How Weightbearing CT Can Be A Valuable Diagnostic Tool
This author discusses the case of a 63-year-old with forefoot pain, noting how a weightbearing computed tomography (CT) scan aided in her diagnosis by providing accurate measurements of the metatarsal heads.
When evaluating the patient with metatarsalgia, there are many anatomic and biomechanical factors to consider: first ray hypermobility, metatarsal length, metatarsal elevation and metatarsophalangeal joint (MPJ) stability (plantar plate). One may use traditional weightbearing radiographs to evaluate metatarsal length but they cannot assess metatarsal sagittal plane position. Sesamoid axial views can evaluate the metatarsal head sagittal plane position but such radiographs are not reliable as the patient or the X-ray technician positions the foot in a way that clearly does not represent a resting stance position.
Weightbearing computed tomography (CT) can accurately measure the relative position of the metatarsal heads to one another and to the weight bearing surface.
A Closer Look At The Patient Presentation
A 63-year-old female presents with persistent left forefoot pain. She points to the plantar margin of the third metatarsal head as the area of discomfort and pressure. She has had four previous foot surgeries by another provider. These surgeries included a first metatarsal base osteotomy, a revision of the base osteotomy with bone grafting and a first metatarsal head osteotomy. She has also had a second metatarsal head osteotomy.
Clinically, the neurovascular and dermatological exams are normal with the exception of a small callus beneath the left third metatarsal head. The plantar fat pad is thin beneath the third metatarsal head. The second metatarsal is shortened and elevated, and does not bear weight. In a relative sense, the third metatarsal head is plantarly prominent. The second MPJ is extended and she has poor flexor strength within the second toe. The third MPJ is slightly extended.
What The Weightbearing Foot CT Scan Reveals
The transverse slices of the weightbearing CT scan allow for the precise evaluation of metatarsal length. Depending on the technique for determining metatarsal parabola and the ideal postoperative position, the surgeon can accurately measure metatarsal length. The sagittal weight bearing slices can identify the position of the metatarsal heads in relation to the ground and one another.