Abnormal morphology of ulna Hypertrophic ulnar styloid process 2024-11-13T22:02:28Z Excessively long styloid process of the ulna. Ulnar styloid large Ulnar styloid impaction syndrome involves impaction between the tip of the ulnar styloid process and the triquetrum bone. This syndrome is most commonly seen in patients with excessively long or hypertrophic ulnar styloid processes and is not necessarily associated with positive ulnar variance. The ulnar styloid process index (USPI), calculated as the difference between the ulnar styloid length and the ulnar variance divided by the transverse diameter of the ulnar head, is commonly used to assess the size of the ulnar styloid. An excessively long ulnar styloid has a length greater than 6 mm or a USPI more than 0.21. Repetitive friction of the proximal pole of the triquetrum and the ulnar styloid tip leads to chondromalacia, synovitis, and ulnar-sided wrist pain.