Knee osteoarthritis (OA) is a prevalent degenerative joint disease that significantly contributes to pain, functional limitation, and reduced quality of life, particularly among older adults. It is multifactorial in origin, with aging, mechanical stress, genetic predisposition, and obesity being major contributing factors. Among these, obesity has emerged as a strong and modifiable risk factor for both the development and progression of knee OA1.

Several systematic reviews and meta-analyses have established a clear association between elevated body mass index (BMI) and increased risk of developing knee OA1,3. The mechanical loading caused by excess body weight accelerates cartilage wear, while adipose tissue also contributes to a pro-inflammatory state that may further exacerbate joint degeneration3,4. Additionally, obese individuals with radiographic OA report higher levels of knee pain and functional limitations compared to those with normal BMI4,5.

Cross-sectional and longitudinal studies have consistently shown that increasing BMI correlates with greater disease severity and reduced physical functioning in patients with OA2,5. Moreover, the healthcare burden associated with OA rises substantially with increasing BMI due to higher utilization of outpatient visits, medications, and surgical interventions6.

Despite the well-established link between obesity and OA globally, there remains a need for localized data to understand population-specific trends. This study aims to evaluate the association between BMI and the severity of knee osteoarthritis among adults in a tertiary care center in South India, using radiographic grading and functional assessment tools. Understanding this relationship may inform preventive strategies and enhance clinical management of OA.

This study aims to assess the association between BMI and the severity of knee osteoarthritis in adults by evaluating radiographic grades using the Kellgren-Lawrence (KL) system and functional status using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). The findings may help underscore the importance of weight management in OA treatment and prevention strategies.

Study Design and Duration:

A hospital-based cross-sectional observational study was conducted over a period of three months, from February to April 2024.

Study Setting:

The study was carried out in the Department of Orthopaedics at Government Medical College, Srikakulam, Andhra Pradesh.

Study Population:

Adults aged 40 years and above, attending the outpatient department with clinical features suggestive of knee osteoarthritis, were screened for inclusion.

Inclusion Criteria:

Patients aged ≥40 years with symptoms of knee pain, stiffness, and functional limitation.

Radiographic confirmation of knee osteoarthritis based on Kellgren-Lawrence (KL) grading system (Grades 1 to 4).

Willingness to provide informed consent.

Exclusion Criteria:

History of recent trauma or knee surgery.

Inflammatory arthritis (e.g., rheumatoid arthritis, gout).

Congenital or developmental joint abnormalities.

Patients with systemic illnesses affecting mobility (e.g., stroke, neurological disorders).

Sample Size:

A total of 120 participants meeting the inclusion criteria were enrolled using a purposive sampling technique.

Data Collection:

Sociodemographic data including age, sex, and duration of symptoms were recorded. Height and weight were measured using standard protocols, and body mass index (BMI) was calculated using the formula:

BMI = Weight (kg) / Height² (m²).

Participants were categorized as:

Normal: <25 kg/m²

Overweight: 25–29.9 kg/m²

Obese: ≥30 kg/m²

Radiographic severity of OA was assessed using the Kellgren-Lawrence grading system. Functional status and symptom severity were evaluated using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), which includes pain, stiffness, and physical function domains.

Statistical Analysis:

Data were analyzed using SPSS software (version XX). Descriptive statistics were presented as mean ± standard deviation for continuous variables and percentages for categorical variables. The chi-square test was used to analyze categorical associations. Pearson’s correlation coefficient was used to assess the relationship between BMI and OA severity (KL grade and WOMAC score). A p-value <0.05 was considered statistically significant.

Ethical Considerations:

Necessary permissions were taken from concerned authorities before starting the study. Written informed consent was obtained from all participants prior to enrollment.

