Bone ingrowth into porous-coated tibial components implanted with autograft bone chips. Analysis of ten consecutively retrieved implants

Cementless Total Knee Arthroplasty: A Resurgence - Who, When, Where, and How?

BACKGROUND

Total knee arthroplasty (TKA) is one of the most common procedures in orthopaedics, but there is still debate over the optimal fixation method for long-term durability: cement versus cementless bone ingrowth. Recent improvements in implant materials and technology have offered the possibility of cementless TKA to change clinical practice with durable, stable biological fixation of the implants, improved operative efficiency, and optimal long-term results, particularly in younger and more active patients.

METHODS

This symposium evaluated the history of cementless TKA, the recent resurgence, and appropriate patient selection, as well as the historical and modern-generation outcomes of each implant (tibia, femur, and patella). Additionally, surgical technique pearls to assist in reliable, reproducible outcomes were detailed.

RESULTS

Historically, cemented fixation has been the gold standard for TKA. However, cementless fixation is increasing in prevalence in the United States and globally, with equivalent or improved results demonstrated in appropriately selected patients.

CONCLUSION

Cementless TKA provides durable biologic fixation and successful long-term results with improved operating room efficiency. Cementless TKA may be broadly utilized in appropriately selected patients, with intraoperative care taken to perform meticulous bone cuts to promote appropriate bony contact and biologic fixation.

A multimodal assessment of cementless tibial baseplate fixation using radiography, radiostereometric analysis, and magnetic resonance imaging

Fixation in cementless total knee arthroplasty is provided by osseous integration. Radiography, radiostereometric analysis (RSA), and magnetic resonance imaging (MRI) were used simultaneously to investigate fixation. Relationships between RSA-measured implant micromotions and MRI-evaluated osseous integration at the component-bone interface were assessed in 10 patients up to 6 months postoperation. Supine MRI (using multispectral imaging sequences) and RSA exams were performed to evaluate osseous integration and measure longitudinal migration, respectively. Inducible displacement was measured from standing RSA exams. Radiolucent lines were detected on conventional radiographs. Of 10 patients, 6 had fibrous membranes detected on MRI. No fluid or osteolytic interfaces were found, and no components were scored loose. Of 10 patients, 6 had radiolucent lines detected. Average maximum total point motion (MTPM) for longitudinal migration at 6 months was 0.816 mm (range 0.344-1.462 mm). Average MTPM for inducible displacement at 6 months was 1.083 mm (range 0.553-1.780 mm). Fictive points located in fibrous-classified baseplate quadrants had greater longitudinal migration than fictive points located in baseplate quadrants with normal interfaces at 2 weeks (p = 0.031), 6 weeks (p = 0.046), and 3 months (p = 0.047), and greater inducible displacements at 3 months (p = 0.011) and 6 months (p = 0.045). Greater early micromotion may be associated with the presence of fibrous membranes at the component-bone interface. Clinical significance: This multimodal imaging study contributes knowledge of the fixation of modern cementless TKA, supporting the notion that osseous integration is important for optimal implant fixation.

How Flat Is the Tibial Osteotomy in Total Knee Arthroplasty?

BACKGROUND

Cementless total knee arthroplasty has been developed to decrease the incidence of failure in younger and more active patients. However, failures are still more common in cementless versus cemented components. It is hypothesized that this is triggered by incomplete bone-tray contact. The present study compares the final contact area of a cementless tray as a function of the initial osteotomy flatness.

METHODS

Eight surgeons prepared 14 cadaveric knees for cementless total knee replacement using standard instrumentation. The topography of each osteotomy was captured with a laser scanner; 3-dimensional computer models of the surfaces were generated. After scanning each tibia, the surgeons implanted cementless tibial trays using a manual impactor. Each tibia was then dissected, embedded in mounting resin, and sectioned. The sectioned blocks were observed under stereomicroscopy to identify points of bone-tray contact which were incorporated into the 3-dimensional models. Maps were then generated illustrating depicting contacting and noncontacting areas.

