Can MRI accurately detect pilon articular malreduction? A quantitative comparison between CT and 3T MRI bone models

Quantitative analysis of sagittal curvatures of the tibial plafond by computed tomography

Background

Although the talar morphology has been well understood, studies on the corresponding tibial plafond are still lacking. Based on computed tomography (CT) data, this quantitative study divided the tibial plafond into anterior and posterior regions on five sagittal sections. The objectives of this study were (I) to determine whether the sagittal curvatures of the tibial plafond can be quantitatively and accurately described using the double-diameter method; (II) to compare the difference between the anterior and posterior diameters on five sagittal sections.

Methods

In this study, CT data were collected from 100 adult ankles, and the three-dimensional (3D) ankle joint model was reconstructed using CT images. An anatomical coordinate system of the 3D ankle joint model was created to establish the standard coronal and sagittal planes. The measurement outcomes of sagittal curvatures included: the anterior and posterior diameters, the distal tibial arc length (TiAL) and the distal tibial mortise depth (TMD) on five sagittal sections (the most medial, medial 1/4, middle, lateral 1/4 and the most lateral section). Subgroup analysis was performed to compare the differences between males and females.

Results

Analysis of the sagittal curvatures showed that the anterior diameter of tibial plafond was significantly smaller than the posterior diameter on five sagittal sections with a mean difference ranging from 3.9 to 6.8 mm (P<0.001). For the anterior diameters, the anteromedial curve had the smallest diameter (35.3±5.3 mm), and the anterolateral curve had the largest diameter (38.0±5.8 mm). For the posterior diameter, the posteromedial curve had the smallest diameter (39.2±6.4 mm), and the posterolateral 1/4 curve had the largest diameter (43.5±6.9 mm). One-way analysis of variance (ANOVA) revealed significant differences in the anterior and posterior diameters among five groups (P<0.012). Subgroup analysis showed that gender partly affected the results of sagittal curvature measurements.

Conclusions

The sagittal curvatures of the tibial plafond can be described quantitatively and accurately using anterior and posterior diameters. Our study showed that there were significant differences between the anterior and posterior diameters, and gender was an important factor influencing the sagittal curvatures of the tibial plafond.

Weight-Bearing CT Scan After Tibial Pilon Fracture Demonstrates Significant Early Joint-Space Narrowing

BACKGROUND

Posttraumatic osteoarthritis (PTOA) is a common and early sequela of tibial pilon fractures resulting in substantial long-term disability. New approaches are needed to objectively and reliably quantify early disease progression in order to critically assess the impact of interventions aimed at preventing or mitigating PTOA. Weight-bearing computed tomography (WBCT) scans provide a means for measuring joint space while the ankle is in a loaded, functional position. We assessed the interrater and intrarater reliability of a standardized, regional method to quantify joint-space loss following tibial pilon fracture compared with the uninjured contralateral ankle.

METHODS

We prospectively enrolled 20 patients with intra-articular tibial pilon fractures that were surgically treated at 1 of 2 level-I trauma centers. Six months after injury, bilateral ankle WBCT scans were obtained. Joint space was measured by 4 reviewers at 9 discrete regions of the tibiotalar articulation on sagittal images. Measurements were repeated by reviewers 2 weeks later. To characterize the measurement method, interrater correlation coefficient estimates and test-retest reproducibility were calculated.

RESULTS

The mean tibiotalar joint space was 21% less in the injured ankles compared with the contralateral uninjured ankles (p < 0.0001). The middle-lateral and middle-central regions of the joint demonstrated the greatest decrease in joint space between injured and uninured ankles. The interrater correlation coefficient of the measurement technique was 0.88, and the test-retest reproducibility was 0.80, indicating good reliability and reproducibility of the method.

CONCLUSIONS

We developed a simple, standardized, and reliable technique to quantify tibiotalar joint space following tibial pilon fracture on WBCT. Significant loss of joint space is seen 6 months after the injury. This tool can be used to longitudinally quantify loss of joint space following pilon fracture and assess the impact of interventions to reduce PTOA.

Comparison of cartilage and bone morphological models of the ankle joint derived from different medical imaging technologies

Background

Accurate geometrical models of bones and cartilage are necessary in biomechanical modelling of human joints, and in planning and designing of joint replacements. Image-based subject-specific model development requires image segmentation, spatial filtering and 3-dimensional rendering. This is usually based on computed tomography (CT) for bone models, on magnetic resonance imaging (MRI) for cartilage models. This process has been reported extensively in the past, but no studies have ever compared the accuracy and quality of these models when obtained also by merging different imaging modalities. The scope of the present work is to provide this comparative analysis in order to identify optimal imaging modality and registration techniques for producing 3-dimensional bone and cartilage models of the ankle joint.

Methods

One cadaveric leg was instrumented with multimodal markers and scanned using five different imaging modalities: a standard, a dual-energy and a cone-beam CT (CBCT) device, and a 1.5 and 3.0 Tesla MRI devices. Bone, cartilage, and combined bone and cartilage models were produced from each of these imaging modalities, and registered in space according to matching model surfaces or to corresponding marker centres. To assess the quality in overall model reconstruction, distance map analyses were performed and the difference between model surfaces obtained from the different imaging modalities and registration techniques was measured.

Results

The registration between models worked better with model surface matching than corresponding marker positions, particularly with MRI. The best bone models were obtained with the CBCT. Models with cartilage were defined better with the 3.0 Tesla than the 1.5 Tesla. For the combined bone and cartilage models, the colour maps and the numerical results from distance map analysis (DMA) showed that the smallest distances and the largest homogeneity were obtained from the CBCT and the 3.0 T MRI via model surface registration.

Conclusions

These observations are important in producing accurate bone and cartilage models from medical imaging and relevant for applications such as designing of custom-made ankle replacements or, more in general, of implants for total as well as focal joint replacements.

Advanced MRI Techniques for the Ankle

OBJECTIVE

The purposes of this article are to present a state-of-the-art routine protocol for MRI of the ankle, to provide problem-solving tools based on specific clinical indications, and to introduce principles for the implementation of ultrashort echo time MRI of the ankle, including morphologic and quantitative assessment.

CONCLUSION

Ankle injury is common among both athletes and the general population, and MRI is the established noninvasive means of evaluation. The design of an ankle protocol depends on various factors. Higher magnetic field improves signal-to-noise ratio but increases metal artifact. Specialized imaging planes are useful but prolong acquisition times. MR neurography is useful, but metal reduction techniques are needed whenever a metal prosthesis is present. An ultrashort echo time sequence is a valuable tool for both structural and quantitative evaluation.