Revision and salvage patellar arthroplasty using a porous tantalum implant

3D preoperative plan assisted total knee arthroplasty after knee arthrodesis with patella absence: a case report

PURPOSE

The conversion of knee arthrodesis to total knee arthroplasty (TKA) is a challenging procedure. This article aims to report a case of fusion knee with patellar absence who was converted to TKA and has achieved good results.

METHODS

The patient, a 23 years old Tibetan Buddhist monk, sustained a left knee joint injury at the age of 12 due to a car accident, leading to subsequent knee arthrodesis at 18 years old as a result of recurrent severe infections. However, this procedure hindered his ability to perform daily meditation practices that required bending both knees and sitting cross-legged. After adequate preoperative preparation, with the help of customized osteotomy guide plate and customized 3D-printed porous tantalum patella, the 3D preoperative plan assisted TKA after arthrodesis was performed. The knee function was followed up to explore the clinical effect of above-mentioned surgical procedure.

RESULTS

A 1-year follow-up showed significant improvement in postoperative knee function with improved scores for function outcomes, and the patient was satisfied with the conversion. The patient's left knee improved significantly from preoperative immobility with 5° of fixed fusion to postoperative ROM of 0° to 100°, and the patient could squat and stand up, walk on the flat ground, and go up and down stairs.

CONCLUSION

Adequate preoperative communication with patients and good expectation management are crucial for ensuring favorable prognoses. Perfect preoperative planning and its reliable implementation during operation are essential. Additionally, postoperative rehabilitation and proactive management of complications play pivotal roles in achieving optimal clinical outcomes.

LEVEL OF EVIDENCE

IV.

Microstructure Optimization for Design of Porous Tantalum Scaffolds Based on Mechanical Properties and Permeability

Porous tantalum (Ta) implants have important clinical application prospects due to their appropriate elastic modulus, and their excellent bone growth and bone conduction ability. However, porous Ta microstructure designs generally mimic titanium (Ti) implants commonly used in the clinic, and there is a lack of research on the influence of the microstructure on the mechanical properties and penetration characteristics, which will greatly affect bone integration performance. This study explored the effects of different microstructure parameters, including the fillet radius of the middle plane and top planes, on the mechanics and permeability properties of porous Ta diamond cells through simulation, and put forward an optimization design with a 0.5 mm midplane fillet radius and 0.3 mm top-plane fillet radius in order to significantly decrease the stress concentration effect and improve permeability. On this basis, the porous Ta structures were prepared by Laser Powder Bed Fusion (LPBF) technology and evaluated before and after microstructural optimization. The elastic modulus and the yield strength were increased by 2.31% and 10.39%, respectively. At the same time, the permeability of the optimized structure was also increased by 8.25%. The optimized microstructure design of porous Ta has important medical application value.

Success Factors of Additive Manufactured Root Analogue Implants

Dental implantation is an effective method for the treatment of loose teeth, but the threaded dental implants used in the clinic cannot match with the tooth extraction socket. A root analogue implant (RAI) has the congruence shape, which reduces the damage to bone and soft tissue. Additive manufacturing (AM) technologies have the advantages of high precision, flexibility, and easy operation, becoming the main manufacturing method of RAI in basic research. The purpose of this systematic review is to summarize AM technologies used for RAI manufacturing as well as the factors affecting successful implantation. First, it introduces the AM technologies according to different operating principles and summarizes the advantages and disadvantages of each method. Then the influences of materials, structure design, surface characteristics, implant site, and positioning are discussed, providing reference for designers and dentists. Finally, it addresses the gap between basic research and clinical application for additive manufactured RAIs and discusses the current challenges and future research directions for this field.

A comprehensive review of biological and materials properties of Tantalum and its alloys

Tantalum (Ta) and its alloys have been used for various cardiovascular, orthopedic, fracture fixation, dental, and spinal fusion implants. This review evaluates the biological and material properties of Ta and its alloys. Specifically, the biological properties including hemocompatibility and osseointegration, and material properties including radiopacity, MRI compatibility, corrosion resistance, surface characteristics, semiconductivity, and mechanical properties are covered. This review highlights how the material properties of Ta and its alloys contribute to its excellent biological properties for use in implants and medical devices.

Biconvex Patellar Components: 96% Durability at 10 Years in 262 Revision Total Knee Arthroplasties

BACKGROUND

The optimal strategy to address osseous deficiencies of the patella during revision total knee arthroplasty (TKA) remains controversial. One possible solution is a cemented biconvex patellar component used such that the non-articular convexity both improves fixation and makes up for bone loss. The aim of this study was to determine the outcomes of the use of biconvex patellar components in a large series of revision TKAs.

