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== Description ==
== Description ==
The sciatic nerve is the largest nerve in the body, and consists of the medially placed tibial nerve and the laterally placed common peroneal nerve. It is formed from the ventral rami of the fourth lumbar to third sacral spinal nerves and is a continuation of the upper band of the sacral plexus.
[[File:Sciatic nerve.png|thumb]]
The sciatic nerve is the thickest (approximately 2cm wide) nerve in the body, which  travels in the posterior compartment of the thigh and supplies a major part of the lower extremity. At the upper aspect of the popliteal fossa, it branches medially to the [[Tibial Nerve]] and laterally to the [[Common Peroneal Nerve]].  It is a mixed nerve.<ref>Giuffre BA, Jeanmonod R. [https://www.ncbi.nlm.nih.gov/books/NBK482431/#:~:text=The%20sciatic%20nerve%20also%20provides,the%20sensation%20of%20the%20sole. Anatomy, sciatic nerve.][Updated 2020 Apr 23]. StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing. 2020.</ref>


The sciatic nerve is the largest nerve in the body, and consists of the medially placed tibial nerve and the laterally placed common peroneal nerve. It is formed from the ventral rami of the fourth lumbar to third sacral spinal nerves and is a continuation of the upper band of the sacral plexus.
== Course ==
It is formed from the ventral rami of the fourth lumbar to third sacral spinal nerves and is a continuation of the upper part of the [[Sacral Plexus|sacral plexus.]]<ref name=":0">Anatomy.tv | 3D Human Anatomy | Primal Pictures [Internet]. Anatomy.tv. 2018 [cited 1 May 2018]. Available from: <nowiki>http://www.anatomy.tv/</nowiki></ref>


It leaves the pelvis through the greater sciatic foramen, below the piriformis muscle, and descends between the greater trochanter of the femur and the ischial tuberosity. Initially deep to piriformis, it runs inferiorly and laterally posterior to the ischium, crossing over the nerve to quadratus femoris. Inferior to piriformis; it lies deep to gluteus maximus. It passes inferiorly crossing obturator internus, the gemelli and quadratus femoris. The posterior cutaneous nerve of thigh and the inferior gluteal artery lie on its medial side. Descending vertically, it enters the thigh at the lower border of gluteus maximus, where it lies on the posterior surface of adductor magnus. It gives off nerves to the hamstring muscles. The nerve is crossed obliquely on its superficial aspect by the long head of biceps femoris. The nerve ends at the upper aspect of the popliteal fossa by dividing into the tibial and common perineal nerves.
It leaves the [[pelvis]] through the greater sciatic foramen, inferior to the [[Piriformis]] muscle, and descends between the greater trochanter of the [[Femur]] and the ischial tuberosity. Initially deep to piriformis, it runs inferiorly and laterally posterior to the ischium, crossing over the nerve to [[Quadratus Femoris]]. Below the piriformis it lies deep to [[Gluteus Maximus]]. It passes inferiorly crossing [[Obturator Internus]], the Gemelli Muscles and Quadratus Femoris. The [[Posterior Femoral Cutaneous Nerve]] and the [[Inferior Gluteal Artery]] lie on its medial side. Descending vertically, it enters the thigh at the lower border of gluteus maximus, where it lies on the posterior surface of [[Adductor Magnus]]. Nerves branch off to the hamstring muscles. The nerve is crossed obliquely on its superficial aspect by the long head of [[Biceps Femoris]]. The nerve ends at the upper aspect of the [[Popliteal Fossa|popliteal fossa]] where it branches to distal nerves (tibial and common peroneal nerve).


The nerve can be represented on the back of the thigh by a line drawn from just medial to the midpoint of the line from the ischial tuberosity to the apex of greater trochanter down to the apex of popliteal fossa.
Prior to diverging, the tibial and common peroneal nerves are structurally separate and only loosely held together as the sciatic nerve. The tibial nerve is derived from the anterior divisions of the sacral plexus, and the common fibular nerve is made up of the posterior divisions of the plexus.


It supplies articular branches to the hip joint, with muscular branches to biceps femoris, semitendinosus and semimembranosus and the ischial head of adductor magnus. The nerve to the short head of biceps is from the common peroneal division, with the other muscular branches emerging from the tibial division.
The nerve can be represented on the back of the thigh by a line drawn from just medial to the midpoint of the line from the ischial tuberosity to the apex of greater trochanter down to the apex of popliteal fossa.<ref name=":2">Gray's anatomy- The anatomical basis of clinical practice. Forty-first edition.</ref>
=== Root  ===
{{#ev:youtube|pWl3s6X9cSk}}<ref>Sciatic Nerve - Anatomy Tutorial.Available from: https://www.youtube.com/watch?v=pWl3s6X9cSk</ref>


=== Branches  ===
== Root ==
*Tibial nerve
*L4, L5, S1,S2, S3
*Common peroneal nerve


== Function  ==
== Branches ==


=== Motor  ===
* '''Articular branches''' arise proximally to supply the hip joint through its posterior capsule, which sometimes may arises from sacral plexus.
* '''Muscular branches''' supplies hamstring muscle and ischial part of adductor magnus.


