Implant stability, histology, RSA and wear--more critical questions are needed. A view point

Low Preoperative BMD Is Related to High Migration of Tibia Components in Uncemented TKA-92 Patients in a Combined DEXA and RSA Study With 2-Year Follow-Up

BACKGROUND

The fixation of uncemented tibia components in total knee arthroplasty may rely on the bone quality of the tibia; however, no previous studies have shown convincing objective proof of this. Component migration is relevant as it has been shown to predict aseptic loosening.

METHODS

We performed 2-year follow-up of 92 patients who underwent total knee arthroplasty surgery with an uncemented tibia component. Bone mineral density (BMD; g/cm²) of the tibia host bone was measured preoperatively using dual energy X-ray absorptiometry. The proximal tibia was divided into 2 regions of interest (ROI) in the part of the tibia bone where the components were implanted. Radiostereometric analysis was performed postoperatively and after 3, 6, 12, and 24 months. The primary outcome was maximum total point motion (MTPM; mm). Regression analysis was performed to evaluate the relation between preoperative BMD and MTPM.

RESULTS

We found low preoperative BMD in ROI1 to be significantly related to high MTPM at all follow-ups: after 3 months (R² = 20%, P_BMD = 0.017), 6 months (R² = 29%, P_BMD = 0.003), 12 months (R² = 33%, P_BMD = 0.001), and 24 months (R² = 27%, P_BMD = 0.001). We also found a significant relation for low BMD in ROI2 and high MTPM: 3 months (R² = 19%, P_BMD = 0.042), 6 months (R² = 28%, P_BMD = 0.04), 12 months (R² = 32%, P_BMD = 0.004), and 24 months (R² = 24%, P_BMD = 0.005).

CONCLUSION

Low preoperative BMD in the tibia is related to high MTPM. Thus, high migration of uncemented tibia components is to be expected in patients with poor bone quality.

Osteolysis in Total Ankle Replacement: How Does It Work?

Aseptic loosening of implants remains the most common reason for revision surgery for hip, knee, or ankle prostheses. Although a great scientific effort has been made to explain the underlying mechanisms it remains poorly understood, complex, and multifactorial. Many factors, including age, body weight, activity lesions, implant design, fixation methods, material proprieties, immunologic responses, and biomechanical adaptations to total ankle replacement all contribute to the development of periprosthetic osteolysis.

Cementless Porous Tantalum Monoblock Tibia vs Cemented Modular Tibia in Primary Total Knee Arthroplasty: A Meta-Analysis

BACKGROUND

With the introduction of new fixation systems and designs, there has been a recent reemergence of interest in cementless fixation of the tibial component in total knee arthroplasty. However, little is known regarding the clinical features and survivorship of the cementless porous tantalum monoblock tibial component compared to the conventional cemented modular tibial component.

METHODS

We conducted a literature search of multiple databases for comparative studies published before June 2015 that investigated the outcomes of cementless porous tantalum monoblock tibia vs conventional cemented modular tibia. A pooled analysis was performed. The outcomes of interest were postoperative functional score, range of motion, Western Ontario and McMaster University Osteoarthritis Index, total complications, reoperation, radiolucent lines, loosening of the tibial component, and length of operation.

RESULTS

Six studies involving 977 patients were eligible for the meta-analysis. The use of a cementless porous tantalum monoblock tibial component may associate with a slightly higher functional score, fewer radiolucent lines, and shorter operation. No significant difference was seen in regard to the range of motion, Western Ontario and McMaster University Osteoarthritis Index, total complications, reoperation, and loosening of the component between the 2 groups.

CONCLUSION

However, due to variation among the included studies, the use of cementless porous tantalum monoblock tibia seems to achieve no substantial superiority over that of the conventional cemented modular tibia at 5-year follow-up. Data concerning the long-term prognosis of this novel implant should continue to be collected and analyzed.

Comparison of a novel porous titanium construct (Regenerex®) to a well proven porous coated tibial surface in cementless total knee arthroplasty - A prospective randomized RSA study with two-year follow-up

BACKGROUND

Regenerex is a novel porous titanium construct with a three-dimensional porous structure and biomechanical characteristics close to that of normal trabecular bone. The aim of this study was to compare this novel construct to a well-proven porous plasma sprayed tibial (PPS) implant after total knee arthroplasty.

