JBJS | Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Fixation with a Modular Stem in Revision Total Hip Arthroplasty*†

The Journal of Bone & Joint Surgery, Volume 81, Issue 9

Instructional Course Lecture | September 01, 1999

Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Fixation with a Modular Stem in Revision Total Hip Arthroplasty*†

JAMES V. BONO, M.D.‡; JOSEPH C. MCCARTHY, M.D.‡; JO-ANN LEE, R.N.‡, BOSTON; ROBERT J. CARANGELO, M.D.§, NEW BRITAIN, CONNECTICUT; RODERICK H. TURNER, M.D.‡, BOSTON, MASSACHUSETTS

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An Instructional Course Lecture, American Academy of Orthopaedic Surgeons

The Journal of Bone & Joint Surgery. 1999; 81:1326-36

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Introduction

The goals of femoral revision arthroplasty are to relieve pain, to restore biomechanical function and bone integrity, and to ensure stable fixation of the component. Restoration of biomechanical function involves correction of limb-length discrepancy and femoral offset. Proper positioning and containment of the implant requires thorough preoperative planning as well as precise operative technique.

Loss of femoral bone stock in a patient who needs a revision presents a difficult challenge to the orthopaedic surgeon. Bone loss is a result of mechanical loosening of the component and bone erosion caused by osteolysis. Segmental defects involve loss of supportive cortical bone, whereas cavitary defects involve cancellous-bone loss that may extend to the endosteal cortical bone.

There are several systems for the classification of femoral bone defects, but we prefer the one developed by the American Academy of Orthopaedic Surgeons Committee on the Hip¹⁴. According to this system, type I comprises segmental defects, type II consists of cavitary defects, and type III includes combined segmental and cavitary defects; each category has subgroups. The system also includes types IV, V, and VI, characterized by malalignment, stenosis, and discontinuity, respectively. Each type is assigned a level and a grade. Level-I lesions extend proximal to the inferior plane of the lesser trochanter, level-II lesions extend ten centimeters distal to the inferior plane of the lesser trochanter, and level-III lesions are distal to level-II lesions. Grade I indicates minimum bone loss, grade II indicates moderate bone loss, and grade III indicates the need for structural bone-grafting in order for the revision to be successful¹⁴.

The amount of bone loss dictates the type of component and the operative technique that are used. If there is mild-to-moderate metaphyseal damage, either a proximally or a distally fixed component is appropriate. If the metaphyseal damage extends to the diaphysis, a proximally or distally fixed component with additional distal rotational stability is needed. Severe segmental proximal femoral bone loss precludes the use of a proximally fixed implant. In this setting, a distally fixed component (designed to be inserted either with or without cement) or a so-called hybrid stem (the proximal portion of the stem is cemented into an allograft inserted in the proximal part of the femur), as described by Chandler¹¹, may be considered.

*Printed with permission of the American Academy of Orthopaedic Surgeons. This article will appear in Instructional Course Lectures, Volume 49, American Academy of Orthopaedic Surgeons, Rosemont, Illinois, March 2000.

†One or more of the authors has received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

‡Department of Orthopedic Surgery, New England Baptist Hospital, 125 Parker Hill Avenue, Boston, Massachusetts 02120. E-mail address for Dr. Bono: jbono@nebh.org.

§Department of Orthopedic Surgery, New Britain Hospital, University of Connecticut, New Britain, Connecticut 06052.

‡Department of Orthopedic Surgery, New England Baptist Hospital, 125 Parker Hill Avenue, Boston, Massachusetts 02120. E-mail address for Dr. Bono: jbono@nebh.org.

§Department of Orthopedic Surgery, New Britain Hospital, University of Connecticut, New Britain, Connecticut 06052.

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Radiographs of a sixty-six-year-old man who was managed with a resection arthroplasty of the left hip (Fig. 1-A) after an infection developed at the site of a total hip replacement. Twelve months later, components were reimplanted (Fig. 1-B). The postoperative course was complicated by a trochanteric fracture (Fig. 1-C) resulting from minor trauma.