=== Sensory  ===
*Distal terminal branches are Tibial nerve and Common peroneal nerve<ref name=":2" />


== Clinical relevance  ==
== Blood supply ==
A great deal of variability exists in relationship of the sciatic nerve to the piriformis muscle and short external rotators. In approximately 85% of cases the sciatic nerve exits the pelvis deep to the muscle belly of the piriformis. It is usually superficial (posterior to the other external rotators). In 11% of individuals a portion of the piriformis muscle splits the common peroneal nerve and tibial nerve. These anatomic variations are important in the interpretation of intra-operative findings.
In the gluteal region, the sciatic nerve is supplied by the inferior gluteal artery and cruciate anastomosis (the medial and lateral circumflex femoral arteries, inferior gluteal artery and the first perforating branch of the profunda femoris artery).  


=== Piriformis Syndrome ===
Lower in the thigh, arterial branches derived from the perforating branches of the profunda femoris artery or the anastomotic chain between them or, occasionally, from the popliteal artery, enter the nerve on its lateral or anterolateral side.


Youngman described 'Piriformis Syndrome' in 1928 as an evolving compression of the sciatic nerve by the piriformis muscle. This is associated with acute trauma to the buttock and occurs when the sciatic nerve exits posterior to the piriformis. The patient finds sitting difficult and participation in activities where hip flexion or internal rotation is required, almost impossible. The pain is in the sciatic nerve distribution.
== Function ==
It provides motor innervation to the posterior compartment of the thigh and its terminal branches provide both motor and sensory innervation to leg and foot.


Physical examination reveals tenderness directly over the piriformis tendinous or in the gluteal area, and the pain can be listed by forced internal rotation of the extended thigh – this is sometimes called 'Pace's sign'. There is sometimes weak abduction against resistance or external rotation against resistance, and the pain may also be reproduced by rectal or vaginal examination.
=== Motor  ===
*[[Hamstrings]]
**Biceps Femoris
**Semitendinosus
**Semimembranosus
*[[Adductor Magnus|Adductor magnus]]- ischial head
*Indirectly innervates (via [[Common Peroneal Nerve|common peroneal]] and [[Tibial Nerve|tibial]] nerves) the all muscles of the leg and foot.


Treatment involves rest and oral anti-inflammatory drugs. The diagnosis can also be confirmed by the injection of local anesthetic under fluoroscopy into the area of injury. Steroid injection may occasionally be necessary. In refractory cases, surgical exploration of the piriformis and/or division of the piriformis muscle and/or mobilization of the sciatic nerve may be necessary.
=== Sensory  ===
*Indirectly innervates (via common peroneal and tibial nerves) the skin of the lateral leg, heel, and both the dorsal and plantar surfaces of the foot.


The piriformis syndrome is thought to be due to irritation of the sciatic nerve as it passes over the piriformis tendon. This causes buttock pain and sciatica. The pain can be reproduced by applying pressure to the piriformis fossa on the posterior aspect of the greater trochanter and by stressing the piriformis muscle. Injections can once again be diagnostic and therapeutic. Some authors have reported good results by sectioning the piriformis to relieve the pain.
== Assessment ==
[[Neurological Assessment|Neurological examination]] is crucial for the assessment of sciatic nerve.


=== Hamstring Syndrome ===
==== Myotomes ====
This pathology commonly affects athletes who present with localised and radiating pain near the ischial tuberosity. The pathophysiology is thought to be that of an insertional tendopathy at the ischium but there may also be involvement of sciatic nerve compression. The pain in hamstring syndrome radiates down the posterior thigh or popliteal region and is exacerbated when the hamstrings are on tension. This is often seen in sprinters or hurdlers. On examination there is exquisite tenderness over the ischial tuberosity and percussion in that region may reproduce the sciatic distribution of pain. Treatment involves rest, anti-inflammatory agents and steroid injections.
[[Myotomes]] of lower extremities are:
*Ankle dorsiflexion (L4)
*Extension of the big toe (L5)
*Eversion of the ankle, contraction of buttock and knee flexion (S1)
*Knee flexion and toe standing (S2)
*Pelvic floor, bladder and genital function (S3)<ref name=":1">Petty NJ, editor. Neuromusculoskeletal Examination and Assessment, A Handbook for Therapists, 4: Neuromusculoskeletal Examination and Assessment. Elsevier Health Sciences; 2011.</ref>