METHODS

From 1996 to 2014, 262 revision TKAs were performed at a single institution using a biconvex patellar component. Implant survivorship, clinical and radiographic results, and complications were assessed. The mean patient age at the TKA revision was 69 years, and 53% of the patients were female. The mean follow-up was 7 years.

RESULTS

The 10-year survivorship free of revision of the biconvex patellar component due to aseptic loosening was 96%. The 10-year survivorship free of any revision of the biconvex patellar component was 87%. The 10-year survivorship free of any rerevision and free of any reoperation was 75% and 70%, respectively. The mean Knee Society Score (KSS) improved from 45.4 before the index revision to 67.7 after it. The mean residual composite thickness seen on the most recent radiographs was 18.1 mm. In addition to the complications leading to revision, the most common complications were periprosthetic patellar fracture (6%), of which 3 required revision; superficial wound infection (6%) requiring antibiotic therapy only or irrigation and debridement; and arthrofibrosis (3%).

CONCLUSIONS

In this cohort of 262 revision TKAs, biconvex patellar components used to treat marked patellar bone loss demonstrated excellent durability with a 10-year survivorship free of patellar rerevision due to aseptic loosening of 96%. The biconvex patellar components were reliable as evidenced by substantial improvements in clinical outcomes scores and a low risk of complications.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The Clinical Application of Porous Tantalum and Its New Development for Bone Tissue Engineering

Porous tantalum (Ta) is a promising biomaterial and has been applied in orthopedics and dentistry for nearly two decades. The high porosity and interconnected pore structure of porous Ta promise fine bone ingrowth and new bone formation within the inner space, which further guarantee rapid osteointegration and bone-implant stability in the long term. Porous Ta has high wettability and surface energy that can facilitate adherence, proliferation and mineralization of osteoblasts. Meanwhile, the low elastic modulus and high friction coefficient of porous Ta allow it to effectively avoid the stress shield effect, minimize marginal bone loss and ensure primary stability. Accordingly, the satisfactory clinical application of porous Ta-based implants or prostheses is mainly derived from its excellent biological and mechanical properties. With the advent of additive manufacturing, personalized porous Ta-based implants or prostheses have shown their clinical value in the treatment of individual patients who need specially designed implants or prosthesis. In addition, many modification methods have been introduced to enhance the bioactivity and antibacterial property of porous Ta with promising in vitro and in vivo research results. In any case, choosing suitable patients is of great importance to guarantee surgical success after porous Ta insertion.

Patellar Rebar Augmentation in Revision Total Knee Arthroplasty

BACKGROUND

In revision total knee arthroplasty, osteolysis, mechanical abrasion, and infection may leave patellar bone stock severely attenuated with cavitary and/or segmental rim deficiencies that compromise fixation of patellar implant pegs. The purpose of this study was to retrospectively review the use of cortical "rebar" screws to augment cement fixation in revision patelloplasty.

METHODS

From 2006 to 2018, dorsal patellar rebar technique was used for patellar reconstruction in 128 of 1037 revision total knee arthroplasty cases (12.3%). Follow-up was achieved with serial radiographs and prospective comparison of Knee Society Scores (KSSs) for clinical outcome. Complications and implant failures requiring reoperation or modified rehabilitation were also assessed.

RESULTS

Of the 128 patellar revisions performed using the rebar technique, 69 patients were women and 59 patients were men. The average age of the group was 69.5 years (range, 32-83 years). The mean follow-up of the cohort was 37 months (range, 13-109 months). The most common causes for revision were kinematic conflict, periprosthetic joint infection, and aseptic loosening. The median number of rebar screws used was 5 (range, 1-13). Preoperative KSSs for the study cohort averaged 50 (range, 0-90) At latest follow-up, mean KSS was 85 (range, 54-100). There were 4 patellar-related complications (3.1%) with no implant failures at study conclusion. Retrieval analysis revealed rigid fixation of the reconstructed patellar component in all cases.

CONCLUSIONS

Patellar rebar screw augmentation is a useful technique when there are significant cavitary deficiencies and limited segmental rim deficiencies. This technique allows the surgeon to extend indications for patellar revision arthroplasty.

Extensor mechanism reconstruction "Tubeplasty" in total knee arthroplasty with previous patellectomy: Surgical technique and clinical outcomes

PURPOSE

to evaluate our consecutive series of tubeplasty and extensor mechanism reconstruction during knee arthroplasty in patients with previous patellectomy.

METHODS

we describe our surgical technique and present a retrospective consecutive series of 4 patients with a minimum 6 months follow-up. Knee society score (KSS), clinical and radiographic outcomes were collected at final follow up.

RESULTS

we included 4 patients (2 males/2 females) with average age 65.5 years (range 58-76). There were 2 primary and 2 revision knee arthroplasties. The follow up ranged from 0.5 to 13 years. All 4 patients regained function and satisfactory clinical outcomes with KSS score 84.7 (range 79-90).

