Modular, Fluted, Tapered, Grit-Blasted Titanium Stems for Femoral Revision





CASE STUDY


A 75-year-old woman presented with a loose cemented stem ( Fig. 65.1 , A ). Evaluation of the radiographs showed that despite appropriate overall bone quality, osteolysis had compromised the bone stock down to the isthmus. Confronted with this Paprosky type IIIB femoral deficiency, it was decided to revise the femur with a modular, fluted, tapered, grit-blasted titanium stem (Revitan, Zimmer, Warsaw, Ind.) (see Fig. 65.1, B ). After the loose stem was extracted, an extended trochanteric osteotomy was performed to facilitate removal of the remaining well-bonded cement mantle and to enable safe and straightforward preparation of the area of primary fixation. A cerclage wire was added prophylactically around the distal femur first. The cup was revised, and a 40-mm head was chosen to reduce the risk of postoperative dislocation.




FIGURE 65.1


A, Loose, cemented femoral stem with a residual type IIIB femoral deficiency. B, Postoperative radiograph shows reconstruction with a long, cementless stem (Revitan, Zimmer, Warsaw, Ind.). An extended trochanteric osteotomy was performed.




Chapter Preview


Chapter Synopsis


The use of a modular, tapered, fluted, grit-blasted titanium stem for femoral revision is an attractive option. These titanium stems are versatile, provide excellent primary stability, and offer unequaled performance in the setting of major femoral defects. After careful preoperative planning, a cone is prepared in the femoral canal to accept the taper of the stem, and the proximal part is built to obtain appropriate stability and leg length. An extended trochanteric osteotomy (ETO) can be used to facilitate extraction of the previous stem and safe insertion of the new stem. Long-term functional and mechanical results are excellent.


Important Points





  • Preoperative planning is an extremely important part of the operation.



  • The decision to perform an ETO should be made during surgical planning because of its effect on the level of fixation of the stem.



  • Taper fixation is the goal to obtain primary diaphyseal stability.



Clinical/Surgical Pearls





  • An ETO is commonly performed to facilitate extraction of the previous stem and to ensure safe insertion of the new stem.



  • A larger stem is preferred to a longer one, provided there is adequate bone stock at that level.



  • A more aggressive taper should be considered to obtain fixation below the isthmus.



  • A guidewire and intraoperative radiographs should be used routinely to rule out a perforation.



Clinical/Surgical Pitfalls





  • Three-point fixation should not be the primary mode of fixation of the implant.



  • Wedging the definitive implant stem and body significantly higher than the reamer suggests proximal three-point fixation.



  • Distal perforation of the anterior cortex can be caused by using a stem that is too long.





Introduction


Approximately 50,000 revision hip arthroplasties are performed each year in the United States, and this number is expected to double by 2030. Fifty percent of these procedures require a revision of the femoral component. Cementless femoral revision prostheses have demonstrated favorable survivorship and clinical performance over the long term. Two uncemented stem designs—the modular, tapered, fluted, grit-blasted titanium stem and the monobloc, cylindrical, diaphyseal, porous-coated cobalt-chrome stem —are frequently used, and both have proponents and opponents. Tapered components have gained attention in North America after having enjoyed popularity in Europe for more than 2 decades based on the work of Wagner and others.


The increased popularity in North America is based on the many mechanical advantages of tapered, fluted titanium stems. The prosthesis obtains axial stability through the wedging effect of the taper in the femoral canal and excellent rotational stability as a result of the flutes rigidly engaging the femur throughout the circumference of the stem. The modularity of some designs allows versatility and fine-tuning of fixation, leg length, and stability. Titanium reduces the amount of stress shielding and facilitates proximal bone restoration. These mechanical advantages have been verified by Böhm and Bischel and Weiss and colleagues, and Richards and co-workers have described excellent clinical outcomes. Due to their versatility, these stems are more suitable than cylindrical, diaphyseal, porous-coated stems in cases with femoral deficiencies that extend beyond the isthmus. Paprosky and asociates failed to demonstrate adequate results with diaphyseal, porous-coated stems for such demanding femoral deficiencies. Despite these advantages, the use of tapered, modular stems requires precise knowledge of the surgical technique, implant nuances, and technical pitfalls.




Indications and Contraindications


Tapered revision stems are indicated for revisions of failed cemented and uncemented femoral components when proximal metaphyseal bone does not provide enough support to use a modular, proximally coated, uncemented stem, such as the S-ROM (DePuy, Warsaw, Ind.). Indications include Paprosky type II, IIIA, IIIB, and IV femoral deficiencies and Vancouver type B2 and B3 periprosthetic femoral fractures.


Medical conditions rendering a major surgical procedure inappropriate and ongoing infection are contraindications. There must be adequate quantity and quality of distal femoral bone to enable axial and rotational stability of the tapered stem. If not, a modular oncology system or allograft prosthetic stem should be considered.




