Stuart D. Miller, Blake L. Ohlson, and Michael Scherb
DEFINITION
Nerves in the peripheral limb are at risk for damage by direct contusion, by stretch injury, and by iatrogenic insult.
Nerve pain can be severe and crippling.
Sensory nerves are expendable in many cases and most patients adapt well to removal.
The resected proximal end of a nerve will usually form a neuroma as new growth seeks to reconnect with the distal nerve; thus, attempts to bury the nerve into a safe haven are desirable.
ANATOMY
There are five sensory nerves in the foot and ankle, but anatomic variability is common.
The tibial nerve splits into medial and lateral plantar nerves (this is mixed motor as well).
The saphenous nerve is an extension of the femoral nerve, found along the lesser saphenous vein.
The deep peroneal nerve lies along the anterior tibia with a neurovascular bundle, passes under the extensor retinaculum, and innervates the first web space. It has some muscle components to the flexor hallucis brevis muscle and some innervation to the sinus tarsi as well.
The superficial peroneal nerve, with the peroneal muscles, emerges from the peroneal retinaculum to innervate the dorsum of the foot. The terminal medial branch, the dorsomedial cutaneous nerve, is at risk with bunionectomy along the dorsomedial hallux.
The sural nerve runs superficial to the gastrocnemius muscle and then between the peroneals and the Achilles tendon to innervate the lateral foot and two toes.
PATHOGENESIS
Nerve injuries are most commonly iatrogenic.
Arthroscopic ankle lateral portal placement risks damage to the superficial peroneal nerve.
FIG 1 • Saphenous nerve neuroma at site of previous ankle fracture open reduction and internal fixation.
Lisfranc fracture open reduction and internal fixation (ORIF) or second metatarsal–cuneiform arthrodesis procedures will challenge the superficial and deep peroneal nerves in the midfoot.
Bunion procedures threaten the dorsomedial cutaneous nerve, a distal branch of the superficial peroneal nerve.
Calcaneal ORIF and fifth metatarsal ORIF incisions risk damage to the sural nerve in the foot.
Achilles tendon procedures and Haglund resections can damage the sural nerve and especially a posterior branch of that nerve.
Ankle fracture ORIF risks damage to the saphenous nerve medially (FIG 1), and the superficial peroneal nerve runs a variable course in front of the fibula laterally.
Nerves can be damaged in a stretch injury (FIG 2). The stretch usually involves a pathologic extreme of motion as might be seen with ankle fracture5 or with ligament sprain.4
NATURAL HISTORY
Neuromas can behave in a variety of ways, from a small benign bulb neuroma (FIG 3) to a massive accumulation of angry hypersensitive nerve endings.
Stretch injuries can cause dysfunction resulting in decreased sensation, in hypersensitivity, or even in severe pain with independent nerve signal generators.
Some nerve injuries will heal with a slow distal progression of symptoms.
Most nerve injuries are unpredictable in their natural course.
PATIENT HISTORY AND PHYSICAL FINDINGS
Examination of these nerve injuries requires understanding of natural anatomy.
The nerves in the foot and ankle do not read the textbooks, and deviations from expected course are common.
FIG 2 • Superior peroneal nerve adherent to muscle and fascia after severe stretch injury.
FIG 3 • Small nonpainful bulb neuroma from superior peroneal nerve buried in muscle.
Nerves can suffer a stretch injury, especially the superficial peroneal nerve with severe ankle inversion due to sprain or fracture. The sural nerve can also be at risk with this injury.
The saphenous nerve is especially at risk with contusion, as are all of the nerves, especially the deep peroneal nerve with a dorsal foot injury.
Iatrogenic injury remains the most common form of nerve injury in the foot and ankle.
Prior surgical intervention can result in confusing symptoms.
Many nerve injuries are initially misdiagnosed. The nerve can often be suspected when the skin or subcutaneous tissues are hypersensitive (or hyposensitive) rather than the deep tissues.
