The purpose of this study is to cast light on the highly complex etiology and cellular landscape of hip osteoarthritis by utilising single-cell and spatial omics.

The specific objectives of this project are:

1. Using the latest single-cell RNA sequencing (scRNAseq) techniques the investigators aim to A) characterize what kind of cell populations are found in different synovial tissues and blood derived samples of OA patients, B) determine how the cell composition differs between arthritic and corresponding non-arthritic tissues, C) map the transcriptional and regulatory landscape of the cells mentioned in A and B focusing on the inflammatory responses, D) determine what are the key molecular pathways activated in OA.
2. To determine if some of the blood-derived immune cell populations or their products could be used as biomarkers for OA.
3. To map the whole transcriptome and proteome of OA and non-arthritic control tissue while keeping the morphological context with spatial omics technologies.
4. Further differentiation and identification of OA endotypes utilizing the single-cell and spatial omics data.

The project includes a Rheumatoid sub-study where the main objective is to compare arthritic tissue and peripheral blood constituents between OA and rheumatoid arthritis patients to explore the differences in the disease mechanisms.

Inclusion Criteria for the main (OA) study:

Cases: Adult patients with osteoarthritis in the hip joint and who are going through an elective total hip arthroplasty.

Controls: Non-arthritis adult patients who are going through a trauma-based emergency total hip arthroplasty.

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Inclusion Criteria for the Rheumatoid sub-study:

Adult patients with rheumatoid arthritis in the hip joint and who are going through an elective total hip arthroplasty.

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Exclusion Criteria:

• The body mass index must be below 35
• Age < 18 or > 74
• The OA patients may not have diabetes, rheumatoid arthritis (RA), or metabolic syndrome.

For the Rheumatoid sub-study, the exclusion criteria are the same as above except for the RA.

Adult patients of the HUS (Joint Authority of the Helsinki and Uusimaa Hospital District) Center of Arthroplasty and the Orto Surgical Hospital of Turku University.