Keywords
lower limb nerve injury - peroneal nerve - poor prognosis
Introduction
The lower limb gets its peripheral nerves from L2 to S2 levels of the spinal cord
through the lumbosacral plexus. These nerves are involved in injury in a multitude
of ways. This article is based on literature review of relevant articles as well as
the authors’ own experience in treating these injuries.
Anatomy
The nerves of the lower limb originate from L2 to S2 spinal levels forming the lumbosacral
plexus that gives rise to the nerves ([Fig. 1]).
Fig. 1 Incisions showing the Socolovsky approach.
The major nerves are
-
Femoral nerve
-
Obturator nerves
-
Sciatic nerve and its components tibial and common peroneal nerve (CPN)
Pure sensory nerves are
-
Lateral cutaneous nerve of the thigh (LCNT)
-
Saphenous nerve
-
Sural nerve
Incidence
There are several large studies on traumatic nerve injuries.[1]
[2] The frequency of the lower extremity nerve injuries is assessed to approximately
20 to 23% of the overall lesions to the peripheral nerve system. Peroneal division
neuropathy is the most common lower extremity nerve palsy.
Etiology of Injury
There are various ways in which the lower limb nerves are injured. Some of the common
etiology is listed as follows:
-
Fractures, particularly the hip, femur, tibia, fibula, and, occasionally, the ankle
-
Crush injury
-
Knife assault
-
Gunshot
-
Iatrogenic
-
Traction
-
Blunt trauma
-
Radiation
Iatrogenic injuries form a significant portion of injuries. They are caused by
-
Intramuscular injection
-
Total hip prosthesis operation
-
Excision of tumor
-
Tourniquet
-
Traction or pressure during operation
Prof. Kretschmer et al[3] have written a detailed article on iatrogenic injury to peripheral nerves. One hundred
twenty-six (17.4%) of the 722 surgically treated cases were iatrogenic in origin.
Most of these injuries occurred during a previous operation.
In other studies nerve referral centers estimate similar rates among the traumatic
injuries they operate on. Approximately 25% (89/353) of the largest series of operated
sciatic nerve lesions[4] and 50% (47/94) of femoral nerve lesions seen[5] were iatrogenic in nature.
The main causes of iatrogenic injuries in lower limb are
-
Femoral nerve during hernia surgery
-
Peroneal and saphenous nerve during varicose vein surgery. Peroneal nerve during fracture
fixation proximally and distally
-
Sciatic nerve by intramuscular (IM) injection especially in children and during hip
arthroplasty and femoral osteosynthesis either due to traction or the cement or the
trauma of the fracture itself, further aided by callus engulfing the nerve, in which
case it cannot really be called iatrogenic.
Approach to Lower Limb Nerve Injury
A complete clinical examination with detailed history and full neurologic testing
usually points clearly to the nerve involved. In the case of the sciatic nerve injury,
it is important to note the level—at or just distal to the notch (typically injection
palsy), mid-thigh (typically fracture femur or assault), and lower than that. It is
important to check (a) hamstring function particularly biceps femoris, (b) gastrocnemius
soleus and tibialis posterior, (c) tibialis anterior and extensor digitorum and hallucis,
and (d) sensation in the foot. This will point to the level and extent of the injury
([Tables 1]
[2]).
Table 1
The LSUHSC grading system for buttock or tight-level tibial division lesions[4]
|
Grade
|
Criteria
|
|
Abbreviation: LSUHSC, Louisiana State University Health Sciences Center.
|
|
0
|
No gastrocnemius–soleus function; no inversion; no toe flexion; little or no sensation
on the plantar surface of the foot
|
|
1
|
Trace gastrocnemius, but no other tibially innervated muscle function; trace to poor
plantar sensation
|
|
2
|
Gastrocnemius contracts vs. gravity only; plantar surface sensation usually ≤ grade
2
|
|
3
|
Gastrocnemius–soleus contracts vs. gravity and some force; trace or better inversion;
plantar sensation ≤ grade 3
|
|
4
|
Gastrocnemius contracts vs. moderate resistance; inversion ≥ grade 3; either a trace
or no toe flexion; sensation ≥ grade 4
|
|
5
|
Gastrocnemius has full function; inversion ≥ grade 4; toe flexion present; plantar
sensation ≥ grade 4
|
Table 2
The LSUHSC grading system for buttock or tight-level peroneal division lesions[4]
|
Grade
|
Criteria
|
|
Abbreviations: AT, anterior tibialis; ED, extensor digitorum; EHD, extensor hallucis
longus; LSUHSC, Louisiana State University Health Sciences Center.
