The importance of the global offset, the sum of femoral and acetabular offset, has been underlined in the literature as a key factor for the functional outcome of total hip arthroplasty (THA). However, the acetabular offset is not defined for bi-plane X-rays, a technology providing 3D measurements of the lower limb and commonly used for patients undergoing THA. The aim of this paper is to introduce a measurement method of the 3D acetabular offset with bi-plane X-rays. Our method combines the use of technical and anatomical coordinate systems. The most appropriate definition will be selected based on the best reliability and measurement error. The consequent reliability of the global offset was also assessed. Twenty-eight patients undergoing primary THA were selected retrospectively. Two operators performed three reconstructions for each patients before and after THA. Intraclass correlation (ICC) and smallest detectable change (SDC) were computed for intra-operator, inter-operator and test–retest conditions for all combinations of technical and anatomical coordinate systems. ICCs were good to excellent. One combination was more reliable than others with a moderate mean SDC of 6.3 mm (4.3–8.7 mm) for the acetabular offset and a moderate mean SDC of 6.2 mm (5.6–6.7 mm) for the global offset. This is similar to the reliability and mean SDC of the femoral offset (4.8 mm) approved for clinical use which indicates that this method of acetabular offset measurement is appropriate. This opens a research avenue to better understand the role of the acetabular offset on THA outcomes, which seems overlooked in the literature.

整体偏移量的重要性，即股骨和髋臼偏移量的总和，已在文献中被强调为全髋关节置换术 (THA) 功能结果的关键因素。然而，双平面 X 射线没有定义髋臼偏移，双平面 X 射线是一种提供下肢 3D 测量的技术，通常用于接受 THA 的患者。本文的目的是介绍一种用双平面 X 射线测量 3D 髋臼偏移的方法。我们的方法结合了技术和解剖坐标系的使用。将根据最佳可靠性和测量误差选择最合适的定义。还评估了由此产生的全球抵消的可靠性。回顾性选择了 28 名接受初次 THA 的患者。两名操作者在全髋关节置换前后为每位患者进行了三次重建。针对技术和解剖坐标系的所有组合，针对操作者内部、操作者间和测试-再测试条件计算了类内相关性 (ICC) 和最小可检测变化 (SDC)。ICC 从优秀到优秀。一种组合比其他组合更可靠，髋臼偏移的平均 SDC 为 6.3 毫米（4.3-8.7 毫米），整体偏移的平均 SDC 为 6.2 毫米（5.6-6.7 毫米）。这与批准用于临床的股骨偏移量 (4.8 mm) 的可靠性和平均 SDC 相似，表明这种髋臼偏移量测量方法是合适的。这开辟了一条研究途径，可以更好地理解髋臼偏移对 THA 结果的作用，这在文献中似乎被忽视了。