This prospective study with a two-group comparison design investigates the effectiveness of 12-weeks of semi-structured and supervised physiotherapist-led treatment on self-reported hip and groin function in patients with femoroacetabular impingement syndrome with and without intra-articular hip pain. Determination of intra-articular hip pain is based on pain relief following an ultrasound-guided intra-articular anesthetic hip injection performed prior to commencing treatment.

The treatment of femoroacetabular impingement syndrome (FAIS) consists of wait-and-see, physiotherapist-led treatment, and/or hip surgery. The primary indication for hip surgery is based on imaging findings, however, limited correlation has been observed between such findings and hip symptoms. As patients with FAIS often show physical impariments, such as impaired hip muscle function, physiotherapist-led treatment aiming to address such factors may be effective in improving hip function and pain in some patients. However, several factors may confound the effect of physiotherapist-led treatement of FAIS, such as whether the patient presents with intra-articular hip joint pain or not.

Thus, the purpose of this prospective study with a two-group comparison design is to investigate the effect of 12-weeks of physiotherapist-led treatment on self-reported hip and groin function, measured with the Copenhagen Hip and Groin Outcome Score (HAGOS), in subjects diagnosed with FAIS, but with and without intra-articular hip pain. Determination of intra-articular hip pain is based on the response to an ultrasound-guided intra-articular anesthetic hip injection performed prior to commencing treatment.

Subjects diagnosed with FAIS based on symptoms, clinical signs and imaging findings will be prospectively recruited from a specialized outpatient hip and groin clinic at Hvidovre Hospital. Following inclusion subjects undergo 12-weeks of semi-structured and supervised physiotherapist-led treatment. The primary outcome measure is the between-group (intra-articular pain vs. no intra-articular pain) difference in mean change of the HAGOS sport subscale from baseline (week 0) to follow-up (week 12).

The primary outcome measure will be publised in the primary paper, which will also include information on between-group difference in change in hip muscle strength and single-leg hop performance as secondary outcome measures.

Secondary papers will be reported with a clear reference to the primary paper.

The sample size calculation is based on the primary outcome measure, being the between-group (intra-articular pain vs. no intra-articular pain) difference in change in the HAGOS Sport subscale following 12 weeks of physiotherapist-led treatment. Based on an expected 1/1 recruitment ratio between subjects with and without intra-articular hip pain and a clinically relevant between-group contrast in change of 15 points corresponding to a moderate effect size 0.6 (Cohen's d), a power and alpha value of 80% and 0.05, respectively, 44 subjects in each group is adequate (G*power software, v.3.1, Heinrich-Heine-Universität, Düsseldorf, Germany). To minimize the risk of underpowering the study in case of uneven allocation to groups, based on the intra-articular anesthetic hip injection, inclusion of participants will continue until a minimum of 55 (44 including 25% dropouts in each group) subjects has been recruited in each group. A blinded member of the research team will be responsible for monitoring this.

Inclusion Criteria:

• Activity-related longstanding hip and/or groin pain for >3 months
• Known anterior and/or medial groin pain during the FADIR test with a pain severity of ≥2/10 on NRS.
• Radiological findings on plain radiographs of cam morphology defined as alpha angle >55° on a lateral view.

Exclusion Criteria:

• Inguinal-related groin pain diagnosed according to Doha Agreement.
• Pubic-related groin pain diagnosed according to Doha Agreement.
• Evidence of pre-existing hip osteoarthritis, defined as a joint space width <3 mm at the lateral sourcil on anterior-posterior pelvic radiograph.
• Previous hip pathology such as Perthes' disease, slipped upper femoral epiphysis, hip dysplasia defined as a Lateral Center Edge Angle <25°, or avascular necrosis.
• Other causes of hip and groin pain identified by the orthopedic surgeon during the clinical examination, such as stress fracture of the femoral neck, referred pain from the facet joint, referred pain from the sacroiliac joint, or other competing diagnosis (rheumatoid arthritis, cancer etc.)
• Previous hip injury such as acetabular fracture, hip dislocation, or femoral neck fracture.
• Previous intra- or extra-articular hip surgery.
• Pregnant.
• Intra-articular steroid hip injection during the preceding 3 months.

Participants will be blinded to the potential value of the diagnostic findings, such as response to intra-articular hip injection.

Outcome assessor will be blinded to diagnostic findings, such as response to intra-articular hip injection.

Care Provider (Physiotherapist supervising the intervention) will be blinded to diagnostic findings, such as response to intra-articular hip injection.