RESULTS

The mean initial flatness of all specimens was 1.1 ± 0.35 mm. After impaction, 79.4% ± 0.3% of the surface had established bony contact. Of the noncontacting areas, 17.6% were within 0.3 mm of the tray. Only 2.6% of the surface was at distances reported to impede ingrowth. Noncontacting areas were typically located centrally. A trend in decreasing percent contact area with increased flatness tolerance was observed (R² = 0.605).

CONCLUSION

(1) There is an inverse correlation between the flatness of the tibial osteotomy and the percentage of the bony surface in contact with underside of the tibial tray. (2) Almost all tray-tibia contact is generated during implantation through flattening of elevated features on the tibial surface. (3) Gaps between the tray and the tibia are consistently located in the central regions of the osteotomy proximal to the medullary canal.

Link Between Clinical Predictors of Heterotopic Ossification and Histological Analysis in Combat-Injured Service Members

BACKGROUND

Heterotopic ossification (HO) is a debilitating condition that occurs following traumatic injury and may restrict range of motion and delay rehabilitation. The timing and efficacy of surgical resection have varied widely, and there is a gap in knowledge between clinical predictors of HO recurrence and histological analysis.

METHODS

Thirty-three service members seen at Walter Reed National Military Medical Center for symptomatic HO were enrolled in an institutional review board-approved study. Participants took oxytetracycline on four scheduled days prior to HO resection to determine the mineral apposition rate (bone growth rate).

RESULTS

Detailed histological analyses included scanning electron microscopy with backscattered electron imaging and light microscopy. Data indicated that the mineral apposition rate of trauma-induced HO was approximately 1.7 μm/day at the time of operative intervention, which was 1.7 times higher than the rate in non-pathological human bone. The mineral apposition rate and postoperative alkaline phosphatase values were demonstrated to be positively and significantly related (ρ = 0.509, p = 0.026, n = 19). When the analysis was limited to patients with no more than a two-year period from injury to excision (thereby removing outliers who had a longer time period than their counterparts) and traumatic brain injury and nonsteroidal anti-inflammatory drugs (known correlates with HO development) were controlled for in the statistical analysis, the mineral apposition rate and recurrence severity were significantly related (ρ = -0.572, p = 0.041, n = 11).

CONCLUSIONS

Data demonstrated a link between benchtop research and bedside care, with the mineral apposition rate elevated in patients with HO and correlated with recurrence severity; however, a larger sample size and more clinical factors are needed to refine this model.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Trabecular metal tibia still stable at 5 years: an RSA study of 36 patients aged less than 60 years

BACKGROUND AND PURPOSE

Clinical results of total knee replacement (TKR) are inferior in younger patients, mainly due to aseptic loosening. Coating of components with trabecular metal (TM) is a new way of enhancing fixation to bone. We have previously reported stabilization of TM tibial components at 2 years. We now report the 5-year follow-up of these patients, including RSA of their TM tibial components.

PATIENTS AND METHODS

22 patients (26 knees) received an uncemented TM cruciate-retaining tibial component and 19 patients (21 knees) a cemented NexGen Option cruciate-retaining tibial component. Follow-up with RSA, and clinical and radiographic examinations were done at 5 years. In bilaterally operated patients, the statistical analyses included only the first-operated knee.

RESULTS

Both groups had most migration within the first 3 months, the TM implants to a greater extent than the cemented implants. After 3 months, both groups stabilized and remained stable up to the 5-year follow-up.

INTERPRETATION

After a high initial degree of migration, the TM tibia stabilized. This stabilization lasted for at least 5 years, which suggests a good long-term performance regarding fixation. The cemented NexGen CR tibial components showed some migration in the first 3 months and then stabilized up to the 5-year follow-up. This has not been reported previously.

