[Bone healing capacity in patients undergoing total hip arthroplasty].

PURPOSE OF THE STUDY: To identify some characteristics of bone repair capacity in elderly patients who undergo total hip arthroplasty, which requires good healing ability of bone for implant osteointegration and bone defect repair, particularly if revision arthroplasty is necessary.

MATERIAL AND METHODS: In a group of 27 patients (mean age, 70 ± 7 years; range, 60 to 81 years) a coincidence of osteoarthritis and osteopenia/ osteoporosis was assessed, and mesenchymal stem cells (MSC) were isolated and their numbers, viability and proliferative capacity were evaluated. The MSC populations were examined for their behaviour on bone tissue scaffolds used in orthopaedic surgery for treatment of bone lesions. Each patient underwent bone densitometry examination before total hip arthroplasty. Bone marrow was harvested intra-operatively from the trochanteric region of the femur. From a portion of bone marrow, MSCs were isolated and cultured, and a mononuclear cell concentrate was obtained. Either whole bone marrow or a mononuclear cell concentrate was applied to selected matrices (allograft, demineralised bone matrix, porous beta-tricalcium phosphate (-TCP), pressed hydroxyapatite or calcium sulphate). The production of new collagen and extracellular mineralized matrix were first assessed in expansion medium and, when the production was low, differentiation medium was used.

RESULTS: A coincidence of osteoarthritis and osteopenia/osteoporosis was found in 50% of the patients. All were women with a low body mass index and had been post-menopausal for an average of 23 years. The isolated MSCs contained a high percentage of viable cells (mean, 95%). The mesenchymal cells of patients with osteopenia, as compared with those having normal bone density, showed markedly lower numbers of fibroblastic colony forming units (CFU-F) per ml and had a lower proliferative capacity because the population doubling time during the first four passages was much longer. Of the scaffolds tested, allografts showed the most marked collagen and extracellular mineralized matrix production in expansion medium with either whole bone marrow or a monocyte concentrate; porous -TCP was the best of bone graft substitutes in collagen and extracellular mineralized matrix production by both whole bone marrow and a monocyte concentrate, but this was only in differential medium.

DISCUSSION: The coincidence of ostearthritis with osteopenia/osteoporosis was found in a higher number of our patients than is reported in the literature. Also, a lower MSC proliferative capacity and a low number of CFU-F/ml in the patients with low bone density were interesting findings. Better bone regeneration would generally be achieved with higher MSC numbers and the use of growth factors for stimulation of osteoinduction and angiogenesis. Bone marrow harvesting for MSC isolation, cultivation and subsequent transplantation is currently feasible only in an experiment. A bone marrow aspirate can be applied, but it may not provide a sufficient number of MSCs. In addition to autologous bone grafts, the best collagen production was on allografts. In bone graft substitutes, the porous structure played an important role because on a non-porous material (calcium sulphate) the formation of collagen was very low. There was no difference in collagen and extracellular mineralized matrix production between whole bone marrow and monocyte concentrates.

CONCLUSIONS: Elderly patients have reduced bone healing capacity also because of osteopenia/osteoporosis that occurs more often than it is generally diagnosed, including its coincidence with osteoarthritis. The mesenchymal stem cells isolated from osteopenic bone give a lower number of CFU-F/ml and have a lower proliferative capacity. Of the matrices for new bone formation, allografts showed the best results because collagen was produced already in expansion medium. Of the graft substitutes, porous -TCP was the best, but with collagen production in differential medium. The use of bone marrow aspirate is currently a method of choice in order to increase MSC numbers at the site of bone healing. The use of growth factors is an expensive treatment. To achieve the goal of reliable promotion of osteogenesis with cultured MSC transplantation and use of composite materials with pro-osteogenic and pro-angiogenic factors will still require many experimental and clinical studies.