Modular Fluted Stems Have Simplified Revision of the Femoral Component in Total Hip Arthroplasty

Revision total hip replacement is among the most challenging procedures in orthopaedic surgery. Revision of the failed femoral component can be complicated by substantial bone loss. The Paprosky classification has traditionally guided the choice of reconstruction technique based on the degree of bone loss. Historically, most femoral revisions have been treated with extensively porous-coated non-modular cylindrical stems. This technique is especially effective for patients with metaphyseal bone loss and relative preservation of the diaphysis (type II) and more extensive diaphyseal bone loss with at least 4 cm of cortical scratch fit (type IIIA). Femurs with less than 4 cm of cortical scratch fit (type IIIB) were recommended to be treated with distally based modular stems. In recent years, the modular fluted titanium stem has become the workhorse for femoral revisions (Fig. 1).

Non-modular revision stems are associated with higher incidence of stress shielding, femoral fracture, subsidence, and thigh pain in revision total hip arthroplasty when compared with modular stems. Specifically, large-diameter cylindrical cobalt-chrome non-modular stems are associated with stress shielding of proximal bone. In addition, placing large non-modular stems into the femoral canal may increase the risk of femur fracture, which can occur because of the size and length of the femoral stem and conflict with the femoral bow. Dislocation can be a problem because the amount of version achievable in the stem is limited by mismatch in shapes between the metaphysis and diaphysis, as well as the femoral bow. These limitations of the non-modular stem greatly increase the technical difficulty and complication rates in complex revisions.

Modular fluted titanium stems have become more widely adopted in revision femoral arthroplasty because they have several advantages which have simplified the operation. Because surgeons can use differently sized proximal and distal segments, they can achieve good host bone contact in both the metaphysis and diaphysis. Surgeons can ream distally until axial and rotational stability is achieved and then seat the distal implant. Proximal reaming is then performed over a centralizer that is seated into the distal implant. This allows for placement of an optimally sized proximal segment that will lock into the distal segment. This modularity also allows for immediate stability in femoral segments with less than 4 cm of scratch fit.

The optimization of femoral version is another advantage of modular stems that has simplified revision surgery and reduced complications. In many revision situations, the proximal bone of the femur is remodeled in retroversion and varus. Distal fixation is achieved with a conical stem. The proximal body can be locked onto the distal stem taper in any position within 360 degrees. That is, the optimal version can be chosen based on trialing and locking in the version into the proximal body. Furthermore, lateral offset can also be adjusted with the proximal body. This combination can help reduce the risk of dislocation and minimize leg-length discrepancy.

The main disadvantage of modular fluted stems is the risk of fracture at the modular junction. This risk is heightened if the proximal body is not supported by bone. If there is insufficient supportive metaphyseal bone, such as after stress shielding or after a proximal femoral osteotomy, the stresses at the taper junction have been shown to result in catastrophic breakage at the taper junction.

In their 2017 study in the Journal of Bone and Joint Surgery, Matthew P. Abdel, MD, FAAOS, and colleagues from Mayo Clinic retrospectively evaluated 519 femoral revisions reconstructed with modular fluted stems with a mean follow-up of 4.5 years. More than 80 percent of the cases had type IIIA or greater bone loss. Outcomes were excellent, with a 10-year survivorship of 98 percent, with revision for aseptic loosening of the femoral stem as the endpoint. In 3 percent of cases, repeat revision of the femoral stem was performed for aseptic loosening, infection, instability, periprosthetic fracture, and stem fracture.

Nicholas M. Brown, MD, FAAOS, and colleagues from Rush University authored a 2015 study, published in Clinical Orthopaedics and Related Research, retrospectively evaluating 70 femoral revisions performed with modular fluted stems with a minimum 2-year follow-up. Patients had major bone loss, with 58 revisions having type IIIB bone loss or greater. Survivorship was 98 percent at 12 years, with revision of the femoral component as the endpoint. Complications included revision for aseptic loosening, instability, and intraoperative femur fracture.

Modular fluted stems have simplified revision of the loose femoral component. The ability to independently place distal and proximal components allows surgeons to mix and match diaphyseal and metaphyseal shapes and diameters to provide optimal fixation. The tapered stem allows for the achievement of immediate axial and rotational stability even in bone with minimal cortical fit. Modularity also allows for independent placement of the proximal body relative to the stem to optimize version and hip stability, as well as leg lengths. Finally, the excellent survivorship of these implants, relatively forgiving technique, and low complication rates have made these implants the go-to femoral implant for revision femoral arthroplasty. The one major caveat is to use these with caution in revisions with massive proximal bone loss. If there is inadequate bony support for the modular junction, there is a risk for fracture at the taper junction of the body and stem. In such cases, a proximal femoral replacement may be necessary.

Michael DeRogatis, MD, MS, is an orthopaedic surgery resident at St. Luke’s University Health Network in Bethlehem, Pennsylvania.

Paul S. Issack, MD, PhD, FAAOS, FACS, is a clinical associate professor in the Department of Orthopaedic Surgery, Weill Cornell Medical College, and a trauma and adult reconstruction orthopaedic surgeon at New York–Presbyterian/Lower Manhattan Hospital. He is also a member of the AAOS Now Editorial Board.

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