The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 93, Issue 1

Scientific Articles | January 05, 2011

Fracture of Cementless Femoral Stems at the Mid-Stem Junction in Modular Revision Hip Arthroplasty Systems

Dror Lakstein, MD¹; Noam Eliaz, PhD, MBA²; Ofer Levi, MSc²; David Backstein, MD, MEd, FRCSC¹; Yona Kosashvili, MD, MHA¹; Oleg Safir, MD, MEd, FRCSC¹; Allan E. Gross, MS, FRCSC¹

¹ Division of Arthroplasty, Orthopedic Department, Mount Sinai Hospital, 600 University Avenue, Suite 476A, Toronto, ON M5G 1X5, Canada. E-mail address for D. Lakstein: drorale@gmail.com
² Biomaterials and Corrosion Laboratory, The Materials and Nanotechnologies Program, Tel-Aviv University, Ramat Aviv, Tel-Aviv 69978, Israel

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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors, or a member of his or her immediate family, received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Zimmer).

Investigation performed at the Division of Arthroplasty, Orthopedic Department, Mount Sinai Hospital, Toronto, Ontario, Canada, and the Biomaterials and Corrosion Laboratory, Materials and Nanotechnologies Program, Tel-Aviv University, Tel-Aviv, Israel

J Bone Joint Surg Am, 2011 Jan 05;93(1):57-65. doi: 10.2106/JBJS.I.01589

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Abstract

Background:

Mechanical failure of femoral stems at the modular junction of revision hip arthroplasty systems has been reported only infrequently. In the current study, the cause of six stem fractures, which occurred in vivo, was analyzed with use of clinical data and failure analysis.

Methods:

Six patients with a fracture at the mid-stem junction of a modular revision hip implant were identified in our database of patients who had undergone revision arthroplasty. The characteristics of the patients with a fractured stem were compared with those of 165 patients from the same prospective database who had a modular stem implanted, had at least two years of follow-up, and had not had a fracture of the stem. Failure analysis of three implants (six fracture surfaces) was carried out, with use of microscopic, chemical, and microhardness characterization techniques.

Results:

Patients with a fractured stem had significantly higher body mass indices than patients without a stem fracture. Radiographs demonstrated that these femoral implants lacked adequate osseous support of the junction area of the stem. All stems failed approximately 1 to 2 mm proximal to the body-stem junction, thus indicating the presence of a bending moment. The chemical composition and microhardness matched those of Ti-6Al-4V. Evidence of wear and fatigue were found on the fracture surface. A wear strip was also observed along the circumference of the stem near the junction.

Conclusions:

We concluded that the stem failure was initiated by a fretting fatigue mechanism and was propagated by a pure bending fatigue mechanism. Risk factors for fractures of the modular junction include excessive body weight and inadequate proximal osseous support because of trochanteric osteotomy, reduced preoperative bone stock, osteolysis, loosening, and/or implant undersizing. Surgeons should consider the use of implants with strengthened junctions when using modular stems in such patients.

Figures in this Article

Introduction

Mechanical failure of the femoral component after total hip arthroplasty is not a common occurrence, but fractures of femoral stems after hip arthroplasty have been previously described^1-3. Factors that predispose to this form of stem failure include excessive patient weight, high levels of physical activity, deficient osseous support, malposition or loosening of the stem, the presence of a stress-riser, and reduced cross-sectional area within the stem^2,4-7.

Cementless revision stems have become an appealing option for the arthroplasty surgeon in treating patients with a deficient femur during the last three decades^8-10. The fixation options available for revision femoral components include distal fixation as well as extensive (both distal and proximal) fixation stems. Both methods have been reported on and both exhibit survival rates of >90% at five to fifteen years of follow-up^8-12. These stems are suitable for use with various types of bone deficiency and are compatible with extended trochanteric osteotomies⁸. Modularity offers the advantage of adjustment and restoration of joint kinematics including leg length, version, and offset, regardless of the exact position of the distal part of the stem.

In addition to the higher cost associated with modularity, concerns have been raised with regard to the potential complications of fretting and fracture at the modular junction^13,14. Fractures of modular stems at other portions of the component have been reported only sporadically^5,15. Lakstein et al.⁸, in a study of seventy-two hips at five to ten years of follow-up, reported one stem failure at the modular junction, and one specific modular femoral stem design was withdrawn from the market because of a higher than expected rate of component failure¹⁶. To our knowledge, there has been no previous report in the literature of a group of stems that had failed mechanically at the modular junction.

