History
A 22-year-old female patient, complaining of persistent pain in the right foot for the past 3 months, presented herself to our orthopedic clinic. The pain was localized at the medial side of the ankle and exacerbated during prolonged standing. Clinical examination revealed a hindfoot valgus and limited subtalar motion. Conventional radiographs showed a typical talar beak sign, suggestive of tarsal coalition. The patient underwent a conservation treatment phase with anti-inflammatory pain medications and responded well. She was then scheduled for surgery. CT was performed to evaluate the size, location and extent of the coalition for preoperative workup. An ultra-high resolution (UHR) scan mode was performed on a photon-counting CT (PCCT), NAEOTOM Alpha®.
Diagnosis
UHR CT images showed an irregular and narrowed subtalar joint, involving both the middle and posterior subtalar facet, with more than 50% of the surface area. There was no evidence of adjacent osteoarthritis. An osseous outgrowth at the mid portion of the superior margin of the talus ("talar beak") was seen as a typical secondary sign of tarsal coalition. No osseous bridging of the subtalar joint was present. A diagnosis of non-osseous coalition was confirmed. The patient was scheduled for a subtalar arthrodesis.
Fig. 1: MPR images (Fig. 1a–1c) and cVRT images (Fig. 1d–1e) of PCCT examination of the right foot show an irregular and narrowed subtalar joint involving both middle and posterior subtalar facet, which are deformed (arrows). There are no signs of bony bridging, confirming the diagnosis of a non-osseous talocalcaneal coalition. Additionally, a talar beak can be seen at the superior aspect of the talus head (arrowhead). Note that the input images for cVRT creation are reconstructed at 0.2 mm, with a very sharp kernel of Br84 and an image matrix of 1024 × 1024.
Comments
Tarsal coalition is an abnormal, congenital bridging of two or more tarsal bones. The bridging can be osseous (bony bridging), or non-osseous (fibrous / cartilaginous bridging). Treatment options range from conservative to surgical. A CT evaluation on the size, location, presence of degenerative changes, additional coalitions and the degree of joint involvement is important for treatment planning.
The first-line treatment is conservative consisting of foot arch support, cast immobilization and non-steroidal anti-inflammatory medications. In refractory cases, surgical treatment is performed, unless significant degeneration in the adjacent joints contraindicates. Arthroscopic or open resection can be performed with or without the use of additional interposition materials, however, in multiple coalitions, individual resections should not be pursued, as they are unlikely to establish a normal functional outcome. Arthrodesis is preferred if more than 50% of the joint surface area are involved and a higher degree of hindfoot valgus is present. Triple arthrodesis, instead of subtalar arthrodesis, is indicated when the midfoot joints show signs of osteoarthritis in subtalar coalitions.
In this case, since more than 50% of the surface area of the subtalar joint is involved, and there is no evidence of adjacent osteoarthritis, a subtalar arthrodesis is indicated. CT findings that are clearly depicted in UHR images play an essential role in surgical planning. Despite the low radiation dose (1.3 mGy) applied to this young patient, high spatial resolution and low image noise are achieved. This is because UHR mode applies a fine collimation of 120 × 0.2 mm, without additional combs or grids to reduce the detector aperture, which improves the spatial resolution at full dose efficiency. Additionally, electronic noise is eliminated and a refined model based iterative reconstruction (Quantum Iterative Reconstruction, QIR) is applied in PCCT contributing to further image noise reduction. As a result, the UHR images can even be used in generating cinematic rendering 3D images which facilitate communications between the physicians and with the patient. The combination of improved spatial resolution with reduced image noise is highly beneficial for musculoskeletal imaging in clinical routine.
Examination Protocol
