The aim of our study is to investigate the effects of emicizumab treatment on the musculoskeletal system in children with hemophilia A.

Hemophilia is a rare inherited coagulation disorder resulting from a deficiency of factor (F) VIII or IX. It is a chronic group of diseases that primarily manifests as intra-articular (hemarthrosis) and intramuscular (hematoma) bleeding and affects quality of life. Easy ecchymosis formation in early childhood, especially spontaneous intra-articular and intramuscular bleeding, and a history of bleeding lasting longer than expected after interventions and trauma should raise the suspicion of hemophilia. The severity of bleeding findings is directly related to the degree of FVIII or FIX deficiency. While the clinical picture varies depending on the duration and frequency of bleeding, the severity of the disease is classified as severe (<1% IU dL-1), moderate (1%-5% IU dL-1), and mild (5%-40% IU dL-1). Hemophilia A occurs in 85% of the population (1 in 5,000 male births), while this rate is 15% in Hemophilia B (1 in 30,000 male births). Treatment of hemophilia is primarily divided into treatment of acute bleeding and prophylaxis. The primary goal in the treatment of acute bleeding is to achieve hemostasis within the first two hours after the onset of symptoms. Patients often recognize a bleeding episode by a tingling sensation or an "aura" before the bleeding begins. In such cases, factor replacement therapy should be administered immediately. In a patient presenting with severe acute bleeding, after determining the location and severity of the bleeding, factor VIII or factor IX and high-dose clotting factor concentrate (CFC) are administered. Factor concentrate doses should be 50 IU/kg factor VIII or 100-120 IU/kg factor IX. Even if bleeding slows or stops, CFC should be administered to maintain healing. Frequent measurement of factor levels should be performed to ensure that desired levels are maintained. Acetylsalicylic acid (ASA) and nonsteroidal anti-inflammatory drugs (NSAIDs) should be avoided during pain management due to their effects on platelet function and increased risk of bleeding. Prophylaxis treatment includes treating acute bleeding as well as replacing the missing factor in cases where there is no bleeding. Prophylactic treatment has many advantages. Prophylaxis is generally initiated at an early age to prevent and reduce the risk of joint bleeding and the development of hemophilic arthropathy. Dosing is personalized and adjusted according to the severity of bleeding. It protects joint health by reducing hemarthrosis episodes and reduces the need for joint surgical interventions. Prophylactic factor replacement in hemophilia treatment is administered two or three times a week via intravenous infusion. Emicizumab, one of the alternative pharmacological treatments developed in recent years, is a subcutaneous treatment method that provides patients with access to the medication within clinical and financial healthcare services in Turkey as of May 2025. Emicizumab, Fitusiran, and Concizumab, both inhibit natural anticoagulant pathways. With these subcutaneous treatments, injection frequency can vary depending on the molecule, but can be daily, weekly, or monthly. One of the most important advantages of these treatments is their effectiveness in the presence of alloantibodies, which are a significant cause of morbidity and mortality in hemophilia. Treatment features such as reduced injection frequency of factor replacements administered subcutaneously, eliminating the need for intravenous infusions, and increasing physical activity opportunities are thought to produce significant benefits affecting quality of life, in addition to controlling and preventing bleeding. Therefore, new drugs that promise less bleeding with fewer and more comfortable injections are quite attractive. It is believed that reduced bleeding will equally reduce musculoskeletal damage, support improved joint health, and increase the individual's level of functionality, resulting in improved quality of life by ensuring independence in daily life. Improved musculoskeletal health and independence in daily life will increase children's exercise habits. The positive contributions to the musculoskeletal system, such as increased overall muscle mass and maintenance of joint health, will also increase the effectiveness of physiotherapy programs. There are no other studies examining the effects of this newly introduced drug on the musculoskeletal system in children in Turkey. Therefore, the aim of our study was to investigate the effects of emicizumab treatment on the musculoskeletal system in children with hemophilia A.

Inclusion Criteria:

• Children who are under 18 years of age,
• Have been diagnosed with Hemophilia A by a physician,
• Have a factor level of 1% (IU) or less,
• Have inhibitors positive or negative,
• Have no obstacles to starting subcutaneous (emicizumab) treatment,
• Willing to participate in the study

Exclusion Criteria:

- Children with a history of cerebrovascular bleeding who present any neurological findings that would prevent participation in the study

Because hemophilia A is an X-linked recessive disease, girls are carriers and boys are affected by the disease. Therefore, the study population consists of boys.

Male patients under 18 years of age diagnosed with hemophilia A will constitute the study population.