The potential of microfracture technique to induce subchondral bone pathology should be considered.

The use of microfracture in hip arthroscopy is increasing dramatically. However, recent reports raise concerns not only about the lack of evidence to support the clinical use of microfracture, but also about the potential harm caused by violation of the subchondral bone plate. The biology and pathology of the microfracture technique were described based on observations in translational models and the clinical evidence for hip microfracture was reviewed systematically. The clinical outcomes in patients undergoing microfracture were the same as those not undergoing microfracture. However, the overall clinical evidence quality is poor in hips. This review identified only one study with Level III evidence, while most studies were Level IV. There were no randomized trials available for review. Repair tissue is primarily of fibrocartilaginous nature. Reconstitution of the subchondral bone is often incomplete and associated with poor quality repair tissue and faster degeneration. Subchondral bone cyst formation is associated with microfracture, likely secondary to subchondral bone plate disruption and a combination of pressurized synovial fluid and inflammatory mediators moving from the joint into the bone. There is a lack of clinical efficacy evidence for patients undergoing microfracture. There is evidence of bone cyst formation following microfracture in animal studies, which may accelerate joint degeneration. Bone cyst formation following microfracture has not been studied adequately in humans.

Percutaneous intramedullary fixation may provide an ideal method for stabilization of bone fractures, while avoiding the need for large tissue dissections. Tibiae in 18 sheep were treated with an intramedullary photodynamic bone stabilization system (PBSS) comprised of a polyethylene terephthalate (Dacron) balloon filled with a monomer and cured with visible light in situ then harvested at 30, 90 or 180 days. In an additional 40 sheep, a mid-shaft tibial osteotomy was performed and stabilized with external fixators or external fixators combined with the PBSS and evaluated at 8, 12 and 26 weeks. Healing and biocompatibility were evaluated by radiographic analysis, microCT and/or histopathology. In non-fractured sheep tibiae, PBSS implants conformably filled the medullary canal, while active cortical bone remodeling and apposition of new periosteal and/or endosteal bone was observed with no significant macroscopic or microscopic observations. Fractured sheep tibiae exhibited increased bone formation inside the osteotomy gap with no significant difference when fixation was augmented by PBSS implants. Periosteal callus size gradually decreased over time and was similar in both treatment groups. No inhibition of endosteal bone remodeling or vascularization was observed with PBSS implants. Intramedullary application of a light curable PBSS is a biocompatible, feasible method for fracture fixation.

Objective To compare the histological and immunohistochemical characteristics of matrix-assisted chondrocyte implantation (MACI) grafts between patients with revision surgery and patients with total joint arthroplasty. Methods Biopsies of MACI grafts from patients with revision and total joint arthroplasty. The graft tissue characteristics and subchondral bone were examined by qualitative histology, ICRS (International Cartilage Repair Society) II scoring and semiquantitative immunohistochemistry using antibodies specific to type I and type II collagen. Results A total of 31 biopsies were available, 10 undergoing total knee arthroplasty (TKA) and 21 patients undergoing revision surgery. Patients in the clinically failed group were significantly older (46.3 years) than patients in the revision group (36.6 years) ( P = 0.007). Histologically, the predominant tissue in both groups was of fibrocartilaginous nature, although a higher percentage of specimens in the revision group contained a hyaline-like repair tissue. The percentages of type I collagen (52.9% and 61.0%) and type II collagen (66.3% and 42.2%) were not significantly different between clinically failed and revised MACI, respectively. The talar dome contained the best and patella the worst repair tissue. Subchondral bone pathology was present in all clinically failed patients and consisted of bone marrow lesions, including edema, necrosis and fibrosis, intralesional osteophyte formation, subchondral bone plate elevation, intralesional osteophyte formation, subchondral bone cyst formation, or combinations thereof. Conclusions MACI grafts in patients with revision and total joint arthroplasty were predominantly fibrocartilage in repair type, did not differ in composition and were histologically dissimilar to healthy cartilage. Clinically failed cases showed evidence of osteochondral unit failure, rather than merely cartilage repair tissue failure. The role of the subchondral bone in relation to pain and failure and the pathogenesis warrants further investigation.