You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Bisphosphonates and risk of subtrochanteric, femoral shaft, and atypical femur fracture: A systematic review and meta-analysis. While there is strong evidence that bisphosphonates prevent certain types of osteoporotic fractures, there are concerns that these medications may be associated with rare atypical femoral fractures (AFF). Recent published studies examining this potential association are conflicting in regards to the existence and strength of this association. We conducted a systematic review and meta-analysis of published studies examining the association of bisphosphonates with subtrochanteric, femoral shaft, and AFF. The random-effects model was used to calculate the pooled estimates of adjusted risk ratios (RR). Subgroup analysis was performed by study design, for studies that used validated outcome definitions for AFF, and for studies reporting on duration of bisphosphonate use. Eleven studies were included in the meta-analysis: five case-control and six cohort studies. Bisphosphonate exposure was associated with an increased risk of subtrochanteric, femoral shaft, and AFF with adjusted RR of 1.70 (95% CI 1.22-2.37). Subgroup analysis of studies using the ASBMR-criteria to define AFF suggests a higher risk of AFF with bisphosphonate use with RR of 11.78 (95% CI 0.39-359.69) as compared to studies using mainly diagnosis codes (RR 1.62, 95% CI 1.18-2.22), although there is a wide confidence interval and severe heterogeneity (I(2) =96.15%) in this subgroup analysis. Subgroup analysis of studies examining at least 5 years of bisphosphonate use showed adjusted RR of 1.62 (95% CI 1.29-2.04). This meta-analysis suggests there is an increased risk of subtrochanteric, femoral shaft, and AFF among bisphosphonate users. Further research examining the risk of AFF with long-term use of bisphosphonates is indicated as there was limited data in this subgroup. The public health implication of this observed increase in AFF risk is not clear. © 2013 American Society for Bone and Mineral Research.
{"Chemical": ["bisphosphonates", "bisphosphonate", "Bisphosphonate", "Bisphosphonates"]}