Osteoarthritis is a chronic degenerative joint disorder characterised by progressive deterioration of articular cartilage, subchondral bone remodelling, osteophyte formation and variable synovial inflammation. The knee is one of the most commonly affected weight-bearing joints, and knee osteoarthritis represents an important cause of pain, stiffness, impaired mobility and disability, particularly among middle-aged and older adults. Increasing age, female sex, obesity, occupational loading, muscle weakness, joint malalignment and previous knee injury are recognised risk factors. The growing prevalence of obesity and population ageing have further increased the clinical and socioeconomic burden associated with knee osteoarthritis.

Primary knee osteoarthritis is generally diagnosed using a combination of clinical findings and radiographic features. The American College of Rheumatology criteria incorporate knee pain with features such as age, morning stiffness, crepitus, bony tenderness and bony enlargement for classifying knee osteoarthritis [1]. Conventional weight-bearing radiography remains a widely available and cost-effective method for assessing structural changes. Radiographic severity is commonly classified using the Kellgren-Lawrence grading system, which grades osteoarthritis from grade 0 to grade 4 according to the presence and extent of osteophytes, joint-space narrowing, subchondral sclerosis and bony deformity [2,3].

Although radiographic examination provides objective evidence of structural damage, the severity of radiographic abnormalities does not always correspond closely with patients’ symptoms or functional limitations. Some patients with advanced radiographic disease report relatively mild disability, whereas others with limited radiographic changes experience substantial pain and restriction of daily activities. This discordance may be influenced by age, body mass index, muscle strength, psychological status, pain perception, comorbidities and the presence of abnormalities that are not adequately demonstrated on plain radiographs. Therefore, treatment decisions based exclusively on radiographic findings may not accurately reflect the individual patient’s clinical burden.

Functional disability in knee osteoarthritis can be evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), a validated disease-specific instrument covering pain, stiffness and difficulty in performing physical activities [4]. Previous studies examining the relationship between radiographic severity and functional status have produced inconsistent findings. While some have demonstrated worsening pain and disability with increasing radiographic grade, others have reported weak or absent correlations [5]. Evaluating this relationship in the local clinical population may help determine whether radiographic severity can serve as an indicator of functional impairment. The present study was therefore undertaken to assess the association between Kellgren-Lawrence radiographic severity and WOMAC-measured functional disability among patients with primary knee osteoarthritis.

AIM

To assess the association between radiographic severity and functional disability among patients with primary knee osteoarthritis.

OBJECTIVES

1. To determine the radiographic severity of primary knee osteoarthritis using the Kellgren-Lawrence grading system.
2. To assess pain, stiffness and functional disability using the WOMAC index.
3. To determine the association between Kellgren-Lawrence grade and WOMAC functional disability scores and identify factors associated with greater disability.

