Objective

Using postoperative 3D CT data, we performed ROM simulation with a 3D template to examine impingement in large-head Metal-on-Metal total hip arthroplasty.

Subjects

• Cases: 20 cases, 20 joints
• Sex: 1 male, 19 female

Implants Used

Evaluation Items

Implant Placement Position

• Cup: anteversion angle, abduction angle
• Stem: anteversion angle, varus/valgus angle, flexion/extension angle

Implant Impingement

• Flexion angle
• Extension angle
• External rotation angle at 0° extension
• Internal rotation angle at 90° flexion

Matching of the Postoperative CT-Derived Implant with the CAD Model

• 

  (Stem)

• 

  (Cup)

Results

Implant Placement Position

Cup

• Anteversion angle: 21.3°±5.8° (10.1°–33.4°)
• Abduction angle: 40.9°±5.1° (29.8°–51.2°)

Stem

• Anteversion angle: 18.0°±9.7° (12.0°–44.6°)
• Varus/valgus angle (varus = +): 0.2°±1.4° (-3.2°–2.3°)
• Flexion/extension angle (extension = +): 4.2°±2.5° (-3.5°–9.0°)
• Combined Anteversion: 43.0°±11.4° (15.6°–66.8°)

Implant Impingement

• Flexion angle: 141°±15.2° (119°–170°)
• Extension angle: 70°±12.8° (30°–90°)
• External rotation angle at 0° extension: 86°±30.2° (33°–179°)
• Internal rotation angle at 90° flexion: 62°±16.1° (34°–101°)

• 

  Case: 74-year-old female

Discussion

Even when using a large-head Metal-on-Metal hip implant with a large oscillation angle, proper cup and stem placement was shown to be critical for achieving a wide range of motion, and ROM simulation with ZedHip proved highly useful.