The aim of this study is to compare vitamin D level between young adults with isthmic spondylolysis and a matched healthy control group.

Deficiency of 25-hydroxy vitamin D has been of recent interest , and its high prevalence has been confirmed across all age groups in many cross sectional studies, particularly in developing countries and in the Middle East and Northern Africa Region . The formation and maintenance of a structurally stiff and resilient skeleton is dependent upon vitamin D's role in absorption of calcium from the gut and in normal bone metabolism thereafter. Failure of adequate mineral accretion reduces normal bone turnover and may result in rickets, osteomalacia, and osteoporosis later in life . Several risk factors for hypovitaminosis D have been described in the literature, including nutrition, little exposure to ultraviolet light, darker skin pigmentation, and lack of physical activity .

Lumbar isthmic spondylolysis is a stress fracture of the pars interarticularis, which is generally considered a disease of adolescents and young adults .

The exact prevalence of spondylolysis in our region is not exactly known, but the general impression among spine surgeons is that it is much higher than the 3-6% prevalence reported for the Caucasian population .

Spondylolysis commonly affects children and young adults . The exact etiology of this fatigue fracture of the pars interarticularis is still not well understood . The most probable mechanism of lumbar spondylolysis is multifactoral with a stress fracture occurring through a weak or dysplastic pars interarticularis. The likely initiating event occurs when the patient engages in repeated extension and/or axial rotation maneuvers .

Vitamin D deficiency may be a predisposing factor to weak bone and subsequent fractures . Despite abundant sunshine, hypovitaminosis D is very common in the Middle East Region and several cross- sectional studies in Egypt , Iran , Tunisia , Jordan , United Arab Emirates, and other Gulf countries have been reported. Symptomatic spondylolysis is indicated for surgical intervention.

Currently, children and adolescents with spondylolysis are treated with pars reconstruction techniques. Adults with symptomatic isthmic spondylolysis or with large defects are treated with spinal fusion.

The hypothesis of this study is that hypovitaminosis D predisposes to weakness of the pars interarticularis and subsequently is a risk factor for developing isthmic spondylolysis. Given the common incidence of hypovitaminosis D in Egyptian population and the negative impact of spondylolysis on the young active age group, this study would have important implications regarding prophylactic vitamin D supplementation as well as the prevention of spondylolysis.

Inclusion Criteria:

• Patients: Adults aged 20 - 45 years with symptomatic isthmic spondylolysis
• Controls: Matched population without spondylolysis indicated for plain x-ray and CT lumbo-sacral spine. These will be recruited mainly from the Trauma Unit. This will not add any non-indicated radiation exposure to healthy individuals

Exclusion Criteria:

• Traumatic spondylolysis
• Pregnant women
• Significant co-morbidities (renal or hepatic diseases, malignancy, malabsorption syndrome, musculoskeletal diseases, steroid therapy)
• Metabolic diseases affecting vitamin D and Calcium metabolism (e.g. hyperparathyroidism)

Detailed history taking (including dietary calcium and vitamin D intakes, Exposure to sun, and Clothing habits)

• Clinical examination
• Imaging: plain x-ray and CT scan
• Laboratory: Free serum calcium, alkaline phosphatase and 25-OH vitamin D