A micro-architecturally biomimetic collagen template for mesenchymal condensation based cartilage regeneration.

The unique arcade-like orientation of collagen fibers enables cartilage to bear mechanical loads. In this study continuous-length aligned collagen threads were woven to emulate the interdigitated arcade structure of the cartilage. The weaving pattern provided a macropore network within which micromass cell pellets were seeded to take advantage of mesenchymal condensation driven chondrogenesis. Compression tests showed that the baseline scaffold had a modulus of 0.83±0.39MPa at a porosity of 80%. The modulus of pellet seeded scaffolds increased by 60% to 1.33±0.37MPa after 28days of culture, converging to the modulus of the native cartilage. The scaffolds displayed duress under displacement controlled low-cycle fatigue at 15% strain amplitude such that load reduction stabilized at 8% after 4500 cycles of loading. The woven structure demonstrated a substantial elastic recoil where 40% mechanical strain was close to completely recovered following unloading. A robust chondrogenesis was observed as evidenced by positive staining for GAGs and type II collagen and aggrecan. Dimethyl methylene blue and sircol assays showed GAGs and collagen productions to increase from 3.36±1.24 and 31.46±3.22 at day 3 to 56.61±12.12 and 136.70±12.29µg/µg of DNA at day 28 of culture. This woven collagen scaffold holds a significant potential for cartilage regeneration with shorter in vitro culture periods due to functionally sufficient mechanical robustness at the baseline. In conclusion, the mimicry of cartilage's arcade architecture resulted in substantial improvement of mechanical function while enabling one of the first pellet delivery platforms enabled by a macroporous network. STATEMENT OF SIGNIFICANCE: Mesenchymal condensation is critical for driving chondrogenesis, making high density cell seeding a standard in cartilage tissue engineering. Efforts to date have utilized scaffold free delivery of MSCs in pellet form. This study developed a macroporous scaffold that is fabricated by weaving highly aligned collagen threads. The scaffold can deliver high density cell condensates while providing mechanical stiffness comparable to that of cartilage. The scaffold also mimicked the arcade-like orientation of collagen fibers in cartilage. A highly robust chondrogenesis was observed in this mesenchymal cell pellet delivery system. Baseline mechanical robustness of this scaffold system will enable delivery of cell pellets as early as three days.

Implant Size Availability Affects Reproduction of Distal Femoral Anatomy.

A total knee arthroplasty system offers more distal femoral implant anterior-posterior (AP) sizes than its predecessor. The purpose of this study is to investigate the impact of increased size availability on an implant system's ability to reproduce the AP dimension of the native distal femur. We measured 200 cadaveric femora with the AP-sizing guides of Zimmer (Warsaw, IN) NexGen (8 sizes) and Zimmer Persona (12 sizes) total knee arthroplasty systems. We defined "size deviation" as the difference in the AP dimension between the anatomic size of the native femur and the closest implant size. We defined satisfactory reproduction of distal femoral dimensions as < 1 mm difference between the implant and native femur size. The NexGen system was associated with a mean 0.46 mm greater implant size deviation than Persona (p < 0.001). When using a 1 mm size deviation as a cutoff for satisfactory replication of the native distal femoral anatomy, 85/200 specimens (42.5%) were a poor fit by NexGen, but a satisfactory fit by Persona. Only 1/200 specimens (0.5%) was a poor fit by Persona, but a satisfactory fit by NexGen (p < 0.001). The novel knee system with 12 versus 8 sizes reproduces the AP dimension of the native distal femur more closely than its predecessor. Further study is needed to determine the clinical impact of these differences.

Important Differences Exist in Posterior Condylar Offsets in an Osteological Collection of 1,058 Femurs.

Posterior condylar offset (PCO) has important implications in total knee arthroplasty (TKA) function and design. In an osteological study of 1,058 femurs, we measured PCO using two separate techniques with a 3D digitizer. Measurements were standardized for the size of the femur. The medial PCO was greater than lateral PCO (32.6mm vs. 31.2mm, P<0.0001). In 53% of individuals, the medial PCO differed between sides by more than 2mm. Age did not affect standardized medial or lateral PCO. Compared with African-Americans, Caucasians had a larger standardized medial (1.3mm vs. 1.2mm, P=0.006) and lateral (1.1mm vs. 1.0mm, P=0.004) PCOs. The standardized medial (1.2mm vs. 1.3mm, P=0.073), and lateral (1.1mm vs. 1.1mm, P=0.098), PCO did not differ between men and women, respectively.

