we aimed to establish the reference intervals (RIs) for outpatients with mild to moderate KOA.
This cross-sectional study enrolled 202 outpatients with KOA from 8 Japanese facilities. For comparison, we included RIs determined in our previous study from 545 advanced KOA patients just prior to knee arthroplasty and from 120 age-matched healthy subjects. We measured 5m maximum walking speed, knee extensor/flexor muscle strength (MS) and knee extension/flexion range of motion (ROM). We used multiple regression analysis to evaluate the sources of variation, including sex, age, body mass index, Kellgren–Lawrence (K-L) classification, bilateral KOA, and exercise habits. Magnitude of between-subgroup differences is expressed as standard deviation ratio (SDR) based on a three-level nested analysis of variance, with SDR ≥0.4 as the threshold for requiring RIs specific for subgroups. RIs were calculated parametrically using two-parameter Box-Cox formula if Gaussian transformation of RVs was successful, otherwise calculated nonparametrically.
The knee motor functions of outpatients were in the middle location between healthy controls and KOA preoperative patients. Partitioning was required by K-L classification for maximum walking speed (SDR=0.54), and by sex extensor, flexor MS (SDR=0.65, 0.57, respectively) and by K-L classification for flexion ROM (SDR=0.54).RIs were determined parametrically for maximum walking speed as 0.48–1.31–2.20 (K-L gradeⅠ/Ⅱ/Ⅲ) m/sec and 0.44–1.03–1.98 (K-L gradeⅣ) m/sec. And RIs were determined parametrically for extensor MS as 0.27–1.19–2.09 (male) and 0.27–0.72–1.54 (female) Nm/kg and for flexor MS 0.18–0.58–1.20 (male) and 0.13–0.41–0.79 (female) Nm/kg. On the other hand, RIs for extension and flexion ROM were determined nonparametrically due to discrete nature of their RVs. The RIs determined for extension ROM were -15°– -5° –0° and for flexion ROM were 105°–135°–150° (for K-L grade Ⅰ/Ⅱ) and 95°–125°–140° (for K-L grade Ⅲ/Ⅳ).
The ranges of RIs determined specifically for patients with mild to moderate KOA were in-between those of age-matched healthy controls and pre-surgical KOA patients, both of which we had reported for use in physiotherapeutic management of KOA patients undergone total knee arthroplasty. The newly derived RIs will provide an objective benchmark for physiotherapy targeting outpatients with mild to moderate KOA.
Clinically, we believe that using the RIs established by outpatients to evaluate the motor function of patients with KOA will help determine the indications for outpatient physical therapy.
muscle strength
range of motion
