Sciatic Nerve
Anatomy
- arises from LS plexus - L4,5 S1,2,3
- emerges from pelvis below piriformis & enters thigh between ischial tuberosity & GT
- in 10% of patients - sciatic N separated in greater sciatic foramen by the piriformis
- accompanied by PFCN (post.fem.cut.N) & inferior gluteal artery
- enters thigh beneath lower border of Gmax.
- descends near middle of thigh, lying on adD magnus & crossed obliquely by long head of biceps femoris
- usually separates in upper part of popliteal space
Tibal Nerve Branch
- from anterior branches of LS plexus L4,5 & S1,2,3
- 2 branches from tibial division - below quadratus femoris
- upper branch to long head of biceps fem. & upper portion of semiT
- lower branch innervates lower portion of semiT & semiM. & portion of adD magnus
Common Peroneal Nerve
- from posterior branches - L4,5 & S1,2
- nerve to short head of biceps fem.
Sciatic N. in THR
- injured by excessive tension when extremity lengthened significantly, especially in pts with DDH
- peroneal division most often affected
Incidence
- 1-2% of primary THR, 3-4% after revision & 5-6% in THR for CDH
- majority of these nerve deficits partial & many will resolve
- females seem to be at significantly higher risk
- sciatic & sup. gluteal N. and vessels course opposite the posterior superior quadrant
- inferior gluteal and pudendal structures are opposite the postero-inferior quadrant
- with EMG evaluation -> 75% incidence of subclinical injury to superior & inf. glut. muscles with use of posterior & lateral approaches
Kocher-Langenbeck Approach
- injury prevented by monitoring of amount of tension applied by assistants retracting the N
Risk factors
- revision THR
- limb lengthening
- female gender
- anticoagulation
- broken trochanteric osteotomy wires
- vascular insufficiency
Prognosis
- recovery from mild injury may occur in days to wks - neuropraxia
- axonal damage - recovery may not occur at all or may be incomplete after 1 to 2 yrs
- consider EMG
Management
- if traction injury -> keep pts leg flexed, N. may recover in the relaxed position
- early treatment consists of AFO
- sciatic N recovery may occur over a 3 yr period
- tendon transfers usually not performed until 3 yr post op
Tibial Nerve
Anatomy
- from anterior branches of LS plexus L4,5 & S1,2,3
- supplies muscles of posterior thigh (except short head of biceps which supplied by peroneal N.)
- in popliteal space
- branches to popliteus muscle, two heads of gastrocnemius, soleus & plantaris muscles
- nerve passes into posterior compartment of the leg
- supplies tib. post., FHL & FDL
- passes behind medial malleolus to plantar side of foot & divides into medial & lateral plantar Nn
- medial branch - counterpart of median N in hand
- lateral branch - counterpart of ulnar N in the hand
Tibial Nerve Palsy
- with tibial nerve palsy foot develops
- if traction injury -> keep pts leg flexed, N. may recover in the relaxed position
- early treatment consists of AFO
- sciatic N recovery may occur over a 3 yr period
- tendon transfers usually not performed until 3 yr post op
Peroneal nerve
Anatomy
- common peroneal N. derived from posterior branches - L4,5 & S1,2 as a part of sciatic N
- supplies short head of biceps fem. in thigh
- crosses posterior to lateral head of gastrocnemius & becomes subcutaneous behind head of fibula
- penetrates the posterior inter-muscular septum & then divides into superficial & deep peroneal nerves
- also gives off a lateral sural cutaneous branch which joins with the medial sural cutaneous nerve (from tibial N) to form the sural N
Deep Peroneal Nerve
- courses anteriorly around fibula to enter the anterior compartment of leg
- immediately below the fibular head lies on the anterior cortex of the fibula for a distance of 3-4 cm</li
- supplies muscles (tib.ant., EHL & EDL) as it travels with anterior tibial artery between tib.ant. & EHL
- sends a sensory branch to 1st webspace
Superficial Peroneal Nerve
- supplies lateral compartment of the leg
- on the lateral cortex of the fibula passes between peroneus longus & brevis</li
- subcutaneous superficial sensory branch lies between peroneus brevis and EDL
- about 10-12 cm above the tip of the lateral malleolus pierces the fascia
- about 6-7 cm distal to the fibula, the superficial peroneal nerve divides into intermediate and medial dorsal cutaneous Nn.
- branches of the superficial peroneal N or the sural N may be injured during ORIF of ankle #s
Peroneal Nerve Palsy
- lead to severe disability with foot drop & paraesthesias
Traumatic peroneal palsy
- may result from supracondylar #, knee dislocation & proximal tibial #
Atraumatic peroneal nerve palsy
- may result from a large fabella which impinges on peroneal nerve behind the knee or from a proximal tibio-fibular synovial cyst
Examination
- always consider lumbar radiculopathy
- there may be an obvious foot drop
- sensory loss may be difficult to determine - variable & small autonomous zone of sensation
- Tinel’s sign over the fibular neck, helps localize the site of nerve compression
- always check for a fabella and check to see if direct compression reproduces nerve symptoms
- in knee dislocation -> test for function of tibial branch of sciatic N as well
- in some cases of peroneal nerve avulsion, there will also be a sciatic nerve traction injury;
EMG
- useful to document conduction block
- should be performed within one month of injury
- amplitude of the sensory potential & decreases in N conduction velocities - confirm sensory & motor deficits, respectively
Prognosis/h2>
- with partial nerve palsy -> 80% recover completely
- with complete palsy - < 40% have complete recovery
Treatment
Nerve in continuity - neuropraxia
- observe first
- if no neurologic improvement after 2-3 months - operative decompression
- external neurolysis of peroneal N at the level of the fibular head
- may be entrapped by thick fibrous bands which arch over the N as it crosses the fibular ne
nerve not in continuity - neurotmesis
- nerve repair
- in knee dislocation - may be concomitant tibial N division palsy
- tendon transfer - tib.post. to dorsum of the foot