Total hip replacement (THR) is the procedure which can improve the quality of life in patients with osteoarthritis. However, deficits in static stability and impairment of the lower limb efficiency can be observed even several months after procedure. The aim of this study was to investigate the static balance of the standing position in patients treated by THR.

The balance platform and one leg standing test (OLS) were used to assess the static balance. The postural balance tests were performed on the Metitur Good Balance platform. Static balance tests on balance platform were performed in several position with different foot placement like: normal standing with eyes open (NS EO) and eyes closed (NS EC) position, tandem position (TP), second form of tandem position (2TP) and one leg standing position (1L). Participants were asked to maintain the motionless upright position with both arms at their sides and eyes staring at a target in front of them.

During the normal standing (NS) position the patient stood on the platform barefoot with the feet placed parallelly (symmetric position of feet) with a 20 cm distance between them. The length of the trials with EO and EC was 30 seconds each.

In TP (tandem position) the width of base of support was narrowed down significantly, therefore test lasted only 10 s. During the test in TP one foot was placed directly in the front of the other (on the line) and the heel of the front foot was touched the toes of the rear foot. Tests were performed tests in TP with the left foot in front (TLF) and with right foot in front (TRF) separately. In THR group the placement of the operated limb in the front stance was called the TOF test, while the placement of the non operated limb in the front stance was called the TNF test. The results obtained in TOF position and TNF position were compared with tandem control index (TC - mean of results obtained from control group in TLF and TRF positions).

In 2TP alternately left or right foot was places in front of the other, but the feet were placed on both sides of the line dividing platform to two parts (line was tangent to the medial edge of feet). The length of exercise was 20 s. Analogically to the tandem test, patients were examined with the operated (2TOF) and non operated limb (2 TNF) in the front. Results were compared to the second tandem control index (2TC) representing the mean results of the control group as was described above.

When testing one leg standing position on the balance platform, the patients were asked to raise one foot half the level of the calf of the supporting leg but not touching the stance limb. The trial lasted for 5 s. The test was stopped when the subject used his arms (touched the handrail) or used the raised foot (touched the floor). Usually after 2 failed attempts or fear of falling down procedure was stopped and results was not recording. The results of the patients after THR when standing on the operated (1 O) and non operated (1 N) leg were compared to the index denoting the mean results of the control group (1 C).

During the static tests we analyzed the mean velocity of sway of the center of feet pressure (COP) in the frontal plane (X, mm/s) and in the sagittal plane (Y, mm/s) and the value of the middle of spectrum in the same planes. The spectrum is characterised by two co-dependent variables such as frequency (Hz) and the excursion (mm).

During the one-leg standing test (OLS) the time of maintain this position by the patients was measured. The placement of the limbs was the same as in the case of the balance platform test. Subjects performed 3 trials on each lower limb. Time ended when subject either: loosed balance and touched raised foot the floor, moved supporting leg on the ground, a significant loss of balance or a maximum of 60 s had elapsed. Results achieved by the subjects after THR on both operated (OLS-O) and non operated limbs (OLS-N) were compared with the index of the control group (OLS-C: mean result of the tests performed on the left and right legs).

Inclusion Criteria:

• for patients: total hip replacement the minimum of 6 months period since the procedure, age above 55 years, unassisted gait, and the minimum of 9 points on the AMTS scale
• for healthy volunteers: without total hip replacement age above 55 years, unassisted gait, and the minimum of 9 points on the AMTS scale

Exclusion Criteria:

• for patients: neurological diseases, muscles diseases, rheumatic diseases (rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis) and sciatica. Additionally we excluded patients who had operations in the area of the spine and lower limbs (knee arthroscopy with ACL reconstruction or meniscectomy, total knee replacement, total hip replacement in both extremities, osteotomy or arthrodesis).
• for healthy volunteers: neurological diseases, muscles diseases, rheumatic diseases (rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis) and sciatica. Additionally we excluded patients who had operations in the area of the spine and lower limbs (knee arthroscopy with ACL reconstruction or meniscectomy, total knee replacement, total hip replacement in both extremities, osteotomy or arthrodesis).