" target="_blank">Ulrich Lanz, Rainer Schmitt, Wolfgang Buchberger. Diagnostic Imaging of the Hand. 2008</a> The scaphoid rotates in a dorsal direction during ulnar deviation. This movement is used to advantage in the common PA scaphoid view with ulnar deviation.	Radial Deviation <a class="external" href="http://books.google.com.au/books?id=67UjC6sFy04C&pg=PA120&lpg=PA120&dq=meniscus+homologue&source=bl&ots=LbhEMWnz-M&sig=yf1l2Js5wqLx8XAzBncGuRnz6Ds&hl=en&ei=D8ETSp6pKtGUkAW0p4T9Dg&sa=X&oi=book_result&ct=result&resnum=11#PPA129,M1" rel="nofollow" target="_blank">Ulrich Lanz, Rainer Schmitt, Wolfgang Buchberger. Diagnostic Imaging of the Hand. 2008</a> The scaphoid seen here on CT imaging moves in a palmar direction during radial deviation.	These saggital CT images demonstrate the position of the scaphoid in ulnar deviation and radial deviation. The scaphoid clearly rotates in a dorsal direction during ulnar deviation. Importantly, this movement mitigates toward a more en face imaging of the scaphoid when undertaking a dedicated scaphoid view.

This video demonstrates the movement of the proximal carpal row (scaphoid, lunate triquetrum) in ulnar and radial deviation. <embed allowfullscreen="true" height="350" src="http://widget.wetpaintserv.us/wiki/wikiradiography/widget/youtubevideo/d878862db6973300fa2f6c5cf41934350072bf02" type="application/x-shockwave-flash" width="425" wmode="transparent"/> source: <a class="external" href="http://www.eatonhand.com/img/img00085.htm" rel="nofollow" target="_blank">e-hand.com</a>

This video demonstrates the movement of the carpus in ulnar and radial deviation. <embed allowfullscreen="true" height="350" src="http://widget.wetpaintserv.us/wiki/wikiradiography/widget/youtubevideo/0e39f2a0c3f16cabe5f64166a13d96a21eeaedf5" type="application/x-shockwave-flash" width="425" wmode="transparent"/>

How Much Tube Angle do I use for the Scaphoid View?

Beware the radiographer who insists on a particular technique but can't explain their viewpoint based on an objective and a balanced appraisal of the advantages and disadvantages of their technique (with supporting evidence). Many techniques are simply historically based (not that there is anything wrong with that per se). The first question is what are you trying to achieve with this view? If your answer is an en face projection of the scaphoid (i.e. without distortion/elongation), the 20 degree angle (as proposed in some textbooks) appears reasonable in a patient who can achieve good ulnar deviation. This is based on the fact that the scaphoid rotates dorsally slightly during ulnar deviation and is likely to be positioned at about 20 degrees to the coronal plane of the wrist (see CT images above). If you are aiming to demonstrate fractures of the scaphoid by producing an elongated image of the scaphoid, 30 degrees of tube angle would achieve that objective in most patients who adequately ulnar deviate their wrists.

Another technique consideration is how much your technique is superimposing the scaphoid over the adjacent bony structures.

Yet another consideration is whether you perform a series of tube angles in patients who have convincing clinical evidence of a scaphoid fracture but no radiographic evidence on routine views. This is arguably reasonable if there are good diagnostic yield in patients who would otherwise be referred for MRI imaging.

Scaphoid Series

A patient referred for a scaphoid series in an Emergency Department (or other acute care setting) might typically be subject to 4 exposures as follows

1. PA wrist with ulnar deviation
2. Lateral wrist
3. Oblique Wrist
4. Scaphoid View (20 - 30 degrees tube angle)

It should be borne in mind that the clinical diagnosis of scaphoid fracture could easily be incorrect- it is a provisional diagnosis only. It is important therefore to include as much of the metacarpals and forearm as would be indicated by the particular case. This would typically extend as far as inclusion of all of the metacarpals, and the distal 1/3 of the radius and ulna.

1. PA with Ulnar Deviation	2. Lateral	3. Oblique	4. Scaphoid View
This is over-collimated for an acute injury case. There is good ulnar deviation	This lateral wrist image is acceptable but is considered by some authors to not constitute a true lateral wrist position.	The oblique view will superimpose the scaphoid in part over the distal radius, capitate and lunate. Despite this limitation, the oblique position does afford good visualisation of the scaphoid and can be the best projection for demonstrating scaphoid tubercle fractures.	This is a 30 degree tube angle which results in some elongation of the scaphoid.

What Went Wrong?

This scaphoid view image suffers from underexposure (signal-to-noise ratio is too low). The central ray is also directed slightly across the scaphoid rather than along its long axis. This is probably of little consequence but is nevertheless noteworthy.

This scaphoid view image suffers from underexposure. In addition, and importantly, the tube angle is too great.

This patient was referred for scaphoid views from orthopaedic clinic. It was not clear why this patient was referred for scaphoid view. The following was clear the patient has a radial metaphysis fracture (probably Salter Harris) ulnar deviation is not possible a scaphoid fracture will be difficult to demonstrate with the patient's wrist in a fibreglass cast If a patient is referred for scaphoid views whist in an immobilising cast (plaster, fibreglass or any other artifact producing material) the radiographer should at the very least ask the referring doctor doctor if he/she had intended for the cast to be removed prior to the X-ray examination

Comment

Performing a scaphoid view is more meaningful if you understand what you are trying to achieve. There is arguably a case for performing a supplementary scaphoid series if the patient has strong clinical indicators of having sustained a scaphoid fracture and the fracture is not revealed on routine views. Performing a supplementary scaphoid series in such patients may facilitate early definitive treatment and avoid the inconvenience and expense of MRI imaging of the wrist.

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