The purposes of the current study were to evaluate the clinical and mechanical characteristics of stem fractures at the modular junction of ZMR stems (Zimmer, Warsaw, Indiana) and to identify predisposing factors in the face of which it may be advisable to take preventive measures when implanting a modular stem. To this aim, a systematic failure analysis was conducted.

Materials and Methods

Six patients with a fracture at the mid-stem junction in a modular revision hip arthroplasty system were identified in our database of patients who had undergone revision surgery between 1999 and 2009. Three of these patients had the index modular revision stem implantation performed at our institution, and the remaining three patients were referred after the stem had already broken. All of the failed stems were of the ZMR brand (Zimmer). This hip system offers three stem designs: taper, porous, and spline. A variety of modular body shapes and sizes allows flexibility to restore hip kinematics by adjusting anteversion, leg length, and horizontal offset. The spout body has a medial curve to provide fill of the proximal part of the femur. The cone body is conical and designed to allow flexibility for version adjustments. The calcar body is also conical but has a collar that is designed to serve as a calcar replacement. The XL (extra large) junction body and stem were designed to provide a strengthened body-stem junction in order to prevent fractures at the modular junction. The taper body, available until 2002, was removed from the market following a safety alert from Zimmer¹⁶, indicating that this component was involved in most of the stem fractures reported. The mid-stem junction between the stem and the body uses a Morse-type taper connection to ensure locking of the proximal body and distal stem components. The compression nut, when torqued to 15 Nm, provides additional security. The diameter of all stems at the junction was 14 mm. In the XL junction stem, this diameter was enlarged to 19.5 mm.

Data were collected from patient charts and radiographs. Institutional review board approval and patient consent were obtained. The age at the time of the index revision, sex, body mass index (BMI), the time between the index surgery and stem fracture, and clinical presentation (whether with an acute or chronic onset of pain) were recorded. We also recorded the type and size (length and diameter) of the stems and bodies used, femoral offsets, and neck lengths (Table I). Standard anteroposterior and cross-table radiographs were analyzed to classify femora, according to the Gross classification system for femoral deficiency¹⁷, and to evaluate osseous support at the level of the modular junction. Osseous support of the junction area was evaluated by assessing local bone deficiency. Furthermore, lack of support because of a trochanteric osteotomy nonunion or fracture or because of an undersized modular body was noted.

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TABLE I Demographic and Operative Variables

Case	Age (yr)	Sex	Body Mass Index	Weight (kg)	Type of Bone Deficiency*	Body Type	Femoral Offset	Stem Type	Stem Length (mm)	Stem Diameter (mm)	Neck Length (mm)	Surgical Approach†	Time to Fracture (mo)	Reconstruction‡	Remarks†
1	81	M	34	109	2	Spout	Extended	Porous	220	15	+7	ETO	13	ZMR XL	ETO fragmented at level of junction
2	79	M	27	75	2	Cone	Extended	Porous	220	16.5	+7	TSO	80	ZMR and proximal femoral allograft	Severe cavitary bone deficiency
3§	52	M	26	78	2	Cone	Standard	Taper	185	19	+3.5	TSO	71	ZMR XL	Undersized modular body
4§	66	F	29	77	2	Cone	Extended	Taper	185	15	+3.5	TSO	44	ZMR and strut	Severe cavitary bone deficiency
5	88	F	25	60	4	Cone	Extended	Taper	185	16	+0	ETO	32	ZMR XL	ETO fragmented and resorbed
6§	37	M	34	110	4	Spout	Standard	Spline	170	15	+0	TSO	40	ZMR XL	Nonunion of TSO

*Classified according to the Gross classification system¹⁷.
†ETO = extended trochanteric osteotomy, and TSO = trochanteric slide osteotomy.
‡ZMR XL hip system (Zimmer, Warsaw, Indiana).
§Referred patient.

