In light of reported problems with metal-on-metal hips and erosion and osteolysis found with other bearing surfaces, an interim study presented at the 13th EFORT Congress 2012 supports the use of couplings with ceramic heads to reduce wear.

“Ceramic heads appear to reduce wear against modern highly crosslinked polyethylene,” study presenter Javad Parvizi, MD, FRCS, said.

Parvizi, an Orthopedics Today Editorial Board member, touted the superiority of ceramic components and noted that he is “not aware of any biological response to ceramic particles.” He added that ceramics have increased lubrication, smaller grain sizes than cobalt chromium and boast a harder surface.

“If you look at scanning microscopy, cobalt chromium has those troughs and valleys,” Parvizi said. “The ceramic head is extremely polished and smooth. It is biologically inert. The wear of ceramic-on-ceramic is the best we have today compared to every other bearing surface.”

Ceramic-on-polyethylene

Parvizi cited an ongoing, multicenter study of 500 patients sponsored by Ceramtec in which he is involved with Richard H. Rothman, MD, PhD;Chitranjan S. Ranawat, MD; and Arthur L. Malkani, MD, that compares the Crossfire and X3 hips (Stryker Orthopedics, Mahwah, N.J.) with metal or ceramic heads. The researchers collected up to 6-year data on the Crossfire and up to 4-year data on the X3. They analyzed data from 162 hips at 6 months, 1 year, 2 years, 4 years and 6 years. They used a Digital Imaging and Communications in Medicine (DICOM) system to digitalize the AP radiographs and then analyzed them using the Martell technique. The researchers analyzed polyethylene wear using the Hip Analysis Suite software. They averaged the wear rate over the life of the prosthesis.

Results

Early results showed that ceramic heads led to reduced wear rates for the two prostheses compared to metal heads. True linear wear rates for the Crossfire with ceramic heads were 0.075 mm/year compared to 0.125 mm/year with metal heads. The wear rate for the X3 was 0.076 mm/year with ceramic heads compared to 0.105 mm/year with metal heads. This resulted in a 30% reduction in wear rates for the X3 with a ceramic head and a 40% reduction in wear for the Crossfire with a ceramic head.

The researchers noted that they used ceramic against polyethylene in younger, more active patients, which presented a study bias. On average in the Crossfire group, they used metal in patients who were 66 years old compared to 63 years in patients implanted with ceramic. In the X3 group, patients who received ceramic heads were 10 years younger than those with metal components.

“If you have got a 4-mm polyethylene, it will last 40 years, theoretically, against metal. It will last 58 years against ceramic,” Parvizi said. “Is that 18 years over the course of 40 years significant? It is for me, and I am sure it is for my patients. If you were the one to choose between metal and ceramic, I hope you will choose ceramic, because it probably does have a longevity compared to the metal.”

Despite the reduced wear rates for ceramic-on-polyethylene, Parvizi noted that trunnionitis may still present a problem. He, therefore, advises a differential diagnosis of possible trunnion erosion in cases with pseudotumor around the hip. – by Renee Blisard Buddle

Reference:

Parvizi J. The influence of head material on polyethylene wear. Presented at the 13th EFORT Congress 2012. May 23-25. Berlin.

For more information:

Javad Parvizi, MD, FRCS, can be reached at the Rothman Institute, 925 Chestnut St., Philadelphia, PA 19107; email: .

Disclosure: Parvizi is a consultant and received sponsorship for this multicenter study from Ceramtec.