Advantages of unicompartmental knee arthroplasty (UKA) compared to total knee arthroplasty (TKA) include shorter hospital stays, faster recovery, fewer infections and readmission, and lower costs. It is well documented in TKA-surgery that high pain responders (HPR), evaluated using the Pain Catastrophizing Scale (PCS), have higher postoperative pain responses compared to low pain responders (LPR). These HPR-patients constitute a vulnerable high risk patient group and potentially benefit from targeted treatment. Currently, the distribution of HPR- and LPR-patients and their association with acute pain following UKA is not well investigated. The knowledge that this research project generates is essential to determine how studies with analgesia interventions should be designed. In the future this will contribute in targeting treatment for high risk patient groups to reduce pain and improve postoperative mobilization, and ultimately decrease length of hospital stay in patients undergoing UKA. By targeting treatment, a potential overtreatment is also avoided.

The aim of this study is to investigate the prevalence of high- and low-pain responders, defined by a PCS score > 20 and ≤ 20 respectively, as well as the acute postoperative course of pain for these groups after unicompartmental knee arthroplasty.

Background:

Primary knee arthroplasty is a frequently performed procedure and is expected to increase in numbers over the next decade. Advantages of unicompartmental knee arthroplasty (UKA) compared to total knee arthroplasty (TKA) include shorter hospital stays, faster recovery, fewer infections and readmissions, and lower costs. The length of hospital stay after UKA is variable, but an increased length of hospitalization has been associated with more complications and higher readmission rates. A recent study has shown that the main reasons for continued hospitalization beyond 24 hours after surgery are pain and lack of mobilization. Strategies to decrease the length of stay after UKA should thus be aimed at improved analgesia and postoperative mobilization.

There is a large interindividual variability in the postoperative pain response. It is well documented in TKA-surgery that high pain responders (HPR), evaluated using the Pain Catastrophizing Scale (PCS), have higher postoperative pain responses compared to low pain responders (LPR). Recently, it has been shown that HPR patients undergoing TKA benefit from a larger preoperative dose of glucocorticoid compared to a previously recommended dose. Interestingly, the same difference has not been found in LPR patients (Nielsen et al.: IN PREPARATION, clinicaltrials.gov ID NCT03758170, EudraCT 2018-002634-20, VEK H-18034756). These HPR patients constitute a vulnerable high-risk patient group and potentially benefit from targeted treatment.

Currently, the distribution of HPR- and LPR patients and their association with acute pain following UKA is not well investigated. The generated knowledge from this research project is essential to determine how studies with analgesia interventions should be designed. In the future, this will contribute to targeting treatment for high-risk patient groups to reduce pain and improve postoperative mobilization, and ultimately decrease the length of hospital stay in patients undergoing UKA. By targeting treatment, a potential overtreatment is also avoided.

Aim:

To investigate the prevalence of high- and low-pain responders, defined by a PCS score > 20 and ≤ 20 respectively, as well as the acute postoperative course of pain for these groups after unicompartmental knee arthroplasty.

Study location:

The inclusion will take place at the Dept. of Orthopaedic Surgery, Arthroplasty unit at Hvidovre Hospital, Capital Region of Denmark.

Study plan:

In the outpatient clinic, the screening procedure will be performed among patients planned to UKA by the surgeons. Patients will be asked if they may be contacted with the purpose of participating in a research project. Patients will undergo a preliminary examination where, as a standard procedure, the patient will receive a PCS questionnaire. Patients will be informed of the research project either in the outpatient clinic or by phone from an investigator.

All patients will receive verbal and written information about the project. All patients must give a signed informed consent on paper prior to inclusion to participate in the study.

Data protection:

All patient-related information will be treated confidentially, and data will be pseudoanonymized. Signed informed consent from participating patients will be stored at the Anesthesiologic Dept. 542, Hvidovre Hospital, in a locked cabinet. All electronic data will be stored in REDCap.

Collected variables:

During the hospital stay, data will be collected by contacting the patient at the Orthopaedic Dept. and by accessing the electronic patient journal. After discharge patients will be asked to fill out an electronic pain diary until 7 days after the operation.

Inclusion Criteria:

• Primary unilateral UKA
• Age ≥ 18 years
• Ability to participate in the study (understand written and spoken Danish language, self-reported pain and satisfaction).
• Filled out the Pain Catastrophizing Scale preoperatively.
• Signed written informed consent form.

Exclusion Criteria:

• Mental disability that could impair a patient's decision-making capability of giving informed consent and not enabling valid data collection.
• Insulin-treated diabetes mellitus
• Patients with known diagnoses of schizophrenia, ongoing psychosis, bipolar disease and/or a history of ongoing anti-psychotic treatment.
• Patients with modulated pain-reception (experience) based on other diseases or injuries, e.g. spinal cord or brain injury, severe polyneuropathies or neurologic disorders.
• Peripheral nerve block per- or postoperatively.

Patients planned for unicompartmental knee arthroplasty at a Danish hospital.

The individual patient data will be made available in anonymized form.

Data will be available from the date of publication.