Early aseptic loosening of a porous tantalum knee prosthesis

Porous tantalum represents a relatively new solution for primary and revision total knee arthroplasty, offering several unmatched properties. Tantalum is a transition metal, with excellent biocompatibility and bioactivity due to its intrinsic physical and structural characteristics. A widespread clinical use of porous tantalum tibial components for primary total knee arthroplasty has been partly hindered by the difficulty in removing this type of implant after bone in growth, often leading to a significant bone defect. On the contrary, in the case here reported, removal of the trabecular metal tibial component was unexpectedly easy at a 7-month follow-up due to the absence of bone ingrowth but with a complete preservation of the tibial plate bone stock. Causes for the lack of bone ingrowth are discussed.

[Mid-term results of 360-degree lumbar spondylodesis with the use of a tantalum implant for disc replacement]

PURPOSE OF THE STUDY

The study presents the mid-term results in patients treated with circumferential, i.e., 360-degreee, fusion of the lumbar spine carried out by posterolateral instrumented spondylodesis and anterior intersomatic fusion using a tantalum implant for replacement of an intervertebral disc. The aim of the study was to verify tantalum implant quality, to evaluate segment fusion and to assess the outcome of this method by patients' subjective findings.

MATERIAL AND METHODS

The prospective non-randomised study included the implantation of 47 tantalum cages in 40 patients by the technique of anterior lumbar interbody fusion (ALIF) and posterolateral spondylodesis. Only patients followed up longer than for one year were included in this evaluation. The patient group comprised 16 men and 24 women, with an average age of 47.9 years. The patients indicated for this procedure had mono- or bisegmental lumbar disc degeneration with advanced chan- ges of articular facets. The procedure involved posterior transpedicular screw fixation with decompression, if spinal stenosis existed, and reposition of the segment, if spondylolisthesis was present, and posterior spondylodesis by the open book method. No autogenous bone grafts were used because of the risk of donor-site pain and because one of the aims of the study was to test tantalum cage properties. Subsequently, ALIF and disc replacement with a tantalum cage were carried out after cage insertion, the anterior borders of the upper and lower adjacent vertebral bodies were adjusted so that the lamellar bone should overlap the cage and thus provide continual bridging for the segment, with an emphasis being on joining the lamellae with preserving their blood supply from the respective vertebral bodies. RESULTS Implant subsidence in a rotation/flexion fashion, i.e. ventrally into the upper endplate of the distal vertebra and dorsally into the lower endplate of the proximal vertebra, was observed in two cases; subsidence in a vertical fashion, i.e., symmetrically into the lower endplate of the upper vertebra was found in one patient. Neither vertical mode of subsidence into the upper endplate of the lower vertebra only, nor rotation/extension type of subsidence was recorded.No frontal/rotational mode of subsidence was found either. No osteolytic lesion between the implant and adjacent bone was diagnosed. No migration of an implant sideways or in a ventral/dorsal direction was detected. Anterior bridging fusion was observed in 32 cages. No fusion dorsal to or lateral to the cage was seen. Evaluation of bone ingrowth into the cage was not possible due to a high X-ray contrast effect of the material. High-quality bridging posterolateral spondylodesis was diagnosed in 33 cases. Subjective evaluation by the patients was based on a visual analogue scale (VAS) and an Oswestry Disability Index (ODI) questionnaire. For the whole group, the average VAS value for back pain dropped from 58.3 points before surgery to 18.1 points at one year post-operatively; there were no differences between the genders. The VAS value for leg pain decreased from 54.1 pre-operatively to 9.4 at one year after surgery. Also, the results of ODI assessment were similar in both genders, with the average value for the whole group having decreased from 53.5 % pre-operatively to 29.0 % at one year post-operatively.

DISCUSSION

By using the mechanical properties of a tantalum implant, i.e., its high strength and flexibility, the structure almost identical to cancellous bone and its high stability following implantation, we avoided the necessity of harvesting autogenous bone grafts from the iliac crest. Instead, we introduced the method of bridging a stable and strong implant with lamellar bone, while preserving its blood supply from the adjacent vertebral bodies. Our results showed that this approach resulted in implant subsidence in 1.8 % of cases only.We achieved good-quality fusion by bridging the whole segment in 68 %, and diagnosed good posterolateral fusion in 71 % of the cases. All patients showed good spondylodesis, which was either ante- rior, posterior or bilateral.

