Osteogenic protein-1 delivered by hydroxyapatite-coated implants improves bone ingrowth in extracortical bone bridging

Abstract

Background: Extracortical bone bridging for treatment of massive bone loss can improve stability and longevity of massive endoprostheses. Osteogenic protein-1 (OP-1), when used with allograft bone, reportedly improves extracortical bone bridging and bone ingrowth.

Questions/purposes: We asked whether OP-1 delivered by hydroxyapatite (HA) without bone grafting could improve bone ingrowth and bone formation in the context of extracortical bone bridging.

Methods: We implanted unilateral segmental femoral diaphyseal replacement prostheses in 18 dogs (three groups of six dogs). The groups consisted of an HA-coated group augmented with OP-1, an HA-coated group, and a plain porous group. Bone grafting techniques were not used to augment bone formation. The implants were retrieved at 12 weeks for histologic assessment.

Results: After removing one specimen owing to a complication, 17 femora were analyzed (six HA-coated augmented with OP-1, five HA-coated, and six plain). We observed better bone ingrowth in the HA-coated OP-1 group than in the plain porous and HA-coated groups, with no difference between the latter two groups. There also was better bone apposition and callus height in the HA-coated OP-1 group than in the plain group but no differences between the HA-coated OP-1 and HA-coated groups or between the HA-coated and plain groups.

Conclusions: OP-1 (2.9 mg) delivered by HA-coated segmental replacement prostheses in this canine extracortical bone bridging model revealed improved bone ingrowth over HA-coated implants without OP-1 or plain porous-coated prostheses.

Fig. 1

A photograph shows the modular bistemmed segmental replacement prosthesis.

Fig. 2A–D

The images are examples of radiographs of harvested femora. The (A) AP and (B) lateral radiographs show little bone formation. These (C) AP and (D) lateral radiographs show bridging callus over the posterior aspect of the implant.

Fig. 3A–F

Longitudinal histologic sections of specimens show various degrees of bone ingrowth and bone formation. (A) A PA-coated implant shows mainly fibrous tissue ongrowth with little new bone formation and ingrowth (Stain, Giesma; original magnification, ×40). (B) The same specimen at a higher magnification is shown (Original magnification, ×100). (C) A PA-coated implant treated with OP-1 shows new bone formation from the adjacent periosteum (black arrow) with good bone ingrowth. Continuity of the newly formed bone and the cortex also can be seen (Stain, Giesma; original magnification, ×40.) (D) Another PA-coated implant treated with OP-1 specimen at higher magnification shows bone ingrowth (Stain, Giesma; original magnification, ×100). (E) A PA-coated implant shows moderate bone formation from the adjacent cortex but minimal bone ingrowth (Stain, Giesma; original magnification, ×40). (F) The same specimen at higher magnification shows fibrous tissue ingrowth but no bone ingrowth (Original magnification, ×100).