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CT with 3D Rendering of the Tendons of the Foot and Ankle: Technique, Normal Anatomy, and Disease¹

¹ From the Department of Radiology, 0279, Indiana University School of Medicine, 550 N University Blvd, Indianapolis, IN 46202-5253. Presented as an education exhibit at the 2001 RSNA scientific assembly. Received May 12, 2003; revision requested June 12 and received July 24; accepted July 25. Address correspondence to R.H.C. (e-mail: rchoplin@iupui.edu).

View larger version (108K): [in a new window]   Figure 1a. Articular facets of the subtalar joint. (a) On an axial MPR image obtained at the level of the talocalcaneal articulations, the posterior calcaneal facet (black arrow) is well depicted, but the middle (arrowhead) and anterior (curved white arrow) facets are not. There is a fracture at the medial end of the navicular bone (straight white arrow). (b-d) Coronal MPR images (b is the most posterior, d is the most anterior) show the posterior facet (arrow in b), middle facet (arrowhead in c), and anterior facet (curved arrow in d). The fracture at the medial end of the navicular bone is again noted (straight arrow in d). (e-g) Sagittal MPR images show the posterior facet (arrow in e), middle facet (arrowhead in f), and anterior facet (arrow in g).

View larger version (115K): [in a new window]   Figure 1b. Articular facets of the subtalar joint. (a) On an axial MPR image obtained at the level of the talocalcaneal articulations, the posterior calcaneal facet (black arrow) is well depicted, but the middle (arrowhead) and anterior (curved white arrow) facets are not. There is a fracture at the medial end of the navicular bone (straight white arrow). (b-d) Coronal MPR images (b is the most posterior, d is the most anterior) show the posterior facet (arrow in b), middle facet (arrowhead in c), and anterior facet (curved arrow in d). The fracture at the medial end of the navicular bone is again noted (straight arrow in d). (e-g) Sagittal MPR images show the posterior facet (arrow in e), middle facet (arrowhead in f), and anterior facet (arrow in g).

View larger version (114K): [in a new window]   Figure 1c. Articular facets of the subtalar joint. (a) On an axial MPR image obtained at the level of the talocalcaneal articulations, the posterior calcaneal facet (black arrow) is well depicted, but the middle (arrowhead) and anterior (curved white arrow) facets are not. There is a fracture at the medial end of the navicular bone (straight white arrow). (b-d) Coronal MPR images (b is the most posterior, d is the most anterior) show the posterior facet (arrow in b), middle facet (arrowhead in c), and anterior facet (curved arrow in d). The fracture at the medial end of the navicular bone is again noted (straight arrow in d). (e-g) Sagittal MPR images show the posterior facet (arrow in e), middle facet (arrowhead in f), and anterior facet (arrow in g).

View larger version (104K): [in a new window]   Figure 1d. Articular facets of the subtalar joint. (a) On an axial MPR image obtained at the level of the talocalcaneal articulations, the posterior calcaneal facet (black arrow) is well depicted, but the middle (arrowhead) and anterior (curved white arrow) facets are not. There is a fracture at the medial end of the navicular bone (straight white arrow). (b-d) Coronal MPR images (b is the most posterior, d is the most anterior) show the posterior facet (arrow in b), middle facet (arrowhead in c), and anterior facet (curved arrow in d). The fracture at the medial end of the navicular bone is again noted (straight arrow in d). (e-g) Sagittal MPR images show the posterior facet (arrow in e), middle facet (arrowhead in f), and anterior facet (arrow in g).

View larger version (117K): [in a new window]   Figure 1e. Articular facets of the subtalar joint. (a) On an axial MPR image obtained at the level of the talocalcaneal articulations, the posterior calcaneal facet (black arrow) is well depicted, but the middle (arrowhead) and anterior (curved white arrow) facets are not. There is a fracture at the medial end of the navicular bone (straight white arrow). (b-d) Coronal MPR images (b is the most posterior, d is the most anterior) show the posterior facet (arrow in b), middle facet (arrowhead in c), and anterior facet (curved arrow in d). The fracture at the medial end of the navicular bone is again noted (straight arrow in d). (e-g) Sagittal MPR images show the posterior facet (arrow in e), middle facet (arrowhead in f), and anterior facet (arrow in g).

