Tapered Fluted Titanium Stems in Revision Total Hip Arthroplasty: A Review
Tapered fluted titanium stems are a type of implant used in revision total hip arthroplasty. This article reviews the indications, contraindications, techniques, and outcomes of using tapered fluted titanium stems in revision total hip arthroplasty.
INTRODUCTION
A wide variety of tapered fluted titanium stems are currently used in the setting of revision total hip arthroplasty (THA). There are no prospective studies comparing all available designs; hence, no clearly superior stem has been demonstrated.
Irrespective of design, the aim of revision THA is to accurately restore the center of rotation and produce a pain-free stable hip.
Modular components allow the surgeon to independently achieve stable diaphyseal fixation while optimizing anteversion, horizontal offset, and leg length. Such intraoperative versatility has made them an attractive option for use in the revision setting. Choosing the correct indication for their use, careful preoperative planning, and good surgical technique have led to promising clinical outcomes with the use of these components (1,2).
ADVANTAGES OF MODULAR TAPERED FLUTED STEMS
Modular tapered fluted stems are ideally suited to cases with Paprosky types II and III bone deficiencies (3,4). They offer the following advantages in the revision setting.
Excellent axial and rotational diaphyseal fixation is achieved with the tapered fluted distal stem segment. The tapered stem forms a wedge that provides axial stability within the femoral isthmus while the cutting flutes engage the endosteum and create rotational stability.
Modular proximal segments with variable offset and length options allow for optimization of length, offset, soft tissue tension, and anteversion.
Independent sizing of the proximal and distal segments facilitates optimization of bone contact with the entire surface area of the implant. This is thought to contribute to the reconstitution of proximal femoral bone stock observed with the use of these stems (5).
Titanium is more flexible than the previously popular cylindrical chrome-cobalt stems, contributing to less flexural stiffness and less stress shielding.
PREOPERATIVE PLANNING
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Careful preoperative planning allows anticipation of technical difficulties that can be encountered during the procedure, choice of the surgical exposure, and availability of the appropriate implant sizes and design to enable restoration of the center of rotation and normal biomechanics of the hip. Accurately templated radiographs are a prerequisite in the revision setting. The entire in situ component must be visible as well as the distal extent of any existing cement mantle. The femoral metaphysis, diaphysis, and isthmus must be clearly visible.
Our practice is to use calibrated digital images, which correspond to the magnification of our template overlays. A transischial line is drawn first to assess for true leg length discrepancy. The acetabulum is templated first and the
center of rotation determined. On the femoral side, the type of implant, mode of fixation, degree of fixation, and its location relative to the center of the canal are noted. The risk of cortical perforation and an iatrogenic fracture during stem extraction is increased in the presence of an eccentric stem or cement mantle as well as in the presence of varus remodeling or greater trochanteric position over the medullary canal.
The point where maximal fixation will be achieved is clearly marked. The need for an extended trochanteric osteotomy (ETO) can also be predicted and is built into the preoperative planning. Our indications for an ETO are
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Presence of a well-fixed uncemented component.
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Varus (coronal plane) and/or flexion (sagittal plane) remodeling of the proximal femur. This will be recognized during templating on both the anteroposterior and lateral radiographs.
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Presence of a well-fixed cement mantle is a relative, yet common, indication.
Placing overlay templates on the lateral radiograph gives an indication of the degree of femoral bow and the need for a bowed or beveled component or the need for a corrective osteotomy in that plane as well. A number of the stems available have an anterior bevel to minimize the risk of perforating the anterior cortex. This also provides another guide to the orientation of the component during the stem insertion.
Once the region of optimal fixation is marked out, the anticipated stem size is chosen. The overlay has a cutout, which allows one to mark the most proximal extent of the stem. This is further referenced from an intact bony landmark such as the greater or lesser trochanter. The proximal (body) segment is templated from this point. The ideal length and offset are also determined. The authors use a large head whenever possible (36 or 40 mm) to reduce the risk of instability. Also, to prevent the risk of junctional fracture, we prefer to use the largest body at the junction that is offered by the manufacturer.
OPERATIVE PROCEDURE
Surgical Setup
The patient is positioned in the lateral decubitus position.
If acetabular reconstruction is contemplated as well, great care must be taken to position the patient so that the coronal plane of the pelvis is positioned perfectly perpendicular to the operating room table. This is achieved by centering the posterior support on the sacrum and the anterior support on the lateral 1/3 of the iliac crest. This anterior support is placed at the level of the umbilicus and angled distally to the iliac crest in order to allow greater than 90 degrees flexion during the procedure. The entire limb is prepped to the iliac crest. It is draped free allowing access to the entire thigh. Old incisions are marked out prior to placing the iodine-impregnated skin drape.
Incision
We routinely use a posterior approach incorporating the old scar if possible. This is extensile, enables exposure of the entire femur if necessary, and allows clear visualization and protection of the sciatic nerve (Fig. 28-1). This also allows an extended femoral osteotomy should that be necessary.
