The First Generation Metal-on-Metal bearings manufactured in
the 1950s and 1960s were produced by the investment casting process (Ring
and McKee Farrar prostheses). From these devices we have recorded the
longest benign clinical history of cobalt chrome alloys with extremely low
linear wear rates.
The BHR™ is produced using the investment casting process from high carbon
cobalt chrome in the As Cast micro-structural condition.
Wear studies have shown that Cobalt Chrome in its As Cast form has superior
wear resistance to other forms of the alloy.
The BHR™ has a hemispherical cup design with a cast-in
porous ingrowth surface called Porocast™. This ingrowth surface does not
require a heat treatment to attach the beads and therefore preserves the
Clearance is the term used to describe the effective gap
between the femoral head and acetabular cup in a Metal-on-Metal bearing. It
is calculated by subtracting the radius of the femoral head from the radius
of the acetabular cup. This difference in radii is used to describe the gap
at the equatorial position on the bearing when the femoral head is in
contact with the acetabular cup in a polar orientation. Polar bearings
operate with a large apparent contact surface area. However the real contact
surface area is very small. It is at this point where the articular surfaces
interact creating friction and wear.
Generation of fluid film
A fluid film is present when the two articulating surfaces are separated by
the lubricant. It is the clearance (entrainment) angle and motion which
generates the fluid film
Conventional total hip replacement has failed the
young active adult. The Birmingham Hip Resurfacing
addresses this difficult patient group.
We have shown that the femoral head remains viable
after hip resurfacing.
Femoral neck fracture is a rare occurrence and in
our experience has only occurred in the presence of poor
Femoral head fixation with cement has been shown by
us and others to be extremely durable.
We have seen early and extensive ingrowth into the
hydroxyapatite coated Porocast™ socket.
It has been shown that thick film lubrication is
possible in these large headed metal on metal hip
resurfacing arthroplasty bearings.
We have observed no wear on retrieved Birmingham Hip
We have measured low blood metal ion levels in a
highly active group of patients fitted with the
Birmingham Hip Resurfacing.
We have measured low frictional torque in these
Birmingham Hip Resurfacing bearings on a realistic
loading pendulum apparatus.
In 1,839 metal metal hip resurfacings performed
between Feb 1991 and Dec 1999 no dislocations have
We have treated a young active patient group with
arthritic hips when they needed their treatment most,
allowing them to return to work.
Patients have achieved excellent functional results
after this procedure with many participating in
recreational sport allowing the health gain associated
In this young and active population we have seen in
our 1,720 hybrid hip resurfacings in the Birmingham
series an overall 99% success rate and in our longest
followups we have a 98% survivorship at 5 – 6 years.
The BIRMINGHAM HIP™ Resurfacing (BHR™) has demonstrated exceptional
clinical results worldwide. High survival rates of 98% or
better were achieved in clinical centres around the world.
1,2,3,4,5 In addition, the recently published Australian
Orthopaedic Association National Joint Replacement Registry
reports BHR as having the lowest revisions per 100 observed
‘component’ years when comparing all resurfacing implants
used in the country. 6 Other clinical studies have focused on predictive
measurements to project long-term survivorship of the
resurfaced femoral head. Researchers at the University of
Oxford, England used roentgen stereophotogrammetric analysis
(RSA) to measure the stability of the femoral head. At 24
months, the total three-dimensional migration of the head
was not statistically significant at 0.2mm.Previous studies have shown that implants that loosen
quickly have rapid early migration. According to the
authors, these results suggest the BHR femoral component is
an inherently stable device predicting a good long-term
performance. 7,8 It is widely accepted that the Bone Mineral Density (BMD)
of the proximal femur generally decreases after cementless
THA using standard designs of femoral components. However,
BMD studies conducted at Osaka University, Japan reported
the post-operative BMD in the proximal femur was
significantly greater in patients treated with the BHR
system compared to the conventional system. The patients
treated with the BHR system demonstrated preservation of the
BMD in Gruen zone 1 and an increase in zone 7.
These results suggest that transfer of load to the
proximal femur was more normal after surface replacement
with the BHR system. These findings also show the BHR system
preserves the bone stock of the proximal femur after
Survivorship: Results Comparable
Shimmin et al 1
Ebied et al 2
De Smet et al 3
6 – 42
Treacey et al 4
McMinn et al 5
Australian Joint Registry.
Australian Nation Joint Registry Annual Report 2006
(Clinical Results)6 :
Resurfacing Hip systems requiring revision.
Observed Component Years
Revisions per 100 Observed Component Years
Additional Radiographic Studies
Glyn-Jones et al 7
Femoral migration < 0.2mm at 2 Years
Itayem et al 8
Vertical migration femoral component < 0.01mm at 5
Vertical migration acetabular component < 0.03mm
at 5 Years
Kishida et al 9
BMD preserved / improved in proximal femur at 2