Letter to the Editor: Kellgren-Lawrence classification for knee osteoarthritis: Clinical value and limitations

Abstract

In this article, we provide a commentary on the article by Alshahrani et al published in the latest issue of World Journal of Orthopedics, with a particular focus on the clinical utility of the Kellgren-Lawrence (K-L) classification in the evaluation of knee osteoarthritis (KOA). The K-L classification serves as a reference standard for assessing the severity of KOA, informing stepwise treatment algorithms and supporting scientific research. It offers distinct clinical value. However, the clinical application of the K-L classification is subject to notable limitations, which stem from the inherent constraints of radiographic imaging, incompleteness of the grading criteria, and the frequent dissociation between structural changes and symptomatic manifestations in patients with KOA. Therefore, this article aims to critically examine the clinical applicability and limitations of the K-L classification in the assessment of KOA.

Key Words: Knee osteoarthritis; Kellgren-Lawrence classification; Clinical value; Limitations; Comments

Core Tip: The Kellgren-Lawrence grading system remains a cornerstone for the radiographic assessment of knee osteoarthritis. Although invaluable for diagnosis, treatment stratification, and research, it has significant limitations. Key limitations include its dependency on radiographic imaging, inability to assess soft tissues or the patellofemoral joint, and variable correlation with subjective symptoms. A multimodal, patient-centered assessment strategy is recommended for optimal knee osteoarthritis evaluation.

TO THE EDITOR

We reviewed the article by Alshahrani et al[1] in the latest issue of the World Journal of Orthopedics, which investigates the correlation between the Kellgren-Lawrence (K-L) grade and the Knee Injury and Osteoarthritis Outcome Score (KOOS). Their study confirmed a negative correlation between the K-L grade and KOOS, and highlighted a clinically significant subset of patients in whom structural joint degeneration diverges from symptom severity. This indicates that the K-L grade alone is insufficient for comprehensively evaluating the overall burden of knee osteoarthritis (KOA).

The K-L grading system, founded on specific radiographic features, including osteophyte formation, joint space narrowing (JSN), and subchondral sclerosis[2], serves as a pivotal tool for quantifying osteoarthritis severity. It provides a standardized framework widely employed in clinical and research settings, particularly for KOA. This article aims to evaluate the clinical applicability and limitations of the K-L grading system, thereby encouraging its informed integration into a holistic patient assessment strategy.

CLINICAL APPLICATION VALUE OF THE K-L GRADING SYSTEM

The K-L grading system for KOA, introduced by Kellgren and Lawrence[2] in 1957, utilizes weight-bearing knee radiographs to assess specific features, including osteophytes, JSN, and subchondral sclerosis, and classifies disease severity into five ordinal grades (0-IV). This system provides a standardized and reproducible method for diagnosis and treatment stratification (Table 1).

Table 1 Kellgren-Lawrence classification criteria for knee osteoarthritis (weight-bearing anteroposterior radiograph)[1,2].

Grade	Imaging findings	Clinical features and significance
Grade 0 (normal)	No osteophyte formation; normal joint space width; absence of subchondral sclerosis, cystic changes, or bony deformity	No knee osteoarthritis-related pain, stiffness, or limited range of motion; fully preserved joint function
Grade 1 (doubtful)	Suspected joint space narrowing; possible mild marginal osteophytes; no definitive subchondral bone morphological abnormalities	Occasional mild joint dull pain; morning stiffness < 10 minutes in duration, with spontaneous symptom resolution; easily conflated with physiological degeneration
Grade 2 (mild)	Definite osteophyte formation; suspected or mild joint space narrowing; no subchondral sclerosis or bony deformity	Mild post-activity pain; stiffness following prolonged sitting or standing, alleviated with movement; minimal to no impairment of daily activities
Grade 3 (moderate)	Multiple osteophytes; definite joint space narrowing; associated mild subchondral sclerosis; possible mild bony deformity	Frequent pain, exacerbated by stair climbing or squatting; morning stiffness lasting 10-30 minutes; mild limitation of joint range of motion
Grade 4 (severe)	Prominent osteophytes; severe joint space narrowing (or complete obliteration); significant subchondral sclerosis; accompanied by bony deformity or subluxation	Persistent moderate-to-severe pain, including resting pain or nocturnal pain; severe limitation of joint range of motion; often complicated by varus or valgus deformity, which impairs daily functioning

The classification criteria are integrated based on original literature and multicenter validation studies, serving as the core basis for the imaging diagnosis of knee osteoarthritis; clinical features are combined with symptoms and functional status to provide references for treatment decision-making[2,4,10].