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TABLE I Demographic and Operative Variables

Case	Age (yr)	Sex	Body Mass Index	Weight (kg)	Type of Bone Deficiency*	Body Type	Femoral Offset	Stem Type	Stem Length (mm)	Stem Diameter (mm)	Neck Length (mm)	Surgical Approach†	Time to Fracture (mo)	Reconstruction‡	Remarks†
1	81	M	34	109	2	Spout	Extended	Porous	220	15	+7	ETO	13	ZMR XL	ETO fragmented at level of junction
2	79	M	27	75	2	Cone	Extended	Porous	220	16.5	+7	TSO	80	ZMR and proximal femoral allograft	Severe cavitary bone deficiency
3§	52	M	26	78	2	Cone	Standard	Taper	185	19	+3.5	TSO	71	ZMR XL	Undersized modular body
4§	66	F	29	77	2	Cone	Extended	Taper	185	15	+3.5	TSO	44	ZMR and strut	Severe cavitary bone deficiency
5	88	F	25	60	4	Cone	Extended	Taper	185	16	+0	ETO	32	ZMR XL	ETO fragmented and resorbed
6§	37	M	34	110	4	Spout	Standard	Spline	170	15	+0	TSO	40	ZMR XL	Nonunion of TSO

We reviewed the cases of all patients in our database in whom a modular stem had been used in femoral revision surgery, for the purpose of comparison. Femoral arthroplasty with use of a modular stem was performed in 190 patients (198 femoral revisions). All operations were conducted by two of the authors (A.E.G. and D.B.) in one hip arthroplasty referral center. Eighteen patients in which the XL junction body had been used were excluded from this analysis. Four patients who had less than two years of follow-up and three patients who had a fracture of the stem were excluded as well. Included in this analysis were 165 patients (173 femoral revisions) who had at least two years of follow-up and had not experienced a fracture of the ZMR stem. Of these, 53% were women and 47% were men. The indications for revision surgery in which this stem was used were aseptic loosening in 130 hips (75%), infection (two-stage revision) in nineteen (11%), periprosthetic fractures in sixteen (9%), fracture of a prior femoral stem in five (3%), and instability in three (2%). The index operation was a first hip arthroplasty revision for ninety-four hips (54%), a second revision for fifty-seven (33%), and a third to fifth revision for twenty-two (13%). The ZMR type of system was used in all revisions. The spout body was used in eighty-four hips (49%), the cone body in seventy (40%), the calcar body in ten (6%), and the taper body in nine (5%). A porous stem was used in eighty-six hips (50%), a taper stem in eighty-four (49%), and a spline stem in three (2%). Osseous support was assessed radiographically with use of the Gross classification system for femoral deficiency¹⁷. Additionally, fractures and nonunions of trochanteric osteotomies were recorded.

Body mass index and the age of the patients who had a stem fracture and those who had not had a fracture were compared with use of the t-test for independent samples.

Failure Analysis

All fractures occurred at the modular stem junction. Three of the failed implants were analyzed at the Biomaterials and Corrosion Laboratory at Tel-Aviv University, Tel-Aviv, Israel. Macroscopic images of whole implants as well as of the six fracture surfaces were acquired with a charge-coupled-device camera. The fracture surfaces were also inspected under a Stemi 2000-C stereomicroscope (Zeiss, Göttingen, Germany). Fractography was performed by means of a Quanta 200 field-emission gun environmental scanning electron microscope (FEI, Eindhoven, The Netherlands). The attached Oxford INCA energy dispersive spectroscopy system (EDS; Oxford Instruments, Bucks, England) was used for chemical analysis at different regions of the fracture surface. Metallographic cross sections were prepared perpendicular to the fracture surfaces. The polished cross sections were imaged, before and after chemical etching in Kroll solution, by an Axio Scope. A1 light microscope (Zeiss, Göttingen, Germany) with a PAXcam3 ARC digital camera (MIS, Villa Park, Illinois). Microhardness tests were conducted in the vicinity of and far away from the fracture surface, with use of an FM-700e (Type A) microhardness tester (Future-Tech, Kanagawa, Japan), the Vickers technique, a load of 25 gf, and a dwell time of ten seconds.

Source of Funding

No outside funding was used for this study.

Results

The clinical and operative details for the patients with a fractured stem are shown in Table I. The stems fractured between thirteen and eighty months (mean, forty-seven months) after surgery. One patient (Case 1) reported moderate pain in the lateral aspect of the thigh since the time of the index operation. In that patient, radiographs made thirteen months after surgery demonstrated a nondisplaced crack of the stem at the modular junction (Fig. 1-A). Five patients experienced the acute onset of thigh pain sometime between thirty-two and eighty months after surgery. None had a history of recent trauma. Two of those patients (Cases 2 and 5) had a periprosthetic fracture at the same level where the stem had broken. A radiograph of one of them (Case 2) is shown in Figure 1-B.