Equipment


In addition to the equipment necessary for revision surgery and the extraction of components in situ, we recommend having a high-speed bur, wires or cables, and the complete kit for implantation of the components chosen. Blood should be available, and a cell saver may be used at the discretion of the surgeon, although our experience suggests that there is insufficient blood loss to retransfuse after the cell saver is primed. The surgeon can also consider the adjuvant use of a tranexamic acid infusion to reduce blood loss and transfusion risk.




Surgical Techniques


Anatomy and Approaches


Four structures should be considered: the femur, the sciatic and femoral nerves, and the femoral artery. When reconstruction with a long, uncemented, straight stem is attempted, the femoral curvature in the coronal and sagittal planes should be considered. The femur has a natural anterior curvature, and a remodeling deformity, most often in varus, and retroversion should be expected. As discussed later, the relation between the primary area of fixation and the isthmus is also important.


The sciatic nerve runs anterior to the piriformis muscle and posterior to the other external rotators. It is at risk mainly during the posterior approach and reconstruction of the acetabulum. The femoral nerve is medial to the anterior column of the acetabulum, between the iliacus and psoas muscles. It is at risk when revising the acetabulum and using a retractor positioned around the anterior wall. The femoral artery runs in the anterior thigh with the sartorius muscle and then bifurcates medially and posteriorly through the adductor canal to become the popliteal artery. It is at risk when cerclage wires are passed around the distal femur if the wire passer is not kept closely juxtaposed to the femur. When wires are being passed, perforating vessels and the profunda femoris artery also may be at risk.


Preoperative Planning


For most patients, an anteroposterior radiograph of the pelvis and the entire femur, a lateral radiograph of the femur, and obturator and iliac oblique views of the pelvis are sufficient. The radiographs provide information necessary to perform the procedure in a safe and precise manner. It is important to record all of the hardware in situ and to obtain labels from previous operations and, if needed, the surgical technique and special tools for implant removal from the manufacturers of existing implants.


Three parameters must be assessed: bone defects, bone quality, and bone morphology. Segmental bone defects already present and those expected from the approach or from removal of the implants contribute to determination of the level of the area of primary fixation. Fixation is necessarily distal to the most distal segmental bone defect. Bone quality is important. Adequate press-fit fixation cannot be reliably obtained on very thin cortices, and fixation more distally may be required. Assessing the bone morphology for remodeling deformities (most commonly in varus) and anterior bowing is essential for determining whether to perform an ETO. If there is doubt about whether to perform an ETO, it is always safer to perform the ETO, provided the surgeon is well versed with the nuances of the procedure. The extent of the ETO should be decided before the operation as part of the templating and planning process.


Della Valle and Paprosky classified femoral deficiencies in an attempt to provide an algorithm for femoral revision. In type I femoral deficiencies, the metaphysis has minimal bone loss, and the diaphysis is intact. Type II femoral deficiencies have extensive metaphyseal bone loss and an intact diaphysis. Type III femoral deficiencies have extensive metaphyseal bone loss and an altered diaphysis. The defect is type IIIA if more than 4 cm of diaphysis is available for distal fixation (i.e., isthmus and above); type IIIB defects have less than 4 cm of diaphysis available. Type IV femoral deficiencies have extensive metaphyseal and diaphyseal bone loss with an ectatic canal. Cylindrical, porous-coated stems are not indicated for type IIIB and IV deficiencies, but modular, fluted, tapered titanium stems can be safely used, obviating the need for more complex techniques, such as revisions with proximal femoral allograft-prosthetic composites or segmental replacement implants.


Preoperative templating is achieved by following several principles:



  • 1.

    The center of rotation is marked, and the level typically should be at the top of the greater trochanter. A leg length discrepancy usually is corrected during the procedure.


  • 2.

    The sagittal and frontal axes of the femur, deformities of the femur, and the most distal segmental bone defect (existing or due to a planned ETO) are identified.


  • 3.

    The area of fixation is determined, accounting for the quality of the cortices and ensuring that a press-fit can be safely obtained. Although the end of the stem usually bypasses a segmental defect by a minimum of two cortical diameters, this is anatomically impossible after the isthmus is passed because of the opposite shapes of the taper ( V shape) and the distal femur (inverted V shape). The proximal taper of the long stem provides a wedging effect, and the flutes provide rotational stability, enhancing fixation and function. Cylindrical, porous-coated stems are less likely to be effective.


  • 4.

    An ETO is considered according to the planned level of fixation and the curvature of the femur. If this technique is employed, the distal end of the ETO is marked, and the surgeon verifies that the chosen location provides adequate exposure to remove the implant without compromising the area of fixation.


  • 5.

