Adolph V. Lombardi, Jr., MD, FACS
While the use of short stem designs in total hip arthroplasty (THA) is not a new concept,1 interest in such designs has surged recently with the increasing popularity of less invasive surgical techniques. Design styles can be categorized into four groups: those influenced by the Mayo Conservative stem (Zimmer) introduced by Morrey in 1988, short and bulky but not neck sparing (e.g. Proxima; DePuy), neck-sparing curved designs (e.g. CFP; Link), and shortened tapered stems (e.g. TaperLoc Microplasty; Biomet). Our practice has had extensive experience with a tapered titanium porous plasma-sprayed stem of standard length (Mallory-Head Porous; Biomet) in primary THA. We recently reported our results with 2000 primary THA performed using this device from August 1984 through July 2001, noting 39 stem revisions at an average follow-up of 10 years yielding 98% survivorship with an endpoint of stem revision for any reason and 99% survivorship with stem revision for aseptic loosening.2 These results have been corroborated in several studies.3-7 Likewise, a number of studies report excellent results at intermediate and long-term follow-up with the TaperLoc (Biomet) stem, which is also a standard length tapered titanium porous plasma-sprayed design.8-12 Given the success of these traditional stems, why would anybody consider short stems? Several reasons exist.
What truly is the optimal length of a tapered femoral component? A survey of tapered and short femoral prostheses currently available for primary THA reveals a wide variety of diameters and corresponding lengths. If the goal of the tapered stem is to load preferentially proximally, why do we need a stem at all? Perhaps the only reason to use a tapered, long stem is to prevent varus. However, studies have shown that varus malalignment of a tapered stem does not affect results.3,13 In an effort to prevent distal off-loading, the TaperLoc stem is available with a reduced profile option. McLaughlin and Lee have reported excellent results using this reduced profile option in several published studies.8-11 Their results raise two questions: what function is the stem serving and do we need a long stem? The philosophy of a tapered design is to load the femur proximally, to achieve a tight fit and deliver the stresses into the proximal bone.
Short stems are easier to insert, especially when using an anterior approach to the hip, such as the anterior supine intermuscular approach in which the proximal femur is elevated anteriorly from the wound during stem insertion. Femoral preparation can be accomplished with straightforward broaching of the canal, without the use of reamers. Short stems are bone conserving. They violate less femoral bone stock, providing more favorable conditions should a revision be required.
However, ease of insertion and conservation of bone matter little if not supported by clinical results. Thus, we review our early experience with 1800 primary THA cases using short, tapered titanium, porous plasma spray-coated femoral components. Since its introduction in January 2006 through March 2011, 1563 patients (1800 hips) have undergone THA at our center with the TaperLoc Microplasty stem. Patient age averaged 63.4 years (range, 27-96 years). There were 701 males (45%) and 862 females (55%). A lateralized stem option was used in 1415 hips (79%). The surgical approach was less invasive direct lateral (LIDL) in 898 THA (50%), anterior supine intermuscular (ASI) in 807 (45%), and standard direct lateral (Std) in 95 (5%).
Follow-up averaged 12.5 months (range 0.2 – 60 months). To date, 17 stems (1.1%) have been revised: 4 due to infection treated with 2-stage radical debridement and reimplantation (4- 19 months, all LIDL approach), 1 same day revision due to intraoperative femoral shaft perforation (LIDL), 1 due to patellar dislocation (3 days, Std), 2 due to subsidence (1 LIDL at 1.4 months, 1 ASI at 4.6 months), and 9 due to periprosthetic fracture (1.4-4.6 months, 1 Std, 8 ASI). There have been no failures from aseptic loosening.
What are the lessons we’ve learned? First, we usually require one or two diameter sizes larger with short porous tapered stem versus the standard length version of the same design. The surgeon should be aggressive with sizing, pushing to the largest size possible. Use the broach like a rasp. Drive the component in valgus during insertion. Upon seating the component, do a trial reduction using the shortest available neck length. The component will generally sit slightly prouder than the broach and may require additional effort to seat completely.
Conservation of existing bone stock, compatibility with soft-tissue sparing surgery, more physiologic loading of the proximal femur, and versatility with varying femoral anatomy make the short taper an attractive implant option. The tapered wedge short stem represents the natural evolution of joint arthroplasty to a smaller, less-invasive, and more efficient implant. Our early results reveal 99% survival at up to 5 years follow-up.
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2. Lombardi AV Jr, Berend KR, Mallory TH, Skeels MD, Adams JB. Survivorship of 2000 tapered titanium porous plasma-sprayed femoral components. Clin Orthop Relat Res. 2009 Jan;467(1):146- 54.
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