One of the best physical diagnostic findings is a nerve block using lidocaine hydrochloride (1% or 2%), Marcaine hydrochloride (0.5%), and a few drops of sodium bicarbonate solution in a mix. The bicarbonate acts to titrate the acidity of the local anesthetic and ease the burning pain of administration. The physician should return a few minutes after the injection to reexamine the patient rather than having him or her report on the effect of the injection at the next office visit.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Routine radiographs may provide evidence of mechanical imbalance, mechanical irritation (cyst or tumor), or osteophyte formation to suggest nerve entrapment.
MRI helps to define any soft tissue irritation and helps to rule out impinging structures such as tumor or cyst. The MRI also helps the diagnostician by illuminating areas of inflammation. An exception is interdigital neuroma, for which MRI has proven less accurate.
Electrodiagnostic studies can help differentiate between local and more proximal nerve pathology. Cervical spine or lumbosacral impingement as well as more generalized neuropathies can masquerade as local phenomena.
Electrodiagnostic studies are not helpful with interdigital neuroma or many small sensory nerves.
Electrodiagnostic studies should be performed in patients suspected of having tarsal tunnel syndrome. Sensory nerve conduction velocity may approach 90% sensitivity.
DIFFERENTIAL DIAGNOSIS
Degenerative disc disease, disc herniation, radiculopathy
Peripheral neuropathy
Leprosy
Diabetic neuropathy
Peripheral vascular disease
Tarsal tunnel syndrome
Joint arthrosis or synovitis
Tenosynovitis
Giant cell tumor of the tendon sheath
Intrinsic nerve damage, crush injury
Rheumatoid arthritis
Ganglion cyst
Lipoma
Neurilemmoma
Abscess or infection
Fracture
Malalignment (varus or valgus foot or ankle)
Plantar fasciitis
NONOPERATIVE MANAGEMENT
Physical support to the limb
Observation often allows a nerve to regenerate, heal, and resume its normal sensitivity.
Periods of immobilization in a short-leg cast or walking boot may allow neuritic symptoms to subside, especially when traction causes pain.
Braces and splints can provide added stability and prevent recurrent stretching injuries, especially to the superficial and deep peroneal nerves.
Tarsal tunnel symptoms caused by mechanical imbalances—such as acquired pes planus secondary to posterior tendon dysfunction—may be alleviated with orthotic devices that restore foot balance.
Multiple forms of pharmacologic intervention exist:
Nonsteroidal anti-inflammatories
Narcotics (caution must be exercised due to addiction potential, especially with chronic nerve pain)
Neuromodulators can help quiet nerve response.
Anticonvulsants such as pregabalin, gabapentin, or tricyclics often quiet nerve hypersensitivity.
Clonazepam and similar benzodiazepines may lessen nerve reactivity.
A variety of newer medications may be helpful; thus, referral to a pain management specialist often aids in complete patient care.
Lidoderm patches: Applied directly over the symptomatic area, lidocaine hydrochloride is released in a time-dependent manner through the skin.
Neuromodulators and local anesthetics and nonsteroidals in an absorbent gel for topical application; these creams can be found in compounding pharmacies.
Steroid injection, combined with local anesthetic, may serve a dual role as both therapeutic and diagnostic agent.
While sometimes useful, symptomatic relief is often temporary.
Injections should be limited to no more than two in a 1-year period.
Risks include skin discoloration, tendon rupture, atrophy of subcutaneous fat, and collateral ligament attenuation.
Ethanol injections: 4% ethanol in a Marcaine solution has been used for interdigital neuroma treatment.
The ethanol has been anecdotally useful for postincisional neuroma pain.
The Morton neuroma protocol involves four injections a week apart, followed by three more injections similarly timed if partial improvement is noted.
The benefit, besides avoiding at trip to the operating room, entails loss of nerve conduction without formation of postresection neuroma.
SURGICAL MANAGEMENT
The decision to embark on surgical manipulation of persistent nerve pain often entails complex decision making. The resection of a nerve remains essentially a “one-way street,” and careful discussion helps alleviate confusing results. Issues surrounding nerve ending regrowth and possible neuroma formation are dealt with easily later if they are understood preoperatively.
