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Late mechanical stability of the proximal coated AML prosthesis
H Sugiyama1, L A Whiteside, C A Engh
1Biomechanical Research Laboratory, St Louis, MO 63141.
Orthopedics
|July 1, 1994
Summary
Bone ingrowth provides stable fixation for anatomic medullary locking (AML) femoral components. However, femur flexibility can lead to increased distal stem micromotion, even with initial tight fit.
Area of Science:
- Orthopedic surgery
- Biomaterials science
- Biomechanics
Background:
- Total hip replacement (THR) utilizes cementless femoral components like the anatomic medullary locking (AML) stem.
- Bone ingrowth is crucial for long-term fixation of cementless implants.
- Understanding implant micromotion is key to assessing fixation stability.
Observation:
- A retrieved AML femoral component showed proximal bone ingrowth but a radiolucent line distally.
- In vitro testing on the retrieved specimen revealed minimal proximal micromotion but significant distal medial-lateral micromotion (44 microns) under axial load.
- Freshly implanted components exhibited greater proximal micromotion than the bone-ingrown specimen.
Findings:
- Bone ingrowth achieved rigid proximal fixation of the AML femoral component.
- Despite initial press-fit, the bone-ingrown stem experienced greater distal micromotion compared to freshly implanted stems.
- Femoral flexibility around the smooth distal stem contributed to increased micromotion.
Implications:
- While bone ingrowth ensures proximal stability, distal stem design and interaction with bone flexibility require consideration.
- Further research into optimizing distal fixation for cementless femoral stems is warranted.
- This study highlights the complex interplay between implant design, bone ingrowth, and host bone mechanics in THR outcomes.