Sian Edwards. Carpal injuries, Don't Forget the Bubbles, 2021. Available at:
Injuries to the hands are extremely common in children and are a frequent reason for their attending the ED. While common, their management can be limited by difficulties in proper assessment as well as a paucity of evidence to guide treatment. That said, documented outcomes remain typically excellent so it seems we must be doing something right! Generally, training is provided with an adult focus, and while some principles from adult trauma can be applied, it is not uniform. As our post on radiographic findings demonstrates, the bones of children are different. This is significant because we know that missed injuries or delays in appropriate treatment can lead to long term loss of function; further compounded by the science that children heal faster and therefore our window for intervention is considerably shorter. Therefore, accurate assessment coupled with appropriate initial management and timely referral if necessary are essential.
As is not uncommon in the paediatric arena, evidence specific to this population is limited although it is stated that carpal fractures in children are being increasingly reported . Perhaps this is as we, as clinicians, get better at diagnosis and radiologists therefore see more and so naturally become more adept at interpreting them. Regardless of radiographic findings, diagnosis is primarily through clinical examination.
While not exclusive to the teenage population, we can expect the majority of carpal injuries to occur in the older child; as children age, become braver and take on more activities with an increased likelihood of higher velocity falls. Falling onto an outstretched hand, otherwise widely known as a FOOSH injury, is a common mechanism, accounting for 30% of non-scaphoid carpal injuries.
Before we get in to it, we can take a moment to re-familiarise ourselves with the bones of the hand and wrist.
The carpal bones are the eight bones of the wrist that articulate the forearm with the hand – this in itself seems confusing as they are quite clearly situated in what we call the hand but go with it. They are divided into the proximal and distal rows, collectively known as the carpus. Proximally we have scaphoid, lunate, triquetrum, pisiform and distally, trapezium, trapezoid, capitate, hamate. The carpal bones develop through the course of childhood and should all be visible on X-ray by approximately 8 years of age.
Literature suggests that carpal fractures account for around 8-19% of all hand injuries worldwide; as we’ve already touched on, the majority will be scaphoid fractures and ED’s are pretty used to dealing with these – they even get their own series of x-rays – for that reason, this post will give some time to carpal fractures NOT including the scaphoid.
What are we looking for on x-ray?
While the AP view allows clear visualization of all of the carpal bones and would appear the ‘easier’ view, particularly to those less experienced with interpreting these x-rays, the lateral view is good for assessing the distal wrist, carpal bones and proximal metacarpals – it can appear confusing at first due to the overlapping bones. Regardless, both radiographs must be evaluated together. As always, we are tracing each individual bone looking for obvious breaks in the cortex before then looking for uniformity of the joint spaces; abnormally widened spaces are often indicative of ligamentous injury however abnormally narrow spaces are often the result of radiographic projection rather than injury. It is often helpful to sit back from the image and see it in its entirety as well as a close-up view.
Recommended questions to ask when looking at the carpal bones:
- Is the scapho-lunate distance less than 2mm wide? – if NO then suspect a tear of this ligament.
- Is there a bony fragment lying posterior to the carpal bones? if YES, then suspect triquetral fracture.
- Is there a bone sitting in the cup of the lunate? If NO, think carpal dislocation involving the lunate.
After the scaphoid bone, the triquetrum is the most commonly fractured bone in isolation with the trapezoid bone being the least frequently fractured. Each will now get it’s moment to shine as we take a minute to go through them.
Triquetral fractures usually occur on the dorsal aspect of the bone and are often the result of perilunate fracture dislocation as well as fracture of distal radius and ulna; they account for about 20% of all carpal fractures and are regularly missed. These may occur by means of impingement from ulnar styloid, shear forces or avulsion from strong ligamentous attachments. The usual mechanism is a FOOSH whilst in ulnar deviation, and less commonly a direct blow to the dorsum of the hand. It is best seen on a lateral projection where the avulsed flake of bone may be seen lying posteriorly to the triquetrum – look for pooping duck sign on the image.