View larger version (124K): [in a new window]   Figure 1f. Articular facets of the subtalar joint. (a) On an axial MPR image obtained at the level of the talocalcaneal articulations, the posterior calcaneal facet (black arrow) is well depicted, but the middle (arrowhead) and anterior (curved white arrow) facets are not. There is a fracture at the medial end of the navicular bone (straight white arrow). (b-d) Coronal MPR images (b is the most posterior, d is the most anterior) show the posterior facet (arrow in b), middle facet (arrowhead in c), and anterior facet (curved arrow in d). The fracture at the medial end of the navicular bone is again noted (straight arrow in d). (e-g) Sagittal MPR images show the posterior facet (arrow in e), middle facet (arrowhead in f), and anterior facet (arrow in g).

View larger version (137K): [in a new window]   Figure 1g. Articular facets of the subtalar joint. (a) On an axial MPR image obtained at the level of the talocalcaneal articulations, the posterior calcaneal facet (black arrow) is well depicted, but the middle (arrowhead) and anterior (curved white arrow) facets are not. There is a fracture at the medial end of the navicular bone (straight white arrow). (b-d) Coronal MPR images (b is the most posterior, d is the most anterior) show the posterior facet (arrow in b), middle facet (arrowhead in c), and anterior facet (curved arrow in d). The fracture at the medial end of the navicular bone is again noted (straight arrow in d). (e-g) Sagittal MPR images show the posterior facet (arrow in e), middle facet (arrowhead in f), and anterior facet (arrow in g).

View larger version (77K): [in a new window]   Figure 2a. VR imaging of the foot and ankle (same patient as in Fig 1). (a) VR image of the bones depicts the osseous structures of the foot and ankle. (b) VR image of the bones and tendons demonstrates the relationship between the two types of tissue. The plantar fascia and some of the plantar musculature have an attenuation similar to that of tendons.

View larger version (117K): [in a new window]   Figure 2b. VR imaging of the foot and ankle (same patient as in Fig 1). (a) VR image of the bones depicts the osseous structures of the foot and ankle. (b) VR image of the bones and tendons demonstrates the relationship between the two types of tissue. The plantar fascia and some of the plantar musculature have an attenuation similar to that of tendons.

View larger version (99K): [in a new window]   Figure 3. SSD image of the foot and ankle (same patient as in Fig 1) again shows the fracture at the medial end of the navicular bone (arrow).

View larger version (115K): [in a new window]   Figure 4. On an MIP image of the foot and ankle, the individual bones and joints and the fracture identified on the SSD image (cf Fig 3) are not clearly depicted.

View larger version (20K): [in a new window]   Figure 5a. Drawings illustrate the steps needed to create a VR image. (a) Step 1: Choose a viewing point. Step 2: Create a histogram of the CT data set to determine the total number of voxels and the total range of Hounsfield units. (b) Step 3: From the histogram, determine the range of Hounsfield units for the tissues of interest. (c) Step 4: Assign opacity values to the tissues of interest. Opacity values range from 0% (transparent) to 100% (fully opaque). The tissue of interest in this example is bone. (d) Step 5: Cast rays from the viewing point to each point in the volume. Step 6: Determine the opacity value of all the voxels along the path of each ray. Step 7: Place the sum of all the opacity values for each ray in the final image. Because the opacity values are summed, there is no depth information (unlike with SSD).