Source of Data The study data were obtained from patients with clinically and radiographically diagnosed primary knee osteoarthritis who attended the outpatient and inpatient services of the Department of Orthopaedics during the study period. Eligible patients who provided written informed consent were consecutively enrolled until the required sample size was achieved. Study Design This was a hospital-based, observational, analytical cross-sectional study. Study Location The study was conducted in the Department of Orthopaedics, in collaboration with the Department of Radiodiagnosis. Study Duration The study was conducted over a period of 12 months, after obtaining approval from the Institutional Ethics Committee. Sample Size A total of 120 patients with primary knee osteoarthritis were included. The sample size was estimated for detecting a statistically significant correlation between radiographic severity and functional disability. Assuming an anticipated correlation coefficient of approximately 0.26, a two-sided significance level of 5% and 80% statistical power, the minimum required sample was approximately 113 patients. After allowing for incomplete questionnaires or unusable radiographs, the final sample size was fixed at 120. The sample size for correlation was estimated using Fisher’s Z transformation: where represented the anticipated correlation coefficient, at a 5% significance level and for 80% power. Sampling Technique Consecutive sampling was used. All patients who fulfilled the eligibility criteria during the study period were approached for participation and recruited sequentially until the sample size of 120 was completed. Inclusion Criteria Patients were included when they: 1. Were aged 40 years or older. 2. Had knee pain for at least three months. 3. Were diagnosed with primary knee osteoarthritis based on clinical and radiographic assessment. 4. Had Kellgren-Lawrence grade 1-4 changes in at least one knee. 5. Were able to understand and complete the WOMAC questionnaire independently or through an interviewer. 6. Provided written informed consent. Exclusion Criteria Patients were excluded when they had: 1. Secondary knee osteoarthritis due to previous major trauma, infection, congenital deformity or metabolic disease. 2. Inflammatory arthropathy, including rheumatoid arthritis, gout, psoriatic arthritis or ankylosing spondylitis. 3. A history of knee arthroplasty or other major knee surgery. 4. Intra-articular fracture or ligament injury affecting the index knee. 5. Intra-articular corticosteroid or viscosupplement injection during the preceding three months. 6. Neurological, vascular, spinal or hip disorders that substantially affected walking or lower-limb function. 7. Severe medical or psychiatric illness interfering with functional assessment. 8. Poor-quality or incomplete radiographs unsuitable for Kellgren-Lawrence grading. 9. Incomplete clinical or WOMAC data. Procedure and Methodology After ethics committee approval, eligible patients were informed about the purpose and procedure of the study. Written informed consent was obtained before enrolment. Each participant underwent a detailed clinical evaluation using a predesigned case-record form. Information regarding age, sex, occupation, duration of symptoms, laterality, previous treatment, comorbidities, history of knee injury and activity limitations was recorded. Height and weight were measured using standardised instruments, and body mass index was calculated as weight in kilograms divided by height in metres squared. Both knees were clinically examined for tenderness, crepitus, swelling, deformity, range of motion and instability. Standard weight-bearing anteroposterior radiographs of both knees were obtained with the patient standing and the knees fully extended or mildly flexed according to the institutional radiographic protocol. Additional lateral and skyline views were obtained when clinically indicated. Radiographs were anonymised before evaluation. Radiographic severity was assessed using the Kellgren-Lawrence classification: • Grade 0: No radiographic evidence of osteoarthritis. • Grade 1: Doubtful joint-space narrowing and possible osteophyte formation. • Grade 2: Definite osteophytes with possible joint-space narrowing. • Grade 3: Multiple osteophytes, definite joint-space narrowing, subchondral sclerosis and possible bony deformity. • Grade 4: Large osteophytes, marked joint-space narrowing, severe sclerosis and definite bony deformity. Radiographs were evaluated independently by an orthopaedic surgeon and a radiologist who were blinded to the WOMAC scores. Any disagreement was resolved by consensus. When both knees were affected, the more symptomatic knee was designated as the index knee. If symptoms were equal, the knee with the higher Kellgren-Lawrence grade was selected. Functional disability was assessed using the validated WOMAC questionnaire. The scale consisted of 24 items divided into pain, stiffness and physical-function domains. Responses were recorded using the selected Likert version, with each item scored from 0 to 4. The pain score ranged from 0-20, stiffness from 0-8, physical function from 0-68 and the total WOMAC score from 0-96. A higher score indicated greater pain, stiffness and disability. Where necessary, the questionnaire was administered by a trained investigator in the participant’s preferred language. The primary outcome was the association between Kellgren-Lawrence radiographic grade and WOMAC physical-function score. Secondary outcomes included associations of radiographic grade with WOMAC pain, stiffness and total scores and the influence of age, sex, body mass index and symptom duration on functional disability. Sample Processing No blood, urine, synovial fluid, tissue or other biological samples were collected; therefore, biological sample processing was not applicable. The radiographic images and completed WOMAC questionnaires constituted the study materials. Radiographs were anonymised, assigned unique study identification numbers and stored digitally. Questionnaires were checked for completeness, coded and entered into the study database. Data Collection Data were collected using a structured case-record form consisting of the following sections: 1. Sociodemographic information. 2. Clinical history and symptom duration. 3. Anthropometric measurements. 4. Findings of knee examination. 5. Radiographic findings and Kellgren-Lawrence grade. 6. WOMAC pain, stiffness, physical-function and total scores. 7. Relevant comorbidities and previous treatment. Each participant was assigned a unique study number. Completed forms were reviewed on the same day to identify missing or inconsistent information. Data were entered into a password-protected electronic database. Participant names and other direct identifiers were not included in the analytical dataset. A random proportion of records was cross-checked against the original forms to ensure data-entry accuracy. Statistical Methods Data were analysed using IBM SPSS Statistics version 28.0 or equivalent statistical software. Continuous variables were assessed for normality using histograms, Q-Q plots and the Shapiro-Wilk test. Normally distributed variables were presented as mean and standard deviation, whereas skewed variables were presented as median and interquartile range. Categorical variables were expressed as frequencies and percentages. Mean WOMAC scores across Kellgren-Lawrence grades were compared using one-way analysis of variance followed by an appropriate post-hoc test when the assumptions were satisfied. The Kruskal-Wallis test followed by adjusted pairwise comparisons was used for non-normally distributed scores. Categorical variables were compared using the chi-square test or Fisher’s exact test. The association between Kellgren-Lawrence grade and WOMAC scores was assessed using Spearman’s rank correlation coefficient because radiographic grade was ordinal. The strength and direction of the correlation were reported with a 95% confidence interval. Multiple linear regression analysis was performed to determine whether radiographic severity was independently associated with WOMAC functional-disability scores after adjusting for age, sex, body mass index, symptom duration, laterality and comorbidities. Regression coefficients with 95% confidence intervals were reported. Interobserver agreement for Kellgren-Lawrence grading was assessed using weighted Cohen’s kappa. All statistical tests were two-sided, and a p value <0.05 was considered statistically significant.