CONCLUSION

satisfactory clinical outcomes can be achieved with extensor mechanism reconstruction and tubeplasty in patients with previous patellectomy undergoing primary and revision knee arthroplasty.

LEVEL OF EVIDENCE

IV.

Ignore the Patella in Revision Total Knee Surgery: A Minimum 5-Year Follow-Up With Patella Component Retention

BACKGROUND

In the setting of aseptic revision, a common question is: what should be done with the previously resurfaced patella? We report on a series of aseptic revision total knee arthroplasties (RTKA) where one or both components were revised and the patella was not.

METHODS

The study group was 147 consecutive RTKA in 137 patients with a mean age of 70.1 ± 9.3 years where the patella was not revised. The average body mass index was 31.0 ± 5.4 kg/m². Follow-up was a minimum of 5 years (range, 5 to 12 years). At final follow-up, 13 patients died and 2 patients were lost to follow-up leaving 122 patients and 130 knees available for review. Mean time from primary surgery to RTKA was 9.2 ± 5.5 years. Both components were revised in 50 knees, the femur only in 11 knees, the tibia only in 12 knees, and 57 had an isolated polyethylene revision. We found 5 patients with a mismatch between the patella and femoral components and 30 cases with patella component wear identified intraoperatively.

RESULTS

At final follow-up, there were no reoperations on any patella and none were at risk of failure. There were 6 knees with a lateral patella tilt beyond 10°, but none were subluxed. Knee Society Scores averaged 85 ± 17.2 points at final follow-up.

CONCLUSION

At midterm follow-up in this group of RTKA where the patella was not revised, we identified no subsequent failures of the patella. This is despite the presence of mild patella polyethylene wear and mismatched shapes in several knees.

LEVEL OF EVIDENCE

III.

A classification-based approach to the patella in revision total knee arthroplasty

Background

There is a paucity of data to guide management of the patella in revision total knee arthroplasty (RTKA). The purpose of this study was to review our experience with patellar management in RTKA.

Methods

We retrospectively reviewed 422 consecutive RTKAs at a minimum of 2 years (mean, 42 months). Patellar management was guided by a classification that considered stability, size, and position of the implanted patellar component, thickness/quality of remaining bone stock, and extensor mechanism competence.

Results

Management in 304 aseptic revisions included retention of a well-fixed component in 212 (69.7%) and revision using an all-polyethylene component in 46 (15.1%). Patella-related complications included 5 extensor mechanism ruptures (1.6%), 3 cases of patellar maltracking (1.0%), and 2 periprosthetic patellar fractures (0.7%). Of 118 2-stage revisions for infection, an all-polyethylene component was used in 88 (74.6%), patelloplasty in 20 (16.9%), and patellectomy in 7 (5.9%). Patella-related complications included 4 cases of patellar maltracking (3.4%), 3 extensor mechanism ruptures (2.5%), and 1 periprosthetic patellar fracture (0.8%).

Conclusions

Septic revisions required concomitant lateral releases more frequently (38.1% vs 10.9%; P < .02) but had a similar rate of patellar complications (6.8% vs 3.3%; P = .40). No cases required rerevision specifically for failure of the patellar component. Patients who had a patelloplasty had worse postoperative Knee Society functional scores than those with a retained or revised patellar component. In most aseptic RTKAs, a well-fixed patellar component can be retained. If revision is required, a standard polyethylene component is sufficient in most septic and aseptic revisions. Rerevisions related to the patellar component are infrequent.

Patellar reconstruction following previous patellectomy: a review of the literature and a case series using distal femoral autograft during total knee arthroplasty

During total knee arthroplasty, the reconstruction of the patella following a previous patellectomy is challenging, and is undertaken to improve functional outcomes and patient satisfaction. In this case series, we have reconstructed the patella using a femoral condyle resected during total knee arthroplasty. The resected femoral condyle with best available bone stock is selected and secured to the extensor mechanism. We reviewed the preoperative indications and postoperative outcomes of two patients who underwent the above procedure at our Institute, and compared this to the literature. The cases include a 68-year old male (6 months follow-up) who sustained a multi-fragmentary fracture of his right patella and underwent a patellectomy 30 years previously, and a 45-year old female (4 years follow-up) who underwent a left-sided patellectomy 15 years previously following polytrauma. As a result of progressive osteoarthritis they required total knee arthroplasty, and simultaneous patella reconstruction with a femoral condyle autograft. Compared to their preoperative range of motion, both patients demonstrated an improvement post-operatively with successful pain-free knee function, with no radiological signs of graft resorption. In this limited, small series we have reported two patients who are clinically and functionally satisfied by the outcome of surgery, with comparable outcomes to alternative methods. We believe the use of a femoral condyle autograft for patellar reconstruction is a safe and simple technique that optimises knee kinematics, without associated donor morbidity.

