The clinical diagnosis of distal radioulnar joint (DRUJ) instability remains challenging. The current diagnostic gold standard is a dynamic computerized topography (CT) scan. This investigation compares the affected and normal wrists in multiple static positions of forearm rotation.. However, its accuracy has been questioned, as the wrist is unloaded and not placed under stress. This may fail to capture DRUJ instability that does not result in static malalignment between the ulnar head and sigmoid notch. The purpose of this biomechanical study was to evaluate the effectiveness of both dynamic and stress CT scans in detecting DRUJ instability.

A customized DRUJ arthrometer was designed that allows for both static positioning, as well as dorsal and volar loading at the DRUJ in various degrees of forearm rotation. Ten fresh frozen cadavers were prepared and mounted in the apparatus. CT scans were performed both in the unloaded condition (dynamic CT) and with each arm subjected to a standardized 50N volar and dorsal force (stress CT) in neutral and maximum pronation/ supination. The TFCC (triangular fibrocartilage complex)was then sectioned peripherally to simulate DRUJ instability and the methodology was repeated. CT scans were then evaluated for displacement using the radioulnar ratio method.

When calculating the radioulnar ratio for intact wrists using the dynamic CT technique, values were 0.50, 0.64, 0.34 for neutral, pronation and supination, respectively. When the TFCC was sectioned and protocol repeated, the values for the simulated unstable wrist for dynamic CT were 0.54, 0.62, 0.34 for neutral, pronation and supination, respectively. There was no statistically significant difference between the intact and sectioned states for any position of forearm rotation using dynamic CT. Usingstress CT, mean radioulnar ratios for the intact specimens were calculated to be 0.44, 0.36 and 0.31 for neutral, pronation and supination, respectively. After sectioning the TFCC, the radioulnar ratios increased to 0.61, 0.39 and 0.46 for neutral, pronation and supination. There was a statistically significant difference between intact and simulated-unstable wrists in supination (p = 0.002) and in neutral (p=0.003).

The radioulnar ratio values used to measure DRUJ translation for dynamic CT scans were unable to detect a statistically significant difference between stable and simulated unstable wrists. This was true for all positions of forearm rotation. However, when a standard load was placed across the DRUJ, statically significant changes in the radioulnar ratio were seen in neutral and supination between stable and simulated unstable wrists. This discrepancy challenges the current gold standard of dynamic CT in its ability to accurately diagnosis DRUJ instability. It also introduces stress CT as a possible solution for diagnosing DRUJ instability from peripheral TFCC lesions.

Longstanding un-united scaphoid fractures or scapholunate insufficiency can progress to degenerative wrist osteoarthritis (termed scaphoid non-union advanced collapse (SNAC) or scapho-lunate advanced collapse (SLAC) respectively). Scaphoid excision and partial wrist fusion is a well-established procedure for the surgical treatment of this condition. In this study we present a novel technique and mid-term results, where fusion is reserved for the luno-capitate and triquetro-hamate joints, commonly referred to as bicolumnar fusion. The purpose of this study was to report functional and radiological outcomes in a series of patients who underwent this surgical technique.

This was a prospective study of 23 consecutive patients (25 wrists) who underwent a bicolumnar carpal fusion from January 2014 to January 2017 due to a stage 2 or 3 SNAC/SLAC wrist, with a minimum follow-up of one year. In all cases two retrograde cannulated headless compression screws were used for inter-carpal fixation. The clinical assessment consisted of range of motion, grip and pinch strength that were compared with the unaffected contralateral side where possible. Patient-reported outcome measures, including the DASH and PRWE scores were analysed. The radiographic assessment parameters consisted of fusion state and the appearance of the radio-lunate joint space. We also examined the relationship between the capito-lunate fusion angle and wrist range of motion, comparing wrists fused with a capito-lunate angle greater than 20° of extension with wrists fused in a neutral position.

The average follow-up was 2.9 years. The mean wrist extension was 41°, flexion 36° and radial-ulnar deviation arc was 43° (70%, 52% and 63% of contralateral side respectively). Grip strength was 40 kg and pinch strength was 8.9 kg, both 93% of contralateral side. Residual pain for activities of daily living was 1.4 (VAS). The mean DASH and PRWE scores were 19±16 and 29±18 respectively. There were three cases of non-union (fusion rate of 88%). Two wrists were converted to total wrist arthroplasty and one partial fusion was revised and healed successfully. Patients with an extended capito-lunate fusion angle trended toward more wrist extension but this did not reach statistical significance (P= 0.07). Wrist flexion did not differ between groups. Radio-lunate joint space narrowing progressed in 2 patients but did not affect their functional outcome.

After bicolumnar carpal fusion using retrograde headless screws, patients in this series maintained a functional flexion-extension arc of motion, with grip-pinch strength that was close to normal. These functional outcomes and fusion rates were comparable with standard 4-corner fusion technique. A capito-lunate fusion angle greater than 20° may provide more wrist extension but further investigation is required to establish this effect. This technique has the advantage that compression screws are placed in a retrograde fashion, which does not violate the proximal articular surface of the lunate, preserving the residual load-bearing articulation. Moreover, the hardware is completely contained, with no revision surgery for hardware removal required in this series.