Effects of tibial components on load transfer in the upper tibia

Area of Science:

• Orthopedic biomechanics
• Biomaterials science
• Surgical implant design

Background:

• Tibial component fixation is critical for knee replacement longevity.
• Understanding the biomechanical behavior of different tibial component designs under load is essential.
• Previous studies have not fully elucidated the strain distribution and load transfer characteristics of various tibial stem designs.

Purpose of the Study:

• To compare the biomechanical performance of different tibial component designs under simulated physiological loading conditions.
• To evaluate the influence of material (metal vs. plastic) and stem geometry on strain distribution and load transfer in the proximal tibia.
• To assess the impact of tibial component coverage and stem length on bone stress.

Main Methods:

• Cadaveric knee specimens were subjected to combined loading (compression, anteroposterior force, rotational torque, varus-valgus moment).
• Strain gauges measured surface strains on the tibia at four levels, both with and without cemented tibial components.
• Strain readings were also taken around central pegs, and variables included all-plastic vs. metal tray, post length, and coverage.

Main Results:

• Metal stems exhibited significantly higher resistance to bending moments compared to plastic stems under varus-valgus and anteroposterior loading.
• Plastic stems carried only small axial loads due to low axial stiffness.
• Incomplete bone contact created a rim of low-stressed bone, while longer metal stems transmitted load directly to the cortex.

Conclusions:

• Metal tibial stems offer superior biomechanical performance in handling bending loads compared to plastic stems.
• Tibial component design, including material, stem geometry, and coverage, significantly influences load transfer and bone strain.
• While metal stems have advantages, potential drawbacks like load by-passing and removal difficulty warrant consideration.