Table 1. Association between radiographic severity and functional disability among patients with primary knee osteoarthritis (N=120)

Trend and correlation analysis

Higher WOMAC scores indicated greater disability. KL: Kellgren-Lawrence; WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index. *Statistically significant at p<0.05.

Table 1 demonstrates a progressive increase in functional disability with increasing radiographic severity of knee osteoarthritis. Of the 120 patients, 17 (14.2%) had KL grade 1, 39 (32.5%) had grade 2, 41 (34.2%) had grade 3 and 23 (19.2%) had grade 4 disease. The mean WOMAC functional-disability score increased from 19.4 (SD 7.2) in grade 1 to 28.7 (SD 8.9), 39.8 (SD 10.1) and 51.6 (SD 8.7) in grades 2, 3 and 4, respectively. Compared with grade 1, the mean disability score was higher by 9.30 points in grade 2 (95% CI: 4.37-14.23), 20.40 points in grade 3 (95% CI: 15.22-25.58) and 32.20 points in grade 4 (95% CI: 27.08-37.32); all differences were statistically significant (p<0.001). The overall difference across the four grades was also significant (F=53.84, p<0.001). A strong positive correlation was observed between KL grade and WOMAC functional-disability score (Spearman’s ρ=0.72; 95% CI: 0.62-0.79; p<0.001). Furthermore, each one-grade increase in radiographic severity was associated with an average increase of 10.71 WOMAC functional-disability points (95% CI: 9.03-12.39; p<0.001).

Table 2. Radiographic severity and radiographic characteristics of primary knee osteoarthritis (N=120)

†One-sample proportion z-test against an expected equal distribution of 25% across the four KL grades.
‡One-sample proportion z-test against a reference proportion of 50%. OA: osteoarthritis; KL: Kellgren-Lawrence. Percentages for KL grades may not total exactly 100% because of rounding. *Statistically significant at p<0.05.

Table 2 presents the distribution of radiographic severity and individual radiographic characteristics. KL grade 3 was the most frequent category, observed in 41 (34.2%) patients, followed by grade 2 in 39 (32.5%), grade 4 in 23 (19.2%) and grade 1 in 17 (14.2%) patients. The proportions of grade 1 and grade 3 disease differed significantly from the expected equal proportion of 25% (p=0.004 and p=0.020, respectively), whereas the proportions of grade 2 and grade 4 did not differ significantly. Overall, 56 (46.7%) patients had mild radiographic osteoarthritis, comprising KL grades 1-2, while 64 (53.3%) had moderate-to-severe disease, comprising grades 3-4. This difference was not statistically significant (p=0.465).

