Comparison of two arthroscopic pump systems based on image quality The effectiveness of arthroscopic pump systems has been investigated with either subjective measures or measures that were unrelated to the image quality . The goal of this study is to determine the performance of an automated pump in comparison to a gravity pump based on objective assessment of the quality of the arthroscopic view . Ten arthroscopic operations performed with a gravity pump and ten performed with an automated pump -LRB- FMS Duo system -RRB- were matched on duration of the surgery and shaver usage , type of operation , and surgical experience . Quality of the view was defined by means of the presence or absence of previously described definitions of disturbances -LRB- bleeding , turbidity , air bubbles , and loose fibrous tissue -RRB- . The percentage of disturbances for all operations was assessed with a time-disturbance analysis of the recorded operations . The Mann -- Whitney U test shows a significant difference in favor of the automated pump for the presence of turbidity only -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.015 -RRB- . Otherwise , no differences were determined -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- > 0.436 -RRB- . A new objective method is successfully applied to assess efficiency of pump systems based on the quality of the arthroscopic view . Important disturbances -LRB- bleeding , air bubbles , and loose fibrous tissue -RRB- are not reduced by an automated pump used in combination with a tourniquet . The most frequent disturbance turbidity is reduced by around 50 % . It is questionable if this result justifies the use of an automated pump for straightforward arthroscopic knee surgeries using a tourniquet . Introduction During arthroscopic surgery , the joint is continuously irrigated with saline fluid which is pressurized to create joint distension . The saline fluid flow removes disturbances in the arthroscopic view such as bleeding , air bubbles or synovial fluid . This improves the visibility of the arthroscopic view , which is an essential condition to perform an operation safe and fast . In this light , the quality of arthroscopic view has been defined as good or optimal if no disturbances are present -LSB- 11 -RSB- . In clinical practice , disturbances can not always be prevented and maintaining a clear view is sometimes difficult -LSB- 7 , 10 -RSB- . In a recent study performed by the authors , post-procedure analysis of 20 routinely performed arthroscopic knee procedures showed that 6 % -LRB- SD 4 % -RRB- of the total operation time was solely dedicated to obtaining a clear view . Since the number of arthroscopic procedures is large and still growing -LRB- 60,000 per year in the Netherlands -LSB- 8 -RSB- , and 1.7 million meniscectomies alone per year worldwide -LSB- 3 -RSB- -RRB- , reducing the operating time by optimizing the view would be desirable . The quality of the arthroscopic view is dependent on a number of factors such as the type of pump system , instruments , and condition of the joint -LSB- 11 -RSB- . In this study , the focus is on the type of pump system . The classical gravity pump and -LRB- automated -RRB- volumetric pumps are available for irrigation -LSB- 10 -RSB- . The main differences between these pumps are that the gravity pump causes a pressure due to a height difference caused by an elevated fluid bag and is manually controlled , whereas the volumetric pumps cause a fluid flow and have some type of automated pressure control . Since the automated pumps are regulated , in theory they should perform better in irrigation in the sense that the percentage of disturbed view over time should be less . In literature , the effectiveness of automated pump systems has been investigated -LSB- 2 , 4 -- 6 -RSB- . However , only subjective measures were used , such as visual clarity on a three-point scale or measures that were unrelated to the image quality , such as the number of fluid bags . The goal of this study is to determine the performance of an automated pump in comparison to the gravity pump based on objective assessment of the quality of the arthroscopic view . Therefore , a quantitative time-disturbance analysis was performed with uniquely described definitions for the different types of disturbances -LSB- 11 -RSB- . Methods Only routinely performed procedures were included such as meniscectomy , cyst removal , debridement of a partial rupture of the anterior cruciate ligament , and diagnostic arthroscopy . Cruciate ligament reconstructions were not included . The patients were not notified of the recordings , because the operation was not affected and the patients ' identities could not be traced from the videos . No power analysis could be performed for this study , because no information was available on the variation of the disturbances . In accordance with other studies , it was decided to use ten operations for each of the two pump systems -LRB- 20 in total -RRB- -LSB- 2 , 4 -RSB- . The matching criteria were the number of operations , the duration of the operations , the duration of shaver usage , the type of operation , and the working experience of the surgeons . Matching of the shaver duration was performed , because some