Linking the Mechanics of HA to Knee Cartilage Biology | Orthopedics This Week
Biologics

Linking the Mechanics of HA to Knee Cartilage Biology

Lawrence Bonassar, Ph.D. / Courtesy of Cornell University

A new, important study out of Dr. Lawrence Bonassar’s lab at Cornell University has tackled one of the central but more difficult questions surrounding viscosupplementation, namely the link between hyaluronic acid’s (HA) lubrication function and the complex biologic processes operating on the arthritic knee.

The study, which was presented at the annual meeting of the Orthopaedic Research Society (ORS) between March 10-13, 2018, is titled “Articular Cartilage Lubrication by HYADD® 4 Reduces Tissue Strains, Chondrocyte Death and Apoptosis.”

As the investigators stated in the introduction to their study: “It remains unclear how the lubricating properties of HA mediate biologic changes in cartilage tissue. Recently, our lab developed methods to measure cellular changes in response to cyclic sliding motion. The objective of this study was to examine the relationship between the lubricating properties of HYADD®4, an HA viscosupplement and chondrocyte health after sliding articular cartilage in HYADD®4.”

To understand the importance of the work coming out of Bonassar’s lab, it’s helpful to understand the original intended purpose of viscosupplementation. Hint: It’s not pain relief.

A Short History of Viscosupplementation

Viscosupplementation, which was first used as a therapy in the 1970s (trade name of Healon®) for ophthalmic use and veterinary use (Hylartil-Vet®), is a standard of care within the continuum of care for symptomatic osteoarthritic knees.

The intended purpose of viscosupplements is to replenish the naturally occurring synovial fluid with a substance as close to normal, healthy synovial fluid as possible. Healthy synovial fluid, in addition to providing nourishment to the cartilage cells, also lubricates the articulating structures of the joint during low impact movement and shock absorption during high impact activities.

Many studies have shown that the early onset of osteoarthritis causes a deterioration of synovial fluid’s properties—specifically elasticity and viscosity. There are various disease processes at work in an arthritic knee including production of certain enzymes and “toxic” precursors. The result is a diseased synovial fluid which cannot perform the functions of lubrication or shock absorption.

At every stage of the osteoarthritic disease process, the deteriorating ability of the synovial fluid can be experienced by the patient as pain, stiffness and reduced function of the joint.

The principal of viscosupplementation, as originally presented to the FDA[1], is to break the cycle of synovial fluid deterioration. In fact, HA viscosupplement products are not registered as drugs but rather as medical devices, like liquid bioprosthesis.

Viscosupplementation helps an osteoarthritic joint by forming a protective layer around the inflamed articulating structures, covering micro-fractures and defects helping to restore the lubrication and protection that healthy synovial fluid offers.

So, physicians and researchers have long assumed that these mechanical functions of HA affected the biology of a deteriorating arthritic knee.

But how?

Enter Bonassar’s lab at Cornell University.

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