Definite osteophytes were present in 103 (85.8%) patients and were significantly more frequent than the 50% reference proportion (95% CI: 78.4%-91.1%; p<0.001). Definite joint-space narrowing was identified in 84 (70.0%) patients (95% CI: 61.3%-77.5%; p<0.001). Subchondral sclerosis was observed in 57 (47.5%) patients and did not differ significantly from 50% (p=0.584), whereas bony deformity was present in only 21 (17.5%) patients (95% CI: 11.7%-25.3%; p<0.001). Bilateral radiographic involvement was noted in 79 (65.8%) patients (p=0.001), and predominantly medial-compartment involvement was observed in 87 (72.5%) patients (p<0.001).

Table 3. Assessment of pain, stiffness and functional disability using the WOMAC index (N=120)

†One-sample t-test against the midpoint of the respective scale: pain=10, stiffness=4, physical function=34 and total WOMAC=48.

‡One-sample proportion z-test against 50%. Functional disability was categorised using the WOMAC physical-function score as mild (<34%), moderate (34%-66%) and severe (>66% of the maximum score). Higher scores indicated worse symptoms or disability.

*Statistically significant at p<0.05.

Table 3 summarises the WOMAC pain, stiffness and disability findings. The mean pain score was 10.7 (SD 3.8) out of 20, with a 95% CI of 10.01-11.39. This score was significantly higher than the scale midpoint of 10 (t=2.02, p=0.046). The mean stiffness score was 4.3 (SD 1.7) out of 8 and did not differ significantly from the midpoint of 4 (p=0.056). Similarly, the mean physical-function score was 35.6 (SD 13.7) out of 68, and the mean total WOMAC score was 50.6 (SD 18.1) out of 96. Neither the physical-function score nor the total score differed significantly from their respective scale midpoints (p=0.204 and p=0.119).

Regarding the severity of functional disability, 26 (21.7%) patients had mild disability, 57 (47.5%) had moderate disability and 37 (30.8%) had severe disability. The proportion with moderate disability did not differ significantly from 50% (p=0.584). However, when the moderate and severe categories were combined, 94 (78.3%) patients had moderate-to-severe functional disability, with a 95% CI of 70.2%-84.8%. This proportion was significantly greater than 50% (z=6.21, p<0.001).

Table 4. Association of Kellgren-Lawrence grade and other factors with WOMAC functional-disability score (N=120)

1. Unadjusted analysis

1. Multivariable linear regression analysis

Model statistics: ; adjusted ; ; p<0.001.

BMI: body mass index; KL: Kellgren-Lawrence; MD: mean difference; WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index. The dependent variable was the WOMAC physical-function score. A positive regression coefficient indicated greater functional disability. *Statistically significant at p<0.05.

In the unadjusted analysis, functional disability showed statistically significant positive correlations with age (r=0.34; 95% CI: 0.17-0.49), BMI (r=0.41; 95% CI: 0.25-0.55), symptom duration (r=0.38; 95% CI: 0.21-0.52) and KL grade (ρ=0.72; 95% CI: 0.62-0.79); all correlations had p<0.001. Of these factors, KL grade showed the strongest unadjusted relationship with functional disability. Female patients had a higher mean disability score than male patients 38.1 (SD 13.6) versus 32.3 (SD 13.2) with a mean difference of 5.84 points (95% CI: 0.95-10.73; p=0.019). Patients with bilateral knee involvement also had substantially higher disability scores than those with unilateral involvement 39.2 (SD 12.7) versus 28.7 (SD 12.5). The corresponding mean difference was 10.54 points (95% CI: 5.77-15.31; p<0.001).

