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Weight Bearing Advantage

CurveBeam was founded in 2009 by a group of individuals with a proven track record in the
advanced and compact 3D imaging device domain.

Overall Benefits

CurveBeam’s pedCAT and LineUP systems permit weight bearing scans, while the patient is standing in a natural stance. Computed tomography with load is referred to as weight bearing CT (WBCT). Historically, foot & ankle specialists have relied on plain (2D) radiographs in standing position for weight-bearing images. Foot & ankle conditions may be more difficult to assess on radiographs due to bone superimposition and rotational distortion due to X-Ray beam angle and patient position.

“Weight bearing CT of the joints can provide important new clinical information in musculoskeletal radiology.” – Tuomeninin et al, American Journal of Roentgenology

While a conventional medical CT (MDCT) will provide 3D bone detail, the patient is supine during the exam, so alignment-dependent conditions cannot be appreciated.

The pedCAT and LineUP provide three-dimensional views of bone morphology, alignment and joint spaces. Foot & ankle specialists may elect to order pedCAT and LineUP scans for the same indications they would have otherwise requested weight bearing radiographs. The indications for weight bearing CT are broader than the indications for MDCT.

WBCT allows more suitable and reliable assessment of anatomy, closer to the demands of normal gait.
In pre-surgical planning, specialists can measure relevant angles in three dimensions.
In post-surgical assessment, specialists can perform a functional and anatomically correct assessment of the correction performed.

Indications for Weight Bearing CT

Case Report

  • WBCT was used for surgical planning and postoperative evaluation in an unusual case of bilateral atraumatic erosive subtalar osteoarthritis with unilateral subtalar collapse. The authors emphasized the value for pre-planning, as it allowed for relevant angles to be measured in three dimensions, helped determine the presence of posterior osteophytes, and the anterior and lateral impact of the ankle. Post-operatively, the WBCT permitted a functional and anatomically correct assessment. (Welck et al, Foot Ankle Surg)

Studies

  • Orientation of the subtalar joint as measured on WBCT could be a determinant factor in the development of ankle arthritis. (Krahenbuhl et al, Foot Ankle Int)

WBCT vs. X-Ray

  • Weight bearing X-Rays and WBCT were compared in 96 patients with OA. Fifty patients had moderate OA and 46 patients had severe OA. The authors documented the presence of abnormal internal rotation of the talus in patients with osteoarthritis in varus, which was more frequently observed in the group with severe OA than those with moderate OA. They emphasized rotation could not be noted in conventional X-Rays since axial images cannot be acquired. (Kim et al, Skeletal Radiol)

Hallux valgus

  • is a lateral deviation of the great toe of the metatarsophalangeal joint.
  • is a slowly progressive condition resulting from a series of biomechanical changes.
  • is a multiplanar deformity with transverse, sagittal and rotational aspects.
  • More than 1/3 of the population over 65 has this deformity
  • Over 100 operative methods have been described in the literature.

WBCT vs. CT

  • There is an increase in medial deviation of the first metatarsal and pronation of the first toe on images with load in patients with hallux valgus. (Collan et al, Foot Ankle Surg)

WBCT vs. x-Ray

  • Weight bearing AP, lateral and oblique view plain radiographs provide limited information because of the rotational, three-dimensional nature of the deformity. On X-Ray, it is difficult to image the sesamoids for relative displacement and chondral wear, and it requires creative positioning, wedges and taping to achieve an adequate view, but the patient is no longer in a natural stance. It is also difficult to assess rotational changes of the metatarsal. Lastly, subchondral cysts in the metatarsal head may be observed, but exact size and orientation may be obscured. (Welck et al, Foot Ankle Clin N Am)
  • “When evaluating hallux valgus the 3D weight bearing CT might be the only imaging study needed. All relevant data can be obtained in a single study” and rotational changes can be measured accurately. (Collan et al, Foot Ankle Surg)

Propose Standardized WBCT Measurements

  • Stanmore classification of hallucal sesamoids

Studies

  • In a case control study with 12 patients (8 with flatfoot valgus and four asymptomatic), less subtalar contact was demonstrated in patients with posterior tibial tendon dysfunction. (Ananthakrisnan et al, J Bone Joint Surg)
  • In a case series with 37 patients with posterior tibial tendon disorder, an increased deformity was demonstrated in these patients when evaluating the talo-navicular and navicular cuneiform joints, and subluxation of the first tarsal-metatarsal joint. (Greisberg et al, Foot Ankle Int)
  • When measuring subtalar alignment using angles between the bottom facet of the talus and the ground and the angle between the upper and lower facets of the talus, both of these angles differ significantly between patients with adult type II acquired flatfoot and normal patients. These measures can be used to identify patients with higher risk of progressive deformity and subtalar joint degeneration. (Cody et al, Foot Ankle Int)

Studies

  • Cone beam CT allows cross-sectional imaging of the tibiofibular syndesmosis while the patient bears weight. This may facilitate more accurate and reliable investigation of injuries to, and reconstruction of, the syndesmosis. (Patel et al, Journal of Bone & Joint Surgery)

WBCT vs. X-Ray

  • Conventional radiographs cannot predict syndesmotic injuries reliably. CT scans outperform plain radiographs in detecting syndesmotic mal-reduction. Additionally, the syndesmotic interval can be assessed in greater detail by CT. (Krahenbuhl et al, Skeletal Radiol)

Studies

  • Significant differences in most measurements: distance between fibula and calcaneum, lateral subtalar joint space, talus-calcaneus overlap, and calcaneus-navicular distance.(Hirschmann et al Eur Radiol)
  • In a case control study with 24 patients (19 with flatfoot valgus and 5 asymptomatic), a higher prevalence of lateral impact in the subtalar joint within the tarsal sinus (92% vs. 0%) and calcaneal-fibular joint (66 vs. 5%) in comparison with controls. (Malicky et al, J Bone Joint Surg)

Lisfranc

A Lisfranc (midfoot) injury is commonly mistaken for a simple foot sprain, especially if the injury is a result of a simple twist or fall. Unfortunately, a Lisfranc injury is not a simple sprain that should be ignored. It is an injury that results if the bones in the midfoot are fractured or the ligaments that hold them together are torn. The severity can vary from simple to complex and may take many months to heal and may require surgery to treat. The midfoot is critical in stabilizing the arch and in gait. It is the Lisfranc joint complex that has specialized bony and ligamentous structures, which stabilize the midfoot: when injured, the foot can collapse and painful arthritis can develop.

WBCT vs. CT

  • Computerized tomography scan (CT): A standard CT scan is more detailed than x-rays and can help evaluate the extent of the injury and the number of joints involved. It is useful to help guide the surgical plan but does not always reveal whether or not midfoot instability is present. A weight-bearing CT scan has all the benefits of a standard CT scan with the additional advantages of revealing the stability of the midfoot. Surgery is recommended for all Lisfranc injuries with a fracture in the joints or with abnormal positioning of the midfoot joints. Weight bearing CT scans can reveal any subluxation/dislocation (abnormal positioning) of the involved joints. (Dr. Neufeld)

WBCT vs. MRI

  • Magnetic resonance imaging (MRI) scan: These studies can create better images of soft tissues but not required to diagnose a Lisfranc injury. It will only show what structures were damaged but not give information about the stability of the midfoot. Instability of the midfoot is the indication to surgically repair the Lisfranc injury. (Dr. Neufeld)

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