Treatment for Wear and Osteolysis in Well-Fixed Uncemented TKR

Background. Traditionally, osteolysis around total knee replacements (TKRs) is treated with complete revision. In certain subsets, polyethylene insert exchange and bone grafting may be applicable. This study reports the clinical outcomes for selective bone grafting in patients with osteolysis without complete revision of the TKR. Methods. This retrospective study analyzes 10 TKRs (9 patients, 66.5 ± 6.1 years old) presenting with osteolysis and revised after 8.7 ± 1.9 years of in vivo function. At index TKR, all patients were implanted with uncemented prosthesis and modular polyethylene insert with anteroposterior articular constraint (Ultracongruent, Natural Knee II, Sulzer Medica). The surgical technique for treating the osteolysis included removal of necrotic bone tissue using curettage, filling of the defect with bone graft materials, and polyethylene insert exchange. Results. Patients have not exhibited any further complications associated with osteolysis after 5.1 ± 2.4 years of followup. Routine radiographic exams show total incorporation of the graft material into the previously lytic regions in all patients. Conclusion. In some TKRs with osteolysis and firmly fixed components, the removal of lytic tissue and subsequent defect filling with bone graft materials can be a viable solution. This case series shows complete resolution of osteolysis in all patients with no complications.

Retrospective evaluation of the Duracon periapatite-coated tibial tray: midterm results and factors affecting success

This study reports the retrospective radiographic outcome of a series of 63 consecutive total knee arthroplasties using an uncemented hydroxyapatite-coated Duracon cruciate-retaining tibial baseplate (Stryker Howmedica Osteonics Corp, Mahwah, NJ). Sixty-three knees were assessed at a mean follow-up of 65 months. The knees were primarily diagnosed with osteoarthritis with a mean age of 61 years. Radiographic analysis showed 6 knees with tibial baseplate radiolucencies, with all of these resolving or improving over the course of the study. All tibial baseplates were implanted with the concomitant use of autologous bone slurry. There were no reoperations for aseptic loosening, fracture, or patellofemoral problems. This intermediate study demonstrates excellent radiographic outcomes for uncemented hydroxyapatite-coated Duracon cruciate-retaining tibial baseplates and evaluates other factors felt to be important in the success of a cementless implant.

Histologic retrieval analysis of a porous tantalum metal implant in an infected primary total knee arthroplasty

Porous tantalum (Zimmer, Inc, Warsaw, Ind) has the theoretical advantage of improved biologic fixation because of its high porosity, interconnected pore space, and modulus of elasticity. We present a case report documenting the retrieval and bone ingrowth analysis of a porous tantalum tibial component in an infected total knee arthroplasty. Results demonstrated a significantly larger amount of bone ingrowth present in the tibial posts (36.7%) when compared with the bone ingrowth into the tibial baseplate (4.9%) (P < .001). The data suggest that bone ingrowth seen in the plugs as well as baseplate was suggestive of viable bone tissue with healthy bone marrow, osteocytes, and lamella, resulting in a well-fixed tibial implant even at revision surgery for an infected total knee arthroplasty.

Does using autograft bone chips achieve consistent bone ingrowth in primary TKA?

BACKGROUND

Cementless fixation remains controversial in TKA due to the challenge of achieving consistent skeletal attachment. Factors predicting durable fixation are not clearly understood, but we presumed bone ingrowth could be enhanced by the quantity of host bone and application of autograft bone chips.

QUESTIONS/PURPOSES

We asked: (1) Did the amount of bone ingrowth exceed the amount of periprosthetic and host bone with the addition of autograft bone chips? (2) Did the amount of bone ingrowth increase with implantation time? And (3) did osteolysis along the porous-coated interface and screw tracts progress with implantation time?

METHODS

We measured the amount of bone in the porous-coated, periprosthetic, and host bone regions in 19 postmortem retrieved cementless primary total knee implants. The amount of bone in apposition to the implant surface, and alternatively lysed bone, was analyzed radiographically to assess the progression of osteolysis.

RESULTS

While bone ingrowth tended to be less than periprosthetic and host bone in all three components, it was only significantly less in the patellar component. Bone ingrowth increased in all three components over time, but progression of osteolysis did not.

CONCLUSIONS

Even after long-term followup, the amount of bone ingrowth did not surpass host bone levels, suggesting the amount of a patient's host bone is a limiting factor in the amount of bone ingrowth achievable for this cementless design. It remains unknown whether compromised osteopenic bone could achieve the amount of bone attachment necessary to provide durable fixation over time.

