Background:

The hip joint is a ball and socket joint where the ball inserts into the socket. The ball shape is round but sometimes the ball has a bony bump on it. When the ball moves in the socket, the bump can hit the edge of the socket causing pain in movements like squatting or kicking a ball. Repeated hitting of the bump in the socket can cause hip pain, damage, and arthritis. This is called hip impingement and is found in 10-15% of young adults.

Does Physiotherapy treatment work? Exercises from a physiotherapist make the muscles stronger around the hip joint which alters the way the ball moves. This stops the bump hitting the socket and this can help reduce the pain. However, an experiment found only 32% of people doing exercises got better.

So, why after strengthening the muscles are some people still in pain? Is there another source of pain?

Other causes of pain? The investigators know things like people's emotions such as 'feeling down' can affect pain. An experiment the investigators did, found neuropathic pain in people with hip impingement. This pain is caused by a disease of the nerves that provide information about your body. This can be a cause of pain even if your muscles are strong. In both situations, strengthening your muscles may not be the best choice. The investigators need to know more about types of pain in people with hip impingement to give better treatment.

Aim To look at causes of hip impingement in people before they have physiotherapy treatment, to see if the investigators can find a reason why some people don't get better after strengthening their muscles.

Project design The investigators will review the research to see if people with hip impingement may feel for example, sad, anxious or scared of moving their hip, which could be a reason why some people don't get better after doing their strengthening exercises.

The investigators will invite 175 adults with hip impingement who have been referred for physiotherapy-led treatment to join this study. The participants will have 2 research appointments, 30-60 minutes each. The first one before the start of their physiotherapy treatment, the second one will be 4 months after starting their physiotherapy treatment. At both appointments the participants will complete special questionnaires designed to explore emotions and causes of pain. The investigators will compare the results of the questionnaires which will give more information about the causes of pain and how people view their pain. This will give the investigators a better understanding why strengthening exercises may not be the best treatment.

Patient and public involvement (PPI) The investigators presented this project to 23 members of the public (who help researchers with their projects) at our monthly meeting. They thought this project was a good idea, especially talking about things like anxiety and depression. This will form part of the questionnaires.

Patients told the investigators about their thoughts of having pain following treatment for hip pain. They felt further knowledge into why they had pain and help with mental and emotional support was important to them. They told the investigators about their concerns over the lack of information about what treatment can and cannot achieve. They were reluctant to suggest treatment.

Three patients would like to help the investigators further design the study so that the information available to the public is clear and concise.

STUDY DESIGN The study flow is shown in Appendix A which summarises the study. Patients will be invited to participate in this observational prospective cohort study.

Setting: Participants will be screened from 4 tertiary hospital sites recognised for the management and treatment for Femoral Acetabular Impingement Syndrome (FAIS). The hospital locations were chosen to cover a diverse population ranging from urban to rural locations, offering a broad range of backgrounds and culture according to the Office for National Statistics Census of Population. Across hospital involvement will reduce spectrum and selection bias. All participants will be approached prior to attending their Physiotherapy-Led Rehabilitation (PLR) with a diagnosis of FAIS at the specialist orthopaedic hip clinics. However, alternative centres are available should the situation change at any of these between application and study onset.

Participants: will be recruited from relevant hip clinics and from the hospital that they are attending. The participants will be approached by a research assistant and a study information pack after identified by a clinician. Participants who have a formal diagnosis of FAIS by an orthopaedic doctor/registrars or physiotherapists will be screened for eligibility.

Consent: Patients with mental capacity who have a proven understanding of the English language will be approached. The consent form, questionnaires and information pack will be accessible on-line via a QR code linked to a free secure web-based data collection platform (REDCap). An information pack including a letter of invitation, Patient Information Sheet explaining the nature of the study and an informed consent form will be included in paper form, if participants would prefer a printed copy of the questionnaires and the results manually inputted.

