Electromyography (EMG) is done using either surface or deep electrodes. Surface electrode studies are limited because of artifacts and poor muscle selectivity. The placement of deep electrodes is painful and thus poorly tolerated in children. Furthermore, EMG studies do not show the strength of contraction, only the electrical activity.
EMG is useful in evaluating peripheral nerve injuries, anterior horn cell degeneration, and diseases such as myotonia and myelitis. In peripheral nerve injuries, denervation causes fibrillation potentials 1–2 weeks after injury. During regeneration, the EMG will show polyphasic wave forms. In anterior horn cell degeneration, fasciculations appear.
Nerve Conduction Velocity
Nerve conduction velocity is measured by the time difference shown between the point of stimulation and the recording by EMG. Normal values change with age, from about 25 m/sec at birth to 45 m/sec at age 3 years to about 45–65 m/sec in mid-childhood. The peroneal, posterior tibial, ulnar, median, and facial nerves are usually studied. In children, perform these studies in evaluating peripheral and hereditary neuropathies.
Diagnostic blocks are most useful in children for evaluating incisional neuroma and for pain of unknown cause around the foot. By this means, it is possible to localize the site of pain precisely.
The biopsy is an important diagnostic procedure, but it is not always a simple process. It is preferable for the same surgeon to perform both the biopsy and any reconstructive or ablative procedures. Planning is important. Generally, open biopsy is routine, with needle biopsy performed for lesions in inaccessible sites such as vertebral bodies. Plan ahead with the lab to coordinate tissue removal [B and C], transfer solutions, frozen sections, and electron microscopic studies. Culture the lesion if there is even the remotest possibility of an infectious etiology.
Joint aspiration is diagnostic and sometimes therapeutic. These studies are indicated whenever an infectious etiology is possible.