- People who rupture their ACL have a 8.2 fold greater risk of knee osteoarthritis within 11 years.
- A new study finds evidence that the less weight and force people put on their injured knee after surgery the more likely they will develop arthritis in their knee.
- The new findings suggest there’s likely a link between the amount of contact force a joint is exposed to and joint degradation.
New research has potentially identified why some people have a higher risk of developing arthritis after anterior cruciate ligament reconstruction (ACL) surgery.
The study, published in the Journal of Orthopaedic Research Wednesday, found that the less weight and force people put on their injured knee after surgery, the greater their risk of developing osteoarthritis — a type of arthritis that involves wear and tear of a joint.
People who rupture their ACL have a 8.2 fold greater risk of knee osteoarthritis within 11 years.
The new findings suggest there’s likely a link between the amount of contact force a joint is exposed to and joint degradation.
“These results continue to reinforce what we have seen in other studies, that the effects of ACL tear and ACL injury and surgery persist well beyond the typical ‘rehabilitation’ period,” Dr. Elizabeth Gardner, an orthopedic sports medicine physician at Yale Medicine and head team orthopedic surgeon for Yale Athletics, told Healthline. Gardner was not involved in the study.
Less joint loading is associated with higher risk of arthritis
The researchers evaluated 46 patients who had ACL surgery for a knee injury.
They measured how joint loading — or the amount of body weight and force a joint experiences — impacted the risk of patellofemoral joint osteoarthritis after the surgery.
To do so, they evaluated each participant’s trunk and lower limb kinematics and ground reaction forces during hops, or small jumps. They used that information to calculate the amount of contact force placed on the joint.
The team took joint magnetic resonance imaging (MRI) scans of 32 participants’ knees five years after they received the surgery.
The team found that young adults who put less contact force on their joints during hopping were more likely to have osteoarthritis one year after surgery along with worsening osteoarthritis up to five years after surgery.
The team also investigated how body weight impacted the risk of osteoarthritis and found that decreases in body weight were associated with less contact force on the joint.
Lower body weight, and therefore less contact force, was linked to a higher risk of osteoarthritis.
“It may be a sign of ongoing altered joint mechanics. It may be that the patient is still protecting the knee joint, out of fear or due to pain or weakness,” says Gardner.
What’s the relationship between ACL injury and arthritis
It’s well known that ACL injury increases the risk of arthritis.
“ACL tears are significant injuries that have long-term consequences,” and the reasons for this are multi-factorial, says Dr. Constance Chu, an orthopedic surgeon and professor of orthopedic surgery at Stanford Medicine.
After an ACL tear, the mechanics of the joint are significantly altered, specifically how the joint shifts, rotates, and pivots, says Gardner.
“In broad strokes, the injury alters mechanics that is not completely restored by reconstructive surgery and subsequent rehabilitation,” Chu said.
In addition, some people have chronic inflammation in the joint or prior injuries making them more susceptible to arthritis due to genetics and aging, Chu adds.
The injury may also cause the bones to shift, knocking against one another, which could further damage the cartilage, says Gardner.
Here’s how ACL surgery plays a role
ACL surgery helps repair the mechanics in the knee, however, doctors are not been able to completely restore the joint mechanisms to their pre-injury state.
“The altered joint mechanics may contribute to the risk of arthritis,” Gardner said.
People may avoid putting too much force on their affected joint following surgery due to fear of worsening their injury or in response to pain, however, over time, the reduced contact force could have long-term consequences on the cartilage and joint health.
“Long-term cartilage health relies upon optimal joint loading, and cartilage becomes thinner, softer, and more susceptible to trauma with insufficient joint loading,” the researchers state.
Some people may be prone to cartilage breakdown, and the reduced contact force could speed up the degenerative process.
“The consequences of ACL reconstruction extend well beyond the typical period of recovery – unfortunately there are long term consequences,” Gardner said.
The bottom line:
New research suggests a connection between ACL injuries and osteoarthritis and that it has to do with how much force and weight people put on their affected knee post surgery. This reduced joint loading may lead to cartilage breakdown, making the joint susceptible to damage and degeneration in the long-term.
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