Mechanical properties of a cemented porous implant interface.

BACKGROUND: Revision arthroplasty often requires anchoring of prostheses to poor-quality or deficient bone stock. Recently, newer porous materials have been introduced onto the market as additional, and perhaps better, treatment options for revision arthroplasty. To date, there is no information on how these porous metals interface with bone cement. This is of clinical importance, since these components may require cementing to other prosthesis components and occasionally to bone. METHODS: We created porous metal and bone cylinders of the same size and geometry and cemented them in a well-established standardized setting. These were then placed under tensile loading and torsional loading until failure was achieved. This permitted comparison of the porous metal/cement interface (group A) with the well-studied bone/cement interface (group B). RESULTS: The group A interface was statistically significantly stronger than the group B interface, despite having significantly reduced depth of cement penetration: it showed a larger maximum tensile force (effect size 2.7), superior maximum tensile strength (effect size 2.6), greater maximum torsional force (effect size 2.2), and higher rotational stiffness (effect size 1.5). INTERPRETATION: The newer porous implants showed good interface properties when cemented using medium-viscosity bone cement. The axial and rotational mechanical strength of a porous metal/cement interface appeared to be greater than the strength of the standard bone/cement interface. These results indicate that cementing of porous implants can provide great stability in situations where it is needed.

Tibial cementing in UKA: a three-dimensional analysis of the bone cement implant interface and the effect of bone lavage.

Loosening is a common cause for revision in cemented UKA. In a cadaver study, we analyzed the three-dimensional cement distribution under the tibial implant and the effect of bone lavage (pulsed lavage, syringe lavage) on maximum cement penetration and penetration volume. Analyses were determined by performing bone cuts in medio-lateral direction and converting this data into a 3D model. Pulsed lavage led to an increased mean maximum cement penetration 5.79 ± 2.63 mm and penetration volume 6471.34 ± 1156.43 mm(3) compared to syringe lavage 4.62 ± 2.61 mm, 5069.81 ± 1177.09 mm(3) (P<0.001; P<0.001). Our results show a complete cement mantle for both investigated lavage techniques. Cleansing the cancellous tibial bone bed using pulsed lavage is more effective than conventional syringe lavage and leads to a deeper cement penetration and lager cement penetration volume under the tibial component.

The influence of the femoral force application point on tibial cementing pressure in cemented UKA: an experimental study.

BACKGROUND: Aseptic loosening is the major cause for implant failure in cemented unicompartmental knee arthroplasty (UKA). Central positioning of the femoral pressure during the tibial cementation process is recommended to achieve equal pressure and a good cementation result. The aim of this study was to verify the central position of the femoral force application point (FFAP) at 45° flexion of the knee and to investigate the influence of ligament tension and cement penetration pressure (CPP) for UKA. MATERIALS AND METHODS: Cemented Oxford UKAs were performed in 24 human legs. CPP and ligament tension forces (LTF) were measured. The FFAP was measured in a standardised manner in relation to the tibial implant length on lateral digital X-rays. RESULTS: The FFAP at 45° of knee flexion is located at 53.5 % and is not significantly different from the FFAP at 0° (p = 0.768). The CPP shows mean values at the anterior portion of 13.97 kPa (SD 16.11), at the implant keel of 24.34 kPa (SD 25.21) and at the posterior portion of 36.58 kPa (SD 26.51). The LTF shows a mean value of 194.35 N (SD 83.77). CONCLUSION: The central position of the FFAP for the investigated cemented UKA with single radius femoral component at 45° flexion of the knee could be confirmed. A flexion angle of <45° does not influence the position of the FFAP significantly. More than 45° of flexion should be avoided because the FFAP shifts backwards significantly and may cause increased pressures posteriorly and therefore tilting of the component occurs during the cementation process.

Toxicity of polyhexanide and hydrogen peroxide on human chondrocytes in vitro.