METHODS

Sixty-one patients scheduled for an uncemented TKA were randomized to receive either a novel highly porous titanium construct Regenerex or the PPS tibial component. Radiostereometric analysis of the tibial components was performed postoperatively and at three, six, 12, and 24months with measurements of migration (segment motion and maximum total point motion (MTPM)).

RESULTS

Knee and function scores improved significantly from preoperatively to two-year follow-up. For both the Regenerex and the PPS the majority of migration appeared during the first three months and then stabilized. No statistically significant differences in MTPM were found in any follow-up between three and 24months. The Regenerex group had a lower migration rate between 12 and 24months compared with the PPS implants (p=0.03) but the PPS group had an initial significantly lower subsidence (p=0.04).

CONCLUSION

In conclusion the Regenerex implant could prove an effective scaffold material for coating of uncemented implants but did no better than the PPS component at 24months of follow-up. ClinicalTrials.gov identifier: NCT01936415.

Monoblock versus modular polyethylene insert in uncemented total knee arthroplasty

Background and purpose - Backside wear of the polyethylene insert in total knee arthroplasty (TKA) can produce clinically significant levels of polyethylene debris, which can lead to loosening of the tibial component. Loosening due to polyethylene debris could theoretically be reduced in tibial components of monoblock polyethylene design, as there is no backside wear. We investigated the effect of 2 different tibial component designs, monoblock and modular polyethylene, on migration of the tibial component in uncemented TKA. Patients and methods - In this randomized study, 53 patients (mean age 61 years), 32 in the monoblock group and 33 in the modular group, were followed for 2 years. Radiostereometric analysis (RSA) was done postoperatively after weight bearing and after 3, 6, 12, and 24 months. The primary endpoint of the study was comparison of the tibial component migration (expressed as maximum total point motion (MTPM)) of the 2 different implant designs. Results - We did not find any statistically significant difference in MTPM between the groups at 3 months (p = 0.2) or at 6 months (p = 0.1), but at 12 and 24 months of follow-up there was a significant difference in MTPM of 0.36 mm (p = 0.02) and 0.42 mm (p = 0.02) between groups, with the highest amount of migration (1.0 mm) in the modular group. The difference in continuous migration (MTPM from 12 and 24 months) between the groups was 0.096 mm (p = 0.5), and when comparing MTPM from 3-24 months, the difference between the groups was 0.23 mm (p = 0.07). Interpretation - In both study groups, we found the early migration pattern expected, with a relatively high initial amount of migration from operation to 3 months of follow-up, followed by stabilization of the implant with little migration thereafter. However, the modular implants had a statistically significantly higher degree of migration compared to the monoblock. We believe that the greater stiffness of the modular implants was the main reason for the difference in migration, but an initial creep in the polyethylene metal-back locking mechanism of the modular group could also be a possible explanation for the observed difference in migration between the 2 study groups.

Small and similar amounts of micromotion in an anatomical stem and a customized cementless femoral stem in regular-shaped femurs. A 5-year follow-up randomized RSA study

BACKGROUND AND PURPOSE

High primary stability is important for long-term survival of uncemented femoral stems. Different stem designs are currently in use. The ABG-I is a well-documented anatomical stem with a press-fit design. The Unique stem is designed for a tight customized fit to the cortical bone of the upper femur. This implant was initially developed for patients with abnormal anatomy, but the concept can also be used in patients with normal femoral anatomy. We present 5-year radiostereometric analysis (RSA) results from a randomized study comparing the ABG-I anatomical stem with the Unique femoral stem.

PATIENTS AND METHODS

100 hips with regular upper femur anatomy were randomized to either the ABG-I stem or the Unique femoral stem. RSA measurements were performed postoperatively and after 3, 6, 12, 24, and 60 months.

RESULTS

RSA measurements from 80 hips were available for analysis at the 5-year follow-up. Small amounts of movement were observed for both stems, with no statistically significant differences between the 2 types.

INTERPRETATION

No improvement in long-term stability was found from using a customized stem design. However, no patients with abnormal geometry of the upper femur were included in this study.

Progressive femoral cortical and cancellous bone density loss after uncemented tapered-design stem fixation

BACKGROUND

Aseptic implant loosening and periprosthetic bone loss are major problems after total hip arthroplasty (THA). We present an in vivo method of computed tomography (CT) assisted osteodensitometry after THA that differentiates between cortical and cancellous bone density (BD) and area around the femoral component.

