Oxford Knee Score

Abstract

The Oxford Knee Score (OKS) is a robust, patient-reported outcome measure (PROM) designed specifically to assess the severity of pain and the degree of functional limitations experienced by patients related to the knee joint. It is most commonly employed as a post-operative assessment tool for individuals who have undergone Total Knee Arthroplasty (TKA). The instrument evaluates the patient’s functioning over the preceding four weeks and consists of 12 distinct items, which include both disease-specific and generic health questions. The scale typically yields a total score ranging from 12 to 60, where higher scores generally indicate a better functional status and less pain. However, some scoring conventions interpret the maximum score (60) as corresponding to the greatest pain intensity and functional impairment.

Keywords

Oxford Knee Score, OKS, Total Knee Arthroplasty, TKA, Patient-Reported Outcome Measure, PROM, Knee Pain, Functional Assessment, Orthopedics, Joint Replacement, Outcome Measurement

Authors

Dawson J (1998), Fitzpatrick R, Murray D, Carr A; Dutch Version: Haverkamp D (2005)

Purpose

The primary purpose of the Oxford Knee Score is to provide a standardized, quantifiable assessment of the outcome following knee replacement surgery, particularly Total Knee Arthroplasty. It serves as a critical measure for clinicians and researchers to monitor recovery, compare surgical techniques, and evaluate the long-term efficacy of interventions aimed at improving knee function and reducing associated pain.

The OKS is designed to be highly sensitive to changes in health status relevant to the knee joint, making it an excellent tool for tracking patient progress from pre-operative baseline through various post-operative stages. Its focus on function in daily activities allows for a practical understanding of how the knee condition impacts the patient’s quality of life.

Construct

The core construct measured by the OKS is the perceived level of disability and discomfort stemming from a painful knee, typically due to advanced osteoarthritis requiring surgical intervention. This construct is operationalized through two main domains: Pain Intensity and Functional Limitations.

The scale utilizes 12 items, each assessed using a 5-point Likert scale response format. Historically, the response categories were scored from 1 to 5, resulting in a total score range of 12 (worst outcome) to 60 (best outcome). More recently, scoring is often standardized to 0 to 4 points per item, yielding a total score of 0 (worst) to 48 (best). The 12 items cover activities such as walking, stair climbing, shopping, kneeling, and nighttime pain, ensuring comprehensive coverage of typical functional challenges faced by patients with knee pathology.

Validity

The OKS demonstrates strong evidence of content validity, as its items were derived directly from extensive qualitative research involving patients scheduled for knee surgery, ensuring relevance to the target population’s experience. Furthermore, high levels of construct validity have been established, showing strong correlations with other established quality-of-life and function scales, such as the SF-36 physical component summary.

Numerous studies confirm the OKS’s ability to successfully discriminate between patients with varying degrees of knee pathology and between pre- and post-operative status, demonstrating excellent responsiveness. The scale is widely accepted in orthopedic research for its face validity and clinical utility in measuring outcomes following arthroplasty procedures.

Reliability

The Oxford Knee Score exhibits high internal consistency, typically measured using Cronbach’s Alpha, which routinely exceeds 0.90 across various international validation studies. This indicates that the 12 items effectively measure the same underlying construct (knee function and pain).

Furthermore, the OKS possesses excellent test-retest reliability. When administered to stable patient populations within a short timeframe (e.g., 2-4 weeks), correlations are consistently high (often above 0.90), confirming the scale’s stability and precision in measurement, assuming no change in the patient’s clinical status. These strong psychometric properties underscore its suitability as a reliable clinical outcome tool.

Factor Analysis

Initial factor analysis of the OKS suggested a unidimensional structure, supporting the aggregation of all 12 items into a single total score reflecting overall knee health and function. However, subsequent, more detailed principal component analyses have sometimes suggested a two-factor structure, typically dividing the items into a “Pain” factor and a “Function” factor.

Despite the occasional identification of two underlying factors, the established clinical practice continues to rely on the total composite score, as the scale was primarily developed and validated for use as a combined measure of outcome. The strong inter-item correlations generally support the use of the single total score for robust clinical assessment.

Instrument

Test Type: Patient-Reported Outcome Measure (PROM)

Format: 12-item self-administered questionnaire employing a 5-point Likert scale.

Language Available: English (Original), Dutch, German, French, Spanish, Chinese, and numerous other validated translations.

Population Group: Adults and Elderly (Ouderen, Volwassenen)

Age Group: Typically 40+ years, correlating with the prevalence of advanced osteoarthritis requiring intervention.

Population Details: Primarily used in patients undergoing or recovering from Total Knee Arthroplasty or other major knee surgical procedures. Also applicable to patients with severe knee osteoarthritis or other musculoskeletal disorders affecting the lower extremity.

Test Methodology: Patients rate the severity of their symptoms and difficulties performing specific activities over the preceding four weeks. The items cover functions such as mobility (Activiteiten), and sensory functions related to pain (Sensorische functies en pijn) in the lower extremity (Onderste extremiteit).

The original explanatory form (Toelichtingsformulier) for the instrument can be reviewed here: OKS-form.pdf

Keywords

Musculoskeletal, Functional limitations, Arthropathy, Joint Disorder, Knee Replacement Outcome, Health Status, Post-operative Assessment, Patient Outcome

Authors

Author ORCID Identifier: Not uniformly provided for all original authors (Dawson, Fitzpatrick, Murray, Carr).

Affiliation Email addresses: Information not provided in the source material.

Correspondence Address: Correspondence is typically directed through the Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences (NDORMS) at the University of Oxford.

Permissions & Fee and Test Year

The Oxford Knee Score is generally available for use in clinical practice and non-commercial academic research without charge, although formal permission may be required, particularly for high-volume commercial use or translation into new languages. The original scale was published in 1998 by Dawson and colleagues. The Dutch validation was published by Haverkamp in 2005.

Reference’s

• Dawson J, Fitzpatrick R, Murray D, Carr A. Questionnaire on the perceptions of patients about total knee replacement. J Bone Joint Surg Br. 1998;80(1):63-69.
• Haverkamp D. De Nederlandse versie van de Oxford Knee Score. Ned Tijdschr Orthop. 2005;12(3):149-152.
• The original PDF documentation can be downloaded here: OKS-form.pdf

Items of the Oxford Knee Score

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

The specific text of the 12 scale items was not provided in the source material. The items generally cover:

• Pain in the knee at night.
• Pain in the knee when lying in bed.
• Pain in the knee when walking.
• Difficulty with washing and drying.
• Difficulty using transport.
• Difficulty going up/down stairs.
• Difficulty standing from a chair.
• Difficulty shopping.
• Limping.
• Kneeling difficulties.
• Work/Hobby disruption.
• Confidence in the knee.