Meniscus Repair After Injury

The menisci are C-shaped cartilage-like tissues located between the bones of the knee. They help the knee to function properly by bearing load, absorbing shock, stabilizing the joint and providing lubrication. Meniscal tears are common and often result from sports injury. Damage to or loss of the meniscus can lead to changes in the articular cartilage and development of knee osteoarthritis (OA).

What Problem Was Studied?

Anatomy Basics
Menisci: The menisci are two pads of cartilaginous tissue that disperse friction in the knee joint between the lower leg (tibia) and the thigh (femur). They act to diffuse the weight of the body and reduce friction during movement. In sports and orthopedics, people will sometimes speak of “torn cartilage” and actually be referring to an injury to one of the menisci.
Researchers from Duke University in Durham, N.C., including Arthritis Foundation-funded scientists Amy L. McNulty, PhD, and Farshid Guilak, PhD, are investigating ways that menisci can be repaired so athletes can avoid future joint changes and possible knee OA. Previous studies have shown that injured joints – and ones with osteoarthritis – have high levels of the pro-inflammatory molecule interleukin-1 (IL-1).

IL-1 is known to increase matrix metalloproteinase (MMP) activity in joint tissues. MMPs play a role in tissue remodeling, which is the normal breakdown and rebuilding of tissues that keep them strong and healthy. Too much MMP activity in the joint results in the degradation of tissues and may negatively affect the ability of the meniscus to repair itself.

The research team set up an experiment to determine what effect IL-1 has on the healing and repair of damaged meniscal tissue. Their hypothesis is that short-term exposure to IL-1 will increase MMP activity and reduce meniscal repair.

What Was Done in the Study?

Menisci were obtained from the knee joints of skeletally mature pigs. Meniscal samples were removed from the tissue and then damaged by punching a ring through the center of each explant, similar to a doughnut hole. Theses inner holes were left in place and then cultured. Some of the menisci were placed in growth medium alone and served as controls. All the others were placed in growth medium with IL-1: some were treated with IL-1 for one day, some were treated with IL-1 for three days, and some were treated with IL-1 for the duration of the experiment. At 14 and 28 days, the menisci were analyzed and tested.

What Were the Study Results?

The scientists found that just one day of IL-1 exposure increased MMP activity and reduced the ability of the menisci to heal and repair. Those samples treated for one or three days had reduced strength, fewer new cells and less tissue repair compared to control samples. Those samples treated with IL-1 for the entire time span of the experiment showed an even poorer ability to repair.

What Does This Mean for People with Meniscal Injury?

The body’s natural reaction to injury – such as a torn meniscus suffered in a soccer game – is inflammation, which includes the release of IL-1. In the study article’s conclusion, the authors state, “Overall, our study suggests that acute exposure to IL-1 may have prolonged effects on the physiology of meniscal cells. As a result, acute inflammation following meniscal injury may decrease meniscal repair.” Understanding the duration and timing of IL-1 exposure after a meniscus tear will help scientists find an appropriate treatment window. Perhaps additional research will find that halting inflammation and stopping the release of IL-1 into the joint within a certain time after the injury will allow the tissue to heal itself, thereby avoiding cartilage damage and osteoarthritis down the road.

Wilusz RE, Weinberg JB, Guilak F, McNulty AL. Inhibition of integrative repair of the meniscus following acute exposure to interleukin-1 in vitro. J Orthop Res 2008;26:504-12.

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