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Radiographs of a woman who had pain at the site of a bipolar hemiarthroplasty with cement (Fig. 2-A). At the time of the revision (Fig. 2-B), when the patient was seventy-eight years old, an extended trochanteric osteotomy was performed to facilitate removal of the cement. The osteotomy did not preclude use of a proximally modular femoral stem. At three months (Fig. 2-C), there was complete healing at the osteotomy site.

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Fig. 3 Photograph showing some of the various combinations that are available with the S-ROM modular total hip system (DePuy [Johnson and Johnson], Warsaw, Indiana). The system allows 8364 potential combinations, which may be customized at the time of the operation.

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Radiographs of a man who had femoral osteolysis and loosening at the site of a total hip arthroplasty (Fig. 4-A) and was managed with revision to an S-ROM femoral component (Fig. 4-B) when he was seventy years old, fifteen years after the primary procedure. At six months (Fig. 4-C), endosteal hypertrophy in response to proximal loading of the femur was noted.

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Radiographs of a sixty-seven-year-old woman, made six years after a primary total hip arthroplasty, showing a stem with ingrowth of bone and cortical density extending to the tip of the proximal sleeve (magnified inside box of Fig. 5-B). The density was a physiological response to stress transferred from the stem to the bone.

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Radiographs of a sixty-eight-year-old man, made four years after a femoral revision arthroplasty, showing subsidence of the stem (Fig. 6-A). A sclerotic ledge of bone (a pedestal) (arrows, Fig. 6-B) is seen distally, supporting the tip of the stem.

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Figs. 7-A, 7-B, and 7-C: Radiographs of a sixty-four-year-old man, made six years after a revision total hip arthroplasty. Fig. 7-A: Radiograph showing the implant in place.

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Fig. 7-B: Radiograph showing endosteal hypertrophy (arrows). Such hypertrophy is commonly seen in response to proximal loading of the bone after revision.

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Fig. 7-C Radiograph showing cortical hypertrophy (arrows) in response to proximal loading of the bone.

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Fig. 8 Radiograph of a sixty-three-year-old man, made six years after a femoral revision arthroplasty, showing reactive endosteal bone (arrows) surrounding the tip of a well fixed femoral stem. The anterior spline of the stem was modified at the time of the revision to avoid anterior cortical perforation.

Options for Revision

The complexity of femoral revision arthroplasty is clearly evident when the vast array of techniques used for similar types of bone loss is considered. The principal techniques that have emerged in the last decade include use of a long-stem implant with cement, distal fixation of a fully coated implant, proximal fixation of a coated modular or nonmodular implant, and endosteal impaction-grafting.

The rate of repeat revision after revision total hip arthroplasty with cement has ranged from 9 percent (twelve of 139) to 29 percent (twenty-nine of ninety-nine) after ten years of follow-up^6,18,24,28; the need for repeat revision is believed to be related to a poor bone-cement interface secondary to the smooth, sclerotic endosteal femoral surface. Often, to gain additional fixation, a long-stem femoral component extending distal to the isthmus of the femur is inserted with cement. Once the stem enters the flare of the distal metaphysis, the effectiveness of a cement restrictor is decreased. Furthermore, the presence of cement in the distal metaphysis, beyond the isthmus, makes future removal of cement difficult and sometimes impractical, if not impossible.

The rate of repeat revision after revision total hip arthroplasty without cement is somewhat better, ranging from 2 percent (two of eighty-seven) to 7 percent (four of fifty-seven) after three to six years of follow-up^17,20,23. Earlier designs of proximally fixed stems with patches of porous coating allowed channels through which wear debris could enter the femoral canal and cause lysis⁴. Consequently, most current designs that we are aware of include circumferential porous coating, which allows proximal fixation as well as a tight seal for the femoral canal that prevents wear debris from entering the canal.

