Intramuscular Injections: Anatomical or medical reason for administering injections on the Arm or Buttocks?

What’s the reason or advantage in doctors preferring to choose a certain part of the body for giving injections to a patient, over others? Is it less painful, or is there a reason tied in with human anatomy and physiology?

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  • That’s because of the concentration of blood available in that area (large muscle areas rich in blood) which helps in rapid absorption of the injected dose into the body. Hence the arm and the butt for what’s called intramuscular injections.

    Anatomically speaking, the gluteus medius muscle is considered the safest area to adminsiter intramuscular injections to a person or patient. Following that is the vastus lateralis muscle (lateral thigh) and the deltoid muscle (shoulder).

    Care must be taken to avoid large nerves while administering such injectons. Specifically the radial nerve in the arm and the sciatic nerve near the femur.

  • As I understand it, specific locations for IM injections are chosen for primarily anatomical reasons, specifically the unlikelihood of accidentally hitting an important structure such as a blood vessel or nerve, or non-muscular tissue. Some practitioners prefer different areas over others based on their own personal confidence in locating it properly as well.

    The reasons for using IM infection over subcutaneous or IV are mainly physiological (absorption is somewhere between the other two methods, and some medications will irritate subcutaneous tissue but not muscle). It’s also faster to infect than IV.

  • Intramuscular injections are administered in the deltoid muscle of arm & gluteus maximus muscle of buttock.
    Following are the reasons of choosing these muscles over others.
    1) Vast volume
    2) Can be easily exposed
    3) Gets motor nerve supply from inside
    4) Neurovascular structures lay very deep

    At first these criterias should be fulfilled before using a muscle for Intramuscular injections.
    Now lets discuss individual points.
    1) Both the muscles are largest muscles of respective areas. Deltoid muscles covers shoulder joint from all the sides & gluteus maximus covers the hip posterioly & laterally.
    2) Both the areas can be easily exposed.
    3) Deltoid muscle gets its motor supply from axillary nerve(posterior division of ventral rami of C5 & C6) & gluteus maximus is innervated by inferior gluteal nerve(L5, S1, S2). Both the nerves innervate respective muscle from inside, not superficially so chance of injury is less.
    4) Axillary nerve & vessels with its branches lie deep to Deltoid muscle, superior & inferior gluteal nerves, sciatic nerve, gluteal vessels, ascending branches of lateral & medial circumflex femoral vessels lie deep to gluteus maximus. As they are large & wide muscles, chances of neurovascular structure injury becomes less.

    No other superficial muscle can fulfil all the four criterias except Deltoid & gluteus maximus so they are used for Intramuscular injections.

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