Application value of extension lag measurement in evaluating the function of knee extension apparatus in patients with osteoarthritis

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Knee extension lag is active knee extension delay caused by disease of knee extension apparatus or other reasons. Visual measurement is frequently used in clinic to examine and measure extension lag.


To evaluate the function of knee extension apparatus by measuring the extension lag in patients with osteoarthritis.


Comparative observation was performed at the Peking Union Medical College Hospital between October 2004 and March 2005.


A total of 47 patients (66 knees) with knee osteoarthritis undergoing total knee arthroplasty in Peking Union Medical College Hospital were selected. The written informed consent was obtained from all patients.


Visualization and Cybex NormTM system were used. The patients were divided into 3 groups: visual measurement group had 18 cases (36 knees) of extension lag; Cybex group had 22 cases (23 knees) of extension lag, which were not discovered by visual measurement; no extension lag group (7 cases, 7 knees), which was not found with extension lag by both visual measurement and Cybex NormTM system. Preoperative HSS scores of each patient were filled by one clinician, and the off-bed time postoperatively and discharge time was recorded.


Average extension lag angle, average torsion of knee extension apparatus, the value HSS score, the off-bed time postoperatively and discharge time.


All 47 patients (66 knees) underwent total knee arthroplasty. No complications were found postoperatively. The incision was healed at the primary stage. There were significant differences among 3 groups in terms of average extension lag angle and HSS scores (P < 0.05). The average extension lag angle, average ratio of flexor/extensor force, and the off-bed time postoperatively of visual measurement group was significantly different from Cybex group (P < 0.05).


Compared with visual measurement, Cybex NormTM system could detect symptoms that are not obvious in clinical examinations. At perioperative period of total knee arthroplasty for patients with knee osteoarthritis, to evaluate the function of knee extension apparatus by extension lag measurement and timely medical treatment can help restore the function of knee joint.

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