Investigating the Biological Link Between Mental Health Status and Outcomes Following Total Knee and Hip Replacement.

This is a single-site, observational pilot study that aims to understand whether there is a biological explanation for why some patients with anxiety or depression experience poorer outcomes after total knee or hip replacement surgery. The study investigates the role of inflammation inside the joint, using tissue, fluid, and blood samples collected during routine care, alongside patient-reported outcome questionnaires.

Study Design and Hypothesis The hypothesis is that patients with pre-existing anxiety or depression will show more inflammation in their joint tissue or blood, and that this may be linked to poorer functional outcomes after surgery. An alternative explanation is that these patients may report worse outcomes without an identifiable biological cause.

The study does not involve any trial drugs or new treatments and does not use a placebo or randomisation.

Patients will be grouped based on whether or not they meet the criteria for anxiety and/or depression as measured by two validated mental health screening tools:

GAD-7 (for anxiety)

PHQ-8 (for depression)

Sampling and Participant Involvement:

The plan is to include 56 patients, equally split between hip and knee replacement groups, and between those with and without anxiety/depression (14 per subgroup). Participants will be identified by the clinical research team from the waiting lists of two lead surgeons and approached by post and phone before their routine preoperative assessment clinic.

At that appointment, consent will be obtained and the participant will complete baseline questionnaires. The same questionnaires will be repeated at 3 and 6 months postoperatively. No additional visits will be required.

Study Procedures and Timeline

1. Preoperative phase (routine clinic visit):

Participants are posted a cover letter, patient information sheet, and consent form ahead of their clinic visit.

A member of the research team calls the patient to explain the study.

At the clinic, a research nurse obtains informed consent.

Participants complete baseline questionnaires assessing pain, quality of life, and mental wellbeing (e.g. Oxford score, EQ-5D, PHQ-8, GAD-7). 2. Day of surgery:

An additional 20 ml of blood is collected at the same time as routine preoperative blood tests, using the same venepuncture.

While under anaesthetic, the operating surgeon collects small tissue samples (synovial fluid, synovial tissue, and fat) from the joint. These samples are normally discarded as part of the operation.

Samples are anonymised and sent to pathology and research laboratories for analysis. 3. Postoperative follow-up:

At the 3-month clinic visit (routine care), participants complete the same questionnaires and provide a further blood sample of approximately 15 ml.

At 6 months, questionnaires are completed remotely via the MyRecovery app, with no further hospital visit or samples required.

All study procedures are aligned with routine NHS care to minimise burden. There are no additional clinic visits required.

Data Handling and Analysis The study will compare inflammation levels (in blood and tissue) between groups and analyse how these relate to patient-reported outcomes. All data will be anonymised. Blood samples will be processed at local NHS labs (Shrewsbury) and at a specialist centre in Sheffield for specific inflammatory markers (e.g. IL-6, CD solubles). Synovial tissue will be histologically analysed on-site for synovitis.