Larger cups and optimal positioning produced lowest ion levels and wear
In a review of 585 blood serum evaluations following hip resurfacing, only
femoral size and cup inclination were found to have an effect on ion levels,
according a study by orthopedic investigators.
The findings were presented at the 2010 Annual Meeting of the American
Academy of Orthopaedic Surgeons.
David J. Langton, MRCS, and his colleagues also found that the size of the
coverage angle of the acetabular component contributed significantly to its
tolerance of suboptimal positioning.
"Larger joints, it must be emphasized, tolerated suboptimal cup position," he
said. "This must be taken into account in all analyses."
Using routinely obtained blood serum metal ion levels from patients under the
care of the two senior authors of the paper being presented – both highly
experienced hip resurfacing surgeons – metal ion results were analyzed regarding
their relationship to femoral and acetabular component size and orientation,
UCLA activity score, age, time post surgery and postoperative femoral head/neck
Langton reported an inverse relationship between metal ion levels and femoral
size. A smaller acetabular coverage arc was associated with higher metal ion
Another significant inverse correlation was noted by Langton between metal
ion levels and contact patch to rim (CPR) distance. CPR is a measurement that
relates the position of the articular contact patch with the patient in standing
position to the cup rim. According to the abstract, CPR less than 5 mm is
associated with a 50% chance of ion levels greater than 30 mg/L.
Words of warning
Langton warned the audience, "To increase metal ion levels as quickly as
possible, use as small a bearing diameter as possible, use a cup with the
smallest coverage arc, and combine very high anteversion with high inclination."
He concluded, "Cups placed with angles between 40° and 50° inclination and 10°
to 20° anteversion have the lowest ion levels and the lowest rates of volumetric
Langton D, Jameson S, Joyce T, et al. A review of 585 serum metal ion results
post hip resurfacing: cup design and position is critical. Paper 006. Presented
at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons.
March 9-13. New Orleans.
Langton has received research or institutional support from DePuy, a Johnson
& Johnson Company, DJ Orthopaedics; he has also received miscellaneous
non-income support (e.g., equipment or services) from DePuy, a Johnson & Johnson