The purpose of this study was to evaluate and to compare the mechanical stability of external fixation with and without ankle spanning fixation using a foot plate in an in-vitro model of periarticular distal tibia osteotomy/fracture.

Ten fresh frozen lower extremities (five pairs) with a simulated distal tibia osteotomy/fracture were stabilised with an Ilizarov hybrid fixator with and without a foot plate. All specimens were loaded using a servohydraulic load frame. Relative interfragmentary motions (vertical and horizontal translations, and rotation) were measured. Statistical analysis was performed as a paired t-test to compare the different frame constructs. A p<0.05 was considered indicative of a significant difference between fixator constructs.

The vertical displacement measured at the centre of the distal fragment under load with the foot plate was such that the bone fragments became closer together (-0.83±0.64 mm). Loading of specimens without the foot plate resulted in distraction of the distal fragment (2.57±0.97 mm). The difference was statistically significant (p<0.05). The horizontal displacement of distal fragment with (1.12±0.98 mm) was not significantly different from the motion without (1.19±1.23 mm) a foot plate and was in the anterior direction in both cases. Loading of the construct with the foot plate caused sagittal plane angulation of the fragments with the osteotomy/fracture gap opening anteriorly (-1.15±0.61 deg.). Loading of the construct without a foot plate resulted in sagittal plane angulation of fragments with the gap opening posteriorly (4.49±0.45 deg.). These motion differences were statistically significant (p<0.05). There was not a statistically significant difference between the order of testing the construct with a foot plate and the construct without it (p>0.05).

Fixators with ankle spanning using foot plates increase the mechanical stiffness of external fixation of periarticular distal tibia osteotomy/fracture.

Background: In the present study, the characteristics and mid-term to long-term outcomes of total knee arthroplasty (TKA) associated infections treated with different types of approaches were evaluated.

Methods: A retrospective study of the results of 71 infected TKA treated between August 1993 and August 2005. The data included medical records, gender, periprosthetic infection (PPI) classification, patients’ comorbidities, PPI diagnostic criteria, microbiology and histopathology results, surgical and antimicrobial therapy, treatment modality, complications, follow up, and treatment results.

Results: Median age was 70 years (range 43–88). Median follow-up 5.8 years (range 2–12). Thirty-three patients had multiple risk-factors for PPI. The main pathogens isolated were Coagulase-negative staphylococci 26 (37%), Staphylococcus aureus 16 (22.4%).

The treatment methods of TKA infection was two-stage exchange in 59 (83%), debridement and retention −5 (7.2%), arthrodesis −5 (7.2%), excision arthroplasty 2 (2.8%). At final followup, 17 knees (24%) had required reoperation: 10 knees (14%) -component removal for reinfection. Two knees were reinfected 3 times, three knees – two times. The median time to first reoperation for reinfection was 1.2 years (range, 0.04–2.5 years). By Kaplan-Meier survival analysis the estimated survivals free of reoperation for infection were 90.5% (confidence intervals, 85.3–96.1%) at 5 years and 82% (confidence intervals, 70.3–94.5%) at 10 years. The Knee Society scores: Pain scores, Functional scores, ROM improved.

Conclusions: TKA infections treatment is a difficult task leading to a high rate of unsatisfactory mid-term and long-term results. About one forth of patient require reoperation, 14% become reinfected in first 2.5 years. Half of reinfected patients get reinfected repeatedly. In most cases patients are reinfected with the same micro-organism but more virulent. TKA infection treatment option should be chosen according to the type of infection (acute or chronic), the duration of infection, the stability of the implant, the type of microorganism causing infection, bone quality and integrity, and the quality of the soft-tissue.

Introduction: To determine the stiffness characteristics of a new proposed hybrid fixator in comparison with more commonly used hybrid external fixators.

Methods: A prospective laboratory investigation was used to evaluate the null hypothesis that there are no differences in the mechanical stiffness between the new proposed hybrid fixator and the Ace-Fischer, DePuy-ACE, Warsaw, IN; Hoffmann II, Stryker Howmedica Osteonics, Rutherford, NJ; Synthes Hybrid, Synthes USA, Paoli, PA; EBI DynaFix®, EBI, Parsippany, NJ. Identical composite tibiae, after modeling OTA 41 – A 2.3 fracture, were fixed with the above fixators. Load-deformation behavior was compared between the different configurations under identical conditions of central-compression, medial compression-bending, posterior compression-bending, posterior-medial compression-bending and torsional loading. Stiffness values were calculated from the load deformation and the torque angle curves.

Results: The new proposed hybrid external fixator was stiffer than all the other fixators tested in all modes of testing, except for torsion. The Hoffman II, DePuyACE, EBI, and Synthes fixators were essentially equivalent in stiffness in all five modes of testing.

Conclusions: Decreasing the distance of the side bar to the center of the bone effectively shortens the length of the half-pins, which decreases their deflection during bending, and thus increases stiffness. We think that a better stiffness of new fixator than of others is due to a shorter distance between the bone surface and points of fixation of wires and half-pins. The proposed hybrid fixator corresponds to the contemporary requirements for external fixation: possibility to control the stiffness, easy to apply, comfortable for the patient (being light and simple).