=== Hip Dislocation ===
==== Dermatomes ====
[[Dermatomes]] of lower extremities are:
*Over the medial malleolus (L4)
*On the dorsum of the foot at the third metatarsophalangeal joint (L5)
*On the lateral aspect of the calcaneus (S1)
*At the midpoint of the popliteal fossa (S2)
*Over the tuberosity of the ischium or infra-gluteal fold (S3)


In view of the high intrinsic stability of the hip, hip dislocations are almost always due to high-energy trauma and require careful assessment. Such injuries typically occur in motor vehicle accidents, falls from great heights and industrial injuries. Regardless of the type of activity involved, the pathological force is transmitted to the hip joint and arises from one of three common surfaces:
==== Reflexes ====
*Knee jerk (L3 and 4)
*Ankle jerk (S1)


*The anterior surface of the flexed knee striking an object.
=== Neurodynamic ===
*The sole of the foot striking an object with the ipsi-lateral knee extended.
Neurodynamic tests can be used to assess the mobility of the nervous system. Assessments that stress the sciatic nerve include straight leg raise and slump tests. Whilst performing the neurodynamic movement the following qualities should be noted:
*A blow to the greater trochanter.
*Resting symptoms
*The quality of movement
*Range of movement
*Resistance through the range and at the end of range
*Behaviour of pain (local and referred)<ref name=":1" />
A test is positive if one or more of the following is found:
*All or part of the patients symptoms are reproduced
*Symptoms different from 'normal' response are produced
*Range of movement in the symptomatic limb is different from that of the contralateral limb.
Sensitising and desensitising movements are essential to rule out any other structures that could be implicated as a source of a patient's pain. When assessing the sciatic nerve the hamstrings are also put on stretch during both tests. Once a position of pain reproduction is identified, dorsiflexion or plantarflexion can be added which will increase and decrease symptoms respectively. Adding dorsiflexion increases the tension on the nerves because they form a continuous structure.


In more rare circumstances, the dislocation force may be applied to the posterior pelvis with the ipsi-lateral foot only acting as a counter-force. The injury sustained depends upon the amount and direction of force and the quality of bone in the proximal femur and acetabulum.
==== Straight leg raise ====
The [[Straight Leg Raise Test]] (SLR) test is a neurodynamic test. Neurodynamic tests check the mechanical movement of the neurological tissues as well as their sensitivity to mechanical stress or compression. These tests, along with relevant history and decreased range of motion, are considered by some to be the most important physical signs of disc herniation, regardless of the degree of disc injury.<ref>David J. Magee;Orthopaedic Physical Assessment; Chapter 9-Lumbar Spine;Fifth Edition: Pg 558-564.</ref>


The classic posterior dislocation of the hip is a dashboard injury where, after rapid deceleration, the body pivots forward and the knee strikes the dashboard with the hip and knee both flexed at 90 degrees. This tends to force the femoral head up posteriorly. If the hip is less flexed at the time of impact, the femoral head strikes the posterior or postero-superior aspect of the acetabulum leading to a fracture dislocation. The amount of hip rotation at the time of impact will influence both the direction and type of dislocation or fracture dislocation. During hip dislocation the femoral head fractures impactions or articular scratches are commonly seen. These can range from tiny cartilaginous avulsion fragments to major osteocartilaginous injuries of the femoral head. Such fragments can become incarcerated between the femoral head and the acetabular articular surface following reduction of dislocation and lead to incongruity and long term degenerative changes.
{{#ev:youtube|v8moZMdXJfI}}


Femoral neck fractures may be associated with femoral head dislocations both because of the high energy at the time of trauma and also because of the forces required during reduction. The severe forces required in order to dislocate the femoral head are such that the threshold deformity for chondrocyte death may be exceeded. This may be one potential explanation for the high incidence of traumatic arthritis following hip dislocation. The fact that osteocartilaginous fragments are also displaced and/or lost is another significant contributing factor. Any significant loss of normal articular congruence or articular contact secondary to femoral head depression or defects seems to predispose to rapid degenerative change.
==== Slump ====
[[Slump Test|Slump test]] is the nerve tension test for sciatic nerve. It is a provocative test in which sciatic nerve is tensed by  flexing spines and hips and extending knees. To begin the test, have the patient seated with hands behind back to achieve a neutral spine. The first step is to have the patient slump forward at the thoracic and [[Lumbar Anatomy|lumbar]] spine. If this position does not cause pain, have the patient flex the neck by placing the chin on the chest and then extending one knee as much as possible.  