CONCLUSIONS

Avery stable fixation of the lumbar spinal segment can be achieved by using posterolateral fusion and ALIF.With this approach, ALIF is augmented with a porous tantalum cage, and the use of autogenous bone grafts, derived from the adjacent anterior vertebral borders and placed before the cage, results in high-quality anterior bridging spondylodesis in a lar- ge proportion of cases. The subjective evaluation by the patients is in agreement with the stability and fusion achieved.

Clinical and radiological evaluation of modular trabecular metal acetabular cups. Short-term results in 64 hips

Bone ingrowth and long-term survival of cementless acetabular implants, both in primary and revision hip arthroplasty, are determined by initial implant stability and by the osteoconductive properties of the metal shell. The outcome of a trabecular metal tantalum modular uncemented cup was evaluated in 64 hips in 62 patients. Eleven cups were used in complex primary total hip replacements, 53 cups were implanted in revision hip arthroplasties. The follow-up ranged from 12 months to 48 months. Clinically the Charnley modified Merle-d'Aubigné Postel score improved from 9 to 16 in the primary arthroplasty group and from 10 to16 in the revision group. Serial radiographs demonstrated excellent stability and bone apposition; in the revision cases, graft incorporation was noted in all but one cup. The number of periacetabular gaps detected on initial postoperative radiographs in the revision cases decreased from 15 to 4 and none of the remainder deteriorated with time. Complications included 2 haematomas, 1 dislocation and 1 cup failure in a Paprosky IIIb defect because of cup undersizing. The early results with the trabecular metal modular cementless cup appear promising in both complex primary and revision hip arthroplasty, even in the presence of considerable bone loss that requires additional bone grafting.

Mitral annular hinge motion contribution to changes in mitral septal-lateral dimension and annular area

OBJECTIVE

The mitral annulus is a dynamic, saddle-shaped structure consisting of fibrous and muscular regions. Normal physiologic mechanisms of annular motion are incompletely understood, and more complete characterization is needed to provide rational basis for annuloplasty ring design and to enhance clinical outcomes.

METHODS

Seventeen sheep had radiopaque markers implanted; 16 around the annulus and 2 on middle anterior and posterior leaflet edges. Four-dimensional marker coordinates were acquired with biplanar videofluoroscopy at 60 Hz. Hinge angle was quantified between fibrous and muscular annular planes, with 0 degrees defined at end diastole, to characterize its contribution to alterations in mitral septal-lateral dimension and 2-dimensional total annular area throughout the cardiac cycle.

RESULTS

During isovolumic contraction (pre-ejection), hinge angle abruptly increased, reaching maximum (steepest saddle shape, change 18 degrees +/- 13 degrees ) at peak left ventricular pressure. During ejection, hinge angle did not change; it then decreased during early filling (change 2 degrees +/- 2 degrees ). Septal-lateral dimension and total area paralleled hinge angle dynamics and leaflet distance (anterior to posterior marker). Pre-ejection septal-lateral reduction was 13% +/- 7% (3.3 +/- 1.5 mm) from 9% muscular dimension fall and 18 degrees +/- 13 degrees hinge angle increase.

CONCLUSIONS

Pre-ejection increase in hinge angle contributes substantially to septal-lateral and total area reduction, facilitating leaflet coaptation. Semirigid annuloplasty rings or partial bands may preserve hinge motion, but possible recurrent annular dilatation could result in recurrent mitral regurgitation. Long-term clinical studies are required to determine who might benefit most from preserving intrinsic hinge motion without compromising repair durability.

Effect of alendronate on bone ingrowth into porous tantalum and carbon fiber interbody devicesAn experimental study on spinal fusion in pigs

