Optimal acetabular cup positioning is attained in less than 50% of cases,
March 9, 2010
NEW ORLEANS – High-volume surgeons are more likely than low-volume surgeons
to attain optimal cup positioning for total hip arthroplasty, but both groups
still attain optimal cup positioning less than half of the time, according to a
study presented here.
The findings were presented by Bryan Jarrett, BS, at the 56th Annual Meeting of
the Orthopaedic Research Society.
Jarrett said the purpose of the study was to attempt to correlate the influence
of various patient factors – body mass index (BMI), age, gender and primary
diagnosis for the total hip arthroplasty (THA) – with the positioning of the
"Cup positioning and implant positioning are extremely important to attain
long-term success," he noted.
Methods and measurements
The researchers compiled data from 2,063 patients who underwent a primary
THA, revision THA or Birmingham hip resurfacing from 2004 through 2008.
Postoperative anteroposterior (AP) pelvis and cross table lateral digital
radiographs were obtained for each patient, and the AP radiographs were measured
to calculate cup inclination and version angles. Version direction was
determined through the lateral radiographs.
Acceptable angle ranges were defined as 30° to 45° for abduction and 5° to 25°
There were 1,954 qualifying patients, with 1,218 (62%) acetabular cups
falling within the optimal abduction range and 1,576 (87%) in the optimal
version range. There were 921 (47%) patients with both inclination and version
angles within the optimal ranges.
In the combined analysis, low-volume surgeons showed a 2-fold increase in risk
for cup malpositioning compared with high-volume surgeons. Minimally-invasive
surgery, as an approach, showed a 6-fold increase in risk for cup malpositioning
when compared to the posterolateral approach. Obesity, defined as a BMI greater
than 30, showed a 1.3-fold increase in risk.
Less than half
With patient influences taken into account, the high-volume surgeons
outperformed their low-volume counterparts, but both still attained optimal
ranges in less than 50% of patients.
"When we just looked at high-volume surgeons, 38% of the patients fell within
the optimal ranges," Jarrett said. "When we just looked at low-volume surgeons,
we saw that 26% of the patients were within the optimal ranges."
Callanan M, Bragdon CR, Zurakowski D, Rubash H. An analysis of cup
positioning in total hip arthroplasty: quality improvement by use of a local
joint registry. Paper 362. Presented at the 56th Annual Meeting of the
Orthopaedic Research Society. March 6-9, 2010. New Orleans.