disturbances were expected to occur more frequently when using the shaver . Besides , a shaver is often used to clarify the view by temporarily increasing the flow . All surgeons who performed the operations had the same education and comparable working experience . Ten arthroscopic knee procedures for which the gravity pump was used were recorded at 6 days within a time frame of 2 months . From the operations that met the inclusion criteria , ten were selected with randomization tables . Ten arthroscopic knee procedures performed with an automated pump were matched postoperatively to eliminate factors other than the irrigation pump systems that influence the arthroscopic view -LRB- Table 1 -RRB- . Table 1Matching of the two pump groups was performed based on the number of operations , the total duration of all operations , and the share of shaver usageOperationTime -LRB- min : s : frames -RRB- Shaver time -LRB- s -RRB- Gravity pump Cyst removal17 : 55:11114 Meniscectomy26 : 03:15363 Meniscectomy33 : 15:09288 Meniscectomy19 : 56:10416 Meniscectomy13 : 37:18313 Meniscectomy17 : 55:13508 Meniscectomy12 : 10:15153 Meniscectomy15 : 09:02150 Debridement partial rupture of anterior cruciate ligament16 : 30:03290 Diagnostic7 : 12:03 Total duration 179:45:2443:15:0 Shaver time as percentage of total duration -LRB- % -RRB- 24.1 Automated pump Meniscectomy30 : 37:11410 Meniscectomy13 : 49:15120 Meniscectomy16 : 07:12122 Meniscectomy22 : 10:01404 Meniscectomy15 : 08:16237 Meniscectomy11 : 05:19290 Meniscectomy27 : 35:00325 Meniscectomy14 : 16:13149 Debridement partial rupture of anterior cruciate ligament17 : 41:10284 Diagnostic7 : 08:21 Total duration 175:40:1839:01:0 Shaver time as percentage of total duration -LRB- % -RRB- 22.2 The recordings of operations with a gravity pump were performed in the day care centre of Academic Medical Center -LRB- Amsterdam , The Netherlands -RRB- . The recordings of operations with an automated pump were performed in the day care centre of the Sint Maartenskliniek -LRB- Nijmegen , The Netherlands -RRB- . The latter hospital utilizes the automated FMS Duo pump -LRB- FMSGroup , Nice , France -RRB- . Table 2 shows the details on the standard operation setting for both hospitals using the different pumps . Most disturbances are more or less independent of the quality of the camera , the light source , and the arthroscope . It was assumed that these devices were functioning properly at the time of recording , because all operations were executed in acknowledged hospitals , in which the technical service department routinely inspects the equipment . A tourniquet was routinely applied at the start of the arthroscopic knee operations with a vacuum level of 300 mmHg . Drills , vaporizing devices , microfracturing , arthroscopic drills or meniscal repair devices were not used . Table 2Standard operation setting for the gravity and the automated pumpGravity pumpAutomated pumpPortalsAnteromedial and anterolateralAnteromedial , anterolateral , and superomedialPump settingsPreset pressure of 49 mmHg -LRB- elevated saline fluid bag at 0.66 m -RRB- Suction pressure of − 500 mmHgIndicated setting for knee arthroscopy is 50 , which implies a preset pressure of 113 mmHg and a continuous flow of 90 ml/minInstrument setØ 4 mm arthroscope -LRB- Karl Storz , Gemany -RRB- Probe and punches -LRB- Dyonics , UK -RRB- Ø 4.5 or 5.5 mm full radius shaver -LRB- Dyonics , UK -RRB- Ø 4 mm arthroscope -LRB- Karl Storz , Gemany -RRB- Probe and punches -LRB- Dyonics , UK -RRB- Ø 4.5 or 5.5 mm full radius shaver -LRB- Dyonics , UK -RRB- The comparison of the pumps was conducted by assessing the quality of the arthroscopic view per operation . Extending the definition of arthroscopic image quality by Tuijthof et al. -LSB- 11 -RSB- to the setting of irrigation performance of the pump systems , it is proposed that the pump for which the least percentage of disturbances occurs is the most effective . Seven disturbances of the arthroscopic view have been uniquely described and defined -LSB- 11 -RSB- . Not all of them can be prevented or removed by irrigation . Therefore , a subset of these disturbances was chosen for comparison of the pump systems : bleeding , turbidity -LRB- caused by synovial fluid and debris , Fig. 1 -RRB- , air bubbles , and loose fibrous tissue . The same recording equipment and quantitative time-disturbance analysis was performed as described in Tuijthof et al. -LSB- 11 -RSB- . Therefore , the recordings of the operations were analyzed frame by frame to assess the presence of the four disturbances in each frame . In addition to the total operation time , each operation was divided into phases to assess dominant prevalence of disturbances in a particular phase : -LRB- 1 -RRB- creation of portals , -LRB- 2 -RRB- joint inspection with or without a probe , -LRB- 3 -RRB- cutting , and -LRB- 4 -RRB- shaving . Phase 1 was the time required to achieve access to the joint by means of the arthroscope ; thus the period from the first frame of the recorded digital video until the frame where a clear sharp arthroscopic view is presented for the first time . Added with this period is the time required to create the second and third portal : the period from the frame where the tip of a needle is seen for the