This study evaluates high power low frequency ultrasound transmitted via a flat vibrating probe tip as an alternative technology for meniscal debridement in the knee. A limitation of this technology is thermal damage in residual meniscal tissue. To compare tissue removal rate and thermal damage for a radiofrequency ablation device and an experimental ultrasound ablation device. Twelve bovine meniscal specimens were treated in an identical fashion with (a) a 3.75mm 50° bipolar radiofrequency wand, Arthrocare Super Multivac 50 Arthrowand (Arthrocare Corporation, Sunnyvale, CA), operated in a free-hand manner in accordance with manufacturers instructions (n=6), and (b) an experimental flat-tipped 3mm 20kHz ultrasound probe, suspended vertically in a 500N force-controlled experimental rig (n=6). Tissue removal rate (TRR), zone of thermal necrosis and zone of thermal alteration were calculated. Histological sections were prepared for each sample (H&E). Independent samples t-test was used to compare TRR, zone of thermal necrosis and zone of thermal alteration. Statistical analysis was performed using PASW Statistics (v.18, IBM SPSS Statistics, Chicago, IL, U.S.A.). The mean TRR for meniscal debridement by the radiofrequency device was 5.59±1.1mg/s. This compared with a mean TRR of 4.74±1.4mg/s for debridement with the ultrasound device at settings (p=0.259, NS). Mean depth of tissue removal using the radiofrequency device was 2.21±0.26mm compared to 3.75±0.25mm (p< 0.001, ?. 2. =0.09). Using the radiofrequency device, the mean depth of zone of thermal alteration was 1282±436µm, compared with 710±251µm for the force-controlled ultrasound device (p=0.29, ?. 2. =0.42). For the radiofrequency device, the mean depth of zone of thermal necrosis was 64±41µm versus 97±44µm for the ultrasound device (p=0.239, NS). We observed a trend towards an increased zone of thermal necrosis and a reduced zone of thermal alteration for the ultrasound device, when compared with the radiofrequency device. Ultrasonic debridement shows comparable thermal damage to existing radiofrequency meniscal debridement technology

Introduction. Hip resurfacing arthroplasty has gained popularity as an alternative for total hip arthroplasty. Usually, cemented fixation is used for the femoral component. However, each type of resurfacing design has its own recommended cementing technique. In a recent investigation the effect of various cementing techniques on cement mantle properties was studied. This study showed distinct differences in cement mantle volume, filling index and morphology. In this study, we investigated the effect of these cement mantle variations on the heat generation during polymerization, and its consequences in terms of thermal bone necrosis. Materials and methods. Two FEA models of resurfacing reconstructions were created based on CT-data of in vitroimplantations (Fig 1). The two models had distinct differences with respect to the amount of cement that was used for fixation. The first model was based on an implantation with low-viscosity cement, with anchoring holes drilled in the bone, and suction applied to maximize cement penetration. The second model was based on an implantation with medium viscosity cement smeared onto the bone, with no holes and no suction, leading to a thin cement layer. Thermal analyses were performed of the polymerization process, simulating three different types of bone cement: Simplex P (Stryker), CMW3 (DePuy J&J) and Osteobond (Zimmer), with distinct differences in polymerization characteristics. The polymerization kinematics were based on data reported previously. During the polymerization simulations the cement and bone temperature were monitored. Based on the local temperature and time of exposure, the occurrence of thermal bone necrosis was predicted. The total volume of necrotic bone was calculated for each case. Results and discussion. The simulations showed distinct differences between the temperature distributions in the various models. The highest temperature was found in the CMW3 model with a large cement volume (Fig. 2, Table 1), while the Osteobond model with a thin cement mantle produced the lowest temperature rise in the bone. The necrotic bone volume was highest in the CMW3 model with a large cement mantle, while the lowest volume was found in the model with a thin cement layer (Table 1). Assuming that the bone that is being penetrated by cement also is affected by thermal and toxic necrosis, more than 70% of the bone inside the resurfacing implant may become necrotic. In contrast, when using a less invasive cementing technique, thermal necrosis can be reduced to approximately 20% of the volume inside the resurfacing implant. A large zone of necrotic bone at the cement-bone interface may have serious implications for the strength and stability of resurfacing arthroplasty. Conclusion. We conclude that the cementing technique and type of cement used for fixation of a resurfacing implant can dramatically affect the viability of the femoral bone, and therefore the survival of the reconstruction. Thermal necrosis may be reduced by minimizing cement penetration, although this may also have consequences for the mechanical stability