Clinical and radiographic evaluation of single tantalum dental implants: a prospective pilot clinical study

OBJECTIVE

The aim of this prospective pilot clinical case series report was to evaluate, through a clinical and radiographic analysis, the peri-implant bone resorption of the tantalum dental implants (TMT) (Zimmer TMT, Parsippany, NJ, USA) one year after prosthetic rehabilitation.

METHODS

Twenty tantalum dental implants were placed in both maxillas and mandibles of 20 patients. Patients were asked to attend a radiographic and clinical follow-up and their previous clinical records and X-rays were assessed. Bone levels were calculated by digitally measuring the distance from the implant shoulder to the first bone-to-implant on periapical radiographs taken at surgery and after 6 and 12 months of functioning. The Pearson correlation analysis was performed to assess it there was a correlation between the measurement of the marginal bone loss (MBL). The Anova Test with a post-hoc analysis using Bonferroni's test was used to compare the three group (0, 6 months and 12 months).

RESULTS

The mean total MBL for the group 0 months was 0.84 mm (SD 0.21), 6 months was 0.87 mm (SD 0.22) and for 12 months was 0.89 mm (SD 0.23). The values of the Pearson's coefficients showed that the data measurement were positively correlated. The Anova test showed a statistically significant difference between the groups.

CONCLUSION

The statistically significant difference in marginal bone loss can be considered physiological. Within the limits of this study it can be concluded that TMT implants have an excellent bone crest's stability, however, to have most accurate information, will be necessary extend the sample.

The impact of patellar resurfacing in two-stage revision of the infected total knee arthroplasty

Evidence for optimal management of the patellofemoral joint in revision surgery for the infected TKA is limited. We reviewed 69 infected TKAs undergoing two-stage revision. Fifty four patellae were resurfaced, 11 had patelloplasty performed, two were augmented with trabecular metal, one had impaction grafting, and one knee underwent patellectomy. Average follow-up was 4.5 years. The patients that received patellar resurfacing at re-implantation experienced statistically significant improvements in KSS pain score, functional KSS, and patellar score (P < 0.03). One further patient treated with impaction grafting improved significantly in terms of pain and function. Patients treated with patelloplasty, trabecular metal augmentation, or patellectomy did not have significant improvements in clinical or functional outcome. Patient age, use of dynamic vs. static spacer, use of extensor mechanism release, and differences in Charlson index did not seem to statistically affect outcome. We recommend that every effort should be made to minimize patellar bone loss in first stage resection, as inability to resurface the patella at time of reimplantation may adversely affect patient outcome.

Immediate loading of trabecular metal-enhanced titanium dental implants: interim results from an international proof-of-principle study

OBJECTIVES

A 3-year proof-of-principle study was initiated to evaluate the clinical efficacy of immediately loading titanium dental implants with surfaces enhanced with porous tantalum trabecular metal (PTTM). First-year interim results are presented.

MATERIALS AND METHODS

Healthy, partially edentulous patients (n = 30) were enrolled and treated per protocol (minimum insertion torque: ≥35 Ncm) with 37 implants placed in one or two premolar or molar locations in either jaw (study group). Implants were immediately provisionalized out of occlusion with single acrylic crowns. After 7 to 14 days of soft tissue healing, implants were definitively restored in occlusion with ceramometal crowns. Because most study group implants (54.1%, n = 20) had less than 1 year of clinical follow-up, this interim analysis was limited to the first 22 consecutively placed implants in 17 subjects (10 women and 7 men) who completed 1 year of clinical follow-up to date (focus group).

RESULTS

To date, one implant failed to integrate in the study group (survival = 97.3%, n = 36/37). Focus group implants achieved 100% (n = 22/22) survival with 0.43 ± 0.41 mm of mean marginal bone loss. There were no serious complications.

CONCLUSION

Early clinical findings indicated that immediate loading of PTTM implants was safe and effective under the controlled study conditions.

Minimum 6-year follow-up of revision total knee arthroplasty without patella reimplantation

Management options for the polyethylene patellar button during a revision total knee arthroplasty (TKA) include retention, revision, or removal of the button without replacement (patelloplasty). Our purpose was to determine the midterm outcome of patients undergoing revision TKA with patelloplasty. We retrospectively reviewed a single surgeon's database for patients undergoing such surgery from May 2001 to June 2005 and identified 33 (34 knees). The 25 patients (26 knees) who had at least 6 years' follow-up formed our study group. We compared preoperative and final follow-up Knee Society Scores and radiographs. Mean Knee Society Scores had increased from 50 (range, 23-88) to 93 (range, 41-100), respectively. No patient required additional surgery. We conclude that, at midterm follow-up, patelloplasty appears to be a satisfactory option in the management of the patella in revision TKA.