Multivariable linear regression showed that radiographic severity remained independently associated with functional disability after adjustment for other relevant factors. Each one-grade increase in KL severity was associated with an adjusted increase of 8.74 WOMAC functional-disability points (95% CI: 7.19-10.29; p<0.001). KL grade had the largest standardised regression coefficient (β=0.58), indicating that it was the strongest independent predictor in the model. Each additional year of age was associated with a 0.18-point increase in disability (95% CI: 0.04-0.32; p=0.012), while each 1 kg/m² increase in BMI was associated with a 0.49-point increase (95% CI: 0.21-0.77; p=0.001). Each additional year of symptoms increased the disability score by 0.53 points (95% CI: 0.16-0.90; p=0.005). Female sex and bilateral involvement were independently associated with increases of 2.71 points (p=0.036) and 3.26 points (p=0.016), respectively. The overall regression model was statistically significant (F[6,113]=30.72, p<0.001) and explained 62% of the variation in functional-disability scores, with an adjusted R² of 0.60. Therefore, greater radiographic severity, older age, female sex, higher BMI, longer symptom duration and bilateral disease were independently associated with greater functional disability.

Association between radiographic severity and functional disability The present study demonstrated a clear dose-response relationship between radiographic severity and functional disability in patients with primary knee osteoarthritis. The mean WOMAC physical-function score increased progressively from 19.4 in KL grade 1 to 51.6 in KL grade 4. Compared with grade 1, functional-disability scores were higher by 9.30, 20.40 and 32.20 points in grades 2, 3 and 4, respectively. The overall difference across the grades was statistically significant. Moreover, KL grade demonstrated a strong positive correlation with functional disability (ρ=0.72), and each one-grade increase was associated with a 10.71-point increase in the WOMAC function score. These results closely agree with Sapkota et al. (2024)[1], who found a strong correlation between KL grade and total WOMAC score (r=0.73) and significant correlations with the pain, stiffness and physical-function domains. Alghadir et al. (2022)[2] similarly observed strong associations of KL grade with pain and impaired physical function. Their multivariable models showed that radiographic severity was the most important predictor and, together with age and BMI, explained 71% of pain and 74% of variation in physical function. These findings are consistent with the present study, in which KL grade had the largest standardised regression coefficient. Ribeiro et al. (2020)[3] reported that patients with grouped KL grades 2-4 had poorer WOMAC and balance scores than those with grades 0-1. Özden et al. (2020)[4] also found that radiographic severity was significantly associated with activity-related pain, poorer physical health and prolonged Timed Up and Go performance. Nikolic et al. (2019)[5] demonstrated that pain, impaired physical function and radiographic characteristics adversely affected the functional ability and quality of life of patients with knee osteoarthritis. Collectively, these studies support the present finding that progressive structural damage is accompanied by increasing limitations in walking, stair climbing, rising from sitting and other daily activities. Nevertheless, the relationship between structural severity and clinical disability has not been uniform across studies. Steenkamp et al. (2022)[6] did not find a significant correlation between radiographic severity and pain or functional scores. Similarly, Son et al. (2020)[7] demonstrated that some individuals with advanced radiographic knee osteoarthritis remained free of pain. Such discrepancies may result from differences in age, pain sensitisation, muscle strength, physical activity, psychological health, radiographic technique and the instruments used to assess function. Plain radiographs quantify structural abnormalities but do not adequately demonstrate synovitis, bone-marrow lesions, meniscal damage or periarticular abnormalities. Therefore, although the present study identified a strong association, radiographic severity should complement rather than replace direct clinical and functional assessment. Distribution of radiographic severity and characteristics KL grade 3 was the most frequent radiographic category in the present study, accounting for 34.2% of patients, followed by grade 2 in 32.5%, grade 4 in 19.2% and grade 1 in 14.2%. Overall, 53.3% of patients had moderate-to-severe radiographic disease. This distribution suggests that many patients sought specialist care only after appreciable structural progression. Sapkota et al. (2024)[1] also reported that KL grade 3 was the most common category among patients attending a tertiary trauma centre. Munawar et al. (2024)[8] reported a comparable distribution, with grade 3 being the most frequent radiographic stage, followed by grades 2, 1 and 4. Definite osteophytes were the most frequent radiographic feature in the current study, affecting 85.8% of patients. Joint-space narrowing was present in 70.0%, subchondral sclerosis in 47.5% and bony deformity in 17.5%. This pattern is consistent with the KL system, in which definite osteophyte formation characterises established radiographic osteoarthritis, while marked sclerosis and bony deformity are features of advanced disease. Kohn et al. (2016)[9] explained that increasing KL grade reflects the sequential accumulation of osteophytes, joint-space loss, subchondral sclerosis and alteration of bony contours. Seifeldein et al. (2019)[10] similarly found osteophytes in 70% of patients with primary knee osteoarthritis and demonstrated associations between structural abnormalities and WOMAC symptoms. Bilateral radiographic involvement was observed in 65.8% of the present sample. Bilateral disease is expected in primary knee osteoarthritis because ageing, obesity, occupational loading and lower-limb biomechanics usually affect both knees, although the severity may remain asymmetrical. The predominance of medial-compartment involvement, observed in 72.5%, was also clinically plausible. During normal walking, the knee adduction moment places a greater proportion of load across the medial tibiofemoral compartment. Varus alignment and meniscal extrusion can further increase focal medial loading, leading to cartilage loss, osteophyte formation and joint-space narrowing. The high prevalence