Total knee arthroplasty is an excellent operation and the results have been well documented for both cemented and cementless techniques. It is generally accepted that the results for cemented total knee outpace the results for cementless total knees. Despite this there remains great interest in developing systems and techniques that might allow predictable biologic fixation for knee arthroplasty. There is a long list of requirements that must be met to predictably allow bone ingrowth. These include viable bone, optimal pore size, optimal pore depth, optimal porosity, minimal gaps between bone and implant and minimal micromotion. Implant design is critical but it is proposed that operative techniques can help with some of these issues. We will discuss these operative issues during the surgical demo. These technique issues include: replication of normal posterior slope of the tibia, irrigation of all cuts to avoid thermal necrosis, and application of autologous bone chips to interface - “bone slurry”. These are obviously not all of the issues to consider but we feel they are some of the more important factors related to the cementless technique. The surgeon also has to be mindful of all of the other techniques that are essential to primary total knee arthroplasty. This demo will also utilise an ultracongruent bearing and with Vitamin E polyethylene

INTRODUCTION. Thermal necrosis of the femoral head, due to heat generation during cement polymerization, is a concern in hip resurfacing. Bone necrosis could cause fractures and/or implant loosening. Some authors. 1. found an inverse relationship between the size of the femoral component and the risk of revision after hip resurfacing. We postulate that smaller implants contain proportionally more cement than larger ones and that this could explain the effect of implant size on revision rate. As such, we investigated the relation between implant size and both, the average cement mantle thickness and the cement-filling index (fraction of cement volume and total volume within the implant). MATERIALS AND METHODS. Nineteen human femoral heads, collected during total hip arthroplasty, were machined for hip resurfacing with original ReCap (Biomet) instruments. The head sizes were chosen so we could implant two resurfacing heads for each even size between 40 and 56 mm, and one for size 58 mm. Each reamed head was provided with a number of anchoring holes proportional to the head size and was kept at 37°C. After pressure-lavage with water at 20°C, polymeric replicas of the original Recap implants were cemented according to a strict protocol. The exact amount of Refobacin Bone Cement LV (Biomet) needed to fill half the volume of the implant was pored into the resurfacing head and 2.5 minutes after starting cement mixing, the implant was manually impacted on the reamed femoral head. Specimens were scanned with computer tomography from the distal border of the resurfacing head to the top of the dome and CT-images were analyzed with an adapted version of validated segmentation software. 2. Based on gray values we identified four different elements: the polymeric stem and the outer shell of the implant, the cement-free cancellous bone and the cement mantle. Both, the average cement mantle thickness and the cement-filling index were calculated as described previously. 3. . RESULTS. The average cement mantle thickness was 2.63 mm (SD: 0.86; 1.65–4.60), the average cement-filling index was 36.65% (SD: 10.81; 21.52–57.60). Cement mantle thickness was poorly correlated with implant size (Pearson's correlation coefficient: −0.12; p=0.628; fig. 1), whereas the cement-filling index had a moderate to good correlation (Pearson's correlation coefficient: −0.51; p=0.026; fig. 2). CONCLUSION. Our results show that the cement mantle thickness is not related to implant size, but that smaller femoral resurfacing heads are easier to fill-up with cement than larger once. As such, we expect more thermal bone necrosis associated to the higher cement-filling index of smaller implants. This could explain their higher early revision rate

