The OKS was designed and developed by researchers within the department of Public Health and Primary Health Care at the University of Oxford in collaboration with surgical colleagues at the Nuffield Orthopaedic Centre.1,2
The Oxford Knee Score is a commonly used, validated PROM, consisting of 12 questions that assesses the subscales of “pain” and “physical function” in patients that have undergone a TKA.
The OKS was developed through interviewing outpatients in consideration of TKA in order to identify their experiences and expressions when describing their problems associated with their knee.
The OKS was then derived from a prospective study of 117 patients prior to undergoing TKA and six months postoperatively through the completion of the generic PROM SF-36 and the developing OKS. Based on the results, the authors developed 20 questions, tested them on patients several times, and revised them. Eventually, 12 questions with 5 categories of response were considered for the final Oxford Knee Score.1 The breakdown of the OKS is as follows:
- The functional component consists of 5 items (questions 2, 3, 7, 11, 12)
- The pain component consists of 7 items (questions 1, 4, 5, 6, 8, 9, 10)
Evaluation of the OKS
Originally, the evaluation of the Oxford Knee Score was as follows. First, each of the 12 answers is assigned a number of points based on a numbering system from the 5 categories of response which range from 1 to 5, 1 being the least difficult and 5 being the most difficult. The 12 ratings are then added together to give a total score used to assess the patient. The possible total score ranges from 12 to 60 points, a low score (e.g. 12 points) indicates a good outcome with a greater degree of joint function with minimal pain and a high score indicates the opposite.1
However, on review of this scoring system, misunderstandings were highlighted and so an alternative scoring system was implemented. In this adjusted version response points range from 0 to 4 with a total score ranging from 0 to 48. Here, a high score (e.g. 48) indicates satisfactory joint function and vice versa.
At present both scoring systems remain valid. In order to avoid misinterpretation, one should always show the scoring system used including in the abstracts of publications.3 However, the adjusted scoring system is more commonly applied and is regarded as being more intuitive to interpret.
The Oxford Knee Score is an established and validated score that has proven to be advantageous with regards to its brevity which facilitates its use in widespread clinical research and patient care.4 This makes it an advantageous PROM compared to more comprehensive questionnaires (WOMAC/KOOS). Studies have illustrated that the patient rate of completion was superior to that of other questionnaires with a greater opportunity of collecting augmented data.1-8
The OKS has been used in trials, audits and has played a pivotal role in national joint replacement registries, including those in the United Kingdom, Sweden and New Zealand. 9
Partridge et al., conducted a non-controlled quality improvement in total knee replacement using PROMs data. Statistically significant differences in outcomes after surgery when using different brands of implant (measured by the OKS) was the reason for changing to the better performing implant.10 Such efforts provide valuable insights into which implantable devices yield better post-surgical results for patient populations.
Studies have revealed that the OKS has a low specificity. Thus, patients with healthy knees but other joint problems, such as complications in the hip or spine, would also score higher in the Oxford Knee Score.11 Moreover the lower discriminating performance of the OKS after surgery may preclude the detection of subtle outcome differences, most notably in patients whose outcome is considered favourable and so more demanding scores would be required for more detailed analysis of outcomes after TKA surgery.
Using the Oxford Knee Score requires licensing by the copyright holder. It is free of charge for non-commercial users, but fees are charged for accompanying materials. Commercial users, large private practices and users whose projects are funded by industry are required to pay royalties.2,3 Our PRO-consultants are more than happy to provide detailed Information.
Overall, the Oxford Knee Score, as an established and validated score suitable instrument for everyday clinical use, particularly because of its significance and small size and is one of the most commonly utilised PROMs in Europe.12 Due to its low specificity however, one should take into account that the score could be falsified by joint problems in adjacent body areas.11
Public and private healthcare providers have used the OKS to assess patient outcomes across multiple facilities as a measure of the performance of individual treatment centers, which can be used to identify high-performing centers and to raise standards through sharing best practices.2