Purpose: The objectives of this project were to compare four commercially available hybrid external fixator systems under multiple loading conditions, and to compare each system to an idealized «rigid» frame to distinguish between motion allowed by the pins and wires and motion allowed by frame deformation.

Methods: A mechanical testing investigation was performed using fifteen fiberglass composite tibias (Pacific Research Laboratories, Vashon Island, WA, USA) with a 2 cm proximal metaphyseal gap osteotomy (simulating OTA classification 41-A3.3) to test four hybrid systems (Ace-Fischer, DePuyACE, Warsaw, IN; Hoffmann II, Stryker Howmedica Osteonics, Rutherford, NJ; Synthes Hybrid, Synthes USA, Paoli, PA; EBI DynaFix®, EBI, Parsippany, NJ) and a custom built «rigid» frame. Setting: A biomechanics laboratory using a servohydraulic load frame (MTS Bionix 858, Minneapolis, MN). Measurements were made of the motion produced when loads were applied to the proximal tibia through a custom load plate.

Results: The only significant difference between commercial systems was in axial loading where the Ace-Fischer allowed less motion than the other frames. In all cases the «rigid» reference frame allowed significantly less motion than the commercial systems. Approximately 50% of the motion comes from frame deformation and 50% from deformation of the pins and wires.

Conclusions/Significance: There are few differences between commercially available hybrid external fixation systems for treating unstable proximal tibia fractures. Approximately half of the motion at the fracture site is due to bending deformation in asymmetric frame designs, which leads to unwanted angular and shear displacements at the fracture site.

Infection is one of the most disturbing and frightening complications of total knee arthroplasty (TKA). The purpose of the present study was to review the management and outcomes of infected total knee arthroplasty.

The management and outcomes in 71 patients with 71 infected TKA was reviewed. Two-stage reimplantation with 8 weeks of intravenous therapy between the stages was used in 49 patients. Twenty-four patients ended with an arthrodesis using external fixation or intramedulary (IM) nailing. A two-stage technique was used with IM nail arthrodesis. Infections after TKA associated with bone destruction and loss were treated using an antibiotic-impregnated cement rod-spacer. Two patients required amputation: one because of soft tissue necrosis around the knee, another because of recalcitrant infection. In two patients the antibiotic-impregnated cement rod-spacer was chosen as a definitive treatment. The re-infection rate was about 25%. In most cases of reinfection the pathogens were the same, but of higher virulence and resistance. Infection was eradicated in 85% of patients. More than half of patients ended up with a functional TKA (average function score was 86.5 points, average range of motion from 2 to 109 degrees). One third of patients had a solid fusion. The infection could not be eradicated in 15% of patients.

The management and outcomes of infected total knee arthroplasty depend on a rapid and accurate diagnosis. A clear and effective management algorithm should yield favorable outcomes according to well-defined criteria. The two-stage reimplantation is the treatment of choice for chronic periprosthetic knee infection. Knee arthrodesis can be an effective treatment option after the failure of a TKA due to infection.

Serological tests including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are frequently used in the preoperative workup to screen for periprosthetic infection (PPI) in total hip arthroplasty (THA). The cut-off points reported in the literature are arbitrarily chosen by investigators. Similarly, the values used in laboratories to distinguish elevated results vary from one institute to another. Therefore, we intended to define the appropriate cut-off points of ESR and CRP that can be used to differentiate infection from aseptic failure of THA.

A review of our joint registry database revealed that 515 THA revisions (131 infected cases) were performed during 2000–2005. Intraoperative samples for culture were taken in all cases. The criteria used for diagnosis of infection were a positive intraoperative culture on solid media, presence of an abscess or sinus tract that communicated with the joint, positive preoperative aspiration culture, and/or elevated fluid cell count and neutrophil differential of the aspirated fluid. Non-infected patients with confounding factors that can elevate ESR and CRP including collagen vascular disease, inflammatory arthropathy, malignancy, and urinary tract infection were excluded. Receiver operator curves were used to determine the ideal cut-off point for both ESR and CRP.

The mean value of ESR in the infected group (77mm/ hr) was significantly higher compared to that of the non-infected cohort (29mm/hr) (p=0.0001). Similarly, infected patients presented with a greater mean CRP (9.8 mg/dl) than their non-infected cohort (1.48 mg/ dl) (p=0.0001). The infection threshold for ESR was 45mm/hr with a sensitivity of 85% and specificity of 79%, while the optimal cut-off value for CRP was defined as 1.6 mg/dl which yielded a sensitivity of 86% and specificity of 83%.

The optimal threshold values we determined are higher than the arbitrarily chosen values cited in the literature for ESR (30mm/hr) and CRP (1mg/dl). Although it has been previously reported that the sensitivity and specificity of CRP are far greater than that of ESR, we found that the two tests have comparable diagnostic value.