The treatment of acute joint infections has an important impact on long-term outcome and remains an unsolved problem. The most frequent bacteria are staphylococci, streptococci, and gram-negative bacteria. In septic surgery, polyhexanide and hydrogen peroxide are the most frequently used local antiseptics. The aim of this study was to examine the hypothesis that antiseptics induce cell death of human chondrocytes after a short incubation time.Human chondrocytes were treated with different concentrations of polyhexanide and hydrogen peroxide. Toxicity analysis was determined by visualization of cell structure using light microscopy, lactate dehydrogenase release, and determination of living and total cell numbers after addition of polyhexanide and hydrogen peroxide. Light microscopic data revealed a defect cell structure after addition of both antiseptics. Lactate dehydrogenase activity showed a significant increase of enzyme expression after a short incubation with polyhexanide. The determination of vital chondrocytes showed a significant decrease of vital and total cell numbers after addition with polyhexanide and hydrogen peroxide.Both antiseptic solutions induce significant cell death of human chondrocytes after a short incubation time. Polyhexanide possibly has more toxic potential than hydrogen peroxide against human chondrocytes after an application >15 minutes. Therefore, both substances should only be applied for a short time (<15 minutes) and the joint irrigated to wash out the antiseptic substance prior to wound closure.

Toxicity of antiseptics against chondrocytes: what is best for the cartilage in septic joint surgery?

In septic joint surgery, the most frequently used antiseptics are polyhexanide, hydrogen peroxide and taurolidine. The aim of this study was to examine the effects of these antiseptics on viability of human chondrocytes. Our hypothesis was that antiseptics and supplemental irrigation with sodium chloride lavage are less toxic on human chondrocytes than treatment with antiseptics only. Primary human chondrocytes were isolated and cultured from six donated human knee joints. Polyhexanide, hydrogen peroxide or taurolidine were added to the cultures. Toxicity analysis was performed by visualisation of cell structure using light microscopy and LDH activity. The determination of vital cells and total cell numbers of chondrocytes treated with antiseptics partly followed by irrigation with sodium chloride solution was performed by using Casy Cell-Counter. Light microscopic data revealed a defect in cell structure after addition of antiseptics. We showed a significant increase of LDH enzyme activity after the treatment with polyhexanide or taurolidine. After treatment with antiseptics followed by sodium chloride solution a significant increase of vital and total cell numbers resulted in comparison with the chondrocytes that were only treated with antiseptics. The data show that treatment with polyhexanid, hydrogen peroxide or taurolidine induces cell death of human chondroctes in vitro. The application of sodium chloride solution after the treatment with polyhexanide and hydrogen peroxide possibly has a protective effect on chondrocyte viability.

Are patients' expectations of hip and knee arthroplasty fulfilled? A prospective study of 130 patients.

Total hip arthroplasty (THA) is the most successful procedure in orthopedic and trauma surgery. Patients' expectations of joint replacement surgery prior to and after the procedure are often discounted. This study investigated the expectations of patients before and 3 years after THA or total knee arthroplasty (TKA). A total of 130 patients (70 hips, 60 knees) received a modified FFbH-OA survey with 6 additional questions concerning patients' expectations before and 3 years after joint replacement surgery. The overall response rate was 78.8% (101 patients). Patients who underwent THA had a mean age of 63.7 years, and those who underwent TKA had a mean age of 67.4 years.Sixty-three percent of all respondents reported that their expectations had been fulfilled or exceeded 3 years postoperatively (THA, 65%; TKA, 61%). A high negative correlation in the THA group could be seen between patients' expectations and clinical scores: the lower the clinical score, the less the patient's expectations had been fulfilled. A statistically significant increase of change in personal relationships was found, as well as a statistically significant decrease in worries and less complications than had been expected before joint replacement.Thirty-seven percent of all respondents felt that their expectations regarding joint replacement had not been fulfilled. Looking at the results of this study, the 37% of patients whose expectations had not been fulfilled did not exhibit a lower postoperative functioning than those who were satisfied.

