Ep 190 Carpal Bone Injuries – The Big 4

With 8 carpal bones in each of our wrists, it’s difficult to know which injuries to concentrate our energies on. Understanding the age-related prevalence and mechanism of carpal bone injuries is a prerequisite to familiarizing yourself with these injuries. Carpal bone injuries occur predominately in young adults, often after a high energy mechanism of injury. In this 2nd part of our 2-part podcast series on wrist injuries, with the expert insights of Dr. Arun Sayal and Dr. Matt Distefano, we highlight the “Big 4” most common carpal bone injuries – triquetrum chip fractures, scapholunate injuries, hook of the hamate fractures, and of course, scaphoid fractures. These can be easily missed in the ED with significant consequences for our patients…

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Podcast production, sound design & editing by Anton Helman; voice editing by Braedon Paul

Written Summary and blog post by Kate Dillon, edited by Anton Helman. January, 2024

Cite this podcast as: Helman, A. Distefano, M. Sayal, A. Episode 190: Carpal Bone Injuries- The Big 4. Emergency Medicine Cases. January, 2024. https://emergencymedicinecases.com/carpal-bone-injuries-big-4. Accessed April 23, 2024

Carpal bones mnemonic memory aid

So Long to Pinky, Here Comes The Thumb mnemonic – starting at proximal row, radial wrist

• Scaphoid
• Lunate
• Triquetrum
• Pisiform
• Hamate
• Capitate
• Trapezoid
• Trapezium

Source: wikipedia

The Big 4 carpal bone injuries

The following carpal bone injures are commonly missed with serious consequences for patients. Other carpal bone injuries are less common and may co-occur with the “Big 4” injuries:

1. Triquetrum chip fractures
2. Scapholunate sprains/dissociation/dislocation
3. Hook of the hamate fracture
4. Scaphoid fracture

Understanding carpal bone injuries: Age related prevalence of disease

Age plays a significant role in determining the prevalence of musculoskeletal injuries. Younger individuals with open growth plates are more likely to sustain fractures involving growth plates or diaphyseal/metaphyseal junction of the distal radius, while older individuals with low bone density are more prone to classic long-bone fractures. For individuals between 15 and 60 years old carpal non-long bone and inter-carpal ligament injuries occur more often. Hence, carpal bone injuries occur predominantly in young adults as a result of a high energy mechanism. 

1. Triquetrum chip fracture – the commonly missed ulnar wrist injury

We tend to concentrate on the radial aspect of the wrist for patients who have sustained a wrist injury. The 2nd most common carpal bone injury comprising 20% of carpal bone fractures, and the most common ulnar wrist injury is a triquetrum chip fracture, highlighting the need to scrutinize the ulnar aspect of the wrist on physical exam and x-ray.

Dorsal aspect of triquetrum avulsed or knocked off.

Mechanism: FOOSH (most common), also fall on back of the hand (volar injuries are more likely to lead to carpal instability and require orthopedic intervention)

Surface anatomy/physical exam: dorsal, ulnar side of hand, palpate the divot distal to the ulnar styloid and proximal to the 4th metacarpal

Surface Anatomy of the triquetrum bone. Source: Adapted from: https://doi.org/10.1016/j.cuor.2005.02.008.

X-ray: whether the mechanism was FOOSH or fall on back of the hand, the x-ray findings are similar, often subtle and most often picked up on the lateral view

Triquetrum chip fracture, lateral x-ray. Source: https://www.orthobullets.com/hand/322147/triquetrum-fracture

Treatment: for dorsal injury mechanism (FOOSH), removable splint x 3-4 weeks; for volar or injury mechanism (fall on back of hand) or unknown mechanism of injury, plaster/fibreglass splint and early orthopedic follow-up

Pearl: a fall on the back of the hand (volar injury), or falling backwards is generally more serious than a FOOSH and resultant wrist injuries usually require immobilization and early orthopedic follow-up due to the higher likelihood of carpal instability

2. Lunate ligamentous injuries are on a spectrum: Scapholunate sprains, dissociation and dislocation

Lunate ligamentous injuries are the 3rd most common carpal bone injury comprising 10% and range in severity from sprains to dissociations to frank dislocations.

Mechanism: most commonly FOOSH.

