Ulnar Impaction Syndrome

Ulnar Impaction Syndrome is a degenerative condition resulting from excessive load transmission between the distal ulna and ulnar carpus (lunate and triquetrum).

Biomechanical Cascade:

1. Positive ulnar variance (constitutional or acquired)
2. Increased ulnocarpal loading (especially lunate-triquetrum)
3. TFCC central wear and perforation (Palmer 2C)
4. Lunate and ulnar head chondromalacia (Palmer 2B-2C)
5. Lunotriquetral ligament tear (Palmer 2D)
6. Ulnocarpal arthritis (Palmer 2E - end-stage)

Ulnar Variance Measurement:

• PA wrist X-ray
• Forearm neutral rotation (key - pronation increases variance)
• Shoulder abducted 90 degrees, elbow flexed 90 degrees
• Perpendicular line from ulnar articular surface to radial articular surface
• Positive variance: ulna extends distal to radius
• Negative variance: ulna proximal to radius

Provocative Tests

Key Radiographic Findings:

• Positive ulnar variance (over 2mm)
• Lunate sclerosis (increased density on PA view)
• Ulnar head cysts (subchondral cystic changes)
• Ulnocarpal joint narrowing (end-stage Palmer 2E)

MRI Findings:

• TFCC central perforation (high signal on T2)
• Lunate bone marrow edema (low T1, high T2 signal)
• Chondromalacia (cartilage thinning or defects)
• LT ligament tear (discontinuity or high signal)

Common Complications

Nonunion after USO (5-10%):

• Risk factors: smoking, diabetes, inadequate fixation
• Management: ORIF with bone graft, compression plating
• Prevention: rigid fixation, compression, smoking cessation

DRUJ Instability:

• Caused by excessive ulnar shortening (over 4mm)
• Worse in supination (dorsal subluxation)
• Management: splinting if mild; SK procedure if severe

Persistent Pain after USO:

• Hardware prominence (most common) - remove plate after union
• Inadequate shortening - consider revision
• Unrecognized pathology (LT tear, arthritis) - MRI, arthroscopy

Return to Work:

• Desk work: 2-3 weeks (wafer), 4-6 weeks (USO)
• Light manual: 6-8 weeks (wafer), 10-12 weeks (USO)
• Heavy labor: 12 weeks (wafer), 16 weeks (USO)

Prognostic Factors:

Long-term Natural History (Untreated):

• Progression from Palmer 2A to 2E over 5-15 years
• Most symptomatic patients eventually require surgery
• Conservative management temporizing only

Epidemiology in Australia: Ulnar impaction syndrome is a common cause of ulnar-sided wrist pain in Australia, particularly in manual laborers in construction, agriculture, and mining industries. Positive ulnar variance prevalence in the general population is approximately 10-15%, with symptomatic UIS developing in a subset of this group. Hand surgeons encounter UIS regularly in practice, making familiarity with diagnosis and treatment algorithms essential.

Management Considerations: Australian hand surgeons typically follow the Palmer classification for TFCC tears and stage-appropriate treatment. MRI is readily accessible and used routinely for diagnosis confirmation and surgical planning. Ulnar shortening osteotomy is the preferred surgical treatment for Palmer 2C-2D pathology with significant positive variance (over 2-3mm), while arthroscopic wafer procedures are increasingly used for mild variance. Conservative management is appropriate for Palmer 2A-2B disease with trial of activity modification, splinting, and corticosteroid injection before proceeding to surgery. Salvage procedures (Darrach, Sauvé-Kapandji, ulnar head replacement) are reserved for end-stage ulnocarpal arthritis after failed USO or primary Palmer 2E disease.

Medicolegal Considerations: Informed consent for ulnar shortening osteotomy should address nonunion risk (5-10%), hardware prominence requiring removal, DRUJ stiffness, and 3-4 month recovery timeline. Pre-operative measurement and documentation of exact ulnar variance is essential for surgical planning and medicolegal protection. Post-operative follow-up should include serial X-rays to monitor healing and detect nonunion early. Consider workers compensation implications for patients in manual occupations, particularly those involving vibration exposure or repetitive forearm rotation. Smoking cessation counseling is important to reduce nonunion risk.