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Predicting the risk of knee instability

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A single measurement can help predict whether a person is at risk for knee instability, according to a new study.

Researchers at Pennsylvania State University found that using magnetic resonance imaging (MRI) to measure the distance between the tibial tubercle (TT) — a bony bump on the tibia, commonly referred to as the shin, below the kneecap — and the trochlear groove (TG) — the joint in which the kneecap sits — is a reliable, precise and accurate diagnostic of problems with the kneecap moving out of its joint.

Issues with stability of the kneecap (patella) are common, especially among women and people who participate in sports. Knee instability may not pose a problem for people who are not physically active, but athletes may consider corrective surgery.

Ideally, the kneecap will align with the midline of the leg, explained John Vairo, clinical associate professor of kinesiology, orthopaedics and rehabilitation at Penn State. A greater TT-TG distance may suggest that the kneecap is off-centre and therefore more likely to slip out of the joint.

The study, published in Clinical Orthopaedics and Related Research, gives clinicians guidance on using the measurement in their practice.

The researchers used medical records from 131 patients, including 48 who had confirmed cases of kneecap dislocation and 83 controls with meniscal tears. TT-TG distance tended to be greater in patients with kneecap instability.

“We found that once this measurement reaches 13 millimetres, that individual may be more likely to experience problems with kneecap dislocation,” Vairo said.

However, he stressed that it’s not the only thing that should be taken into account when considering surgery to decrease this distance, as the procedure requires significant recovery time.