Weight-bearing CT Scans in Clinical Practice
In addition to helping surgeons understand foot and ankle biomechanics and pathologies, WBCT scans are increasingly changing clinical practice by allowing surgeons to better assess deformities and preoperatively plan for surgical intervention. At this time, WBCT scans may be especially valuable to the clinician in assessing deformities such as subtalar and subfibular impingement in AAFD, hindfoot alignment, and pronation of the first metatarsal in HV.
In AAFD, surgeons may use WBCT scans to look for subtalar impingement at the angle of Gissane on sagittal views or subfibular impingement on coronal views. Patients with severe subtalar or subfibular impingement may require a subtalar arthrodesis to properly align the foot and prevent future impingement or recurrence because current techniques such as a medializing calcaneal osteotomy and lateral column lengthening may not address these deformities. Future work may identify patients who are likely to fail reconstructive procedures.
WBCT scans could also be used clinically to better evaluate hindfoot alignment. This may be particularly helpful in AAFD and in cases of chronic lateral ankle instability. Subtle varus and valgus deformities may be difficult to quantify on physical examination and on radiographs. WBCT scans may be an important tool to assist surgeons in titrating correction based on an individual patient's specific deformity.
WBCT scans can also be used in practice to determine pronation and instability of the first metatarsal in patients with HV. Because sesamoid position and first ray pronation are distinct deformities, the rotational deformity of the first metatarsal cannot be determined using sesamoid position on weight-bearing radiographs as a proxy for metatarsal pronation. Using WBCT scans to preoperatively understand the amount of pronation of first ray may help surgeons calibrate the appropriate surgical correction of the rotational deformity. In addition, surgeons may choose to use WBCT scans in patients with HV to evaluate for instability at the first tarsometatarsal (TMT) joint, which could assist in identifying which patients require a first TMT arthrodesis.
Finally, there may be a role for WBCT scans in the creation of patient-specific instrumentation, although there is no evidence at this time that demonstrates an advantage of WBCT scans for this use. WBCT scans may be used to more accurately model a patient's anatomy and create three-dimensional implants or cutting guides to help surgeons better treat complex deformities.
J Am Acad Orthop Surg. 2020;28(14):e595-e603. © 2020 American Academy of Orthopaedic Surgeons