Department of Orthopedics, University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
Department of Radiology, University Hospital Balgrist, University of Zurich, Zurich, Switzerland.
Arch Orthop Trauma Surg. 2022 Nov;142(11):3149-3155. doi: 10.1007/s00402-021-03947-4. Epub 2021 May 12.
This study aimed to quantify the effect of lower limb rotational parameters on the difference in the tibial-tubercle-trochlear-groove (TTTG) distance when assessed with magnetic resonance imaging (MRI) and computed tomography (CT) in patients with patellar instability. It was hypothesized that an increased native knee rotation angle significantly contributes to an underestimation of TTTG by MRI.
Forty patients with patellar instability who had undergone standard radiographs, MRI and CT scans were included in this retrospective study. A musculoskeletal radiologist assessed all imaging for TTTG, femoral and tibial rotation, knee rotation and flexion angle, and trochlear dysplasia. ΔTTTG was defined as the TTTG measured on MRI subtracted from the TTTG measured on CT. Statistical analysis determined the effect of these parameters on the calculated difference between TTTG when measured on CT and MRI.
Equal knee flexion in MRI and CT resulted in a ΔTTTG of 0.1 ± 0.3 mm compared to 4.0 ± 3.3 mm in patients with different knee flexion angles in both imaging acquisitions (p = 0.036). The knee rotation angle measured on CT (native knee rotation angle) was negatively correlated with ΔTTTG (r = - 0.365; p = 0.002), while neither tibial nor femoral rotation showed any associations with TTTG (n.s.). Trochlear dysplasia did not show any significant correlation with ΔTTTG, regardless of classification by Dejour or Lippacher (n.s.). Both the native knee rotation angle and the MRI knee flexion angle were independent predictors of ΔTTTG, yet with an opposing effect (knee rotation: 95% Confidence Interval [CI] for β - 0.468 to - 0.154, p < 0.001; knee flexion 95% CI for β 0.292 to 0.587, p < 0.001). Patients with a native knee rotation angle > 20° showed a ΔTTTG of - 5.8 ± 4.0 mm (MRI rather overestimates TTTG) compared to 0.9 ± 4.1 mm Δ TTTG (MRI rather underestimates TTTG) in patients with < 20° native knee rotation angle.
The native knee rotation angle is an independent, inversely correlated predictor of ΔTTTG, thus opposing the effect of knee flexion during MRI acquisition. Consequently, these results suggest that not only knee flexion but also knee rotation should be appreciated when assessing TTTG during patellar instability diagnostic evaluation as it can potentially lead to a false estimation of the TTTG distance on MRI.
Level III.
本研究旨在量化下肢旋转参数对髌股关节不稳患者 MRI 和 CT 检查时滑车沟-胫骨结节-髌腱（TTTG）距离差异的影响。假设膝关节自然旋转角度增加会导致 MRI 对 TTTG 的低估。
本回顾性研究纳入了 40 例髌股关节不稳患者，他们接受了标准的 X 线、MRI 和 CT 扫描。一位肌肉骨骼放射科医生评估了所有影像学检查的 TTTG、股骨和胫骨旋转、膝关节旋转和弯曲角度以及滑车发育不良。TTTG 的差值定义为 MRI 测量的 TTTG 减去 CT 测量的 TTTG。统计分析确定了这些参数对 CT 和 MRI 测量的 TTTG 差值的影响。
MRI 和 CT 测量的膝关节相同屈曲度时，TTTG 的差值为 0.1±0.3mm，而在两种影像学采集时膝关节屈曲度不同的患者中，差值为 4.0±3.3mm（p=0.036）。CT 测量的膝关节旋转角度（自然膝关节旋转角度）与 TTTG 的差值呈负相关（r=-0.365；p=0.002），而胫骨或股骨旋转均与 TTTG 无相关性（n.s.）。无论采用 Dejour 还是 Lippacher 分类，滑车发育不良与 TTTG 的差值均无显著相关性（n.s.）。自然膝关节旋转角度和 MRI 膝关节屈曲角度都是 TTTG 差值的独立预测因素，但作用相反（膝关节旋转：β的 95%置信区间为-0.468 至-0.154，p<0.001；膝关节屈曲 95%置信区间为 0.292 至 0.587，p<0.001）。自然膝关节旋转角度>20°的患者 TTTG 差值为-5.8±4.0mm（MRI 高估 TTTG），而自然膝关节旋转角度<20°的患者 TTTG 差值为 0.9±4.1mm（MRI 低估 TTTG）。
自然膝关节旋转角度是 TTTG 差值的独立、负相关预测因素，与 MRI 采集时膝关节屈曲的作用相反。因此，这些结果表明，在髌股关节不稳诊断评估中评估 TTTG 时，不仅要考虑膝关节屈曲，还要考虑膝关节旋转，因为这可能会导致 MRI 上 TTTG 距离的错误估计。
III 级。