Recent studies have reported that bisphosphonates reduce the resorption of grafted bone and inhibit bone resorption at a bone-implant interface. However, it is not known whether bisphosphonates affect bone ingrowth into porous biomaterial or spine fusion interbody devices with an autograft. In this study, 18 pigs (9 in each group) underwent anterior intervertebral lumbar arthrodeses at L2-3, L4-5 and L6-7. Each level was randomly allocated to one of the 3 implants: a solid piece of porous tantalum (Hedrocel), a porous tantalum ring or a carbon fiber cage both packed with an autograft. Alendronate was given orally to one of the groups. The radiographic and histological findings in the two groups 3 months after operation were similar in these devices. Histological examination showed that the original graft was entirely replaced by new trabecular bone in both groups. On histomorphometric analysis, the bone volume fraction, both inside the central hole of porous tantalum ring and in the porous tantalum, was larger in the pigs given alendronate than in the controls, but the fraction inside and around the central hole of the carbon fiber cage was not affected by this treatment. Short-term alendronate treatment, in a relatively low dose, does not impair the formation of new bone, but increases bone ingrowth into the central hole of the porous tantalum ring and the pores of the porous tantalum in this porcine model. This may be an effective way to enhance early biologic fixation of porous intervertebral implants.

Insertion of tantalum beads in RSA of the hipVariations in incidence of extra-osseous beads with insertion site

Radiostereometric analysis (RSA) is a technique that can be used to measure the in-vivo micro-motion of the components of hip arthroplasty. It requires the insertion of tantalum beads into the bone permitting analysis of the radiographs. Extra-osseous beads reduce the usable bead pattern and previous studies have reported their incidence in the proximal femur as between 11% and 13% of all inserted beads. We reviewed the relative incidence of extra-osseous beads by examining 1038 radiographs of 97 patients who were part of an ongoing RSA hip study. Extra-osseous beads were seen in 44% of our patients with most having a single extra-osseous bead. The relative incidence of extra-osseous beads was 2% and 6% in the femur and pelvis, respectively. We observed a reduction in the incidence of the femoral beads with time, but not of the pelvis, which suggests that experience in the insertion technique improves the insertion rates at least of the femur. Our findings indicate that the incidence of extra-osseous beads is lower than previously reported. However, care should be taken in the design of studies to ensure that an adequate number of beads are placed in locations which are both surgically achievable and technically useful.

Clinical experience with porous tantalum cervical interbody implants in a prospective randomized controlled trial

A prospective randomized study was undertaken to evaluate the radiological appearance and clinical effectiveness of two porous tantalum (Hedrocel) implants in achieving a stable cervical interbody fusion. A prerandomization protocol was used to allocate patients to the three arms of the study: a ring implant containing autologous cancellous bone graft, a solid block implant or autologous tricortical iliac crest bone graft. Patients were followed for 2 years with plain radiological studies, SF-36, and Neck Disability Index questionnaires and neurological assessment. Early in the study the postoperative radiographs of four patients receiving Hedrocel implants showed inferior end-plate lucency raising concerns about delayed or non-fusion. Recruitment to the study was halted by the investigators to allow longer-term follow-up of the implanted patients when only 24 patients had been recruited to the study. Although fusion was subsequently noted in all patients at 12 months there was no further enrolment to the study. At 2 years the radiological and clinical outcomes of the three groups appeared comparable, but the study numbers were too small for any statistical analysis. This study highlights the difficulties that can arise when clinical caution takes precedence over objective measures of clinical progress during a study. In the absence of an independent safety monitoring committee, the investigators were under an ethical obligation to suspend recruitment to this study, until it was clear that the radiological features were not associated with poor clinical outcomes. The use of safety monitoring committees and the clarification of stopping criteria in relation to outcome measures should be considered in open randomized trials of spinal surgical techniques and implants.

Demonstration of a cavity coupler based on a resonant waveguide grating

Thermal noise in multilayer optical coatings may not only limit the sensitivity of future gravitational wave detectors in their most sensitive frequency band but is also a major impediment for experiments that aim to reach the standard quantum limit or to cool mechanical systems to their quantum ground state. Here, we present the experimental realization and characterization of a cavity coupler, which is based on a surface relief guided ode resonant grating. Since the required thickness of the dielectric coating is dramatically decreased compared to conventional mirrors, it is expected to provide low mechanical loss and, thus, low thermal noise. The cavity coupler was incorporated into a Fabry-Perot resonator together with a conventional high quality mirror. The finesse of this cavity was measured to be F = 657, which corresponds to a coupler reflectivity of R = 99.08 %.

