Wrist Tangential (Carpal Canal) is a radiography positioning projection of the Upper Extremity. Seated, wrist hyperextended. CR angled 25–30° to long axis of hand. The centering point is located approximately 1 inch distal to the base of the third metacarpal. Wrist hyperextended, forearm pronated on the IR. The central ray is CR angled 25–30 degrees to long axis of hand, entering 1 inch distal to 3rd metacarpal base. Image-quality criteria include hook of hamate shown in profile without foreshortening, pisiform visible as a distinct structure. A sample technique is 70 kVp with DR 1.25 or CR 2.5 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Hook of hamate in profile without overlap.
- Pisiform clearly visible as a separate structure.
- Carpal tunnel space defined by hook and pisiform.
- Capitate and other distal carpals.
- Trapezium and its tubercle, and the scaphoid.
Patient preparation
- WARNING: if wrist trauma is possible, do not attempt this position before a routine wrist series has been completed and evaluated to rule out a distal forearm or wrist fracture (Bontrager).
- Verify patient identity using two identifiers.
- Remove watches, bracelets, and radiopaque items from the arm.
- Seat the patient at the end of the table.
- Place forearm on the IR with palm down.
- Hyperextend the wrist as far as possible, then rotate the hand and wrist about 10 degrees internally (toward the radial side).
Position & centering point
Approximately 1 inch distal to the base of the third metacarpal. Wrist hyperextended, forearm pronated on the IR.
Central ray
CR angled 25–30 degrees to long axis of hand, entering 1 inch distal to 3rd metacarpal base.
Exposure / technique
- kVp
- 70
- mAs
- DR 1.25 / CR 2.5
- SID
- 40" (102 cm)
- Notes
- Tabletop technique. Hyperextension is critical to opening the carpal canal. Bontrager lists 60 to 70 kV analog and 60 ± 5 kV digital; the sample below is Merrill's chart, which uses 70 kVp. Sample technique: DR 1.25 / CR 2.5 mAs at 70 kVp, 40 in SID, for a 6 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Hook of hamate shown in profile without foreshortening.
- Pisiform visible as a distinct structure.
- Carpal tunnel space open and clearly defined.
- Carpals in an arch arrangement.
- No motion blur; hook borders sharp.
- Collimation: four sides to the area of interest (Bontrager); 1 inch on the three sides of the wrist shadow (Merrill's).
Common errors
- 1 Limited wrist hyperextension not allowed for: the total CR angle to the IR must be increased.
- 2 Hand and wrist not rotated about 10 degrees internally, which superimposes the pisiform and hamate.
- 3 CR not about 1 inch distal to the base of the third metacarpal.
Clinical indications
- Suspected hook of hamate fracture.
- Pisiform fracture evaluation.
- Carpal tunnel syndrome assessment.