View larger version (20K): [in a new window]   Figure 5b. Drawings illustrate the steps needed to create a VR image. (a) Step 1: Choose a viewing point. Step 2: Create a histogram of the CT data set to determine the total number of voxels and the total range of Hounsfield units. (b) Step 3: From the histogram, determine the range of Hounsfield units for the tissues of interest. (c) Step 4: Assign opacity values to the tissues of interest. Opacity values range from 0% (transparent) to 100% (fully opaque). The tissue of interest in this example is bone. (d) Step 5: Cast rays from the viewing point to each point in the volume. Step 6: Determine the opacity value of all the voxels along the path of each ray. Step 7: Place the sum of all the opacity values for each ray in the final image. Because the opacity values are summed, there is no depth information (unlike with SSD).

View larger version (20K): [in a new window]   Figure 5c. Drawings illustrate the steps needed to create a VR image. (a) Step 1: Choose a viewing point. Step 2: Create a histogram of the CT data set to determine the total number of voxels and the total range of Hounsfield units. (b) Step 3: From the histogram, determine the range of Hounsfield units for the tissues of interest. (c) Step 4: Assign opacity values to the tissues of interest. Opacity values range from 0% (transparent) to 100% (fully opaque). The tissue of interest in this example is bone. (d) Step 5: Cast rays from the viewing point to each point in the volume. Step 6: Determine the opacity value of all the voxels along the path of each ray. Step 7: Place the sum of all the opacity values for each ray in the final image. Because the opacity values are summed, there is no depth information (unlike with SSD).

View larger version (44K): [in a new window]   Figure 5d. Drawings illustrate the steps needed to create a VR image. (a) Step 1: Choose a viewing point. Step 2: Create a histogram of the CT data set to determine the total number of voxels and the total range of Hounsfield units. (b) Step 3: From the histogram, determine the range of Hounsfield units for the tissues of interest. (c) Step 4: Assign opacity values to the tissues of interest. Opacity values range from 0% (transparent) to 100% (fully opaque). The tissue of interest in this example is bone. (d) Step 5: Cast rays from the viewing point to each point in the volume. Step 6: Determine the opacity value of all the voxels along the path of each ray. Step 7: Place the sum of all the opacity values for each ray in the final image. Because the opacity values are summed, there is no depth information (unlike with SSD).

View larger version (23K): [in a new window]   Figure 6a. Drawings illustrate the steps required to create an SSD image. (a) Step 1: Choose a viewing point. Step 2: Select a threshold value (in Hounsfield units) for the tissue of interest (eg, bone >150 HU). (b) Step 3: Cast rays from the viewing point to each point in the volume. Step 4: Identify the first point along each ray that is at the selected threshold value. Step 5: Measure the distance from the viewing point to the threshold point and place a gray pixel in the final image; discard all other points along the ray. Short distances produce bright pixels and longer distances produce dark pixels. This coding provides depth information by means of shading.

View larger version (50K): [in a new window]   Figure 6b. Drawings illustrate the steps required to create an SSD image. (a) Step 1: Choose a viewing point. Step 2: Select a threshold value (in Hounsfield units) for the tissue of interest (eg, bone >150 HU). (b) Step 3: Cast rays from the viewing point to each point in the volume. Step 4: Identify the first point along each ray that is at the selected threshold value. Step 5: Measure the distance from the viewing point to the threshold point and place a gray pixel in the final image; discard all other points along the ray. Short distances produce bright pixels and longer distances produce dark pixels. This coding provides depth information by means of shading.

View larger version (97K): [in a new window]   Figure 7. SSD image of the ankle shows how the bones and tendons are rendered separately and then fused into a single image.

View larger version (51K): [in a new window]   Figure 8. Drawings illustrate the steps needed to create an MIP image. Step 1: Choose a viewing point. Step 2: Cast rays from the viewing point to each point in the volume. Step 3: Determine the maximum pixel value of all the pixels along the path of each ray. Step 4: Place the maximum pixel value of each ray in the final image.

View larger version (80K): [in a new window]   Figure 9a. Three-dimensional rendering with metal present. (a) On a multitissue VR image, artifacts from metal (arrows) interfere with tendon visualization. (b) MIP image shows the bone and metal but not the soft tissues and tendons.