    The ideal combination of implant stem, body, and neck lengths is determined to restore adequate leg length from a fixed area of primary fixation. The combination should allow some incremental play around the planned leg length, and after the definitive stem is inserted in the distal femur, a shorter or a longer reconstruction should be possible with various implant body lengths. Modular proximal options allow fine-tuning of the leg length and offset to maximize hip stability.


  • 6.

    One or two landmarks on the proximal femur can guide the reconstruction procedure. The graduated reamers used in most systems are designed to reference the greater trochanter, which is suitable if an ETO is not required. If an ETO is needed, the lesser trochanter is used as a landmark. In most cases, the distance between the lesser trochanter and the desired center of the prosthetic femoral head is 50 to 65 mm. Aided by a femoral head center mark on the shaft, the conical reamers are advanced until this distance has been reproduced. The relationship between the greater and lesser trochanters before the ETO also may be used as a backup measurement but is seldom required. Alternatively, referencing can be done from the area where the ETO has been beveled if the ETO length is known.



Positioning


The patient is positioned in the lateral position with the pelvis rigidly maintained on the operative table with appropriate holders. The operated limb should be mobile and have at least 90 degrees of hip flexion. Pressure areas should be carefully padded. When draping, the entire area from the iliac crest to the knee joint should be exposed. A Foley catheter should be inserted and invasive monitoring of vital signs established. We usually have the cell saver on standby and decide on its use within 30 minutes of making the incision. We use it routinely if the case is uncommonly complex or there are restrictions by the patient on the use of blood products. We favor the use of tranexamic acid in revision hip arthroplasty but finalize that decision in consultation with our colleagues in anesthesia.


Surgical Exposure


We prefer the posterior approach for exposure because it is extensile and safe, provides excellent exposure, and allows any type of trochanteric osteotomy, including an ETO. The skin incision is centered over the greater trochanter, extends distally along the femur, and proximally is curved toward the sciatic notch. The iliotibial band is exposed and divided in line with the skin incision distally. Anterior and posterior flaps are then prepared, and proximally, the gluteus maximus is split to give access to the posterior aspect of the hip joint and hip abductors. The sciatic nerve is identified at that time and protected during the remainder of the operation.


The joint is accessed by posteriorly reflecting a flap composed of the short rotators and capsule or the prior posterior repair and neocapsule in the case of a previous posterior approach. This posterior flap is tagged with sutures and reflected posteriorly to protect the sciatic nerve and allow repair at the end of the procedure. This flap should be made as long as possible to facilitate later repair.


The capsule is then released from the proximal and anterior aspect of the femur, and the joint is dislocated. The acetabulum and femur are addressed with or without an ETO, depending on the particulars of the case. Because the indications for and surgical technique of the ETO have been described elsewhere, they are not detailed here. However, it is worth mentioning that this approach is useful for removing the stem in situ and for preparation of the distal femur. The factors to consider for an ETO are the ability to remove the femoral component (cemented or uncemented) without damaging the femur and without fracturing the greater trochanter. The surgeon should look for varus remodeling of the proximal femur, subsidence of the stem, and osteolysis of the greater trochanter. After the stem has been explanted, an ETO can be considered to safely remove a well-fixed cement mantle, which may deviate the reamers during preparation of the distal femoral cone. Most importantly, an ETO should be considered to facilitate preparation of the area of primary fixation and maximize fixation.


Procedure


Step 1. Exposure and Removal of Previous Components


The exposure is done as described previously. A mark, such as on the lesser trochanter, is made on the femur, from which all distances can be measured. The previous component is extracted with or without an ETO.


Step 2. Evaluation of Bone Defects


Segmental bone defects are assessed and correlated with the preoperative radiographs. If the preparation is made from the top, the most distal segmental defect can guide how far distally the reamers should be pushed to bypass the defect by the appropriate amount. Preoperative planning determines the depth needed to obtain adequate fixation.


Step 3. Preparation of the Area of Primary Fixation


Straight conical reamers are used to prepare a cone-shaped femur to accept a tapered stem. Sequential reamers ( Fig. 65.2 ) are inserted in the femur down to the level that was planned during templating. The depth of reaming should be determined from preoperative planning, and reaming should be done only to that level; otherwise, a stem that is longer than necessary will be required. After a reamer has reached the planned level, the next-sized reamer is chosen, and the procedure is repeated until axial and rotational stability are obtained at that level. The reamers are usually graduated to help the surgeon reproduce the planned level of preparation ( Fig. 65.3 ). A larger stem is preferred to a longer one if there is adequate bone stock at that level. For a 2-degree taper, the taper diameter decreases by 1 mm for every 57 mm of length; for a 3.5-degree taper, it is only 46 mm. A stem with a larger taper angle engages sooner than a stem with a smaller angle.


May 29, 2019 | Posted by in ORTHOPEDIC | Comments Off on Modular, Fluted, Tapered, Grit-Blasted Titanium Stems for Femoral Revision
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