EOS Imaging or CT Scan: which 3d imaging should be performed before total hip replacement?

The limitations of 2D Planning

In 2026, most surgeons still plan hip replacement surgery using two-dimensional imaging (simple radiographs), sometimes with the help of planning software. However, this 2D approach does not reflect real anatomy and does not allow anticipation of operative difficulties nor perfectly controlled implant placement.

At Inside the Hip , we favor 3D planning.

Two types of 3D imaging are commonly used:

• EOS imaging
• CT scan

EOS Imaging : a global view of the skeleton

EOS imaging is a low-radiation radiological technique that allows full-body assessment in a standing position. It provides an overall view of the spine and lower limbs and makes it possible to visualize and quantify deviations in the frontal, sagittal, and axial planes.

Advantages of EOS Imaging

• Useful in cases of scoliosis or pelvic obliquity
• Allows assessment of lumbopelvic-femoral parameters (relationships between the lumbar spine, sacrum, pelvis, and femur)
• Reveals lower-limb deformities : genu valgum, genu varum, knee or hip flexion contractures
• Measures bone segment lengths and detects leg length discrepancies

Limitations of EOS Imaging

EOS does not provide detailed information about bone structure. It is a global skeleton model, not suitable for millimetric bone analysis and does not allow the design of custom-made implants.

CT Scan: The gold standard for prosthetic planning

The CT scan is a true 3D cross-sectional imaging technique performed with the patient lying down. Its highly precise calibration allows life-size measurements : ten millimeters on the scan equal ten millimeters in the body.

Strengths of CT Scan

• Provides precise visualization of the pelvis and lower limbs through scout views (AP and lateral)
• Measures bone length, visualizes deformities, and quantifies leg length discrepancies
• Offers very fine bone detail: morphology, density, cysts, osteophytes, joint space narrowing, sclerosis
• Accurately measures coxofemoral anatomical parameters : acetabular diameter, hip orientation relative to the anterior pelvic plane, neck–shaft angle, femoral offset, femoral neck anteversion or retroversion

The CT scan also visualizes the femoral medullary canal, where the prosthesis will be anchored, and assesses the muscle groups around the hip to detect atrophy or fatty degeneration.

CT Scan: a tool for planning and postoperative assessment

3D CT imaging allows precise planning of hip prosthesis placement and the creation of a custom-made implant, perfectly adapted to the patient’s anatomy.

After surgery, a postoperative CT scan can verify implant positioning with millimetric precision. This ensures respect for joint geometry and long-term prosthetic stability.

Why CT Scan is essential before THR

Implanting a hip prosthesis without a preoperative CT scan reduces the patient’s chances of optimal recovery. Surgery irreversibly alters the native hip anatomy, making precise 3D control of implant positioning impossible afterwards.

Whenever a custom implant is considered (complex hip, young patient, athlete, dancer, atypical morphology, high demanding patient), the CT scan is the reference examination. It allows anatomical analysis, custom implant design, and perfect alignment.

When should EOS imaging be added?

EOS may be prescribed in addition whenever spinal disorders or global lower-limb deformities are present.

Thus CT scan remains the key examination for precise 3D planning, while EOS provides a full-body weightbearing assessment.

Understanding the Hip in 3D to anticipate surgery

Understanding the hip in 3D before prosthesis implantation means:

• anticipating operative difficulties
• precisely planning implant placement
• and, when needed, designing a custom prosthesis

This approach, used systematically at Inside the Hip in Lyon and Paris, ensures safety, performance, and long-term durability for every total hip replacement.