METHOD

Cortical and cancellous periprosthetic femoral BD (mg CaHA/mL), area (mm(2)) and contact area between the prothesis and cortical bone were determined prospectively in 31 patients 10 days, 1 year, and 6 years after uncemented THA (mean age at implantation: 55 years) using CT-osteodensitometry.

RESULTS

6 years postoperatively, cancellous BD had decreased by as much as 41% and cortical BD by up to 27% at the metaphyseal portion of the femur; this decrease was progressive between the 1-year and 6-year examinations. Mild cortical hypertrophy was observed along the entire length of the diaphysis. No statistically significant changes in cortical BD were observed along the diaphysis of the stem.

INTERPRETATION

Periprosthetic CT-assisted osteodensitometry has the technical ability to discriminate between cortical and cancellous bone structures with respect to strain-adapted remodeling. Continuous loss of cortical and cancellous BD at the femoral metaphysis, a homeostatic cortical strain configuration, and mild cortical hypertrophy along the diaphysis suggest a diaphyseal fixation of the implanted stem. CT-assisted osteodensitometry has the potential to become an effective instrument for quality control in THA by means of in vivo determination of periprosthetic BD, which may be a causal factor in implant loosening after THA.

A trabecular metal tibial component in total knee replacement in patients younger than 60 years: a two-year radiostereophotogrammetric analysis

We compared the performance of uncemented trabecular metal tibial components in total knee replacement with that of cemented tibial components in patients younger than 60 years over two years using radiostereophotogrammetric analysis (RSA). A total of 22 consecutive patients (mean age 53 years, 33 to 59, 26 knees) received an uncemented NexGen trabecular metal cruciate-retaining monobloc tibial component and 19 (mean 53 years, 44 to 59, 21 knees) a cemented NexGen Option cruciate-retaining modular tibial component. All the trabecular metal components migrated during the initial three months and then stabilised. The exception was external rotation, which did not stabilise until 12 months. Unlike conventional metal-backed implants which displayed a tilting migration comprising subsidence and lift-off from the tibial tray, most of the trabecular metal components showed subsidence only, probably due to the elasticity of the implant. This pattern of subsidence is regarded as being beneficial for uncemented fixation.

Effect of femoral head size on polyethylene wear and synovitis after total hip arthroplasty: a sonographic and radiographic study of 39 patients

BACKGROUND AND PURPOSE

The role of synovitis and high fluid pressure in the loosening process after total hip arthroplasty has gained increasing attention. We investigated the correlation between head size, polyethylene wear, and capsular distention.

PATIENTS AND METHODS

We analyzed 39 unrevised, radiographically stable hips that had been operated with 28 or 32 mm femoral heads 10 years earlier because of osteoarthritis. We evaluated radiographic signs of loosening, linear and volumetric polyethylene wear, body mass index, activity level, and age. Sonographic examination was performed to measure capsular distance i.e. the distance between the prosthetic femoral neck and the anterior capsule.

RESULTS

Linear wear was 0.09 mm/year and 0.18 mm/year in the 28 mm and 32 mm groups, respectively (p < 0.001). The volumetric wear was 51 mm(3)/year and 136 mm(3)/year (p < 0.001) and the capsular distance was 13 mm and 17 mm, respectively (p < 0.001). There was a correlation between linear wear (r = 0.54), volumetric wear (r = 0.62), and capsular distance (p < 0.001).

INTERPRETATION

Wear was greater for the larger femoral head and was correlated to capsular distension.

Uncemented HA-coated implant is the optimum fixation for TKA in the young patient

Fixation of the tibial component in total knee arthroplasty in younger patients remains controversial. We evaluate the results of three different types of fixation of the Profix total knee arthroplasty in a randomized controlled trial of 97 consecutive knees (85 patients) with osteoarthrosis or inflammatory arthritis with 2-year followup of all patients. We randomized patients to three different types of fixation of the tibial component: cemented, uncemented (HA coated) with screws, or uncemented (HA coated) without screws. We performed clinical evaluations and radiostereometric analysis at 6 weeks, and 3, 6, 12 and 24 months postoperatively. The knees in the uncemented groups migrated more than those in the cemented group during the first 3 months, but at 2 years we observed no differences. The uncemented implants displayed all migration within the first 3 months. The cemented implants did not stabilize but had continuously increasing migration during the followup. Cementless implants without screws did not migrate more than implants with screws and displayed similar pattern of migration, indicating screws do not improve fixation. Uncemented fixation using hydroxyapatite-coated implants without screws seems to be the best solution for the younger patient.