Motor nerves can be sectioned but at a higher cost. The motor loss of the deep peroneal nerve branches is relatively well tolerated, while the posterior tibial nerve governs much more muscle activity in the foot. The posterior tibial nerve has been resected only in salvage procedures as a precursor to possible amputation if unsuccessful. Some surgeons continue to manage these problems with implantable nerve stimulators.
Preoperative Planning
The preoperative planning includes patient education, careful patient evaluation, and decisions regarding the location of nerve burial. The final location of the proximal end of the nerve may be tender; thus, resection of the saphenous nerve just above the ankle in a patient who wears boots that may hit this level would be less desirable and a more proximal burial site would be advised.
The best preoperative indicator of success remains the patient's response to a local anesthetic block. The surgeon should confirm the location of the nerve tenderness and further discuss postoperative expectations.
Instrumentation is relatively simple. Appropriate retractors make the job easier, as does a small drill, a 2.5-mm and a 3.5-mm drill bit, and drill sleeves for creation of the bone hole.
A tourniquet should be available but is often not used in order to better visualize the vessels accompanying the nerve. Under tourniquet, the vessel and the nerve can look very similar; thus, examination of the cross-section of the presumed nerve is essential at the time of surgery. Even the most experienced surgeons have been fooled by a vein impersonating the nerve: better to know at surgery than to be told by the pathologist the next day.
If a patient had reflex sympathetic dystrophy or a complex regional pain syndrome involved with the leg, then consideration should be given to performing the surgery under epidural anesthesia. In theory, the diminution of painful stimulation may diminish the chance of triggering further hypersensitivity reactions.
Positioning
Positioning depends on the location of the neuroma.
The saphenous nerve is best explored with the patient supine and the leg externally rotated.
The superficial and deep peroneal nerves are best approached with the patient positioned supine. A rolled towel placed beneath the ipsilateral hip may facilitate exposure.
Sural nerve exposure often requires use of a rolled towel beneath the ipsilateral hip to provide better access to the nerve as it courses posteriorly. Currently, due to resection of the sural nerve very proximally in the leg, the patient is positioned in a semilateral decubitus position with the use of a beanbag.
Approach
While each nerve dictates the appropriate surgical approach, a basic extensile exposure, following the line of the neurovascular structures, seems ideal.
The incision is made with a scalpel and deeper dissection is usually performed with dissecting scissors. The variability of several nerves, especially the superficial peroneal nerve, warrants careful exposure and identification.
The nerve can be fully exposed and separated from the vessels before resection and burial.
If burying the nerve into bone, the surgeon should expose the area of bone to receive the nerve, incising the periosteum and drilling the appropriate hole.
TECHNIQUES
SURAL NERVE RESECTION AND BURIAL
Regional or general anesthesia may be used.
A local block is performed along the course of the nerve.
A tourniquet may help with exposure, but the vein and branches are better identified without.
The sural nerve, perhaps the easiest to find, has anecdotally proved difficult postoperatively with nerve regrowth. The current choice for burial is very proximal in the leg.
The lesser saphenous vein serves as a key landmark in the posterior leg as it courses alongside the sural nerve. The nerve does not possess a lumen.
Begin the incision just distal to the point of maximal tenderness and carry it proximally along the posterolateral ankle and posterior leg.
Dissection usually proceeds distal to proximal (TECH FIG 1).
TECH FIG 1 • Progressive incisions made along the course of the sural nerve.
Several skip incisions, usually three or four, can be made along the course of the nerve.
These skip incisions can be avoided with one long incision, depending on the patient's preferences (TECH FIG 2).
Identify the nerve proximally beneath the gastrocnemius fascia.
Tension is placed on the proximal end of the nerve while it is sharply cut in an oblique fashion and allowed to retract into the surrounding tissues.
TECH FIG 2 • A long sural nerve harvest.