View larger version (90K): [in a new window]   Figure 9b. Three-dimensional rendering with metal present. (a) On a multitissue VR image, artifacts from metal (arrows) interfere with tendon visualization. (b) MIP image shows the bone and metal but not the soft tissues and tendons.

View larger version (165K): [in a new window]   Figure 10a. Limitations of 3D rendering technique. (a) Sagittal MPR image obtained in a 23-year-old man who sustained an acute twisting injury and presented with pain and swelling of the left ankle shows a small fracture of the anterior process of the calcaneus (arrow). (b, c) Neither a VR image of the bones (b) nor an SSD image (c) demonstrates the anterior process fracture.

View larger version (90K): [in a new window]   Figure 10b. Limitations of 3D rendering technique. (a) Sagittal MPR image obtained in a 23-year-old man who sustained an acute twisting injury and presented with pain and swelling of the left ankle shows a small fracture of the anterior process of the calcaneus (arrow). (b, c) Neither a VR image of the bones (b) nor an SSD image (c) demonstrates the anterior process fracture.

View larger version (113K): [in a new window]   Figure 10c. Limitations of 3D rendering technique. (a) Sagittal MPR image obtained in a 23-year-old man who sustained an acute twisting injury and presented with pain and swelling of the left ankle shows a small fracture of the anterior process of the calcaneus (arrow). (b, c) Neither a VR image of the bones (b) nor an SSD image (c) demonstrates the anterior process fracture.

View larger version (101K): [in a new window]   Figure 11a. Global assessment of fractures involving joints. (a) SSD image demonstrates a pilon fracture of the distal tibia (white) and fibula (light blue). Arrows indicate fracture, dark blue area indicates the tarsal bones. (b) Disarticulated SSD image of the joint surface shows the fracture components in the tibia (white) and fibula (blue).

View larger version (83K): [in a new window]   Figure 11b. Global assessment of fractures involving joints. (a) SSD image demonstrates a pilon fracture of the distal tibia (white) and fibula (light blue). Arrows indicate fracture, dark blue area indicates the tarsal bones. (b) Disarticulated SSD image of the joint surface shows the fracture components in the tibia (white) and fibula (blue).

View larger version (114K): [in a new window]   Figure 12a. Normal tendinous foot and ankle anatomy. (a) VR image (posterior medial view) shows the tibialis posterior tendon (1), flexor digitorum tendon (2), flexor hallucis longus tendon (3), and plantar aponeurosis (4). (b) VR image (lateral view) demonstrates the Achilles tendon (5), peroneus brevis tendon (6), and peroneus longus tendon (7). (c) VR image of the dorsum of the midfoot shows the tibialis anterior tendon (8), extensor hallucis longus tendon (9), and extensor digitorum tendon (10). The origins, insertions, and actions of these tendons are shown in Table 2.

View larger version (109K): [in a new window]   Figure 12b. Normal tendinous foot and ankle anatomy. (a) VR image (posterior medial view) shows the tibialis posterior tendon (1), flexor digitorum tendon (2), flexor hallucis longus tendon (3), and plantar aponeurosis (4). (b) VR image (lateral view) demonstrates the Achilles tendon (5), peroneus brevis tendon (6), and peroneus longus tendon (7). (c) VR image of the dorsum of the midfoot shows the tibialis anterior tendon (8), extensor hallucis longus tendon (9), and extensor digitorum tendon (10). The origins, insertions, and actions of these tendons are shown in Table 2.

View larger version (86K): [in a new window]   Figure 12c. Normal tendinous foot and ankle anatomy. (a) VR image (posterior medial view) shows the tibialis posterior tendon (1), flexor digitorum tendon (2), flexor hallucis longus tendon (3), and plantar aponeurosis (4). (b) VR image (lateral view) demonstrates the Achilles tendon (5), peroneus brevis tendon (6), and peroneus longus tendon (7). (c) VR image of the dorsum of the midfoot shows the tibialis anterior tendon (8), extensor hallucis longus tendon (9), and extensor digitorum tendon (10). The origins, insertions, and actions of these tendons are shown in Table 2.

