Objective The purpose of this work was to compare measurements of talar cartilage thickness and cartilage and bone surface geometry from clinically feasible magnetic resonance imaging (MRI) against high-accuracy laser scan models. Measurement of talar bone and cartilage geometry from MRI would provide useful information for evaluating cartilage changes, selecting osteochondral graft sources or creating patient-specific joint models. Design Three-dimensional (3D) bone and cartilage models of 7 cadaver tali were created using (1) manual segmentation of high-resolution volumetric sequence 3T MR images and (2) laser scans. Talar cartilage thickness was compared between the laser scan– and MRI-based models for the dorsal, medial, and lateral surfaces. The laser scan– and MRI-based cartilage and bone surface models were compared using model-to-model distance. Results Average cartilage thickness within the dorsal, medial, and lateral surfaces were 0.89 to 1.05 mm measured with laser scanning, and 1.10 to 1.22 mm measured with MRI. MRI-based thickness was 0.16 to 0.32 mm higher on average in each region. The average absolute surface-to-surface differences between laser scan– and MRI-based bone and cartilage models ranged from 0.16 to 0.22 mm for bone (MRI bone models smaller than laser scan models) and 0.35 to 0.38 mm for cartilage (MRI bone models larger than laser scan models). Conclusions This study demonstrated that cartilage and bone 3D modeling and measurement of average cartilage thickness on the dorsal, medial, and lateral talar surfaces using MRI were feasible and provided similar model geometry and thickness values to ground-truth laser scan–based measurements.

Risk, III.

Background: The purposes of this study were to determine (1) if cartilage thicknesses on the talar dome and medial/lateral surfaces of the talus were similar, (2) whether there was sufficient donor cartilage surface area on the medial and lateral talar surfaces to repair talar dome cartilage injuries of the talus, and (3) whether the cartilage surface could be increased following anterior talofibular ligament (ATFL) and sectioning of the tibionavicular and tibiospring portion of the anterior deltoid. Methods: Medial and lateral approaches were utilized in 8 cadaveric ankles to identify the accessible medial, lateral, and talar dome cartilage surfaces in 3 conditions: (1) intact, (2) ATFL release, and (3) superficial anterior deltoid ligament release. The talus was explanted, and the cartilage areas were digitized with a coordinate measuring machine. Cartilage thickness was quantified using a laser scanner. Results: The mean cartilage thickness was 1.0 ± 0.1 mm in all areas tested. In intact ankles, the medial side of the talus showed a larger total area of available cartilage than the lateral side (152 mm2 vs 133 mm2). ATFL release increased the available cartilage area on the medial and lateral sides to 167 mm2 and 194 mm2, respectively. However, only the lateral talar surface had sufficient circular graft donor cartilage available for autologous osteochondral transplantation (AOT) procedures of the talus. After ATFL and deltoid sectioning, there was an increase in available graft donor cartilage available for AOT procedures. Conclusion: The thickness of the medial and lateral talar cartilage surfaces is very similar to that of the talar dome cartilage surface, which provides evidence that the medial and lateral surfaces may serve as acceptable AOT donor cartilage. The surface area available for AOT donor site grafting was sufficient in the intact state; however, sectioning the ATFL and superficial anterior deltoid ligament increased the overall lateral talar surface area available for circular grafting for an AOT procedure that requires a larger graft. These results support the idea that lateral surfaces of the talus may be used as donor cartilage for an AOT procedure since donor and recipient sites are similar in cartilage thickness, and there is sufficient cartilage surface area available for common lesion sizes in the foot and ankle. Clinical Relevance: This anatomical study investigates the feasibility of talar osteochondral autografts from the medial or lateral talar surfaces exposed with standard approaches. It confirms the similar cartilage thickness of the talar dome and the ability to access up to an 8- to 10-mm donor graft from the lateral side of the talus after ligament release. This knowledge may allow better operative planning for use of these surfaces for osteochondral lesions within the foot and ankle, particularly in certain circumstances of a revision microfracture.