No effect on BMD between cement, cementless TKR fixation

Using cemented or cementless fixation also appears to have no effect on relative bone mineral density around the implant site.

Neither cemented nor cementless fixation of total knee replacement components appear to significantly affect periprosthetic bone mineral density, according to a study by researchers in Scotland.

R.M. Dominic Meek, MD, FRCP, and colleagues at the Southern General Hospital, Glasgow, compared the bone mineral density (BMD) around the femoral and tibial components of TKR patients implanted with an LCS rotating platform prosthesis (DePuy Orthopaedics) using either cemented or cementless fixation. They also compared relative BMD differences between patients’ operated and nonoperated knees.

They published their findings in the British edition of the Journal of Bone and Joint Surgery.

At two years’ follow-up the researchers found low levels of BMD and relative BMD differences in several periprosthetic regions, regardless of fixation method. This suggests that “the introduction of the prosthesis itself was associated with a reduction in periprosthetic bone density,” the authors said in the study.

Unilateral TKR patients

Meek and colleagues compared BMDs measured using DEXA scanning between unilateral TKR patients who received an LCS prosthesis implanted using either cemented or cementless fixation between October 2001 and May 2002. They had excluded from the study patients with known metabolic bone disease, osteoporosis, inflammatory arthropathy or previous boney knee surgery, according to the study.

The cement fixation group included 18 patients — 10 men and eight women with a mean age of 71 years. The cementless fixation group included 20 patients — nine men and 11 women with a mean age of 69 years. There was no significant difference between groups in terms of mean age or clinical scores, the authors noted.

All patients received anteroposterior (AP) DEXA scans of four regions (one femoral and three tibial) and lateral DEXA scans of six regions (four femoral and two tibial) at a minimum of two years follow-up. Researchers also obtained DEXA scans of the lumbar spine and hip to identify patients with osteopenia or osteoporosis.

Some systemic bone loss

Overall, DEXA scans of the lumbar spine and hip revealed seven cemented and 11 cementless patients with evidence of systemic bone loss, with no significant difference between groups. Of the 18 cemented patients, five had evidence of osteopenia and two had evidence of osteoporosis. For the cementless fixation group, eight had osteopenia and three had osteoporosis, according to the study.

ANCOVA analysis showed no significant differences in BMD between fixation methods for any of the four AP or six lateral regions studied.

The researchers did find a significant difference in BMD between fixation methods for one of the 10 areas studied on patients' nonreplaced knees — the AP-T2 region (P=.036). However, the authors noted the discrepancy was probably due to chance because the fixation method is not likely to affect nonreplaced knees. “The lack of significance for the results of BMD in nine of the 10 regions of interest in the nonreplaced knee was taken to indicate the absence of significant selection bias between the cemented and cementless groups,” they said.

Relative BMD difference also appeared unaffected by fixation method for most regions evaluated. Only Lat-T6 showed a significant difference (P=.0289), with cementless fixation having 9% less relative density difference, according to the study. But the authors noted this finding should be interpreted with caution because it had not shown a significant difference in [intergroup] BMD and was the only significant result for the 20 regions compared.

For more information:
Abu-Rajab RB, Watson WS, Walker B, et al. Peri-prosthetic bone mineral density after total knee arthroplasty. J Bone Joint Surg Br. 2006;88-B:606-613.