Leg Length Discrepancy

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

 

THR LLDTHR LLD with secondary 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

 

THR Template LLDTHR Leg Length Ischial LineCentre of Rotation Ranawat Method

 

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

 

LLD with hip adduction

 

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