Abstract
Background: Ulnar impaction syndrome (UIS) is a painful wrist disorder caused by increased load transmission and repetitive impaction between the ulna and lunate, often accompanied by triangular fibrocartilage complex (TFC) tears. While typically associated with ulna-positive variance, asymptomatic ulna-positive individuals are common in the general population.
Objective: To compare selected posteroanterior radiographic parameters of the distal radius and lunate between symptomatic UIS patients and asymptomatic individuals.
Methods: This retrospective comparative study included 31 patients with symptomatic UIS (19 females, 12 males) and 85 asymptomatic controls (46 females, 39 males) with an ulnar variance of +1 to +5 mm. Five distal radial parameters radial inclination (RI), radial height (RH), scaphoid facet inclination (SFI), lunate facet inclination (LFI), and interfacet angle (IFA), and three carpal parameters lunate shift ratio (LSR), capitate shift ratio (CSR), and lunate midcarpal morphotype were measured and results were compared.
Results: RI, SFI, and RH were significantly higher in UIS patients compared with controls, particularly in females. Carpal shift parameters also tended to be higher in patients, with CSR showing more consistent differences than LSR. Type I lunate morphology was more prevalent in female UIS patients. Moderate to strong correlations were found between certain radial and carpal parameters.
Conclusions: Increased radial inclination, Increased SFI, and specific carpal morphology patterns may contribute to ulnar-side carpal shift, potentially predisposing ulna-positive individuals to symptomatic UIS. CSR may serve as a more reliable measure of carpal shift than LSR.

Key words: Ulnar impaction syndrome; ulnar abutment; lunate; distal radius; radiographic parameters; carpal shift; morphotype.