Fig. 1-A Fig. 1-B Fig. 1-C

Radiographs of the hips in three patients (Cases 1, 2, and 6) showing lateral and slightly anterior failure of the femoral stem. Fig. 1-A Case 1. Fig. 1-B Case 2. Fig. 1-C Case 6. An extended trochanteric osteotomy fragmented and failed to heal at the same level as the stem fracture. Refer to Table I for more details.

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Patients with a fractured stem had a significantly higher body mass index (29.3 ± 4.1 kg/m²) than did patients without a stem fracture (24.1 ± 5.5 kg/m²; p = 0.02). No significant difference in the mean age of the patients with a stem fracture (67 ± 29 years) and those without a fracture (69 ± 14 years) was found (p = 0.98).

Radiographic analysis demonstrated that all patients had a lack of adequate osseous support of the modular stem-junction area. Three patients had trochanteric or extended trochanteric osteotomies that fragmented or failed to heal (Fig. 1-C). Two patients had severe proximal medial cavitary bone deficiencies. One patient had only a minor proximal bone deficiency, but the body was deemed undersized radiographically and therefore it was not in close contact with the surrounding bone. All stems had rigid distal fixation. One stem fracture was a nondisplaced crack, and the other five collapsed into varus angulation.

Femoral deficiencies in patients in whom the implant stem did not fracture were classified with use of the Gross classification system¹⁷. One hundred and nine hips (63%) had a minimal or cavitary (type-1 or 2) deficiency. Forty-four hips (25%) had a type-3 segmental defect, and seven hips (4%) had a type-4 segmental defect. Thirteen hips (8%) had type-5 periprosthetic fractures. Eight hips (5%) had a fracture of the greater trochanter at the level of the modular junction or nonunion of a trochanteric osteotomy.

All patients underwent revision of the broken stem. All stems were found to be well fixed distally, and extended trochanteric osteotomies were used to facilitate stem extraction. Those osteotomies were extended as far distally as required to facilitate stem removal, as long as doing so did not preclude distal fixation with at least 5 cm of diaphyseal bone. In order to remove the well-fixed distal portion of the stem, trephines were utilized to separate the stem from the bone. Reconstruction was dictated by femoral bone loss after extraction of the broken stem. Four patients were treated with the ZMR XL junction stem, one patient was treated with a ZMR stem and a strut allograft, and one patient had severe distal bone loss and therefore received a proximal femoral allograft-prosthesis composite. With one to six years of follow-up, five of the patients had no signs of loosening and required no further surgery. One patient who received a ZMR XL junction stem had early subsidence of the stem and underwent another revision four months later, with a femoral allograft-prosthesis composite.

Failure Analysis

Radiographic images revealed a lateral and slightly anterior failure in all three hips (Cases 1, 2, and 6) (see Figs. 1-A, 1-B, and 1-C). Macroscopic imaging of the retrieved implants (Fig. 2) revealed that all stem fractures were located approximately 1 to 2 mm proximal to the visible body-stem junction (i.e., "hidden" beneath the body). This indicates that the junction was subjected to a bending moment during crack initiation.

Fig. 2

Photograph of the retrieved implant from one patient (Case 1), demonstrating the location of the fracture approximately 1 to 2 mm proximal to the visible body-stem junction, which indicates that the junction was subjected to a bending moment.

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Further visual examination of the fracture surfaces revealed the origin and different textures on the fracture surface. Three distinct textures were identified (marked as A, B, and C and separated by dashed lines in Figure 3, a). Area A covers approximately 40% of the fracture surface area. It is characterized by a smooth texture and planar orientation, which consists of beach marks emanating around an origin point at the edge of the fracture surface; this localized point is at the outer side of the stem. Area C is characterized by rough texture and lusterless shade with shiny islands. It covers approximately 30% of the fracture surface area. Area B, which also covers approximately 30% of the fracture surface area, has mixed characteristics of areas A and C, namely, rough texture and beach marks at the sides.

Fig. 3

Photographs of two stem fractures "hidden" beneath the bodies of implants retrieved from Case 6 (a) and Case 3 (b). Three distinct textures (marked as A, B, and C and separated by dashed lines) are evident in the implant from Case 6 (a). Area A consists of beach marks emanating around an origin point at the outer side of the stem. Wear islands are evident across the fracture surface. The arrow indicates the origin zone.