Machine oil inhibits the osseointegration of orthopaedic implants by impairing osteoblast attachment and spreading.

The most important factor contributing to short-term and long-term success of cementless total joint arthroplasties is osseointegration. Osseointegration leads to a direct structural and functional connection between living bone and the surface of an implant. Surface contaminants may remain on orthopaedic implants after sterilization procedures and impair osseointegration. For example, specific lots of hip replacement Sulzer Inter-OP(TM) acetabular shells that were associated with impaired osseointegration and early failure rates were found to be contaminated with both bacterial debris and machine oil residues. However, the effect of machine oil on implant integration is unknown. Therefore, the goal of this study was to determine if machine oil inhibits the osseointegration of orthopaedic implants. To test this hypothesis in vivo we used our murine model of osseointegration where titanium alloy implants are implanted into a unicortical pilot hole in the mid-diaphysis of the femur. We found that machine oil inhibited bone-to-implant contact and biomechanical pullout measures. Machine oil on titanium alloy discs inhibited early stages of MC3T3-E1 osteogenesis in vitro such as attachment and spreading. Inhibition of osteoblast attachment and spreading occurred in both areas with and without detectable oil. Osteoblast growth was in turn inhibited on discs with machine oil due to both a decrease in proliferation and an increase in cell death. Later stages of osteogenic differentiation and mineralization on titanium alloy discs were also inhibited. Thus, machine oil can inhibit osseointegration through cell autonomous effects on osteoblast cells. These results support routine testing by manufacturers of machine oil residues on orthopaedic implants.

Predictors of range of motion in patients undergoing manipulation after TKA.

BACKGROUND: Knee stiffness or limited range of motion (ROM) after total knee arthroplasty (TKA) may compromise patient function. Patients with stiffness are usually managed with manipulation under anesthesia (MUA) to improve ROM. However, the final ROM obtained is multifactorial and may depend on factors such as comorbidities, implant type, or the timing of MUA. QUESTIONS/PURPOSES: We asked whether diabetes mellitus, implant type, and the interval between TKA and MUA influenced post-MUA ROM. METHODS: From a group of 2462 patients with 3224 TKAs performed between 1999 and 2007 we retrospectively reviewed 96 patients with 119 TKAs (4.3%) who underwent MUA. We determined the presence of diabetes mellitus, implant type, and the interval between TKA and MUA. RESULTS: The average increase in ROM after MUA was 34°. Patients with diabetes mellitus experienced lower final ROM after MUA (87.5° versus 100.3°) as did patients with cruciate-retaining (CR) prostheses versus posterior-stabilized (92.3° versus 101.6°). The interval between TKA and MUA inversely correlated with final ROM with a decrease after 75 days. CONCLUSIONS: Most patients experience improvements in ROM after MUA. Patients with diabetes mellitus or CR prostheses are at risk for lower final ROM after MUA. Manipulation within 75 days of TKA is associated with better ROM.

Adherent lipopolysaccharide inhibits the osseointegration of orthopedic implants by impairing osteoblast differentiation.

Osseointegration is the process by which an orthopedic implant makes direct bone-to-implant contact and is crucial for the long-term function of the implant. Surface contaminants, such as bacterial debris and manufacturing residues, may remain on orthopedic implants after sterilization and impair osseointegration. For example, specific lots of implants that were associated with impaired osseointegration and high failure rates were discovered to have contaminants including bacterial debris. Therefore, the goals of this study were to determine if bacterial debris exists on sterile orthopedic implants and if adherent bacterial debris inhibits the osseointegration of orthopedic implants. We found that debris containing lipopolysaccharide (LPS) from Gram-negative bacteria exists on both sterile craniofacial implants and wrist implants. Levels of bacterial debris vary not only between different lots of implants but within an individual lot. Using our murine model of osseointegration, we found that ultrapure LPS adherent to the implants inhibited bone-to-implant contact and biomechanical pullout measures. Analysis of osseointegration in knock-out mice demonstrated that adherent LPS inhibited osseointegration by signaling through its primary receptor, Toll-like receptor 4, and not by signaling through Toll-like receptor 2. Ultrapure LPS adherent to titanium alloy discs had no detectable effect on early stages of MC3T3-E1 osteogenesis in vitro such as attachment, spreading or growth. However, later stages of osteogenic differentiation and mineralization were inhibited by adherent LPS. Thus, LPS may inhibit osseointegration in part through cell autonomous effects on osteoblasts. These results highlight bacterial debris as a type of surface contaminant that can impair the osseointegration of orthopedic implants.

