Issue
Most common reason for litigation against orthopaedic surgeons in THR
Usually from lengthening
Complications of LLD
1. Nerve palsy
Sciatic nerve - tolerate average 4.4cm lengthening
Common peroneal nerve - tolerate average 2.7 cm lengthening
Lengthen by up to 15-20% of the resting nerve length
- but in reality is unknown and multifactorial
2. Lower back pain / scoliosis
3. Abnormal gait
2 - 4 cm discrepancy
- significant increase in oxygen consumption
- also risk of falls
Assessment of LLD
Preoperative
Examination
Functional LLD
- blocks
Apparent LLD
- umbilicus to medial malleolus
True LLD
- ASIS to medial malleolus
Apparent shortening
- FFD & adduction hip
Apparent lengthening
- abduction contracture
- scoliosis, fixed pelvic tilt
Consent
Very important
- must mention LLD
X-ray Assessment
AP pelvis
- both femurs IR 15o
- compensate for anteversion
Templating
Leg Length
1. Horizontal line through two points at inferior aspect of ischial tuberosities
- compare to lesser tuberosity
2. Acetabular teardrop
- vertical line to centre of femoral head
- calculate difference
- multiply by 0.8 to account for 20% magnification
Tear drop more reliable
- less affected by rotation
- closer to centre of rotation of hip
Note: ensure one femur is not abducted, adducted
1. Establish Centre of rotation
Acetabular Templating
A. Ilioischial line / Inter-tear drop line / Superior edge acetabulum
B. Ranawat
- intersection of ilioishial and shenton's
- 5 mm laterally
- 1/5 pelvis up and 1/5 pelvis in
C. Rule of thumb
- 2 cm horizontal and 4 cm vertical from teardrop
2. Calculate LLD
- draw line LT / ischial tuberosity / inferior teardrop
- up to centre of femoral head / centre of rotation
- beware adducted hip on x-ray / false shortening
3. Femoral Templating
A. Size implant
B. Determine offset
C. Determine femoral osteotomy from lesser trochanter to restore LLD
Intra-operative
1. Leg to leg comparison
Careful patient positioning
- ASIS perpendicular to floor and patient stable
- ability to palpate both knees and feet
- small pillow to prevent adduction of superior leg
- feel LLD before surgery in this position
- upper femur often feels 1 cm short even if no LLD due to adduction
- aim to reduce LLD to normal after reduction of THR at end of case
2. Intra-operative measurement
System
- proximal pin in superoacetabular region
- distally diathermy mark in vas lateralis
- calliper measures horizontal distance (LLD) and vertical distance (offset)
- must place leg in similar position each time to measure leg distance
3. Tests
Shuck test
- distract femoral head from acetabulum
- should be only few mm of shuck with correct tension
Drop Kick Test
- with thigh extended, knee should remain flexed
- if tension too tight, knee will extend
ROM
- if hip tension too tight, ROM especially IR / ER / extension is limited
Postoperative
Transient Perception of LLD
- 14% patients
- usually passes
- may have had LLD before which has been adjusted
- will then feel that leg is longer / which is true
Overlengthening
- may get back pain
Shortening
- abductor weakness
- even dislocation
Management
Delay using shoe lift for 6/12
- allows perceived LLD to resolve
Rarely revision surgery is required
- persistent neurological pain
- beware instability