Extensively porous-coated long-stem components that rely more on distal fixation for stability have been associated with a rate of revision of 6 percent (ten of 174) at five years²⁵. The literature suggests that extensive porous coating can lead to considerable proximal bone loss². There is justifiable concern about the difficulty involved in the retrieval of a well fixed extensively porous-coated implant.

Operative Considerations

Preoperative evaluation of the geometric configuration of the proximal part of the femur is essential. The anteroposterior radiograph must be scrutinized for overhang of the greater trochanter—that is, when the medial portion of the trochanter will block the removal of the prosthesis and the site of entry of the revision implant. With the femoral stem template aligned within the canal on the radiograph, a line is drawn proximally to predict the path of insertion of the femoral component. If an excessive amount of the trochanter is seen to be overhanging, one of several complications can occur (Figs. 1-A, 1-B, and 1-C). First, if the overhanging trochanteric bone is not resected, the new femoral stem will be placed in varus, which may result in perforation of the lateral femoral cortex when the prosthesis is inserted. Second, if too much lateral force is placed on the trochanter during preparation of the canal or insertion of the stem, a trochanteric fracture can result. Third, if the trochanteric bed is thinned too much in order to introduce the stem into the femoral canal, a trochanteric fracture or an avulsion of the abductor tendon may result. The temptation to preserve the trochanter can result in too much thinning of the bone or inadvertent detachment of the abductor tendon. A trochanteric slide, extended trochanteric osteotomy, or transverse femoral osteotomy should be considered in these situations. Although a femoral osteotomy may seem somewhat radical, it avoids the potential pitfalls of trochanteric fracture or injury to the abductor tendon and may actually be a more conservative option.

The heightened awareness of trochanteric complications has led to increased use of the extended trochanteric osteotomy¹⁵. This procedure reduces the risk of distal femoral perforation, decreases the operative time, allows neutral positioning of the femoral component, and preserves the trochanteric bone and abductor muscle. The rate of nonunion is minimum, primarily because of the abundant soft-tissue coverage¹³. The extended trochanteric osteotomy lends itself to distal fixation, with the osteotomized segment of the proximal part of the femur secured around the stem after implantation. Under these circumstances, the use of cement is suboptimum, as poor pressurization of cement impairs fixation and extravasation of cement reduces the ability of the osteotomy site to heal. We have successfully used a modular proximally coated stem after an extended trochanteric osteotomy¹³ (Figs. 2-A, 2-B, and 2-C). Reaming and preparation of the femur for insertion of the component can be accomplished before the osteotomy site is reduced; in this case, the medial portion of the proximal part of the femur is prepared, and the osteotomized lateral portion is attached later with cerclage wires. Alternatively, the osteotomy site can be reduced before preparation of the proximal part of the femur.

Advantages of Modular Components

Revision arthroplasty is often a complex procedure involving the use of bone grafts and modular or custom implants. The goals of revision and primary arthroplasty are to achieve immediate stability of the implant, to restore the biomechanical function of the hip by correcting femoral offset and limb-length discrepancy, to restore femoral and acetabular integrity, and to create a painless range of motion of the hip joint.

Immediate stability is an absolute necessity when components designed to be inserted without cement are used for revision. Because it has been shown that there is no proportional relationship between the metaphyseal and diaphyseal geometry in the proximal part of the femur, the theory of so-called fit and fill is often too difficult to achieve in practice²⁷; this is especially true in revision operations, as there is often altered anatomy and loss of proximal femoral bone stock. Conventional one-piece proximally porous-coated implants designed to be inserted without cement often do not provide complete proximal bone contact because of mismatch between the stem geometry and the proximal part of the femur, from which bone has been lost. Most proximally coated implants, to our knowledge, do not develop distal rotational stability because of the smooth distal surface with its resultant lack of osseous ingrowth; thus, the implant may loosen if metaphyseal stability is not attained. Extensively porous-coated implants rely on distal fixation through an interference fit and then bone ingrowth; thus, proximal femoral geometry and bone loss are of less concern. The consequence of distal fixation is additional bone loss proximally through stress-shielding and a more complicated revision¹. Modularity allows more options intraoperatively to optimize fixation, stability, version, and length.