Augmentation with transcortical wiring of an onlay-type prosthesis for a deficient patella during revision total knee arthroplasty

The management of patellae with a severe bony deficiency during revision total knee arthroplasty is a challenging problem. However, using a technique of augmentation with transcortical wiring of an onlay-type prosthesis allowed the authors to revise a deficient patellae successfully. After making the decision to revise the existing patellar component, the procedure was found to be technically straightforward. Furthermore, the procedure does not require sophisticated instruments, only an onlay-type prosthesis, cement and wires. This technique entails fixing wires to the three pegs of the patellar component, passing the wires through drill holes in the anterior cortex and, after compression of a cemented prosthesis, augmenting the fixation by twisting the wires anteriorly. We believe that stable fixation and painless articulation will be obtained with the described technique for deficient patellae.

Porous tantalum patellar components in revision total knee arthroplasty minimum 5-year follow-up

Revision total knee arthroplasty can be complicated by severe patellar bone loss, precluding the use of standard cemented patellar components. This study evaluated the midterm outcomes of porous tantalum (PT) patellar components. Twenty-three PT components were used in 6 men and 17 women (average age, 62 years). All patellae had less than 10-mm residual thickness. The PT shell was secured to host bone, and a 3-peg polyethylene component was cemented onto the shell. In 2 patients, the PT component was sutured directly to extensor mechanism. Average follow-up was 7.7 years (range, 5-10 years). At follow-up, the Knee Society scores for pain and function averaged 82.7 and 33.3, respectively, whereas the mean Oxford knee score was 32.6. Four patients underwent revision surgery. Survivorship was 19 (83%) of 23 patients. Porous tantalum patellar components can provide fixation where severe bone loss precludes the use of traditional implants. Failures were associated with avascular residual bone and fixation of components to the extensor mechanism.

In vivo outcomes of tissue-engineered osteochondral grafts

Tissue-engineered osteochondral grafts have been synthesized from a variety of materials, with some success at repairing chondral defects in animal models. We hypothesized that in tissue-engineered osteochondral grafts synthesized by bonding mesenchymal stem cell-loaded hydrogels to a porous material, the choice of the porous scaffold would affect graft healing to host bone, and the quality of cell restoration at the hyaline cartilage surface. Bone marrow-derived allogeneic mesenchymal stem cells were suspended in hydrogels that were attached to cylinders of porous tantalum metal, allograft bone, or a bioactive glass. The tissue-engineered osteochondral grafts, thus created were implanted into experimental defects in rabbit knees. Subchondral bone restoration, defect fill, bone ingrowth-implant integration, and articular tissue quality were compared between the three subchondral materials at 6 and 12 weeks. Bioactive glass and porous tantalum were superior to bone allograft in integrating to adjacent host bone, regenerating hyaline-like tissue at the graft surface, and expressing type II collagen in the articular cartilage.

Patellar management in revision total knee arthroplasty: is patellar resurfacing a better option?

The management of the patella during revision total knee arthroplasty (TKA) depends on the indication for revision, the type and stability of the patellar component in place, and availability of bone stock. We prospectively compared the clinical outcome and satisfaction rates in revision TKA patients managed with patellar resurfacing (n = 13, group I) to retention of the patellar component (n = 22, group II) or patelloplasty (n = 11, group III) at a minimum follow-up of 2 years. There were no differences in the improvement of Knee Society Scores, Short-Form 36 Scores, and satisfaction rates between the groups. There were no revision surgeries for patellar component failure or patellar fractures. Satisfactory results can be achieved using a variety of methods of patellar management in revision TKA by individualizing the treatment modality depending on the clinical scenario.

The cemented inset biconvex patella in revision knee arthroplasty

Evaluation of a cemented biconvex inset patellar component used in revision knee arthroplasty at minimum five year follow-up was undertaken. Of the initial cohort of 89 knees in 85 patients, two patellar implants were revised for aseptic loosening following a transverse fracture of the patella associated with avascular necrosis. A further four implants were judged radiographically loose. Aseptic loosening of the implant was strongly correlated with the presence of avascular necrosis radiographically. Fracture of the patellar bone remnant was associated with a radiographically measured thickness of residual patellar bone of less than 6 mm. Survivorship of the implant using aseptic revision as the endpoint was 98% at 10 years and 86% at 14 years given one late failure. We conclude that the cemented biconvex inset patellar component can give satisfactory results in revision of patellar components if avascular necrosis does not occur.

Case reports: Tantalum debris dispersion during revision of a tibial component for TKA

Porous tantalum nonmodular tibial components for TKA were introduced in 1999. We revised three well-fixed tantalum tibial trays. For removal, we used osteotomes and revision oscillating saw blades. Removal of the components was laborious and resulted in generation of abundant tantalum debris that seeded the periarticular soft tissues despite meticulous protection with gauze. The retained metallic debris that is visible on postoperative radiographs has the potential for generation of third-body wear. We alert the orthopaedic community about this phenomenon and recommend minimizing the use of motorized revision instruments for removal of trabecular metal implants.

