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Weight Bearing Advantage

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

icons-TRADITIONAL-CT

Traditional CT

  • See bones in 3D
  • Cannot stand/weight bear
  • Cannot see bones in functional position
  • Higher radiation dose
WEIGHT-BEARING-CT

Weight Bearing CT

  • See bones in 3D
  • Stand naturally
  • See bones in functional position
  • Low radiation dose
icons-WB-X-RAY

WB X-Ray

  • Only see bones in 2D
  • Bones are superimposed & distorted
  • Stand naturally
  • Low radiation dose

WBCT Helps Diagnose Functional Deformities

CurveBeam systems provide 3-dimensional views of bone morphology, alignment and joint spaces.

Indications for Weight Bearing CT

The midfoot is critical in stabilizing the arch and in gait. The Lisfranc joint complex has specialized bony and ligamentous structures which stabilize the midfoot: when injured, the foot can collapse and painful arthritis can develop.
A Lisfranc injury is commonly mistaken for a simple foot sprain, especially if the injury is a result of a simple twist or fall. However, bones in the midfoot may be fractured or the ligaments that hold them together may be torn.
The severity can vary from simple to complex, may take many months to heal, and may require surgery to treat. Subtle Lisfranc injuries remain a challenge to diagnose.

With weight bearing CT imaging ,“you can solve that Lisfranc case no one else can. It opens up the midfoot, which historically has been a problem for us.” – Dr. Gary Briskin, DPM

WBCT VS. MRI

MRI, which has a wide consensus as the preferred modality to directly assess a ligament’s integrity, has also been utilized to evaluate these injuries with a high sensitivity and good specificity. However, MRI cannot be routinely obtained under weight-bearing conditions. Resultantly, pathalogical alignment, which is an important parameter to determine the efficacy of an operation, may not be detected. Due to these discussed shortcomings of MRI, WBCT may be the preferred imaging modality when assessing joint space assymetry of the foot. (Sripanich et al, Skeletal Radiol)

MRI studies can create better images of soft tissues, but are but not required to diagnose a Lisfranc injury. The studies 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. (Clinical insight provided by Dr. Steven Neufeld, MD)

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. (Clinical insight provided by Dr. Steven Neufeld, MD)

WBCT vs. X-RAY

Although of questionable accuracy, the current gold standard to assess these injuries is through bilateral weight-bearing radiography. Current criteria for diagnosis delineates observance of a 2-mm widening of the first metatarsal-medial cuneiform and second metatarsal joint space relative to the contralateral side on bilateral weight bearing radiography. However, unavoidable overlapping osseous structures may obscure visualization when using radiography, making interpretation less reliable. WBCT, which provides clearer visualization of bony landmarks, can also be utilized for evaluation. (Sripanich et al, Skeletal Radiol)

PROPOSED STANDARDIZED WBCT MEASUREMENTS

Panchbhavi et al reported external rotation of the M2 relative to the C1 from their three-dimensional evaluation of diastasis in their simulated disruptive model. Consequently, widening between the dorsal portion of the C1-M2 joint space may be the first appreciated abnormality when compared with the adjacent articulations of the medial and middle cuneiform (C1-C2) and the second metatarsal base and middle cuneiform (M2-C2). As this resultant deformity resembles an asymmetric Greek letter, lambda, we aim to novelly coin this finding as such (asymmetric lambda sign) and utilize it as a diagnostic aid.
An asymmetric lambda sign is a simple and useful indicator for a complete Lisfranc ligamentous complex injury in partial-weight bearing and full-weight bearing conditions using a cadaver model. (Sripanich et al, Skeletal Radiol)

Osteoarthritis occurs when the protective cartilage that cushions the ends of bones wears down over time. Osteoarthritic findings in the foot are often characterized by asymmetric joint space narrowing, subchondral cyst, subchondral sclerosis, and osteophyte formation. Common sites for arthritis in the foot include the first metatarsophalangeal joint, as well as the metatarsosesamoid joints.

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)

Limitations of plain radiographs may contribute to poor sensitivity in the detection of knee osteoarthritis and poor correlation with pain and physical function. Three‐dimensional (3D) joint space width (JSW), measured from weight‐bearing computed tomography (CT) images, may yield a more accurate correlation with patients’ symptoms (Kothari et al, J Orthop Res).

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

Hallux valgus is a lateral deviation of the great toe of the metatarsophalangeal joint. It is a slowly progressive condition resulting from a series of biomechanical changes, and 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.

Studies

WBCT allowed demonstration that hypermobility of the first tarsometatarsal joint occurs not only in the sagittal plane with increased dorsiflexion, but also into other planes, with increased inversion and adduction. The hypermobility was shown to be present not only in the first TMT joint but to extend across the whole first ray. (Netto et al , Foot Ankle Clin N, 2020)

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)

Weight bearing conventional radiographs provide limited, sectorized, and biased information regarding the complex and 3-dimensional nature of hallux valgus (HV) deformity, leading to potential misinterpretation and poor understanding. (Netto 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

Measurements of pronation deformity in HV using WBCT do not correlate with traditional weight bearing conventional radiograph HV and itermetatarsal angulations. Surgical planning of HV should sonsider the 3-dimensional pattern of the deformity, and WBCT images should be used when available. (Netto et al, Foot Ankle Clin Am)

Stanmore Classification of Hallucal Sesamoids: Metatarso-sesamoid joint space narrowing should be a parameter for hallucal sesamoid classification, and should be used in addition to the 4-stage AOFAS scale for sesamoid position. (Welck et al, Foot Ankle Surg)

Blog Posts

Adult acquired flatfoot deformity (AAFD) is a progressive, complex 3-dimensional pathology characterized by peritalar subluxation (PTS) of the hindfoot. Although this debilitating disorder is commonly associated with dysfunction in the posterior tibial tendon, there are various underyling bone and joint abnormalities. Because each component plays an important role in the structural stability of the medial longitudinal arch, compromise of these structures leads to various components of the overall deformity.

