Epidemiology
Ranges
- up to 4%
Clinical
Focal pain
- typically anterolateral thigh
- often tender
- corresponds to tip of stem
Aetiology
1. Instability
Types
- early
- late / failed bony ingrowth
Cause
- micromotion at distal stem
- disadvantage of proximal coating
2. Mismatch modulus of elasticity
A. Component material
- mismatch between femoral component and surrounding bone
- lower with titanium stems compared with cobalt chrome stems
- titanium components less stiff & tend to have lower incidence of thigh pain
B. Stem size
- more commonly seen in larger stems
- increases relative stiffness of stem compared to bone
3. Stem design
- distal flutes can decrease distal stiffness
- fully porous coating decreases incidence, but increases proximal stress shielding
4. Osteoporotic bone
- more commonly seen with lower bone quality
DDx
Loosening
- start up pain
Infection
Xray
Loosening
- migration
- progressive radiolucent lines
- abscence of spot welds
Bone Scan
No correlation of findings with thigh pain
Management
Non operative
Up to 2 years
- allows for remodelling
NSAIDS
Physio
Operative
1. Cerclage wire cortical strut grafts
Theory
- improve bony rigidity over distal stem
Technique
- application to lateral femur
- overlap tip proximally and distally 8 cm
- must get host bone integration
- periosteal elevation / bone graft / rigid fixation
- TWB 6 weeks post op
Results
- good results reported
2. Revision