How to address the patella in revision total knee arthroplasty

Patellar issues need to be carefully addressed during any revision TKA and the surgeon often faces the question of what to do with the patella at the time of revision. The choice of treatment is often made by balancing what is technically feasible with the risk of potential complications and takes into account the reason for the revision, the type of implant (i.e., metal-backing or all-polyethylene), the duration of implantation, the fixation, the stability, the sterilization technique, the wear, the presence of osteolysis, the compatibility with the femoral component, and most importantly the remaining bone stock. The various treatment options then include retention of the patellar component, revision of the patellar component, removal of the component with retention of the patellar bony shell (patelloplasty or resection arthroplasty), excision of the patella (partial or total patellectomy), secondary resurfacing, and reconstruction/augmentation of the patellar bone stock. Isolated patellar revision is associated with a high complication rate and recurrent failure when poor patellar tracking, incongruent designs and malalignment of the femoral and tibial components exist. Retention of a well-fixed all-PE (non-oxidized) patella is advocated where possible and revision of metal-backed patella is recommended (unless well fixed with poor bone stock). In the situation of a deficient patella, patelloplasty, augmentation procedures and very rarely patellectomy are other viable options.

Techniques for managing anatomic variations in primary total knee arthroplasty

Primary total knee arthroplasties have high success rates, but certain patient anatomic or other variations may adversely affect the performance or the clinical outcomes of these procedures. Various technologies and techniques have been developed in attempts to overcome these challenges. However, there is controversy concerning whether these innovations are beneficial. This article assessed the scientific evidence regarding the use of these technologies to address various anatomic variations by examining the complete body of literature. The anatomic variations that were examined included extra-articular deformities, bone deficiencies, ligamentous instability, post-patellectomy knees, patella baja, variations in bone size and high-flexion knees. Recommendations for each circumstance were presented based upon the available scientific evidence.

Isolated all-polyethylene patellar revisions for metal-backed patellar failure

The outcome of isolated patellar component revisions after metal-backed patellar failure is variable with satisfactory results reported from 78% to 100%. To supplement information in the literature we determined the failure rate and the functional outcome based on the Knee Society clinical and roentgenographic evaluation systems of isolated patellar component revisions after metal-backed patellar component failure. We retrospectively reviewed 27 patients with 28 isolated patellar component revisions for metal-backed patellar component failure performed between 1988 and 2005. Twenty-five knees in 24 patients were available for review with a minimum followup of 24 months (mean, 90 months; range, 24-210 months). All knees were revised with a cemented all-polyethylene patellar component and all tibial polyethylene components were routinely exchanged. One failure (4%) occurred 122.6 months after the isolated patellar component revision secondary to femoral and tibial component loosening. The average Knee Society knee score improved from 73 to 89 points, whereas the average Knee Society function score improved from 56 to 65. Our data confirm those in the literature suggesting a successful outcome can be achieved with an isolated patellar component revision for metal-backed patellar component failure.

LEVEL OF EVIDENCE

Level IV, retrospective case series. See the Guidelines for Authors for a complete description of levels of evidence.

Management of the deficient patella in revision total knee arthroplasty

There are a number of options available to manage the patella when revising a failed total knee arthroplasty. If the previous patellar component is well-fixed, undamaged, not worn, and compatible with the femoral revision component, then it can be retained. When a patellar component necessitates revision and is removed with adequate remaining patellar bone stock, an onlay-type all-polyethylene cemented implant can be used. Management of the patella with severe bony deficiency remains controversial. Treatment options for the severely deficient patella include the use of a cemented all-polyethylene biconvex patellar prosthesis, patellar bone grafting and augmentation, patellar resection arthroplasty (patelloplasty), performing a gull-wing osteotomy, patellectomy, or the use of newer technology such as a tantalum (trabecular metal) patellar prosthesis. Severe patellar bone deficiency is a challenging situation because restoration of the extensor mechanism, proper patellar tracking, and satisfactory anatomic relationships with the femoral and tibial components are critical for an optimal clinical outcome.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

The management of bone loss in revision total knee replacement

The management of bone loss in revision replacement of the knee remains a challenge despite an array of options available to the surgeon. Bone loss may occur as a result of the original disease, the design of the prosthesis, the mechanism of failure or technical error at initial surgery. The aim of revision surgery is to relieve pain and improve function while addressing the mechanism of failure in order to reconstruct a stable platform with transfer of load to the host bone. Methods of reconstruction include the use of cement, modular metal augmentation of prostheses, custom-made, tumour-type or hinged implants and bone grafting. The published results of the surgical techniques are summarised and a guide for the management of bone defects in revision surgery of the knee is presented.

