gms | German Medical Science

Objectives/Interrogation: In 1993, Viegas et al. investigated the incidence and distribution of intracarpal arthrosis in 393 dissected cadaver wrists: 45% had cartilage damage at the proximal pole of the hamate, and 36% degenerative tears of the TFCC. The two conditions were rarely found in the same wrist. Indeed, a TFCC tear tends to be associated with positive ulnar variance, and this tends to coexist with a lunate type I. A luno-hamate impingement is expected to coexist with a type II lunate.

We hypothesized that a long hamate, associated with a lunate type II, tends to have a negative UV, while a short hamate, associated with a lunate type I, tends to have a positive UV. Hence we investigated whether there exists a relationship between the midcarpal inclination (MI) angle, type of lunate and the ulnar variance (UV) in the general population and patients with proven ulnar impaction syndrome.

Methods: A retrospective, quantitative, population based analysis (asymptomatic patients taken from the hospital data base) was performed assessing 342 postero-anterior radiographs of normal wrists taken in pronated position with the arm in 90°abduction and 40 postero-anterior radiographs of patients with ulnar impaction syndrome. We estimated the type of lunate and measured the midcarpal inclination angle (MI) angle and UV. A statistical analysis was performed to assess the relationship between these parameters.

Results and Conclusions: We found a weak correlation between the MI angle and ulnar variance in the general population. Type II lunate wrists have a greater MI angle than those with Type I lunate (p<0;05).

In patients with ulnar impaction syndrome who have lunate type II, a smaller positive ulnar variance is symptomatic compared to those who have lunate type I. In this ulnar impaction population there is an inverse linear correlation between ulnar variance and MI angle (R² 0,15).

In the general asymptomatic population we could not confirm our hypothesis of a negative relation between the MI angle and ulnar variance. In the symptomatic ulnar impaction population we do see a negative correlation between MI angle and ulnar variance. The clinical relevance is that positive ulnar variance is better tolerated by the type I lunate wrist compared to the type II lunate wrist who has a higher risk to develop and ulnar impaction syndrome even with slight ulnar positive variance.