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Bone Coverage around Hydroxyapatite/Poly(L-Lactide) Composite Is Determined According to Depth from Cortical Bone
Kazuaki Morizane1, Koji Goto1, Toshiyuki Kawai1
1The Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 602-8570, Japan.
Materials (Basel, Switzerland)
|April 3, 2021
Summary
Hydroxyapatite (HA) and poly(L-lactide) (PLLA) composite pins promote bone formation when implanted fully within bone. Protrusion above the bone surface can hinder new bone growth and may cause adverse reactions.
Area of Science:
- Biomaterials Science
- Orthopedic Surgery
- Regenerative Medicine
Background:
- Biodegradable, bioactive, and ultrahigh-strength hydroxyapatite (HA) and poly(L-lactide) (PLLA) composites are promising for bone regeneration.
- Foreign body reactions and physical irritation can occur with PLLA-based implants if not adequately covered by bone.
Purpose of the Study:
- To investigate the relationship between the depth of implantation of HA-PLLA composite threaded pins and new bone formation.
- To evaluate the impact of pin protrusion on osseointegration and inflammatory responses.
Main Methods:
- HA-PLLA composite threaded pins (2.0 or 4.5 mm diameter) were implanted into rabbit femurs and tibias.
- Pin head positions were varied: 1 mm below, level with, or protruding 1-2 mm above the cortical bone surface.
- Radiological and histological assessments were performed at multiple time points.
Main Results:
- Complete bone bridging was observed around pins inserted 1 mm below the bone surface by approximately 12 weeks.
- Bone formation varied for pins inserted level with the surface and was absent for pins protruding >1 mm.
- No inflammation was noted around implants by 25 weeks, but protrusion above bone may elicit foreign body reactions.
Conclusions:
- Intraosseous fixation of HA-PLLA composite pins is crucial for optimal new bone formation and to avoid adverse tissue reactions.
- Countersinking or using double-threaded screws can ensure proper implant depth and enhance clinical outcomes.
