Vitamin D is a vital nutrient and hormone needed for many essential functions in overall health. There is growing literature examining the role of vitamin D not only in the general population but also in athletes. The most predominantly studied area of vitamin D pertains to bone health. Recently, there has been increased investigation into the relationship of vitamin D and stress fractures, including genetic polymorphisms, levels of 25-hydroxyvitamin D, and bioavailable vitamin D. This review will address the most recent developments of vitamin D research and its important role in bone health in athletes.

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Purpose The purpose of this study was to use 3-dimensional magnetic resonance imaging modeling of the skeletally immature knee to help characterize safe and reproducible tunnel positions, diameters, lengths, trajectories, and distances from anatomic landmarks and the physeal and articular cartilage for physeal-sparing anterior cruciate ligament (ACL) reconstructive surgery. Methods Magnetic resonance imaging from 19 skeletally immature knees with normal anatomy were gathered. The 3-dimensional models were created, and the relevant anatomic structures were identified. Cylinders simulating tunnel length, diameter and trajectory were superimposed onto the models, and descriptive measurements were performed. Results A safe position for the creation of an 8 mm diameter femoral tunnel was described in the lateral femoral condyle. The femoral tunnel length averaged 25.5 ± 2.6 mm. The bony entry point was located 3.8 ± 2.4 mm proximally and 12.7 ± 2.2 mm posteriorly to the lateral epicondyle. The shortest distance from the tunnel edge to the physis and femoral articular cartilage was 2.8 ± 0.7 mm and 3.7 ± 0.9 mm, respectively. The safe position for an 8 mm diameter tibial tunnel was also identified and described in the proximal tibia. The epiphyseal tibial tunnel length from the ACL footprint to the physis averaged 15.5 ± 1.6 mm. The proximal tibial epiphysis was found to accommodate a tibial crosspin measuring 63.5 ± 5.9 mm in length and 8.2 ± 1.5 mm in diameter without disrupting the physis or articular cartilage. Conclusions Three-dimensional modeling created from magnetic resonance imaging can help define important anatomic relationships for physeal-sparing ACL reconstructive surgery in skeletally immature knees and may assist in reducing the risk of injury to local anatomic structures. Clinical Relevance Knowledge of the anatomic relationships in skeletally immature knees serves as a valuable reference for surgeons performing physeal-sparing ACL reconstruction surgery.

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Objective To determine the sensitivity and specificity of ultrasound imaging (USI) compared to the reference‐standard of MRI in the diagnosis of bone stress injury (BSI). Methods A prospective blinded cohort study was conducted. Thirty seven patients who presented to an academic sports medicine clinic from 2016 to 2020 with suspected lower‐extremity BSI on clinical exam underwent both magnetic resonance imaging (MRI) and USI. Participant characteristics were collected including age, gender and sport. Exclusion criteria included contraindication for dedicated MRI, traumatic fracture, or severe tendon or ligamentous injury. The primary outcome measure was BSI diagnosis by USI. An 8‐point assessment system was utilized on USI for diagnosis of BSI, and the Fredericson and Nattiv22 criteria were applied to classify MRI findings. Results Thirty seven participants who met study criteria were consented to participate. All participants completed baseline measures. Using MRI, there were 30 (81%) athletes with a positive and seven participants with a negative BSI diagnosis. The most common BSIs in the study were in the metatarsal (54%) and tibia (32%). Compared to MRI, USI demonstrated 0.80 sensitivity (95% confidence interval [CI], 0.61–0.92) and 0.71 specificity (95% CI, 0.29–0.96) in detecting BSI, with a positive predictive value of 0.92 (95% CI, 0.75–0.99) and negative predictive value of 0.45 (95% CI, 0.17–0.77). Conclusions USI is a potentially useful point‐of‐care tool for practicing sports medicine providers to combine with their clinical evaluation in the diagnosis of BSIs. Further research is ongoing to determine the role of USI in follow‐up care and return‐to‐play protocols.

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