Patients with primary hip osteoarthritis (OA group) and patients with inflammatory hip disease (RA group) and healthy subjects (control group) are enrolled in the study. The aim of our study is to determine the postural control in patients suffering from OA and RA of the hip joint during different conditions, i.e., on both stable and compliant surfaces with opened or closed eyes to determine the possible differences between these two diseases in this respect.

Determination of functional status, using the following outcome measures: Harris Hip Score, the Functional status of the hip joint is rated with the Harris Hip Score (HHS), Visual Analogue Scale, Western Ontario and McMaster Universities Osteoarthritis Index, Timed Up & Go test.

Posturography measurements, Postural control tests

The Clinical Test of Sensory Interaction on Balance (CTSIB) uses different conditions to test how people adapt to changing sensory conditions during the maintenance of stance. We used the modified CTSIB by NeuroCom to perform the test on a computerized force plate to measure the body sway. Static postural stability [displacement of Centre of Pressure (CoP)] was measured during standing on a single force platform (Stabilometer, ZWE-PII) for 20-s periods in a quiet room. Signals were amplified and sampled at 16 Hz via an analogue-to-digital converter. Subjects stood barefoot on the platform, with the feet positioned side by side and arms hanging freely at their side. Toe-out was positioned to subjects' comfort. The CoP excursions along antero-posterior (AP) and medio-lateral (ML) axes were performed both on firm (the stable surface of the platform) and foam surfaces [an Airex Balance Pad (dimensions: 50 cm length x 41 cm width x 6 cm height) placed on the platform], always starting with standing on the stable surface. In each condition, subjects had to stand first with the eyes open (EO), when subjects had to look at a target fixed at eye level at a distance of approximately 1 m, and then measurements were also performed with closed eyes (EC).

Inclusion Criteria:

• C-reactive protein and Westergreen values had to be under the upper level of the normal values.
• Patients should have unilateral hip pain on most of the days for several months
• Controls should have no hip pain or functional impairment in the hip joint or any other joint of the lower extremities.

Exclusion Criteria:

• history of trauma to the hip joint or in the pelvic region,
• previous hip fracture or hip surgery,
• hip joint infection and congenital or developmental diseases
• any complaints in the other joints of the lower limbs
• any disease that could worsen their physical or balance parameters
• cancer,
• endocrine,
• cerebrovascular disease,
• Parkinson's syndrome,
• epilepsy,
• polyneuropathy,
• neuromuscular disorder,
• cardiovascular disease without medication,
• atherosclerosis of the lower extremities

Patients with primary hip osteoarthritis (OA group), patients with inflammatory hip disease (RA group) and healthy subjects (control group) are enrolled in the study. All subjects were independent and capable of self-care and daily household tasks.