Evaluating nerve injury and regeneration
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This document discusses the evaluation and assessment of nerve injuries. It outlines the important factors to consider in a patient's history and presentation including mechanism of injury, time since injury, and associated injuries. Sensory examination tools like the Tinel's sign and water immersion test are described to help localize the site and severity of injury. Nerve conduction studies and electromyography can further aid in distinguishing between conduction block and axonal degeneration and provide prognostic information. Imaging modalities like ultrasound and MRI are also discussed for visualizing nerve injuries.
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Evaluating nerve injury and regeneration
- 1. Evaluating nerve injury and regeneration Robert Yap Department of Hand and Reconstructive Microsurgery Singapore General Hospital
- 2. Approach to nerve injuries - history • Age • Occupation • Hand dominance • Background medical history • Mechanism of injury – the sharpness and width of the cutting object – the proportion of traction or crushing, and an estimate of the approximate force that was involved – and its duration of application. • The time of presentation since the accident • Associated injuries • Any previous history of nerve injury or neuropathy
- 3. Approach to nerve injury – presentation and examination • The early signs – – alteration or loss of sensibility – Impairment of function and sometimes pain. – weakness or paralysis of muscles – vasomotor and sudomotor paralysis – abnormal sensitivity over the nerve at the point of injury – Warm and dry skin
- 7. Water immersion test • In the child, uncooperative or unconscious patient – Hand immersed in water at 40°C – Innervated finger tips wrinkle within 4 minutes – Positive test - absence of puckering of a finger.
- 8. Tinels sign –it’s significance • Tinel (1915, 1917) - “growing point” of the regenerating axons signalled by the production of paraesthesiae by tapping over the course of the nerve • The sign can help determine – Site of injury – Severity of injury – Whether a nerve suture has succeeded or failed – Whether regeneration is rapid and satisfactory, or reduced to a few insignificant fibres » Clinical Aspects of Nerve Injury; R. Birch, Surgical Disorders of the Peripheral Nerves
- 9. Interpretation of the tinel’s sign • Strongly positive over a lesion soon after injury - rupture of axons or severance of the nerve • The centrifugally moving Tinel sign- persistently stronger than that at the suture line - axonotmesis or after repair which is going to be successful, • Tinel sign at the suture line remains stronger than that at the growing point - repair which is going to fail • Failure of distal progression the Tinel sign in a closed lesion indicates rupture or other injury not susceptible of recovery by natural process
- 10. Eliciting the Tinel’s Sign • Finger percusses along the course of the nerve from distal to proximal • The patient is asked if he elicits a wave or a surge of pins and needles or abnormal sensations • The level of the sign should be measured from a fixed point - tip of the coracoid, the medial or lateral epicondyle and the styloid process of the radius • Regeneration demonstrated by centrifugal progression of the sign which becomes progressively stronger at the distal level
- 12. value of a static or advancing Tinel sign in predicting recovery in degenerative lesions after closed injury Clinical Aspects of Nerve Injury; R. Birch, Surgical Disorders of the Peripheral N
- 14. Nerve Conduction Studies and Electromyography in the Evaluation of Peripheral Nerve Injuries
- 15. NCS & EMG • essential in the evaluation of nerve disorders • localizing the site of injury • distinction of conduction block from axonal degeneration • prognostic information • dependent on the skills of the examiner • Augment physical examination
- 17. Investigations – NCS . • Amplitude, conduction velocity, latency – Health of axons – About their myelination – Whether there is continuity between the exposed nerve and the spinal cord. • Conduction across lesion - some of the axons are intact. • Some conduction for some days after transection - wallerian degeneration not complete.
- 18. Investigations - EMG • Fibrillation potentials - earliest electromyographic signs of muscle denervation –Onset depends on the distance between the site of the nerve lesion and the muscle. –10 to 14 days • Spontaneous activity in muscle 2-6 weeks
- 21. Imaging • US and MRI -most used • Ultrasound -inexpensive and safe – Reliable visualization of nerve injury - axonal swelling, neuroma formation, and partial laceration- high correlation with intraoperative findings – Extensive edema and/or obesity can be can limit diagnostic accuracy » Toros T et al. Evaluation of peripheral nerves of the upper limb with ultrasonography: a comparison of ultrasonographic examination and the intra-operative findings. J Bone Joint Surg Br. 2009 Jun;91(6):762- 5.
- 22. • MRI can provide resolution of fascicular patterns and can demonstrate nerve edema. • Can differentiate neurotmesis from high- grade axonotmesis. – Grant GA et al. The utility ofmagnetic resonance imaging in evaluating peripheral nerve disorders. Muscle Nerve.2002 Mar;25(3):314-31
- 23. Thank You
Editor's Notes
- A history of trauma to the upper extremity that results in an open wound, crush injury, or traction injury is all it takes to raise the suspicion of injury to a peripheral nerve. As noted previously, the mechanism of injury determines how much degeneration occurs in the proximal segment. It also gives clues as to whether to anticipate a nerve tissue deficit. It is important, therefore, to determine is also information that should be obtained from the patient. Most nerve injuries are seen within the first 24 hours, but, for a variety of reasons, many injuries do not present until much later. Delayed presentation means there is scar tissue at the nerve ends and suggests the possibility of intractable nerve retraction. In addition, return of motor function may be extremely poor, depending on the level of injury and the length of time that the muscle has been denervated.
