THR Resurfacing

ConceptBirmingham Hip Resurfacing

 

Femur

- removal of femoral head cartilage

- resurfacing with metal

- cemented / uncemented

 

Acetabulum

- standard technique

 

Bearing surface

- metal on metal

 

Indications

 

Relatively young man (40 - 50)

OA

 

Absolute Contra-indications

 

Severe bone loss femoral head

Large femoral neck cyst

Small acetabulum

 

Relative Contra-indications

 

Osteoporosis

Age > 65

BMI > 35

 

Caution

 

RA

Female

AVN femoral head

 

Advantages (many theoretical)

 

1.  Bone preservation

- preserves femoral bone stock

- however makes acetabular preparation more difficult

 

2.  Improved stress transfer to proximal femur

- less proximal stress shielding

- improved proximal bone density

 

3.  Reduced dislocation rates

- heads 36-54 have reduced rates compared with 22-32

- can occur though if poor technique or component loosening

 

Dislocated Birmingham Hip ResurfacingDislocated Birmingham Resurfacing

 

4.  Better kinetics

- faster walking speeds

- may be better ROM

- possible better proprioception

- may be element of selection bias (i.e. is done in younger, fitter patients)

 

4.  Easier revision of femoral component

- better bone stock

- simply recut and use stem

 

6.  Possible improved longetivity

- very low wear rates metal on metal

 

Disadvantages

 

1.  Poor modularity

- difficult to adjust LLD

- difficult to adjust offset

- patients with very abnormal abnormality better off with conventional THA

 

2.  Not suitable for elderly / poor bone stock

- increased risk femoral neck fracture

 

3.  Femoral neck fracture

 

 

4.  Metal ions

- in serum, RBC, urine

 

Problems

- risk metal sensitivity

- risk carcinogenesis / teratogenesis

- CI in woman of child bearing age

 

5.  Loosening

 

Complications

 

Femoral Neck Fracture

 

Incidence 0-4%

- 1.5% in a study of 3500 BHR in Australia (JBJS Br 2005)

- early in learning curve

- early in prosthesis life

 

Risk Factors

- decreased bone mass / osteoporosis

- elderly

- inflammatory arthritis

- females (risk x2)(AJR)

- femoral head and neck cysts

- femoral neck notching

- varus femoral component (< 130o neck shaft angle)

- cup impingement on neck

- improper implant seating

- AVN femoral Head

 

BHR femoral neck notchingBHR Femoral Neck Notching 2

 

Revision

- relatively simple

- recut neck

- femoral implant with large metal head

 

Revision BHR

 

Early loosening

 

Machining

 

Initially due to poor early manufacturing

- decreased clearance

- inadequate polar bearing

- increased peripheral bearing, seizing, cold welding and loosening

 

Modern machining

- small surface asperities

- improved fluid film lubrication

- polar bearing with small clearances

- very low wear and little particle production

 

Causes

 

A.  Oversized heads / notching

 

BHR Oversized Femoral HeadBHR Loosening

 

B.  Varus Femoral Component

 

BHR Valgus v Varus Femoral Component

 

C.  Femoral head AVN

 

Due to extensive releases required to expose / surgically dislocate femoral head

 

BHR Femoral Head AVN

 

D.  Open Acetabular Component

 

Theorised to cause point loading

- increased metal wear

- best to close cup

 

BHR Open v Closed Acetabular Component

 

E.  Other

 

BHR Acetabular Component Protrusio

 

Australian Joint Registry 2023

 

15387 procedures

 

Best outcome

- Male < 65 with OA

- Able to get 55mm head or larger

 

Revision rate

 

Cumulative

- 11% @ 20y for OA

 

Reason for revision

- Loosening (25%) - most common after 10y

- Metal disease (22%) - also late, after 10y

- Fracture (20%) - peaks early

 

Revision by diagnosis at 20y

- OA 11%

- DDH 19%

- AVN 16%

 

Revision by prosthesis

- Adept 6.5% @ 15y

- BHR 9.5% @ 15y, 12% @ 20y

 

Revision by age at 20y

- < 55 = 11%

- 55-64 = 12%

- > 65 = 9%

 

Revision by sex at 20y

- Male 8%

- Female 22%

 

Revision by head size at 20y

- < 45 = 31%

- 45-49 = 15%

- 50-54 = 8%

- > 55 = 6%