Observational, Cross- sectional study (one shot study), design will used (Correlation study) This study aims to investigate the relationship between hip muscles performance and balance in patients with chronic ankle instability using the Star Excursion Balance Test (SEBT) and Isokinetic biodex system III.

this study is to answer the question ; Is there a relationship between hip muscles (extensors/flexors, abductors /adductors, internal rotator/ lateral rotator) performance and balance in patients with chronic ankle instability?

Inclusion Criteria:

1. Age range between 18 and 40 years from both genders.
2. Had a history of at least one significant lateral ankle sprain to the same side that resulted in pain and loss of function of more than one day.
3. Had a history of at least two episodes of 'giving way' in the past six months.
4. Each member of the CAI group will require to answer yes to at least 5 questions on the Ankle Instability Instrument (AII) questionnaire and score 24 on the Cumberland Ankle Instability Tool (CAIT)

Exclusion Criteria:

1. A history of neural or vestibular disorders.
2. Previous lower limb surgeries
3. Trauma to the lower limbs for at least 3 months prior to the study;
4. Physiotherapy within the last 3 months or current participation in supervised physical rehabilitation.
5. Consumed drugs or alcohol within 24 hours prior to testing that could interfere with performance.

Patients will be recruited in the study from outpatient clinic of Cairo University and orthopedic physician.