Percutaneous osseointegrated prostheses for amputees: Limb compensation in a 12-month ovine model

Percutaneous osseointegrated prostheses are being investigated as an alternative strategy to attach prosthetic limbs to patients. Although the use of these implants has shown to be promising in clinical trials, the ability to maintain a skin seal around an osseointegrated implant interface is a major challenge to prevent superficial and deep periprosthetic infections. The specific aim of this study was to establish a translational load-bearing ovine model to assess postoperative limb compensation and gait symmetry following a percutaneous osseointegrated implant. We tested the following hypotheses: (1) the animals would return to pre-amputation limb loads within 12-months; (2) the animals would return to a symmetrical gait pattern (stride length and time in stance) within 12-months. The results demonstrated that one month following surgery, the sheep loaded their amputated limb to a mean value of nearly 80% of their pre-amputation loading condition; by 12-months, this mean had dropped to approximately 74%. There was no statistical differences between the symmetry of the amputated forelimb and the contralateral forelimb at any time point for the animals stride length or the time spent in the stance phase of their gait cycle. Thus, the data showed that while the animals maintained symmetric gait patterns, they did not return to full weight-bearing after 12-months. The results of this study showed that a large animal load-bearing model had a symmetric gait and was weight bearing for up to 12 months. While the current investigation utilizes an ovine model, the data show that osseointegrated implant technology with postoperative follow-up can help our human patients return to symmetric gait and maintain an active lifestyle, leading to an improvement in their quality of life following amputation.

Evaluating antimicrobials and implant materials for infection prevention around transcutaneous osseointegrated implants in a rabbit model

Transcutaneous osseointegrated implants can improve function for select amputee patients, but infection serves as a significant limitation of implantable transcutaneous devices. This study examined the efficacy of an antimicrobial, pexiganan acetate (SUPONEX), and a porous tantalum implant material (Trabecular Metal) in preventing pin tract infection of osseointegrated implants in a rabbit model. Thirty-seven rabbits were randomized to three groups: Ti-control group (n = 11) with titanium alloy implant and no antimicrobial, Ti-Pexiganan group (n = 8) with titanium alloy implant and topical pexiganan acetate 1% applied daily at the skin/implant interface, and Ta-control group (n = 18) with porous tantalum implant and no antimicrobial. All implants were placed transcutaneously through skin, muscle, and bone. Rabbits were monitored for infection for 24 weeks. We observed a 75% reduction in rates of pin tract infection in the Ti-Pexiganan group compared to that observed in the Ti-control group (p = 0.019). No difference in rates of infection was observed between the Ta-control group and the Ti-control group (p = 0.230). In conclusion, pexiganan acetate may be an important antimicrobial for transcutaneous osseointegrated implants. Porous tantalum will not likely prevent pin tract infection without additional methods of soft tissue immobilization around the implant site.

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.

Cementless total knee arthroplasty in patients 50 years or younger

Total knee arthroplasty now is being advocated for use in younger patients with posttraumatic and rheumatoid arthritis. Advances in technology, design, and materials potentially have allowed for more predictable results. There has been continued interest in cementless fixation for use in younger patients. Between 1986 and 1998, 75 total knee replacements in 57 patients 50 years or younger were done. All surgeries were done by one surgeon (AAH). There were 35 left knees and 40 right knees. The average age of the patients was 42 years (range, 31-50 years). Followup averaged 111 months. Preoperative range of motion was 5 degrees to 106 degrees and postoperative range of motion was 2 degrees to 113 degrees. Modified Hospital for Special Surgery knee scores improved from an average of 67 points preoperatively to an average of 97 points postoperatively. The majority of the diagnoses were posttraumatic arthritis or osteoarthritis (57%), indicating a young, active group of patients. There were two infections and 12 polyethylene exchanges. There were no revisions for loosening or implant failure. There was a correlation between prior knee surgeries and the need for a manipulation. Radiographically, there were no loose implants. Cementless fixation in the young patient with high physical demands was clinically reliable.

