Epidemiology
Primary THR 1%
Revision THR 3%
DDH 5%
Sciatic nerve 90% of nerve palsy
Other
- femoral nerve
- CPN
- ulna / radial nerve from positioning
Aetiology
Direct
Laceration
- exposure / sciatic and superior gluteal nerve
- drill reamer / obturator nerve
- spike of cement / obturator nerve
Thermal
- diathermy
- cement / obturator nerve
Indirect
Compression
- cerclage wires
- anterior acetabular retractors / femoral nerve
- posterior femoral retractors / sciatic nerve
Haematoma
- post op sciatic nerve palsy
Strap / Pillow (COPN)
Traction
- LLD > 4cm
- dislocation
Prognosis Nerve injury
Femoral > COPN > Sciatic
- most have some residual loss
- 80% incomplete recovery over 18 month period
- none after this
Good prognostic signs
- retention of motor function
- recovery of motor function initial few days
Document neurological status prior to indexed procedure
Poor prognostic signs
- nil recovery by 7 months
- causalgia
- elderly
- poor medical condition
- DM, alcoholism
- spinal stenosis (double crush)
- smoking, steroids
Superior Gluteal Nerve
Anatomy
- L4/5 S1
- sciatic notch above piriformis
- runs between G. medius and minimus
- supplies G. medius and minimus & TFL
Injury
- anterior / SP approach injure branches to TFL
- lateral / Hardinge approach respect safe zone in G. medius 3-5 cm proximal to GT
Obturator Nerve
Anatomy
- L2-4 posterior division
- along sacral alar
- emerge obturator foramen
- sensation to medial thigh
- adductor muscles
Injury
- screws / cement / reamers / retractors
- antero-inferior quadrant of acetabulum
Sciatic Nerve
Epidemiology
- most frequently injured nerve
- 1.5%
Anatomy
L4/5 S1-3
- emerges at G. sciatic notch
- usually tibial and peroneal components combined
- below piriformis
- below gluteals and above short ER
Variations
- can be in tibial and CPN divisions
- one or both divisions can run through piriformis
- both emerge above pirifomis
- always treat pirifomis with care in posterior approach
Runs over long head of biceps femoris under gluteal insertion
- passes between LHB and adductor magnus
- SHB only thigh muscles supplied by CPN component
Motor
- CPN: DF and evertors
- Tibial: PF and invertors
Sensory
- Sural: medial sural from tibial / lateral sural from CPN
- Superficial and Deep Peroneal nerve
- Tibial nerve
Aetiology
Traction
- > 4cm lengthening in DDH 30% nerve palsy
- 0% if less than 4 cm
Compression
- posterior retractors / posterior acetabular wall
- post operative haematoma (CT scan)
- wires or cables (around femur)
- sutures (in closure at end of case)
Direct laceration
- revision surgery
- posterior approach
- DDH, Protrusio (nerve in abnormal position)
Ischaemia
CPN division
More vulnerable than Tibial branch
- fixed at fibular head
- more superficial than sciatic nerve
- less surrounding connective tissue
Examination
Sciatic nerve / CPN only / Tibial nerve only (very rare)
NCS
Determine if CPN at level of hip or knee
- function of short head of biceps
Management
Explore if cause is haematoma
- delayed onset or late progression of palsy in setting of haematoma
- CT may be useful to diagnose
Explore if believe major direct injury
- transection or entrapment in cerclage wires
- sutured
Otherwise few indications to explore
Femoral Nerve
Anatomy
L2-4
- enters femoral triangle between psoas and iliacus
- power to quadriceps
- sensation to medial thigh and calf
Aetiology
Compression
- anterior retractors above psoas in anterior approaches to the hip
- iliacus hematoma / bleeding tendencies
Femoral nerve blocks
Injury
- cement extrusion / screws AS quadrant
Clinically
Anteromedial numbness
Difficulty climbing stairs
Prognosis
Very rare 0.4%
- usually recovers in full