Avascular necrosis of the femoral head secondary to vascular embarrassment at the time of hip dislocation is also a common consequence. The incidence in literature varies from 1% to 70%. This may be particularly related to incidences where the hip is left dislocated for a long period. The latter suggests that there may be a number of mechanisms for osteonecrosis. Firstly, there may be an immediate complete disruption of the blood supply and to the femoral head at the time of violent dislocation. Later there may be a slower process where prolonged abnormal stretching of the arterial supply leads to spasm or thrombosis. Finally, there could be a venous thrombus tension and the vascular drainage leads to venous occlusion, back pressure and ultimate arterial obstruction. The latter two mechanisms can be influenced by early and rapid reduction of the dislocated hip.
If extending the knee causes pain, have the patient extend the neck into neutral. If the patient is still unable to extend the knee due to pain, the test is considered positive.


The natural history of post-traumatic osteonecrosis of the femoral head may be different from that of idiopathic osteonecrosis in that isolated segments may go on to sclerosis and collapse without the rest of the femoral head being affected. This may affect the type of salvage procedure that is performed.
If extending the knee does not cause pain, ask the patient to actively dorsiflex the ankle. If dorsiflexion causes pain, have the patient slightly flex the knee while still dorsiflexing. If the pain is reproduced, the test is considered positive.


Hip dislocations are secondary to high-energy trauma and therefore are often associated with multi-system injuries. It is particularly important to examine for occult knee ligament injuries and for sciatic nerve injuries. The common peroneal division of the sciatic nerve is most commonly involved. Great care is required when there is a concomitant femoral fracture and this may mask the otherwise obvious hip dislocation.
Then, the test is repeated on opposite side.
{{#ev:youtube|zdbIa96e-pk}}<ref>Slump test for Sciatic Nerve pain. Available from: https://www.youtube.com/watch?v=zdbIa96e-pk lasted accessed: 24th July 2022</ref>


Hip dislocations are typically sub-divided into anterior or posterior. The so called central dislocation of the hip is essentially an acetabular fracture. Thompson and Epstein have classified posterior hip dislocations. A 'Type 1' dislocation is a pure dislocation with an insignificant posterior wall fragment. A 'Type 2' dislocation is associated with a single large posterior wall fragment. A 'Type 3' dislocation is a comminuted distal wall fracture, and a 'Type 4' fracture dislocation is an acetabular floor fracture. A 'Type 5' dislocation is complicated by femoral head fracture. Pipkin has classified posterior hip dislocations associated with femoral head fractures based on the location of the femoral head fracture. With a 'Type 1' injury the femoral fracture is inferior to the fovea centralis. In a 'Type 2' injury the fracture line extends superior to the fovea centralis and typically includes the fovea. In a 'Type 3' injury the femoral head fracture is associated with the femoral head fracture, and in a 'Type 4' injury the femoral head fracture is associated with an acetabular fracture.
== Clinical Relevance  ==
There is some variability between the relationship of the sciatic nerve, piriformis muscle and short external rotators. In approximately 85% of cases the sciatic nerve exists as described above. In 11% of individuals a portion of the piriformis muscle splits the common peroneal nerve and tibial nerve. <ref name=":0" />
[[File:Sciatic nerve 2.jpg|thumb]]


Such classification systems help to guide treatment particularly now that CT scanning and MRI are widely available.
=== Piriformis Syndrome ===


In Type 1 hip dislocation the hip can typically be reduced with ease. This is best done with sedation and/or anesthesia with the availability of image intensification. No great force or leverage should be applied lest the femoral neck should be fractured. Post-reduction films would typically demonstrate a concentric reduction with no widening of the joint and no incarcerated fragments between the articular surfaces. CT scan can confirm this. A small bone fragment within the acetabular fossa secondary to a ligamentum teres avulsion is thought to be a benign finding that does not require surgical intervention. Management of posterior hip dislocations are based on a congruent reduction, the restoration of normal articular surfaces and the restoration of hip stability. This can be achieved in a number of ways by addressing inroads to the acetabulum, posterior wall, the femoral head and the soft tissues respectively.
Youngman described '[[Piriformis Syndrome]]' in 1928 as compression of the sciatic nerve by the piriformis muscle. This is associated with acute trauma to the buttock and occurs when the sciatic nerve exits posterior to the piriformis. The patient's may report that sitting and activities that require hip flexion or internal rotation as aggravate the pain. The pain radiates in a sciatic nerve distribution.<ref name=":0" />