The resected nerve is usually quite long (TECH FIG 3).
Electrocautery may also be used on the distal fragments to prevent nerve regeneration via production of neurotrophic signals.
Subcutaneous and skin sutures are usually bioresorbable to avoid any irritation in neuritic patients.
TECH FIG 3 • A long incision exposing the sural nerve with a neuroma at its end.
DEEP PERONEAL NERVE RESECTION AND BURIAL
The deep peroneal nerve runs along the anterior border of the distal tibia; thus, the bone offers a fine burial site for the proximal nerve ending.
A straight anterolateral incision over the distal lateral border of the tibia works well; in cases of simultaneous superior peroneal nerve resection, a curved-S incision from this site more proximal and posterior allows an easy dual procedure.
Incise the superficial retinaculum over the extensors in line with the incision and bluntly separate the muscles. The deep peroneal nerve usually lies between the extensor digitorum longus and the extensor hallucis longus muscles. Two large anterior tibial veins and the artery are close by the nerve; careful dissection avoids a messy field.
Isolate and cut the nerve distally and cauterize the distal end.
Bring the proximal nerve to a resting location over the tibia.
The periosteum can be incised and drilled as above. Use a drill sleeve and round off or bevel the proximal edge of the hole to avoid a sharp edge for the nerve entry.
Copiously irrigate the wound and then place the nerve into the distal tibial hole without tension.
Allow the muscles to fall back over top the burial site. Repair the retinaculum if possible.
Subcutaneous and skin sutures are bioabsorbable.
SUPERIOR PERONEAL NERVE RESECTION AND BURIAL
Start with a longitudinal incision over the anterior compartment of the leg.
Find the superficial peroneal nerve as it pierces the crural fascia about 10 to 12 cm proximal to the tip of the fibula.
The course is variable; the surgeon may need a more distal exposure to find the nerve and then trace it back proximally.
Isolate the nerve and decide on the burial site in the fibula (TECH FIG 4) or into muscle (TECH FIG 5).
The peroneal muscles can be split manually and the bone easily palpated.
The fibula can then be held in easy exposure with two small Hohmann retractors on each side of the bone.
The flat anteromedial wall of the fibula provides a fine resting place for the nerve.
Incise the periosteum longitudinally if it is thick enough to merit such action.
TECH FIG 4 • Diagram of burial of superior peroneal nerve into fibula bone.
TECH FIG 5 • Diagram of burial of superior peroneal nerve into peroneal musculature.
Cut the nerve sharply in the distal aspect of the dissection.
Careful observation for a proximal split and a high medial superior peroneal nerve branch is important. If found, bury both branches or resect the nerve before the split.
Hold the distal portion of the nerve with a hemostat and cauterize it to prevent leakage of neurotrophic hormones.
With a 3.5-mm drill bit, make a unicortical drill hole 3 to 4 cm proximal to the distal extent of the cut superior peroneal nerve to allow sufficient slack to bury the nerve without tension (TECH FIG 6). Carefully retract the nerve to prevent it from getting caught in the drill. Once the hole is made, angle the drill proximally to bevel the edge, allowing soft entry into the bone.
Place the cut end of the proximal superior peroneal nerve into the hole after irrigation (TECH FIG 7).
The nerve should have little tension on it and should be stable with ankle plantarflexion or dorsiflexion.
TECH FIG 6 • Drilling unicortical hole in fibula for transected superior peroneal nerve ending. (Note: drill guard removed for illustrative purposes.)
The periosteum does not need to be sutured to the nerve epineurium to hold position.
Gently remove the retractors, allowing the muscle to fall back over the fibula.
Close the subcutaneous tissues with resorbable suture and close the skin with a resorbable suture as well, eliminating the need for suture removal.
A splint is optional, depending on concomitant procedures and the amount of dissection.
TECH FIG 7 • Final position of superior peroneal nerve into fibula hole.
DORSOMEDIAL CUTANEOUS NERVE
This nerve is commonly damaged near the first metatarsal head in bunion surgery (TECH FIG 8). If a local block at the base of the metatarsal or cuneiform relieves the pain, then distal burial is a preferred solution.