The UniSpacer™: correcting varus malalignment in medial gonarthrosis.

While options for operative treatment of leg axis varus malalignment in patients with medial gonarthrosis include several established procedures, such as unicompartmental knee arthroplasty (UKA), total knee arthroplasty (TKA) or high tibial osteotomy (HTO), there has been little focus on a less invasive option introduced more recently: the UniSpacer™ implant, a self-centering, metallic interpositional device for the knee. This study evaluates clinical and radiological results of the UniSpacer™, whether alignment correction can be achieved by UniSpacer™ arthroplasty and alignment change in the first five postoperative years. Anteroposterior long leg stance radiographs of 20 legs were digitally analysed to assess alignment change: two relevant angles and the deviation of the mechanical axis of the leg were analysed before and after surgery. Additionally, the change of the postoperative alignment was determined one and five years postoperatively. Analysing the mechanical tibiofemoral angle, a significant leg axis correction was achieved, with a mean valgus change of 4.7 ± 1.9°; a varus change occurred in the first postoperative year, while there was no significant further change of alignment seen five years after surgery. The UniSpacer™ corrects malalignment in patients with medial gonarthrosis; however, a likely postoperative change in alignment due to implant adaptation to the joint must be considered before implantation. Our results show that good clinical and functional results can be achieved after UniSpacer™ arthroplasty. However, four of 19 knees had to be revised to a TKA or UKA due to persistent pain, which is an unacceptably high revision rate when looking at the alternative treatment options of medial osteoarthritis of the knee.

Correlation of positioning and clinical results in Oxford UKA.

In a prospective clinical study, 59 patients with anteromedial osteoarthritis of the knee (61 knee joints) underwent minimally invasive medial Oxford unicompartmental arthroplasty phase 3. Clinical and radiographic examinations of 56 knees were carried out at five (4-7) years. American Knee Society (AKS) scores improved from mean 45.5 (20-80) points (knee score) and 55 (15-100) points (function score) before surgery to 90 (30-100) points in both scores after surgery. The position of each implant was determined on screened radiographs using an image intensifier. The implant position was analysed according to the Oxford X-ray rating system. We evaluated nine measures, and there was no detectable correlation between implant position and clinical result. However, long-term studies are needed before it is possible to elaborate an evidence-based guideline on positioning.

Macroscopic third-body wear caused by porous metal surface fragments in total hip arthroplasty.

Implants with surfaces of various porosities and pore sizes are in clinical use. This article demonstrates how macroscopic porous metal fragments can detach from the implant surface in total hip arthroplasty (THA) and cause significant third-body damage such as deep scratches and indentations in implants' bearing surfaces. Radiographs prior to revision surgery due to aseptic loosening of the acetabular component revealed the presence of numerous small metal fragments approximately 1 to 2 mm in size in the periarticular area. The size, shape, and material of the metal fragments (cobalt-chromium-molybdenum [CoCrMo]) indicated that they originated from the porous metal surface. In this case, the acetabular liner composite material consisted of two-thirds polyurethane and one-third aluminium oxide ceramic. The femoral head was made of aluminium oxide ceramic. The aluminium oxide femoral head, which had been in situ for 21 years, showed no signs of macroscopic indentations or scratches, suggesting that an aluminium oxide bearing surface, which is significantly harder than the CoCrMo debris, is not significantly affected by metal debris embedment in the counterface material. The polyurethane-aluminium oxide composite material used for the acetabular liner is not comparable to a traditional ceramic bearing surface material. Debris damaged the surface of and became embedded in the liner, causing accelerated wear of the femoral head. In porous metal surface THA, ceramic-on-ceramic bearing couples should, due to their superior hardness, be considered to prevent excessive wear, including debris embedment and scratching of the bearing surfaces, especially in revision cases.

