Jarcho, Clin Orthop Relat Res 1981 - Calcium Phosphate Ceramics as Hard Tissue Prosthetics - Article Summary

Calcium Phosphate Ceramics as Hard Tissue Prosthetics

Jarcho·Clin Orthop Relat Res·1981·2,003 citations·Review article

Jarcho's 1981 narrative review surveys the preparation, material properties, biologic behavior, and early clinical use of calcium phosphate ceramics — primarily hydroxyapatite (HA) and tricalcium phosphate (TCP) — as candidates for hard tissue prosthetics and bone graft substitutes. It asks: what do we know about biocompatibility, bioresorbability, and mechanical limits, and where can these materials realistically be used?

Key Findings

TCP dissolves 12.3× faster than HA in acid (pH 5.2) and 22.3× faster in alkaline solution (pH 8.2) when materials of equivalent purity, density, and microstructure are compared. Bioresorption rate tracks TCP content — composition is the primary dial for tuning resorption speed in a mixed HA-TCP ceramic.
CaP ceramics are osteoconductive, not osteoinductive. In millipore chamber studies, marrow-alone controls formed new bone in 90% of chambers vs. only 35% of HA-marrow chambers. The material cannot initiate bone formation and actually impeded induction relative to marrow alone. These materials guide bone growth; they do not trigger it.
All CaP ceramics share a consistent favorable biologic profile regardless of composition: no local or systemic toxicity, no inflammatory or foreign body response, no fibrous encapsulation, and direct chemical bonding to bone. The authors attribute this to the calcium-phosphate ionic composition matching that of native bone mineral.
Minimum 100 µm pore diameter is required for effective bone ingrowth into porous CaP structures. Most clinically investigated porous implants used 100–400 µm interconnecting macropores to permit vascular and osseous penetration.
Mechanical brittleness is the defining clinical limitation. Porous CaP compressive strength approximates cancellous bone (1–10 × 10³ psi) but falls far short of stainless steel (80–145 × 10³ psi), ruling out use as bone plates, IM rods, screws, or free-standing tooth implants. These materials belong in low-load, compressive environments.
Autogenous bone consistently outperforms CaP ceramics in healing speed. In a rabbit tibia bridging model, autograft achieved bony bridging at 4–6 weeks, porous TCP at 14–16 weeks, and a 50/50 mixture at 6 weeks. The data point clearly toward CaP as an autograft extender, not a replacement.
Dense CaP implants bond directly to bone without mechanical interlock. The bond is strong enough that removal requires fracturing the implant or the surrounding bone. The mature bonding zone is a mineralized amorphous band approximately 500–2000 Å wide, histochemically similar to natural bone cementing substance. This bone-bonding property is what makes HA coatings on metallic implants mechanistically rational.

Board PearlCalcium phosphate ceramics are osteoconductive but not osteoinductive — TCP resorbs 12× faster than HA, making composition the tunable lever for bioresorption rate.

Supplemental

Calcium Phosphate Ceramics as Hard Tissue Prosthetics.

JarchoClin Orthop Relat Res19812,003 citationsReview article