View larger version (104K): [in a new window]   Figure 13a. Hypertrophic peroneal tubercle in a 22-year-old man who presented with a hard, tender mass on the lateral aspect of the foot. (a) SSD image of the skin shows a protuberance just distal to the lateral malleolus (arrow). (b) Lateral VR image of the bones and tendons shows that a hypertrophic peroneal tubercle of the calcaneus is responsible for the protuberance. The peroneal tendons are splayed around the tubercle (arrow). (c) Lateral SSD image shows enlargement of the peroneal tubercle (arrow). Blue area indicates the fibula.

View larger version (110K): [in a new window]   Figure 13b. Hypertrophic peroneal tubercle in a 22-year-old man who presented with a hard, tender mass on the lateral aspect of the foot. (a) SSD image of the skin shows a protuberance just distal to the lateral malleolus (arrow). (b) Lateral VR image of the bones and tendons shows that a hypertrophic peroneal tubercle of the calcaneus is responsible for the protuberance. The peroneal tendons are splayed around the tubercle (arrow). (c) Lateral SSD image shows enlargement of the peroneal tubercle (arrow). Blue area indicates the fibula.

View larger version (106K): [in a new window]   Figure 13c. Hypertrophic peroneal tubercle in a 22-year-old man who presented with a hard, tender mass on the lateral aspect of the foot. (a) SSD image of the skin shows a protuberance just distal to the lateral malleolus (arrow). (b) Lateral VR image of the bones and tendons shows that a hypertrophic peroneal tubercle of the calcaneus is responsible for the protuberance. The peroneal tendons are splayed around the tubercle (arrow). (c) Lateral SSD image shows enlargement of the peroneal tubercle (arrow). Blue area indicates the fibula.

View larger version (104K): [in a new window]   Figure 14. Rheumatoid arthritis in a 43-year-old woman with severe erosive joint destruction. Lateral VR image shows marked thinning of the peroneus brevis tendon (black arrow). White arrow indicates the peroneus longus tendon.

View larger version (104K): [in a new window]   Figure 15. Rheumatoid arthritis in a 43-year-old woman with severe erosive joint destruction. Medial multitissue VR image emphasizes the tendons. Marked synovial proliferation is seen (arrow) and appears similar to muscles and tendons because of similar attenuation.

View larger version (83K): [in a new window]   Figure 16a. Degenerative joint disease with tendon thinning in a 51-year-old man with ankle pain. (a) VR image of the bones shows osteophytes and bone proliferation at the ankle joint (arrows). (b-d) Medial VR image (b) and axial MPR images (c, d) show thinning of the posterior tibial tendon (arrow).

View larger version (99K): [in a new window]   Figure 16b. Degenerative joint disease with tendon thinning in a 51-year-old man with ankle pain. (a) VR image of the bones shows osteophytes and bone proliferation at the ankle joint (arrows). (b-d) Medial VR image (b) and axial MPR images (c, d) show thinning of the posterior tibial tendon (arrow).

View larger version (107K): [in a new window]   Figure 16c. Degenerative joint disease with tendon thinning in a 51-year-old man with ankle pain. (a) VR image of the bones shows osteophytes and bone proliferation at the ankle joint (arrows). (b-d) Medial VR image (b) and axial MPR images (c, d) show thinning of the posterior tibial tendon (arrow).

View larger version (104K): [in a new window]   Figure 16d. Degenerative joint disease with tendon thinning in a 51-year-old man with ankle pain. (a) VR image of the bones shows osteophytes and bone proliferation at the ankle joint (arrows). (b-d) Medial VR image (b) and axial MPR images (c, d) show thinning of the posterior tibial tendon (arrow).