Current state and future of joint replacements in the hip and knee

Joint replacements of the hip and knee are among the most clinically successful operations. According to figures compiled by the American Academy of Orthopaedic Surgeons, the number of primary total hip replacements performed in the USA was 220,000 in 2003. This was 38% more than in 1996 and this number is expected to rise to 572,000 (plus another 97,000 revisions) by 2030. The number of primary total knee replacements performed in 2003 was approximately 418,000 and is expected to rise exponentially with the increasing numbers of baby boomers and the aging population. Current research focuses not only on extending implant longevity, but also on improving function to meet the increased demands of today's patients, who are likely to be younger and more active than their predecessors two decades ago. Potential advancements in arthroplasty surgery include new, more wear-resistant bearing surfaces, porous metals to enhance osseointegration and replace lost bone stock, a clearer understanding of the biological processes associated with periprosthetic osteolysis, minimally invasive surgery and computer assisted surgery. Long-term studies are needed to establish the efficacy of these new technologies.

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.

Use of porous tantalum metaphyseal cones for severe tibial bone loss during revision total knee replacement

BACKGROUND

The best treatment method for large tibial bone defects during revision knee replacement has not been established. The purpose of this study was to determine the initial results obtained with a unique reconstructive implant, the porous tantalum metaphyseal cone, designed as an alternative treatment for severe tibial bone loss following total knee arthroplasty.

METHODS

Porous tantalum metaphyseal cones were implanted during fifteen revision total knee replacements in eight women and seven men who had an average age of 68.1 years at the time of the procedure. The patients had had an average of 3.5 prior total knee replacements. According to the Anderson Orthopaedic Research Institute bone defect classification, eight knees had a Type-3 defect and seven knees had a Type-2B bone defect. All patients were followed clinically and radiographically.

RESULTS

The patients were followed for an average of thirty-four months (range, twenty-four to forty-seven months). Overall, the average Knee Society clinical scores improved from 52 points preoperatively to 85 points at the time of the final follow-up. At the final follow-up evaluation, all fifteen porous metaphyseal cones showed evidence of osseointegration with reactive osseous trabeculation at points of contact with the tibia. There was no evidence of loosening or migration of any of these tibial reconstructions at the time of final follow-up.

CONCLUSIONS

At the time of short-term follow-up, the porous tantalum metaphyseal tibial cones effectively provided structural support for the tibial implants in this series. The potential for long-term biologic fixation may provide durability for these tibial reconstructions. Long-term follow-up and comparison with alternative reconstructive techniques will be required to evaluate the true effectiveness of this treatment approach.

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.

Porous tantalum patellar augmentation: the importance of residual bone stock

Trabecular metal augmentation of bone defects has been associated with favorable bone ingrowth. Animal studies also suggest fibrous tissue attachment to trabecular metal can be achieved. We treated 16 patients with total knee arthroplasty (18 knees) with severe patellar bone loss using trabecular metal patellar reconstruction. The patients were divided into two groups based on the amount of residual patellar bone stock present at the time of surgery: Group 1 (six patients, seven knees) with no patellar bone stock and Group 2 (10 patients, 11 knees) in whom at least 50% of the patellar component surface was covered by host bone. All seven patellar components in Group 1 loosened within 1 year. Two of these developed necrosis of the extensor mechanism leading to extensor mechanism discontinuity. One component in Group 2 became infected and loosened, whereas the remaining 10 components remained stable at minimum 12-month followup. Our results suggest stable fixation of a trabecular metal patellar component can be achieved when residual bone is present for implant fixation, but early loosening is likely to occur when soft tissue is used for fixation to the implant.

Bacterial adherence to tantalum versus commonly used orthopedic metallic implant materials

OBJECTIVES

Evaluation of bacterial adhesion to pure tantalum and tantalum-coated stainless steel versus commercially pure titanium, titanium alloy (Ti-6Al-4V), and grit-blasted and polished stainless steel.

DESIGN

Experimental in vitro cell culture study using Staphylococcus aureus and Staphylococcus epidermidis to evaluate qualitatively and quantitatively bacterial adherence to metallic implants.

METHODS

A bacterial adhesion assay was performed by culturing S. aureus (ATCC 6538) and S. epidermidis (clinical isolate) for one hour with tantalum, tantalum-coated stainless steel, titanium, titanium alloy, grit-blasted and polished stainless steel metallic implant discs. Adhered living and dead bacteria were stained using a 2-color fluorescence assay. Adherence was then quantitatively evaluated by fluorescence microscopy and digital image processing. Qualitative adherence of the bacteria was analyzed with a scanning electron microscope. The quantitative data were related to the implant surface roughness (Pa-value) as measured by confocal laser scanning microscopy.