LEVEL OF EVIDENCE

Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

Aseptic loosening, not only a question of wear: a review of different theories

Today, aseptic loosening is the most common cause of revision of major arthroplasties. Aseptic loosening accounts for more than two-thirds of hip revisions and almost one-half of knee revisions in Sweden. Several theories on the cause of aseptic loosening have been proposed. Most of these theories, however, are based on empiric observations, experimental animal models or anecdotal cases. In this review, we discuss the most common theories concerning aseptic loosening. It emerges from this review that aseptic loosening has a multifactorial etiology and cannot be explained by a single theory.

The stress-inducible displacement detected through RSA in non-migrating UKR

Roentgen stereophotogrammetric analysis (RSA) under stress conditions was used to investigate possible stress-inducible displacement of the tibial component of unicompartmental knee prostheses (UKR) in which the stability was previously assessed by radiographic evaluation and standard supine RSA examinations. Sixteen patients, implanted with Duracon UNI(R) prosthesis, were selected for this study. The RSA protocol included examinations in plain upright standing posture and during execution of stress-inducing tasks in weight-bearing stance. The first follow-up was performed at an average of 14 months, and the second one at 26 months. The results showed non-negligible stress-induced rotations of the prosthetic tibial component in all the patients in most of the stress tasks performed. Rotational stress tasks and squatting turned out to be the stress conditions in which induced displacement reached the most significant values (p<0.05). These micromotions occurred mainly around the transverse axis of the knee joint and in one examination around the sagittal axis. Stress-induced translations were negligible in all the examinations. Moreover, we focused our attention on two patients suffering from inexplicable pain, and we observed a significant difference in the inducible rotation around the x-axis between these patients and the remaining fourteen. Stress-inducible displacement is a common finding in knee prostheses, but we observed that in patients with inexplicable pain, these micromotions reached values greater than the median calculated on patients without any pain. This result suggests the introduction of the stress-inducible displacement as a new parameter to be taken into consideration when analyzing the outcome of patients treated by UKR.

Effect of a bisphosphonate, disodium pamidronate, on the quasi-static flexural properties of Palacos R acrylic bone cement

Aseptic loosening is a major complication of joint replacements and is thought to be associated with a heavy macrophage infiltrate in response to wear particles. Bisphosphonates are compounds known to inhibit osteoclastic activity and are used to reduce osteolysis in Paget's disease, osteoporosis, and metastatic bone disease. Oral bisphosphonates have also been used to decrease osteolysis and therefore prevent aseptic loosening of joint replacements. It has been suggested that bisphosphonates mixed in bone cement can reduce bone resorption in joint replacement surgery. This would be an excellent therapeutic option to prevent or control osteolysis. The present aim was to study the mechanical properties of a commercially available acrylic bone cement, Palacos R, mixed with the bisphosphonate pamidronate. The liquid monomer of Palacos R was mixed with liquid pamidronate. Two groups of bone-cement strips were produced, one with added pamidronate and one without. The flexural properties of the cement strips were examined. A significant reduction in both the bending modulus and bending strength of the specimens with added pamidronate was found. In conclusion, the use of liquid pamidronate mixed with the acrylic bone cement Palacos R in order to reduce osteolysis is not recommended because of its effect on the mechanical properties of Palacos R.

The effects of hydroxyapatite coating and bone allograft on fixation of loaded experimental primary and revision implants

We used our established experimental model of revision joint replacement to examine the roles of hydroxyapatite coating and bone graft in improving the fixation of revision implants. The revision protocol uses the Søballe micromotion device in a preliminary 8-week period of implant instability for the presence of particulate polyethylene. During this procedure, a sclerotic endosteal bone rim forms, and a dense fibrous membrane is engendered, having macrophages with ingested polyethylene and high levels of inflammatory cytokines. At the time of revision after 8 weeks, the cavity is revised with either a titanium alloy (Ti) or a hydroxyapatite (HA) 6.0 mm plasma-sprayed implant, in the presence or absence of allograft packed into the initial 0.75 mm peri-implant gap. The contralateral limb is subjected to primary surgery with the same implant configuration, and serves as control. 8 implants were included in each of the 8 treatment groups (total 64 implants in 32 dogs). The observation period was 4 weeks after revision. Outcome measures are based on histomorphometry and mechanical pushout properties. The revision setting was always inferior to its primary counterpart. Bone graft improved the revision fixation in all treatment groups, as also did the HA coating. The sole exception was revision-grafted HA implants, which reached the same fixation as primary Ti and HA grafted implants. The revision, which was less active in general, seems to need the dual stimulation of bone graft and HA implant surface, to obtain the same level of fixation associated with primary implants. Our findings suggest that the combination of HA implant and bone graft may be of benefit in the clinical revision implant setting.