Micrometer scale guidance of mesenchymal stem cells to form structurally oriented cartilage extracellular matrix.

Tissue engineering is a possible method for long-term repair of cartilage lesions, but current tissue-engineered cartilage constructs have inferior mechanical properties compared to native cartilage. This problem may be due to the lack of an oriented structure in the constructs at the microscale that is present in the native tissue. In this study, we utilize contact guidance to develop constructs with microscale architecture for improved chondrogenesis and function. Stable channels of varying microscale dimensions were formed in collagen-based and polydimethylsiloxane membranes via a combination of microfabrication and soft-lithography. Human mesenchymal stem cells (MSCs) were selectively seeded in these channels. The chondrogenic potential of MSCs seeded in these channels was investigated by culturing them for 3 weeks under differentiating conditions, and then evaluating the subsequent synthesized tissue for mechanical function and by type II collagen immunohistochemistry. We demonstrate selective seeding of viable MSCs within the channels. MSC aligned and produced mature collagen fibrils along the length of the channel in smaller linear channels of widths 25-100 µm compared to larger linear channels of widths 500-1000 µm. Further, substrates with microchannels that led to cell alignment also led to superior mechanical properties compared to constructs with randomly seeded cells or selectively seeded cells in larger channels. The ultimate stress and modulus of elasticity of constructs with cells seeded in smaller channels increased by as much as fourfolds. We conclude that microscale guidance is useful to produce oriented cartilage structures with improved mechanical properties. These findings can be used to fabricate large clinically useful MSC-cartilage constructs with superior mechanical properties.

An initial experience with hip resurfacing versus cementless total hip arthroplasty.

BACKGROUND: Hip resurfacing is an alternative to total hip arthroplasty. QUESTIONS/PURPOSE: We aimed to compare an experienced hip surgeon's initial clinical results of hip resurfacing with a new cementless total hip arthroplasty (THA). METHODS: The first 55 consecutive hip resurfacing arthroplasties were compared to 100 consecutive cementless THAs using a cylindrical tapered femoral stem. The learning curve between the two procedures was compared utilizing the incidence of reoperation, complications, Harris Hip Scores (HHS), and implant survivorship. RESULTS: The reoperation rate was significantly higher (p = 0.019) for hip resurfacing (14.5%) versus THA (4%). The overall complication rate between the two groups was not significantly different (p = 0.398). Preoperative HHS were similar between the two groups (p = 0.2). The final mean HHS was similar in both the resurfacing and THA groups (96 vs. 98.3, respectively, p < 0.65). Kaplan-Meier survival analysis with an endpoint of reoperation suggests complications occurred earlier in the resurfacing group versus the THA group (log-rank test, p = 0.007). CONCLUSIONS: In comparison to our initial experience with a cementless THA stem, operative complications occur earlier and more often after hip resurfacing during the learning period. The clinical outcomes in both groups however are similar at 5 year follow-up.

Retrieval analysis of Harris-Galante I and II acetabular liners in situ for more than 10 years.

BACKGROUND AND PURPOSE: There have been few reports documenting the wear and oxidation performance of the polyethylene bearing surface of HGPI and HGPII THA devices. We evaluated retrieved HGPI and HGPII acetabular liners that had been in situ for more than 10 years and determined whether there was a relationship between clinical and radiographic factors, surface damage, wear, and oxidation. MATERIALS AND METHODS: 129 HGPI and II acetabular liners with implantation times of > 10 years were retrieved at 4 institutions between 1997 and 2010. The liners were made from a single resin and were gamma radiation-sterilized in air. Surface damage, linear wear, and oxidation index (OI) were assessed. Differences in clinical and radiographic factors, surface damage, linear wear, and OI for the 2 designs were statistically evaluated separately and together. RESULTS: Articular surface damage and backside damage was similar in the 2 designs. The linear penetration rate was 0.14 (SD 0.07) mm/year for the HGPI liners and 0.12 (SD 0.08) mm/year for the HGPII liners. For both cohorts, the rim had a higher OI than the articular surface. 74% of the liners had subsurface cracking and 24% had a complete fracture through the acetabular rim. INTERPRETATION: Despite modification of the HGP locking mechanism in the HGPII design, dissociation of the liner from the acetabular shell can still occur if fracture of the rim of the liner develops due to oxidative degradation.