Ten- to 14-year clinical followup of the cementless Natural Knee system

Of 300 consecutive knees (238 patients) that had undergone arthroplasty with the cementless Natural Knee prosthesis from 1985 to 1989, 176 knees (141 patients) were available for followup at an average of 12 +/- 1 years after the operation. Knee function was improved significantly. Modified Hospital for Special Surgery knee scores improved from 59.1 +/- 13.2 points preoperatively to 97.8 +/- 4.7 points at last followup. At last followup, knee range of motion averaged 0 degrees +/- 2 degrees to 120 degrees +/- 10 degrees. Implant survival was 93.4% (including infection and simple polyethylene exchanges) and 95.1% (excluding infection and simple polyethylene exchanges) at 10 years when applying the Kaplan-Meier survival analysis, using loose components, revision, or both as failure criteria. Besides the three revisions for infection, only two femoral and one tibial component required revision. The patellar component survivorship at 10 years was 95.1%. All patellar revisions were attributed to edge wear. Subsequent operative and design changes, including patellar component medialization and countersinking, have decreased the incidence of patellar revision. The long-term results of this cementless knee system compare favorably with those of cemented systems. The Natural Knee design has provided excellent and predictable long-term clinical results in the current series of active patients.

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.

Tibial component fixation in porous- and hydroxyapatite-coated total knee arthroplasty: a radiostereo metric evaluation of migration and inducible displacement after 5 years

A total of 51 knees (45 patients) with osteoarthrosis were stratified in a randomized study to receive a hydroxyapatite-coated Freeman-Samuelson (FS HA) or a porous-coated Miller-Galante II (MG II) uncemented total knee arthroplasty. Repeated clinical, radiographic, and radiostereometric analysis (RSA) evaluations of the tibial components were done for 5 years. The clinical outcome was equal at the 5-year follow-up (mean Hospital for Special Surgery score, 93). Standard radiographs displayed more zones around the tibial stem in the MG II group. RSA revealed that the FS HA components migrated less (smaller maximum total point motion and maximum subsidence) after 5 years and showed less inducible displacements at the 1-year follow-up. The stability of the implants obtained is equal to or better than cemented implants after 5 years. Key words: knee prosthesis, cementless, hydroxyapatite, radiostereometry, inducible displacement.

Porous-coated metal-backed patellar components in total knee replacement. A postmortem retrieval analysis

The use of porous-coated metal-backed patellar components to achieve consistent fixation by bone ingrowth and to provide relief of pain warrants serious scrutiny. We conducted a quantitative postmortem investigation of eleven consecutively retrieved components with use of high-resolution contact radiographs, electron microscopy, and histological analysis. The implants had been in situ for a mean (and standard deviation) of 45+/-36 months (range, one to eighty-four months). Analysis of the high-resolution contact radiographs revealed that a mean of 86+/-12 per cent (range, 61 to 100 per cent) of the porous coating was in contact with the host bone. Backscattered electron imaging showed that the mean volume fraction of bone ingrowth was 13+/-9 per cent (range, 0 to 30 per cent). No significant difference was detected, with the numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone in the patellae.

Postmortem analysis of consecutively retrieved asymmetric porous-coated tibial components

The objective of this investigation was to conduct a postmortem analysis of 8 porous-coated asymmetric tibial components to measure the extent of radiolucencies and bone ingrowth. With the use of radiographic, electron microscope, and histologic analysis techniques, a quantitative postmortem study of 8 consecutively retrieved porous-coated tibial components was conducted. Time in situ averaged 47+/-36 months. The components were secured with 4 pegs and 2 screws. Autograft bone chips were applied to the resected tibia during implantation. Contact radiographs of an average of 8 3-mm sections from each implant revealed that 73%+/-17% of the porous coating had no apparent radiolucencies present between the host bone and porous coating for the series. Backscattered electron imaging showed that the bone ingrowth averaged 6%+/-2%. Histologic analysis was unable to demonstrate any adverse cellular response. The analysis suggested that this asymmetric implant design is stable and biocompatible and has potential for long-term clinical durability.

