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Cost the only major difference between modular, non-modular TKA

Investigators reported similar outcomes when comparing modular metal-backed baseplates to a non-modular all-polyethylene tibial baseplate.

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A randomized, multicentered trial showed no significant difference, other than cost, between modular and non-modular total knee replacements in patients over 70 years of age with debilitating arthritis.

Scott Wotherspoon, MD, the study’s lead researcher, presented the findings at the American Academy of Orthopaedic Surgeons 73rd Annual Meeting (AAOS) in Chicago. The study included 127 total knee replacements (TKR) performed in 126 patients from centers in London, Ontario, and Halifax, Nova Scotia, between Sept. 1995 and Aug. 1997. Patients were randomized to receive either a modular metal-backed baseplate or a non-modular, all-polyethylene tibial baseplate.

The modular group included 68 patients — 49 women and 19 men with an average age of 76.3 years. The non-modular group included 59 patients — 30 women and 29 men with an average age of 75.9 years.

Surgeons resurfaced patellas and used a midline longitudinal incision with medial parapatellar arthrotomy in all cases. Investigators conducted follow-up evaluations at six weeks and at three, six and 12 months postop, with yearly follow-up thereafter.

According to Wotherspoon, there were no significant differences in Knee Society Clinical Rating System scores. However, the did find significant differences in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores and Short-Form 12 (SF-12) scores.

“With the WOMAC scores, there was significance at three years, with the non-modular having slightly higher scores (P=.012). With respect to the physical component of the [SF-12] questionnaire, there was significance at one year (P=.029), but no significant differences for the remaining years,” Wotherspoon said.

Four of the 68 patients in the modular group and four of the 59 patients in the non-modular group underwent revision surgery. Revisions performed in the modular group were due to three failed patellas and one case of instability, with an average time to failure of 1.7 years. Revisions performed in the non-modular group were due to one case of sepsis and three instances of pain and stiffness, with an average time to failure of 1.54 years, according to the study.

Researchers discovered the major difference between modular and non-modular TKR to be cost related, as non-modular TKR is 35% to 77% less costly than modular TKR, Wotherspoon noted.

For more information:

• Wotherspoon S, Bourne R, McCalden R, et al. A multicentered clinical trial comparing non-modular to modular total knee replacements. #229. Presented at American Academy of Orthopedic Surgeons 73rd Annual Meeting. March 22-26, 2006. Chicago.