X-Linked Hypophosphataemia (XLH) is a rare, progressive, hereditary phosphate-wasting disorder characterised by excessive activity of fibroblast growth factor 23. The International XLH Registry was established to provide information on the natural history of XLH and impact of treatment on patient outcomes. The cross-sectional orthopaedic data presented are from the first interim analysis.

The XLH Registry (NCT03193476) was initiated in August 2017, aims to recruit 1,200 children and adults with XLH, and will run for 10 years. At the time of analysis (Last Patient In: 30/11/2020; Database Lock: 29/03/2021) 579 subjects diagnosed with XLH were enrolled from 81 hospital sites in 16 countries (360 (62.2%) children, 217 (37.5%) adults, and 2 subjects of unknown age).

Of subjects with retrospective clinical data available, skeletal deficits were the most frequently self-reported clinical problems for children (223/239, 93.3%) and adults (79/110, 71.8%). Retrospective fracture data were available for 183 subjects (72 children, 111 adults); 50 had a fracture (9 children, 41 adults). In children, fractures tended to occur in tibia/fibula and/or wrist; only adults reported large bone fractures. Joint conditions were noted for 46 subjects (6 children, 40 adults). For adults reporting osteoarthritis, knees (60%), hips (42.5%), and shoulders (22.5%) were the most frequently affected joints. Retrospective orthopaedic surgery data were collected for 151 subjects (52 children, 99 adults). Osteotomy was the most frequent surgery reported (n=108); joint replacements were recorded for adults only.

This is the largest set of orthopaedic data from XLH subjects collected to date. Longitudinal information collected during the 10-year Registry duration will generate real-world evidence which will help to inform clinical practice.

Authors acknowledge the contribution of all International XLH Registry Steering Committee members.

Introduction: The presence of low levels of vitamin D in osteoarthritic patients has been reported as a substantial problem. We are not aware of any previous studies that have assessed the function of osteoarthritic patients undergoing joint replacement who are vitamin D deficient. This may be an important factor infiuencing preoperative function and postoperative outcome. The aim of this study was to investigate whether low vitamin D levels are associated with functional deterioration in patients with osteoarthritis of the hip undergoing total hip arthroplasty.

Methods: We measured plasma 25-hydroxyvitamin D3 (25(OH)D3) levels in 62 consecutive Caucasian patients undergoing total hip arthroplasty for osteoarthritis. The patients were divided into two groups based on whether they were vitamin D sufficient or deficient. The groups were matched for age, gender and ASA grade.

Results: The prevalence of vitamin D deficiency in our cohort of patients was comparable to recent population-based studies performed in the UK. Patients with vitamin D deficiency had lower preoperative Harris hip scores (Mann-Whitney test, p = 0.018) and were significantly less likely to attain an excellent outcome from total hip arthroplasty (Chi-square test, p = 0.038). Vitamin D levels were found to positively correlate with both preoperative and postoperative Harris hip scores.

Discussion: Our results warrant further study of vitamin D deficiency in patients undergoing joint replacement as it is a risk factor for suboptimal outcome which is relatively simple and cheap to correct.