Study design
It was a cross-sectional study. KP, physical function, and extension lag ROM were dependent variables. EQT was the independent variable. KP and physical functions were measured by reduced WOMAC questionnaire [16], [17], and extension lag ROM and eccentric quadriceps strength were measured by Biodex Isokinetic Dynamometer. [18]
Participants
Before conducting the study, the sample size was calculated using Software G*Power 3.1.9.4. Eighty-four participants were shown to be necessary based on an alpha level of 0.05 and power (1-β) of 0.80, therefore, 90 female patients between the age group 30 and 50 yrs. having OA of grade I or II as per Kellgren and Lawrence system, of unilateral/bilateral knees, were selected for participation in the study. However, out of 90 participants, 15 participants had grade ≥III OA, thus did not meet the inclusion criteria and 5 participants reported pain on their isokinetic strength measurement test and thus not recruited into the study. Therefore, a total of 70 participants (41.1 ± 7.1 yrs.) successfully participated and completed the study (Table 1). OA was diagnosed with X-rays of the knee by a radiologist and in the case of bilateral OA, the more affected knee was chosen for the study. Kellgren and Lawrence grading system for the classification of OA was used to grade the severity of OA (Grades 0 to 4). [19]
Table 1. Demographic properties of participants with knee OA, n = 70
Characteristics
|
Mean ± SD
|
Age (years)
|
41.1 ± 7.1
|
Height (cm)
|
157.8 ± 19.7
|
Weight (kg)
|
69.2 ± 13.9
|
BMI (kg/cm2)
|
27.33 ± 5.5
|
BMI: Body mass index
Individuals having deformity in the ipsilateral lower extremity, previous ipsilateral lower extremity surgery, corticosteroid injection in ipsilateral knee joint in the last 6 months, other diseases of musculoskeletal, cardiovascular, neurological, and/or respiratory systems were excluded from the study. 68 participants presented with both anteroposterior and lateral x-rays of the affected knee and 12 presented with anteroposterior x-rays only. The protocol of the study has been deposited on protocols.io (DOI: dx.doi.org/10.17504/protocols.io.bqxwmxpe)
Questionnaire
Participants read and filled the reduced WOMAC questionnaire which is a valid and reliable health instrument to assess pain and physical functions in individuals with osteoarthritis of the knee. [16, 17] The test questions were scored on a scale of 0-4, which correspond to None (0), Mild (1), Moderate (2), Severe (3), and Extreme (4). Then the scores for each subscale are summed up, with a possible score range of 0-20 for pain, and 0-28 for physical function. Higher scores on the reduced WOMAC questionnaire indicate worse pain and functional limitations.
Participants preparation and Isokinetic evaluation
Isokinetic dynamometer (Biodex Multi-Joint System 4, Biodex Medical Inc., NY, USA) was used to measure eccentric quadriceps strength. [18] Before data collection, the isokinetic dynamometer was calibrated according to the manufacturer’s instructions. Then participants were made to sit (with hip and knee joints bent at 900) on the dynamometer chair as per the manufacturer’s recommendations with trunk and thighs stabilized by a belt. The resistance was applied by knee attachments of the dynamometer at 5 cm above the medial malleolus and the rotational axis was aligned 5 cm away from the lateral epicondyle of the femur. Then EQT was evaluated at a speed of 900/s using “The Reactive Eccentric Mode”. [15] Speed of 900/s was chosen to facilitate comparison of results of this study with a previous study performed by Serrão PR et al on male osteoarthritic patients.
Extension Lag ROM measurement
Extension lag ROM was measured using the isokinetic dynamometer by asking the participants to fully extend the knee, then lag in full extension (to achieve 00 knee flexion) was measured. A negative ROM score meant the subject could not bring his leg to the position defined as horizontal by the protocol for ROM measurements.
Eccentric strength measurement
Afterward, participants were familiarized with the test by performing one bout of three submaximal eccentric isokinetic contractions with a ROM from 20° to 90° (being 00 meaning full knee extension). After that, they performed 1 bout of 3 maximal contractions with their best possible effort. The rest between each contraction was 30-second. For statistical analysis, the average of the peak torques of the three maximal contractions was taken. No subject complained of pain during the test. Verbal commands were used to encourage the participants to produce maximum torque during the procedure. Torque was measured in Nm, then this data was normalized by body weight (in kg) using the formula: (Nm torque /kg body weight) X 100. [15] The procedure and protocol of the study are presented in figure 1.
Data analysis
The data were analyzed using the SPSS statistical software version 26 (SPSS Inc., Chicago, IL, USA). Data collected for dependent variables (reduced WOMAC subscales for pain and physical function, and extension lag) and independent variable (the normalized mean EQT) showed normal distribution (p>0.05) therefore the parametric test was chosen. Pearson’s correlation coefficient was used to analyze the correlation between the independent and dependent variables. The correlation was considered significant at the p-value < 0.01. Following categories were used to interpret the r values: none/mild = 0.00 to 0.19; low = 0.20 to 0.39; moderate = 0.40 to 0.69; strong = 0.70 to 0.89; and very strong = 0.9 to 1.00. [20]