• Outcome measures: Baseline physical hip characteristics will be collected from MRI or Xray findings: Cam size (alpha angle), Osteoarthritis (OA)(Kellgren Lawrence staging of OA), and radiological co-morbidities on MRI (e.g., gluteal tendinopathy) Pain Phenotyping • Douleur Neuropathique-4, Widespread Pain Index, Neuropathic Pain Symptom Inventory. Psychometric measurements, Tampa scale of Kinesiophobia (TSK-17), Hospital Anxiety and Depression scale (HADS), Pain Catastrophising Scale (PCS), Credibility/Expectancy Questionnaire (CEQ), Treatment Expectation Questionnaire (TEX-Q), Quality of Life: International Hip Outcome Tool (iHOT-33). • Visual analogue scale for average pain over 4 weeks, Hip range of movement The two additional outcome measures in the form of questionnaires (CEQ and TEX-Q) have been included based on feedback from the PPIE group. For participants unable to access the QR code, a paper copy of the questionnaires will be provided with a self-addressed stamped envelope.

Data collection: Baseline data will be collected and include patients' mobile number, postal code, landline number and email address, cross checked with the patient to confirm correct contact details. Participants demographics: age, sex, ethnicity, weight, height, body Mass index (BMI), duration of symptoms, smoking history, laterality of the hip pain, level of education, marital and social status, work status, medication, patient expectations of PLR, hospital location and comorbidity data. Alpha angles calculated by consultant radiologists and other features from the MRI e.g. gluteal tendinopathy (to document potential confounders) and other characteristics identified from the systematic review. The results of the patient reported questionnaires will be collated and anonymised and recorded electronically.

Sample size calculations: The investigators have based the sample size calculations on the primary purposes of the data analyses exploring the strength of the relationships between variables. The investigators plan for 9 variables identified from the questionnaires and ongoing systematic review where the number of participants required per variable for a multivariable linear regression model is 10-15. Allowing for 15 participants per variable and a 30% attrition rate lost to follow up, an a priori power analysis indicated that a minimum sample size of 175 patients would provide 80% statistical power with an alpha set at 0.05 based on the primary purposes of the data analyses. Power calculations will be crossed checked with a statistician.

Statistical analyses:

The investigators will undertake descriptive analysis of the data and will document counts, means, standard deviations or medians and interquartile ranges where appropriate. A multiple regression analyses will be performed exploring the association of the baseline variables and Correlational statistics will be used to explore the relationships between the variables.

Data management: All data will be recorded on REDCap which is a secure web-based data collection platform. Clinical data will be stored separately from patient identifying data. All data will be password and firewall protected. All paper records will be kept in a secured locked room in locked filing cabinets used to store patient data at the Physiotherapy Research Unit (Nuffield Orthopaedic Centre).

Participants will be issued appropriate questionnaires after 4 months from commencement of their PLR program. This will be done via either paper copy of the questionnaires or via a QR code that is linked to REDcap secured database or emailed automatically by REDcap.

Aim and objective. To identify whether pain phenotypes, psychological, social and demographics associate with poor outcomes after a PLR programme as defined by ongoing pain and/or hip stiffness and limited range of hip movement.

The questionnaires along with patient characteristics identified from the systematic review will be collected to determine if there is an association between the variables and poor outcome.

Recruitment and retention strategy. Clinical staff will be notified of the study via presentations in governance meetings, posters in clinic rooms and waiting areas and emails and a clear effective line of communication will be available for clinical staff to contact me. The posters are aimed to recruit the patients but will remind clinicians of the study. Regular visits are planned for the 4 sites to ensure a close working relationship with clinical staff and to monitor the recruitment process is on target and address any issues. Ongoing communication with the Patient and Public Involvement Engagement group to discuss strategies they identify which could be implemented to assist in recruitment and retention. Furthermore, strategies will be used for recruitment and retention using methods identified by including:

• Information on nature of the study, participants requirements detailing potential benefits and follow up.
• Create project identity and logo on all study correspondence.
• Contact and scheduling methods.
• Non-financial incentives including a letter of appreciation.
• Providing reminders to complete the questionnaires and self-stamped addressed envelopes for return of post.
• Obtaining multiple contacts for each participant Data collection time points (from baseline to 4 months): Prior to starting PLR, the research assistant will measure hip range of movement (flexion, extension, abduction, adduction, internal rotation and external rotation, and two impingement tests Flexion Adduction Internal Rotation (FADIRS) and Flexion Abduction External Rotation (FABERS). The participant will be given the study Questionnaires: iHOT33 (Health related Quality of Life) and Visual Analogue Scale (VAS) for pain intensity, TSK, WPI, HADS, PCS, DN4, NPSI, CEQ and TEX-Q.

At 4 months after commencement of treatment the participant will be given the iHOT33 questionnaire and pain intensity score (VAS). No other measurements will be taken.

A standard routine physiotherapy-led rehabilitation and follow up provides routine care that is provided in an National Health Service (NHS) setting. A PLR programme including (i) an individualised and progressive exercise program, (ii) education and its management, and (iii) advice regarding pain relief and avoiding positions of discomfort and activity are key features to the intervention, individualisation, progression and supervision. A treatment log will be kept documenting clinical treatment type, progression and exercise prescription with sets and repetitions. Fidelity will be checked by randomly selecting 10 sets of Physiotherapy notes to ensure routine standard care physiotherapy as detailed above is adhered to. Four months will mark the duration of the study from commencement of PLR to follow up irrespective whether the participant is still undergoing PLR. At the beginning of PLR the patient's pain, function and hip range of movement will be documented.

At 4 months, the physiotherapist will direct the patient to the QR code (or a paper copy if required) to complete the questionnaires if still undergoing PLR or REDcap will automatically email the questionnaires if the participant has finished their PLR. Working closely with the PPIE group will ascertain preferred methods of filling out the questionnaires whether electronically or paper format and to advise on retention strategies. It is planned that non responders will be contacted via a follow-up telephone call and letter and email if data is still missing but this will be reviewed on feedback from the PPIE group. After three attempts contacting the participant, no further attempt will be used to contact the participant. Paper copies of the questionnaire will be posted with a self-addressed stamped envelope if requested by the participant.

Recruitment Four centres have been selected from existing clinical and research networks. The four hospital locations were chosen to cover a diverse population ranging from urban to rural locations and offering a broad range of backgrounds and culture according to the ONS Census of Population. These centres have been identified as tertiary referral centres for management of hip conditions.

Patients will be identified when attending hip clinics at their participating hospital. Following a clinical assessment by the clinician (Consultants, Registrars in Orthopaedics or Sports and Exercise Medicine or advanced practitioner physiotherapist working in the hip clinic) and appropriate imaging/referral for imaging and formal diagnosis of FAIS, patients will be introduced to the study by the assessing clinician. The initial sites for this study are the 4 sites mentioned above. The Orthopaedic and Sports and Exercise Medicine team will be informed of the study by formal meetings and posters in clinic rooms to remind them of the study and to identify potential participants.

If the participant expresses an interest in the study, they will be introduced to a research assistant. The research assistant will provide an information pack with a QR code to scan which will provide more details of the study. A paper information pack will be given upon request. If the patient agrees to register for the study and participate, then the research assistant will use a clinic room and collect baseline data and consent the patient to the study. Clinicians will not be asked to obtain consent due to the nature of the busy clinics.

Description of study intervention(s), comparators and study procedures (clinical) The participants will be referred to a PLR as part of the 'routine standard care' pathway following the diagnosis of FAIS and is not part of the study. This study is purely observational and no treatment intervention or comparators. A treatment log will be kept documenting treatment type, progression and exercise prescription with sets and repetitions. Fidelity will be checked by randomly selecting 10 sets of Physiotherapy notes to ensure routine standard care physiotherapy as detailed above is adhered to.

