Tapered, fluted, modular titanium stems offer better quality of life for patients

Cylindrical, nonmodular cobalt chromium stems led to lower patient satisfaction scores.

Issue: September 2006

Cylindrical, nonmodular, cobalt chromium stems deliver the promise of extra long-term fixation after femoral revision surgery. But when it comes to quality of life for patients, tapered, fluted, modular titanium stems show superior results.

In a cross-sectional matched cohort series, researchers found that patients treated with the tapered, modular stems demonstrated better WOMAC, Oxford Hip, SF-12 and patient satisfaction scores, according to Donald Garbuz, MD, MHSc, FRCSC, of the University of British Columbia in Vancouver.

"In recent years, modular tapered stems have come out to the market and these basically give you ... off-the-shelf customization," Garbuz said at the American Association of Hip and Knee Surgeons Specialty Day meeting. "They have multiple options for the proximal femur and usually separate or different stem lengths of multiple diameters for the distal femur."

The options provide several advantages, Garbuz said: intraoperative adjustment to leg lengths, horizontal offset and neck version, as well as reduced pain and stiffness and better function for the patient.

Garbuz and his colleagues enrolled 220 patients treated at the university from August 1998 to December 2003. They originally found 34 eligible patients treated with the tapered, fluted, modular stems (Zimmer Modular Revision Stem, Zimmer) but excluded two for insufficient data and another for a fracture in the modular junction, Garbuz said. The remaining 31 patients served as the cohort.

The control group included 189 patients who underwent femoral revisions with the cylindrical, nonmodular, cobalt chromium stems (Solution Stem, DePuy).

The researchers matched patients by age and gender. "[Patients] had to have a minimum two-year follow-up, and they were excluded if they had a revision for infection or recurrent dislocation," Garbuz said.

Patients were also excluded if their acetabular reconstruction required a reconstruction cage, structural allograft or constrained liner.

Quality-of-life results

All quality-of-life measurements favored the tapered, modular stem. Oxford Hip Scores were statistically and clinically significantly better for these stems (P=.006), and patient satisfaction scores reflected the same findings (P<.0001).

"Similarly, when we look at WOMAC pain, again, there is a statistically and clinically significant difference (P=.03)," Garbuz said. "Greater than 9 points on a WOMAC score is considered clinically significant, and here we see [the tapered, modular stems achieved greater than] 9 points."

WOMAC function scores (P=.02) and overall WOMAC scores (P=.02) were also higher for the patients treated with tapered, modular stems, he said.

Although not a study goal, the researchers also recorded the intraoperative fracture rate for the two stems. They found a 15% to 17% intraoperative fracture rate for the cobalt chromium stem patients and a fracture rate of less than 5% for the modular, fluted stem, Garbuz said.

Ruling out bias

"There was an association between improved quality of life and the use of a modular, tapered, titanium stem, compared to the ... cobalt chromium stem," Garbuz said. "I say 'association' because you have to look for other reasons."

Garbuz said he and his colleagues needed to also rule out any bias or other potential confounders. They confirmed that surgeons chose the cylindrical cobalt chromium stems as their first-line stem choice for femoral revisions, but chose modular, tapered stems for patients who they felt could not obtain a 4-cm to 5-cm fit.

Researchers also reported no clinical or significant difference in preoperative scores between the two groups, and found no difference between the groups for comorbidity, surgical approach or allograft use.

For more information:
Garbuz D. Femoral revision arthroplasty with fluted, modular titanium stems. Presented at the American Association of Hip and Knee Surgeons Specialty Day Meeting. March 25, 2006. Chicago.