Computer-assisted navigation during total knee replacement has been advocated to improve component alignment and hence reduce failure rates and improve quality of life. The technique involves the placement of trackers via pins placed in both the femur and tibia throughout the surgery. It has been proposed that complication rates are higher in knee arthroplasty when computer navigation is used, compared to when it is not, due to increased risks from the pin tracker sites. Potential risks from pin sites include infection, fractures of the tibia or femur and pin site pain. In this study we present the post-operative complication rates related to pin tracker sites of computer navigated knee arthroplasty from a single surgeon at one centre. A database was compiled including all patients undergoing knee arthroplasty with computer navigation between January 2009 and December 2013 performed by a single surgeon at one centre. A retrospective study was undertaken having identified a total of 321 patients (642 pin sites) with 287 having undergone total knee replacement, 29 Uni-condylar knee replacement and five having undergone patellofemoral knee replacement. There 131 males and 190 females with a mean age of 69.4 [range 48–89]. There were no exclusions. The patient's notes were reviewed for any complications that occurred as a result of pin sites including infection, pin site pain and fracture. Only one patient (0.03%) was identified with a superficial pin site infection that was successfully managed with oral antibiotics only. There were no fractures or other complications identified in any of the other patients. In this series, the complication rates resulting from pin tracker sites was very low suggesting computer navigation does not increase the risks of knee arthroplasty. There were no cases of femoral or tibial fractures in this series, as have previously been reported. It is therefore likely that the technique of pin site placement is important in limiting the risk of complications. In this series a standard technique was used in all cases. Stab incisions are always used rather than a percutaneous technique and the wounds closed with clips and protected with dressings at the end of the surgery. Uni-cortical drilling is sufficient to provide stability of the trackers intra-operatively and minimises the risk of thermal necrosis therefore bi-cortical placement is avoided. Self-drilling pins are used on power and inserted perpendicular to the bone on high torque and low speed. The tourniquet is not inflated until after the pins have been inserted. It is thought that using this technique offers a safe method of pin tracker placement ensuring low complication rates

Total knee arthroplasty (TKA) is a successful operation associated with a high rate of clinical success and long-term durability. Cementless technology for TKA was first explored 30 years ago with the hope of simplifying the performance of the procedure and reducing an interface for potential failure by eliminating the use of cement. Poor implant design and the use of first generation biomaterials have been implicated in many early failures of these prostheses due to aseptic loosening and reflected the failure of either the tibial or patellar component. Despite this, many excellent intermediate and long-term series have clearly demonstrated the ability of cementless TKA to perform well with good to excellent survival, comparable to that of cemented designs. Lessons learned from the initial experiences with cementless technology in TKA have led to improvements in prosthetic design and materials development. One of the most innovative biomaterials introduced into orthopaedics for cementless fixation is porous tantalum. Compared to other commonly used materials for cementless fixation, porous tantalum has the highest surface friction against bone, optimizing initial stability at the implant-bone interface as a prerequisite for long-term stability of the reconstruction. At the 2013 AAOS Annual Meeting, Abdel presented the 5-year Mayo Clinic experience with cementless TKA utilizing a highly porous monoblock tibial component in 117 knees and found NO difference in survivorship compared to cemented fixation with a re-operation rate of 3.5% in both groups. They had no revisions for aseptic loosening. These early to intermediate results reflect our own experience with all cementless TKA utilizing a cobalt-chromium fibermesh femoral component, as well as monoblock porous tantalum tibial and patellar components with up to 11-year follow up. In that series of 115 patients, there was a 95.7% survival of implants, with no revisions of any components for aseptic loosening. Further advantages to using cementless fixation include the elimination of concerns with regard to monomer-induced hypotension, thermal necrosis from PMMA polymerization, and third body wear secondary to retained or fragmented cement. Savings are also realised from elimination of the costs of cement, a PMMA mixing system, cement gun, pulse lavage system, and irrigation solution. Perhaps the greatest cost savings is derived from the reduction in operating room time. At our institution–a Level 1 county trauma center with an orthopaedic residency training program–we typically spend an average of 19 minutes of operating room time for the cementing of a total knee arthroplasty. Our average time expended for insertion of all three cementless implants is 47 seconds–representing a significant savings in the hospital operating room time charge. From the standpoint of the patient, the shorter operating time reduces the time under anesthesia, the blood loss, the risk of venous thromboembolism, as well as the infection risk–optimizing the conditions for a reduction in post-operative complications, directly impacting a potential reduction in morbidity and mortality. Overall, the performance of all cementless TKA at our facility is cost-saving, is easily performed and reproduced by orthopaedic residents, and brings potential advantages to the patient in the form of a reduction in complications and an improvement in outcomes. Cementless fixation is the wave of the future, and the future is now

