Small Random Angular Variations in Pelvic Tilt and Lower Extremity Can Cause Error in Static Image-based Preoperative...

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical simulation

Background:

• Current total hip arthroplasty (THA) simulation models often use limited static radiographs, potentially overlooking dynamic pelvic and lower extremity motion.
• These models may not fully account for random angular variations or the impact of coronal and axial pelvic tilt on prosthetic impingement.

Purpose of the Study:

• To investigate prosthetic impingement risk resulting from random variations (±5°) in pelvic tilt and lower extremity alignment.
• To compare the effect of coronal and axial pelvic tilt changes versus sagittal tilt on impingement risk.

Main Methods:

• A validated MATLAB computer model simulated THA motions using CT-derived patient anatomy.
• Simulations included random variations (±5°) in pelvic tilt (sagittal, coronal, axial) and hip alignment during functional activities.
• Prosthetic impingement was defined as mechanical abutment; logistic regression analyzed the impact of angular variations.

Main Results:

• Static models without variation showed no impingement; however, ±5° variations led to impingement during pivoting, sit-to-stand, and squatting, especially with smaller femoral heads (28-32mm).
• Sagittal, axial, and coronal pelvic tilt variations significantly increased impingement risk (p < 0.001).
• Hip flexion variation also strongly impacted impingement risk (OR 4.11, p < 0.001).

Conclusions:

• Even minor changes (2°-3°) in pelvic tilt or hip alignment can cause prosthetic impingement.
• Relying solely on static radiographs for preoperative planning may be insufficient to predict impingement-free range of motion.
• Dynamic simulation models are crucial for accurately assessing THA implant positioning and minimizing impingement risk.