first time until the frame where the tip of an instrument occurs . Phases 3 and 4 were defined as the frames in which the specific instrument was present in the arthroscopic view . The remainder of the operation time was indicated as Phase 2 inspection . Fig. 1Three images of the disturbance turbidity , which consists of synovial fluid and small particles The 20 digital videos were analyzed by two testers who each assessed an equal number of operations of each group . Their tester agreement was determined prior to the time-disturbance analyzes by means of the adjusted kappa -LSB- 1 , 9 -RSB- . For each of the four disturbances , the adjusted kappa was larger than 0.80 indicating good agreement . Statistical analysis was performed with SPSS 12.0.2 -LRB- SPSS Inc. , Chicago , IL , USA -RRB- . The presence of a normal distribution for both datasets was determined with the Kolmogorov -- Smirnov and Shapiro -- Wilk tests . With the help of a one-way analysis of variance test -LRB- ANOVA -RRB- significant statistical differences were assessed in case the data were normally distributed . Otherwise , the nonparametric Mann -- Whitney U test -LRB- Wilcoxon rank sum test -RRB- was applied . Results Almost 3 h of digital video material has been analyzed for both groups -LRB- Table 1 -RRB- . The mean operation time is around 18 1/2 min for the gravity pump , and 17 1/2 min for the automated pump . In each pump group , the total time of shaver usage is around 23 % -LRB- Table 1 -RRB- . The Kolmogorov -- Smirnov and Shapiro -- Wilk tests show that the datasets are not distributed normally . As a consequence , the results of the percentages of each disturbance of the total operation time are presented with the median , minimum and maximum -LRB- Fig. 2 -RRB- . The disturbances show a substantial variation per operation . Turbidity was the dominant disturbance in both pump groups -LRB- median of 18 % of the total operation time for the gravity pump versus 8 % for the automated pump -RRB- . The Mann -- Whitney U test shows a significant difference for the presence of Turbidity -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.015 -RRB- between both pump groups in favor of the automated pump . No significant differences are found for the other three disturbances -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- > 0.436 -RRB- -LRB- Fig. 2 -RRB- . Fig. 2Results of the share of disturbances in the arthroscopic view as percentage of the total operation time for each operation and each of the two groups . The results are presented with the median , minimum , and maximum numbers , because the datasets were not distributed normally . * The Mann -- Whitney U test shows a significant difference for Turbidity -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.015 -RRB- Not all of the four operation phases were present in the 20 operations . Phases 3 and 4 were absent in both diagnostic arthroscopies . Additionally , punches were not used in five operations in the gravity pump group , and three in the automated pump group . As was expected the creation of portals was the shortest phase -LRB- 10 % for the gravity pump versus 5 % for the automated pump -RRB- , and inspection was the longest phase -LRB- 59 % for the gravity pump versus 51 % for the automated pump -RRB- . Punches were used more frequently in the automated group -LRB- 7 % for the gravity pump versus 21 % for the automated pump -RRB- . Analyzing each of the four operation phases separately shows a significant difference in favor of the automated pump for Turbidity in Phase 2 -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.019 -RRB- . For all other disturbances and operation phases no significant differences are determined -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- > 0.165 -RRB- . The Mann -- Whitney U test within each of the pump groups shows a significant difference for loose fibrous tissue -LRB- Fig. 3 -RRB- . In detail , the gravity pump shows the following results : Phase 1 versus 3 -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.002 -RRB- , Phase 1 versus 4 -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.010 -RRB- , and Phase 2 versus 3 -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.002 -RRB- . The automated pump shows these results : Phase 1 versus 2 -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.017 -RRB- , Phase 1 versus 3 -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.001 -RRB- , and Phase 2 versus 3 -LRB- Exact Sig . -LSB- 2 * -LRB- 1-tailed Sig . -RRB- -RSB- = 0.022 -RRB- . Fig. 3Results of the share of disturbances in the arthroscopic view as percentage of the phase time for each operation in the gravity pump group -LRB- a -RRB- , and the automated pump group -LRB- b -RRB- . The results are presented with the median , minimum , and maximum numbers , because the datasets were not distributed normally . * The Mann -- Whitney U test shows only a significant difference for loose fibrous tissue in both pump groups Discussion The objective of this study was to compare two types of irrigation pump systems -LRB- the classic gravity pump and a widely used automated pump -RRB- based on their effectiveness in maintaining a clear arthroscopic view . Comparison of the effectiveness of pump systems