The perpendicular distance from the centre of the femoral head to the long axis of the femur
Harris 1992
- aim for supra-physiologic offset
- avoid making offset less than original at all costs & makes longer if possible
Soft tissue balancing equals restoring femoral offset
1. Abductor lurch / Trendelenburg gait
Templating
Approach
Fixation
Bearing Surface
Head Size
Offset
Disabling hip pain
Severe functional impairment
Failed non operative management
Painless deformity
The removal of material, with the generation of wear particles under an applied load and in relative motion
Tribology is the study of wear and lubrication
Adhesion
- bonding of the surfaces when pressed together
- may pull away material from the weaker surface
Abrasion
- asperities on the harder surface cut and plough
Migration of the femoral head past the medial wall of the acetabulum / ilioischial line
Centre edge angle > 40o
Primary
Otto's Disease
- bilateral in one third
- middle aged females
- pain & decreased ROM early
- coxa vara & OA common
- ? causally related to osteomalacia
Decreased tone
- Polio
- Down's syndrome
- spina bifida
Increased tone
- cerbral palsy
- Parkinson's
- CVA
Rare
- case reports only
Acetabular dysplasia not uncommon in this group
Results
Severe LBP
- most common indication
Ipsilateral knee pain
- less beneficial
Malposition
- especially abduction
Absent abductor mechanism
Flail
Active infection
Insufficient bone stock
LLD
Femur
- removal of femoral head cartilage
- resurfacing with metal
- cemented / uncemented
Acetabulum
- standard technique
Bearing surface
- metal on metal
Relatively young man (40 - 50)
OA
Extraskeletal bone formation in periarticular tissues
- HA crystals within osteoid matrix
Different to calcification
- osteoid matrix laid down
1. Myositis Ossificans
- post traumatic