|
|
0
|
No or little function in short head of biceps; no peroneally innervated muscle function;
no AT, EHD, or ED function
|
|
1
|
Short head of the biceps contracts; no distal peroneally innervated muscle function
|
|
2
|
Short head of the biceps contracts; peroneally innervated muscles contract vs. gravity
or better; no trace of AT; no other distal motor function
|
|
3
|
Short head of the biceps contracts; peroneally innervated muscles ≥ grade 3; AT contracts
vs. gravity, but function of EHD and ED for toes usually absent
|
|
4
|
Short head of the biceps and peroneally innervated muscles contract, as does AT, which
is ≥ grade 3; EHD and ED may have trace function
|
|
5
|
Short head of the biceps and peroneally innervated muscles contract, as does AT, which
is ≥ grade 4; EHD and ED contract, at least vs. gravity
|
Investigations
-
3T magnetic resonance imaging (MRI)[6]: It can give excellent visualization.
-
Musculoskeletal ultrasonography: It is also good and less expensive than MRI.
-
Electrodiagnostics (EDx).
MRI and ultrasonography (USG) help delineate the site of lesion and extent of physical
lesion. EDx will help determine severity, type of lesion, reinnervation, if any, and
differentiate neuropraxia from axonotmesis.
Nerve Repair
The techniques used include the following:
-
Neurolysis under magnification
-
End to end repair
-
Nerve grafting
-
Nerve Transfers
-
Nerve decompression
Exposure at buttock level: The author would highly recommend Prof. Mariano Socolovsky's technique of buttock
level exposure. See [Figs. 1]
[2]
[3]. Details are available in his paper.[7] For thigh and knee levels standard exposure is simple and straightforward.
Fig. 2 Partly intact sciatic nerve.
Fig. 3 Nerve graft across peroneal component.
-
Neurolysis under magnification: Commonly used in injection palsy[8] where one can find an area of swelling and petechiae in the sciatic trunk. It is
useful to open the epineurium under full magnification and release the fascicles.
Stimulation intraoperatively before and after the lysis is a useful guide to determine
if this has helped. If an area of fascicle destruction and fibrosis is noted, selective
excision of concerned fascicles and end-to-end repair or grafting (in case gap is
too large) is recommended. It is important to maintain the integrity of unaffected
fascicles—usually of the tibial division.
In our experience, the same technique is useful in cases in which the sciatic nerve
is encased within a callus in the mid-thigh level following a fracture shaft femur.
It is important to know functional parts of the distal nerve preoperatively by clinical
examination and EDx.
-
2. End-to-end repair: Typically used in cases of assault where the nerve is sharply divided by a plunging
knife. This is feasible within the first few weeks. Later the nerve is likely to end
up with fibroses and retract, leading to the need for nerve grafts ([Figs. 4]
[5]
[6]
[7]
[8]
[9]
[10]).
-
3. Nerve grafts: How much can one pull two ends together? This is the question. The author first debrides
the two ends until healthy sprouting axons are seen. Both side nerve trunks are then
atraumatically mobilized while trying to keep segmental blood supply intact. After
this is achieved, if a 6–0 nylon suture through the epineurium can hold the nerve
ends together while the limb is in neutral position without abnormal joint movement,
then it is suitable for end-to-end repair. If not, then nerve grafts are used. Typical
donor is the ipsilateral sural nerve ([Figs. 11]
[12]
[13]).
-
4. Nerve transfers: Unlike the upper limb where nerve transfers are very common and done frequently,
the lower limb has far fewer established techniques for nerve transfers and they are
not commonly used. A few examples are cited in the following text.
-
5. Nerve compression: The peroneal nerve at the neck of Fibula can be compressed with a cyst/ganglion needed
decompression. Diagnosis is made with MRI/EDx. In author's experience, a tight closure
after ALT flap led to a femoral nerve palsy and was relieved by decompression at the
inguinal level ([Figs. 14]
[15]).
Fig. 4 X-ray showing fracture femur.
Fig. 5 Incision for exposure.
Fig. 6 Nerve injured and stuck in callus.
Fig. 7 Partial injury to peroneal division.
Fig. 8 End-to-end repair of peroneal division.
Fig. 9 Old stab wound and incision for exploration.
Fig. 10 Two healthy nerve ends ready for repair.
Fig. 11 Multiple stab wounds.
Fig. 12 Showing two ends with gap.
Fig. 13 Grafts ready for repair.