Anterior hip dislocations are classified on the basis of their location. Their prognosis is far less favorable than previously thought. They can also be classified according to their stability such that Type 1 injuries have no significant associated fractures and no clinical instability following concentric reduction. Type 2 injuries are irreducible dislocations without significant femoral head or acetabular fracture. Irreducible in this setting implies that a reduction has been attempted under general anesthesia with muscle paralysis. Type 3 injuries are unstable hips following reduction due to incarcerated fragments of cartilage or bone. In Type 4 injuries there is an associated acetabular fracture requiring reconstruction to restore hip stability or joint congruity. In Type 5 injuries there is associated femoral neck injury.
Objective examination reveals tenderness directly over the piriformis or in the gluteal area, and the pain can be replicated by internal rotation of the extended thigh. This finding is called the 'Pace's sign'. There is sometimes weak abduction or external rotation against resistance. The pain may also be reproduced by rectal or vaginal examination.


Computerized tomography with multiple bony cuts through the hips and sacro-iliac joints is often very helpful. 1mm slices allow a very accurate three-dimensional CT reconstruction. Magnetic resonance imaging is very useful to evaluate the soft tissues and to later verify the vascularity of the femoral head.
Initial medical management is oral anti-inflammatory medication. Steroid injection and surgical exploration may be considered for chronic cases.


Management of acetabular dislocations involves a reduction as early as possible. Regardless of the direction on the dislocation, reduction can be attempted with in line traction with the patient lying supine. This is preferably performed under general anesthesia. The most common method is to apply traction in the line of the deformity. Someone should apply counter-traction by stabilizing the patient's pelvis. If a hip cannot be reduced by closed manipulation under general anesthesia, then immediate open reduction must be performed if the patient's general condition or other injuries allow this. The approach used will be determined by associated acetabular and femoral head injuries.
=== Hamstring Syndrome ===
This pathology commonly affects athletes who present with localised and radiating pain near the ischial tuberosity. The pathophysiology is thought to be that of insertional tendinopathy at the ischium but there may also be involvement of sciatic nerve compression. The pain in hamstring syndrome radiates down the posterior thigh or popliteal region and is exacerbated when the [[hamstrings]] are in tension.<ref name=":0" /> This is often seen in sprinters or hurdlers. On examination there is exquisite tenderness over the ischial tuberosity and percussion in that region may reproduce the sciatic distribution of pain. Treatment involves rest, anti-inflammatory agents and steroid injections.


The typical problems associated with hip dislocations are missed and delayed diagnosis, particularly in a multiply injured patient, osteonecrosis, traumatic arthritis, recurrent dislocation, sciatic nerve injury. Post-surgical complications include infection, sciatic nerve injury, both early and late heterotopic ossification and thrombo-embolism.
=== Hip Dislocation ===


The femoral head is supplied by three terminal arterial sources: the artery of the ligamentum teres, a terminal branch of the lateral femoral circumflex artery and the terminal branch of the medial circumflex artery, the lateral epiphyseal artery. The latter is the critical blood supply to the majority of the weight bearing superior portion of the femoral head. This artery is particularly at risk during posterior fracture dislocation. The adult femoral head ranges in diameter from 40mm to 60mm and is not a perfect sphere. Its subtle ace veracity is reflected on the acetabular side. Accurate reduction of femoral head fragments is necessary in order to maximize contact area between the femoral head and the acetabulum and to minimize stresses across the articular cartilage. The management of femoral head fractures involves adequate imaging with plain X-rays and CT scans followed by open reduction and internal fixation. The specific procedure undertaken will depend on any associated hip instability and/or acetabular injuries.
Hip dislocations are most commonly associated high-energy trauma and therefore are often associated with multi-system injuries. It is important to examine for sciatic nerve injuries. The common peroneal division of the sciatic nerve is most commonly involved. Care is needed during assessment as a femoral fracture can mask otherwise obvious hip dislocation.<ref name=":0" />


==== Kocher-Langenbeck Approach (Posterior Approach) ====
====Surgical Approach for viewing of sciatic nerve injury post hip dislocation ====
'''Kocher-Langenbeck Approach (Posterior Approach)'''
*'Kocher-Langenbeck' approach is the standard posterior approach to the hip joint.
*Performed in a lateral decubitus position without use of a traction table.
*To access the sciatic nerve the gluteus maximus muscle is split, where the nerve can be identified and examined.
*After identifying the sciatic nerve, the tendinous insertions of the piriformis muscle and the obturator internus are identified.
*When surgeons perform capsulotomies they take care not to injure the acetabulum labrum. The joint can then be assessed, any fracture fragments removed or stabilised and the entire area thoroughly washed out.<ref name=":0" />


