Stemmed Birmingham Hip Replacement
What are large metal on metal bearings?
Common sizes of femoral heads used in total hip replacement are 22 mm, 28 mm, 32 mm and 36 mm. Joint replacements uses heads bigger than this are often considered large headed bearings.
Large metal on metal bearings have been around since the 1960’s (for example McKee-Farrar and Ring total hip replacement).
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A McKee-Farrar total hip replacement.
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Some patient still have functioning implants in situ after 20-30 years. The main determinant for failure or good long term survivorship has been the engineering tolerances used in the traditional component manufacturing process.
Equatorial bearings have been replaced by more favourable polar bearing configurations and optimal clearances values are now better understood.
The most common use of the large metal on metal bearing is in the form of a “hip resurfacing”. Initial results with this procedure appear encouraging but femoral neck fractures ( incidence around 2%), requirement for an extensive approach to the hip and the as yet unknown long term sequele of metal particles on the human immune response are unresolved issues.
Certain risk factors have been identified which could indicate a higher failure rate of resurfacing such as increased body weight, extreme activities, large femoral head cysts and patients who have had previous hip surgery.
Patients with a varus neck where a “valgus” orientation of the resurfacing leads to supero-lateral notching also precludes the use of a resurfacing prosthesis.
In certain situations where hip resurfacing may not be indicated a modular Birmingham hip replacement may be a possible alternative.
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What is a modular Birmingham Hip Replacement (BHR)?
A modular BHR consists of the same socket and femoral head as a hip resurfacing.
The main difference is that the femoral head is placed on a femoral stem just like a total hip replacement.
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This X-Ray shows a total hip replacement using a modular large bearing.
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What is the advantage of a modular BHR total hip replacement?
A modular Birmingham hip replacement maintains the advantages associated with a large, low wearing bearing and at the same time avoids the possibility of neck fracture, reduces the chance of impingement and can be introduced with less soft tissue disruption.
It can often be used when there are some contra-indications to carrying out hip resurfacing.
Having a femoral stem gives the patient a 0.3% chance of having thigh pain.
