Clinical Outcomes of Biomaterial-Based Cartilage Repair Strategies for Knee Chondral Defects: A Systematic Review and Meta- Analysis

Inside the knee, a smooth, slippery layer of tissue called articular cartilage acts as a cushion between the bones. This material is designed to let joints glide without friction and to absorb the shock of walking or running. However, unlike skin or muscle, this cartilage has very few blood vessels and cells, which means it has almost no ability to heal itself when damaged. When a focal defect, or a specific hole, forms in this layer, it often does not go away on its own. Instead, the injury can lead to persistent pain, limited movement, and eventually, the breakdown of the joint into osteoarthritis. For decades, surgeons have tried to fix these holes, often using a technique called microfracture, which involves drilling tiny holes into the bone to release marrow and stimulate healing. While this method is common, the new tissue that grows back is often a weaker, scar-like version of the original cartilage, leading to questions about how long the repair will last.

In recent years, scientists have turned to a different approach to help the body rebuild this tissue: hydrogels. These are jelly-like scaffolds made from natural or synthetic materials that can be placed into the defect to hold the marrow clot in place and provide a supportive environment for new tissue to grow. The idea is that by giving the body a better structure to work with, the repair tissue might be stronger and more durable. But because there are many different types of these hydrogels and many ways to use them, it has been difficult for doctors to know which ones work best or what kind of results patients can realistically expect. To answer this, a team of researchers from Florida Atlantic University and other institutions set out to gather and analyze the available evidence on how well these hydrogel-based repairs actually work.

The researchers conducted a systematic review, which is a rigorous method of finding every relevant study on a topic, checking their quality, and combining their data to find a clearer picture than any single study could provide. They searched medical databases for studies published between 2016 and 2026 that looked at adults with focal cartilage defects in the knee who were treated with a hydrogel. They focused specifically on studies that reported results at one year after surgery, a standard time to see if the repair tissue has matured. The team looked at two main things: how the repair looked on magnetic resonance imaging, or MRI, and how the patients felt and functioned. For the MRI results, they used a scoring system called MOCART, which rates the quality of the repair tissue based on how well it fills the hole and matches the surrounding cartilage. For patient feelings, they looked at the IKDC score, a common questionnaire that asks patients about their pain, swelling, and ability to perform daily activities.

After sifting through hundreds of articles, the team identified seven studies that met their strict criteria, involving a total of 160 patients whose outcomes were successfully reported. These studies used various hydrogel materials, including some made from natural substances like chitosan and others that were a mix of natural and synthetic components. The researchers found that, on average, the hydrogel-assisted repairs produced encouraging results. The pooled MRI score for the quality of the repair tissue was 71.2 out of a possible 100, suggesting that the new tissue filled the defect well and looked structurally sound. In terms of how patients felt, the average score was 70.2, indicating a moderate to favorable level of function and a reduction in symptoms.

The analysis also looked at whether specific types of hydrogels performed differently. When the researchers focused on a group of studies using a specific natural hydrogel called CarGel, the results were very consistent, with a similar average MRI score and almost no variation between the different studies. This suggests that this particular material produces reliable short-term structural repairs. Another study that used a hybrid material, combining synthetic and natural elements, reported the highest individual MRI scores, hinting that mixing materials might offer some advantages, though the data was too limited to say for sure. The researchers noted that while the results were positive, the evidence is not yet strong enough to declare one type of hydrogel superior to all others or to prove that these methods are better than existing treatments. The studies included were relatively small, and many were observational rather than large, randomized comparisons.

Ultimately, the review concludes that using hydrogel scaffolds to assist in cartilage repair is a promising strategy that appears to help the body form better-quality repair tissue in the short term. The findings support the idea that these materials can act as useful tools to improve the outcome of standard surgical techniques. However, the authors emphasize that more research is needed. Future studies should compare different hydrogel types directly against each other, track patients for longer periods to see if the repairs last, and standardize how results are reported. For now, the choice of which hydrogel to use remains a decision that must be made carefully, taking into account the specific details of the patient's injury and the surgeon's expertise, as the science is still evolving to determine the very best path forward for restoring the knee.