Design revision of a partially cemented hip stem

Area of Science:

• Orthopedic biomechanics
• Biomaterials engineering
• Medical device design

Background:

• The prototype cement-locked uncemented (CLU) hip prosthesis demonstrated good primary stability but raised concerns regarding high cement stress and relative motion.
• Previous analysis indicated potential issues with cement integrity and implant-bone interface in the initial CLU design.

Purpose of the Study:

• To evaluate the efficacy of an improved CLU hip stem design in mitigating stress shielding and cement-related complications.
• To verify if design modifications eliminated the high stresses and relative motion observed in the prototype CLU prosthesis.

Main Methods:

• Finite element analysis (FEA) of the revised CLU stem within a complete human femur model.
• Experimental assessment of cement damage in synthetic femurs using the improved CLU stem and a conventional cemented stem under cyclic loading.

Main Results:

• The revised CLU stem maintained excellent primary stability and reduced metal-cement relative micromotion compared to the prototype.
• FEA revealed significantly lower cement stresses in the improved CLU design, with 99% of the cement volume experiencing principal tensile stress below 4 MPa.
• Experimental results showed the improved CLU stem had approximately ten times fewer cement cracks than the fully cemented stem under identical severe load conditions.

Conclusions:

• The design modifications to the CLU hip stem successfully reduced cement stress and micromotion while maintaining high primary stability.
• The improved CLU stem demonstrates favorable mechanical performance and enhanced cement durability compared to both the prototype CLU design and a traditional cemented stem.
• These findings suggest the improved CLU hip stem design is a viable alternative for hip arthroplasty, potentially offering improved long-term outcomes.