背景和目的：以尺骨截骨縮短術治療有症狀之正尺骨變異而其遠端橈尺關節為Tolat第三型者，和以橈骨截骨縮短術治療負尺骨變異之Kienböck疾病，已被注意到術後可能增加發生遠端橈尺關節退化性關節炎的風險。本研究的目的是要探討遠端橈尺關節包括其尺骨變異之各種類型，並瞭解在台灣成人中各類型之分佈情形，尤其注意上述兩種類型之盛行率，以助手術治療之術前評估與決策。方法：回顧264張標準之成人正常腕部正面X-光影像，以橈骨乙狀切迹偏向遠端或近端5度為基準，以判定Tolat氏原始分類之類型，加上尺骨變異之類型，將遠端橈尺關節更完整詳細地分類。結果：遠端橈尺關節有8種類型，其中有問題的兩種；IIc型（橈骨乙狀切迹面向近端而尺骨為負變異）與IIIb型（橈骨乙狀切迹面向遠端，尺骨為正變異）之盛行率各為8.3%與11.4%，而女性具IIIb型者遠多於男性。結論：台灣成人正常手腕有19.7%具有上述兩種類型之一的遠端橈尺關節，當需要手術修改尺骨變異時，可修正的長度會受到乙狀切迹的限制，因此術前要謹慎評估，尤其是女性，IIIb型遠較男性為多，施行尺骨縮短術時需要格外謹慎。

Background and purpose: Ulnar shortening osteotomy for symptomatic positive ulnar variance with Tolat’s type Ⅲ distal radioulnar joint (DRUJ) and radial shortening for treating Kienböck's disease in the wrist of negative ulnar variance with type II DRUJ have been noticed to have increased risk of post- operative DRUJ osteoarthritis. The purpose of our study was to indentify various configurations of DRUJ relating to the ulnar variance and determine their prevalences in our population with special attention to these two potentially problematic configurations. Methods: The standard posteroanterior view of 264 normal adult wrist radiographs were reviewed. The sigmoid notch obliquity angle was measured and the cut-off values to determine the Tolat’s type were defined at 5 drgress either facing proximal or distally. The DRUJ was further classified by adding ulnar variance to the original Tolat’s classification system. Results There were 8 radiographic types of DRUJ. The prevalences of the potentially problematic types IIc(proximally facing radial sigmoid notch with negative ulnar variance) and IIIb(distally facing radial sigmoid notch with positive ulnar variance) were 8.3% and 11.4% respectively. The females had much higher prevalence of type IIIb than males. Conclusions: A total of 19.7% of our adult wrists are with one of these two problematic types of DRUJ which limit the length of correction and require prudent preoperative planning when surgeries altering the ulnar variance become indicated. Special attention is recommended for the females as they have much higher prevalence of type IIIb than the males.