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Scanning electron microscopic analysis required extremely careful examination because of the extensive wear islands across the fracture surface (see Figure 4, a and b, as well as Figure 3). These islands may be related to the action of dynamic motion as failure developed. Nevertheless, dimples characteristic of overload were observed in area C (Fig. 4, f), whereas fatigue striations, fatigue tears, and subsidiary cracks were observed in area A (Fig. 4, c through e). Visual examination under a stereomicroscope of the circumferential surface of the stem in the vicinity of the fracture surface revealed a wear strip, approximately 1 to 2 mm wide, which is common in failures with a fretting fatigue mechanism. Scanning electron microscopic imaging of the circumferential surface at the origin revealed a smeared area due to cyclic motion between the stem and the surrounding body as well as subsidiary cracks with an orientation parallel to the original fracture surface (see Appendix).

Fig. 4

Scanning electron microscopic images of fracture surfaces demonstrating wear islands on the fracture surface (a), a low-magnification backscattered electron image of a fracture surface revealing an area such as A in Figure 3, a (b), fatigue tears and secondary cracks (c through e), and dimples of overload in area C (f).

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Chemical analysis (energy dispersive spectroscopy) revealed that the stem was composed of Ti-6Al-4V alloy, as required (see Appendix). Metallographic cross sections revealed (1) a microstructure after chemical etching that was typical of Ti-6Al-4V, with no forbidden phases or inclusions, and (2) a layer of worn material with a deformed microstructure and underlying cracks on the circumferential surface of the stem (see Appendix). These findings indicate that the failure was associated with wear between the stem and the body but cannot be related to the metallurgical condition of the raw material. The mean values (and standard deviation) of microhardness (VHN) measured near the fracture surfaces of three stems were 282 ± 28, 334 ± 17, and 321 ± 15 VHN. The microhardnesses measured in the same stems far from the fracture surfaces were 306 ± 16, 329 ± 20, and 298 ± 20 VHN, respectively. Hence, neither a hardening nor a softening effect in the vicinity of the fracture surface may be claimed. Moreover, all values satisfy the requirement of a minimum 126 kpsi of tensile strength (equivalent to a minimum 278 VHN) according to ASTM International F136 and International Organization for Standardization 5832-3 standards.

Discussion

The rate of fracture of modular, cementless, distal fixation stems after revision total hip arthroplasty has been reported to be quite low^2,8,18. However, considering the serious implications of such a complication, necessitating further major surgery on a hip that has already had multiple operations, this problem should not be underemphasized. Several predisposing factors have been mentioned, including patient-related factors such as excessive body weight and high levels of activity, surgery-related factors such as deficient osseous support and implant malpositioning, and implant-related factors such as the presence of a stress-riser within the stem and a reduced cross-sectional area of the stem^2,4-7. The coalescence of several of these predisposing factors likely accounts for most fractures. It should be noted that five of the six stems in this series fractured within the first six years postoperatively.

Some limitations of this study should be mentioned. First, this is a small series of six fractured stems, with only three available for failure analysis. Second, our ability to assess proximal osseous support of the stems that did not fracture was limited. Although the type of osseous defect according to the Gross classification was reported, an actual determination of the adequacy of support to the proximal part of the stem and the level of the modular junction, in particular, was difficult to obtain in past cases. In addition, the use of allograft bone for local augmentation was inconsistent. However, the finding of an obvious lack of adequate support in all fractured stems was striking.

Excessive body weight has been demonstrated repeatedly in most reports of broken stems^2,4,19,20. All of our patients had BMI values in the overweight (25 to 30) or obese (>30) range, and their average weight was significantly higher than that of patients with no stem fracture. Inadequate proximal support has also been consistently associated with fractures of cemented and cementless stems in previous studies and may be related to a trochanteric osteotomy, reduced preoperative bone stock, osteolysis, loosening, and/or undersizing of the proximal part of the implant^2,3,19,20. Murphy and Rodriguez¹⁸, who reported on a series of fifty-four revisions of deficient femora with no stem fractures at two to ten years of follow-up, suggested that allograft support of the proximal part of the implant for proximal bone loss is unnecessary when a distal fixation modular stem is used. However, a later report of fracture of the same stem challenged this observation⁵. Finite element analysis of the proximal part of the femur with extensively porous-coated prosthetic femoral components demonstrated that proximal femoral bone loss, ununited femoral osteotomies, and periprosthetic fractures can result in substantial elevation of stress within these components. This stress may exceed the fatigue strength of the stem²¹. Following several fractures of an earlier version of the ZMR stem, the manufacturer modified the labeling of the device to highlight the importance of osseous support¹⁶. All stem fractures in the current study had inadequate osseous support as a result of trochanteric osteotomy, osteolysis, or modular body undersizing.