A total of 120 participants were included in the study, with a mean age of 58.4 ± 10.2 years. The majority were female (65%), and the average body mass index (BMI) was 29.6 ± 4.7 kg/m². Most participants had bilateral knee involvement (69.2%), and 60% showed moderate to severe osteoarthritis (Kellgren-Lawrence [KL] Grade ≥3) on radiographs (Table 1).

Table 1: Baseline Demographic and Clinical Characteristics of Study Participants (n = 120)

When participants were stratified by BMI categories, a clear trend emerged between increasing BMI and osteoarthritis severity. Among those with normal BMI (<25 kg/m²), 62.5% had mild osteoarthritis, whereas in the obese group (BMI ≥30 kg/m²), nearly half (48.1%) had severe osteoarthritis (KL Grade 4) (Table 2). This suggests a positive association between higher BMI and radiographic severity.

Table 2: Distribution of Participants by BMI Category and Severity of Knee Osteoarthritis

Functional impairment was also assessed using the WOMAC index. Mean total WOMAC scores increased significantly with BMI. Obese participants reported higher levels of pain (7.5 ± 2.1), stiffness (2.8 ± 1.0), and reduced physical function (28.3 ± 7.2), resulting in the highest overall WOMAC total score (38.6 ± 7.9) among all groups (Table 3).

Table 3: Mean WOMAC Scores by BMI Category

\Correlation analysis further supported these findings. BMI demonstrated a strong positive correlation with Kellgren-Lawrence grade (r = +0.61, p < 0.001), WOMAC total score (r = +0.68, p < 0.001), and pain subscore (r = +0.59, p < 0.001), indicating that higher BMI is significantly associated with increased structural damage and functional limitations in knee osteoarthritis (Table 4).

Table 4: Correlation between BMI and OA Severity Parameters

This study demonstrated a significant positive association between body mass index (BMI) and the severity of knee osteoarthritis (OA), both radiographically and functionally. Participants with higher BMI were more likely to have advanced Kellgren-Lawrence grades and elevated WOMAC scores, indicating greater joint degeneration and functional impairment.

The findings are consistent with previous studies that have reported increased mechanical loading and systemic inflammation as key mechanisms through which obesity exacerbates OA progression7,11. Manek et al. highlighted the complex interplay between genetic and environmental factors, such as obesity, in the pathogenesis of knee OA7. In addition to mechanical stress, adipose tissue contributes to a chronic low-grade inflammatory state, which further accelerates cartilage degradation11.

Interestingly, while some studies suggest a direct association between obesity and quadriceps weakness in OA patients, others such as Segal et al. found no significant link between BMI and quadriceps-specific strength, suggesting that other biomechanical and inflammatory pathways may be more critical in disease progression8. Moreover, Loures et al. reported that BMI served as a significant prognostic indicator in knee OA, reinforcing the clinical value of BMI in disease monitoring and risk stratification9.

Our results also align with findings from Keng et al., who observed a higher prevalence of cartilage damage in asymptomatic individuals with elevated BMI, underscoring the subclinical impact of obesity on joint integrity10. Additionally, Alghadir and Khan noted that higher BMI was significantly associated with increased pain and reduced physical function in OA patients, consistent with our WOMAC score trends12.

Despite the study’s cross-sectional nature, which limits causal inference, the significant correlations observed underscore the importance of weight management in the prevention and management of knee OA. Integrating lifestyle interventions focused on weight reduction could mitigate disease severity and improve functional outcomes.

This observational study highlights a significant association between higher body mass index (BMI) and increased severity of knee osteoarthritis (OA) in adults. Obese individuals demonstrated more advanced radiographic changes and greater functional impairment, as reflected by elevated Kellgren-Lawrence grades and WOMAC scores. These findings underscore the dual impact of mechanical stress and obesity-related inflammation in OA progression. Early identification of overweight and obese individuals at risk may allow for timely interventions, such as weight reduction, physical therapy, and lifestyle modification. Addressing obesity should be an integral component of OA management strategies to reduce disease burden, improve patient outcomes, and enhance overall quality of life.

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