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Proximally modular stems prove good choice for THR

Study finds only two aseptic loosenings, no stem-sleeve dissociations in 517 primary cases.

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ORLANDO, Fla. — Appropriately designed modular stems can be valuable in total hip arthroplasty, a recent study shows.

At two to 17-year follow-up, researchers at Sunnybrook & Women’s College Health Sciences Center, Toronto, experienced only two cases of aseptic loosening, no stem-sleeve dissociations and no sleeve fractures in 517 primary THA cases using the S-Rom Modular Hip System (DePuy, Johnson & Johnson), a proximally modular stem.

The researchers have used the stem for 18 years. “It’s easy to put in, it takes less than 40 minutes, there’s a minimal number of complications, which can be dealt with easily because the S-Rom’s a ... good revision stem,” Hugh U. Cameron, MB, FRCS(C), said at the 22nd Annual Current Concepts in Joint Replacement Winter 2005 meeting.

In the past, distally modular stems underperformed and were withdrawn from the market. Mid-stem modular stems sometimes broke at the taper modular junction, and many proximally modular stems without positive locking also underperformed and were withdrawn. However, the S-Rom offers a positive locking ability — the higher the load, the firmer the fixation. “[Positive locking] means that when you stand on the stem and you press on the head, it forces the male part deeper into the female part so that the taper junction is more stable,” Cameron said.

The S-Rom fills the distal canal for angular control and provides rotational control. Surgeons can lock the porous-coated sleeve in any version, which helps prevent sleeve fractures. The sleeve also provides proximal rotational control and resistance to sink, which is typical in undersized tapered stems, he said, noting the device allows for distal fixation when the stem is left unpolished.

“The problem with distal fixation is removal will be difficult,” Cameron said. “I believe you need distal stability, but not distal fixation.”

At a mean follow-up of 11.5 years, Cameron found two aseptic loosenings among 517 primary THA cases. One loosening was a calcar episiotomy with failure of bone in-growth and developed distal osteolysis. The other was a subtrochanteric osteotomy nonunion. Cameron performed three stem revisions due to fracture — one at the stem tip and two after subtrochanteric osteotomy — and six revisions for late sepsis.

Cameron also combined his results with those of Lou Keppler, MD, of Cleveland, which contains an additional 450 primary THA cases without aseptic loosenings, giving a combined loosening rate of 0.2%. The combined results will be presented at the AAOS this year.

Dr. Cameron is a paid consultant for DePuy and has a financial interest in the S-Rom Modular Hip Stem.

For more information:

• Cameron H. Modularity in primary THA: Is there a role? #13. Presented at 22nd Annual Current Concepts in Joint Replacement Winter 2005. Dec. 14-17, 2005. Orlando, Fla.