The overall aim of the study is to assess the reliability and validity of Autocad software to measure JPS in PFPS, especially:

1. To assess the intra-tester and between day reliability of measurement of JPS using Autocad software.
2. To assess the validity of these measurements against those found during an IKD.

Patellofemoral pain syndrome (PFPS) is a common painful musculoskeletal condition that affects physically active young adults and adolescents.

Joint position sense (JPS) is considered as a component of proprioception as it provides the clinician with information regarding the accuracy of movement as well as its relationship with movement performance and injuries. Therefore researchers use advanced instruments as 3 D video systems and isokinetic dynamometer. Since these instruments are less portable and expensive, therefore researchers used another method to evaluate JPS using high precision software using video analysis and markers in the joints. Unfortunately, video analysis requires difficult and time-consuming tasks and that this slow the evaluation process.

Although immediate feedback could help physiotherapists and athletic trainers to monitor athletes and make decisions during the training session and the rehabilitation process, such immediacy is not available for proprioceptive tests in field situations. Autocad software is available and inexpensive and provides immediate feedback

inclusion criteria:

1. Anterior or retropatellar knee pain from at least 2 of the following Activities : (1) prolonged sitting; (2) stair climbing; (3) squatting; (4) running; (5) kneeling; (6) hopping/jumping; (7) kneel sitting
2. Insidious onset of symptoms unrelated to a traumatic incident.
3. Age of the subject 18-35 years to limit the possibility that PFPS over age 35 may have been complicated by arthritic changes, and also the subjects should have closed epiphyseal growth plates.
4. Patient with chronic PFPS (pain > 3 months)

Exclusion Criteria:

1. Meniscal or other intraarticular pathologic conditions; cruciate or collateral ligament involvement.

2. A history of traumatic patellar subluxation or dislocation.

3. Previous surgery in the knee, ankle and hip joints.

4. Knee, ankle and hip joints osteoarthritis.

5. athletes weren't included.

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thirty-eight patients(males and females) with PFPS will be recruited from the outpatient clinic of the faculties of Physical Therapy, Cairo University, Egypt.