Human postmortem retrieval of total hip arthroplasty

Postmortem retrieval of well-functioning prostheses from total hip arthroplasty is essential in determining the quality and success of the implant, implant fixation, and operative technique. This report describes the retrieval procedure, including details on informed consent, retrieval procedure, and types and benefits of specimen analysis. Bone densitometry, roentgenography, and microscopy studies permit a level of assessment of operative and prosthetic performance not obtainable from clinical and in vivo roentgenographic evaluation alone. Findings from these techniques yielding data on stress shielding, bone mineral density, extent of bone-prosthesis apposition and osseointegration, and histologic activity are ultimately of considerable clinical significance. The implementation of retrieval programs, along with establishing early family and patient cooperation and proper planning practices, will continue to contribute invaluably to advances in orthopaedic science.

Postmortem analysis of bone growth into porous-coated acetabular components

Microradiography, backscattered electron microscopy, and histological analysis were used to conduct a quantitative postmortem study of seven consecutively retrieved anatomical porous replacement acetabular components that had been inserted during total hip arthroplasties. Screws had been used for the initial fixation of six components. The microradiographic analysis of all seven components showed that an average (and standard deviation) of 84 +/- 9 per cent (range, 72 to 93 per cent) of the porous coating was in direct apposition to the periprosthetic bone. The backscattered electron images demonstrated that an average of 12 +/- 6 per cent (range, 4 to 21 per cent) of the space available in the porous coating was occupied by ingrown bone. The amount of bone ingrowth was not significantly different among the three zones delineated by DeLee and Charnley. Uniformity of bone growth into the porous coating suggests that the preferential loading that occurs in the superior region did not differentially affect the bone ingrowth. The present study showed that consistent bone growth into anatomical porous replacement acetabular components can be achieved.

Progression of human bone ingrowth into porous-coated implants. Rate of bone ingrowth in humans

We report the measured progression of human cancellous bone ingrowth into load-bearing porous-coated titanium implants over 5 time periods (0, 3, 6, 9, and 12 months). There was a statistically significant progression of bone ingrowth into the implants over a 9-month period, but the 9- and 12-month data were not different. Investigators are advised to analyze time "0" implants in order to distinguish mechanical impaction of bone from the biological process of bone ingrowth.

6- to 10-year experience using countersunk metal-backed patellas

Three hundred two consecutive cementless total knee arthroplasties (Natural Knee, Intermedics Orthopedics, Inc., Austin, TX) were performed using a metal-backed, porous-coated patellar component. Fifty-nine patients died and 31 were lost to follow-up evaluation, resulting in 212 knees available for evaluation at 6 to 10 years. The mean follow-up period was 91 months. The mean modified Hospital for Special Surgery total knee score improved from 58 before surgery to 98 at the most recent follow-up visit. Mean patellar translation and tilt were 2.75 mm and 3.5 degrees, respectively. There were no patellar lucencies nor loosening. Eleven patients (5%) underwent revision of the patellar component. Overall patellar survivorship was 96%. Comparatively good results can be achieved with the use of a metal-backed patellar component if component design, surgical technique, and patellar alignment are properly addressed.

Reproducibility of techniques using Archimedes' principle in measuring cancellous bone volume

Researchers have been interested in developing techniques to accurately and reproducibly measure the volume fraction of cancellous bone. Historically bone researchers have used Archimedes' principle with water to measure the volume fraction of cancellous bone. Preliminary results in our lab suggested that the calibrated water technique did not provide reproducible results. Because of this difficulty, it was decided to compare the conventional water method to a water with surfactant and a helium method using a micropycnometer. The water/surfactant and the helium methods were attempts to improve the fluid penetration into the small voids present in the cancellous bone structure. In order to compare the reproducibility of the new methods with the conventional water method, 16 cancellous bone specimens were obtained from femoral condyles of human and greyhound dog femora. The volume fraction measurements on each specimen were repeated three times with all three techniques. The results showed that the helium displacement method was more than an order of magnitudes more reproducible than the two other water methods (p < 0.05). Statistical analysis also showed that the conventional water method produced the lowest reproducibility (p < 0.05). The data from this study indicate that the helium displacement technique is a very useful, rapid and reproducible tool for quantitatively characterizing anisotropic porous tissue structures such as cancellous bone.