The incision often incorporates a prior incision over the dorsal metatarsal and is brought proximally over the cuneiform. Visualize the nerve and transect it as distally as possible; the surgeon need not find the distal neuroma if a proximal block relieved the pain. Cauterize the distal end and dissect the proximal end free.
Using a 2.5-mm drill bit, drill a hole in the base of the first metatarsal or the medial cuneiform, whichever bone seems best anatomically for the nerve to inhabit. Bevel the hole proximally to allow a smooth gliding entrance for the nerve.
Irrigate the wound and place the nerve into the hole; a tagging suture is usually unnecessary.
Close the skin and subcutaneous tissues in a standard fashion with resorbable suture.
TECH FIG 8 • Neuroma of the dorsomedial cutaneous nerve.
SAPHENOUS NERVE RESECTION AND BURIAL
Make a longitudinal incision over the lesser saphenous vein in the supramalleolar region of the medial ankle. The deep dissection should allow identification of the vein as well as the saphenous nerve. The nerve can be deceptively small here and has sometimes been found directly behind the vein. Take care to look for any branching (TECH FIG 9).
TECH FIG 9 • Saphenous nerve neuroma and small anterior branch.
Cut the nerve distally and cauterize all distal branches to limit postoperative leakage of any chemoattractants.
Dissect the proximal nerve ending free and clear an appropriate spot on the medial tibia.
Incise the periosteum and use a 2.5-mm or 3.5-mm drill bit (depending on the size of the nerve) to drill a unicortical hole. Tilt the drill bit proximally to round off the proximal edge and allow atraumatic nerve entry.
Perform final irrigation of the wound. Place the nerve in the bone hole without tension. A suture from the periosteum to the epineurium is optional but rarely used any more.
Close the subcutaneous tissues and then the skin with absorbable suture to limit any postsurgical irritation of the surgical site.
MEDIAL PLANTAR NERVE
Make a longitudinal incision along the course of the nerve on the plantar foot, attempting to avoid the heel and the ball, the primary weight-bearing areas.
Gently carry the dissection through the subcutaneous tissues. The nerve lies just under the deep fascia. Take care to dissect the various branches to ensure adequate denervation (TECH FIG 10).
Transect the nerve distally and bring it as far proximally in the midfoot as possible. Cut the nerve obliquely with an adequate length to allow burial into the deep musculature of the quadratus (TECH FIG 11).
Close the subcutaneous tissues and skin with resorbable suture.
TECH FIG 10 • Dissection of the medial plantar nerve and branches.
TECH FIG 11 • Transection of medial plantar nerve and burial deep into quadratus musculature.
TIBIAL NERVE
Approach the tibial nerve in the supramalleolar space, similar to the tarsal tunnel incision. Resection of this nerve is for extreme salvage as a possible precursor to amputation.
Resect the tibial nerve and branches, including possible high calcaneal branches, as distally as possible, cauterizing the distal ends to reduce chemoattractants.
Obliquely resect the nerve proximally, leaving a length adequate for tension-free burial into the medial tibia.
Using a 3.5to 5.0-mm drill, acquire a burial site in the tibia. Bevel the unicortical hole proximally to allow an easy slide of the nerve into the tibia without a sharp edge.
Close the subcutaneous tissues and skin with bioresorbable suture.
POSTOPERATIVE CARE
The postoperative rehabilitation must strike a balance between early return of motion and avoidance of mechanical trauma to the resected nerve.
If the nerve is buried, immobilization time allows scarring into place.
Many of these patients have some element of complex regional pain syndrome or reflex sympathetic dystrophy, so any stiffness will take a great deal of rehabilitation to recover full motion.
The use of resorbable suture material seems especially prudent in these nerve patients, who are often hypersensitive after surgery.
For simple neurectomy, the patient should have a soft compressive dressing with early range-of-motion exercises. Desensitization and nerve retraining should begin early.