Standard posterior approach to the hip is the 'Kocher-Langenbeck' approach. This is typically performed in a lateral decubitous position without use of a traction table. After splitting the gluteus maximus muscle, the sciatic nerve is identified and examined for contusion, hemorrhage or partial or complete laceration. The gluteus maximus must not be split too proximally as this can lead to denervation secondary to injury of the inferior gluteal nerve. After identifying the sciatic nerve, the tendinous insertions of the piriformis muscle and the obturator internus are identified and tagged with heavy absorbable sutures. If torn, they are detached and retracted. Care must be taken not to injure the acetabulum labrum when performing capsulotomies. Quite frequently, however, capsulotomies have already been created by the injury. The joint can then be assessed, any fracture fragments removed or stabilized and the entire area thoroughly washed out.
==== Anterior Approach ====
The anterior approach to the hip for injuries can be performed through the 'Smith Peterson' or 'Watson Jones' approaches. These can be performed with the patient in the semi-lateral or lateral dicubitous position. The latter has particular advantages if a simultaneous or posterior approach is also to be considered.
== Assessment ==


== Treatment ==
'''Anterior Approach'''
*The anterior approach to the hip for injuries can be performed through the 'Smith Peterson' or 'Watson Jones' approaches.
*These can be performed with the patient in the semi-lateral or lateral decubitus position.<ref name=":0" />


== Resources  ==
=== Intramuscular Injections ===
The path of the sciatic nerve must be considered when administering intramuscular injections into the gluteal region. The region can be divided into quadrants using two lines, marked by bony landmarks:
*One line descends vertically from the highest point on the iliac crest.
*The other horizontal line passes through the vertical line half way between the highest point on the iliac crest and ischial tuberosity.
The sciatic nerve passes through the lower medial quadrant. To avoid damaging the sciatic nerve therefore, intramuscular injections are given only in the upper lateral quadrant of the gluteal region.<ref>The Sciatic Nerve [Internet]. TeachMeAnatomy. 2018 [cited 10 May 2018]. Available from: <nowiki>http://teachmeanatomy.info/lower-limb/nerves/the-sciatic-nerve/</nowiki></ref>


== References  ==
== References  ==
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[[Category:Anatomy]] [[Category:Nerves]]
[[Category:Anatomy]]  
[[Category:Nerves]]
[[Category:Hip]]
[[Category:Hip - Anatomy]]
[[Category:Hip - Nerves]]
[[Category:Assessment]]
[[Category:Hip - Assessment and Examination]]

Latest revision as of 03:53, 30 January 2024

Original Editor - George Prudden

Top Contributors - George Prudden, Manisha Shrestha, Kim Jackson, Lucinda hampton, Candace Goh and Joao Costa

Description[edit | edit source]

Sciatic nerve.png

The sciatic nerve is the thickest (approximately 2cm wide) nerve in the body, which travels in the posterior compartment of the thigh and supplies a major part of the lower extremity. At the upper aspect of the popliteal fossa, it branches medially to the Tibial Nerve and laterally to the Common Peroneal Nerve. It is a mixed nerve.[1]

Course[edit | edit source]

It is formed from the ventral rami of the fourth lumbar to third sacral spinal nerves and is a continuation of the upper part of the sacral plexus.[2]

It leaves the pelvis through the greater sciatic foramen, inferior to the Piriformis muscle, and descends between the greater trochanter of the Femur and the ischial tuberosity. Initially deep to piriformis, it runs inferiorly and laterally posterior to the ischium, crossing over the nerve to Quadratus Femoris. Below the piriformis it lies deep to Gluteus Maximus. It passes inferiorly crossing Obturator Internus, the Gemelli Muscles and Quadratus Femoris. The Posterior Femoral Cutaneous Nerve and the Inferior Gluteal Artery lie on its medial side. Descending vertically, it enters the thigh at the lower border of gluteus maximus, where it lies on the posterior surface of Adductor Magnus. Nerves branch off to the hamstring muscles. The nerve is crossed obliquely on its superficial aspect by the long head of Biceps Femoris. The nerve ends at the upper aspect of the popliteal fossa where it branches to distal nerves (tibial and common peroneal nerve).

Prior to diverging, the tibial and common peroneal nerves are structurally separate and only loosely held together as the sciatic nerve. The tibial nerve is derived from the anterior divisions of the sacral plexus, and the common fibular nerve is made up of the posterior divisions of the plexus.

