An ulnar styloid fracture is a break in the small bony projection at the distal end of the ulna (the ulnar styloid process). Often this injury occurs in association with a wrist fracture, particularly a fracture of the distal radius. Although the styloid itself may seem secondary, its involvement can influence wrist stability, especially at the distal radioulnar joint (DRUJ).

Anatomy and Biomechanics

The ulna is one of the two bones of the forearm, and at its distal end sits the ulnar styloid process, a small prominence that provides an attachment for critical stabilising structures of the wrist: the triangular fibrocartilage complex (TFCC) and ligaments that help stabilise the DRUJ. When the ulnar styloid process fractures, the integrity of these attachments may be compromised.

Biomechanically, the wrist and forearm rely on smooth coordination between the radius, ulna, and carpal bones. The DRUJ allows for pronation and supination of the forearm. A fracture of the ulnar styloid can disrupt this coupling by altering ligament tension or causing instability of the ulna relative to the radius during forearm rotation and load bearing.

Etiology and Risk Factors

Mechanism of Injury

The most common mechanism is a fall on an outstretched hand (FOOSH), where force is transmitted through the wrist, injuring the distal radius and concurrently the ulnar styloid. Direct trauma to the ulnar side of the wrist, twisting injuries of the forearm, or high-impact sports or accidents may also cause isolated or associated ulnar styloid fractures.

Risk Factors

• Wrist fractures, especially distal radius fractures
• Osteoporosis or reduced bone density, which makes even low-energy mechanisms capable of causing fractures
• Participation in contact or high-impact sports, falls from height, or trauma
• Previous wrist injury or instability of the DRUJ or TFCC
• Older age, female sex (in the presence of bone loss,) or metabolic bone conditions

Classification and Fracture Patterns

Ulnar styloid fractures are classified by the anatomical location of the fracture and whether the DRUJ or ligaments are compromised:

• Tip fractures: at the distal tip of the styloid; typically small fragments and less likely to affect joint stability
• Waist or mid-styloid fractures: between tip and base; may or may not be stable
• Base fractures: at the base of the ulnar styloid, where the TFCC and DRUJ ligaments attach; these are more likely to be associated with instability of the DRUJ and may require surgical management

The pattern of the fracture (displacement, comminution, fragment size), associated injury (DRUJ instability, TFCC tear, distal radius fracture), and joint involvement are fundamental in guiding treatment and prognosticating outcomes.

Clinical Presentation

Symptoms

Patients typically experience pain on the ulnar side (little-finger side) of the wrist following trauma. It may present as wrist pain in general, but often with tenderness specifically over the ulnar styloid region. Swelling, bruising, or visible deformity may occur. Sometimes the patient experiences difficulty with forearm rotation (pronation/supination), grip weakness, or experiences a “click” or sense of instability.

Physical Examination

On examination:

• Tenderness on palpation of the ulnar styloid process
• Swelling or bruising on the ulnar side of the wrist
• Pain with ulnar deviation or forearm rotation
• Assessment of DRUJ instability: examination for excessive ulna motion relative to the radius during pronation/supination or a “piano key” sign at the distal ulna
• Evaluation of wrist alignment, motion (flexion/extension), grip strength, and forearm rotation
• Because ulnar styloid fractures frequently accompany distal radius fractures, the wrist and DRUJ should be examined for associated injuries and joint instability

Diagnostic Evaluation

Imaging

Standard radiographs (anteroposterior and lateral views of the wrist) will often show the ulnar styloid fracture. Oblique or specialised views may help delineate the fragment size, displacement, and involvement of the ulnar base. In case of suspected DRUJ instability or ligamentous injury, advanced imaging, such as CT or MRI, may be required to evaluate fracture morphology, joint congruity, fragment displacement, and soft tissue (TFCC) injury.

Additional Assessment

Clinical evaluation of DRUJ stability is important. If instability is present (e.g., persistent pain with forearm rotation, swivel, or dislocation signs), further studies or surgical consultation may be needed. Assessment of bone density or metabolic bone health may be considered in fractures from low-energy mechanisms.

Treatment

The overarching goal is to relieve pain, ensure stability of the wrist and forearm (especially DRUJ stability), restore function, and prevent long-term complications such as chronic instability, non-union, or degenerative changes.

Non-operative Management

For non-displaced or minimally displaced fractures without DRUJ instability, conservative treatment is common. This often includes:

• Immobilisation (splint or cast) for comfort and initial healing
• Elevation and protection of the wrist to reduce swelling
• Early movement of fingers and proximal joints to prevent stiffness
• After the acute phase, progressive rehabilitation focusing on wrist and forearm motion, strengthening, and functional return
• Many isolated ulnar styloid fractures heal uneventfully with this approach when the DRUJ is stable.

Surgical Management

Surgery may be indicated when there is: significant displacement, a large fragment at the base of the ulnar styloid, evidence of DRUJ instability, associated wrist injuries requiring fixation (such as distal radius fracture), or persistent symptoms (ulnar-side wrist pain, non-union). Surgical options include open reduction and internal fixation (ORIF) of the ulnar styloid fragment (e.g., screws, tension band wiring), repair or reattachment of TFCC ligaments, and assessment/repair of the DRUJ. Postoperative care involves immobility followed by rehabilitation.

Rehabilitation and Follow-Up

Rehabilitation is crucial for restoring wrist motion, forearm rotation, grip strength, and returning to full activity. A graduated program is used, starting with protected motion, progressing to strengthening of wrist, forearm, and hand muscles, and finally returning to full functional loading and sports or heavy tasks. Regular follow-up is needed to monitor healing of the fracture, assess DRUJ stability, evaluate for non-union or chronic pain, and ensure the absence of long-term complications.

Complications and Prognosis

Complications may include: delayed union or non-union of the ulnar styloid fragment, persistent DRUJ instability, ulnar-sided wrist pain during rotation or gripping, reduced grip strength or forearm rotation, degenerative changes (arthritis) in the DRUJ or wrist, and requirement for further surgery.

Prognosis is generally good in ideal cases (small, stable fragment, no DRUJ instability, prompt treatment). However, if the base of the ulnar styloid is fractured with DRUJ instability or the associated wrist injury is more complex (e.g., distal radius fracture), the risk of residual dysfunction is higher.

Prevention and Patient Education

Prevention strategies include promoting protective wrist posture and control during high-risk activities (e.g., falls, sports). Use of wrist guards in sports or for high-fall risk individuals may help. Patients should be educated on recognising symptoms of ulnar-side wrist pain or instability after wrist trauma, seeking prompt evaluation, adhering to immobilisation and rehabilitation protocols, and avoiding premature return to full activity until wrist and forearm stability are confirmed. Patients with low-energy injuries should be screened for bone health and risk factors for osteoporosis.

References

Hauck, R. M., Skahen III, J., & Palmer, A. K. (1996). Classification and treatment of ulnar styloid nonunion. The Journal of hand surgery, 21(3), 418-422.

May, M. M., Lawton, J. N., & Blazar, P. E. (2002). Ulnar styloid fractures associated with distal radius fractures: incidence and implications for distal radioulnar joint instability. The Journal of hand surgery, 27(6), 965-971.

Mulders, M. A., Fuhri Snethlage, L. J., de Muinck Keizer, R. J. O., Goslings, J. C., & Schep, N. W. (2018). Functional outcomes of distal radius fractures with and without ulnar styloid fractures: a meta-analysis. Journal of Hand Surgery (European Volume), 43(2), 150-157.