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In osteoarthritis of the knee, the same treatment does not work for everyone. How to know when to operate?

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In osteoarthritis of the knee, the same treatment does not work for everyone. How to know when to operate?

Researchers from the UPF BCN MedTech research unit, the IMIM-Hospital del Mar and the Hospital del Mar have studied the relationship between clinical treatment options for osteoarthritis of the knee and the functionality, speed and forces involved in each patient's stride. The results reveal that two patients with the same symptoms may need different treatment depending on their age and body mass index.

Osteoarthritis is a chronic disease characterized by the deterioration of joint cartilage. This deterioration is clinically manifested in the form of pain, stiffness and loss of mobility. Data from the report by the World Health Organization and the Institute of Metrics and Health Assessment, the Global Burden of Disease 2019, show that prevalence is three times higher in women than in men and that it increases with age and with the person's weight, among other factors.

Osteoarthritis is responsible for between 1 and 3% of years lived suffering disability. In Spain, the prevalence of symptomatic osteoarthritis is at 29.35%, and 13.83% for osteoarthritis of the knee, according to data from the EPISER2016 study carried out by the Spanish Society of Rheumatology, with the knee being the most affected joint.

There is currently no treatment to regenerate knee cartilage degraded by osteoarthritis, so the solution for those suffering from this disease is through conservative treatments that seek to limit pain and improve joint function, or treatments that involve undergoing total knee replacement (knee prosthesis).

"Total knee replacement is not free from risk and complications for the patient", explain doctors Jordi Monfort and Joan Carles Monllau, in charge of the clinical study associated with the research at Hospital del Mar. The decision to place a knee prosthesis is not always objective. Radiology is a method to confirm the diagnosis and classify the severity of the damage, not to decide upon treatment. Monllau clarifies that "the decision to proceed with surgery is based on pain, functional deficit and patient expectations". As a result, the number of knee replacements can vary strongly depending on the hospital, the region, and the type of health system (public or private) where someone is being treated. The authors of the study stress that this situation highlights the lack of robustness and subjectivity of such an important clinical decision.

Using objective criteria to decide who needs a knee prosthesis or who would most benefit from conservative treatment is no easy task. "Each person is unique, and cartilage degradation can be influenced by lifestyle and the body's biomechanics, among many other things", explains Simone Tassani, a postdoctoral researcher at the UPF Department of Information and Communication Technologies (DTIC) and first author of the study published in the journal Frontiers in Bioengineering and Biotechnology. "Even the way pain is perceived and how this pain is experienced will mean that two patients with apparently similar degrees of osteoarthritis will have a preference for different treatments", Tassani continues.

"Treating a joint and treating the perceived pain can become two very different things, and it is worth trying to decipher as objectively as possible if total knee replacement is preferable to conservative treatment", adds Jérôme Noailly, principal investigator of the study at UPF, along with Miguel Ángel González Ballester, ICREA and UPF researcher. Meanwhile, Jordi Monfort, head of the Cell research on Inflammation and Cartilage research group at the Hospital del Mar Medical Research Institute (IMIM-Hospital del Mar), stipulates that pain due to sensitization of the central nervous system, for example, is not resolved by traditional treatments for osteoarthritis, including surgery.

To assess whether non-invasive, objective examination can ascertain which treatment would be most appropriate for each patient, the researchers at UPF and the IMIM-Hospital del Mar used concepts of functional biomechanics. They studied the relationship between the choice of a given treatment, and the functionality, speed and forces involved in the stride. "We wanted to look at functionality through simple analysis, that was relatively simply sustainable and reproducible", Tassani comments.

The study involved 87 patients divided according to sex, age (between 60 and 67 years and between 68 and 75 years) and body mass index (non-obese, BMI <30 and obese, BMI> 30). Following clinical criteria, the patients were referred by their physicians to either follow conservative treatment or undergo knee replacement. They were distributed into two equal numbered groups. All clinical and biomechanical examinations were conducted prior to treatment.

At the UPF biomechanics laboratory, the researchers calculated the effective load on the knee, using a reverse process that uses the recording of the reaction forces exerted by each foot on the ground, and the recording of the movement of all the leg joints. The time each patient needed to take a stride, the time each patient remained with both feet on the ground, and the average speed of a walking cycle were also measured in slow motion.

The study revealed that some variables are good indicators that reflect the decision as to whether or not to receive a prosthesis. "Patients who were slower to take a stride spending more time with both feet on the ground and whose speed was lower, were the ones who were most frequently indicated for knee replacement", Tassani says. "Our results suggest that functionality is a better candidate than mechanical forces to help decide who does or does not require a prosthesis".

Noailly underlines that this result is most encouraging. "It would require confirmation by means of an extended clinical study, but it already shows statistical significance and suggests that motion analysis could help physicians to prioritize conservative treatment or not. The decision for the treatment of osteoarthritis would be released, in part, from the complex interpretation of pain, since pain is a symptom that requires more accurate diagnosis to be treated separately and specifically".

Nevertheless, the results also show that age must come into the equation. In young groups, people who would need a prosthesis take much longer to take a stride than those for whom conservative treatment is indicated. However, this difference is attenuated in the older aged groups.

Finally, the possible influence of the emotional aspect should be stressed regarding the time that a patient remains with both feet on the ground when walking. A person who feels more insecure tends to extend this time. Studying the emotional component (for instance how each patient experiences pain, fear of pain, or fear of falling) could be a future research topic.

This study was carried out with the support of the Spanish government through the HOLOA project (Clinical and virtual examination of patients for holstic and objective description of the osteoarthritis progression mechanisms - DPI2016-80283- C2-1/2-R), Ramon and Cajal funding (RYC-2015-18888) and the DTIC's Data-Driven-Knowledge Extraction Maria de Maeztu Unit of Excellence (MDM-2015-0502) funding.