Evolution of the bone-titanium interface on implants coated/noncoated with xenogeneic bone particles: quantitative microscopic analysis

Titanium cylinders having a sandblasted surface were implanted in holes drilled in the internal condyles of rabbit femurs. The right side received a titanium implant coated with xenogeneic bone particles and the left side received a titanium cylinder alone and was used as control. The femoral extremities were removed at 1, 2, and 3 months postsurgery and embedded undecalcified in methacrylic resins. Sections were studied by quantitative analysis and the interface contact between bone and titanium was measured at two microscopic magnifications due to the fractal dimension of this parameter. In addition the amount of bone volume in a given referent volume provided automatically by the image analyzer was obtained. No differences could be evidenced between the two series of implants, supporting the view that xenogeneic particles were ineffective in improving the attachment of bone to the implant. The bone-to-implant interface measured at the low magnification reflected the anchorage of the implant. In both series a progressive increase upon time of the bone-to-implant interface at the highest microscopic magnification evidenced the importance of late remodeling changes responsible for bone bonding and the fractal characteristics of this interface, related to surface quality of the implant responsible for stress transfer.

Effects of hydroxyapatite tricalcium phosphate coating and intracancellous placement on bone ingrowth in titanium fibermetal implants

The purpose of this study was to compare the host-bone response to hydroxyapatite/tricalcium phosphate (HA/TCP)-coated and noncoated titanium fibermetal implants placed in a load-sharing cancellous bone environment of the distal femurs of rabbits. The influence of implantation site was also investigated by comparing these intracancellous implants with intramedullary implants evaluated in a previous study. Three parameters were measured: percentage implant perimeter surface length in contact with new bone, percentage internal fibermetal surface length in contact with ingrown bone, and percentage of available pore space filled with bone. The HA/TCP coating significantly accelerated and increased bone ongrowth, new bone formation on the perimeter and internal surface of the implants. This effect was evident as early as 2 weeks after implantation. In contrast, there was no difference between HA/TCP-coated and noncoated implants in the bone ingrowth parameter, percentage of available pore space filled with bone, or pull-out strength. Scanning electron microscopy in the backscatter mode demonstrated that new bone formed directly onto the HA/TCP-coated fibers and did not usually form directly on noncoated fibers. Analysis of fluorochrome labeling revealed that bone formation in weeks 1 through 4 was primarily woven and thereafter lamellar. Compared with intramedullary placement, intracancellous placement significantly accelerated the apposition of bone to the perimeter and internal surface of HA/TCP-coated implants and both accelerated and increased bone ingrowth as a percentage of available pore volume. These data show that the host response to titanium fibermetal implants is influenced both by HA/TCP coating and by the implantation site.

Bone ingrowth and wear debris in well-fixed cementless porous-coated tibial components removed from patients

Bone ingrowth and the distribution of wear debris within the porous coating of 13 primary cementless porous-coated tibial components removed for reasons unrelated to fixation or infection were quantitatively described. The average length of implantation was 15.3 months (range, 3-30 months). The implants were all of the same design, made for Ti6A14V with a commercially pure titanium fiber-metal porous coating, which covered the undersurface of the tray and the four fixation pegs. In all but one component, supplemental screw fixation was used. The average extent of bone ingrowth within the tray was 27.1 +/- 16.1%, and the average volume fraction was 9.5 +/- 7.5%. There was significantly more bone ingrowth within the fixation pegs than within the tray and also more bone ingrowth in the anterior half of the tray than posteriorly. There was no correlation between the amount of bone ingrowth and the length of implantation, age, or sex of the patient; however, the depth and orientation of the resection plane were found to correlate with the topographic distribution of bone ingrowth. Particulate debris appeared to gain access to the interface via soft tissue pathways both at the periphery and through the holes for adjuvant screw fixation.

