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Modular Tapered Stems for Femoral Revision

The authors outline their surgical approach when using their preferred modular tapered stem in femoral revision procedures.

By Benjamin Frye - February 24, 2014 0 Feature Articlesfemoral revisionmodular stems

Authors

Benjamin M. Frye, MD; Keith R. Berend, MD; Michael J. Morris, MD; Joanne B. Adams, BFA; and Adolph V. Lombardi, Jr., MD, FACS

Introduction

The primary goals of revision hip surgery are pain relief and long-term stable implant fixation. Femoral bone stock in revision arthroplasty is commonly compromised by osteolysis, stress shielding, and iatrogenic damage from implant removal and sometimes multiple revision surgeries.

The proximal bone is typically deficient and cannot support stems that rely on proximal fit and fill. This had led to the development of diaphyseal engaging stems that load the diaphysis and bypass the deficient proximal femur, including:

• Monoblock extensively porous coated stems
• Monoblock fluted tapered stems
• Modular fluted tapered stems

Other common challenges in femoral revision include:

• Expansion of cortices
• Varus remodeling
• Leg length discrepancy
• Instability

Indications for Using Modular Stems in Revision Procedures

These challenging situations can make it difficult to attain stable implant fixation while maintaining hip stability with monoblock stems. Modular stems allow surgeons to establish stable diaphyseal fixation while attaining appropriate leg length and hip stability independently.

The authors currently use a modular fluted tapered stem for most of their femoral revisions. The indications for a modular tapered stem depend on the amount of bone loss and surgeon philosophy.  Some surgeons, including the authors, use this style of implant for most femoral revisions due to the ease of implantation and the versatility of the modular design.

Other surgeons prefer proximal loading stems for Paprosky Type 1 [1] (Table 1) and Mallory Type 1 [2] (Table 2) femurs with an intact proximal metaphysis. Still others may choose extensively porous coated stems for Paprosky Type 2 and 3A and Mallory Type 2 femurs that have intact diaphyseal bone or an isthmus of at least 4 cm for a good scratch fit.

Table 1. Paprosky Classification of Femoral Defects [1]

Table 2. Mallory Classification of Femoral Defects [2]

Modular tapered stems are recommended by the authors and others for severe diaphyseal bone loss, including Paprosky Type 3A femurs with a diameter greater than 19 mm and Paprosky Type 3B femurs with an isthmus less than 4 cm. These situations have shown unsatisfactory failure rates with extensively porous coated stems [1].

Some surgeons have had success with modular tapered stems in Paprosky Type 4 femurs with extensive loss of diaphyseal bone; however, this stem is contraindicated when stable fixation of the implant is unachievable. Megaprostheses and impaction grafting with cemented stems are other options in this situation. Periprosthetic fractures requiring femoral component revision are effectively treated with modular tapered stems.

A concern with modular tapered stems is an unsupported taper junction that can be weakened by repetitive stresses. Fractures at the modular junction are reported in the literature on multiple stem designs [3-7]. Manufacturers have developed methods for strengthening the taper junction. The authors currently use a stem design that has undergone a proprietary process of roller-hardening of the taper junction (Biomet, Inc., Warsaw, IN), which, according to the manufacturer, provides up to three times more strength in cantilever beam testing.