Fig. 14 Post ALT compressive neuropathy of femoral nerve.
Fig. 15 Decompressed femoral nerve.
Nerve Transfers in lower limb: In the clinical space there are two instances.[9]
[10] In case of neuroma of superficial peroneal nerve at ankle level during ankle arthrodesis
surgery, a transfer of the superficial to the deep peroneal nerve with conduit or
allograft is described to alleviate pain.
In cases of complete palsy of sciatic, transfer of distal motor branches of the femoral
nerve to the quadriceps muscles are transferred to branches to gastrocnemius along
with transfer of saphenous nerve to sural nerve for sensation. Results show 3+ power
of ankle flexion and improved ambulation.
Experimentally,[11]
[12] contralateral L6 root has been transferred to ipsilateral L6 root both in rats and
Rhesus monkeys with encouraging results.
In cadavers an investigation was done[13] to determine transfers from tibial to peroneal division. The most suitable pairs
were
-
For tibialis anterior either nerve to lateral gastrocnemius or nerve to popliteus
-
For extensor hallucis longus (EHL), nerve to flexor hallucis longus (FHL)
In a personal communication, Prof. Bertelli who is an acknowledged expert in nerve
transfers had the following to say “I have done Gracilis motor branch to Sciatic,
Quadriceps medial head motor branch to Peroneal nerve, branch to Soleus to Tibialis
anterior motor branch, branch to Gastrocnemius to Tibialis anterior, branch to FHL
to tibial anterior motor branch and free Gracilis innervated by Quadriceps motor branch.
All this with unsatisfactory results, if any. Some recovery I got by transferring
the Abductor Hallucis motor branch for reinnervation of Extensor Digitorum Brevis
muscle. I am, in general, disappointed with nerve transfers in the lower limb.”
Peroneal Nerve
The peroneal nerve deserves special mention because it is often the peroneal division
that is affected more in a sciatic injury and because it has a poorer prognosis unless
detected early and treated aggressively. There has been a lot of discussion about
why the peroneal nerve is different. Some of the reasons (1–4 below) are discussed
by Immerman et al[14] as well as Cush and Irgit,[15] and Giuffre et al,[16] reasons 5–7 are from the Louisiana group[16] and 8–10 are the authors’ own experience:
-
The peroneal nerve is tethered at two places, proximally in the greater sciatic notch
and distally where it passes through fibrous tunnel around the knee.
-
This anatomic feature limits potential mobility to 0.5 cm.
-
It also has less connective tissue and fewer and larger fascicles than the tibial
division.
-
The distance to reinnervation of key muscle groups is longer than that for the tibial
nerve.
-
The tibial nerve has a better blood supply and regeneration.
-
The tibial nerve has a higher force-absorbing fascicle/connective tissue count than
the CPN.
-
The tibial nerve-innervated gastrocnemius soleus requires less reinnervation for functional
contraction than deep peroneal branches, which innervate long, thin extensor muscles
at multiple sites and require coordinated nerve input for effective contraction.
-
At the point of classical IM injection in buttocks, it is more superficial or lateral
than the tibial division.
-
In cases of fractures around the proximal tibial fibula, the peroneal has no escape
when the neck of fibula fractures.
-
If there is additional compartment syndrome, the anterior compartment is much tighter
and therefore muscle damage is more common.
As a result, the peroneal division is injured more frequently, and recovery is often
worse than for the tibial division.
Results in Sciatic nerve Surgery
A comprehensive review from The Louisiana State University of 806 cases operated for
sciatic Nerve injury[17] shows that acute lacerations undergoing suture repair were best for the thigh-then-buttock-level
tibial (93%/73%) and then same-level common peroneal divisions (69%/30%); at the knee
level, tibial outcomes (100%) were better than those for the common peroneal nerve
(CPN) (84%). Secondary graft repairs for lacerations had good outcomes for the thigh-then-buttock-level
tibial (80%/62%), followed by common peroneal divisions at the same levels (45%/24%).
The knee/leg-level tibial nerve (94%) did better than the CPN (40%) here. In-continuity
lesions with positive intraoperative nerve action potentials underwent neurolysis
with better results for the thigh-then-buttock-level tibial division (95%/86%) than
for same-level CPN (78%/69%). The knee/leg-level tibial nerve did better than the
CPN (95%/93%).
Conclusions
Lower limb nerve injuries must be treated early to get good results. Tibial division
does better than peroneal. Best results are at knee level followed by thigh level
and finally at buttock level. Iatrogenic injuries are more common than one would imagine.