- Periphrela nerve injuries. Birch One almost infallible sign is always present in the first 48 hours after deep injury to a nerve with a cutaneous sensory component: because of the involvement of small as well as large fibers,
- In the upper extremity, three key organelles provide sensory input: Merkel cells, Meissner's corpuscles, and pacinian corpuscles. Merkel cells, which are located in the dermoepidermal juncture, are slowly adapting sensory receptors that possess a small, discrete field well-suited to two-point testing. As a result, these organelles respond best to constant touch or pressure. Meissner's corpuscles are located in the dermal papilla and are abundant in the fingertips. They are maximally sensitive to vibration at 30 cycles/second (cps). As rapidly adapting sensory receptors, they are best designed for detecting rapidly changing stimuli, such as moving two-point discrimination. Pacinian corpuscles are rapidly adapting sensory receptors present in the subcutaneous tissue throughout the body. They respond maximally to a stimulus of 250 cps and have a large receptive field up to 2 to 3 cm. The slowly adapting receptors (Merkel cell neurite complex and Ruffini end-organs) respond to static touch, whereas the quickly adapting receptors (Meissner and pacinian corpuscles) respond to moving touch. The threshold and tactile discrimination of the quickly and slowly adapting receptors can be evaluated. Threshold is the minimum stimulus required to elicit a response and is assessed with vibration thresholds (quickly adapting receptors) and with cutaneous pressure thresholds (slowly adapting receptors). Tactile discrimination reflects the number of innervated sensory receptors and is assessed with moving and static two-point discrimination. Vibration and cutaneous pressure thresholds will permit quantification of the early changes that occur with chronic nerve compression. Changes in sensory receptor innervation density will occur in the later stages of chronic nerve compression, and therefore two-point discrimination measures will become abnormal only in the more severe stages of nerve compression.
- As far as possible, sensation to light touch and pinprick, vibration sense, and position sense should be tested, and the area of skin affected should be recorded. The timing of the response to pinprick should, if possible, be noted. Anhidrosis is easily perceptible; vasomotor paralysis is shown by warming of the skin and, in the fingertips, by capillary pulsation as well as by changing color. Trumble Threshold testing determines the level of stimuli necessary to elicit a response. Threshold is the minimum stimulus required to elicit a response and is assessed with vibration thresholds (quickly adapting receptors) and with cutaneous pressure thresholds (slowly adapting receptors). Tactile discrimination reflects the number of innervated sensory receptors and is assessed with moving and static two-point discrimination. Vibration and cutaneous pressure thresholds will permit quantification of the early changes that occur with chronic nerve compression.It is useful for nerve compression syndromes, in which a normal number of functioning sensory receptors have depressed levels of activation.[23] One may conduct threshold testing with either Semmes-Weinstein monofilaments, which are fine filaments that exert a discrete amount of pressure on the fingertips, or vibration testing that ranges from 30 cps (low frequency) to 256 cps (high frequency). Density testing, done with moving two-point and static two-point tests, relies on the concept that an area must possess a minimum number of functioning sensory end organs to discriminate between two stimuli.[24] Because interpreting sensory input and reliably distinguishing a two-point stimulus require considerable cortical reinnervation, these tests are best suited for patients who have achieved almost complete sensory recovery. The empiric testing is an inherently subjective method that was devised by the British Medical Research Council (BMRC) during World War II for testing in nerve injury. It gives qualitative information about sensory loss and muscle recovery by means of clinical examination, but the inherent observer variability among examinations prevents the development of reliable standards. In this system, sensory recovery is graded as shown in Box 15-1. In this classification, A proper digital nerve injury will result in an isolated sensory deficit along the radial or ulnar aspect of the thumb or digit. Static 2-point discrimination (S2PD) and moving 2PD (M2PD) testing will be greater than 25 mm on the affected side(s, which is equivalent to a complete sensory loss. Normal S2PD is 6 mm or less, whereas 15 mm is equivalent to a loss of protective sensation. Semmes Weinstein monofilament (SWM) testing will be greater than 6.65 These nylon monofilaments vary in diameter and thus differ in application force and produce different pressure thresholds. The set of Semmes-Weinstein monofilaments increases in diameter on a logarithmic scale (log10 force of 0.1 mg). The examiner applies pressure with each successive nylon filament until the filament just begins to bend. The smallest monofilament that the patient can perceive is documented as the pressure threshold. Each monofilament size is associated with a grading of sensory impairment (normal, diminished light touch, diminished protective sensation
- (1) a strongly positive Tinel sign over a lesion soon after injury indicates rupture of axons or severance of the nerve; (2) in favorable degenerative lesions (axonotmesis) or after repair which is going to be successful, the centrifugally moving Tinel sign is persistently stronger than that at the suture line; (3) after repair which is going to fail, the Tinel sign at the suture line remains stronger than that at the growing point; (4) failure of distal progressionthe Tinel sign in a closed lesion indicates rupture or other injury not susceptible of recovery by natural process; (5) a positive Tinel sign means the lesion is degenerative, not a ofconduction block for, at least, a significant number of axons within the nerve. It is important always to remember Tinel’s own advice that a positive sign should not be confused with the “hypersensitivity seen in some cases of neuralgia” (Tinel 1917). The Tinel-like sign elicited by percussion over schwannoma or over nerves in the early stages of entrapment neuropathy, such as the ulnar nerve at the elbow or the median nerve at the wrist, does not indicate that axons have been ruptured, rather that nerve fibres have become sensitised because of focal demyelination and changes in the expression of voltage gated ion channels at the level of lesion.
- initial studies at 7 to 10 days may be useful at localization and separating conduction block from axonotmesis. On the other hand, when clinical circumstances permit waiting, studies at 3 to 4 weeks postinjury will provide much more diagnostic information, because fibrillations will be apparent on needle electromyography (EMG). greens
- 24. 25.. 26. McDonald CM, Carter GT, Fritz RC, Anderson MW, Abresch RT, Kilmer DD. Magnetic resonance imaging of denervated muscle: comparison to electromyography. Muscle Nerve. 2000 Sep;23(9):1431-4.