ANATOMIC GUIDANCE METHODS
Anatomic guidance techniques rely on surface anatomy, knowledge of cross-sectional anatomy, palpation, and passive or active range of motion (PROM, AROM). The majority of anatomic reference guides used by physicians when performing BoNT injections were not developed for this purpose. These atlases were written to guide needle placement for diagnostic EMG procedures (11-13). While these texts may be useful for BoNT injections, they have limitations both for their original purpose and when used to guide BoNT injections. More recently, two anatomic atlases were published specifically for BoNT and/ or other chemodenervation procedures (14-16).
Once a muscle or muscles have been localized using a combination of surface anatomy, palpation, and PROM or AROM, the skin is disinfected and cleansed as per the physician or institution's protocol. Standard single-use hypodermic needles are used for the injection. Needle size and length are determined by the estimated depth of the muscle. For superficial muscles, a 30 g, 1-inch needle may be sufficient, for deeper muscles 26 to 27 g, 1- to 1.5-inch needles or even a 25 g, 2.5- to 5-inch spinal needle may be required.
Surface anatomy and/or cross-sectional reference guides, hypodermic needles of various lengths, and other injection supplies (gloves, skin cleansers, gauze, band aids/plasters).
ADVANTAGES AND LIMITATIONS OF ANATOMIC GUIDANCE FOR BoNT THERAPY
• All physicians receive training in anatomy in medical school.
• Most physicians have access to a variety of anatomic reference guides and are familiar with their use, and the guides are relatively inexpensive.
Anatomic simulators can provide physicians with detailed information about orientation and function of muscles.
• A physician's training in the anatomy lab and therefore his or her last review of gross anatomy may have been many years ago.
• Positioning: When treating patients with spasticity, positioning the patient as described in reference guides may be challenging, at best or may be unfeasible. When the patient is not positioned as described in the reference guide, the recommended site for needle insertion into the target may be incorrect. This limits the use of reference guides when performing BoNT injections in many patients.
• Even when used to guide diagnostic EMG, as they were designed to do, studies of the accuracy of surface anatomy and/or reference guides has been called into question, see Evidence discussion.
• Palpation and surface anatomy: While a few muscles may be easily identified by their surface anatomy and/ or by using palpation, it may be difficult or impossible to correctly identify many muscles including:
- Muscles of the neck or forearm where complex overlapping may make it difficult to correctly identify a target muscle
- Deeply situated muscles in the limb or neck; where it may be impossible to palpate the target muscle and/ or estimate muscle depth
- Obesity obscures surface landmarks or palpation of the target muscle and limiting depth/location estimation
- Disuse atrophy or atrophy caused by repeated BoNT injections may limit estimation of muscle depth
- Patients in whom spasticity has caused anatomic rearrangements or deformities
- Postoperative muscle changes following lengthening or transfers
- Patient cooperation
Evidence supporting or refuting the use of anatomic guidance for BoNT injections: There is an increasing body of evidence that calls into question the practice of relying solely on anatomic guidance when performing BoNT injections.