Radiographic cup position following posterior and lateral approach to total hip arthroplasty. An explorative randomized controlled trial

The two most common surgical approaches to total hip arthroplasty are the posterior approach and lateral approach. The surgical approach may influence cup positioning and restoration of the offset, which may affect the biomechanical properties of the hip joint.
The primary aim was to compare cup position between posterior approach and lateral approach. Secondary aims were to compare femoral offset, abductor moment arm and leg length discrepancy between the two approaches. Eighty patients with primary hip osteoarthritis were included in a randomized controlled trial and assigned to total hip arthroplasty using posterior approach or lateral approach. Postoperative radiographs from 38 patients in each group were included in this study for measurement of cup anteversion and inclination. Femoral offset, cup offset, total offset, abductor moment arm and leg length discrepancy were measured on preoperative and postoperative radiographs in 28 patients in each group. We found that mean anteversion was 5° larger in the posterior approach group (95% CI, -8.1 to -1.4; p = 0.006), while mean inclination was 5° less steep (95% CI, 2.7 to 7.2; p<0.001) compared with the lateral approach group. The posterior approach group had a larger mean femoral offset of 4.3mm (95% CI, -7.4 to -1.3, p = 0.006), mean total offset of 6.3mm (95% CI, -9.6 to -3; p<0.001) and mean abductor moment arm of 4.8mm (95% CI, -7.6 to -1.9; p = 0.001) compared with the lateral approach group. We found a larger cup anteversion but less steep cup inclination in the posterior approach group compared with the lateral approach group. Femoral offset and abductor moment arm were restored after total hip arthroplasty using lateral approach but significantly increased when using posterior approach.

全髋关节置换术(total hip arthroplasty)最常用的两种手术入路为后入路(posterior approach)与外侧入路(lateral approach)。手术入路可影响臼杯(cup)位置及髋部偏距(offset)的重建，进而改变髋关节的生物力学特性。
本研究的首要目的为对比后入路与外侧入路下的臼杯位置；次要目的为比较两种入路间的股骨偏距、外展肌力矩臂及下肢长度不等情况。本研究纳入80例原发性髋骨关节炎患者，开展随机对照试验，将其随机分配至接受后入路或外侧入路全髋关节置换术组。本研究纳入两组各38例患者的术后放射影像，用于测量臼杯前倾角与臼杯外展角。两组各28例患者的术前及术后放射影像均用于测量股骨偏距、臼杯偏距、总偏距、外展肌力矩臂及下肢长度不等。
研究结果显示：与外侧入路组相比，后入路组的平均臼杯前倾角大5°（95%置信区间：-8.1~-1.4；p=0.006），而平均臼杯外展角更平缓5°（95%置信区间：2.7~7.2；p<0.001）。与外侧入路组相比，后入路组的平均股骨偏距增加4.3mm（95%置信区间：-7.4~-1.3；p=0.006）、平均总偏距增加6.3mm（95%置信区间：-9.6~-3.0；p<0.001）以及平均外展肌力矩臂增加4.8mm（95%置信区间：-7.6~-1.9；p=0.001）。本研究发现，相较于外侧入路组，后入路组的臼杯前倾角更大、臼杯外展角更平缓。采用外侧入路行全髋关节置换术后，股骨偏距与外展肌力矩臂可得到有效重建，而采用后入路时则会出现显著升高。