Twenty-eight studies were included (n=3,122, range seven to 1,200): six RCTs; one prospective cohort; and 21 case series (12 prospective and nine retrospective). Overall validity was acceptable. Mean quality score was 58.2 points out of 100 (range 22 to 97). Scores were relatively high (at least 80%) for diagnostic certainty, follow-up rate and description of outcomes. Scores were relatively low for study design, methods of selection and outcomes assessment.
All relevant studies (24 out of 24) reported improved knee function after microfracture with greatest improvement in the first 24 months. Among five studies (one RCT and four case series) that reported clinical results at least five years after microfracture, 67% to 87% of participants reported improvement.
Defect fill rates in MRI studies (two RCTs and seven case series) were inconsistent, but fill rates correlated positively with functional outcomes (three studies). Studies of second-look arthroscopy (three RCTs and six case series) found normal or near-normal macroscopic cartilage repair grading in 45% to 77% of defects at eight to 24 months’ follow-up. In studies with histological data (n=six), fibrocartilage alone was found in 33% to 57% of cases and hybrid fibrohyaline cartilage in 39% to 64%.
Complications and procedure-related adverse events were rare. Failure rates were variable and time-dependent: in RCTs, the revision rate was 23% to 31% at two- to five-year follow-up.
Other results were reported in the review; these included a summary of factors associated with functional outcomes of microfracture.