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More accurate acetabular inclination found with cemented THA
National registry data shows a higher revision rate of dislocation for cementless vs. cemented components.
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Using cemented total hip arthroplasty systems during primary procedures results in more accurate positioning of the acetabular component and may lead to a decreased rate of dislocation, according to a study conducted by researchers in the United Kingdom.
“Revision for dislocation is more likely for primary cementless THA [total hip arthroplasty] than cemented,” David Roberts, MRCS, an orthopedist at Royal National Orthopaedic Hospital Stanmore, said during his presentation at the 12th EFORT Congress 2011. “Acetabular inclination is more accurate using a cemented implant, and this is an important consideration when selecting acetabular component fixation for arthroplasty.”
Assessing accuracy
To determine whether the method of fixation impacted the position of the acetabular component, Roberts and his colleague Nicholas Garlick, FRCS, analyzed 80 cemented and 46 cementless primary THAs performed at The Royal Free Hospital in 2008. Two independent observers measured the angles of inclination among the groups using a picture archiving and communication (PACS) system.
“We drew a line through the long axis of the implant and then compared it with a line parallel to the pubic bones underneath,” Roberts said. “The cemented implants, obviously, the polyethylene is radiolucent, but we used the wire ring embedded in the implant to measure the angle.” Using this method, they found good inter- and intra-observer reliability of their measurements.
Roberts and Garlick assessed the number of implants within 5° of the target angle of insertion.
“Different surgeons had a different target angle. Some implanted at 40° and some implanted at 45°, but our assessment considered implantation angle to be correct if it was within 5° of what the surgeon intended,” Roberts said.
The investigators discovered that more cementless implants were off target than cemented implants, which “indicates that the cementless implants are harder to implant as accurately,” Roberts said.
Registry findings
To compare the rate of revisions due to dislocation, the investigators reviewed National Joint Registry data between 2004 and 2009. They found that 266 of the 69,822 cementless THAs were revised for this reason compared with 262 of the 92,928 cemented procedures (0.381% vs. 0.282%).
“On insertion of a cemented implant, fine micro-adjustments are possible as the cement is setting the first few seconds,” Roberts said. “Position of a cementless implant, however, is determined largely by your angle of reaming. But even if your angle of reaming of your acetabular component is dead on target,” Roberts continued, “as you are impacting the component, the tiny microvariances in the bone may jog the implant off course, so the implant may not sit exactly as intended.”– by Renee Blisard
Reference:
- Roberts D, Garlick N. Increased rate of total hip replacement dislocation with cemented components: Accuracy of acetabular inclination. Paper #464. 12th EFORT Congress 2011. June 1-4. Copenhagen, Denmark.
- David Roberts, MRCS, can be reached at Royal National Orthopaedic Hospital Stanmore, Brockley Hill, Stanmore, Middlesex HA7 4LP U.K.; 020 8954 2300; email: david.roberts@rnoh.nhs.uk.
- Disclosure: Roberts and Garlick have no relevant financial disclosures.