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FIGURE 28-1 The extensile posterior approach allows exposure of the entire length of the femur if required.
Surgical Procedure (See Videos 28-1 through 28-5)
After extraction of the failed prosthesis, acetabular revision, if required, is the next step followed by insertion of the femoral component, which is the focus of this chapter. Femoral component insertion can be performed with or without an ETO. Both techniques are described in this chapter.
Technique without an Extended Trochanteric Osteotomy Endofemoral Technique
If the surgeon is confident that the prosthesis and complete cement removal can be performed via the proximal femur, and no significant deformity of the femur exists, then an ETO usually is not required. The femoral canal is cleared of all soft tissue and/or cement. This is achieved by using a combination of reverse cutting hooks. All soft tissue and debris from the medial aspect of the greater trochanter is removed using rongeurs and curettes.
An olive-tipped guide wire is passed into the femoral canal to confirm intramedullary location. If necessary, an intraoperative radiograph can be obtained. From this point, incremental conical hand reamers are used until axial and rotational stability is achieved. This can be demonstrated by applying axial and rotational loads to the hand reamer. It is essential that excellent initial stability is obtained at this stage. The reamer handles of most modular systems have etchings, which correspond to the chosen center of rotation (Fig. 28-2). In general, the tip of the greater trochanter is used as a reference as it corresponds to the correct center of rotation in the majority of cases (Fig. 28-3). The definitive distal stem component is inserted and firmly seated to achieve maximal stability (Fig. 28-4). A taper protector is placed over the exposed trunnion of the stem component.
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FIGURE 28-2 The initial conical reamer used to prepare the diaphyseal region of the femur. The burr tip is indicating the etchings, which correspond to the center of rotation for the femoral stem.
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FIGURE 28-3 Distal canal preparation using handheld conical reamers.
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FIGURE 28-4 Insertion (A) and seating (B) of the distal component using the tip of the greater trochanter as a reference point for the center of rotation.
Preparation of the proximal femur for the body segment is the next step. Handheld reamers placed over a taper protector are used for this (over the junction reamers). The in situ distal stem functions to maintain the orientation of the proximal reamer with this technique (Fig. 28-5). The taper protector is removed and a provisional body applied based on previously templated sizes. A trial reduction is performed next (Fig. 28-6). Multiple body shapes and sizes with variable offsets are available. This improves the surgeon's chances of achieving maximal implant-bone contact and support and optimizing the biomechanics of the hip. This modularity also allows the surgeon to “dial in” the optimal anteversion within a range of +/- 30 degrees.
After the trials are assembled and inserted, leg length, stability, abductor tension, and anteversion are assessed prior to opening the final prosthesis. Once this is done, reference points for the leg length (using the tip of the greater trochanter as a reference) and anteversion (using the lesser trochanter) are marked out.
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FIGURE 28-5 Proximal femoral preparation. The definitive stem has been inserted, the taper protector inserted, and the proximal handheld reamer passed over this.
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FIGURE 28-6 A: A trial body segment attached to the previously inserted stem segment. The trial reduction is performed (B).
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FIGURE 28-7 The final body is inserted (A) and press fitted onto the taper of the stem component (B).
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FIGURE 28-8 A: The set screw used to attach the proximal and distal segments (white arrow). B: Tightening the set screw with a torque wrench (white arrow) and a device that captures the trunnion and maintains version (yellow arrows).
The final component body is inserted and press fitted over the trunnion of the stem component (Fig. 28-7A, B). The components are firmly locked together with a set screw. A torque wrench and instruments for maintaining neck anteversion are used during this step (Fig. 28-8A, B).
Alternatively, the entire prosthesis can be assembled on the back table and inserted as a single construct. This is most easily done in cases with minimal bone loss and no significant bowing or varus remodeling of the proximal femur.
Technique with an Extended Trochanteric Osteotomy
The decision to perform an ETO is made at the preoperative planning stage. The length of the ETO is
referenced from the tip of the greater trochanter and allows 4 to 7 cm of intimate bone-prosthesis contact distal to the osteotomy.
We perform the osteotomy in the sagittal plane, elevating a minimal amount of the vastus lateralis off the femur. After the osteotomy, a myoosseous flap is created and retracted anteriorly. This allows the hip abductors to not be violated, unlike the classic Wagner osteotomy, in which the vastus lateralis is incised in its midsubstance and a coronal femoral osteotomy that bisects the greater trochanter and splits the hip abductors is created. The distal transverse cut is beveled in a rounded matter in a caudad direction (Fig.
28-9). A cerclage cable is placed 1 cm distal to the osteotomy site to minimize the risk of an iatrogenic fracture propagating distally during reaming and stem insertion (Fig. 28-10).
After the ETO is performed, the failed component and/or cement is removed. Femoral preparation continues with conical hand reamers. Reaming is continued until excellent axial and rotational stability is achieved. In general, reaming should be done to accept an intermediate body height.
