orthopaedics

1. Weight bearing CT Scans For Foot
& Ankle Surgery
(cone beam technology)
Ahmed Ashour Dr.
Orthopedic department
Khoula hospital

2. Why do we need weight-bearing
cone beam CT?
• Highly complex anatomical and mechanical structure:
• The foot and ankle form a complex system which consists of 28 bones 33 joints,
112 ligaments controlled by 13 extrinsic and 21 intrinsic muscles in a maze of 3D architectural
arrangements
• Subject to acute and chronic structural changes with the
repeated compression stresses of gravity and ground reaction force

3. Why do we need weight-bearing
cone beam CT?
• Understanding of how these structures interact and react under
stresses is essential to our understanding of the pathology we
Treat.
• 2D radiographs (XR) have inherent limitations
-The angles and distances measured by old methods do not correspond to the
angles and distances in the real object even when weight bearing,

4. Why do we need weight-bearing
cone beam CT?
• limitations of Standard CT combined with standing XR :
– high radiation dose
– absence of weight- bearing pertaining to CT;
– poor reproducibility and poor reliability of measurements with XR
– time necessary for and cost of comparative, bilateral dorsal
plantar, lateral and anteroposterior (AP) XR and CT sets.

5. Why do we need weight-bearing
cone beam CT?
• limitations of conventional CT scan:
– Partial weight-bearing potentially underestimates the impact of load
– Passive external loads underestimates the actions of active muscle forces
when actually standing.

6. Why do we need weight-bearing
cone beam CT?
•

7. Weight bearing CT Scans
• A cone beam:
is a rotating XR where the center
of rotation is the investigated object.
– the photon source is at one
end of the diameter axis.
– the target (a digital silicon
detector panel) at the other end
of diameter axis.

8. Weight bearing CT Scans
• The target is continuously projected with the photons which have traversed the object
– the result is an intermingled array of lines and shades called a sinogram, which has to be
interpreted using mathematical transforms
•Fournier - reconstructs multiple simple sinus functions from a single complex one.
•Radon - reconstructs a set of 3D coordinates

9. Intermingled array of lines and shades called a sinogram

10. Original notes about the
first Cone-Beam 3D Scan
performed on July 1, 1994

11. Weight-Bearing CT International
Study Group
• Goals:
– to investigate the possibilities
– validate new measurement
systems
– organize and focus the international research
effort
– produce common guidelines for the clinical use of WBCT
https://www.wbctsociety.org/

12. Examples of 3D reconstructions, soft tissues or bony!

13. Weight bearing CT Scans
- WBCT scan Allows surgeons to make
measurements from 2D reconstructed
radiographs, but
• Lower quality than conventional
Radiographs.

14. Weight bearing CT Scans
• The main fields of interest to date:
1 – Flat foot: (AAFD) adult acquired flat foot deformity
2 – Subtalar joint : arthritis, alignment, impingement
3 – Distal tibiofibular joint (syndesmosis) and lateral ankle instability
4– Tibiotalar osteoarthritis.
5– First ray hypermobility
6– Hallux rigidus
7– Hallux valgus
8- maxilla-fascial
9- arthroplasty and reconstruction surgery

15. Weight bearing CT Scans
• AAFD: Flat foot measurements may be obtained using WBCT with better detection of
Severity
• Patients with flat foot deformity have more innate valgus in their talar shape
and in their subtalar alignment.
• de Cesar Netto C, Schon LC, Thawait GK, et al. Flexible adult acquired flatfoot deformity: comparison between weight bearing
and non-weight-bearing measurements using cone-beam computed tomography. J Bone Joint Surg [Am] 2017;99:e98.

16. Weight bearing CT Scans
• Patients with flat feet relative to controls :
- the fifth metatarsal demonstrates plantarflexion relative to the first metatarsal
- Subtalar joint orientation may be a risk factor for the development of ankle joint osteoarthritis
• Yoshioka N, Ikoma K, Kido M, et al. Weight-bearing three dimensional computed tomography analysis of the forefoot
in patients with flatfoot deformity. J Orthop Sci 2016;21:154-158

17. Weight bearing CT Scans
• Mortise and Tibiofibular joint:
– internal rotation of the talus (in a varus OA ankle) increases with severity of OA
– weight-bearing rotation of the talus within the normal mortise is around 10 degrees, fibular
posterior translation is 1.5 mm, external rotation 3°
– comparison with the contralateral side seems to be more reliable than with the population
norm.( compare subject with AAFD with himself).

18. Weight bearing CT Scans
• (HV )Hallux Rigidus : have metatarsus primus elevatus increasing with the severity
• (HR) Hallux Valgus : mobility is increased NOT ONLY in the tarso-metatarsal joint
BUT ALSO in all joints of the first ray.
Compared measurements performed on 2D XR, CT and WBCT :
- only WBCT was able to provide the true measurements independent from rotational
or projection bias.
• Cheung ZB, Myerson MS, Tracey J, Vulcano E. Weightbearing CT scan assessment of foot alignment in patients
with hallux rigidus. Foot Ankle Int 2018;39:67-74.