RESULTS

Bacterial adherence of S. aureus varied significantly (p = 0.0035) with the type of metallic implant. Pure tantalum presented with significantly (p < 0.05) lower S. aureus adhesion compared to titanium alloy, polished stainless steel, and tantalum-coated stainless steel. Furthermore, pure tantalum had a lower, though not significantly, adhesion than commercially pure titanium and grit-blasted stainless steel. Additionally, there was a significantly higher S. aureus adherence to titanium alloy than to commercially pure titanium (p = 0.014). S. epidermidis adherence was not significantly different among the tested materials. There was no statistically significant correlation between bacterial adherence and surface roughness of the tested implants.

CONCLUSIONS

Pure tantalum presents with a lower or similar S. aureus and S. epidermidis adhesion when compared with commonly used materials in orthopedic implants.

CLINICAL IMPLICATION

Because bacterial adhesion is an important predisposing factor in the development of clinical implant infection, tantalum may offer benefits as an adjunct or alternative material compared with current materials commonly used for orthopedic implants.

Experimental and clinical performance of porous tantalum in orthopedic surgery

Porous tantalum, a new low modulus metal with a characteristic appearance similar to cancellous bone, is currently available for use in several orthopedic applications (hip and knee arthroplasty, spine surgery, and bone graft substitute). The open-cell structure of repeating dodecahedrons is produced via carbon vapor deposition/infiltration of commercially pure tantalum onto a vitreous carbon scaffolding. This transition metal maintains several interesting biomaterial properties, including: a high volumetric porosity (70-80%), low modulus of elasticity (3MPa), and high frictional characteristics. Tantalum has excellent biocompatibility and is safe to use in vivo as evidenced by its historical and current use in pacemaker electrodes, cranioplasty plates and as radiopaque markers. The bioactivity and biocompatibility of porous tantalum stems from its ability to form a self-passivating surface oxide layer. This surface layer leads to the formation of a bone-like apatite coating in vivo and affords excellent bone and fibrous in-growth properties allowing for rapid and substantial bone and soft tissue attachment. Tantalum-chondrocyte composites have yielded successful early results in vitro and may afford an option for joint resurfacing in the future. The development of porous tantalum is in its early stages of evolution and the following represents a review of its biomaterial properties and applications in orthopedic surgery.

Management of bone loss: augments, cones, offset stems

Trabecular metal augmentation has added new treatment options for severe proximal tibial bone defects in revision knee arthroplasty. Porous tantalum tibial cones provide mechanical support for the tibial component and have the potential for long-term biologic fixation. These cones facilitate restoration of the proximal tibia metaphysis in Type 2 and 3 defects. Ten tantalum tibial cones were press-fit into the prepared cavitary defect of a series of revision knee arthroplasties. Voids between the cone and host bone were filled with morselized grafting material. The core tibial component was cemented into the implanted tibial cone; fixation was enhanced with stem extensions, which were press-fit in four knees and cemented in six knees. Extensions ranged from 75-200 mm with length dependent upon the residual bone quality. Offset stems were used in 3 tibias. At follow-up (average 10 months), radiographic evaluation revealed no evidence of loosening or change in position. Strength, range of motion, and stability were comparable to previously reported series of revision arthroplasties. Trabecular metal cones can help reconstruct large cavitary defects and, along with stem extensions and offset stems, may eliminate the need for extensive bone grafting or structural allograft in revision knee arthroplasty.

LEVEL OF EVIDENCE

Therapeutic study, level V (expert opinion). See the Guidelines for Authors for a complete description of levels of evidence.

Revision of the patella with deficient bone using a biconvex component

Revision surgery on a failed patellar component can be difficult because of deficient residual bone that may compromise the functional outcome of the revision. We reviewed 20 knees in 20 patients in whom the residual patellar bone was less than 10 mm at the time of revision and used the Genesis Biconvex Patella implant to reconstruct the patella. The patients were followed up for an average of 34 months (range, 24-65 months), and were followed up clinically and radiographically by Knee Society criteria. Patellar revisions and complications were noted and standard radiographic studies to ascertain radiolucent lines and patella/patellar component thickness were evaluated. The Knee Society Scores improved from an average of 45 points to 89 points. Function scores improved from an average of 47 points to 65 points. None of the patients has required revision surgery and no patellar fractures have been seen. Radiographs showed complete lucencies at the cement-bone interface in two knees. The mean residual central patella bone thickness was 6.5 mm and the average postoperative composite thickness was 14.5 mm. The data indicate that the use of the Genesis Biconvex Patella implant is a satisfactory method of treating revision of the patella when there is major bone deficiency.

LEVEL OF EVIDENCE

Retrospective study, Level IV-1 (case study). See the Guidelines for Authors for a complete description of levels of evidence.