The relevance of hydroxyapatite and spongious titanium coatings in fixation of cementless stems. An experimental comparative study in rat femur employing histological and microangiographic techniques

Pure titanium rods plasma-spray coated with hydroxyapatite (HA) or porous titanium (Ti) of controlled roughness were implanted bilaterally in the distal femur of Sprague-Dawley rats to compare the extent of bone growth on the two types of coating. The relevance of other factors, like mechanical stability and biological adaptation of the bone to the insertion of a foreign body implant, were investigated in femora which were over-reamed (absence of primary fit) or reamed without insertion of the rod. Continuous tetracycline labeling for the first 30 days and for the last 2 weeks in the 90-day group was performed; histological/histometric, fluorescence and microangiographic studies were carried out on serial sections of the implanted and control femora. In the group of stable implants, HA-coated rods showed 90% integration versus 53% with Ti-coated implants (P < 0.001); in over-reamed implants neither surface bone growth nor endosteal fixation occurred, and both types of rods were surrounded by a thick layer of connective tissue. The study documented early adhesion of osteoblasts and direct deposition of bone matrix on the substrate, while on spongious titanium osteogenesis was observed only in proximity to the surface. Remodeling of the reactive, primary bone to mature, lamellar bone took the form of a capsule surrounding the implants and radial bridges connecting the latter to the endosteal surface. The number, height and thickness of these bridges appeared to be the factors determining implant stability, rather than the extent of the bony capsule on the perimeter of the implant. Integration was a function not only of mechanical conditions and surface geometry, but also of the biological response of the whole bone to changes in the vascularization pattern. The reported phenomena can be seen more easily in experimental models involving small rodents because of their fast bone turnover and revascularization, but it is expected that they take place, even at a lower speed, in clinical situations like cementless stems of total hip replacement.

The effect of surface roughness on early in vivo plaque colonization on titanium

THE STUDY ASSESSES IN VIVO the surface roughness necessary to reduce plaque colonization on titanium after 24 hours. Three groups of 16 titanium disks were assigned to 3 different polishing groups (A, B, and C). The roughness was evaluated with a laser profilometer and the morphology with a scanning electron microscope (SEM). Eight volunteers were enrolled and two stents were applied in the mandibular posterior region of each. Each stent supported 3 disks, one per group. The volunteers suspended oral hygiene for 24 hours, after which the stents were removed; one was processed for evaluation of the adherent biomass and the other for SEM study. On each specimen a global area of 100 x 125 microns was examined with SEM. The area was composed of five 20 x 25 microns randomly selected fields. For each field the density of bacteria and the morphotypes were recorded. The data quoted for the global area are cumulative of those observed in the 20 x 25 microns fields. Group A had a significantly smoother surface than groups B and C. The adherent microbial biomass determination and SEM evaluation revealed that group A contained less bacteria than the roughest group. The bacterial population was composed of cocci in group A, and of cocci and short and long rods in groups B and C. We conclude that a titanium surface with Ra < or = 0.088 microns and Rz < or = 1.027 microns strongly inhibits accumulation and maturation of plaque at the 24-hour time period and that such smoothness can be achieved in transgingival and healing implant components.

Titanium nitride as a coating for surgical instruments used to collect human tissue for trace metal analysis

When metallic surgical instruments are used to collect human tissue, metal contamination may occur, making accurate ultra-trace metal determinations very difficult. In order to reduce this risk as much as possible, surgical instruments made from a stainless-steel core covered by a film of titanium nitride, a very hard compound with high chemical stability and very good wear resistance, were prepared. The degree of risk from trace metal contamination during sample collection was investigated by neutron activation analysis and a radio-release in vitro serum test. As examples of their application, the titanium nitride coated instruments were used to determine Co, Cr and W in the skin of unexposed subjects and of uraemic patients under regular dialysis treatment.

[Juvenile malignant osteopetrosis. Clinico-radiological study of 7 cases]

Clinical and radiological studies of seven patients with autosomic recessive malignant osteopetrosis are presented. Diagnosis was established before the age of 3 months in six cases and at 7 months in one. In all cases the presenting signs were pallor and hepatosplenomegaly with associated neurological involvement in five. All patients had normocytic normochromic anemia, leucopenia and thrombocytopenia with features of extramedullary hematopoiesis. Radiological studies revealed increase in the density of bones with "mask" appearance of facial bones and diminished size of optic foramina. Long bones showed absence of normal trabeculae and anomalies in modeling with methaphiseal bands and "bone within bone" images. There was hypocalcemia and hypophosphatemia with slight increases in alkaline phosphatase; parathormone was normal. Clinical course was characterized by progressive pancytopenia, recurrent infections and neurological deterioration with convulsions, nistagmus and optic atrophy. Five out of the seven patients died after a median of 3 months, due to infections or haemorrhage. The patient diagnosed at 7 months of age presented bilateral optic atrophy and moderate anemia; no other complications appeared after 2 year follow-up. Histological findings included substitution of bone marrow by chondro-osseous tissue; focal obsteoblastic and osteoclastic activity in calcified cartilage, and myeloid metaplasia in liver, spleen, lymph nodes and kidneys. The lesions are in agreement with the concept of a defect in bone formation-resorbtion balance; dysfunction of both osteoclasts and osteocytes is implicated in the pathogenesis. Unlike experimental disease, osteopetrosis in man is probably an heterogeneous disease and appropriate therapy should be individualized. Nevertheless, at present, the only favorable results have been obtained with bone-marrow transplantation.