Michael R. Sarkar

Calcium phosphates are frequently used as bone substitute materials because of their similarity to the mineral phase of bone, absence of antigenicity, and excellent osteoconductivity. However, in most currently available mineral substitutes, resorption occurs slowly if at all. In contrast, calcium phosphate cements have shown rapid resorption and remodeling in animal studies. In two prospective studies, a novel amorphous calcium phosphate cement (Biobon) was implanted in human patients for the first time. After 2-12 months, ten biopsies were obtained from nine individuals during secondary surgical interventions, for example, for implant removal. In all specimens, partial replacement of the material by new bone was observed, while residues of the cement were still visible. Undecalcified sections revealed extensive bone formation in immediate contact to the cement without fibrous interface. Polynucleated cells and superficial lacunae were indicative of resorptive activity, but inflammatory tissue response was absent. The new bone displayed regular trabecular and osteonal patterns. The histologic findings are in accordance with the excellent biocompatibility observed in the clinical follow-up. Though still incomplete, the resorbability of this cement appears superior to sintered calcium phosphates in these biopsy specimens. Presumably this is due to its amorphous crystalline structure. Biobon merits further studies as a promising substance for bone defect reconstruction in non-stress-bearing areas.

We studied a 4-year-old boy from Angola who presented with 2 cutaneous ulcerations of the right hip and osteomyelitis of the left knee and right ankle. Mycobacterium ulcerans disease was confirmed by direct smear examination and by polymerase chain reaction. The patient was treated with antimycobacterial drugs, repeated surgical debridement, skin grafting, and daily hyperbaric oxygenation. Despite significant improvement of the local lesions in response to hyperbaric oxygenation, swelling of the right knee, without associated skin lesions, was noted. Radiological evaluation and open biopsy revealed extensive metaphyseal osteomyelitis of the right distal femur. A 99technetium bone scan revealed an additional focus in the diaphysis of the left humerus, without soft-tissue involvement. This case documents, for the first time (to our knowledge), the systemic spread of M. ulcerans, with subsequent multifocal osteomyelitis and secondary involvement of soft tissues and supports the hypothesis that low tissue oxygen levels promote hematogenous spread of M. ulcerans. Sickle cell anemia, with associated microthrombosis and microinfarction, may have contributed to tissue hypoxia.

Despite the long-standing use of metals as orthopedic implants there still are unsolved problems with these materials and open questions about their behavior in a biological environment. Cell-culture studies provide a useful tool for investigations. In addition to the determination of biochemical or molecular biological parameters, the morphology of adhering cells reflects their interaction with the substrata. This article describes an investigation of the morphology of human osteoblasts on stainless steel, cobalt chromium alloy, commercially pure titanium, Ti-6Al-4V, and Ti-6Al-7Nb with surface designs similar to those used as clinical implants. A cell culture plastic surface was used as a control material. The materials were examined by scanning electron microscopy at different points of time. The cells spread, proliferated, and formed nodules on all test substrates in a time-dependent manner, without signs of a disturbing influence from any of the materials. On the smooth surfaces the cells showed a flattened fibroblast-like morphology and only slight differences could be detected. Therefore, the cellular morphology seems not to be markedly affected by the different chemical material compositions. In contrast, the titanium alloy with a rough, sandblasted surface induced a three-dimensional growth. This three-dimensional cellular network could be the basis for the known earlier differentiation of osteoblasts on rough surfaces in vitro and a better osseointegration in vivo.