One of the routinely used intraoperative tests for diagnosis of periprosthetic infection (PPI) is Gram stain that is reported to carry a very high specificity and a poor sensitivity. However, it is not known if the result of this test can vary according to the type of joint affected or the number of specimen samples collected. This study intended to examine the role of this diagnostic test in a large cohort of patients from single institution.

A review of our joint registry database revealed that 453 total knee arthroplasty (TKA) and 551 total hip arthroplasty (THA) of which 171 and 150 cases were respectively infected underwent revision surgery during 2000–2005 and had intraoperative cultures available for interpretation. A positive gram stain was defined as the visualisation of bacterial cells or ‘many leukocytes’ (> 5 per high power field) under the smear. The sensitivity, specificity, and predictive values of each individual diagnostic arm of Gram stain were determined. Combinations were performed in series that require both tests to be positive to confirm infection and in parallel that necessitate both tests to be negative to rule out infection. This analysis was performed for THA and TKA separately and later compared for each joint type.

The presence of organism cells and ‘many’ neutrophils on a Gram smear had high specificity (98%–100%) and positive predictive value (89%–100%) in both THA and TKA. The sensitivities (30%–50%) and negative predictive values (70%–79%) of the two tests were low as expected among both joint types. When the two tests were combined in series the specificity and positive predictive value were absolute (100%). The sensitivity (43%–64%) and the negative predictive value (82%) improved among both THA and TKA.

The presence of organisms or ‘many’ leukocytes on the Gram smear can confirm PPI in TJA. As expected, the sensitivity and negative predictive value of the two tests were low, and therefore infection could not be safely ruled out. Although the two diagnostic arms of Gram stain can be combined to achieve improved negative predictive value (82%), Gram stain continues to have poor value in ruling out PPI. With the advances in the field of molecular biology, novel diagnostic modalities need to be designed that can replace these traditional and poor tests.

INTRODUCTION: We have previously demonstrated the efficacy of a modified Ti-surface tethered with antibiotics in preventing bacterial colonization. It is not known if coverage of this surface with serum or other physiological material may hinder the bactericidal properties of such a surface.. The in vitro activity and efficacy of such a surface against S. aureus and S. epidermidis was tested following coverage of the surface with serum.

METHODS: Vancomycin was coupled to Ti6Al4V pins by aminopropylation, linker addition, and vancomycin coupling (VancTi). Bactericidal activity was tested in solutions of bacteria (Ci=1×104cfu/ml) incubated with pins±pre-incubation with fetal bovine serum (FBS). Anti fibronectin and anti-vancomycin antibodies were used to detect surface coating or modification. Bacteria were detected by fluorescent labeling (Syto9) or by direct counting after solubilization.

RESULTS: By immunofluorescence, pins were extensively covered with serum fibronectin which did not interfere with the diffuse, intense vancomycin staining. When incubated with S. epidermidis or S. aureus, VancTi showed little colonization compared to control pins (> 95% reduction in cfu).

DISCUSSION: In a physiological environment, implants will be coated with serum proteins. Activity of the VancTi was unaffected by this coating and maintained potent inhibition of bacterial colonization. We have described a surface modification that allows Ti implants to resist colonization and subsequent periprosthetic infection. Such surfaces hold great promise for the prevention and treatment of periprosthetic infections.

Introduction: We have previously described modification of Ti that renders the implant surface bactericidal and prevents bacterial colonization in vitro. This study evaluates the efficacy of the same surface in preventing periprosthetic infection in a small mammal model.

Methods: Control or VancTi rods were incubated with S. aureus (Ci=104CFU/mL) in TSB containing 0, 5×10-3, 4, or 100 μg/mL vancomycin at 37°C for 24h. Bacteria were detected by fluorescence (Live/Dead BacLight) and imaged by confocal microscopy. Resistance was tested by incubating control or VancTi rods with S. aureus for 0–8 weeks. Adherent bacteria were tested every 7 days on vancomycin screening agar (6μg/mL).

Results: Using a percutanous approach, the intercondylar region of the knee in rats were identified. The intrameduallry canal of the femur was retrograde reamed using an 18-gauge needle. Infection was induced by injection of 103 CFU S. aureus in 150uL of saline into the femoral canal followed by insertion of a 20 mm Ti implant. Animals were harvested at various time points. At harvest, animals were euthanized with CO2.. Detailed analysis including radiographic, micro-CT, histological, bacteriological, and clinical evaluation was performed.

Results: All animals showed signs of infection within the first few post-operative days with increased soft tissue swelling and limited mobility. At 1 week 75% of the animals showed radiographic signs of periprosthetic infection including periosteal reaction, abscess formation, widened canal, bone destruction, and formation of involucrum. PPI could be prevented in 92% of cases when modified Ti-Van was used. In one animal despite the use of antibiotic-tethered implant, PPI occurred partially due to the pin insertion penetrating the bone cortex.

Discussion: Biologically modified implants with bactericidal surface can have a promising role in management of periprosthetic infection. The modified implant described herein contains a nanoscale surface of covalently linked antibiotics that can potentially confer bactericidal properties throughout the life of the implant