Primary stability in total hip replacement: A biomechanical investigation

Area of Science:

• Orthopedic biomechanics
• Biomaterials science
• Surgical implant technology

Background:

• Primary stability is crucial for successful total hip replacement (THR) outcomes.
• Traditional uncemented press-fit and cemented stems have limitations.
• A novel locking screw hip (LSH)-stem was developed to enhance primary stability using monocortical locking screws.

Purpose of the Study:

• To biomechanically evaluate the primary stability of the LSH-stem.
• To compare the LSH-stem's performance against an uncemented press-fit stem.

Main Methods:

• Human cadaveric femora (n=6 pairs) were used.
• Specimens were implanted with either an LSH-stem or an uncemented press-fit stem.
• Biomechanical testing involved cyclic axial loading to failure, measuring stiffness, failure load, and cycles to failure.

Main Results:

• Both stems exhibited comparable axial stiffness.
• The LSH-stem demonstrated significantly higher failure load and cycles to failure compared to the uncemented press-fit stem (P=0.04).

Conclusions:

• The LSH-stem provides superior primary stability, supporting up to 507% of body weight.
• The uncemented press-fit stem supported up to 404% of body weight.
• Both stem designs achieve adequate primary stability for immediate post-THR rehabilitation loads.