Evaluation of the horizontal approach to the medial malleolar facet in sagittal talar fractures through dorsiflexion and plantarflexion positions

Abstract

Background: Talar fractures often require osteotomy during surgery to achieve reduction and screw fixation of the fractured fragments due to limited visualization and operating space of the talar articular surface. The objective of this study was to evaluate the horizontal approach to the medial malleolus facet by maximizing exposure through dorsiflexion and plantarflexion positions.

Methods: In dorsiflexion, plantarflexion, and functional foot positions, we respectively obtained the anterior and posterior edge lines of the projection of the medial malleolus on the medial malleolar facet. The talar model from Mimics was imported into Geomagic software for image refinement. Then Solidworks software was used to segment the medial surface of the talus and extend the edge lines from the three positions to project them onto the "semicircular" base for 2D projection. The exposed area in different positions, the percentage of total area it represents, and the anatomic location of the insertion point at the groove between the anteroposternal protrusions of the medial malleolus were calculated.

Results: The mean total area of the "semicircular" region on the medial malleolus surface of the talus was 542.10 ± 80.05 mm2. In the functional position, the exposed mean area of the medial malleolar facet around the medial malleolus both anteriorly and posteriorly was 141.22 ± 24.34 mm2, 167.58 ± 22.36mm2, respectively. In dorsiflexion, the mean area of the posterior aspect of the medial malleolar facet was 366.28 ± 48.12 mm2. In plantarflexion, the mean of the anterior aspect of the medial malleolar facet was 222.70 ± 35.32 mm2. The mean overlap area of unexposed area in both dorsiflexion and plantarflexion was 23.32 ± 5.94 mm2. The mean percentage of the increased exposure area in dorsiflexion and plantarflexion were 36.71 ± 3.25% and 15.13 ± 2.83%. The mean distance from the insertion point to the top of the talar dome was 10.69 ± 1.24 mm, to the medial malleolus facet border of the talar trochlea was 5.61 ± 0.96 mm, and to the tuberosity of the posterior tibiotalar portion of the deltoid ligament complex was 4.53 ± 0.64 mm.

Conclusions: Within the 3D model, we measured the exposed area of the medial malleolus facet in different positions and the anatomic location of the insertion point at the medial malleolus groove. When the foot is in plantarflexion or dorsiflexion, a sufficiently large area and operating space can be exposed during surgery. The data regarding the exposed visualization area and virtual screws need to be combined with clinical experience for safer reduction and fixation of fracture fragments. Further validation of its intraoperative feasibility will require additional clinical research.

Fig 1. The anterior and posterior edge lines of the projection of the medial malleolus on the medial surface of the talus (red lines).

A In the functional position, the anterior edge lines of the projection of the medial malleolus. B In the functional position, the posterior edge lines of the projection of the medial malleolus. C In dorsiflexion, the posterior edge lines of the projection of the medial malleolus. D In plantarflexion, the anterior edge lines of the projection of the medial malleolus.

Fig 2. The measurement of exposed area of medial malleolar facet.

A The "semicircular" area of the medial malleolar facet. B The projected lines on the medial malleolus facet in the three positions (Black-Functional position; Red-Plantarflexion position; Green-Dorsiflexion position).

Fig 3. The measurement of virtual screws in the model.

A The insertion point of the virtual screw is within the groove between the anteroposternal protrusions of the medial malleolus. B Anatomic location of virtual screw (L1: the distance of the insertion point to the top of the talar dome; L2: the distance of the insertion point to the medial malleolus facet border of the talus trochlea; L3: the distance of the insertion point to the tuberosity of the posterior tibiotalar portion of the deltoid ligament complex).

Fig 4. After applying traction, the joint space widens (red lines).

A In the neutral position (no traction). B In the neutral position (with traction). C In the lateral position (no traction). D In the lateral position (with traction).