19. Weight bearing CT Scans
• (FAO) Foot Ankle Offset( four points) :
– software-based measurement
– semi-automatic algorithm built in a WBCT
– uses three points on the sole of the foot : calcaneal lowest, head 1st MTB , head 5th MTB.
– 4th point in the center of the ankle joint.
- the direction of body weight was approximated through the anatomical median axis of the tibia
- ground reaction force through the lowest point of the calcaneus.
• Lintz F, Welck M, Bernasconi A, et al. 3D biometrics for hindfoot alignment using weight bearing CT. Foot Ankle Int.
2017;38(6):684-689.

20. Weight bearing CT Scans
• Hindfoot alignment (HA) in 3D, Measuring (FAO) Foot Ankle Offset:
- where body weight is applied through the ankle joint and where ground reaction force is
through the sole of the foot.
- Individual positions of bones in the foot and ankle may not be predictive of local
Pressure but,
• The whole 3D structure of the foot seems to be responsible for maintaining the
centre of pressure in line with the direction of body weight.

21. (HA) hind foot alignment, (FAO) foot ankle offset

22. (HA) hind foot alignment, (FAO) foot ankle offset

23. How WBCT may change our concepts about foot and
ankle surgery ?
Examples :

24. Weight bearing CT Scans
- WBCT Scans :
– Better assessment
Of fractures in the F&A
( ex., sesamoid )

25. Weight bearing CT Scans
- WBCT Scans :
– Better assessment
Of fractures in the F&A
ex., lisfranc injuries,
tip of medial malleolus.

26. Weight bearing CT Scans
- WBCT Scans :
– Better assessment
of fractures in the F&A
( ex., lateral process of
talus)

27. Weight bearing CT Scans
- WBCT Scan while
using shoes :
– Better assessment
of soft tissues .
– Better assessment of
alignment in the F&A

28. Weight bearing CT Scans
WBCT Scans:
– better image quality:
- Less scatter/shadows from metallic
hardware
• also, Better assessment of healing

29. Osteoarthritis of Lisfranc joint:
Conventional and WBCT
Scan: through 2nd TMT joint,
left showed instability and
cartilage damage

30. 1- (AAFD) Adult acquired flat foot deformity

31. Subtalar impingement and
narrowing of the subtalar joint
space is more clearly seen on
the weight-bearing CT scan
compared with the non weight-
bearing CT scan

32. (AAFD): collapse of the medial longitudinal arch especially at the
naviculocuneiform joint is more readily apparent on the weight-bearing CT scan
than on the non weight-bearing CT scan .

33. (AAFD) adult-acquired flatfoot
deformity:
-Weight-bearing CT scans
demonstrating Talocalcaneal
(subtalar) impingement at the angle of
Gissane.
-Calcaneofibular (subfibular)
impingement.

34. With help of WBCT scan: At 50% of the AP length of the posterior facet, patients with (AAFD) has
a notable valgus alignment of their subtalar joint, as demonstrated by the inferior facet of the talus
and the horizontal line. In a patient with HV, a slight varus alignment of the subtalar joint is noted.

35. 2- hallux valgus (HV)

36. A 3D computer-aided design: pronation of the first metatarsal in (HV).
Also, to demonstrate how the deformity can be quantified in three dimensions.

37. (HV)hallux valgus: Coronal weight-bearing CT image demonstrating lateral
sesamoid subluxation in hallux valgus.

38. 3- Weight-bearing CT Scans to
Evaluate the Syndesmosis and Lateral Ankle
Instability.

39. bilateral axial weight-bearing CT scan : widening of the syndesmosis on the left side
compared with the normal right syndesmosis.

40. - CT scan in supine position: symmetric talocrural joint and almost normal-appearing joint space
width.
-WBCT : reveals medial displacement of talus and widened lateral joint space, Medial talar
and tibial bony articular surfaces come into contact showing advanced cartilage damage.

41. Summary
1- Cone-beam CT technology has the advantage of reducing ionizing radiation
exposure to the patient.
2- It has two-thirds the effective radiation dose of a conventional CTscan
but,
approximately 2.5 times as much radiation as a standard, three-view weight-
bearing radiograph of the foot

42. Summary
3- better demonstrates the true orientation of the bones and joints during
loading conditions and help to identify underlying pathologies such as
malalignment, impingement, instability and fractures.
4- provided new insight into common foot and ankle disorders such as AAFD,
HV, and lateral ankle instability.
5- however, have not replaced lower cost weight-bearing radiographs, which
are often sufficient to adequately diagnose and manage most foot and ankle
pathologies.

43. Conventional and WBCT scan reveals:
- lateral instability of tibiofemoral joint with impingement of tibial spines against lateral femoral
condyle , narrowing of joint space, Medial displacement of polyethylene component of
prosthesis, and less metal artifacts.

44. finally thinking upside down !!!

45. Cone beam technology in Maxillofacial surgery

46. Cone beam technology in Maxillofacial surgery

47. Maxillofacial surgery

48. Systematic Literature Review,
Why Do We Need WBCT?

49. Systematic Literature Review,
Why Do We Need WBCT?

50. Systematic Literature Review,
Why Do We Need WBCT?

51. Systematic Literature Review,
Why Do We Need WBCT?