Pulsed lavage reduces the incidence of radiolucent lines under the tibial tray of Oxford unicompartmental knee arthroplasty: pulsed lavage versus syringe lavage.

The aim of the study was to determine whether the incidence of radiolucencies can be reduced using pulsed lavage before cementing the tibia in unicompartmental knee arthroplasty (UKA). We prospectively studied a consecutive series of 112 cemented Oxford UKA in 100 patients in two centres. In group A (n = 56) pulsed lavage and in group B (n = 56) conventional syringe lavage was used to clean the cancellous bone. The same standardised cementing technique was applied in all cases. At a minimum follow-up of one year patients were evaluated clinically and screened radiographs were obtained. The cement bone interface under the tibial plateau was divided into four zones and evaluated for the presence of radiolucent lines. All radiographs were evaluated (n = 112), and radiolucencies in all four zones were found in two cases in group A (4%) and in 12 cases in group B (22%) (p = 0.0149). Cement penetration showed a median of 2.6 mm (group A) and 1.5 mm (group B) (p < 0.0001). We recommend the routine use of pulsed lavage in Oxford UKA to reduce the incidence of radiolucency and to improve long-term fixation.

Saw cuts in unicompartmental knee arthroplasty: an analysis of Sawbone preparations.

Unicompartmental knee arthroplasty (UKA) has become a frequently used treatment option for anteromedial osteoarthritis (OA) of the knee due to good clinical and functional results. However, serious complications like tibial plateau fractures have been reported. These can be associated with saw cuts during surgery. The purpose of this study was to analyse saw cuts during Sawbone preparations at instructional unicompartmental knee courses and to identify potential sources of surgical error. One hundred Sawbone preparations were performed by knee surgeons inexperienced with UKA. Sawing errors during preparation were analysed and quantified. Tibial and femoral errors can occur during preparation. At the proximal tibia three errors can be found: extended vertical cuts (A), extended horizontal cuts (B) and perforation of the posterior cortex. An ascending cut at the posterior femoral condyle (C) is possible during femoral preparation. Errors type A were found at a mean length of 2.4 mm+/-2.3 mm with a maximum value of 10.1 mm. In 18% errors of more than 4.0 mm were found. Type B errors showed an average value of 2.0 mm+/-1.7 mm with maximum values of 7.4 mm. Type C errors were found at a mean of 1.3 mm+/-1.0 mm (maximum value 5.1 mm). Our data showed that in 18% of the cases, vertical cutting errors of more than 4.0 mm occurred in inexperienced surgeons.

Fracture load for periprosthetic femoral fractures in cemented versus uncemented hip stems: an experimental in vitro study.

This cadaveric study examined fracture loads in cemented and uncemented hip stems. Additionally, individual data and bone quality were analyzed and correlated to fracture patterns and fracture load. Cemented or uncemented hip stems were implanted in a randomized fashion in 10 matched paired fresh-frozen femora (donor median age, 78 years, and donor median weight, 74.2 kg). Bone density was measured before the femurs were fractured under load (maximum load of 10,000 N), and fracture patterns were analyzed according to the Vancouver and Johansson classification systems. In the uncemented group, all of the femurs fractured with a median load of 2625 N (range, 1725-7647 N). In the cemented group, 5 femurs fractured with a median maximum load of 9127 N (range, 2845-10,000 N) and 5 femurs did not fracture with a maximum load of 10,000 N. Fracture load corresponded to 4 times and 8.8 times body weight in the uncemented and cemented groups, respectively. Fracture patterns corresponded to Vancouver type A fractures in uncemented stems and Vancouver type C fractures in cemented hip stems. Analysis showed a significant correlation between fracture load and bone density in the uncemented group, whereas there was no correlation in the cemented group. Patients with poor bone quality treated with an uncemented hip stem are at higher risk for periprosthetic fractures; therefore, we recommend cemented stems in this group of patients. Cementation appears to protect against periprosthetic fractures, probably from internal stiffening of the femoral cavity.