Current options include a modular head and neck that can be used to modify head size, neck length, and offset (Fig. 3). Proximal sleeves allow adjustment in the anteroposterior and mediolateral dimensions, and proximal pads and distal sleeves compensate for differences in proximal fill and distal fit. Stems are available in various lengths and diameters with variable proximal neck offset.

The evolution of the modular stem for use in revision arthroplasty was stimulated by the acceptance of the modular head-and-neck Morse taper in primary arthroplasty. The complexity of femoral revision requires a versatile system that can be adjusted for proximal femoral bone loss, bone quality, altered anatomy, limb-length discrepancy, and offset. A modular hip system such as the S-ROM (DePuy [Johnson and Johnson], Warsaw, Indiana) allows independent proximal and distal sizing of the femoral component by combining six different stem sizes with ten different proximal modular sleeves for each stem diameter. With the variety of neck lengths and head sizes, a total of 8364 possible combinations are available, enabling the surgeon to assemble the ideal implant that will provide maximum proximal femoral bone contact and optimum distal fit for each patient. The versatility of the S-ROM total hip system is unique, considering the complexity of revision total hip arthroplasty.

Disadvantages of Modular Components

There are many theoretical questions concerning modularity. The potential for micromotion occurring at the stem-sleeve interface may result in fretting and generation of metallic particulate debris. Bobyn et al. addressed this issue with use of dry and wet laboratory testing as well as examination of in vivo prostheses and reported that, given sufficient load and loading cycles, fretting is inevitable³. However, the generation of particulate debris (range, one to three micrometers) with modular femoral components is minimum compared with that seen in association with a polyethylene articulation^2,3. It is not known how many particles need to be released before there is macrophage-mediated osteolysis or increased third-body wear of the articular surface.

Since 1987, more than 900 S-ROM modular femoral stems have been implanted at the New England Baptist Hospital. Despite clinical success, concern lingers over the potential generation of metallic debris emanating from the modular junction between the stem and the proximal sleeve. To detect the presence of titanium debris generated by the S-ROM modular femoral component, specimens of synovial fluid were obtained from nineteen patients who had no evidence of loosening or mechanical failure⁵. Six specimens were collected at the time of removal of hardware that had been causing pain; six, at the time of revision of the acetabular component; two, at the time of attempted reattachment of an ununited trochanteric osteotomy fragment; two, at the time of a resection arthroplasty; two, at the time of an arthroplasty of the contralateral hip; and one, at the time of a hip aspiration performed because of suspected infection. The average duration for which the S-ROM prosthesis had been in place before the sampling of the synovial fluid was thirty-eight months (range, six to eighty-nine months). The average age of the seven male and twelve female patients was fifty years (range, thirty-three to eighty-five years). All specimens of synovial fluid were sent to an independent laboratory for measurement of the amount of titanium with use of inductively coupled plasma atomic-emission spectroscopy. In seventeen of the nineteen specimens, no titanium debris was detected. The two remaining specimens contained 250 and 400 micrograms of titanium debris per liter; these specimens were from a patient who had a loose titanium cup with broken screws and a patient who had several broken wires from a previous trochanteric reattachment. It was concluded that use of the S-ROM modular femoral stem had not resulted in substantial accumulation of titanium debris in patients who had a well fixed stem⁵.

Neither in vivo nor in vitro dissociation of the modular connections has been reported, to our knowledge. Furthermore, Bobyn et al.³ reported that there was no gross movement of the stem-sleeve interface with loading at three to eight times body weight or at torque of as much as fifty newton-meters.

