Peripheral Nerve & Brachial Plexus | Diagnosing the injury and urgency

A stretched nerve may keep its outer covering, so some function can remain and recovery may occur without surgery; severe stretch can damage even that covering. A completely cut nerve has both layers damaged, so fibers lose their pathway and surgery is often needed to restore continuity. Doctors distinguish them by careful neurologic examination, electrodiagnostic testing and, when needed, intraoperative nerve action potentials. Stretch injuries are often observed for three to five months because neuropraxic injuries may improve spontaneously; if no recovery occurs, exploration may be needed. Divided nerves are assessed for tension and tissue loss, which influence whether direct repair or grafting is considered by the surgeon in a case-specific plan.

In avulsion, the nerve is pulled from its attachment or bone margin; in rupture, traction divides the nerve but both ends remain visible. Root avulsion in brachial plexus injury is often accompanied by dural tearing and a cerebrospinal fluid leak with cyst formation called pseudomeningocele; sometimes the root is avulsed at its origin with an intact dural cone, called avulsion in situ. Because only the distal end is available, repair differs from a rupture where both ends can be joined, and planning depends on which end is available and on timing. Level 1 root avulsion is pre-ganglionic, while levels 2 to 4 are rupture injuries; nerve transfer is best within five months when only the distal end is available.

Peripheral nerve recovery depends on injury severity and time. Minor bruising or stretch injuries may recover satisfactorily, but satisfactory outcomes are usually limited to relatively minor injuries reflecting neurapraxia or axonotmesis; a fully cut nerve cannot recover on its own. Even after repair, regeneration is slow, about 1 mm per day, so distant targets wait longer. Delayed referral is common after iatrogenic nerve injury, and fewer than 40% of patients in two large retrospective studies had surgery within six months. If total muscle denervation exceeds 18 months, meaningful functional recovery is unlikely, although sensory improvement may still be possible for longer but diminishes with time. Age-related changes can also reduce regenerative capability.

Electrodiagnostic testing helps localize injury, estimate prognosis and identify possible donor nerves. Sensory conduction measurements are often more sensitive than motor ones for mild problems. Denervation changes may appear as early as ten days after surgery, but fibrillation and denervation potentials are useful only after at least three weeks of denervation. Serial studies can monitor axonal regeneration and reinnervation, yet signs of reinnervation do not guarantee useful clinical function. Nerve conduction studies can localize the injured segment, and variants of innervation may confuse findings, so clinical correlation is essential. They also document recovery after injury or repair. Working with the same electrophysiologist and a concise clinical summary helps tailor testing.

MR neurography can resolve nerve detail to about 0.3–0.5 mm and assess diameter, contour, fascicular pattern, continuity, signal and fat planes, helping distinguish milder stretch injury, partial nerve damage, or complete cut. Ultrasound is less costly and more accessible; in a cadaver study of 12 arms it detected transection with 89% sensitivity and 95% specificity, and it can show continuity, enlargement, transection, neuroma, hematoma or scar. However, ultrasound is operator-dependent, and MRI can be limited by metal artifact. Some data suggest ultrasound may be more sensitive than MRI for peripheral nerves, and it allows real-time, dynamic comparison with the opposite limb, but defined diagnostic cut-offs remain elusive. MRI and ultrasound can also relate nerve structure to electrophysiological findings.

Electromyography and nerve conduction studies are helpful adjuncts for localizing injury, predicting recovery and identifying possible donor nerves. Denervation changes may appear as soon as ten days after surgery, but findings are not reliable until about four weeks. Initial testing is often deferred until at least six to eight weeks after injury to assess axonal injury and root-level avulsion. Serial testing can then reveal nascent potentials and motor unit potentials, often before clinical recovery is evident. After a release procedure, repeat testing may show improvement in previously abnormal values, although return to normal values may not occur because remyelination produces thinner and shorter internodes.

Nerve fibers regrow at roughly 1 mm per day, so longer distances take longer. Muscle denervation begins soon after injury and reinnervation potential falls by about 1% per week; after about 12 months fibrosis, scarring and fatty infiltration can make recovery harder. Proximal injuries have farther to regenerate and generally worse outcomes than distal ones. Age, smoking, diabetes, hypothyroidism and vascular disease may also influence recovery. Reported successful functional recovery after repair ranges from 50% to 80%, depending on nerve and injury location. Electrodiagnostic studies at about three months may help assess prognosis after closed injury. Hand therapy supports recovery but does not replace timely assessment.

Denervation begins soon after nerve injury, and reinnervation potential decreases by roughly 1% per week. Atrophic changes in denervated muscle and changes around motor end plates can worsen functional outcomes after prolonged denervation. Functional reinnervation may still be possible within a critical window of about 12 to 18 months. Early repair can improve outcomes compared with delayed repair, and some surgeons advocate urgent brachial plexus exploration within 7 days for selected injuries. Absence of detectable motor unit action potentials on EMG at 3 months suggests a relatively poor prognosis. Nerve recovery after repair is unpredictable, with reported successful functional recovery between 50 and 80% depending on the nerve and injury location.

In a mixed nerve, motor and sensory fibers travel together, but they are not equally vulnerable. Motor and position-sense fibers are often more susceptible, while sensory fibers can be more robust, so loss may be incomplete from the outset. This motor-sensory dissociation means useful motor function can be lost while some sensation remains. A conduction block can make function look totally lost on day one, then sensibility may return as individual territories switch back on. Injury type matters: sharp clean cuts generally fare better than crush or avulsion injuries. Even with good treatment, some level of permanent dysfunction can remain.

Combined injuries can include single or multiple tendon injuries, blood-vessel damage and fractures, sometimes with extensive tissue damage or a contaminated wound. Such procedures must be carefully and meticulously done before nerve repair or reconstruction is prepared. Ideally, repair occurs in a well-nourished tissue bed of muscle or fat. Tendons may be repaired before vessels and nerves to restore preinjury elastic tension-length, which helps determine vessel repair length. Blood flow within the nerve matters, and re-establishing vascular networks is critical in nerve regeneration. Extensive debridement and cleaning may be needed before repair, and sharply transected nerves are easier to manage than crushed or avulsed ones.