chronic ankle instability previously approved in many studies that it may lead to more proximal adaptations and negative long term consequences. one of those studies reported, ankle instability patients has hamstring muscle shortening in comparison with non sprained subjects. another one concluded that gluteus maximums muscle has delayed activation and weakness in CAI patients. Both muscles (hamstring and gluteus Maximus ) contribute to sacroiliac joint stability. therefore, this study asked a novel research question, was sacroiliac joint dysfunction (SIJD) associated with CAI?

The sample size of this study had been calculated based on the primary outcome that was the association between CAI and SIJD after a pilot study done in order to detect odd's ratio. , calculation made by a program developed by the Centers for Disease Control and Prevention with the following inputting data :

Two-sided confidence interval 95%, power 80%, ratio of controls to cases 1, percent of control exposed 4.5% , odds ratio 32%. The sample size calculations required for this study was 28 participants (14 in each group).

Data distributions was checked for normality using Shapiro-Wilk test and for equality of variance using Box's test. Box and whiskers plots were used for detecting the outliers. Descriptive statistics calculated for demographic data. Intraclass correlation coefficients (ICC) and standard errors of measurement (SEM) were calculated to estimate the intratester reliability and precision of measurement for the static pelvic rotation

The outcomes of these study were:

1. Association between CAI and SIJD represents through odd's ratio (primary outcome)
2. Pelvic torsion difference between CAI and control Calculated by Mann- Whitney test (secondary outcome)
3. Correlations between pelvic torsion with perceived ankle instability and number of giving way episodes calculated Pearson correlation coefficient(secondary outcome) Effect size analysis was calculated to determine the clinical significant difference. Statistical analysis was conducted using the statistical package for social studies (SPSS) for windows, version 24 (SPSS, Inc., Chicago, IL). The normative data presented as Mean ± standard deviation (SD) while non-normative data presented as median. Significance was set at p < 0.05 and total study power was set 80%

Inclusion Criteria:

1. young active people between 18-30 years old
2. CAI group has a self-report of a past history of unilateral ankle inversion injury since at least more than 1 year before the study onset
3. Required a period of protected weight bearing and/or immobilization at least one day
4. The patient reported a tendency to give way or repeatedly turn over during functional activity
5. At least 2 giving way episodes during the year before the study onset and/or recurrent ankle sprain
6. Perceived that the ankle was chronically weaker, more painful, and/or less functional than other non-injured ankle or than before first injury.
7. Positive anterior drawer test and /or talar tilt test

Exclusion Criteria:

• Exclusion Criteria for both groups (CAI and Control )

  1. Trunk asymmetry angle 5 - 7 degrees
  2. Leg length difference more than 0.5 cm
  3. History of autoimmune diseases, complains of ankylosing spondylitis and morning stiffness
  4. Participation in physical therapy regimen within a year before enrolling in the study
  5. Bilateral ankle sprain injury
  6. Ankle sprain within 3 months of participation
  7. If they had only midline or symmetrical pain above the level of L5 or radicular pain with neurological deficits (sensory or motor deficits)
  8. History of spinal surgery, infection, tumors, fracture of the spine, pelvis or lower extremities within 2 years before enrolling in the study.
  9. Hospitalization for severe trauma or car accident
  10. Pregnant women
  11. Any neurological and orthopedics diseases could affect the conditions

Recruited from faculty of physical therapy through announcements for volunteering to participate in noninvasive study include patients complaining of ankle instability and others did not have any injury in their ankle before