Endosteal lytic lesions of the femur are encountered routinely during revision arthroplasty. When we have used a proximally fixed implant, we have observed that these lesions reconstitute over time (Figs. 4-A, 4-B, and 4-C). This is probably related in part to the initial débridement of the inflammatory tissue and to the later physiological loading of the bone.

Results of Clinical Studies of the S-ROM Prosthesis

Clinical trials of the S-ROM prosthesis were begun in 1984 by Cameron⁷. Since that time, several authors have reported on its use in primary and revision total hip arthroplasty. Cameron reported the three-to-six-year results after primary arthroplasty. Of the forty-eight patients who did not need a revision because of mechanical failure, forty-five (94 percent) had an excellent result. Only two (5 percent) of forty-three patients reported pain in the thigh in association with a stem that had a clothespin split distally⁷.

Cameron also reviewed the results two to six years (average, 3.5 years) after use of the S-ROM prosthesis in ninety-one revision procedures⁸. Of the twenty-nine patients who had had insertion of a standard-length stem, twenty-three (80 percent) had an excellent result. No patient had thigh pain at the end of the stem, subsidence, osteolysis, or radiographic loosening. One hip was revised again because of migration of the acetabular component; thus, the total rate of repeat revision was 3 percent (one of twenty-nine). Of the remaining sixty-two patients, who had sufficient proximal bone loss to need a long curved stem, ten (16 percent) had a repeat revision: four, because of perforation of the anterior aspect of the femur; three, because of infection; and one each, because of migration of the acetabular component, recurrent dislocation, and trochanteric nonunion. No patient had failure of the implant at the stem-sleeve interface, loss of rotational stability, subsidence, metallosis, or osteolysis. The prevalence of radiographic loosening was only 3 percent (two of sixty-two)⁸.

Chandler et al. reported the results at an average of three years after fifty-two complex revision total hip arthroplasties with use of the S-ROM system¹⁰. Twenty-two hips needed a structural allograft because of severe bone loss. Only two patients (4 percent) reported pain in the thigh, and both had a stem with a diameter of more than seventeen millimeters. There was no evidence of fretting at the modular stem-sleeve junction or osteolysis distal to the sleeve. Thirty-one (84 percent) of thirty-seven patients who responded to an outcome questionnaire were satisfied with the result. Of the fifty-two stems, three were loose radiographically and two (which were undersized) were revised because of aseptic loosening; thus, the rate of mechanical loosening for the entire series was 10 percent. Chandler et al. concluded that the S-ROM is a unique system that has the versatility to accommodate complex hip reconstruction.

Chandler et al. also reviewed the results of use of an S-ROM prosthesis-allograft composite for reconstruction of the proximal part of the femur because of major segmental bone loss in twenty-nine patients (thirty hips)⁹. The sleeve was cemented into the proximal femoral allograft, and a long-stem curved femoral implant then was press-fit into the host femur. At an average of twenty-two months, all but two of the thirty allografts had united to the host bone clinically and radiographically. In a subsequent study, Chandler and Carangelo reported on forty-four patients who had had reconstruction with use of an S-ROM prosthesis-allograft composite; at an average of six years postoperatively, radiographic union of the graft to the host had occurred in forty-two patients (95 percent)¹².

Our Clinical Experience

We retrospectively reviewed the results of sixty-three consecutive complex revision total hip arthroplasties in sixty-two patients, performed between December 1988 and June 1993 by two of us (R. H. T. and J. C. McC.) at the New England Baptist Hospital with use of the S-ROM modular titanium-alloy femoral component²⁶. There were thirty-four men and twenty-eight women, and the average age at the time of the revision was fifty-seven years (range, twenty-four to eighty-three years). These patients had extensive bone loss that was difficult to treat, which reflects the fact that New England Baptist Hospital is a referral institution. The patients had had an average of two previous hip operations (range, one to four procedures). Forty-three revisions (68 percent) were performed because of failure of a cemented femoral component, fourteen (22 percent) were performed because of loosening of a component that had been inserted without cement, and six (10 percent) were conversions from a Girdlestone arthroplasty after treatment of a deep infection. The acetabular component was revised in fifty-six (89 percent) of the sixty-three hips. All hips had grade-II or III proximal femoral bone loss according to the classification system of the American Academy of Orthopaedic Surgeons¹⁴. These cavitary, segmental, or combined defects affected, or had the potential to affect, the structural integrity of the femur. Thirty-eight hips (60 percent) needed bulk allograft to provide support or to replace extensive femoral bone loss. Cortical onlay strut grafts were used in thirty-two hips (51 percent), and proximal femoral allograft was used in six hips (10 percent).