Synergistic effect of particles and cyclic pressure on cytokine production in human monocyte/macrophages: proposed role in periprosthetic osteolysis

Macrophages, activated by particulate wear debris, are important in the process of osteolysis, which occurs during joint implant loosening. We previously found increased levels of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha in cultured macrophages subjected to cyclical pressure of 0.138 MPa, suggesting that cyclic pressure may be another relevant cause of macrophage activation. The current study first investigated the effects of a range of cyclic pressures on cultured macrophages, including an investigation of the time course of cytokine expression. At 0.138 MPa, supernatant levels of TNF-alpha were maximal at 12 h, whereas IL-6 and IL-1beta were maximal at 24 h. All four cyclic pressure levels tested (without particles) resulted in increased production of all three cytokines relative to control. These increases were most marked at 0.069 and 0.035 MPa, and the increase in cytokine production at 0.017 MPa was not statistically significant. Further studies demonstrated that conditioned media from cyclically pressurized macrophages stimulated bone resorption in a neonatal mouse calvarial assay system. There were increased levels of calcium released from calvaria cultured in conditioned media from pressurised monocytes, and an increase in tartate-resistant acid phosphatase-positive osteoclasts was observed microscopically. As particulate wear debris is important in implant loosening, ultra high molecular weight polyethylene particles were also added to the pressurized cell cultures. The experiments compared the effect of atmospheric pressure, cyclic pressure alone, particles alone, and particles and cyclic pressure combined. A combination of ultra high molecular weight polyethylene particles and cyclic pressure at 0.017 MPa resulted in a dramatic synergistic elevation of levels of all three cytokines compared with the levels found with either pressure or particles alone. We propose that monocyte/macrophage activation by cyclic pressure plays a major role in the osteolysis seen in aseptic loosening of implants. The synergistic effect observed between particles and pressure could accelerate implant loosening, and implies that reduction in either cyclic pressure (by improving implant fixation) or wear debris load would reduce osteolysis.

Total hip arthroplasty with a modified cementing technique using hydroxyapatite granules

Results of total hip arthroplasties with a modified cementing technique using hydroxyapatite were evaluated. Femoral and acetabular components were inserted with cement after hydroxyapatite granules (phi = 100-300 microm). The study group comprised 268 hips in 232 patients. The diagnosis was osteoarthritis in 197 patients. After a mean follow-up of 10.3 years, 5 patients died and 30 patients were lost to follow-up, leaving 218 hips (197 patients; mean age, 58.2 years) for evaluation. Three hips were revised because aseptic (1) and septic (2) loosening of acetabular components. Six other sockets were defined as radiologically loose, and no femoral component was loose. Osteolysis was identified in 2 femora and 0 acetabula. The overall loosening rate was 3.2% for acetabular components and 0% for femoral components. These results show that the loosening rate of cemented total hip arthroplasty components, especially the acetabulum, is reduced markedly with this modified cementing technique.

Hydroxyapatite granules interposed at bone-cement interface in total hip replacements: histological study of retrieved specimens

The effect of hydroxyapatite (HA) granules interposed between bone and polymethylmethacrylate (PMMA) bone cement in total hip replacement was histologically evaluated. The technique consisted of smearing 2-5 g of HA granules (straight phi = 100-300 microm) onto the bone surface just before cementing. Four specimens containing well-fixed bone-cement interface were retrieved at 1, 2, 6, and 10 years postoperatively and examined with back-scattered electron microscopy and light microscopy. The majority of HA granules were incorporated into remodeled trabeculae, and highly convoluted bone-cement interface was maintained up to 10 years. The presence of active remodeling in the adjacent bone was observed. There were no significant inflammatory or foreign body reactions against interposed HA granules. In one specimen retrieved from a patient with rheumatoid arthritis, bone formation around HA granules was limited after 1 year. These results have provided histological evidence for the significantly reduced incidence of radiolucent lines in total hip replacement with this cementing technique, reported elsewhere.

