What is ulnar impaction syndrome?

Ulnar Impaction Syndrome: Definition and Clinical Overview

Ulnar impaction syndrome (UIS), also known as ulnar abutment, is a degenerative condition where the ulnar head impacts against the triangular fibrocartilage complex (TFCC) and ulnar carpus, causing progressive degeneration of these structures and resulting in ulnar-sided wrist pain. 1, 2

Pathophysiology

• The condition results from excessive load-bearing across the ulnocarpal joint, leading to a spectrum of pathologic changes including chondral damage, subchondral edema, and mechanical impingement of the articular disc 3, 4
• Progressive degeneration affects the TFCC, distal ulna, proximal lunate, and proximal triquetrum, with chondromalacia developing in these structures 3
• The syndrome can lead to wrist bone necrosis and disruption of wrist joint stability, significantly impairing wrist function 1

Anatomic Predisposition

• UIS typically occurs in patients with ulnar-positive or ulnar-neutral variance (where the ulna is longer than or equal to the radius on posteroanterior radiographs) 5, 4
• The condition may be congenital or acquired through malunion of distal radius fractures, daily activities causing excessive intermittent loading, or structural abnormalities 2, 4
• Ulnar variance can be assessed on standard radiographs, which show the relationship between ulnar and radial length 6

Clinical Presentation

• Patients present with ulnar-sided wrist pain that worsens with activity and does not improve with rest 3
• Limitation of wrist motion is a common finding 2
• The condition is often associated with central traumatic or degenerative defects in the TFCC 3

Diagnostic Approach

Initial Imaging

• Standard radiographs (posteroanterior, lateral, and oblique views) are the first imaging study, allowing assessment of ulnar variance, joint spaces, and impaction syndromes 6

Advanced Imaging When Radiographs Are Nonspecific

• MRI without IV contrast is highly accurate for TFCC lesions, particularly for radial (central) zone disc tears using high-resolution sequences 6
• MR arthrography has higher sensitivity than non-contrast MRI for TFCC tears, especially for ulnar attachment and peripheral ligament tears 6
• CT arthrography is superior to MRI for identifying articular cartilage defects in the wrist and has accuracy similar to MR arthrography for TFCC lesions 6

Important Diagnostic Caveat

• CT arthrography is less sensitive than MRI for extra-articular abnormalities that can cause ulnar-sided pain, making it a second-line choice unless MRI is contraindicated or metallic artifacts are problematic 6

Differential Diagnosis Considerations

• Ulnar impingement syndrome must be distinguished from UIS, as these are separate entities 2
• Distal radioulnar joint arthrosis or incongruity can present similarly and must be evaluated 2
• Structural abnormalities of the distal radioulnar joint, distal radius, and ulnar carpus must be carefully identified before treatment planning 2

Treatment Principles

Conservative Management

• Symptomatic treatment is the initial approach for patients without severe structural abnormalities 2, 5
• Treatment aims to decrease ulnar load across the wrist 2

Surgical Indications

• Surgery is indicated when nonoperative treatment fails 4
• Arthroscopic wafer procedure is appropriate for ulnar-positive variance less than 3 mm with concomitant central TFCC tears, involving debridement of the TFCC tear and distal ulnar pole to achieve ulnar-neutral or slightly ulnar-negative variance 5
• Ulnar shortening osteotomy is the treatment of choice when relative instability of the ulnar ligamentous complex is present 2
• Corrective radial osteotomy is preferred for malunion of the distal radius causing UIS, addressing the primary deformity 2

Surgical Approach Selection

• Arthroscopic treatment (TFCC debridement with arthroscopic ulnar wafer resection) provides a single-stage, minimally invasive approach with similar efficacy and fewer complications than open procedures 3
• Arthroscopic management avoids complications of open procedures such as nonunion and symptomatic hardware 5
• Combined abnormalities (UIS with distal radioulnar joint pathology) must be addressed simultaneously at surgery 2

Key Clinical Pitfall

• The Darrach procedure is not recommended as first-line treatment but may be used as a salvage procedure in properly selected patients 2