View larger version (119K): [in a new window]   Figure 17a. Healed calcaneal fracture with displaced peroneal tendons in a 43-year-old man. (a) Coronal MPR image shows calcaneal deformity with lateral displacement of a large caudal fragment. The peroneal tendons are also laterally displaced (arrow). In addition, there is lateral fibular displacement and disruption of the normal distal tibiofibular articulation. (b) Anterolateral VR image of the ankle and foot again demonstrates lateral displacement of the peroneal tendons (arrow). Note also the proximal fibular osteophyte. (c) Lateral VR image shows that the peroneal tendons are impinged upon by the fibular osteophyte (arrow).

View larger version (94K): [in a new window]   Figure 17b. Healed calcaneal fracture with displaced peroneal tendons in a 43-year-old man. (a) Coronal MPR image shows calcaneal deformity with lateral displacement of a large caudal fragment. The peroneal tendons are also laterally displaced (arrow). In addition, there is lateral fibular displacement and disruption of the normal distal tibiofibular articulation. (b) Anterolateral VR image of the ankle and foot again demonstrates lateral displacement of the peroneal tendons (arrow). Note also the proximal fibular osteophyte. (c) Lateral VR image shows that the peroneal tendons are impinged upon by the fibular osteophyte (arrow).

View larger version (108K): [in a new window]   Figure 17c. Healed calcaneal fracture with displaced peroneal tendons in a 43-year-old man. (a) Coronal MPR image shows calcaneal deformity with lateral displacement of a large caudal fragment. The peroneal tendons are also laterally displaced (arrow). In addition, there is lateral fibular displacement and disruption of the normal distal tibiofibular articulation. (b) Anterolateral VR image of the ankle and foot again demonstrates lateral displacement of the peroneal tendons (arrow). Note also the proximal fibular osteophyte. (c) Lateral VR image shows that the peroneal tendons are impinged upon by the fibular osteophyte (arrow).

View larger version (126K): [in a new window]   Figure 18a. Acute calcaneal fracture with tendon entrapment in a 25-year-old man. (a) Sagittal MPR image shows fracture of the calcaneus with depression of the Boehler angle. (b) Coronal MPR image shows lateral and superior displacement of the calcaneal fragment, which results in entrapment of the peroneal tendons (arrow). (c) Posterolateral VR image shows entrapment of the peroneal tendons between the fibula and calcaneus (arrow). (d) Posterolateral VR image of the bones shows the proximity of the fibula to the calcaneus.

View larger version (149K): [in a new window]   Figure 18b. Acute calcaneal fracture with tendon entrapment in a 25-year-old man. (a) Sagittal MPR image shows fracture of the calcaneus with depression of the Boehler angle. (b) Coronal MPR image shows lateral and superior displacement of the calcaneal fragment, which results in entrapment of the peroneal tendons (arrow). (c) Posterolateral VR image shows entrapment of the peroneal tendons between the fibula and calcaneus (arrow). (d) Posterolateral VR image of the bones shows the proximity of the fibula to the calcaneus.

View larger version (94K): [in a new window]   Figure 18c. Acute calcaneal fracture with tendon entrapment in a 25-year-old man. (a) Sagittal MPR image shows fracture of the calcaneus with depression of the Boehler angle. (b) Coronal MPR image shows lateral and superior displacement of the calcaneal fragment, which results in entrapment of the peroneal tendons (arrow). (c) Posterolateral VR image shows entrapment of the peroneal tendons between the fibula and calcaneus (arrow). (d) Posterolateral VR image of the bones shows the proximity of the fibula to the calcaneus.

View larger version (101K): [in a new window]   Figure 18d. Acute calcaneal fracture with tendon entrapment in a 25-year-old man. (a) Sagittal MPR image shows fracture of the calcaneus with depression of the Boehler angle. (b) Coronal MPR image shows lateral and superior displacement of the calcaneal fragment, which results in entrapment of the peroneal tendons (arrow). (c) Posterolateral VR image shows entrapment of the peroneal tendons between the fibula and calcaneus (arrow). (d) Posterolateral VR image of the bones shows the proximity of the fibula to the calcaneus.