Analysis of two bone-prosthesis interfaces and membranes from non-cemented trapeziometacarpal prostheses

The non-cemented Ledoux trapeziometacarpal prosthesis has a high failure rate. In order to better understand the mechanism responsible for pain and loosening, we thoroughly analysed the membranes surrounding the prosthesis and the bone-prosthesis interface in two trapezia, each containing a Ledoux cup, which were resected after unsuccessful implantation. Serial sections, perpendicular to the longitudinal axis of the implanted cup, allowed histological examination of the interface and were used to quantify bone apposition. The tissues surrounding the prosthesis showed a foreign-body reaction to particles identified as titanium. The interface showed bony integration of the cup, mainly on the radial side and on the proximal part of the cup, with an appositional index of 28%. Our findings suggest that bony apposition might not be sufficient to ensure successful anchoring of the Ledoux cup in the trapezium in the presence of an intense foreign body reaction to titanium. Moreover, the presence of metal might be secondary to micromotion of the wings of the metallic part of the cup, induced by axial movement of the underlying polyethylene during pinch grip. The combination of polyethylene as an expander and titanium may need to be reviewed.

Hydroxyapatite-enhanced tibial prosthetic fixation

Sixty-two knees (60 patients) were randomized to four noncemented groups. In Groups 1, 3, and 4, the bone cuts were made with a cooled saw blade. In Group 1, 15 patients were operated on with the porous coated Osteonic 7000 tibial component. In Group 2, 15 patients were operated on with the same tibial component as in Group 1 but with the use of a standard saw blade. In Group 3, 16 patients were operated on with the hydroxyapatite-coated Osteonic tibial component, and in Group 4, 16 patients were operated on with the hydroxyapatite Duracon tibial component. All patients were followed up clinically and with roentgenstereometric analysis. There were no differences among the groups regarding clinical outcome. One knee was revised (Group 2) after 1 year because of loosening of the tibial component. The maximum migration at 1 year was 1.7 mm in Group 1, 1.9 mm in Group 2, 1.3 mm in Group 3, and 1 mm in Group 4. At the 2-year followup, the migrations were 1.8 mm, 1.5 mm, 1.4 mm, and 1 mm in Groups 1, 2, 3, and 4, respectively. The inducible displacement that occurred at 1 year was 0.6 mm in Group 1, 0.5 mm in Group 2, 0.4 mm in Group 3, and 0.4 mm in Group 4. The hydroxyapatite coating had a strong positive effect on the tibial component fixation. No prosthesis in the hydroxyapatite groups showed continuous migration.

Comparative micromotion of fully and proximally cemented femoral stems

This investigation studied the differences of in vitro micromotion between two stem designs. The two stem types investigated were a proximally cemented stem with distal press fit and a fully cemented stem. After initial micromotion testing to 2250 N in simulated single leg stance and stair climb, six of each stem type were loaded dynamically for 1 million cycles at 950 N at 1 Hz. Micromotion studies were repeated. The two stem types had similar micromotion. For the single leg stance, fully cemented implant motion averaged (+/- 95% confidence) 18 +/- 8 microns toggle, 41 +/- 5 microns axial, and 59 +/- 22 microns rotation. Proximally cemented implant motion averaged 20 +/- 6 microns toggle, 42 +/- 6 microns axial, and 31 +/- 15 microns rotation. For the simulated stair climb, fully cemented implant motion averaged 24 +/- 10 microns toggle, 45 +/- 8 microns axial, and 92 +/- 32 microns rotation. Proximally cemented implant motion averaged 19 +/- 10 microns toggle, 42 +/- 9 microns axial, and 87 +/- 53 microns rotation. For both loading conditions, there were no significant differences measurable between the two systems. After dynamic testing of the fully cemented implants, there were no significant changes in the micromotion of either the toggle or the rotation, but an average of 18 microns increase of axial motion was measured in the fully cemented stem. For the proximally cemented implants, there were no significant changes after dynamic testing. This differences was not considered clinically significant because roentgen stereophotogrammetric analysis studies have shown that more than 4 mm of migration is required before clinical symptoms manifest. The protocol developed in this study may help provide a screening process to determine the stability of femoral stem designs before these devices are used clinically.

