This study looks at how physical activity levels are in the long term after hip surgery. Arthritis can make everyday movement difficult, and hip replacement surgeries-such as total hip arthroplasty (THA) and hip resurfacing-help reduce pain and improve function. However, it is not clear how these surgeries affect long-term physical activity.

To learn more, researchers are following up with patients who had one of these surgeries 15 years ago. Participants will wear two small activity-tracking devices (accelerometers): one on their wrist for 10 days and one on their thigh for 48 hours. These devices will measure how much and how intensely they move. Participants will also complete short physical activity questionnaires.

By comparing activity levels between the two types of hip surgery, the study aims to understand their long-term effects on mobility and health. The results could help doctors improve treatment and recovery plans for future patients. All data will be kept private, and participation is voluntary.

Arthritis significantly impacts patients' quality of life, leading to pain, fatigue, and reduced mobility. Treatment strategies include medication, lifestyle changes, and surgical interventions such as total hip arthroplasty (THA) and hip resurfacing. While these procedures improve function and alleviate pain, their long-term effects on physical activity levels remain unclear. Given the importance of physical activity in maintaining health and reducing mortality risks, understanding post-surgical activity levels is crucial.

Wearable technology has revolutionized the measurement of physical activity, providing objective, large-scale data collection. This study utilizes accelerometers to evaluate physical activity in patients who underwent hip resurfacing or THA 15 years ago. By comparing these groups, researchers aim to understand the long-term impact of different surgical interventions on mobility and activity levels.

The primary objective of the study is to compare the volume and intensity of physical activity in patients who underwent hip resurfacing versus those who had a total hip replacement. We will also explore associations between physical activity levels and functional outcome scores.

This is a cross-sectional observational study involving a follow-up of patients who participated in a randomized controlled trial 15 years ago. Participants will be asked to complete questionnaires and wear two different accelerometers to monitor their physical activity. They will wear a GENEActiv triaxial accelerometer on the non-dominant wrist for 10 days and nights. They will also wear an Axivity AX3 Logging triaxial accelerometer on the surgical thigh for 48 hours. Both will measure physical activity energy expenditure (PAEE), intensity distribution of PAEE, and step count.

All participants will receive an information letter and provide informed consent before participation. Data privacy will be maintained through coded identifiers, and no personally identifiable information will be stored with the accelerometry data.

This study will provide valuable insights into the long-term mobility outcomes of patients who have undergone hip resurfacing or total hip arthroplasty. The findings will help clinicians understand the implications of surgical choices on patients' activity levels and overall health, potentially influencing future treatment recommendations and rehabilitation strategies.

Inclusion Criteria:

• Patient must have participated in a previous randomised controlled trial that was conducted in Rijnstate hospital between 2007-2008.

Exclusion Criteria:

• None.

Patients that have previously participated in a randomised controlled trial during which they received either hip resurfacing or total hip arthroplasty.