Surface contaminants inhibit osseointegration in a novel murine model.

Surface contaminants, such as bacterial debris and manufacturing residues, may remain on orthopedic implants after sterilization procedures and affect osseointegration. The goals of this study were to develop a murine model of osseointegration in order to determine whether removing surface contaminants enhances osseointegration. To develop the murine model, titanium alloy implants were implanted into a unicortical pilot hole in the mid-diaphysis of the femur and osseointegration was measured over a five week time course. Histology, backscatter scanning electron microscopy and X-ray energy dispersive spectroscopy showed areas of bone in intimate physical contact with the implant, confirming osseointegration. Histomorphometric quantification of bone-to-implant contact and peri-implant bone and biomechanical pullout quantification of ultimate force, stiffness and work to failure increased significantly over time, also demonstrating successful osseointegration. We also found that a rigorous cleaning procedure significantly enhances bone-to-implant contact and biomechanical pullout measures by two-fold compared with implants that were autoclaved, as recommended by the manufacturer. The most likely interpretation of these results is that surface contaminants inhibit osseointegration. The results of this study justify the need for the development of better detection and removal techniques for contaminants on orthopedic implants and other medical devices.

Nondestructive evaluation of hydrogel mechanical properties using ultrasound.

The feasibility of using ultrasound technology as a noninvasive, nondestructive method for evaluating the mechanical properties of engineered weight-bearing tissues was evaluated. A fixture was designed to accurately and reproducibly position the ultrasound transducer normal to the test sample surface. Agarose hydrogels were used as phantoms for cartilage to explore the feasibility of establishing correlations between ultrasound measurements and commonly used mechanical tissue assessments. The hydrogels were fabricated in 1-10% concentrations with a 2-10 mm thickness. For each concentration and thickness, six samples were created, for a total of 216 gel samples. Speed of sound was determined from the time difference between peak reflections and the known height of each sample. Modulus was computed from the speed of sound using elastic and poroelastic models. All ultrasonic measurements were made using a 15 MHz ultrasound transducer. The elastic modulus was also determined for each sample from a mechanical unconfined compression test. Analytical comparison and statistical analysis of ultrasound and mechanical testing data was carried out. A correlation between estimates of compressive modulus from ultrasonic and mechanical measurements was found, but the correlation depended on the model used to estimate the modulus from ultrasonic measurements. A stronger correlation with mechanical measurements was found using the poroelastic rather than the elastic model. Results from this preliminary testing will be used to guide further studies of native and engineered cartilage.

Post damage in contemporary posterior-stabilized tibial inserts: influence of implant design and clinical relevance.

The mechanisms of damage at the polyethylene post in 3 contemporary tibial insert designs were evaluated and compared with a historical standard (Insall-Burstein II; Zimmer, Warsaw, Ind). One hundred five gamma sterilized posterior-stabilized tibial inserts were revised after an average of 4.7 years (0.05-13.6 years). Retrievals were classified according to their designs: Insall-Burstein II (n = 28); PFC (Johnson & Johnson, Raynham, Mass; n = 30); NexGen (Zimmer; n = 32); and Scorpio (Stryker Orthopaedics, Mahwah, NJ; n = 15). Reasons for revision and patient details were available. Surface damage scoring and photogrammetry were performed on all the retrieved tibial inserts. Oxidation analysis was carried out for traceable historical, gamma air-sterilized and conventional, gamma inert-sterilized tibial inserts (n = 61) with the use of infrared spectroscopy. The posts for all 3 contemporary designs exhibited damage similar to the historical controls. Articular, post, and backside damage scores significantly increased with implantation time. Post damage was insensitive to design and patient factors but was exacerbated by oxidation. An association between damage at the post and articular surface was also confirmed. Logistic models suggested an interaction between post damage, backside surface damage, and implant loosening.

