The use of the contact Nd:YAG laser in arthroscopic surgery: effects on articular cartilage and meniscal tissue

The contact Nd:YAG laser's small size, tip variety, fiberoptic application, and suitability for use in a saline medium make it a particularly appealing tool for use in arthroscopic procedures. This study was performed to investigate the laser's effects on articular cartilage and meniscal tissue with respect to depth of damage (canine cadaver model) and healing response (rabbit model). Depth of damage in the canine cadaver model was greater in meniscal tissue than in articular cartilage at each wattage level. In the presence of a saline bath, depth damage in both tissues was diminished. Scalpel articular cartilage lesions showed no response over time. Electrocautery lesions uniformly showed significant wide margins of hyaline cartilage necrosis which increased over time. Laser articular cartilage lesions showed vigorous healing responses characterized by fibrocartilage healing by 6 weeks. Scalpel meniscectomies showed characteristic fibrocartilagenous remodeling by 6 weeks, while electrocautery meniscectomies showed wide margins of necrosis with no specimen showing remodeling capability. Laser meniscectomies showed an intermediate response with a small number of menisci remodeling in a normal fashion. This article represents the first comprehensive look at the effects of the Nd:YAG laser on articular cartilage and meniscal tissue in terms of depth of damage and healing response over time, and indicates this laser's biological advantage over scalpel and electrocautery in arthroscopic procedures.     

Extended long-term culture reveals a highly quiescent and primitive human hematopoietic progenitor population

Long-term culture-initiating cells (LTC-IC) are hematopoietic progenitors able to generate colony-forming unit-cells (CFU) after 5 to 8 weeks (35 to 60 days) of culture on bone marrow (BM) stroma and represent the most primitive progenitors currently detectable in vitro. We have recently reported that long-term cultures initiated with CD34+CD38- cells from BM or cord blood are able to continue generating CFU for at least 100 days, ie, beyond the standard LTC-IC period. In this report, single-cell cultures from cord blood and retroviral marking of cord blood and BM were used to study whether the subpopulation of CD34+CD38- cells able to generate CFU beyond 60 days ("extended long-term culture-initiating cells" or ELTC-IC) are functionally distinct from LTC-IC in terms of timing of initial clonal proliferation and generative capacity. All cord blood LTC-IC formed clones of greater than 50 cells by day 30. In contrast, cord blood ELTC- IC proliferated later in culture, 50% forming clones after day 30. Although efficient retroviral marking of LTC-IC was seen (25% to 45%), marking of ELTC-IC was inefficient (< 1%), consistent with a more quiescent progenitor population. There was a positive correlation between time of clonal proliferation and generative capacity. ELTC-IC generated threefold to fourfold more progeny than did LTC-IC (P < .002). These studies show that there is a functional hierarchy of progenitors in long-term culture which correlates with their level of quiescence. By extending the LTC-IC assay, a more primitive progenitor may be studied that may be functionally closer to the human long-term repopulation stem cell in vivo.