Distinguishing wear and creep in clinically retrieved polyethylene inserts

There is an increasing awareness of the clinical problems associated with ultra-high-molecular-weight polyethylene (UHMWPE) wear and failure in orthopedics. To better understand the reasons for wear and failure, methods were developed using polarized light microscopic analysis and backscattered electron (BSE) imaging with correlated elemental analysis to distinguish the contributions of wear, creep, and third-body particulate. This study determined that microscopic metal particles (< 10 microns) previously not observed with the stereomicroscope could be easily observed with the BSE technique. BSE imaging identified embedded metal in 5/5 of the tibial and 2/4 of the acetabular inserts, which were thought to be free of metal debris after stereoscopic examination. Correlated elemental analysis showed that the microscopic particles could be traced to the elements known to be present in the porous coatings of the retrieved uncemented implants. Creep was distinguished from wear in the total hip and total knee inserts by using polarized light microscopic techniques. Continued development of polarized light microscopic techniques applied in this investigation should assist biomaterials experts in the future to better distinguish wear and creep in retrieved clinical inserts. The correlated BSE and elemental analysis will assist in determining the roll of microscopic third-body particular in wear and osteolysis in total joint replacement.

Mineral apposition rates of human cancellous bone at the interface of porous coated implants

Human cancellous bone ingrowth studies were conducted on 19 consenting bilateral total knee arthroplasty (TKA) patients. Titanium porous coated cylinders were implanted into the medial femoral condyle of the contralateral knee during the first of two TKAs. Retrieval was performed at the time of the second TKA (6-131 weeks later), and fluorochrome analysis was conducted. Mean mineral apposition rates (MAR) at the interface measured 1.0 micron/day, whereas 4 mm away, the peripheral bone had a mean MAR of 0.8 micron/day. This represented a 25% acceleration in the interface bone remodeling rate when compared with the periphery (P < .05). This study showed the bone advanced appositionally at the interface at a rate of approximately 1 micron/day. Analysis showed that when bone was over 50 microns from the porous coating, bone ingrowth did not occur. These results emphasize the need for surgical precision and careful postoperative management to achieve bone ingrowth.

Postmortem comparative analysis of titanium and hydroxyapatite porous-coated femoral implants retrieved from the same patient. A case study

The results of bilateral postmortem analysis of titanium and plasma-sprayed hydroxyapatite (HA) porous-coated femoral components of the same Anatomic Porous Replacement design retrieved from a 35-year-old female donor are reported. Analysis was conducted using backscattered electron imaging, histology, and radiographic techniques. The appositional bone index, percent bone ingrowth, and mineral content were measured for both implants. The results showed a 177% higher appositional bone index (P = .014) for the HA porous-coated Anatomic Porous Replacement component compared to the titanium Anatomic Porous Replacement component. Backscattered electron analysis showed 50% more bone in the HA porous-coated implant (P = .028). The mineral content analysis demonstrated that the bone ingrown into the HA porous-coated device was 23% less mineralized (P = .016). The data from this case study suggested that plasma-sprayed HA porous-coated implants may assist in increasing the amount of bone ingrowth and skeletal attachment in total hip arthroplasties.

Comparative study of human cancellous bone remodeling to titanium and hydroxyapatite-coated implants

The human cancellous bone response was compared in weight-bearing porous hydroxyapatite (HA) and titanium-coated implants placed in the distal medial femoral condyles of consenting staged bilateral knee patients. The Institutional Review Board approved study quantified the amount of bone ingrowth, the mineral apposition rate, and the bone mineral content. Results showed that the osteoconductive HA coating increased the amount of bone ingrowth by 8% (P = .018). The HA coating did not effect the mineral apposition rate of the bone but had an 8% lower bone mineral content at the implant interface (P = .042). The influence of HA coatings on human cancellous bone appears highly focal along the coating surface. Gaps of 50-500 microns filled with fibrous connective tissue were observed along the porous-coated surfaces of both implant types suggesting that HA coatings still require precision placement adjacent to human cancellous bone.