Preliminary investigation of a novel controlled stiffness proximal femoral prosthesis

Previous studies have suggested that a controlled stiffness prosthesis is required to address the conflicting requirements of minimizing stress shielding and micromotion. The design for a controlled stiffness prosthesis is proposed and a preliminary analytical investigation performed to assess its predicted performance before fabrication of a prototype component. The novel prosthesis consisted of a cobalt-chrome core and a flexible composite outer layer. Varying the composite layer thickness allowed the prosthesis stiffness to be controlled. Three variants of the controlled stiffness prosthesis were critically assessed using the finite element method and their predicted performance compared with those of conventional prosthesis designs. The potential for stress shielding was assessed by examining the periosteal strain energy and the potential for migration assessed by examining the endosteal minimum principal cancellous bone stresses. Both the conventional and controlled stiffness implants performed poorly as press-fit prostheses. All the press-fit prostheses generated high cancellous bone stresses, suggesting that excessive migration of these implants would be likely. The controlled stiffness implants performed better than the conventional implants when bonded to the surrounding bone. Although the controlled stiffness implants did not eliminate stress shielding of the calcar, they produced higher strain energies than the conventional designs. The findings of this study are that osseointegrated controlled stiffness implants may perform better than current osseointegrated cementless prostheses and therefore it is worth while progressing to the next stage, of prototyping an implant.

Scandinavian multicenter porous coated anatomic total hip arthroplasty study. Clinical and radiographic results with 7- to 10-year follow-up evaluation

Four hundred ninety-four patients (539 hips) with a mean age of 50.1 (SD, 9.7) years entered a prospective, multicenter study of the Porous Coated Anatomic (Howmedica, Rutherford, NJ) total hip arthroplasty. The preoperative diagnoses were primary osteoarthrosis (297 hips), secondary osteoarthrosis to childhood diseases (88 hips), fracture (73 hips), inflammatory arthritis (26 hips), idiopathic avascular necrosis (28), and miscellaneous (27 hips). After a mean follow-up period of 6 years and 10 months, 71 hips had been revised. The mean Harris hip score increased from 43 (15.7) to 94 (7.4) at the last follow-up evaluation, without any deterioration with time. After 7 years, the combined survival rate for the cup and/or stem using revision as endpoint was 92.2%. Radiographic failure, defined as migration of either component more than 5 min and/or focal osteolysis, was registered in 72 stems and 96 cups. The combined clinical (revision) and radiographic 7-year survival rates were 61.1 (+/-5.2) and 59.7 (+/-5.3) for the stem and cup, respectively. Statistical analysis revealed that young age and poor fill rate influenced the rate of stem failure, whereas cup failure was difficult to predict. Four variables were associated with stem subsidence: loosening of beads, pedestal formation, sclerotic lines in Gruen zone 7, and acetabular granuloma. According to our findings, the 5- to 10-year complication rate with this implant is high. Therefore, continuous radiographic follow-up evaluation of these cases is strongly recommended, to enable revision before severe destruction of bone or catastrophic clinical failure has occurred.

Calcitonin gene-related peptide, substance P, and tyrosine hydroxylase-immunoreactive innervation of rat bone marrows: an immunohistochemical and ultrastructural investigation on possible efferent and afferent mechanisms

The presence of nerve fibers in bone marrow has been noted by various investigators, and recent developments in immunohistochemistry have enabled differential localization of the intramedullary nerve fibers. Much interest has been devoted to the efferent activities of the afferent fibers, which probably act on the target tissues by secreting a variety of neurotransmitters. The present study aimed to further characterize intramedullary substance P, calcitonin gene-related peptide, and tyrosine hydroxylase-immunoreactive nerve fibers of the rat lower limb by comparing those of the knee, ankle, and tarsal joints. The ultrastructural details of intramedullary calcitonin gene-related peptide-immunoreactive axons were also investigated to provide a morphological basis for their possible efferent actions. Intramedullary calcitonin gene-related peptide and substance P-immunoreactive fibers in the proximal tibia and the knee joint were found to be as reported earlier, but the marrow of the distal metaphysis was also noted to be richly innervated, and the tarsal joints displayed dense innervation at the subchondral regions that underlie the joint cartilage. The articular and intramedullary innervations that function for joint protection might participate in characteristic clinical features of joint damage secondary to the neuropathies. Ultrastructurally, the intramedullary calcitonin gene-related peptide-immunoreactive axons were minimally engulfed by the Schwann cell, and naked intramedullary calcitonin gene-related peptide-immunoreactive axons were noted along an extraordinarily long extension, suggesting much efferent activity.