of bilateral and medial-compartment disease may also explain the considerable functional burden in this study. Bilateral structural involvement limits the ability of the opposite knee to compensate during walking, stair climbing or rising from a chair. Seifeldein et al. (2019)[10] found medial meniscal extrusion in 40% of patients, illustrating the importance of medial-compartment abnormalities in symptomatic knee osteoarthritis. Zhu et al. (2021)[11] likewise demonstrated meaningful relationships between specific radiographic features and clinical symptoms in patients with late-stage knee osteoarthritis. WOMAC pain, stiffness and functional-disability findings The mean WOMAC scores in the present study were 10.7 for pain, 4.3 for stiffness, 35.6 for physical function and 50.6 for the total scale. The pain score was significantly higher than the scale midpoint, whereas stiffness, physical function and total WOMAC scores were not significantly different from their respective midpoints. However, categorisation revealed that 47.5% of patients had moderate disability and 30.8% had severe disability. Thus, 78.3% had moderate-to-severe functional disability, demonstrating a substantial clinical burden even though the mean physical-function score was not significantly above the mathematical midpoint. Seifeldein et al. (2019)[10] reported mean WOMAC scores of 10.08 for pain, 3.34 for stiffness, 26.26 for physical function and 39.68 for the total score. The pain score was almost identical to that observed in the present study, whereas the physical-function and total scores were lower. This difference may be attributable to the greater proportion of KL grades 3-4 in the present population. Pang et al. (2015)[12] found that increasing pain severity was associated with worse WOMAC domains and poorer health-related quality of life, reinforcing the effect of persistent pain on physical and psychosocial functioning. Gandek (2015)[13] concluded that WOMAC has adequate reliability, construct validity and responsiveness for evaluating pain, stiffness and physical function in hip and knee osteoarthritis. Its use in the present study therefore allowed functional burden to be quantified beyond what could be inferred from radiographs alone. The large proportion with moderate-to-severe disability indicates the need for comprehensive management incorporating pain control, exercise therapy, quadriceps strengthening, weight management, gait modification and assistive devices where required. The clinical effect of knee osteoarthritis also extends beyond the WOMAC domains. Kawano et al. (2015)[14] found significantly impaired quality of life among patients with knee osteoarthritis, particularly in physical functioning and pain-related domains. Similarly, Nikolic et al. (2019)[5] reported that both clinical manifestations and radiographic changes negatively affected quality of life. These observations indicate that increasing WOMAC disability may be accompanied by reduced independence, restricted participation and deterioration in general well-being. Factors associated with functional disability On unadjusted analysis, functional disability correlated significantly with age, BMI, symptom duration and KL grade. Female patients had disability scores 5.84 points higher than male patients, while patients with bilateral involvement had scores 10.54 points higher than those with unilateral disease. These findings indicate that functional disability represents the combined influence of structural severity, demographic characteristics and overall disease burden. After multivariable adjustment, KL grade remained the strongest independent predictor. Each one-grade increase was associated with an 8.74-point increase in the WOMAC function score. Alghadir et al. (2022)[2] similarly found that KL grade was the strongest predictor of physical impairment, even after age and BMI were considered. The consistency between the studies supports a genuine relationship between progressive structural disease and declining function, although individual variability remains important. Age was independently associated with disability, with each additional year corresponding to a 0.18-point increase in the WOMAC function score. Ageing may increase disability through sarcopenia, reduced proprioception, impaired balance, comorbidity and decreased physiological reserve. Ribeiro et al. (2020)[3] found that radiographic severity was related to poorer balance and physical health among older adults. de Rooij et al. (2016)[15] also identified several demographic, clinical and psychosocial characteristics that influenced the prognosis of pain and physical functioning in knee osteoarthritis. BMI showed an independent positive association with disability, with a 0.49-point increase in WOMAC function score for every 1 kg/m² increase. Obesity increases mechanical loading across the knee during weight-bearing activities and may also contribute through systemic metabolic inflammation. Alghadir et al. (2022)[2] reported significant associations of BMI with both pain and physical impairment. Consequently, weight reduction may provide clinically important improvements in symptoms and mobility in overweight patients. Longer symptom duration was independently associated with greater disability, possibly reflecting cumulative structural damage, chronic pain, muscle deconditioning and avoidance of physical activity. Female sex also remained significant after adjustment. Biological factors, differences in muscle strength, pain perception, hormonal influences and a higher frequency of obesity may contribute to worse disability among women. However, Alghadir et al. (2022)[2] did not identify sex as a significant predictor, demonstrating that sex differences may vary according to population characteristics and adjustment variables. Bilateral involvement independently increased the WOMAC function score by 3.26 points. Patients with disease in both knees may experience greater difficulty transferring body weight, maintaining balance and compensating with the contralateral limb. The final regression model explained 62% of the observed variability in functional disability. This relatively high explanatory value indicates that radiographic severity, age, sex, BMI, symptom duration and bilateral involvement were important determinants. The remaining variation may be related to muscle strength, joint alignment, physical activity, socioeconomic status, depression, fear of movement, pain sensitisation and soft-tissue pathology, none of which were represented in the model.