Radiography offers distinct advantages over other imaging modalities in visualizing tibiofemoral osseous architecture, including bone density, joint space integrity, and limb alignment. The K-L system benefits from the widespread availability, cost-effectiveness, and technical simplicity of radiographic imaging. Consequently, it remains the primary method for diagnosing KOA and standardizing its assessment in both clinical practice and research.

The K-L grade is pivotal in guiding treatment decisions. For patients with mild to moderate KOA (K-L grades I and II), conservative management, including patient education, physical therapy, and analgesics such as non-steroidal anti-inflammatory drugs, is typically recommended. For patients with K-L grade III, in whom conservative measures may yield suboptimal results, intermediate interventions such as arthroscopic surgery, high tibial osteotomy, or unicompartmental knee arthroplasty may be considered prior to total knee arthroplasty (TKA)[3]. In end-stage KOA (K-L grade IV), TKA often represents the definitive treatment of choice. Thus, the K-L grade remains a central, evidence-based criterion for implementing stepwise treatment pathways.

Beyond directing management, the K-L system is valuable for prognostic prediction and clinical research. Alshahrani et al[1] confirmed a negative correlation between K-L grade and KOOS scores. Previous studies have also indicated that patients with higher K-L grades are at increased risk of progression to end-stage joint degeneration, eventual total knee replacement, and related complications such as joint deformity and functional disability[4]. Moreover, as an internationally recognized classification, the K-L system serves as a key statistical measure in osteoarthritis research and provides a benchmark for evaluating emerging imaging modalities.

LIMITATIONS OF THE K-L GRADING SYSTEM

With advancements in imaging technology and an increasing emphasis on early and precise diagnosis, several limitations of the traditional K-L grading system have become more evident.

First, the conventional K-L system relies on radiographic assessment and historically did not mandate weight-bearing views, which are now considered essential for accurate grading. Weight-bearing radiographs more reliably reflect the true joint space width and mechanical alignment under physiological load and are currently recommended for accurate K-L classification.

Second, the K-L classification system is undergoing refinement and digital transformation. As a subjective tool for orthopedic surgeons to evaluate structural features on knee radiographs, the K-L system is inherently associated with inter-observer variability. The integration of artificial intelligence-powered computer-aided assessment systems has emerged as a pivotal advancement, mitigating such inter-observer discrepancies and substantially enhancing the diagnostic consistency and overall accuracy of KOA among board-certified orthopedic surgeons[5]. Specifically, semi-automated and computer-assisted scoring tools have rendered the assessment of JSN more objective and quantitatively robust. Additionally, population-specific adaptations to the K-L criteria have been validated, demonstrating improved assessment precision in select demographic cohorts[6].

Nevertheless, fundamental constraints persist due to the inherent nature of radiography. KOA is a whole-joint disorder involving not only bone but also the articular cartilage, synovium, menisci, ligaments, and subchondral bone[7]. A comprehensive assessment of KOA should ideally include evaluation of all these structures. Unfortunately, the inferior soft tissue contrast of radiography compared to magnetic resonance imaging (MRI) limits the K-L system's capacity to evaluate peri-articular soft tissues[8].

Additionally, the standard K-L system is based on two-dimensional weight-bearing anteroposterior views, which primarily assess the tibiofemoral compartment. The patellofemoral joint (PFJ), a critical knee compartment, is not adequately evaluated. Consequently, PFJ pathologies such as cartilage wear or osteophytosis are not captured, which represents a significant blind spot[9]. Clinicians must be aware of this limitation and consider supplemental imaging (e.g., skyline or Merchant views) when PFJ involvement is suspected.

Another critical shortcoming is the system's sole reliance on imaging findings, disregarding patient-reported symptoms and functional status. Alshahrani et al[1] confirmed that K-L grade does not consistently correlate with symptom severity. This structure-symptom dissociation underscores that the K-L grade may not fully reflect the disease impact in all individuals, thereby limiting its utility in cases where imaging and symptoms are discordant.

CONCLUSION

In summary, the K-L grading system retains considerable value in the clinical evaluation of KOA. It provides a standardized, accessible, and cost-effective method for diagnosis, severity stratification, treatment guidance, and research. Its global acceptance and simplicity underpin its role as a benchmark in osteoarthritis assessment.

However, it is crucial to acknowledge its inherent limitations, including its dependence on suboptimal imaging techniques (e.g., non-weight-bearing views), inability to assess soft tissue or patellofemoral pathology, and inconsistent correlation with patient-reported outcomes. Therefore, the K-L grading system should not be used in isolation but must be integrated with other diagnostic tools, such as MRI or ultrasound, comprehensive clinical evaluation, and patient-centered outcome measures to facilitate a holistic and individualized management strategy for KOA. A multimodal approach combining structural imaging, functional assessment, and patient-reported outcomes is strongly recommended to optimize the diagnosis, prognosis, and treatment of KOA.