Surface anatomy/physical exam: divot distal to Lister’s tubercle and a few millimetres ulnar is the scapholunate space; also 2cm ulnar to the snuffbox.

Surface Anatomy of the Lunate and Scapholunate Junction. Source: Adapted from: https://doi.org/10.1016/j.cuor.2005.02.008.

The spectrum of lunate ligamentous injuries from least morbid to most includes:

Grade 1 scapholunate ligament sprain – normal standard x-rays and normal clenched fist view – if there is clinical suspicion, immobilize in a splint and follow-up with orthopedics

Grade 2 scapholunate ligament sprain – normal standard x-rays but slight gap (<3-5 mm) on clenched fist view, splint for 6-10 weeks

Clenched fist view revealing right widened scapholunate space, Grade 2 scapholunate lilgament sprain. Source: Radiopaedia https://radiopaedia.org/articles/wrist-clenched-fist-view-1

Grade 3 scapholunate dissociation – complete tear/rupture of scapholunate ligament, surgical management in the first few weeks

SLAC (Scapholunate Advanced Collapse) is a consequence of untreated scapholunate dissociation (complete tear/rupture of ligament) where the capitate puts stress on the dissociated scaphoid and lunate, especially in wrist flexion, and can lead to advanced collapse of the capitate towards the radius with long term consequences such as arthritis of the wrist.

X-ray for scapholunate dissociation: Widening of the scapholunate space (3-5 mm) or Terry Thomas sign or David Letterman sign (these performers’ front incisors appear wide). To properly assess for scapholunate dissociation, a clenched fist view is required (Note: actively clenching, not just closing the fist gently, is important to reveal the gap in the scapholunate space)

Pearl: To pick up a subtle scapholunate dissociation and distinguish it from baseline physiologic widening of the scapholunate space, consider bilateral X-rays of the wrist as some people have baseline physiologic widening.

Terry Thomas/David Letterman sign. Widening of the scapholunate space on the AP x-ray view of the wrist. Source: https://www.orthobullets.com/hand/6041/scapholunate-ligament-injury-and-disi

X-Rays for suspected Lunate and Peri-lunate dislocation – on the normal lateral view of the wrist the head of the radius, the lunate and capitate are all aligned and appear as 3 “teacups” stacked on top of one another in the vertical axis

“Cups of Tea” normal alignment of the radius (yellow), lunate (red) and capitate (blue) on a lateral wrist x-ray. Source: https://www.emcurious.com/blog-1/2015/7/8/1ftadghymctqd2flw27ao4zwl1m6tb

Lunate dislocation – high energy mechanism in a young adult, best seen on lateral x-ray, Spilled teacup sign where the lunate tips anteriorly

Spilled Teacup Sign in Lunate Dislocation on lateral x-ray. Source:https://emcow.wordpress.com/2013/03/28/lunate-dislocation/

Perilunate (posterior capitate) dislocation – high energy mechanism in a young adult, more accurately termed posterior dislocation of the capitate, best seen on lateral x-ray: while the alignment of the radius and lunate remain intact the capitate no longer sits in the concavity of the lunate – termed an Empty teacup sign

Empty teacup sign of Perilunate dislocation, lateral x-ray wrist. Source: doi:10.1017/CBO9781316084328.004

Reduction of Lunate and Perilunate dislocations: both require reduction in the ED to reduce pain and to reduce the chance of avascular necrosis of the lunate.

1. Palpate the contralateral normal wrist for comparison and to establish a goal for reduction
2. Attain adequate muscle relaxation with sedation +/- finger traps
3. Place the wrist in the position that the injury occurred (i.e. usually a FOOSH position), stabilize the lunate on the palmar aspect of the wrist, and then flex the wrist; you should feel the lunate clunk into place.

It is important to avoid multiple reduction attempts if the first attempt was not initially successful, as this can cause further injury to the wrist; if a single attempt at reduction fails, consider orthopedic consultation in the ED.