All procedures were performed with the patient in lateral decubitus. A trochanteric osteotomy or slide was performed for exposure in forty-four hips (70 percent); a posterior approach was used in all hips. The Dall-Miles cable-claw system (Stryker Howmedica Osteonics, Allendale, New Jersey) was used for reattachment of the trochanteric osteotomy fragment in each hip. Fifty-two hips (83 percent) had insertion of a stem that was longer than 200 millimeters. A calcar-replacement femoral stem was used in nineteen hips (30 percent). In fifteen hips (24 percent), the femoral neck of the prosthesis was longer than forty millimeters. In the hips that had insertion of a proximal femoral allograft, the modular proximal sleeve was cemented into the graft before the stem was press-fit into the distal host bone, a method that was similar to that described by Chandler¹¹. The cortical onlay strut grafts were held to the host bone with 16-gauge Luque cerclage wires.

The preoperative radiographs were reviewed for bone defects and deficiency according to the American Academy of Orthopaedic Surgeons classification system for femoral abnormalities¹⁴. The postoperative radiographs were assessed according to the criteria for stability established by Engh et al.¹⁶ as well as with components of the system proposed by Hedley et al.²². Radiographs were examined for the presence of radiolucent lines according to the zones described by Gruen et al.¹⁹ as well as for changes in the position or alignment of the component, femoral remodeling, and incorporation of the allograft.

At an average of 5.9 years (range, four to nine years) after the operation, fifty-four (86 percent) of the sixty-three hips, all of which had had a grade-II or III femoral defect, had an intact and radiographically stable prosthesis. No hip had mechanical failure, uncoupling of the modular components, or fracture of the stem. Nine procedures (14 percent) failed, necessitating a repeat revision. The failure was due to infection in five hips (8 percent); two of these hips had a proximal femoral allograft with a cemented sleeve, and three had a press-fit component that had been inserted without cement. In the remaining four hips (6 percent), the failure was due to aseptic loosening; in all four, the implant had been inserted without cement.

The radiographic analysis included fifty-four hips in which the reconstruction had been performed without cement and four in which the proximal sleeve had been cemented into the allograft. (Five hips in which the procedure failed because of infection were excluded.) According to the criteria of Engh et al.¹⁶, forty-six (85 percent) of the fifty-four hips that had had a revision without cement had bone ingrowth (Figs. 5-A and 5-B), four (7 percent) had stable fibrous ingrowth, and four had radiographic loosening (Figs. 6-A and 6-B). The four hips that had stable fibrous ingrowth had subsidence that averaged 5.3 millimeters (range, two to thirteen millimeters) early in the postoperative period; the subsidence leveled off when the proximal sleeve came into contact with medial cortical bone that was strong enough to support the prosthesis. Of these four hips, two had massive cortical onlay strut grafts that provided partial proximal support, one hip had been irradiated postoperatively because of a metastatic bone tumor, and one hip had an undersized prosthesis that shifted into a slight varus position. All cortical onlay strut grafts appeared incorporated. In the four hips that had a proximal femoral allograft with a cemented sleeve, the reconstruction was radiographically stable proximally and distally, with a united graft-host junction.

