Extensive diaphyseal femoral bone loss with less than 4-5 cm of isthmic support is frequently treated with the use of a distally tapered implant. Advocates of modular stems that employ separate body and stem components argue that this design allows for improved version control, implant sizing, and leg-length equalization compared with nonmodular designs.
We retrospectively reviewed the clinical records of 58 patients who underwent revision total hip arthroplasty using a distally tapered femoral stem. Femoral defects were classified as Paprosky type IIIA in 36 patients, IIIB in 17, and IV in five. Implants were modular in 15 and nonmodular in 43.
Leg-length discrepancy improved from a mean 1.5 cm preoperatively to 0.79 cm postoperatively. The mean difference in preoperative and postoperative leg-length discrepancy measured 0.61 cm and 0.99 cm for nonmodular and modular implants, respectively. Mean subsidence among all implants was 0.3 cm (range, 0.0 to 1.2 cm); subsidence averaged 0.28 cm and 0.38 cm for nonmodular and modular implants, respectively. A nonmodular stem at our institution is $558 less expensive than its modular counterpart; this difference translates to a hypothetical overall cost savings of $32,364 in this small series.
The advantages of modularity may not outweigh the potential disadvantages, which include the possibility of corrosive wear or fracture at the taper junction and higher implant cost. Additional well-designed, prospective, randomized research should be performed to determine the benefit of this design compared with nonmodular implants.