[Osteointegration of porous tantalum stems implanted in avascular necrosis of the hip]

Efficacy of osteointegration of tantalum porous systems has been demonstrated through animal experimentation. However, there is a lack of studies that evaluate osteointegration of implants retrieved after a period of implantation in humans. For this study, eight rod implants used for the treatment of avascular necrosis of the femoral head were retrieved following collapse of the femoral head and conversion to total hip arthroplasty. The time of implantation ranged between six weeks and twenty three months. Observation during this study has confirmed effectiveness of osseointegration within this period of time. New bone was observed around and within the porous system of the on rod devices at retrieval date. Bone in growth however, proved to be of a slower and less intense degree than that resulting within animal species during first months after implantation. Nevertheless, the results obtained in the quantitative evaluation of this process proved to be similar to those results achieved by other authors in previous experimental studies.

Primary human osteoblasts grow into porous tantalum and maintain an osteoblastic phenotype

Porous tantalum (Ta) has found application in orthopedics, although the interaction of human osteoblasts (HOB) with this material has not been reported. The aim of this study was to investigate the interaction of primary HOB with porous tantalum, using 5-mm thick discs of porous tantalum. Comparison was made with discs of solid tantalum and tissue culture plastic. Confocal microscopy was used to investigate the attachment and growth of cells on porous Ta, and showed that HOB attached successfully to the metal "trabeculae," underwent extensive cell division, and penetrated into the Ta pores. The maturation of HOB on porous Ta was determined in terms of cell expression of the osteoblast phenotypic markers, STRO-1, and alkaline phosphatase. Despite some donor-dependent variation in STRO-1/AlkPhos expression, growth of cells grown on porous Ta either promoted, or did not impede, the maturation of HOB. In addition, the expression of key osteoblastic genes was investigated after 14 days of culture. The relative levels of mRNA encoding osteocalcin, osteopontin and receptor activator of NFkappaB ligand (RANKL) was not different between porous or solid Ta or plastic, although these genes were expressed differently by cells of different donors. However, bone sialoprotein and type I collagen mRNA species showed a decreased expression on porous Ta compared with expression on plastic. No substrate-dependent differences were seen in the extent of in vitro mineralization by HOB. These results indicate that porous Ta is a good substrate for the attachment, growth, and differentiated function of HOB.

The use of a tantalum-based Augmentation Patella in patients with a previous patellectomy

Patients with previous patellectomies for anterior knee pain syndrome, can remain symptomatic and develop osteoarthrosis or instability. We report our experience of the use of a novel implant to substitute for the absent native patella. Seven patients, with previous patellectomies, were treated with the Augmentation Patella (Zimmer, Allendale, USA). This implant was sutured to the patellar tendon, as part of a patello-femoral joint replacement (four cases) or total knee replacement (three cases). In three patients, the implant loosened and failed within 15 months. Two patients remained symptomatic despite solid fixation. One patient developed wound complications due to the bulk of the implant, and the procedure was abandoned in one patient as wound closure was not possible. The results of this implant in our patients with previous patellectomies have been disappointing. Previous studies where this implant has been used, have also shown high loosening and failure rates. We do not recommend its use to substitute for the absent patella.

The use of tantalum porous metal implants for Paprosky 3A and 3B defects

Complex acetabular defects are difficult to reconstruct. For severe pelvic defects, tantalum metal acetabular implants may provide a viable solution over traditional implants. This short-term follow-up reviews 43 acetabular revisions treated with tantalum acetabular implants. These revisions included 33 Paprosky type 3A defects, involving 30% to 50% of host acetabulum loss, and 10 type 3B defects, having similar or greater bone loss with a pelvic discontinuity. Tantulum acetabular modular augments were used in 26 cases to support the shell. At a mean of 2.8 years' follow-up, 42 components were stable, and 1 failed because of septic loosening. The overall success rate was 98%. One revision was performed because of loosening secondary to sepsis; none were performed for aseptic loosening. Implants made from highly porous tantalum metal provide a surface that is highly conducive to bone ingrowth. Combined with the ability to use modular augments for added support and stability, this technology may change the way major defects are reconstructed.