Incidence of postthrombotic syndrome in patients undergoing primary total hip arthroplasty for osteoarthritis.

BACKGROUND: Postthrombotic syndrome (PTS) is a chronic condition in the lower extremity that develops after deep vein thrombosis (DVT). The incidence of PTS after total hip arthroplasty (THA) is not well established. QUESTIONS/PURPOSES: We (1) determined the incidence of PTS after DVT in patients undergoing primary THA for osteoarthritis; and (2) determined whether the incidence of PTS was greater in patients with DVT than without. METHODS: We retrospectively reviewed records of all 1037 patients who underwent primary THA for osteoarthritis during a 4-year period. All patients underwent postoperative screening ultrasound. We identified 21 (2%) patients with a DVT by ultrasound of whom 14 had a minimum 1-year followup (mean, 3.4 years; range, 1.0-6.0 years). PTS was diagnosed if any two of the six clinical signs were documented. RESULTS: Three of 14 patients with DVT had at least two signs consistent with PTS; two of these had a DVT proximal to the soleal arch. Three of 91 randomly matched patients undergoing THA without DVT had at least two signs of PTS. The incidence of developing PTS after THA appeared higher in patients with DVT than in patients without DVT. CONCLUSIONS: While we observed a difference between the incidence of PTS after THA in patients with and without DVT, that incidence was based on only three of 1037 patients with DVT after THA. PTS does not appear to be a major complication after DVT in patients undergoing THA. LEVEL OF EVIDENCE: Level III, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Revision of hip resurfacing arthroplasty.

Metal-on-metal (MOM) hip resurfacing has become an increasingly popular treatment for young, active patients with degenerative disease of the hip, as bearing surfaces with better wear properties are now available. One proposed advantage of resurfacing is its ability to be successfully revised to total hip arthroplasty (THA). In addition, radiographic parameters that may predict failure in hip resurfacing have yet to be clearly defined. Seven MOM resurfacing arthroplasties were converted to conventional THAs because of aseptic failure. Using Harris Hip Scores (HHS) and Short Form 12 (SF-12) questionnaire scores, we compared the clinical outcomes of these patients with those of patients who underwent uncomplicated MOM hip resurfacing. In addition, all revisions were radiographically evaluated. Mean follow-up periods were 51 months (revision group) and 43 months (control group). There was no significant difference between the 2 groups' HHS or SF-12 scores. There was no dislocation or aseptic loosening after conversion of any resurfacing arthroplasty. Valgus neck-shaft angle (P < .03) was associated with aseptic failure of MOM hip resurfacing. Conversion of aseptic failure of hip resurfacing to conventional THA leads to clinical outcomes similar to those of patients who undergo uncomplicated hip resurfacing. The orientation of the femur and the components placed play a large role in implant survival in hip resurfacing. More work needs to be done to further elucidate these radiographic parameters.

Bacterial pathogen-associated molecular patterns stimulate biological activity of orthopaedic wear particles by activating cognate Toll-like receptors.

Aseptic loosening of orthopaedic implants is induced by wear particles generated from the polymeric and metallic components of the implants. Substantial evidence suggests that activation of Toll-like receptors (TLRs) may contribute to the biological activity of the wear particles. Although pathogen-associated molecular patterns (PAMPs) produced by Gram-positive bacteria are likely to be more common in patients with aseptic loosening, prior studies have focused on LPS, a TLR4-specific PAMP produced by Gram-negative bacteria. Here we show that both TLR2 and TLR4 contribute to the biological activity of titanium particles with adherent bacterial debris. In addition, lipoteichoic acid, a PAMP produced by Gram-positive bacteria that activates TLR2, can, like LPS, adhere to the particles and increase their biological activity, and the increased biological activity requires the presence of the cognate TLR. Moreover, three lines of evidence support the conclusion that TLR activation requires bacterially derived PAMPs and that endogenously produced alarmins are not sufficient. First, neither TLR2 nor TLR4 contribute to the activity of "endotoxin-free" particles as would be expected if alarmins are sufficient to activate the TLRs. Second, noncognate TLRs do not contribute to the activity of particles with adherent LPS or lipoteichoic acid as would be expected if alarmins are sufficient to activate the TLRs. Third, polymyxin B, which inactivates LPS, blocks the activity of particles with adherent LPS. These results support the hypothesis that PAMPs produced by low levels of bacterial colonization may contribute to aseptic loosening of orthopaedic implants.

