In addition to the well-known toxicological harms of intravenous drug (IVD) use, there can also be local tissue complications, including infections, venous sclerosis, tissue necrosis, and drug needle fragment retentions. Drug needle fragments in subcutaneous tissue may cause local symptoms (usually pain and infections), but they have also been identified as causing emboli to organs. The literature has described numerous case reports of people who inject drugs (PWIDs) and have retained needle fragments. The prevalence of the condition is not known, and the researchers therefore aim to perform the first cross-sectional study of PWIDs to estimate how common needle fragment retentions are and what their risk factors are in this population.

The clinical significance of retained needle fragments remains unknown. Needle retentions can be asymptomatic, cause local symptoms, and can sometimes even lead to dangerous complications such as needle emboli to the heart or lungs. The most common injection sites are likely the peripheral veins of the arms. However, continuous IVD use leads to vein sclerosis, and patients with long-term use may therefore also use peripheral veins of their lower limbs and even the central veins of the groin or neck. Subcutaneously retained needles can pose a risk of needlestick injury to medical staff during clinical examination and treatment procedures. Unrecognized retained needles can also cause hazards during magnetic resonance imaging.

The study protocol received a positive review from the Tampere University Hospital Ethics Committee (study code: R22037). The researchers subsequently received the organizational permissions necessary to conduct the study. PWIDs will be asked to give written informed consent prior to any study procedures. Participants will be asked to fill in a questionnaire about their basic information, drug use history, previous injection sites, and whether they have had any local complications due to injecting drugs. After the completion of the questionnaire, participants will undergo targeted X-ray imaging of the injection sites. As metallic objects, needle fragments can be visualized with standard X-ray imaging. Female participants of childbearing potential (< 50 years) will undergo urine sample pregnancy testing prior to X-ray imaging. A pilot study with 20 participants will be conducted first. Experiences from the pilot will be used to refine the study protocol if needed. If modifications are made, they will be subjected to ethics review and will be provided on ClinicalTrials.gov. After the pilot study, the researchers aim to recruit an additional 80 patients (totaling up to 100 participants).

Our research questions are 1) What is the prevalence of radiologically confirmed needle retention among PWIDs*? The secondary research questions are

1. Do patient-reported symptoms and the suspicion of a retained needle fragments correspond to radiologically confirmed needle retention?
2. What are the predisposing factors to needle fragmentation?
3. Have PWIDs sought medical attention prior to the study for possible symptoms in the injection sites?
4. How frequently are verified needle fragments surgically removed within five years after their detection, and are verified needle fragments a proxy or a risk factor for mortality? *As only patients in outpatient care will be recruited, the sample is not entirely representative of all PWIDs in the study area (e.g., people who are hospitalized or imprisoned are not recruited).

Inclusion Criteria:

• History of intravenous drug use
• Current treatment of the drug abuse problem at a local low-threshold drug abuse service unit or primary health care centre.
• Adherence to fill in the questionnaire
• Participation to X-ray imaging of injection sites

Exclusion Criteria:

• No history of intravenous drug use
• Does not adhere to fill in the questionnaire or refuses X-ray imaging
• Pregnancy
• Underage (18 years old)

The population base is the adult IVD users from the drug abuse treatment centres in Tampere, Finland.

No plans to share individual-level data with other investigators.