As opposed to nonmodular stems, which fail in the middle third, where the maximal lateral tensile and medial compressive forces develop^3,4,19,21,22, all six stems in the current study fractured at the mid-stem modular junction. Several factors probably contribute to this finding. First, the ZMR type of stem was designed with a diameter at the junction of 14 mm (for all stem sizes), for the practical purpose of modularity and compatibility of all bodies with all stems. Small-sized stems and small cross-sectional area have been shown repeatedly to be a risk factor for failure^2,3,19,20. Second, the mid-stem junction is located adjacent and slightly distal to the level of the lower end of the greater trochanter and the vastus lateralis ridge. The sliding trochanteric osteotomy, with a reported nonunion rate of 4.8%²³, and the extended trochanteric osteotomy, with the propensity to fragment at this level^24,25, may result in corresponding locations of weakness in both the bone and the stem.

The third, and most important, factor is the mechanics of the body-stem junction. When the stem is being assembled before implantation, if the surgeon does not make sure that the (Morse) taper fits perfectly, accelerated failure (e.g., fretting and fatigue) might result. However, the system used in this study includes instruments that ensure proper placement and prevent partial engagement. Failure analysis revealed that the stem failed because of a crack that was initiated in a fretting fatigue mechanism and propagated in a bending fatigue mechanism. This conclusion is supported by the location of the fracture (1 to 2 mm proximal to the junction between the stem and the body), fatigue tears on the fracture surface, wear marks on the fracture surface as well as on the adjacent circumference, and subsidiary cracks parallel to the fracture surface.

Fretting fatigue takes place when contacting components are subjected to cyclic loading while small, oscillatory motion of small amplitude occurs between them. Fretting increases the tensile stress as well as the shear stress at the contact interface and generates flaws, which lead to premature crack nucleation. Furthermore, fretting fatigue results in a drastic reduction (by a factor of =2) in the fatigue endurance limit and orders of magnitude decrease in fatigue lifetime from that seen under pure axial cyclic loading alone^26-29. The generation of multiple cracks is a feature of fretting fatigue failures. This failure mechanism has been observed in fracture fixation devices (such as bone plates and Kuntscher nails) as well as in total joint replacements^26,30. Titanium and its alloys are particularly prone to this type of damage, especially in a corrosive environment²⁶.

It should be noted that, in an early stage of this study, it was hypothesized that corrosion was one of the contributors to failure, e.g., in fretting corrosion or crevice corrosion mechanisms^31-34. Hence, all fracture surfaces and the adjacent circumferences were carefully inspected for etching, pitting, chloride formation, corrosion products, and other possible indications of corrosion. However, no such evidence was found, and thus corrosion was ruled out.

Several approaches may be applied to prevent stem-junction failure. Of prime importance is the avoidance of stress-risers. This can be achieved, for example, by using a body with an inner diameter that is substantially larger than the diameter of the stem and "filling the gap" with a generous fillet radius. Alternatively, a stress-relieving groove could be introduced to the stem near the junction zone²⁶. Other measures such as introducing compression into the surface layers by either mechanical (e.g., shot peening^26,28 or rolling²⁶) or chemical (e.g., nitride) processes²⁶ are also recommended. The application of certain metallic coatings²⁶ on the stem (at least at the junction zone) may also be helpful. There are also certain preventative measures that the surgeon can take whenever risk factors are recognized. In heavier patients or in patients with compromised proximal osseous support, protection of the junction with an implant specifically designed for such situations can be pursued and allograft supplementation may be considered. Finally, undersizing of the metaphyseal portion of the implant should be avoided, in particular in the case of solid distal fixation.

Appendix

The electronic version of this article contains two additional microscopic images: a scanning electron microscopic image of the circumferential surface at the fracture origin and a light micrograph of a metallographic cross section, as well as a chemical spectrum of the stem material. These can be viewed at jbjs.org (go to the article citation and click on "Supporting Data").

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Topics

fracture ; femur ; femoral osteotomy ; hip arthroplasty revision

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Dror Lakstein, Noam Eliaz, Ofer Levi, David Backstein, Yona Kosashvili, Oleg Safir, Allan E. Gross; Fracture of Cementless Femoral Stems at the Mid-Stem Junction in Modular Revision Hip Arthroplasty Systems. The Journal of Bone & Joint Surgery. 2011 Jan;93(1):57-65.

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