Porous tantalum in reconstructive surgery of the knee: a review

Porous tantalum represents an alternative metal for primary and revision total knee arthroplasty (TKA) with several unique properties. Tantalum is a transition metal, which in its bulk form has shown excellent biocompatibility and is safe to use in vivo as evidenced by its current application in pacemaker electrodes, cranioplasty plates, and as radiopaque markers. Current designs for orthopedic implants maintain a high volumetric porosity (70%-80%), low modulus of elasticity (3 MPa), and high frictional characteristics, making this metal conducive to biologic fixation. The low modulus of elasticity of such components allows for more physiologic load transfer and relative preservation of bone stock. Its more bioactive nature and ingrowth properties have led to its use in primary as well as revision knee components with good early clinical results reported. In revision arthroplasty, it has been used as a structural bone graft substitute. Formation of a bone-like apatite coating in vivo affords strong fibrous ingrowth properties and allows for substantial soft-tissue attachment with the potential for use in cases such as mega-prostheses and patella salvage. Although porous tantalum is in its early stages of evolution, the initial clinical data and basic science studies support its use as an alternative to traditional orthopedic implant materials.

Comparison between X-ray photon and secondary electron damage to DNA in vacuum

Both monolayer and thick (20 microm) films of dry pGEM-3Zf(-) plasmid DNA deposited on tantalum foil were exposed to Al Kalpha X-rays (1.5 keV) for various times in an ultrahigh vacuum chamber. For monolayer DNA, the damage was induced mainly by low energy secondary electrons (SEs) emitted from the tantalum. For the thick films, DNA damage was induced chiefly by X-ray photons. Different forms of plasmid DNA were separated and quantified by agarose gel electrophoresis. The exposure curves for the formation of nicked circular (single strand break, SSB), linear (double strand break, DSB), and interduplex cross-link forms 1 and 2 were obtained for both monolayer and thick films of DNA, respectively. The lower limits of G values for SSB and DSB induced by SEs were derived to be 86 +/- 2 and 8 +/- 2 nmol J(-1), respectively. These values are 1.5 and 1.6 times larger than those obtained with 1.5 keV photons. The projected X-ray energy dependence of the low energy electron (LEE) enhancement factor for the SSB and DSB in monolayer DNA is also discussed. This new method of investigation of the SE-induced damage to large biomolecules allows direct comparison of the yield of products induced by high energy photons and LEEs under identical experimental conditions.

Evolution of tibial fixation in total knee arthroplasty

Cementless total knee arthroplasty (TKA) implants were designed as an alternative to cemented implants. They were touted to provide long-term fixation without the fear of cement debris particle generation and cement degradation resulting in late prosthetic loosening and failure. They were envisioned as a superior solution for TKA in younger patients. However, critical studies revealed a unique set of complications, which included poor fixation as evidenced by frequent occurrence of radiolucent lines, aseptic loosening, osteolysis, and patellar polyethylene dissociation from metal-backed cementless patellar components. At the same time, cemented prostheses continue to yield excellent results. To address some of the issues with cementless implants, porous metal devices have been produced. Although in vitro and early in vivo clinical studies show promising results, these devices must be measured against cemented fixation, which continues to be the "gold standard" in TKA.

Direct tendon attachment and healing to porous tantalum: an experimental animal study

BACKGROUND

The ability to directly attach soft-tissue to metal would have broad clinical application. Previous attempts to obtain normal tendon-to-bone attachment strength have been unsuccessful. In the present study, we hypothesized that when the initial interface mechanical environment is carefully controlled, a highly porous form of tantalum metal would allow the ingrowth of tendon tissue with clinically relevant tendon-to-implant fixation strength approaching that of an intact tendon-to-bone insertion.

METHODS

Supraspinatus tendons from forty skeletally mature dogs were reattached to the greater tuberosity between two custom-designed porous tantalum washers. Clinical function as judged on the basis of gait analysis, reattachment fixation strength and stiffness, and tendon function as seen through muscle volume were evaluated preoperatively, immediately postoperatively, and at three, six, and twelve weeks after surgery. Qualitative and quantitative histomorphologic evaluation was performed at three, six, and twelve weeks after surgery.

RESULTS

Gait analysis with use of force-plate measurements demonstrated return to a normal gait pattern by three weeks after surgery. Tendon-implant strength as a percentage of normal, contralateral controls increased significantly, from 39% at the time of surgery to 67% at three weeks, 99% at six weeks, and 140% at twelve weeks (p < 0.0014). The stiffness of the construct also increased and approached that of normal tendon, measuring 47% at the time of surgery, 62% at three weeks, 94% at six weeks, and 130% at twelve weeks (p < 0.0299). Supraspinatus muscle volume initially decreased by 33% but recovered to 92% of normal by twelve weeks (p < 0.01). Histomorphologic evaluation showed Sharpey-like fibers inserting onto the surface of the porous tantalum. Quantitative histomorphometric analysis revealed a time-dependent increase in the density of the collagen tissue filling the metal voids below the implant surface of first the bottom washer and then the top washer.