The nerve can be represented on the back of the thigh by a line drawn from just medial to the midpoint of the line from the ischial tuberosity to the apex of greater trochanter down to the apex of popliteal fossa.[3]

[4]

Root[edit | edit source]

  • L4, L5, S1,S2, S3

Branches[edit | edit source]

  • Articular branches arise proximally to supply the hip joint through its posterior capsule, which sometimes may arises from sacral plexus.
  • Muscular branches supplies hamstring muscle and ischial part of adductor magnus.
  • Distal terminal branches are Tibial nerve and Common peroneal nerve[3]

Blood supply[edit | edit source]

In the gluteal region, the sciatic nerve is supplied by the inferior gluteal artery and cruciate anastomosis (the medial and lateral circumflex femoral arteries, inferior gluteal artery and the first perforating branch of the profunda femoris artery).

Lower in the thigh, arterial branches derived from the perforating branches of the profunda femoris artery or the anastomotic chain between them or, occasionally, from the popliteal artery, enter the nerve on its lateral or anterolateral side.

Function[edit | edit source]

It provides motor innervation to the posterior compartment of the thigh and its terminal branches provide both motor and sensory innervation to leg and foot.

Motor[edit | edit source]

Sensory[edit | edit source]

  • Indirectly innervates (via common peroneal and tibial nerves) the skin of the lateral leg, heel, and both the dorsal and plantar surfaces of the foot.

Assessment[edit | edit source]

Neurological examination is crucial for the assessment of sciatic nerve.

Myotomes[edit | edit source]

Myotomes of lower extremities are:

  • Ankle dorsiflexion (L4)
  • Extension of the big toe (L5)
  • Eversion of the ankle, contraction of buttock and knee flexion (S1)
  • Knee flexion and toe standing (S2)
  • Pelvic floor, bladder and genital function (S3)[5]

Dermatomes[edit | edit source]

Dermatomes of lower extremities are:

  • Over the medial malleolus (L4)
  • On the dorsum of the foot at the third metatarsophalangeal joint (L5)
  • On the lateral aspect of the calcaneus (S1)
  • At the midpoint of the popliteal fossa (S2)
  • Over the tuberosity of the ischium or infra-gluteal fold (S3)

Reflexes[edit | edit source]

  • Knee jerk (L3 and 4)
  • Ankle jerk (S1)

Neurodynamic[edit | edit source]

Neurodynamic tests can be used to assess the mobility of the nervous system. Assessments that stress the sciatic nerve include straight leg raise and slump tests. Whilst performing the neurodynamic movement the following qualities should be noted:

  • Resting symptoms
  • The quality of movement
  • Range of movement
  • Resistance through the range and at the end of range
  • Behaviour of pain (local and referred)[5]

A test is positive if one or more of the following is found:

  • All or part of the patients symptoms are reproduced
  • Symptoms different from 'normal' response are produced
  • Range of movement in the symptomatic limb is different from that of the contralateral limb.

Sensitising and desensitising movements are essential to rule out any other structures that could be implicated as a source of a patient's pain. When assessing the sciatic nerve the hamstrings are also put on stretch during both tests. Once a position of pain reproduction is identified, dorsiflexion or plantarflexion can be added which will increase and decrease symptoms respectively. Adding dorsiflexion increases the tension on the nerves because they form a continuous structure.

Straight leg raise[edit | edit source]

The Straight Leg Raise Test (SLR) test is a neurodynamic test. Neurodynamic tests check the mechanical movement of the neurological tissues as well as their sensitivity to mechanical stress or compression. These tests, along with relevant history and decreased range of motion, are considered by some to be the most important physical signs of disc herniation, regardless of the degree of disc injury.[6]

Slump[edit | edit source]

Slump test is the nerve tension test for sciatic nerve. It is a provocative test in which sciatic nerve is tensed by flexing spines and hips and extending knees. To begin the test, have the patient seated with hands behind back to achieve a neutral spine. The first step is to have the patient slump forward at the thoracic and lumbar spine. If this position does not cause pain, have the patient flex the neck by placing the chin on the chest and then extending one knee as much as possible.

If extending the knee causes pain, have the patient extend the neck into neutral. If the patient is still unable to extend the knee due to pain, the test is considered positive.

If extending the knee does not cause pain, ask the patient to actively dorsiflex the ankle. If dorsiflexion causes pain, have the patient slightly flex the knee while still dorsiflexing. If the pain is reproduced, the test is considered positive.

Then, the test is repeated on opposite side.