Thermal damage to bone related to the exothermic polymerisation of bone cement (PMMA) remains a concern. A series of studies were conducted to examine PMMA bone interface during cemented arthroplasty. In vitro and in vivo temperature distributions were performed in the laboratory and human and animal surgery. In vivo (10 patients) measurements of cement temperature during cementing of BHR femoral prosthesis using thermocouples. Intra-operative measurement of cement temperature in BHR in the presence of femoral head cysts was examined in patients. The BHR femoral heads were sectioned to assess cement mantle as well as position of thermocouples. An additional study was performed in sheep with PMMA implanted into cancellous defects. Thermocouples were used to monitor temperature in the cement as well as adjacent bone. Histology and CT was used to assess any thermal damage. The exothermic reaction of PMMA during polymerization does indeed result in an increase in temperature at the interface with bone. The in vivo study recorded a maximum temperature of 49.12C for approximately three minutes in the cancellous bone underneath the BHR prosthesis. This exposure is probably not sufficient to cause significant injury to the femoral head. The maximum temperature of the cement on the surface of the bone was 54.12C, whereas the maximum recorded in the cement in the mixing bowl was 110.2C. In the presence of artificial cysts within the bone, however, temperatures generated within the larger cysts, and even at the bone-cement interface of these cysts, reached levels greater than those previously shown to be harmful to bone. This occurred in one case even in the 1 cc cyst. Routine histology revealed a fibrous layer at the cement bone interface in the sheep study. Fluorescent microscopy demonstrated bone label uptake adjacent to the defect site. Histology did not reveal thermal necrosis in the defects in terms of bony necrosis. CT data was used to measure the amount of PMMA placed into each defect. This analysis revealed a range of volumes that did not seem to influence the histology. The heat of cement polymerisation in resurfacing as performed in our study is not sufficient to cause necrosis. This may reflect the ability of the body to rapidly conduct heat away by acting as a heat sink. The temperature-conducting properties of the metal prosthesis are also likely to be important

INTRODUCTION. The cement quantity and distribution within femoral hip resurfacings are important for implant survival. Too much cement could cause thermal bone necrosis during polymerisation. Insufficient cement and cement-implant interfacial gaps might favour mechanical loosening. Exposed cancellous bone within the implant, might facilitate debris-induced osteolysis. This study assessed the impact of the cementing technique on the cement mantle quality in hip resurfacing. METHODS. We prepared 60 bovine condyles for a 46 mm ReCap (Biomet) resurfacing and cemented polymeric replicas of the original implant using five different techniques: low-viscosity cement filling half the implant with and without suction (LVF+/−S), medium-viscosity cement spread inside the implant (MVF), medium-viscosity cement packed on bone (Packing) and a combination of both last techniques (Comb.). Half the specimens had six anchoring holes. Specimens were CT-scanned and analyzed with validated segmentation software [1]. We assessed, with an analysis of covariance, the effect of the cementing technique (fixed factor), the presence of anchoring holes (fixed factor) and the bone density (covariate) on the cement mantle quality. RESULTS. In contrast to both fixed factors, bone density had no significant effect on the cement mantle quality. Both LVF techniques, created a heterogeneous cement mantle with large quantities of cement especially in the dome of the implant (Fig. 1 & 2). Large areas of uncovered cancellous bone were found at the base (Fig. 2). Suction had no major effect. The MVF technique allowed a better control of the cement quantity (Fig. 1) but cement mantle heterogeneity and exposed cancellous bone distally persisted. With the combined technique, large cement quantities were found within the implant (Fig. 1), the cement mantle remained heterogeneous but the amount of uncovered bone distally decreased. Cement packing controlled the cement quantity and distribution within the implant best (Fig. 1 & 2). However, interfacial gaps [2] covered 10% of the proximal cement-implant interface and exposed bone distally could not be prevented (Fig. 2). When large quantities of cement were available (LVF+/−S and Comb.), anchoring holes allowed even more cement to be pressurised into the cancellous bone (Fig. 1). DISCUSSION & CONCLUSIONS. During implantation with a filling technique (LVF+/−S, MVF & Comb.), cement inside the implant was scraped along the reamed head and forced to accumulate proximally. This overfilled the dome and left bone exposed at the base. During cement packing, the air-filled implant scraped excessive cement from the reamed head. This resulted in the thinnest, most homogeneous cement mantle and avoided overfilling. However, air got trapped below the implant and formed interfacial gaps. Anchoring holes in cancellous bone of the reamed head should be avoided to prevent overfilling the reamed head with cement