CONCLUSIONS

Robust biologic ingrowth of tendon into a porous tantalum implant surface can be achieved under conditions of secure initial mechanical fixation. The strength and stiffness of the tendon-implant construct reached normal levels by six to twelve weeks in this animal model.

Accurate Detection of Stent-Graft Migration in a Pulsatile Aortic Model Using Roentgen Stereophotogrammetric Analysis

PURPOSE

To evaluate the feasibility and accuracy of Roentgen stereophotogrammetric analysis (RSA) versus computed tomography (CT) for detecting stent-graft migration in an in vitro pulsatile circulation model and to study the feasibility of a nitinol endovascular clip (NEC) as an aortic wall reference marker for RSA.

METHODS

An aortic model with stent-graft was constructed and connected to an artificial circulation with a physiological flow and pressure profile. Tantalum markers and NECs were used as aortic reference markers for RSA analysis. Stent-graft migrations were measured during pulsatile circulation with RSA and CT. CT images acquired with 64 x 0.5-mm beam collimation were analyzed with Vitrea postprocessing software using a standard clinical protocol and central lumen line reconstruction. RSA in the model with the circulation switched off was used as the reference standard to determine stent-graft migration. The measurement errors of RSA and CT were determined during pulsatile circulation.

RESULTS

The mean measurement error +/- standard deviation (maximum) of RSA during pulsatile circulation using the tantalum markers was -0.5+/-0.16 (0.7) mm. Using the NEC, the mean (maximum) measurement error was -0.4+/-0.25 (1.1) mm. The mean (maximum) measurement error of CT was -1.1+/-1.17 (2.8) mm.

CONCLUSION

RSA is an accurate and feasible tool to measure stent-graft migration in a pulsatile environment. Migration measurement with RSA was more accurate than CT in this experimental setup. The nitinol clip tested in this study is potentially feasible as an aortic reference marker in patients after endovascular repair.

Porous tantalum implant in early osteonecrosis of the hip: preliminary report on operative, survival, and outcomes results

Porous tantalum implants are used in early osteonecrosis of the hip. Device evaluation included surgical time, blood loss, hospitalization, patient-controlled analgesia use, transfusions, implant survival, and outcomes. Mean blood loss was 70 mL. Mean operative time was 36 minutes. Average hospitalization was less than 1 day. No patient required patient-controlled analgesia use or transfusions. Results were compared to a historical vascularized fibular graft population. All parameters were less than the fibular graft groups (P < .00001). All surviving implants (86%) resulted in good to excellent outcomes. Kaplan-Meier analysis at 39 months was 86% and 67% for the implant and fibular graft, respectively (P = .21). Early outcomes demonstrate that porous tantalum implants are a safe option for femoral head salvage. Continued follow-up is necessary to determine the long-term success.

Early migration pattern of the uncemented CLS stem in total hip arthroplasties

We performed this investigation to determine the possible migration starting immediately after surgery and the effect of different weightbearing regimens on the migration pattern of an uncemented hip stem (CLS). Stem migration was determined with radiostereometry analysis with baseline when the patients still were anesthetized. Subsequent examinations were done up to 1 year. Twenty-nine patients (mean age, 55 years; range, 26-63 years) were randomized to either unrestricted weightbearing combined with intensive physiotherapy from the first day after surgery or to partial weightbearing and a conservative training regimen for the first 3 months after surgery. At 1 week, subsidence was -0.03 mm in the unrestricted weightbearing group and 0.01 mm in the partial weightbearing group. At 1 year, subsidence was 1.01 mm in the unrestricted weightbearing group and 0.51 mm in the partial weightbearing group. One patient in the unrestricted weightbearing group had revision surgery because of aseptic loosening at 1.5 years after surgery. The CLS stem did not have any migration from the end the surgery until 1 week, but there was small migration from 1 week to 3 months after which the stem remained stable. The degree of early weightbearing did not affect the migration pattern.