This randomised controlled trial will compare the effects of a weight loss and exercise program to exercise only on clinical outcomes in 100 people with hip osteoarthritis (OA) and overweight or obesity. The primary aim is to find out whether a weight loss and exercise program will improve hip pain more than an exercise program alone at 6 months follow-up

Clinical guidelines recommend exercise as the core treatment for symptoms, but provide conflicting recommendations about weight loss for people with hip OA. Irrefutable health benefits are associated with weight loss for those with overweight or obesity, but it remains uncertain whether weight loss in addition to exercise and regular physical activity is superior to exercise alone for hip OA symptoms.

This study is a randomized controlled trial for which the aim is to determine whether a weight loss and exercise program improves hip pain more than an exercise program alone at 6 months among people with hip OA who have overweight or obesity.

A total of 100 people with hip osteoarthritis and overweight or obesity will be recruited from the community. Participants will be assessed for eligibility, including review of a hip x-ray. They will be enrolled into the study following informed consent and completion of baseline questionnaires and laboratory-based measures. Each participant will be randomly allocated to receive either: a) weight loss plus exercise program or; b) exercise program alone, over 6 months.

The randomisation schedule will be prepared by a biostatistician (permuted block sizes 2 to 6) stratified by site and sex. Participants allocated to the exercise group will be randomly allocated to a physiotherapist. Participants allocated to the exercise plus weight loss group will be randomly allocated to one of the same physiotherapists as the exercise group, and to a dietitian. The schedule will be stored on a password-protected platform at the University of Melbourne and maintained by a researcher not involved in either participant recruitment or administration of outcome measures. Group allocation will be revealed after completion of baseline measures and randomisation.

Dietitians will complete training in best-practice OA management (half day workshop led by investigators), motivational interviewing skills (2-day training course), weight management (the ketogenic very low calorie diet) and trial procedures. Physiotherapists will be trained in trial procedures, best practice OA management, strengthening and physical activity program, behaviour change techniques to promote adherence and resources for use in the program.

Study participants in both groups will attend 5 individual physiotherapy consultations via video-conference over 6 months and will undertake a home-based lower limb muscle strengthening exercise and physical activity program. Those in the weight loss and exercise group will also undertake a ketogenic very low calorie diet (VLCD), which has been demonstrated as a safe and effective means of achieving rapid weight loss in the adult population with overweight/obesity. They will receive meal replacements (maximum 2 per day) for up to 6 months as well as educational resources.

A biostatistician will analyse blinded data. The statistical method will be outlined in a Statistical Analysis Plan.

Inclusion Criteria:

• American College of Rheumatology classification criteria with pain in the groin or hip region on most days of the past month and femoral or acetabular osteophytes and joint space narrowing (superior, axial and/ or medial) on x-ray;
• aged 50 years or older;
• report history of hip pain ≥ 3months;
• report an average pain score of at least 4 on an 11-point numeric rating scale (anchored at 0=no pain, 10=worst pain imaginable) over the previous week;
• access to a device with internet connection;
• have a BMI >27 kg/m2;
• willing and able give informed consent and participate fully in the interventions and assessment procedures;
• have ability to weigh themselves (e.g. access to scales);
• pass the Exercise and Sports Science Australia stage 1 adult pre-exercise screening system or obtain general practitioner clearance for participation in the study.

Exclusion Criteria:

• weight >150 kgs (due to the added complexities of additional nutritional requirements for individuals above this weight);

• inability to speak and read English;

• on waiting list for/planning back/lower limb surgery or bariatric surgery in next 12 months;

• previous arthroplasty on affected hip;

• recent hip surgery on affected hip (past 6 months);

• self-reported inflammatory arthritis (e.g. rheumatoid arthritis);

• weight loss of > 2 kg over the previous 3 months;

• already actively trying to lose weight by any of the following mechanisms:

  1. using meal replacements for weight loss
  2. being a member of a commercial weight loss program (e.g. weight watchers)
  3. receiving support from another health care professional for weight loss
  4. using any drugs prescribed to aid in weight loss
  5. using structured meal programs for weight loss such as 'Lite n' Easy'

• unable to undertake ketogenic VLCD without closer medical supervision including self-reported:

  1. diagnosis of Type 1 diabetes
  2. Type 2 diabetes requiring insulin or other medication apart from metformin
  3. warfarin use
  4. stroke or cardiac event in previous 6 months
  5. unstable cardiovascular condition
  6. fluid intake restriction
  7. renal (kidney) problems (unless clearance is obtained from GP, including GP confirmation that estimated glomerular filtration rate >30 mL/min/1.73m2)

• any neurological condition affecting lower limbs;

• pregnancy or planned pregnancy

• vegan dietary requirements due to complexity of delivering a nutritionally complete diet within the ketogenic diet regime.

PD can be shared

Available upon publication of results

Upon reasonable request

Participants will not be informed about the study hypotheses, until the study is completed, at which time they will be provided a lay summary of study findings. However, the components of each treatment arm will be disclosed during recruitment, allowing us to test the interventions in a way whereby potential participants are fully informed about the nature of the components before deciding whether to participate. As the primary and some of the secondary outcomes are participant-reported, participants are also the outcome assessors and are unblinded. Physiotherapists and dietitians will not be blinded to group allocation or study hypothesis. Staff collecting the secondary outcome body composition data will be blinded to group allocation. Research staff administering and entering the participant-reported data will be blinded. Statistical analyses will be performed blinded.