The osseous response of the fifty-four hips with severe bone loss that were reconstructed without cement was notable. Evaluation of the calcar region revealed no measurable change in the cortical thickness in forty-six hips (85 percent). Five hips (9 percent) had hypertrophy of the calcar in zones 1 and 7 of Gruen et al.¹⁹, around the proximal porous-coated modular sleeve, indicating proximal stress transfer. Only three hips (6 percent) had evidence of stress-shielding or distal stress transfer; one had rounding of the calcar, and two had measurable resorption of the calcar. Twenty-nine hips (54 percent) had endosteal hypertrophy, mostly in zones 2 and 6 (Figs. 7-A and 7-B). Thirteen hips (24 percent) had lateral cortical hypertrophy in zones 4, 5, and 6 that was not related to onlay strut-grafting (Fig. 7-C).

Radiolucent lines were noted in sixteen hips (30 percent); in seven, the lines were nonprogressive and were found in only one of the proximal zones (zone 1 or 7). The remaining nine hips had radiolucent lines in multiple zones. Six hips (11 percent) had proximal bone resorption in a pattern consistent with osteolysis; these hips included one that had a clinically stable segmental allograft with a cemented sleeve and another that had a stable implant with bone ingrowth distal to lesions. The other four hips had failure both clinically and radiographically. No osteolysis was seen distal to the porous-coated proximal sleeve of any of the ingrowth stems. Four hips (7 percent) had parallel reactive sclerotic lines distal to the sleeve of the ingrowth stem (Fig. 8).

Overview

Implants used for femoral reconstruction without cement may be classified as either proximally or distally fixed. The clinical results of these two groups are roughly equivalent after intermediate-term follow-up, but the osseous responses are distinctly different. The distally fixed implants are stress-shielded proximally, resulting in bone loss. This is a direct response to Wolff's law²¹. Our data show that proximally fixed implants loaded proximal bone, resulting in endosteal hypertrophy and cortical hypertrophy, with a rate of aseptic loosening of 6 percent (four of sixty-three) at an average of 5.9 years. Therefore, while the clinical results of distally and proximally fixed implants are equivalent after intermediate-term follow-up, the proximal bone resorbs with use of the former and reconstitutes with use of the latter.

We believe that, in the setting of revision, proximal circumferential porous coating and additional rotational stability provide optimum fixation. In our experience, use of the S-ROM proximally modular femoral stem in complex revision arthroplasty allows intraoperative customization and results in reliable fixation.

The theoretical concerns regarding modularity must be weighed against the potential advantages. The generation and accumulation of titanium particles in the synovial fluid after implantation of a proximally modular stem has not been documented in vitro or in vivo. The absence of measurable amounts of titanium particles, at an average of thirty-eight months, in the synovial fluid of patients managed with a well fixed S-ROM implant⁵ suggests that the sleeve-stem interface is secure, although longer follow-up studies are necessary. Thus far, modular femoral stems represent a unique solution to many complex problems encountered in revision hip arthroplasty.

References

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Christensen, C.: Extended trochanteric osteotomy for femoral revision using a modular proximally coated femoral stem. Unpublished data.

D'Antonio, J.; McCarthy, J. C.; Bargar, W. L.; Borden, L. S.; Cappelo, W. N.; Collis, D. K.; Steinberg, M. E.; and Wedge, J. H.: Classification of femoral abnormalities in total hip arthroplasty. Clin. Orthop.,296: 133-139, 1993.296133 1993 [PubMed]

Emerson, R. H., and Head, W. C.: Extended trochanteric osteotomy. In Revision Total Hip Arthroplasty, pp. 277-299. Edited by J. V. Bono, T. S. Thornhill, B. E. Bierbaum, and R. H. Turner. New York, Springer, 1999.

Engh, C. A.; Glassman, A. H.; Griffin, W. L.; and Mayer, J. G.: Results of cementless revision for failed cemented total hip arthroplasty. Clin. Orthop.,235: 91-110, 1988.23591 1988 [PubMed]

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