Hamate fractures are rare, only accounting for approximately 2% of carpal fractures, potentially due to under reporting. They generally don’t happen in isolation, often being associated with dorsal fracture dislocation of 4th and 5th carpometacarpal (CMC) joints, ulnar nerve injury and flexor tendon rupture, especially of 4th and 5th fingers. Common mechanisms are from blunt trauma e.g. fist punch, falls and through impact from racquet sports.
Like hamate fractures, capitate fractures are also frequent injuries which seldom occur in isolation. A capitate fracture is uncommon, accounting for approximately 1.3% of carpal fractures and can be associated with a scaphoid fracture. It is uncommon to have a combined capitate-hamate fracture. The primary mechanism is a FOOSH with the wrist in hyperextension. Injury can result in ‘scaphoid capitate’ syndrome (1-2% incidence) where the capitate actually rotates by 180o – this latter presentation will need open reduction.
Lunate fractures account for about 1% of carpal fractures, and like its predecessors rarely occur independently. They are associated with injuries to the distal radius, carpus or metacarpals. Subluxations / dislocations of the carpus are most commonly centred around the lunate bone and key to their detection is the apple, cup, saucer analogy- the cup of the lunate should never be empty – the distal radius, lunate and capitate articulate with each other in a straight line on the lateral radiograph, so when examining the image, if the capitate (apple) is not sitting in the cup of the lunate on the saucer of the radius then injury is present. Failure to recognise this anatomy means that dislocations are often overlooked. Where scapho-lunate ligament injury has occurred, missed diagnosis can lead to chronic pain around the joint due to its instability. In the younger population, surgery will be considered to restore full function and relieve pain.
More commonly, injury can occur at the scapho-luncate ligament – on x-ray, expect to see a widened joint space which is often referred to as the “Terry Thomas” or “Madonna” sign (named for the gap between the front teeth) demonstrating such injury. While conservative management may often be trialled, surgical reconstruction can be needed.
Trapezium fractures comprise between 3% and 5% of all carpal fractures and <1% of all hand injuries; they can occur in isolation or in combination with another carpal bone e.g. fracture of the 1st metacarpal base and/or subluxation or dislocation of the 1st carpometacarpal (CMC) joint although this is extremely rare. They are often the result of high energy trauma, usually involving axial loading force. Isolated trapezium fractures can be easily missed on x-ray due to the overlying bones, particularly on AP view.
Pisiform fractures account for 0.2% of all carpal fractures and of those, half are in association with other carpal injuries; rarely it may dislocate without fracture and displace radially. Its rarity is attributed to the sturdy ligaments that encase it.
Trapezoid fractures are incredibly rare, with only about 10 cases reported in the literature. Their anatomic location and stable articulation with the 2nd metacarpal together with their strong ligamentous attachments to neighbouring carpal bones are thought to be responsible for the low incidence of fracture.
So how do we manage these injuries?
Inevitably there will be some local differences, but the general principles are:
- Closed manipulation can prove difficult and often unsuccessful so orthopaedic review is required if displacement exists.
- If no displacement, and no concern about ligamentous injury, then conservative management is often indicated. There is frequently no requirement to formally immobilise so analgesia may be the only treatment.
- If carpal subluxation is suspected, always refer to the orthopaedic team for specialist evaluation. If you are unsure, the literature discusses obtaining a radiograph of the uninjured hand to use as comparison – this is not always a well received request so do consider utilising your local reporting radiologist, and if unavailable or in doubt then refer for follow up.
The take home
So, what essentially is our take home message? We need to keep in mind that carpal fractures, dislocations and ligamentous injuries do occur in children, albeit rarely. We need the ability to recognise the ‘normal’ so we can pick out the ‘abnormal’. As with all injuries, diagnosis should be mainly clinical with the x-ray being our confirmation. As cannot be said enough, if it presents like a fracture, or considerations of acute injury like swelling and pain inhibit your ability to confidently exclude it, then treat it as such and refer onwards to the specialists that can!
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