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BHR Hip Device

Hip Resurfacing and Total Hip Replacement at Hips for You Posted on by

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
carbide structure.

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

Summary

  • 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
    bone quality.
  • 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
    Resurfacing bearings.
  • 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
    occurred.
  • 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
    with activity.
  • 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
surgery. 9

Survivorship: Results Comparable
Globally

Author Site n Survival Follow Up
(months)
Shimmin et al 1 Melbourne 231 99.14 % 33 (25-52)
Ebied et al 2 Liverpool 100 99.00 % 17 (mean)
De Smet et al 3 Ghent 200 99.50 % 6 – 42
Treacey et al 4 Birmingham 144 98.00 % 60 (minimum)
McMinn et al 5 Birmingham 1,626 98.4 % 60 (minimum)

 

Australian Joint Registry.
Published Figures

Australian Nation Joint Registry Annual Report 2006
(Clinical Results)6 :
Resurfacing Hip systems requiring revision.

Resurfacing Head Number Revised Total Number % Revised Observed Component Years Revisions per 100 Observed Component Years
ASR 18 503 3.6 446 4.0
Adept 0 19 0.0 3 0.0
BHR 126 5799 2.2 13487 0.9
Conserve Plus 2 48 4.2 82 2.4
Comnet 2000 14 333 4.2 649 2.2
Durom 12 423 2.8 451 2.7
Recap 2 41 4.9 41 4.9
Total 177 7205 2.5 15179 1.2

 

Additional Radiographic Studies

Autor Type n Findings
Glyn-Jones et al 7 RSA 22 Femoral migration < 0.2mm at 2 Years
Itayem et al 8 RSA 20 Vertical migration femoral component < 0.01mm at 5
Years
Vertical migration acetabular component < 0.03mm
at 5 Years
Kishida et al 9 BMD 26 BMD preserved / improved in proximal femur at 2
years

 
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