Knee osteoarthritis (KOA) patients, have impairments in gait and balance. Accurate gait and postural balance analysis is needed to detect this impairments. Nevertheless methodological quality about the recording of gait and balance analysis in KOA patients is lacking in literature.

In patients with knee osteoarthritis (KOA), impairments in gait and balance are well recognized and therefore objective and accurate gait and postural balance analysis is crucial to detect potential alterations in balance and gait function in this patient group.

Gait analysis in orthopaedic patients has been mainly investigated during level walking at a self-selected speed or at pre-determined gait velocities. Nevertheless, walking at a comfortable speed may not necessary result in any gait impairments and therefore the use of more challenging tasks is probably required. In addition, some patients are not able to walk at a required walking speed or slope, because of pain and disability. Therefore it seems reasonable to evaluate gait parameters of KOA patients while walking at different speeds and surface inclinations.

Postural balance parameters are also important outcome measures in the assessment of KOA patients. Postural stability is generally assessed throughout the quantification of the displacement and velocity of the centre of pressure (COP) with larger excursions and higher velocities indicating poorer balance.

Recently, instrumented treadmill systems (ITS) have been introduced for the evaluation of spatiotemporal and kinetic gait as well as postural balance parameters throughout a capacitance-based foot pressure platform. Further, they permit an assessment of the gait parameters at different speeds and slopes. Spatiotemporal and kinetic gait parameters provided by ITS have been shown to be valid and reliable during level walking in healthy young and elderly persons and during walking at different speeds and slopes. ITS can also be used for the quantification of static balance, because they are able to provide the velocity and displacement changes of COP. However the validity and reliability of gait and postural balance analysis at different slopes and speeds in patients with KOA are lacking.

Similarly to ITS, photoelectric cell systems (PCS) also permit the quantification of spatiotemporal gait parameters but in addition they are portable, their set up is very quick, they are relatively cheap and can be adapted to a treadmill. PCS have been shown to be both valid and reliable for the assessment of spatiotemporal gait parameters in healthy adults and also in KOA patients.

The main aim of this study is to evaluate the methodological quality of postural and gait parameters assessed at different treadmill inclinations and velocities using an ITS in patients with KOA. In particular, we will investigate the test-retests reliability, the discriminant validity and the concurrent validity.

Inclusion Criteria:

• 45 to 85 years.
• Men and women.
• Unilateral symptomatic KOA.
• Patient in waitlist at the Schulthess Clinic for knee arthroplasty.
• Living place: Canton of Zurich or neighbouring Cantons.
• Signed written informed consent.

Exclusion Criteria:

• Symptomatic OA in lower extremity joints other than the knee.
• Bilateral symptomatic KOA.
• Usage of walking aids.
• Surgery to the lower limbs in the prior 12 months.
• BMI >35 kg/m2.
• Disorders that affect gait or balance function.