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Background: Ulnar styloid triquetral impaction (USTI), one of many causes of ulnar sided wrist pain, is a pathological entity with clear clinical and radiographic features, distinct and different from the impaction of the ulnar head against the lunate or ulno-carpal impaction (UCI). Pain is ulnar and point-tenderness is present precisely over the ulnar styloid as opposed to the proximal lunate in UCI. The provocative maneouvre of dorsiflexion in pronation followed by supination is markedly different from the ulnar deviation grind test maneouvres used to diagnose UCI. Multiple anatomical and pathological features interplay to produce a situation in which the distance between the tip of the ulnar styloid and the triquetrum is reduced resulting in USTI. The concept of ulnar styloid variance is introduced and anatomical variations of ulnar styloid length are demonstrated.

Methods: The clinical and radiographic features of 56 patients diagnosed with USTI were analysed. One thousand standardised film-file wrist radiographs were measured to determine the average length of the ulnar styloid in the population as well as the average projection of the styloid above the radius (ulnar styloid variance).

Results: An aetiological classification system for USTI was developed based on the clinical and radiographic features of the aforementioned patients and radiographs.

Conclusions: The causes of this syndrome are often complex and classification of the aetiological features is clinically useful. It is important for physicians and surgeons to recognise the clinical and radiographic features of this syndrome in order to properly manage the symptoms and prevent an iatrogenic production of USTI.

Background: There are significant variations in the anatomy of the dorsal cutaneous branch of the ulnar nerve (DCBUN). The DCBUN is at risk for iatrogenic injury during surgeries around the ulnar side of the wrist. The purpose of this study was to demonstrate the relationship between the ulnar styloid process and the DCBUN and to confirm the DCBUN's change in location with different forearm positions.

Methods: We examined 9 fresh frozen cadaveric limbs to establish the course of this nerve. The DCBUN was dissected and traced around the ulnar border of the wrist. The distance from the tip of the ulnar styloid process to the origin of the DCBUN was measured. The distances from the ulnar styloid process to the DCBUN were measured in supination, pronation, and in a neutral position of the forearm.

Results: The DCBUN originated on average 4.92 cm proximal to the ulnar styloid process. In all cases, the DCBUN crossed the ulnar distal to ulnar styloid process and it moved more closely to the ulnar styloid process with a forearm position change from supination to pronation.

Conclusions: We recommend making a skin incision on the ulnar side around the styloid process with the forearm in supination or neutral position was another method to avoid injury of DCBUN.