Abstract
Key Points:
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Historically, 22.25, 26, 28, or 32 mm metal femoral heads were used in primary total hip arthroplasty, but innovations in materials now permit head sizes 36 mm or larger.
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Stability and wear of primary total hip arthroplasty are related to the diameter and material of the femoral head.
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Larger diameter femoral heads are associated with increased joint stability through increases in arc range of motion and excursion distance prior to dislocation.
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Fixation of the acetabular component may be related to the size of the femoral head, with increased frictional torque associated with large diameter heads and certain polyethylene.
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Linear wear of highly crosslinked polyethylenes seems unrelated to femoral head diameter, but larger heads have been reported to have higher volumetric wear.
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Mechanically assisted crevice corrosion at the connection between the modular femoral head and neck may be associated with the femoral head size and material.
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Cobalt chromium alloy, alumina ceramic composite, or oxidised zirconium femoral heads on highly crosslinked polyethylene are the most commonly used bearing surfaces, but each may have unique risks and benefits.
Conclusions
At present, there is a wave of enthusiasm for the routine use of “large” (32, 36 mm, or larger) femoral heads with highly crosslinked polyethylene for the vast majority of patients having a primary THA. It may be reasonable to consider the “graduated femoral head-outer acetabular diameter system”, using 28 mm femoral heads with “smaller” acetabular components (<50 mm), 32 mm femoral heads with acetabular components 50 – 56 mm outer diameter, and 36 mm or larger femoral heads with acetabular components 58 mm or larger in diameter, to minimise both the risk of dislocation and the frictional torque. Although the linear wear of highly crosslinked polyethylene appears to be independent of head size, the reported increase in volumetric wear with large femoral heads and highly crosslinked polyethylene requires further study, and should temper the use of femoral heads 36 mm or larger in younger and more active patients. With its long and successful history, it is difficult to recommend the complete abandonment of the cobalt chromium alloy femoral head in all patients having a primary THA. Alumina ceramic or oxidised zirconium heads may be considered for younger, heavier, and more active patients, who seem to have the highest risk of trunnion corrosion. Surgeons and patients should be aware of the unique possible complications of these two newer femoral head materials.
