Ulnar impaction syndrome

Ulnar impaction syndrome, also known as ulnar abutment or ulnocarpal loading, is a degenerative wrist condition caused by the ulnar head impacting upon the ulnar-sided carpus with the injury to the triangular fibrocartilage complex(TFCC).

Epidemiology

Ulnar impaction syndrome most commonly presents in middle-aged patients. The majority of cases occur in association with positive ulnar variance or increased dorsal tilt of the distal radius, which may be congenital or due to a previous fracture, premature growth plate closure or radial head resection (such as may follow an Essex-Lopresti fracture-dislocation). Ulnar impaction syndrome is rare in the absence of such anatomic predispositions but can occur if there is excessive repeated loading of the ulnar-carpus in daily activity ⁵.

Clinical presentation

Patients present with chronic or subacute ulnar-sided wrist pain exacerbated by activity. There is often associated swelling and limitation of forearm and wrist movement. Anything that results in a relative increase in ulnar variance such as firm grip, pronation and ulnar deviation of the wrist, can exacerbate the symptoms.

Pathology

As the name suggests, ulnar impaction syndrome involves impaction of the distal ulnar upon the ulnar-sided carpal bones, particularly the lunate. This results in a continuum of pathologic changes which are represented in the class II subsection of the Palmer classification of TFCC lesions. ²

• IIA TFC complex wear
• IIB TFC complex wear, lunate or ulnar chondromalacia
• IIC TFC complex perforation, lunate or ulnar chondromalacia
• IID TFC complex perforation, lunate or ulnar chondromalacia, lunotriquetralligament perforation
• IIE TFC complex perforation, lunate or ulnar chondromalacia, lunotriquetral ligament perforation, ulnocarpal osteoarthritis

Radiographic features

Imaging findings of ulnar impaction may precede the onset of symptoms. Recognising the distribution pattern (ulnar, lunate, triquetral) is the key to making the diagnosis. 

Plain radiograph

Plain radiographs can appear normal in early disease. General features include:

• presence of a predisposing factor
  • positive ulnar variance
  • previous distal radial fracture with shortening or dorsal tilt
  • distal radial resection
  • Madelung deformity
• subchondral sclerosis and cysts in specific ulnar impaction distribution
  • distal ulnarulna
  • proximal ulnar aspect of lunate
  • radial aspect of triquetral
• ulnocarpal osteoarthritis in more advanced disease

MRI

MR imaging is the investigation of choice in both detection of early disease and characterisation of more advanced disease. Can demonstrate the bone, cartilage and ligamentous features of the syndrome. ³

Location of bone signal changes ⁴

• ulnar side of proximal lunate ~ 90~90% 
• radial side of proximal triquetrum ~ 40~40%
• distal ulnar ~ 10ulna ~10%

Types of bone signal change

• subchondral sclerosis (low T1 and T2) most common in lunate
• bone oedema (high T2, low-intermediate T1) 
• subchondral cysts (round T2 hyperintensities)

Cartilage and ligamentous changes

• chondromalacia of distal ulnar cartilage (altered signal)
• central TFCC signal increase often with tear (T2 hyperintense fluid)
• lunatotriquetral ligament tear (T2 hyperintense fluid) with proximal arc offset

Treatment and prognosis

Treatment varies depending on the amount of ulnar variance, the Palmer lesion class, the contour of the distal ulnar and the presence of lunotriquetral instability.

Palmer class IIA and IIB lesions (no TFC perforation) are managed with open wafer procedure (surgical resection of the distal 2–3-3 mm of the dome of the ulnar head) or formal ulnar shortening (excision of a 2-3 mm slice of the ulnar shaft followed by fixation).

When the TFC is perforated (Palmer class IIC and IID lesions), the head of the ulna can be burred down with the help of arthroscopic instrumentation (arthroscopic wafer procedure). This procedure is minimally invasive, highly effective, and allows rapid return to normal activities.

Class IIE lesions are managed with salvage procedures such as complete or partial ulnar head resection (Darrach procedure) or arthrodesis of the distal radioulnar joint with distal ulnar pseudoarthrosis (Sauve-Kapandji procedure).

Differential diagnosis

• Kienböck disease
  • signal change in lunate is usually more diffuse and radial sided
  • no ulnar or triquetral abnormality
  • more often with negative ulnar variance

• traumatic TFCC injuries
• degenerative arthritis of the wrist (SLAC wrist)
  • radio-carpalradiocarpal joint involved
• intraosseous ganglia
  • usually radial side of the lunate or distal lunate

See also

• ulnar-sided wrist impaction and impingement syndromes