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FIGURE 28-9 Our extended trochanteric osteotomy. The beveled distal cut is indicated by the arrows. This enables a larger surface area of bony contact to facilitate healing than if a transverse cut was used.
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FIGURE 28-10 The prophylactic cerclage cable is applied prior to reaming when an ETO is used.
Component Insertion
The distal stem segment is inserted first (Fig. 28-11). If a bowed or beveled stem is used, the orientation is carefully assessed prior to insertion. The final stem often sinks a few millimeters further down than the reamer. The surgeon should not be concerned by this. The aim is to achieve the most stable initial fixation possible. Height and offset are adjusted with the modular body options. Etchings on the inserter handle will indicate the most appropriate body height to be used.
Selecting the most appropriate body segment is next. Most systems include a range of body segments with a variety of sizes, shapes, lengths, and offsets to optimally fit and fill the metaphysis. Further trial reductions can therefore be performed with different body options until optimal length and offset are obtained.
Modularity of this segment allows anteversion to be “dialed in” as appropriate for optimal stability. The
trunnion of the stem is cleaned and the body applied. The system we use has a specific instrument for press fitting the body onto
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the stem trunnion (Fig. 28-7B). The 2 segments are then firmly coapted with a locking screw, which is
applied using a torque wrench while maintaining the anteversion (Fig. 28-8B). The hip is then reduced with
a trial head and all parameters reassessed. The final head is applied and reduction performed.
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FIGURE 28-11 Femoral component insertion. A: The distal stem is inserted first. B: The proximal component is attached after a trial reduction.
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FIGURE 28-12 The ETO is closed using cerclage cables (blue arrow). The vastus lateralis is then closed over this (black arrow).
If an ETO was used, the reflected segment is folded onto the prosthesis and fixed with cerclage cables or wires (Fig. 28-12). A high-speed burr is used to machine the contour of the osteotomized fragment to the shape of the prosthesis. Final fixation is achieved using 2 to 3 cerclage cables.
Closure is performed in layers to minimize dead space. The short external rotators and posterior capsule are reattached to the greater trochanter using transosseous sutures placed via drill holes in the posterior aspect of the greater trochanter. Skin is closed with staples and a sterile pressure dressing applied.
POSTOPERATIVE MANAGEMENT
We routinely obtain postoperative radiographs in the postanesthetic care unit, including the shaft of the femur. This confirms reduction of the hip joint, reveals any fractures, and serves as a baseline for further investigations. Antibiotics are continued for 24 hours postoperatively.
In most cases, protected weight bearing is continued for 6 weeks and toe-touch weight bearing only if the reconstruction was particularly complex, especially on the acetabular side. After clinical and radiographic
evaluation at 6 weeks, weight bearing and rehabilitation are advanced.
COMPLICATIONS
Implant fractures occurring at the modular junction have been reported by several authors (1,6). These have occurred primarily in stems less than 17 mm in diameter and following the use of older taper junction designs.
Femoral fractures can occur during insertion of the stem segment. Such fractures occur particularly in cases with poor bone quality and if an ETO has been used, hence the use of a prophylactic cerclage wire prior to femoral stem insertion. Intraoperative or postoperative radiographs in the recovery room facilitate early detection and management should such a fracture occur.
Subsidence is a potential concern with these stems. The incidence of this has been shown to decrease with increasing surgeon experience. It is minimized by careful pre-op planning, femoral preparation, choosing the most stable component, and seating it until excellent stability is achieved.
REFERENCES
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Van Houwelingen AP, Duncan CP, Masri BA, et al.: High survival of modular tapered stems for proximal femoral bone defects at 5 to 10 years followup. Clin Orthop Relat Res 471(2): 454-462, 2013.
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Restrepo C, Mashadi M, Parvizi J, et al.: Modular femoral stems for revision total hip arthroplasty. Clin Orthop Relat Res 469(2): 476-482, 2011.
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Weeden SH, Paprosky WG: Minimal 11-year follow-up of extensively porous-coated stems in femoral revision total hip arthroplasty. J Arthroplasty 17(4 Suppl 1): 134-137, 2002.
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Munro JT, Garbuz DS, Masri BA, et al.: Tapered fluted titanium stems in the management of Vancouver B2 and B3 periprosthetic femoral fractures. Clin Orthop Relat Res 472(2): 590-598, 2014.
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Munro JT, Masri BA, Garbuz DS, et al.: Tapered fluted modular titanium stems in the management of Vancouver B2 and B3 peri-prosthetic fractures. Bone Joint J 95-B(11 Suppl A): 17-20, 2013.
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Lakstein D, Eliaz N, Levi O, et al.: Fracture of cementless femoral stems at the mid-stem junction in modular revision hip arthroplasty systems. J Bone Joint Surg Am 93(1): 57-65, 2011.