Radiographic severity was strongly and positively associated with functional disability among patients with primary knee osteoarthritis. WOMAC functional-disability scores increased progressively across Kellgren-Lawrence grades, and radiographic grade remained the strongest independent predictor of disability after adjustment for other relevant factors. Older age, female sex, higher BMI, longer symptom duration and bilateral knee involvement were also independently associated with greater functional impairment. These findings support the combined use of radiographic grading and patient-reported functional assessment when evaluating disease severity and planning individualised management for knee osteoarthritis.

Limitations

This study had several limitations. Its cross-sectional design demonstrated associations but could not establish temporal or causal relationships between radiographic progression and functional disability. As it was conducted at a single hospital, the findings may not be generalisable to community populations or other healthcare settings. Consecutive sampling may have introduced selection bias, particularly because patients attending a tertiary hospital may have had more severe symptoms than those managed in primary care.

The WOMAC index was self-reported and was therefore susceptible to recall bias, response bias and variations in pain perception. Plain radiographs could not adequately evaluate soft-tissue abnormalities, synovitis, meniscal injury, bone-marrow lesions or early cartilage damage. Although radiographs were independently assessed, some interobserver variability in Kellgren-Lawrence grading was possible. Potential determinants such as muscle strength, knee alignment, physical activity, occupational loading, analgesic use, depression, pain sensitisation and socioeconomic status were not fully assessed. Finally, the moderate sample size and relatively small number of patients in some KL categories may have limited the precision of subgroup estimates.

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