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Device reliably measures knee flexion gap for TKA

Michele Malavolta

Published results showed reproducible and reliable measurement of the knee flexion gap with use of a device for this purpose among patients undergoing total knee arthroplasty.

Michele Malavolta, MD, and colleagues evaluated the femoral external rotation angle using Tensor (Medacta International) in 87 patients with everted patella, as well as with a pure subluxated patella, undergoing TKA. According to the researchers, the Tensor device measures the lateral or medial opening angle of the bone gap in extension and in flexion with 1° resolution, as well as the opening space of the gap in millimeters. Researchers subdivided patients into subgroups based on gender, preoperative varus or valgus deformity and patellar height and evaluated the influence using a linear regression model.

Results showed high precision of the Tensor device, with excellent interobserver reproducibility. On average, researchers found a difference of 1.77° between the measurements obtained with a subluxated patella compared with an everted patella. Linear regression model showed preoperative alignment and preoperative patellar position statistically significantly influenced the difference of the flexion gap. However, researchers noted gender and BMI did not influence the difference of the flexion gap.

“Our study advises against evaluation of the flexion gap with everted patella due to high risk of underestimating of the external laxity. In other words, the surgeon can give, after this evaluation, less degrees of external rotation as required with a final external laxity in flexion with the patella in situ,” Malavolta told Healio.com/Orthopedics. “This flexion evaluation is less important in [a] kinematic alignment technique because the flexion gap is a natural consequence of the perfect rectangle obtained in extension and does not need an evaluation.” – by Casey Tingle

 

Disclosures: Malavolta reports he is a consultant of Medacta International. Please see the study for a list of all other authors’ relevant financial disclosures.

Michele Malavolta

Published results showed reproducible and reliable measurement of the knee flexion gap with use of a device for this purpose among patients undergoing total knee arthroplasty.

Michele Malavolta, MD, and colleagues evaluated the femoral external rotation angle using Tensor (Medacta International) in 87 patients with everted patella, as well as with a pure subluxated patella, undergoing TKA. According to the researchers, the Tensor device measures the lateral or medial opening angle of the bone gap in extension and in flexion with 1° resolution, as well as the opening space of the gap in millimeters. Researchers subdivided patients into subgroups based on gender, preoperative varus or valgus deformity and patellar height and evaluated the influence using a linear regression model.

Results showed high precision of the Tensor device, with excellent interobserver reproducibility. On average, researchers found a difference of 1.77° between the measurements obtained with a subluxated patella compared with an everted patella. Linear regression model showed preoperative alignment and preoperative patellar position statistically significantly influenced the difference of the flexion gap. However, researchers noted gender and BMI did not influence the difference of the flexion gap.

“Our study advises against evaluation of the flexion gap with everted patella due to high risk of underestimating of the external laxity. In other words, the surgeon can give, after this evaluation, less degrees of external rotation as required with a final external laxity in flexion with the patella in situ,” Malavolta told Healio.com/Orthopedics. “This flexion evaluation is less important in [a] kinematic alignment technique because the flexion gap is a natural consequence of the perfect rectangle obtained in extension and does not need an evaluation.” – by Casey Tingle

 

Disclosures: Malavolta reports he is a consultant of Medacta International. Please see the study for a list of all other authors’ relevant financial disclosures.

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