Iran Red Crescent Med J. 2018 June; 20(6):e59364. Published online 2018 August 8. doi: 10.5812/ircmj.59364. Research Article The Associations of Vitamin - D Deficiency with Knee Pain and Biomechanical Abnormalities in Young Iranian Patients with Patellofemoral Pain Syndrome: A Case-Control Study Fariba Eslamian 1, * , Fatemeh Jahanjoo 1 , Vahideh Toopchizadeh 2 and Banafshe Kharrazi 3 1 Physical Medicine & Rehabilitation Research Center, Aging Research Institute, Imam Reza Hospital, Tabriz University of Medical Sciences, Tabriz, Iran 2 Physical Medicine & Rehabilitation Research Center, Padiatric Hospital, Tabriz University of Medical Sciences, Tabriz, Iran 3 Ophtalmolgy Departement, Nicookari Hospital, Tabriz University of Medical Sciences, Tabriz, Iran * Corresponding author: Physical Medicine & Rehabilitation Research Center, Aging Research Institute, Imam Reza Hospital, Tabriz University of Medical Sciences, Tabriz, Iran. Tel: +98-4133373967, Fax: +98-4133361651 , Email: eslamiyanf@tbzmed.ac.ir Received 2017 August 02; Revised 2017 December 03; Accepted 2017 December 21. Abstract Background: Patellofemoral pain syndrome (PFPS) is characterized by anterior knee pain due to arthralgia in the joint between the patella and femur. Many factors, including improper biomechanics and skeletal disorders, are associated with PFPS. The role of Vitamin D deficiency in the pathogenesis of patellar chondromalacia has been known for several years. Objectives: The aim of the present study was to determine the prevalence of Vitamin D deficiency in young people with Patellofemoral Pain Syndrome (PFPS) and compare this with the prevalence in a healthy matched control group and to determine the correlation between the occurrence of biomechanical abnormalities and serum levels of 25(OH)D in patients with PFPS. Methods: In this case-control study, 40 patients aged 15 to 40 years old with a diagnosis of PFPS, that had referred to the rehabilita- tion clinic of a university hospital in Tabriz, Iran, were selected as the case group and 40 normal subjects of the same age range were selected as the controls. Serum 25(OH)D levels were assessed, and a postural examination was performed on both groups, while the severity of knee pain, plain knee radiographs, and serum levels of calcium and phosphorous were assessed only in PFPS patients. Results: Among the 80 participants, Vitamin D deficiency (cut-off level of 25(OH)D ≤ 20 ng/mL) was observed in 55 participants (68.75%), including 35 (87.5%) patients and 20 (50%) controls, with a statistically significant difference (P < 0.001). Females had a higher prevalence of Vitamin D deficiency than males, yet the difference was not statistically significant (71.21% versus 57.14%, P = 0.348). The serum levels of Vitamin D and pain severity were significantly and inversely related in the case group (P = 0.005). Clinical and imaging findings showed that 18 (45%) of the patients and two (5%) of the controls had abnormalities, such as genu varus, genu valgus, or patellar tracking, indicating a high coexistence of biomechanical deficits in PFPS (P < 0.001). Conclusions: Severe and moderate Vitamin D deficiencies were more prevalent in young adults with PFPS than in normal adults. Knee pain severity and joint deformities were correlated with low levels of Vitamin D in the case group. Therefore, attention to diet, vitamin supplementations, and biomechanical correction are the mainstay treatment of PFPS. Keywords: Arthralgia, 25-HydroxyVitamin D, Knee, Patellofemoral Pain Syndrome, Vitamin D, Deficiency 1. Background Patellofemoral pain syndrome (PFPS), also known as patellofemoral arthralgia or chondromalacia, refers to pain in the joint between the patella and the femur. Arthralgia is the most common cause of knee pain in the younger population, especially in those, who participate in professional or recreational sports activities (1, 2). Furthermore, PFPS is usually felt in activities, such as climbing up and down stairs or squatting and sitting for long periods of time. Although PFPS can follow an acute trauma to the patella or the cartilage under the kneecap, it usually has a gradual onset and chronic nature, due to joint overuse or overload (3, 4). Other factors, such as the Q-angle increase (angle be- tween the shaft of the femur and the tibia), biomechan- ical factors, such as muscle imbalance around the knee, patella medial tracking, patella lateral tracking, and joint curvature, such as genu varus (bow knee) and genu val- gus (knock-knee), are the main underlying factors for PFPS. Other mechanical factors, such as flat foot, pes cavus (claw foot), lower-extremity alignment abnormalities, including outward twist of the tibia, femoral anteversion, and leg length discrepancy; muscle dysfunction, such as weakness Copyright © 2018, Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited