Modular Femoral Neck Research Articles

Appraisal of evidence base for introduction of new implants in hip and knee replacement: a systematic review of five widely used device technologies

Objective To determine the evidence of effectiveness and safety for introduction of five recent and ostensibly high value implantable devices in major joint replacement to illustrate the need for change...

Fracture of the cobalt-chromium modular femoral neck component in total hip arthroplasty

Total hip prostheses using cervico-metaphyseal modularity were designed to better replicate the geometry of the native extra-medullary femur. However, they are associated with numerous complications including corrosion, disassembly, pseudotumours and, most notably, fractures of the modular neck. All reported cases of modular neck fractures occurred with titanium components (Ti-6Al-4V). To prevent this weakness, manufacturers developed modular necks made of cobalt-chromium (Co-Cr). We report a fracture of a long, 8° varus, Co-Cr modular neck connected to a 36-mm short (–3.5mm) femoral head. The fracture occurred 22 months post-implantation in a woman who had a low level of physical activity and a body mass index of 28.7 kg/m2. To our knowledge, this case is the first reported instance of Co-Cr modular neck fracture. It may challenge the wisdom of further developing this modularity design, as our patient had none of the known risk factors for modular neck fracture. In addition, cases of pseudotumour have been reported with Co-Cr modular necks subjected to fretting corrosion, which contributed to the fracture in our patient.

Effect of femoral neck modularity upon the prosthetic range of motion in total hip arthroplasty.

In total hip arthroplasty, aseptic loosening and dislocation are associated with not being able to achieve the correct prosthetic component orientation. Femoral neck modularity has been proposed as a solution to this problem by allowing the surgeon to alter either the neck-shaft or version angle of the prosthetic femoral component intra-operatively. A single replicate full factorial design was used to evaluate how effective a modular femoral neck cementless stem was in restoring a healthy prosthetic range of motion in comparison with a leading fixed-neck cementless stem with the standard modular parameters. It was found that, if altered to a large enough degree, femoral neck modularity can increase the amount of prosthetic motion as well as alter its position to where it is required physiologically. However, there is a functional limit to the amount that can be corrected and there is a risk with regard to the surgeon having to select the optimum modular neck before any benefit is realised.Electronic supplementary materialThe online version of this article (doi:10.1007/s11517-014-1171-9) contains supplementary material, which is available to authorized users.

Hip & Pelvis

The June 2014 Hip & Pelvis Roundup360 looks at: Modular femoral necks: early signs are not good; is corrosion to blame for modular neck failures; metal-on-metal is not quite a closed book; no excess failures in fixation of displaced femoral neck fractures; noise no problem in hip replacement; heterotopic ossification after hip arthroscopy: are NSAIDs the answer?; thrombotic and bleeding events surprisingly low in total joint replacement; and the elephant in the room: complications and surgical volume.

Femoral neck modularity: A bridge too far—Affirms

The use of femoral stems with dual-taper modularity in total hip arthroplasty offers increased flexibility in restoring hip-center anatomy. Independent of femoral fixation, the modular neck offers the surgeon additional options in recreating femoral version, correcting limb length, and altering offset. Additionally, proponents cite smaller incisions, less dissection, reduced impingement and dislocation, and ease of revision. However, adverse events associated with modular femoral neck usage, including local and systemic effects of corrosion, fracture, and complexities of revision, are now well documented. This review highlights the most current basic science and clinical literature regarding the complications associated with modular femoral necks and their mechanisms of failure.

Femoral neck modularity: A bridge too far—Opposes

Femoral neck modularity in total hip arthroplasty has met with variable success over the years. Following the rise and fall of large metal heads, greater attention has been paid to the effects of trunnion corrosion and modular femoral neck failure. Fretting, galvanic corrosion, and mechanically assisted crevice corrosion challenge all modular junctions. Nonetheless, there are substantial clinical benefits with the use of modularity. Proper design is essential. When well implemented, modularity is an important tool that can contribute to successful total hip arthroplasty.

Fretting and Corrosion in Modular-Neck Total Hip Arthroplasty Femoral Stems

During total hip arthroplasty, use of a modular femoral neck on a stemmed implant allows optimization of neck anteversion, length, and offset, resulting in more accurate balance. We performed a retrospective analysis of a consecutive cohort of patients who had undergone total hip arthroplasty with a modular-neck hip system with ceramic-on-ceramic bearings. We reviewed the results in fifteen patients who had received an ABG II dual modular hip system (Stryker Orthopaedics, Mahwah, New Jersey) from May 2007 to August 2008. Anteroposterior radiographs of the pelvis were reviewed and scored with regard to medial calcar erosion. Magnetic resonance imaging (MRI) was performed to assess for adverse local tissue reaction around the hip joint. Calcar resorption was correlated with subsequent MRI findings. Retrieval analysis was performed on the implants removed at revision. The mean duration of follow-up for all patients was 42.3 months (range, thirty-three to sixty months). Cobalt-ion levels were elevated in all patients; chromium levels were within the normal range. Medial femoral calcar erosion was noted in seven of the fifteen cases. All patients with grade-2 or 3 calcar erosion on radiographs had positive MRI findings consistent with adverse local tissue reaction. At the time of writing, seven patients had undergone revision arthroplasty. Intraoperatively, tissue staining with tissue and bone necrosis and pseudotumor formation were observed in all revision cases. Histological analysis confirmed the presence of metal-on-metal synovitis, with changes similar to those seen with metal-on-metal bearings. The ABG II dual modular hip system is associated with a high rate of early failure secondary to fretting and corrosion at the femoral neck-stem taper. The component has subsequently been recalled and is no longer in use. Surgeons using modular hip systems with a titanium stem and cobalt-chromium neck should be vigilant about annual follow-up with radiographs, and use of MRIs as indicated.

Editorial Comment: Symposium: 2013 Hip Society Proceedings

This symposium is comprised of selected papers delivered at the 2012 Fall (Closed) Meeting of the Hip Society in Rochester, MN, and the Open Scientific Meeting of the Hip Society, in conjunction with the 2013 Annual Meeting of the American Academy of Orthopaedic Surgeons (AAOS) in Chicago. These meetings focused on current clinical and applied research, and elucidated new information on subjects such as alternative bearing surfaces, outcome of different prosthesis designs, surgical techniques for hip arthroplasty, hip joint preserving procedures, and complications such as infection and thromboembolic disease. During the last decade, metal-on-metal (MOM) articulations have seen a dramatic decline worldwide due to adverse effects associated with the generation of nanometer-sized metal particulates and ions. New studies suggest that the development of pseudotumors occurs even in well-functioning MOM implants, and that metal ion levels, the presence of a pseudotumor, and the clinical function of the patient are not exactly concordant. This fact points to the need for ongoing clinical and laboratory surveillance of patients with MOM implants. Additionally, the production of metallic byproducts and adverse local tissue reactions are now being reported in some patients with total hip replacements with large femoral heads articulating with a highly cross-linked polyethylene, and with modular femoral necks. These patients will also need close surveillance. The success of other bearing surfaces continues to be reported, including ceramic-on-ceramic, ceramic-on-highly crosslinked polyethylene. Although the material properties of these newer bearings are vastly improved, these implants must be implanted with precision to avoid complications such as striped wear, squeaking, impingement, chipping, breakage, and incomplete seating. Implant designs with modular parts offer more options for the surgeon to reconstruct the hip optimally, taking into account factors such as femoral configuration, length, offset, bone quality, the presence of a periprosthetic fracture. These implants offer surgeons new capabilities for optimizing and restoring normal hip biomechanics. However, modular junctions may fail mechanically or corrode, yielding new problems. Long-term studies are needed to compare the outcomes of newer modular designs with more established nonmodular implants. Perioperative and late infections are dreaded complications that the reconstructive surgeon is facing with increasing frequency. New methods for expeditious and accurate diagnosis of infection are forthcoming, including laboratory, cellular and molecular tests. Indeed, many of our “single-stage” revisions for diagnoses such as aseptic loosening, polyethylene wear, and recurrent dislocation may in fact be septic cases, if the effort is taken to aggressively culture the operative field and implant for longer periods of time. Current research is examining novel methods of prevention of infection via local and systemic means (implant coatings, enhanced patient prophylactic measures) to mitigate this complication. Recently, both the AAOS and the American College of Chest Physicians have updated their guidelines for prevention of thromboembolic disease after hip arthroplasty. These new guidelines emphasized individualization of prophylaxis based on patient characteristics and complexity of the procedure. Newer physical and pharmacologic agents have entered the marketplace since the previous guidelines, and now have a prominent role. In some patients, hip preservation procedures may be a better option than hip replacement. Patient selection and surgical experience may be the most important determinants of outcome. Further research in this area is needed, as these younger patients (and their hips) must endure a long life following their surgical procedure. This symposium underscores the important research that members of the Hip Society and their collaborators undertake, and serves a valuable educational purpose for surgeons interested in disorders of the hip. All studies reported in this symposium have undergone rigorous peer review. The members of the Hip Society and I (Fig. 1) are pleased to share their research. Fig. 1 Stuart B. Goodman MD, PhD.

Modular versus Nonmodular Neck Femoral Implants in Primary Total Hip Arthroplasty: Which is Better?

Restoration of the hip center is considered important for a successful THA and requires achieving the right combination of offset, anteversion, and limb length. Modular femoral neck designs were introduced to make achieving this combination easier. No previous studies have compared these designs in primary THA, and there is increasing concern that modular designs may have a higher complication rate than their nonmodular counterparts. We therefore asked (1) whether use of a stem with a modular neck would restore limb length and offset more accurately than a stem with a nonmodular neck, and (2) whether patients who received modular neck systems had better hip scores or a lower frequency of complications and reoperations than those receiving a comparable nonmodular stem. Two cohorts of patients undergoing primary THAs, 284 patients with a nonmodular neck and 594 patients with a modular neck, were treated by one surgeon through a posterior approach. These were two nearly sequential series with little overlap. Harris hip scores and SF-12 outcomes surveys were administered at followup with a mean of 2.4 years (maximum, 5.9 years). In the modular neck cohort, a greater proportion of patients had equal (within 5 mm) radiographic limb lengths (89%, compared with 77% in nonmodular cohort p = 0.036), and a smaller offset difference (6.1 versus 7.5 mm, p = 0.047) was observed. Whether these statistical differences are clinically important is unclear. A smaller proportion of patients in the modular neck cohort achieved equal apparent or clinical limb length at 1 year (85% versus 95%, p < 0.001) and at 2 years (81% versus 94%, p < 0.001). In addition, these differences did not appear to result in better Harris hip or SF-12 scores, fewer complications, or reduced likelihood of revision surgery. Use of modular neck stems did not improve hip scores nor reduce the likelihood of complications or reoperations. Because of their reported higher risks, there is no clear indication for modularity with a primary THA, unless the hip center cannot be achieved with a nonmodular stem, which is rare. Level III, therapeutic study. See the Instructions to Authors for a complete description of levels of evidence.

Unique Failure Mechanism of a Femoral Component After Revision Total Hip Arthroplasty

As the prevalence of revision total hip arthroplasty increases, the mechanisms of failure of these revisions have become better delineated. Several studies have indicated infection, instability, and aseptic loosening to be the more common mechanisms of failure in revision surgery. However, with increasing numbers of revisions performed, unique mechanisms of failure are being seen, likely related to the implants that are used in the revision setting. Revision implants offer certain advantages over primary implants with the use of modular components. The revision implants allow the surgeon to increase offset and leg length with modular femoral bodies and necks. However, these modular junctions represent additional areas for implant failure. These new methods of failure associated with modular implants are slowly presenting as the use of these implants continues to increase. The authors recently encountered a mechanism of failure that, to their knowledge, has not been described in the literature. They report a 57-year-old man with dissociation of the proximal body from the diaphyseal component of a Wright Medical Link (Memphis, Tennessee) stem prosthesis. The patient presented with an audible click on physical examination, and radiographs confirmed dissociation of the proximal body. The intraoperative findings, treatment method, and proposed mechanisms for this type of failure are presented, as well as insight into potential ways to avoid this type of failure.

Femoral neck modularity: A bridge too far

Modular femoral neck use in total hip arthroplasty (THA) affords the operating surgeon increased intra-operative flexibility with regard to offset, version, and leg length. Proponents also advocate a reduced dislocation rate, reduced impingement issues, and ease of revision of acetabular component, head, or neck. However, the increased intra-operative flexibility and potential postoperative advantages come at a significant price. Adverse events and complications associated with modular femoral neck usage are being reported with increasing frequency. Modular femoral neck fractures as a result of patient- and implant-related factors are prevalent. Corrosion at the neck–stem interface is associated with a number of sequelae, including osteolysis, synovitis, adverse local tissue reactions (ALTRs), and aseptic lymphocyte-laminated vascular-associated lesions (ALVAL). Systemic complications of metallosis are also pertinent following corrosion at the neck–stem junction. Failure to disassemble the neck from the stem due to corrosion and cold welding is a documented complication and obviates a potential benefit of modularity at the time of revision. Modular femoral necks have a twofold increase in overall revision rate in the Australian registry data as compared to fixed-neck stems. Lastly, modular femoral necks add significant cost to each THA. The purpose of this review article is to discuss the current state of femoral neck modularity and provide the readership with pause prior to the continued use of modular femoral neck THA. Given the current and emerging literature, the modular femoral neck is a bridge too far.

Poor Short Term Outcome with a Metal-On-Metal Total Hip Arthroplasty

Metal-on-metal (MoM) bearings for total hip arthroplasty (THA) have come under scrutiny with reports of high failure rates. Clinical outcome studies with several commercially available MoM THA bearings remain unreported. We evaluated 78 consecutive MoM THAs from a single manufacturer in 68 patients. Sixty-six received cobalt–chrome (CoCr) monoblock and 12 received modular titanium acetabular cups with internal CoCr liners. Femoral components were titanium with modular necks. At average 2.1years postoperatively, 12 THAs (15.4%) demonstrated aseptic failure (10 revisions, 2 revision recommended). All revised hips demonstrated capsular necrosis with positive histology reaction for aseptic lymphocytic vasculitis-associated lesions/adverse local tissue reactions. Prosthetic instability following revision surgery was relatively common. Female gender was a strong risk factor for failure, though smaller cups were not. Both monoblock and modular components fared poorly. Corrosion was frequently observed around the proximal and distal end of the modular femoral necks.

Caveat Emptor: Adverse Inflammatory Soft-Tissue Reactions in Total Hip Arthroplasty with Modular Femoral Neck Implants

Modular femoral neck (MFN) implants in total hip arthroplasty facilitate optimizing femoral offset and version while minimizing femoroacetabular impingement1, but component fracture and dissociation have been reported with titanium-alloy MFN implants2-6. Cobalt-chromium MFN components have improved strength compared with earlier designs, but the long-term consequences of wear and corrosion at the femoral neck-stem junction are unknown3,7. Inflammatory metal-hypersensitivity reactions have been most frequently reported in cobalt-chromium metal-on-metal articulations used in total hip arthroplasty and hip resurfacing arthroplasty8,9, but to our knowledge, these reactions have not been described in MFN implants with metal-on-polyethylene articulations. We present two patients with MFN implants who developed partially cystic peri-implant soft-tissue masses with histologic features suggestive of metal hypersensitivity requiring revision arthroplasty. Both patients were informed that data concerning their cases would be submitted for publication, and they provided consent. Case 1. A sixty-three-year-old woman (body mass index, 31.3) with severe osteoarthritis had undergone a left total hip arthroplasty with a 50-mm Trilogy Shell (Zimmer, Warsaw, Indiana), a 36-mm highly crosslinked polyethylene liner (Zimmer), an uncemented titanium-alloy ABG II size-3 modular femoral stem with a 130° cobalt-chromium MFN (Stryker, Mahwah, New Jersey), and a +5-mm 36-mm cobalt-chromium head (Stryker). The patient had an uneventful postoperative course and was discharged on postoperative day three. Seven months later, the patient presented with progressive pain in the left hip. Radiographs showed satisfactory component positioning with no osteolysis, aseptic loosening, or periprosthetic fracture. Blood work showed an elevated erythrocyte sedimentation rate (ESR), C-reactive protein level (CRP), and serum metal ion levels without leukocytosis (Table I). Computed tomography (CT) of the hip demonstrated a 2.3 × 3-cm fluid collection between the gluteus maximus and medius muscles. Aspiration of the hip yielded 2 mL of orange-tainted …

Modular Femoral Neck Fracture After Primary Total Hip Arthroplasty

The use of modular femoral stems in primary total hip arthroplasty has increased considerably in recent years. These modular components offer the surgeon the ability to independently alter version, offset, and length of the femoral component of a hip arthroplasty. This increases the surgeon's ability to accurately recreate the relevant anatomy but increases the possibilities of corrosion and fracture. Multiple case reports have highlighted fractures of these modular components. We present a case of a fracture of a modular design that has had no previously reported modular neck fractures. The patient was informed that data concerning the case would be submitted, and he consented.

Fracture of the Modular Femoral Neck Component in Total Hip Arthroplasty

The use of modularity, specifically dual modular femoral stems, in total hip arthroplasty has increased in popularity over the past 2 decades. While offering several distinct advantages intraoperatively, the long-term success of adding a second modular junction has yet to be established. One potential complication of increasing modularity is component fracture. We present a case of modular femoral neck prosthesis fracture necessitating revision surgery to treat this complication. Careful preoperative planning during revision of these failures is essential to avoid morbidity and unnecessary subsequent revision surgeries, as demonstrated in this case. The combined effects of crevice and fretting corrosion, large-diameter femoral head, long modular neck, metal-on-metal articulation, patient size, and activity level may have all played integral roles in creating an environment susceptible to this classic pattern of fatigue fracture.

In vitro assessment of strength, fatigue durability, and disassembly of Ti6Al4V and CoCrMo necks in modular total hip replacements

Modularity in total hip replacement offers advantages with regard to biomechanical adjustments and leg lengths. Recently, modular femoral necks were introduced as an added advantage to head modularity permitting further adjustments in femoral version as well as offset and ease of revision. Currently, most necks are made of Ti6Al4V for which cases of in vivo fractures and inseparable neck-stem junctions have been reported. Therefore, we investigated CoCrMo head-Ti6Al4V stem hip replacements with necks made of CoCrMo as an alternative to Ti6Al4V. We compared the two materials with respect to (1) compressive load bearing capacity; (2) fatigue durability; and (3) component distraction. We performed in vitro fatigue-pull-off, microscopy, fatigue durability and compression investigations. The CoCrMo neck showed a load bearing capacity of 18 kN, 38% higher than 13 kN for the Ti6Al4V neck. A fatigue load of 11.2 kN for 1 million cycle failure was achieved with CoCrMo translating into nearly 1000 times longer fatigue life compared to Ti6Al4V necks. The neck-stem distraction force showed large statistical variation and was similar for both neck materials. Overall, the results suggest a superiority of CoCrMo over Ti6Al4V as neck material with regard to mechanical behavior. However, the corrosion behavior was not appropriately assessed and necessitates additional investigations.

The Proximal Modular Neck in THA: A Bridge Too Far: Affirms

Modular necks are a relatively new innovation in total hip arthroplasty (THA), with several companies now offering modular neck options. The proposed advantages of reduced impingement, reduced dislocation rate, and better reconstitution of leg length and offset are compelling. However, few reports in the literature address the outcomes of these devices, and those that are published at best demonstrate equivalence to conventional THA. There are numerous disadvantages to this new technology. Neck dissociation has been reported with a specific design of the modular taper. Numerous case reports exist of the fracture of titanium modular femoral necks, with 1 large series of 5000 cases reporting a fracture rate of 1.4%. Fractures occurred more frequently in heavy men (>100 kg), with the preponderance of fractures occurring around the 2-year mark. Retrieval analysis demonstrates failure of the titanium components at the Morse taper junction of the neck and femoral stem at the point of maximal tension, likely related to notch sensitivity. The additional interface of modular necks in the effective joint space has the potential to generate significant metal ions through a pitting corrosion process. Evidence exists of highly elevated serum cobalt and chromium ions in a modular junction used in large-head THA supporting these concerns. The use of particular neck geometries, such as long retroverted necks, may adversely affect the local biomechanical forces on the femoral component. The proposed mechanism is an increased lever arm leading to increased torque on stair climbing or rising from a chair. Finally, modular necks add significant costs to the implant and the health care system. On balance, based on the literature, the proximal modular neck in THA is a bridge too far.

Early Failure of a Modular Femoral Neck Total Hip Arthroplasty Component

The PROFEMUR Z modular total hip arthroplasty component (Wright Medical Technology, Arlington, Tennessee) is a primary total hip replacement system that offers surgeons the ability to alter the length and version of the femoral neck after the femoral stem has been implanted. The modularity is achieved through taper interfaces at the distal and proximal ends of the femoral neck. The proximal femoral neck taper engages with the femoral head, and the distal taper engages with the femoral stem. In this report, we present the case of a patient who twice underwent total hip arthroplasty revision surgery. The first revision was due to a fractured ceramic femoral head. The second revision was due to a complete fracture of the modular femoral neck. This report will focus on the second revision, and, specifically, the failure of the modular femoral neck at the junction of the neck to the femoral stem. The patient was informed that data concerning the case would be submitted for publication, and he consented. A sixty-two-year-old man (height, 181 cm; weight, 84 kg; body mass index, 25.6 kg/m2) presented with severe primary osteoarthritis of the left hip. He underwent uneventful primary total hip replacement surgery in November 2006. The components implanted were a 58-mm Lineage cup fixed with two screws; a size-5 PROFEMUR Z modular stem with a modular, long, 8° retroverted neck; a 32-mm ceramic femoral head with a +3.5-mm offset; and a ceramic Transcend liner (Wright Medical Technology). The patient recovered well with no postoperative complications. In February 2007, the patient presented to the emergency department with a painful left hip. Radiographs revealed superior migration of the femoral head, and a fracture of the ceramic head was suspected. The patient was hospitalized, and revision total hip arthroplasty was performed. During the procedure, the head was found …

Fracture of a Modular Femoral Neck After Total Hip Arthroplasty

The use of modularity in femoral stem designs for total hip arthroplasty has increased substantially over the past several years. The theoretical advantages of this design include the optimization of femoral anteversion, limb length, and offset of the femoral component. We report on a previously unreported fracture of a modular femoral neck device. The patient was informed that data concerning the case would be submitted for publication, and he consented. A forty-nine-year-old man underwent a primary total hip arthroplasty of the left hip, in June 2005, because of degenerative osteoarthritis and received a size-4 PROFEMUR Z femoral stem (Wright Medical Technology, Arlington, Tennessee) and a 64-mm CONSERVE acetabular component (Wright Medical Technology). The patient was 6 ft 6 in (198 cm) tall and weighed 340 lb (154.2 kg). An anterolateral surgical approach was utilized, and the bearing surface chosen was metal on metal. This proximal femoral cementless component is a dual-tapered rectangular stem that has a modular neck. The modular neck has an oval taper distally that is inserted into the femoral stem at a fixed angle. This allows the surgeon to independently adjust the offset and length as it is available in six different neck geometries and two lengths. Five different head options, ranging from –3.5 mm to +10.5 mm, are also available with this design. The head and neck are connected by means of a standard 12/14 Morse taper. Both the femoral stem and the modular neck are manufactured from a titanium alloy (Ti-6Al-4V). The patient had a 56-mm head with a –3.5-mm neck length. The neck geometry was a long varus anteverted neck (AR/VV2). The patient was otherwise healthy. The postoperative course was uneventful, and he was pain-free within three months after the procedure. In January 2009 (four years postoperatively), the patient slipped on ice and fell …

A modular femoral neck and head system works well in cementless total hip replacement for patients with developmental dysplasia of the hip

We compared a modular neck system with a non-modular system in a cementless anatomical total hip replacement (THR). Each group consisted of 74 hips with developmental hip dysplasia. Both groups had the same cementless acetabular component and the same articulation, which consisted of a conventional polyethylene liner and a 28 mm alumina head. The mean follow-up was 14.5 years (13 to 15), at which point there were significant differences in the mean total Harris hip score (modular/non-modular: 98.6 (64 to 100)/93.8 (68 to 100)), the mean range of abduction (32 degrees (15 degrees to 40 degrees )/28 (0 degrees to 40 degrees )), use of a 10 degrees elevated liner (31%/100%), the incidence of osteolysis (27%/79.7%) and the incidence of equal leg lengths (> or = 6 mm, 92%/61%). There was no disassociation or fracture of the modular neck. The modular system reduces the need for an elevated liner, thereby reducing the incidence of osteolysis. It gives a better range of movement and allows the surgeon to make an accurate adjustment of leg length.