About 240 million individuals worldwide suffer from Knee Osteoarthritis (OA), which is a serious public health concern that greatly lowers quality of life and causes disability.¹ With a 22% to 39% prevalence rate in people over 65, Knee OA is a significant burden in India. ²

The etiology of OA knee is complex. Changes in the surrounding soft tissues, hyaline cartilage, bones, synovial fluid, ligaments, and muscles, as well as tissue proliferation and                                    osteophyte formation, ³ induce deficits such as stiffness, joint damage, restricted range of motion, and decreased strength.

The clinical presentation of OA varies from one individual to another and generally worsens and becomes debilitating over a period of time. Prevalent clinical manifestations include pain in the knee, the increase with activity, and is associated with swelling, stiffness, pain on rest, and increases in intensity over time. ⁴

As a major weight-bearing joint subject to mechanical stress and wear over time, knee OA is the most common type among the various forms of OA. Degeneration of articular cartilage is the main pathological characteristic of OA, resulting in pain, stiffness, and functional impairment in the affected joint. ⁵  The highly specialized connective tissue known as articular cartilage coats the ends of the bones in synovial joints, allowing the transfer of stresses with the least amount of friction and offering a smooth, lubricated surface for articulation.⁶

In contrast to other tissues, cartilage depends on the diffusion of nutrients from the synovial fluid rather than the presence of blood arteries, nerves, or lymphatics. Due to its special structure, cartilage is prone to damage and heals slowly, which adds to the chronic character of OA.⁷

Diagnosis of knee OA can be confirmed on imaging. Radiographs are the preliminary mode of imaging used to investigate an osteoarthritic knee. Its benefits include convenience, relatively inexpensive, and the capacity to identify skeletal irregularities such as abnormal bone formation and sclerosis. One of radiography’s major drawbacks is its inability to directly visualize soft tissues. Joint space width (JSW) and Joint space narrowing (JSN) measurements are used as a substitute for cartilage. Furthermore, radiographic assessment methods for OA regularly necessitate the existence of osteophytes. Changes in articular cartilage are not always linked to the cause of osteophytes.^8,9

X-rays have a limited capacity to identify early alterations in cartilage and soft tissue involvement. Magnetic resonance imaging (MRI) allows for an in-depth evaluation of the cartilage, ligaments, and soft tissue components. MRI is highly sensitive to changes in cartilage composition and thickness¹⁰  but it is time-consuming and expensive, and feasibility is an issue in certain rural and primary hospital settings.  

Ultrasound (USG) imaging is now recognized as an effective alternative to assess joint cartilage. It offers real-time imaging and is noninvasive nonionizing and is relatively less expensive when compared to MRI. McCune et al. (1989)¹¹ demonstrated a significant correlation between cadaveric investigation and cartilage thickness, evaluated using USG.  Psychometric properties of using USG, in human subjects were confirmed by further studies by De Miguel et al. (2009)^12,13 and Grassi et al. (1999)¹⁴ which ascertained, its validity and reliability, confirming USG to be a useful measure in the evaluation of the cartilage degradation, in the preliminary stages of the disease.  USG has shown to be reliable, and a strong correlation has been demonstrated between USG and MRI and histological data signifying the utility of USG in both research and clinical settings.¹³ 

Although imaging techniques offer objective information about joint anatomy, the patient-reported outcomes (PROs), display the patient’s perception of overall health, and their subjective experience and perception of their condition. Knee Injury and Osteoarthritis Outcome Score (KOOS)¹⁵  is the standard tool, used to evaluate knee health in persons afflicted with Knee OA. KOOS is a standard PRO measure for evaluating knee health and function and health of an individual across 5 domains - pain, symptoms, activities of daily living (ADL), sports and recreation, and quality of life (QoL). The KOOS has been validated in a variety of populations and

making it a valid and reliable tool, to be used in clinical and research settings. ¹⁵

Existing literature on the Western population has shown characteristics like body mass index, age, and gender to influence cartilage thickness.  Cicuttini et al. (1996),¹⁶ concluded in their study that cartilage thickness is inversely proportional to an individual’s age, and an increase in BMI is also linked with heightened mechanical stress, leading to cartilage degeneration. Normative cartilage thickness values for the Indian population are, however, not well documented. It is imperative to establish population-specific reference values in India due to the country’s diverse lifestyle characteristics and genetic diversity.

Given the ethnic diversity in the Indian population, establishing normative values specific to the Indian population becomes essential. This study aims to provide baseline data that reflects the unique characteristics of the Indian population. Thereby contributing to the existing pool of scientific evidence. Such data becomes imperative in comparison studies, allowing researchers to differentiate between pathological and normal conditions more efficiently. 

Normative cartilage thickness will serve as a baseline for understanding the progress of knee OA. By comparing these values with those that have OA, researchers can identify early changes and risk factors associated with the condition. Alongside, correlating cartilage thickness with the 5 domains of the KOOS scores will enable researchers to gain insights into how cartilage health affects KOOS score and various aspects of overall well-being. Early identification of individuals at risk for OA is crucial for effective management.

Ultimately, the goal of this research is to improve clinical outcomes for individuals with knee OA. By providing a comprehensive understanding of cartilage health and its impact on knee function, this study will inform better clinical decision-making. Patients can benefit from more accurate diagnoses, personalized treatment plans, and improved monitoring of disease progression and treatment efficacy.

In conclusion, this study aims to create a foundational understanding of the normative cartilage height in the Indian population and its association with physical function as measured by KOOS, which will thereby fill the existing gap in the literature and pave the way for improved prevention, early detection and management of knee OA, thereby enhancing the quality of life of the affected individuals