The biology and clinical evidence of microfracture in hip preservation surgery.

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.