In orthopaedic manual therapy translatoric grades of movement are used to determine the intensity of force applied during the mobilization. Different clinical effects are described for each translatoric grade of movement but there are not published studies evaluating these clinical effects.

The objective of this trial is to determine if force magnitude during hip traction in resting position affects immediate and short-term outcomes (pain, physical function, hip muscle length and hip range of motion) in patients with hip osteoarthritis. For this purpose, investigators conduct a randomized clinical trial, double-blind (patient and physical therapist examiner). Participants entering the study were randomized into 1 of 3 treatment groups: grade I- grade IISZ mobilization, grade IITZ mobilization or grade III mobilization. Participants attend three sessions on alternate days (monday, wednesday, friday) and at the same hour. Measurements are taken prior to treatment, immediately after each session treatment.

The participants are recruited from physiotherapy groups or referred by general practitioners and orthopedic surgeons.

Participants were assigned to 1 of the 3 study groups through concealed allocation (sealed envelopes) and independent blocked randomization, using a random number generator.

One physical therapist enroll patients in the study, while an independent research assistant performed the randomization and prepared the sealed envelopes, which are opened after baseline data collection by the physiotherapist performing the treatments. Participants are treated in a private treatment area and have no knowledge of treatments received by other participants.

A second experienced orthopaedic manual therapist applies the standardized hip traction mobilization in resting position at either level of force, during 10 minutes. This amount of mobilization is consistent with clinical practice and previous studies in osteoarthritis patients.

Two physiotherapists (third and fourth) with 5 years of experience, who were blinded to participant group, performed all measurements.The outcome measures are pain, physical function, hip muscle length and hip passive range of motion. Pain is registered with visual analogic scale (VAS), Pressure Pain Threshold ( PPT) and WOMAC pain subscale. Physical function is registered using Timed Up & Go test (TUG), the 20-Meter Walking Test (20MWT) and the physical function subscale of WOMAC index. The hip muscle length is measured using Ely´s test, Active Knee Extension test and modified Ober´s test. The passive hip range of motion is measured using inclinometer or goniometer.

Inclusion Criteria:

• unilateral primary hip OA according to the clinical criteria of the American College of Reumathology,
• a grade III Kellgren & Lawrence (K-L) classification in their most recent hip X-rays,
• mild to moderate pain from hip OA categorized using the WOMAC pain subscale (2 to 8 as mild pain; greater than 8 to 12 as moderate pain),
• the ability to walk at least 20 meters, with or without an aid.

Exclusion Criteria:

• neurological, vascular or other lower extremity musculoskeletal conditions that affected sensation, gait or functional performance,
• contraindications for manual therapy
• insufficient understanding of the Spanish language