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More complete bone ingrowth and less pain with HA-coated stems
Coated-stem patients also report less pain.
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ORLANDO, Fla. — Hydroxyapatite coatings for noncemented femoral fixation provide faster and more complete in-growth without risking third-body wear — results that justify the additional costs associated with the coating, according to Chitranjan S. Ranawat, MD, of Lenox Hill Hospital, in New York.
Some studies have questioned hydroxyapatite’s (HA) utility when used with porous coatings. Others have shown that it increases bone ingrowth and benefits noncemented fixation, yielding 90% to 100% clinical survivorship up to 15 years postop. “The best evidence is in autopsy findings showing increased amounts of bone ingrowth, compared to just noncemented porous-coated fixation,” Ranawat said at the 22nd Annual Current Concepts in Joint Replacement Winter 2005 Meeting.
No difference in HA, non-HA
Ranawat presented the results of a prospective, randomized study, which he published in 2002 in the Journal of Arthroplasty. The study represents the first to “show the efficacy of HA in providing clinical evidence of early osteointegration and better outcomes,” he said. Researchers found no difference in radiographic and other findings between patients treated with HA-coated stems and those treated without such stems. However, patients treated with HA-coated stems had significantly less pain.
The researchers randomly assigned 177 patients into two groups, with 82% of patients received plasma-sprayed proximally coated stems. The remaining patients received an identical stem, but with an HA coating over the plasma-sprayed surfaces. The two treatment groups had similar demographics, and a primary diagnosis of degenerative joint disease. Ranawat performed all procedures using posterior exposure, hypertensive epidural anesthesia and the Ring-Loc Acetabular (Biomet) noncemented fixation cup, he said.
At final follow-up of three to eight years, Ranawat and colleagues found that both patient groups had good results, including Hospital for Special Surgery scores, walking abilities, sports activities and overall patient satisfactions. However, “there was significantly less pain (P<.05) in the HA group and this pain was thigh pain and trochanteric pain,” Ranawat said.
The study found no differences between groups in radiographic evaluations, bone ingrowth, or in head socket wear penetration. “We concluded that there is no evidence, at least in this study, that HA coating leads to increased polyethylene wear,” Ranawat said. He explained that the goal of noncemented femoral fixation is to provide reproducible and durable fixation. The most durable HA coating is 50 µm to 75 µm thick with 95% crystallinity and a 99% porosity. Thicker coatings may peel and fragment, leading to increased third-body wear, he said.
Indications for cemented stems
Ranawat uses a cemented femoral stem in patients aged 65 to 80 years, except in those who have significant coronary artery disease. “This is mainly because of the postop complications of cemented pressurization,” he said.
Typically, noncemented fixation does not transfer stress to the bone as completely as cemented fixation. However, this may not be the case for patients with a cortical index of at least 38%. “At 38% cortical index, 6 cm below the lesser trochanter is a good indicator of how good the quality of bone is,” Ranawat said.
For more information:
- Ranawat C. The HA taper: Any added value? #11. Presented at 22nd Annual Current Concepts in Joint Replacement Winter 2005 Meeting. Dec. 14-17, 2005. Orlando, Fla.
- Rasquinha VJ, Ranawat CS, Mauriello AJ. Hydroxyapatite: Catalyst or conjurer? J Arthroplasty. 2002;4(Suppl 1):113-117.