Dynamics of manual impaction instruments during total hip arthroplasty

Area of Science:

• Orthopaedic Surgery
• Biomechanical Engineering

Background:

• Manual impaction is the standard technique for inserting cementless acetabular cups during total hip arthroplasty (THA).
• The accuracy and precision of manual impaction strikes are not well quantified, potentially impacting surgical outcomes and implant placement.

Purpose of the Study:

• To quantify the accuracy and precision of manual impaction strikes during acetabular component seating in THA.
• To identify potential areas for improvement in surgical techniques and the development of novel impaction technologies.

Main Methods:

• Posterior approach total hip arthroplasties were performed on three cadavers.
• An instrumented mallet and introducer system was used to seat cementless acetabular cups.
• Mallet motion relative to the introducer was analyzed for strike vector, strike offset, and mallet face alignment across 110 strikes.

Main Results:

• The average misalignment of the force vector relative to the introducer axis was 18.1°, leading to 6.1% wasted strike energy.
• The mean strike offset from the introducer axis center was 19.8 mm.
• Mallet face misalignment relative to the introducer strike face averaged 15.2°.

Conclusions:

• Manual impaction of acetabular cups demonstrates significant inaccuracies and imprecision in strike vector direction.
• There is a clear need for enhanced surgical training and advanced instrumentation to improve the accuracy of acetabular component impaction in THA.