There is no comparator in this study design. Description of study procedure(s)

Physical examination:

At the recruitment and screening process the research assistant will collect baseline demographics and will do a physical examination measuring the following movements via a goniometer:

Passive hip range of movement in all planes in supine: flexion, abduction and adduction and hip internal and external rotation in supine with the hip at 90 degrees flexion. Hip extension will be measured in prone lying.

Two hip impingement tests will be performed in supine: FABERS and FADIRS which are validated tests for FAIS. The pain response will be documented.

These measurements are planned to be completed after attending the hip clinic on the same day.

Questionnaires:

The investigators will use a battery of validated questionnaires to evaluate patient's characteristics. These questionnaires are commonly used in research.

Evaluation of Imaging data This study will include results from imaging as part of the participants routine standard care (if available), but imaging will not be ordered as part of the inclusion criteria. It is presumed that any participant attending a secondary care hip clinic for an orthopaedic consultation will fulfil a criterion for further investigations in the context of X-ray, MRI/A or CT.

Subsequent Visits The participants may have completed their PLR or may still be undergoing treatment. The follow up period is 4 months after starting the PLR irrespective of whether the participant is still undergoing PLR or not. This is part of usual care and not related to this study.

It is planned that the Research assistants will follow the patient up after 4 months from commencement of PLR and collect the Patient Reported Outcome Measures (PROMS) whilst in the physiotherapy department. If a research assistant is not available, then the physiotherapist can direct the participant to the QR code with a link to the questionnaires. Furthermore, REDcap can automatically email the two questionnaires if the participant is not present in the hospital. If the participant has finished their PLR prior to 4 months, then REDcap will automatically email the PROMs to the participant. If the participant is still undergoing PLR, then the PROMS will be collected either by either QR code or the participant will be given a paper copy of the PROMS. However, if this is not possible then the research assistant will contact the participant via telephone and collect the PROMS or by post or electronically via email if requested. Reminders to participants will be sent to attempt to gather the PROMS in a timely fashion to reduce the risk of recall bias and prevent non-responder and lost-to-follow-up bias.

Clinical measurements will be taken from the individual treating physiotherapist notes at the final treatment session in the format of hip range of movement and impingement test. In the event of missing data from the questionnaires, the participant will be contacted by the research assistant. Missing information from the questionnaire can be gathered from a telephone consultation.

Treatment compliance will be gathered from the physiotherapist's notes, noting how many missed appointments (did not attend, DNA, or unable to attend, UTA) and the number of visits and compliance of the rehabilitation program.

It is planned that the participant will attend as part of their usual care two hospital visits. The first visit will be in the hip clinic where baseline measures will be taken. The second visit at 4 months will collect information from the two questionnaires. If the participant is no longer under the care of the physiotherapist, then REDcap will automatically send out the questionnaires. The visits to hospital will be part of the usual care for the participant i.e. attending their hip clinic appointment and their PLR appointment

Inclusion Criteria:

• Participants aged between 18 and 55 years
• Diagnosis of symptomatic FAIS following a formal clinical assessment - Appropriate imaging: MRI/Arthrogram, and /or Xray and/or CT (secondary care pathway for diagnosis but this is optional).
• Awaiting PLR
• No previous surgery to the index hip
• Have capacity to give informed consent
• English as a spoken language

Exclusion Criteria:

• Presence of hip dysplasia, femoral stress fracture, synovitis or other inflammatory arthropathy (psoriatic arthropathy)
• Kellgren-Lawrence grading of Osteoarthritis ≥2 (to exclude moderate OA which could be a confounding influence on pain)
• Avascular necrosis of the femoral head
• Previous surgery to index hip
• Previous physiotherapy treatment to the index hip in the past 6 months
• Current pregnancy
• Perthes disease
• Involved in a current research study involving the hip

Adult male or female participants with a formal diagnosis of FAIS who meet the inclusion criteria