Linear Anterior-Posterior Computed Tomography Parameters Used to Quantify Trochlear Dysplasia Are More Reliable Than Angular Measurements.

PURPOSE: (1) To evaluate the reliability of 9 commonly used quantitative parameters of the trochlear morphology on computed tomography (CT) and (2) to analyze for differences in the reliability regarding patient subgroups (patellofemoral instability [PFI] vs non-PFI). METHODS: A retrospective analysis of lower-limb CT scans performed between August 1996 and February 2013 was performed. The CT scans of all patients with PFI and 30 randomly selected cases without a history of PFI (non-PFI) were included. The following measurements were performed on 1 proximal axial CT slice at the entrance of the trochlear groove and 1 slice 5 mm further distal: relative medial, central, and lateral trochlear height; trochlear depth; relative transverse trochlear shift; trochlear facet asymmetry; sulcus angle; and medial and lateral trochlear slope. Four investigators performed the measurements independently, and intraclass correlation coefficients (ICCs) were calculated for the entire study group, as well as for the PFI and non-PFI groups separately. RESULTS: In total, 66 cases (36 PFI cases) were included in the study. We found almost perfect inter-rater and intrarater agreement for the trochlear height on both axial CT slices (ICC, 0.831-0.977). For the other measurements, we found only fair reliability (ICC < 0.4) on the proximal CT slice, whereas on the distal CT slice, at least moderate reliability (ICC > 0.4) was observed. ICCs were lower for many parameters in the PFI group. Angular values were less reliable than linear values. In particular, measurements involving the medial facet (i.e., sulcus angle, medial trochlear slope, and trochlear facet asymmetry) were less reliable. CONCLUSIONS: When interpreting quantitative parameters defining the trochlear morphology, one must taken into account the considerably lower reliability of angular parameters such as the commonly used sulcus angle compared with linear measurements. Radiologic measurements are less reliable in cases of PFI than in subjects without instability. LEVEL OF EVIDENCE: Level III, retrospective case-control study.

Three-dimensional computed tomography reconstruction improves the reliability of tibial pilon fracture classification and preoperative surgical planning.

PURPOSE: In the present study, we aimed to evaluate the impact of two-dimensional multi-planar computed tomography (2D-MP-CT) scans and three-dimensional surface rendering computed tomography reconstruction (3D-SR-CT) on the inter- and intra-observer reliability of four commonly used classification systems for tibial pilon fractures, and on the reliability and validity of surgical treatment planning for fracture fixation. METHODS: Four observers evaluated computed tomography images of 35 cases with pilon fractures according to the classifications of Rüedi and Allgöwer, AO/OTA, Topliss, and Tang, and recommended a surgical treatment plan, including the surgical approach, implant position, and need for bone graft augmentation. Fractures were first evaluated using 2D-MP-CT, followed by 3D-SR-CT. We calculated the Kappa values for the correlation between the fracture classifications, types of surgical approaches, implant positions, and bone graft recommendations by the observers. Furthermore, we assessed the correlation between the treatment plans recommended by the observers and the actual surgical procedure performed. RESULTS: All classifications showed poor inter-observer reliability and moderate intra-observer reliability with 2D-MP-CT scans. The inter-observer reliability of the Rüedi and Allgöwer, AO/OTA, and Tang classifications improved to moderate, whereas the intra-observer reliability of the AO/OTA classification improved to good with additional 3D-SR-CT. The correlation between the suggested and the actually performed surgical approaches was poor with 2D-MP-CT, but improved to moderate with 3D-SR-CT. The suggested plate positions showed a moderate correlation with the actually performed plating; although the correlation improved significantly, it remained moderate with 3D-SR-CT. CONCLUSION: The use of 3D-SR-CT reconstruction can improve the reliability of the Rüedi and Allgöwer, AO/OTA, and Tang classifications. Furthermore, three-dimensional imaging enables a more valid planning of the surgical approach and implant position.

Segmental torsion assessment is a reliable method for in-depth analysis of femoral alignment in Computer Tomography.

PURPOSE: De-rotational osteotomies are indicated in patients with pathologic femoral torsion. However, there is disagreement whether an osteotomy should be performed proximally or distally. Conventionally only the total torsion is measured, which does not allow differentiation between a torsional deformity located in the proximal or distal metaphysis or the diaphysis. The aim of this study is to validate a new multi-level measurement protocol for evaluation of the magnitude of torsion of the respective femoral segments in CT. PATIENTS AND METHODS: The torsional profile of 30 femora was evaluated in CT scans. For separate measurements of the torsion of the metaphysis and the diaphysis, four axes where determined: one through the femoral neck, a second determined by the midpoint of the femoral shaft and the lesser trochanter, a third determined by a tangent dorsal to the popliteal surface, and a fourth axis posterior to the condyles. The total femoral torsion was measured between the first and the fourth axis, proximal torsion between the first and the second, mid torsion between the second and the third, and distal torsion between the third and the fourth axis. Four investigators performed all measurements independently and intra-class correlation coefficients (ICC) were calculated to evaluate intra- and inter-rater reliability. RESULTS: Average total femoral torsion was 22.6 ± 8.7°, proximal torsion 47.7 ± 10.6°, mid torsion -33.4 ± 9.9°, and distal torsion 8.3 ± 3.2°. Intra-rater ICC ranged between 0.504 and 0.957 and inter-rater ICC between 0.643 and 0.992. The majority of the ICC were graded as "almost perfect" and some as "substantial" agreement. CONCLUSION: Evaluation of the segmental torsion of the femur allows in-depth analysis of femoral alignment. High reliability was shown for this measuring method in computed tomography, which can be deployed when studying interdependencies between joint pathologies and torsional deformities or when planning the site for an osteotomy. LEVEL OF EVIDENCE: Level III.