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)

WBCT vs. X-Ray

To date, weight-bearing radiographs have been the cornerstone for planning surgeries on flatfoot. The technique, however, has limitations due to the superimposition of the bones and the lack of reproducibility.  Weight bearing CT scan is a very useful technique for evaluation of flatfoot associated complications. It overcomes the limitations of radiographs by providing multiplanar three-dimensional assessment of the foot in the natural weight-bearing position and at the same time being easily reproducible and consistent for the measurements around the foot (Pilania et al, Indian J Radiol Imaging)

WBCT is a more sensitive modality that can better quantify structural deformity compared to plain radiographs. (Day et al, Foot Ankle Int)

Further Reading: AAFD: Conventional Radiographs are not Enough!  I Need the Third Dimension

WBCT vs. CT

Weight-bearing CT scan is a very useful technique for evaluation of flatfoot and associated complications. The definite advantage over the conventional cross-sectional scanners is the weight-bearing capability. (Pilania et al, Indian J Radiol Imaging)

Proposed Standardized WBCT Measurements

For many years, PTS was measured at the posterior facet of the subtalar joint. More recently, subluxation of the middle facet has been proposed as a more accurate and reliable marker of symptomatic AAFD, enabling earlier detection. This study is the first to compare WBCT measurements of subtalar joint subluxation at the posterior and middle facets as markers of PTS in patients with AAFD. We found a positive linear correlation between the measurements, with subluxation of the middle facet being significantly more pronounced than that of the posterior facet by an average of almost 18%. This suggests that middle facet subluxation may provide an earlier and more pronounced marker of progressive PTS in patients with AAFD. (de Cesar Netto et al, Foot Ankle Int)

3D WBCT semiautomatic measurements of foot ankle offset (FAO) made via the TALAS tool significantly correlated with some traditional markers of pronounced AAFD. Measurements of FAO were also found to be slightly more reliable than the manual measurements. The FAO offers a simple and more complete biomechanical and multiplanar assessment of the AAFD, representing in a single measurement the 3D components of the deormity. (de Cesar Netto 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)

WBCT vs. CT

Weight bearing CT demonstrates significantly greater diastasis in unstable ankles than conventional non-weightbearing CT (del Rio et al, Foot Ankle Surg)

Bilateral Advantage

This study…underscores the substantial utility and importance of using contralateral, uninjured side as a valid internal control whenever the need for confirming potential syndesmotic injury arises. (Hagermeijer et al, Foot Ankle Int)

Without the contralateral ankle, researchers could not determine whether syndesmosis was attributable to an injured syndesmosis or a consequence of loading of normal syndesmosis. (Osgood et al, Foot Ankle Surg)

Dynamic change in area and weight bearing comparison with the contralateral uninjured ankle are two parameters that may prove useful in the future for predicting syndesmotic instability (del Rio et al, Foot Ankle Surg)

Proposed Standardized WBCT Measurements

Syndesmotic Area Measurement: Localize the midpoint of the tibial plafond’s articular surface in the axial, coronal, and sagittal planes. Create an axial image 10 mm proximal to the tibial plafond’s midpoint, with a standardized field of view of 100 mm. On this selected image, use an angle measurement tool to draw two intersecting lines along the anterior and posterior cortical surfaces of both the distal fibula and tibia. Use a free hand area measurement tool to trace the region of interest bound by the anterior line, posterior line, medial fibular cortex, and lateral tibial incisura to create a syndesmotic area. Teh Syndesmosis Area Measurement is reliable and reproducible (del Rio et al, Foot Ankle Surg)

Problems associated to the subtalar joint can have a significant impact on function, preventing participation in sports and normal daily activities. Common pathologies affecting the joint include instability following ligamentous injury and painful flat feet in children and adults.

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)

When Supinated external rotation injuries were evaluated using WBCT, even though the Medial clear space distance was restored, residual findings included posterior malleolar involvement, fibular shortening, fibular rotation, fracture comminution, and asymmetry of the distal tibiofibular joint. The results of a prior study suggest that measuring MCS distance on a WB-CBCT scan may be able to distinguish between potentially stable and unstable fractures and, by extension, determine which ankles may be considered for operative intervention. (Lawler et al, Quant Imaging Med Surg, 2020)

WBCT vs. X-Ray

A substantial amount of malrotation of the distal fibula can be missed on radiographs and contribute to a poor outcome when SER injuries are inadequately reduced. For determining stability of the ankle mortise in a supination external rotation, weight bearing radiographs may miss a substantial amount of rotation of the distal fibula and can contribute to a poor outcome when supinated external injuries (SER) are inadequately reduced. The reliability of MCS measures based on standard radiographs has been debated. Bone overlap and variability in ankle position and radiographic technique are some of many factors that can make interpretation of radiographs difficult in SER ankle fracture evaluations. (Lawler et al, Quant Imaging Med Surge, 2020)

Proposed Standardized WBCT Measurements

A novel method enables quantification of inversion-eversion at the subtalar joint based on WBCT in combination with 3D full field digital volume correlation (DVC) computed displacement. (Fernandez et al, Sci Rep 2020)

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