We report the results of using impacted cancellous allografts and cement for fixation of the femoral component when revision arthroplasty is required in the face of lost bone stock. In 56 hips reviewed after 18 to 49 months there were few complications and a majority of satisfactory results with evidence of incorporation of the graft. Further study and review are necessary, but the use of the method appears to be justified.

This study analyzed the in vivo performance of composite degradable bone repair products fabricated using the TheriForm process, a solid freeform fabrication (SFF) technique, in a rabbit calvarial defect model at 8 weeks. Scaffolds were composed of polylactic-co-glycolic acid (PLGA) polymer with 20% w/w beta-tricalcium phosphate (beta-TCP) ceramic with engineered macroscopic channels, a controlled porosity gradient, and a controlled pore size for promotion of new bone ingrowth. Scaffolds with engineered macroscopic channels and a porosity gradient had higher percentages of new bone area compared to scaffolds without engineered channels. These scaffolds also had higher percentages of new bone area compared to unfilled control defects, suggesting that scaffold material and design combinations could be tailored to facilitate filling of bony defects. This proof-of-concept study demonstrated that channel size, porosity, and pore size can be controlled and used to influence new bone formation and calvarial defect healing.

The in vivo bone response of 3D periodic hydroxyapatite (HA) scaffolds is investigated. Two groups of HA scaffolds (11 mm diameter x 3.5 mm thick) are fabricated by direct-write assembly of a concentrated HA ink. The scaffolds consist of cylindrical rods periodically arranged into four quadrants with varying separation distances between rods. In the first group, HA rods (250 microm in diameter) are patterned to create pore channels, whose areal dimensions are 250 x 250 microm(2) in quadrant 1, 250 x 500 microm(2) in quadrants 2 and 4, and 500 x 500 microm(2) in quadrant 3. In the second group, HA rods (400 microm in diameter) are patterned to create pore channels, whose areal dimensions of 500 x 500 microm(2) in quadrant 1, 500 x 750 microm(2) in quadrants 2 and 4, and 750 x 750 microm(2) in quadrant 3. Each group of scaffolds is partially densified by sintering at 1200 degrees C prior to being implanted bilaterally in trephine defects of skeletally mature New Zealand White rabbits. Their tissue response is evaluated at 8 and 16 weeks using micro-computed tomography, histology, and scanning electron microscopy. New trabecular bone is conducted rapidly and efficiently across substantial distances within these patterned 3D HA scaffolds. Our observations suggest that HA rods are first coated with a layer of new bone followed by subsequent scaffold infilling via outward and inward radial growth of the coated regions. Direct-write assembly of 3D periodic scaffolds composed of micro-porous HA rods arrayed to produce macro-pores that are size-matched to trabecular bone may represent an optimal strategy for bone repair and replacement structures.

Tight control of pore architecture in porous scaffolds for bone repair is critical for a fully elucidated tissue response. Solid freeform fabrication (SFF) enables construction of scaffolds with tightly controlled pore architecture. Four types of porous scaffolds were constructed using SFF and evaluated in an 8-mm rabbit trephine defect at 8 and 16 weeks (n = 6): a lactide/glycolide (50:50) copolymer scaffold with 20% w/w tri-calcium phosphate and random porous architecture (Group 1); another identical design made from poly(desaminotyrosyl-tyrosine ethyl ester carbonate) [poly(DTE carbonate)], a tyrosine-derived pseudo-polyamino acid (Group 2); and two poly(DTE carbonate) scaffolds containing 500 microm pores separated by 500-microm thick walls, one type with solid walls (Group 3), and one type with microporous walls (Group 4). A commercially available coralline scaffold (Interpore) with a 486-microm average pore size and empty defects were used as controls. There was no significant difference in the overall amount of bone ingrowth in any of the devices, as found by radiographic analysis, but patterns of bone formation matched the morphology of the scaffold. These results suggest that controlled scaffold architecture can be superimposed on biomaterial composition to design and construct scaffolds with improved fill time.

Use of tissue-engineered collars with microgrooving seems to promote bone and soft tissue attachment along the collar and facilitate development of a biological width.