Most patients will have some degree of adjacent sensory nerve hypersensitivity; it can be better tolerated with advance warning.
Many patients also get “zingers” starting at 7 to 14 days or so and lasting up to a month or so. These “electric” jolts of pain follow the resected nerve's distal sensory distribution and represent irritation of the cut proximal nerve ending. They usually begin to lessen in frequency and intensity after a week or so and gradually disappear. Again, discussion with the patient beforehand eliminates frantic office calls about the nerve growing back so quickly.
For nerve resection and burial, the patient usually has a fairly high amount of pain simply from the mobilization of the muscle to allow nerve implantation. A well-padded splint similar to a Robert Jones dressing gives nice compression and stabilization for the initial 12to 14-day postoperative period. After this time, a simple compressive wrapping will usually be sufficient and allows gradual recovery of range of motion.
OUTCOMES
Chiodo and Miller1 compared superior peroneal nerve resection and burial into muscle versus bone; the results favored burial into the fibula when possible.
Sixteen patients had burial into muscle, with improvement in the verbal analogue pain score (0 to 10) of 3.1 points and 46% relief of pain. Four required reoperation for neuroma.
Fifteen patients had burial into bone, with improvement in the pain score (0 to 10) of 5.4 points and 75% pain relief (statistically better than the muscle group).
Dellon and Aszmann2 reviewed 11 cases of superior peroneal nerve resection into anterior muscle with good or excellent results. They recommended compartment release as well.
Miller3 reviewed nine cases of dorsomedial cutaneous nerve resection and burial into the dorsal bones of the foot, with a verbal analogue scale improvement from 8.6 to 2.0 (on a 0-to 10 scale). All patients had relief of symptoms but most had a concurrent procedure to correct foot abnormality.
COMPLICATIONS
Wound infection
Neuroma
Neuroma can be expected to form at the end of a cut nerve as the nerve tries to reconnect with the distal end. Nerves can grow into:
Bulb neuroma: a small thickening on the end of the nerve; usually causes little pain (FIG 4)
FIG 4 • Simple bulb neuroma after sural nerve resection.
FIG 5 • Previous burial of superior peroneal nerve into bone with mild neuritis and small more proximal branch.
Unorganized neuroma: a thick mass of nerve endings, usually with small very irritable extensions causing pain
Nerve can regrow and reinnervate the distribution.
The speed of nerve regrowth should be 1 mm/day but can be faster.
Nerves can sprout new “rootlets” that will attempt to reinnervate the target area. Sometimes it may be difficult to determine whether a more proximal branch was missed at the prior surgery or if a new branch developed (FIG 5).
Adjacent nerves can sometimes provide an unexpected “feeder” innervation to the distal aspect of the resected nerve.
Dysesthesias can be troublesome, with persistent pain in the distal nerve distribution.
Denervation hyperesthesias can be horrible, with difficulty eradicating pain from nerve surgery.
REFERENCES
· Chiodo CP, Miller SD. Surgical treatment of superficial peroneal neuromas. Foot Ankle Int 2004;25:689–694.
· Dellon AL, Aszmann OC. Treatment of superficial and deep peroneal neuromas by resection and translocation of the nerves in the anterolateral compartment. Foot Ankle Int 1998;19:300–303.
· Miller SD. Dorsomedial cutaneous nerve syndrome: treatment with nerve transection and burial into bone. Foot Ankle Int 2001;22: 198–202.
· O'Neill PJ, Parks BG, Walsh R, et al. Excursion and strain of superficial peroneal nerve strain during inversion ankle sprain. J Bone Joint Surg Am 2007;89A:979–986.
· Redfern DJ, Sauve PS, Sakellariou A. Investigation of incidence of superficial peroneal nerve injury following ankle fracture. Foot Ankle Int 2003;24:771.
· Schon, LC, Anderson, CD, Easley ME, et al. Surgical treatment of chronic lower extremity neuropathic pain. Clin Orthop Relat Res 2001;389:156–164.