Reproduce the normal anatomical centre of rotation
Restore femoral offset
Maintain equal leg lengths
Usually template off normal hip
1. LLD
2. Offset
3. Femoral component
4. Acetabular component
5. Osteotomy / femoral seating
THR in dysplastic hips has a higher failure rate
- due to anatomic abnormalities
- due to generally younger age
Restore normal biomechanics and preserve bone stock
Soft tissues
Most common reason for litigation against orthopaedic surgeons in THR
Usually from lengthening
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