[7]

Clinical Relevance[edit | edit source]

There is some variability between the relationship of the sciatic nerve, piriformis muscle and short external rotators. In approximately 85% of cases the sciatic nerve exists as described above. In 11% of individuals a portion of the piriformis muscle splits the common peroneal nerve and tibial nerve. [2]

Sciatic nerve 2.jpg

Piriformis Syndrome[edit | edit source]

Youngman described 'Piriformis Syndrome' in 1928 as compression of the sciatic nerve by the piriformis muscle. This is associated with acute trauma to the buttock and occurs when the sciatic nerve exits posterior to the piriformis. The patient's may report that sitting and activities that require hip flexion or internal rotation as aggravate the pain. The pain radiates in a sciatic nerve distribution.[2]

Objective examination reveals tenderness directly over the piriformis or in the gluteal area, and the pain can be replicated by internal rotation of the extended thigh. This finding is called the 'Pace's sign'. There is sometimes weak abduction or external rotation against resistance. The pain may also be reproduced by rectal or vaginal examination.

Initial medical management is oral anti-inflammatory medication. Steroid injection and surgical exploration may be considered for chronic cases.

Hamstring Syndrome[edit | edit source]

This pathology commonly affects athletes who present with localised and radiating pain near the ischial tuberosity. The pathophysiology is thought to be that of insertional tendinopathy at the ischium but there may also be involvement of sciatic nerve compression. The pain in hamstring syndrome radiates down the posterior thigh or popliteal region and is exacerbated when the hamstrings are in tension.[2] This is often seen in sprinters or hurdlers. On examination there is exquisite tenderness over the ischial tuberosity and percussion in that region may reproduce the sciatic distribution of pain. Treatment involves rest, anti-inflammatory agents and steroid injections.

Hip Dislocation[edit | edit source]

Hip dislocations are most commonly associated high-energy trauma and therefore are often associated with multi-system injuries. It is important to examine for sciatic nerve injuries. The common peroneal division of the sciatic nerve is most commonly involved. Care is needed during assessment as a femoral fracture can mask otherwise obvious hip dislocation.[2]

Surgical Approach for viewing of sciatic nerve injury post hip dislocation[edit | edit source]

Kocher-Langenbeck Approach (Posterior Approach)

  • 'Kocher-Langenbeck' approach is the standard posterior approach to the hip joint.
  • Performed in a lateral decubitus position without use of a traction table.
  • To access the sciatic nerve the gluteus maximus muscle is split, where the nerve can be identified and examined.
  • After identifying the sciatic nerve, the tendinous insertions of the piriformis muscle and the obturator internus are identified.
  • When surgeons perform capsulotomies they take care not to injure the acetabulum labrum. The joint can then be assessed, any fracture fragments removed or stabilised and the entire area thoroughly washed out.[2]


Anterior Approach

  • The anterior approach to the hip for injuries can be performed through the 'Smith Peterson' or 'Watson Jones' approaches.
  • These can be performed with the patient in the semi-lateral or lateral decubitus position.[2]

Intramuscular Injections[edit | edit source]

The path of the sciatic nerve must be considered when administering intramuscular injections into the gluteal region. The region can be divided into quadrants using two lines, marked by bony landmarks:

  • One line descends vertically from the highest point on the iliac crest.
  • The other horizontal line passes through the vertical line half way between the highest point on the iliac crest and ischial tuberosity.

The sciatic nerve passes through the lower medial quadrant. To avoid damaging the sciatic nerve therefore, intramuscular injections are given only in the upper lateral quadrant of the gluteal region.[8]

References[edit | edit source]

  1. ↑ Giuffre BA, Jeanmonod R. Anatomy, sciatic nerve.[Updated 2020 Apr 23]. StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing. 2020.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Anatomy.tv | 3D Human Anatomy | Primal Pictures [Internet]. Anatomy.tv. 2018 [cited 1 May 2018]. Available from: http://www.anatomy.tv/
  3. ↑ 3.0 3.1 Gray's anatomy- The anatomical basis of clinical practice. Forty-first edition.
  4. ↑ Sciatic Nerve - Anatomy Tutorial.Available from: https://www.youtube.com/watch?v=pWl3s6X9cSk
  5. ↑ 5.0 5.1 Petty NJ, editor. Neuromusculoskeletal Examination and Assessment, A Handbook for Therapists, 4: Neuromusculoskeletal Examination and Assessment. Elsevier Health Sciences; 2011.
  6. ↑ David J. Magee;Orthopaedic Physical Assessment; Chapter 9-Lumbar Spine;Fifth Edition: Pg 558-564.
  7. ↑ Slump test for Sciatic Nerve pain. Available from: https://www.youtube.com/watch?v=zdbIa96e-pk lasted accessed: 24th July 2022
  8. ↑ The Sciatic Nerve [Internet]. TeachMeAnatomy. 2018 [cited 10 May 2018]. Available from: http://teachmeanatomy.info/lower-limb/nerves/the-sciatic-nerve/
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