The force at the implant cannot be assessed by the mallet force-Unless supported by a model

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device testing

Background:

• Press-fit fixation of uncemented prostheses requires precise force application to balance stability and bone damage.
• Measuring forces directly at the implant-bone interface is often infeasible, leading to indirect measurements.
• Existing measurement methods may not accurately reflect forces at critical interfaces due to transmission path dynamics.

Purpose of the Study:

• To quantify force reduction along the transmission path during femoral head-stem taper assembly.
• To develop and validate a numerical model for simulating force transmission in prosthesis implantation.
• To assess the influence of measurement position and surgical instruments on recorded forces.

Main Methods:

• In vitro force measurements at the mallet tip, impactor, and stem taper.
• Development of a validated semi-empirical numerical model incorporating springs and masses.
• Simulation of various responding tissue properties and surgical instrument variations.

Main Results:

• Peak forces were attenuated to 35% at the impactor and 21% at the stem taper relative to applied mallet forces.
• The numerical model accurately replicated measured force curves (median RMSE of 3.8% and 3.6%).
• Force measurement location and surgical instruments significantly impact measured values.

Conclusions:

• Force attenuation is significant, necessitating careful consideration of sensor placement and instrument type.
• The validated numerical model aids in predicting forces at the point of interest (PoI) and optimizing experimental design.
• Standardized reporting of measurement conditions is essential for comparing studies on prosthesis implantation forces.