Intra-articular hyaluronans: the treatment of knee pain in osteoarthritis.

The etiology of pain in osteoarthritis is multifactoral, and includes mechanical and inflammatory processes. Intra-articular injections of hyaluronans (HAs) are indicated when non-pharmacological and simple analgesics have failed to relieve symptoms. The HAs appear to reduce pain by restoring both mechanical and biomechanical homeostasis in the joint. There are five FDA-approved injectable preparations of HAs: Hyalgan(®), Synvisc(®), Supartz(®), Orthovisc(®) and Euflexxa(®). They all appear to relieve pain from 4 to 14 weeks after injection and may have disease-modification properties. Although several randomized controlled trials have established the efficacy of this treatment modality, additional high quality randomized control studies with appropriate comparison are still required to clearly define the role of intra-articular HA injections in the treatment of osteoarthritis.

Revision total knee arthroplasty for aseptic and septic causes in patients with rheumatoid arthritis.

UNLABELLED: Revision total knee arthroplasty in patients with rheumatoid arthritis can be challenging. We asked whether we could confirm previously reported high failure rates following revision total knee arthroplasty in patients with rheumatoid arthritis. We therefore determined the Knee Society knee score and function scores, radiographic evidence of failure, and overall survival of the revision procedure in these patients. We retrospectively reviewed 39 patients with rheumatoid arthritis who underwent 45 TKA revisions from 1994 to 2006. Twenty-seven of the 45 TKA revisions were for mechanical failure of the prosthetic components and 18 for infection. Five of the 27 knees (19%) revised for mechanical failure subsequently failed a second time. Five of the 18 patients who underwent revision for infection died within 6 months and three of the remaining knees failed secondary to reinfection. Excluding the knees that failed, the average Knee Society knee score and function score improved in both subgroups. Two knees had radiographic evidence of nonprogressive tibial radiolucencies. The probability of survival for all knees (revision as the end point) was 76% +/- 9% at 5 years. We confirmed the previously reported high mortality and subsequent failure rates following revision total knee arthroplasty for both mechanical issues and infection in patients with rheumatoid arthritis and emphasize the potential difficulties in treating these patients. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Fibroblast growth factor-2 enhances proliferation and delays loss of chondrogenic potential in human adult bone-marrow-derived mesenchymal stem cells.

We compared human mesenchymal stem cells (hMSCs), expanded long term with and without fibroblast growth factor (FGF) supplementation, with respect to proliferation, and the ability to undergo chondrogenesis in vitro. hMSCs expanded in FGF-supplemented medium proliferated more rapidly than the control cells. Aggregates of FGF-treated cells exhibited chondrogenic differentiation at all passages tested although, in some preparations, differentiation was diminished after seventh passage. Aggregates made with control cells differentiated along the chondrogenic lineage after first passage but exhibited only marginal differentiation after fourth and failed to form cartilage after seventh passage. Microarray analysis of gene expression identified 334 transcripts differentially expressed in fourth passage control cells that had reduced chondrogenic potential, compared with the fourth passage FGF-treated cells that retained this capacity, and 243 transcripts that were differentially expressed when comparing them to the first passage control cells that were also capable of differentiating into chondrocytes. The intersection of these analyses yielded 49 transcripts differentially expressed in cells that exhibited chondrogenic differentiation in vitro compared with the cells that did not. Among these, angiopoietin 1, secreted frizzled-related protein 1, and six transmembrane epithelial antigen of the prostate 1 appear to be of higher relevance. These preliminary data must now be validated to verify whether different gene expression profiles translate into functional differences. In summary, these findings suggest that the chondrogenic potential of hMSCs is vulnerable to cell expansion and that care should be exercised when expanding these cells for cartilage tissue engineering applications. Supplementation with FGF-2 allows reaching target cell numbers more rapidly and extends the level of expansion within which these cells are useful for tissue-engineered cartilage repair.