3. Hook of the hamate fracture – a key palmar carpal bone injury that is easy to miss

4th most common carpal bone injury comprising 2%, which if missed and not immobilized, may lead to non-union and the need for surgical intervention

Mechanism of injury: classically a result of a sudden stop of a swinging elongated implement held in the hand (golf club, ski pole, tennis racket etc.) that rests against the hamate, but equally commonly results from a FOOSH, which in under-recognized

Surface anatomy/physical exam: 1-2 cm distal and radial to pisiform (which is at the base of the hypothenar eminence of the palm) on the radial border of the hypothenar eminence in line with the 4th finger

Hook of Hamate Surface Anatomy. Source: Adapted from: https://doi.org/10.1016/j.cuor.2005.02.008.

Extra x-ray view: Hook of the Hamate or Carpal Tunnel view is more sensitive than the standard wrist x-ray views for hook of hamate fractures but only about 50% sensitive. This view is also useful to pick up subtle pisiform and triquetrum fractures.

Carpal Tunnel/Hook of Hamate X-Ray View. Source: https://www.sportsmedreview.com/blog/diagnosing-hook-of-hamate-fractures/

Method for Acquisition of Carpal Tunnel/Hook of Hamate View. Source: http://www.wikiradiography.net/page/Carpal_Tunnel_Radiography

Pitfall: a pitfall is assuming no fracture if clinically a hook of hamate fracture is suspected and the standard wrist views as well as the hook of hamate/carpal tunnel view are negative. The sensitivity of the hook of hamate view is only about 50% for hook of hamate fracture, so if clinically suspected, immobilize and arrange orthopedic follow-up regardless of the x-ray findings.

Treatment of suspected or confirmed hook of the hamate fracture is immobilization and orthopedic follow up. If missed and not immobilized, a hook of hamate fracture can lead to non-union and chronic pain and require surgical intervention.

4. Scaphoid fractures – nuanced recognition and ED management of occult scaphoid fractures

Most common carpal bone fracture – about 2/3 of all carpal bone fractures.

Age related prevalence – scaphoid fractures occur predominantly in young adults.

Mechanism of injury – high energy FOOSH.

There are 3 physical exam tests, with some nuances in performing them, that our experts recommend for suspected scaphoid fracture

If any are positive in the patient with a consistent history, consider immobilization in a removable velcro or radial gutter splint, even if the x-rays do not show a fracture:

1. Snuffbox tenderness should be done with the wrist in ulnar deviation to bring the proximal scaphoid into the snuffbox
   

   Palpation of anatomical snuffbox in ulnar deviation. Source: Adapted from: https://doi.org/10.1016/j.cuor.2005.02.008.
2. Palmar scaphoid tenderness at base of thenar eminence with the wrist in neutral or radial deviation to bring out the scaphoid
   

   Surface anatomy of the scaphoid on the palmar/volar wrist. Source: https://www.aafp.org/pubs/afp/issues/2004/0415/p1941.html

3. Thumb axial load tenderness (note: false positives occur in older patients with CMC osteoarthritis)

Two additional signs for scaphoid fractures:

1. Pain on resisted supination of the wrist has been shown to have a 100% sensitivity for scaphoid fracture
2. Clamp sign, patient uses a pincer grasp around their scaphoid with their thumb in the snuff box and index finger over the palmar scaphoid when asked where the point of maximal pain is; high positive likelihood ratio for scaphoid fracture

Clamp Sign Scaphoid Fracture. Source: https://doi.org/10.1111/acem.12317

Options for further imaging for suspected scaphoid fracture after negative standard wrist x-ray views:

1. Scaphoid cone view x-ray
2. CT scaphoid

Note: CT may miss significant scapholunate ligament injuries and may falsely reassure clinicians to not immobilize the wrist/provide follow-up, as well as delay CT imaging for other patients in the ED with more morbid conditions.

ED management of suspected scaphoid fracture that is occult to standard wrist x-rays according to our experts:

1. Obtain scaphoid cone view x-ray
2. Immobilize in removable Velcro or radial gutter splint, follow up 10-14 days for re-examination +/- x-ray (only remove for bathing)

Pitfall: In some centers, CT wrist is done in the ED after a negative wrist x-ray for suspected scaphoid fracture. A common pitfall is assuming that there is no significant injury if the CT in negative. Scapholunate ligament injuries may be missed by CT.

Pearl: The most commonly missed occult fracture involving the wrist is the distal radius (not the scaphoid)

Drs. Helman, Distefano and Sayal have no conflicts of interest to declare