CT for Orthopedic Surgical Planning (Robotic / Custom Arthroplasty)

Indications

• Robotic-assisted arthroplasty planning (hip, knee, shoulder, ankle)
• Patient-specific implants and custom cutting guides
• Mechanical axis / version analysis for revision or deformity surgery

Patient prep

• Obtain the specific vendor's protocol sheet BEFORE scanning — coverage, slice thickness, series naming and upload requirements are exam-specific and studies that deviate get rejected
• Strict immobilization: legs fully extended, feet secured perpendicular with footboard/straps; NO pillows or sponges under knees or ankles
• Move contralateral hardware out of the scan volume when possible (flex/pad the other leg)
• No IV or intra-articular contrast unless the vendor explicitly requires it (most reject arthrographic contrast)

Contrast

Technique

• The generic pattern behind all vendors: acquire the required joint 'blocks' (e.g. hip + knee + ankle for a mechanical-axis knee plan; pelvis + proximal femur ± knee for hip) with the patient NOT moving between blocks, keeping table position, centering and DFOV coordinates identical — every block must live in one coordinate system
• Thin contiguous slices (0.6-1 mm) with a bone algorithm; no gantry tilt; no motion — repeat any block with motion
• Include the vendor-specified landmarks in full (entire femoral head/pelvis, femoral condyles, ankle mortise; whole scapula including inferior angle for shoulder)
• Use MAR or ~15% higher kVp if hardware must remain in the field
• Export the complete thin-slice DICOM dataset per the vendor's naming/upload instructions

Series / Sequences

Key points

• One coordinate system is the whole exam: patient movement or a table/FOV change between blocks invalidates the mechanical-axis calculation and the study will be rejected
• Motion, missing landmarks and intra-articular contrast are the three most common rejection reasons
• This page is the generic pattern — the individual vendor spec sheet (MAKO, ConforMIS, Materialise, Blueprint, etc.) always wins on specifics
• Dose stays modest: bone-only question, no repeats if positioning is done right the first time

References