Rigidity of initial fixation with uncemented tibial knee implants.

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Biomaterials Science

Background:

• Total knee arthroplasty (TKA) is a common procedure to address debilitating knee osteoarthritis.
• Tibial component fixation is crucial for long-term TKA success, with cemented and uncemented options available.
• Understanding implant-bone micromotion is essential for optimizing fixation strategies and prosthesis design.

Purpose of the Study:

• To quantify and compare the in vitro motion between bone and both cemented and uncemented tibial components under cyclic loading.
• To determine the effect of load magnitude on implant-bone interface motion for different fixation types.
• To assess the potential of observed motion to inhibit bony ingrowth in uncemented implants.

Main Methods:

• Utilized liquid metal strain gauges to measure in vitro motion at four locations on eight cadaver tibiae.
• Applied cyclic loads ranging from 10 to 2,000 N to simulate physiological conditions.
• Analyzed two types of motion: reversible inducible displacement and irreversible liftoff/separation.

Main Results:

• Both cemented and uncemented components exhibited reversible inducible displacement under cyclic loads.
• Uncemented tibial components demonstrated significantly greater interface motion and liftoff compared to cemented components (P < .05).
• Liftoff in uncemented components persisted even after load removal, indicating instability.

Conclusions:

• Uncemented tibial components exhibit substantially higher interface motion and separation than cemented components.
• The observed interface motion in uncemented implants, even at low physiological loads, may be sufficient to impede bony ingrowth.
• These findings suggest potential challenges for osseointegration with current uncemented tibial component designs and pore sizes.