has been performed -LSB- 2 , 4 -- 6 -RSB- . However , none of these studies measured the arthroscopic image quality objectively in detail . Besides the objective comparison , the time-disturbance analysis gave quantitative values for the frequency of four disturbances . Turbidity was the dominant disturbance in both pump groups being present in a considerable percentage of the operation time -LRB- Fig. 2 -RRB- . The results show that for routinely performed arthroscopic knee operations , the automated pump was significantly more effective in reducing the presence of turbidity with 50 % on average . This finding can be explained by the continuous flow of 90 ml/min that is activated by the automated pump as opposed to the lower flow cause by leakage along the portals when using the gravity pump and a two-portal technique . No difference was determined for the other three disturbances . The low percentage of bleeding can be attributed to the use of a tourniquet in all operations . In order to determine the effectiveness of pump systems for this disturbance , analysis of shoulder surgeries would be more convenient . The found variation in the duration of disturbances per operation could have been caused by the condition of the knee joints , because this factor could not be completely eliminated with precise matching . With this knowledge , a future suggestion is to analyze a larger number of patients per pump group to determine possibly other significant differences in pump performance . Comparison of the operation phases independently showed similar results for the inspection phase compared to the total operation time , probably because this was the longest phase . Since the creation of portals was a relatively short phase , and the use of punches was absent for almost half of the operations , no significant differences were found . However , analysis of both groups internally showed that the presence of loose fibrous tissue was generally significantly higher in when an instrument was used -LRB- Phases 3 and 4 -RRB- . This is in accordance with the general expectation and confirms the applicability of this method for quantification of disturbances in the view . Concluding , this study shows that important disturbances as bleeding , air bubbles , and loose fibrous tissue are not affected by a pump system when performing a routine knee arthroscopy with a tourniquet . The most frequent disturbance turbidity is reduced by around 50 % when using an automated pump . It is questionable if this justifies the use of an automated pump for straightforward arthroscopic knee surgeries using a tourniquet , since the purchase of an automated pump is more costly .

O O O O B O O O B I O O O O B O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O B O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O B O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O B O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B B O O O O O B O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O

arthroscopy
image quality
irrigation
pump


Asian wasp envenomation and acute renal failure : a report of two cases Acute renal failure is an unusual complication of wasp stings . We report two cases of renal failure after multiple wasp stings -LRB- Vespa affinis -RRB- . Both patients had evidence of intravascular haemolysis , hepatic dysfunction , oligo-anuria and azotaemia and required dialysis . The first patient had severe hemolysis , rhabdomyolysis , pigment and venom nephropathy and died on the 8th day in hospital . The second patient , who recovered completely in 3 weeks time with steroid and antihistaminic therapy , had interstitial nephritis . Although acute renal failure after wasp stings is typically caused by acute tubular necrosis -LRB- ATN -RRB- in the setting of haemolysis or rhabdomyolysis , in some patients , acute renal failure may result from a direct nephrotoxic effect or acute interstitial nephritis from a hypersensitivity reaction . INTRODUCTION In the Pokhara Valley , Nepal , there are many unpublished cases of wasp poisoning which take a heavy death toll annually . Wasp stings usually cause local allergic reactions but can sometimes lead to intravascular haemolysis , rhabdomyolysis , thrombocytopenia , acute tubular necrosis , acute hepatic injury -LRB- 1 -RRB- and even myocardial infarction -LRB- 2 -RRB- in addition to various respiratory and neurological -LRB- 3 -RRB- manifestations . Death from wasp envenomation is a rare event and results from acute renal failure -LRB- ARF -RRB- involving various mechanisms . Although ARF after wasp stings is typically caused by ATN in the setting of haemolysis or rhabdomyolysis , in some patients , renal failure may result from a direct nephrotoxicity of wasp venom or acute interstitial nephritis from a hypersensitivity reaction . We here we report two cases of acute renal failure after wasp stings -LRB- Vespa affinis -RRB- . CASE 1 A 55-year-old farmer who had been collecting fodder from a jungle was admitted with dyspnea , hoarse voice and myalgia within 8 hours of being attacked by several wasps . The patient was given intravenous saline , oxygen , salbutamol -LRB- β2-adrenergic receptor agonist -RRB- , chlorpheniramine -LRB- antihistamine -RRB- , cyproheptadine -LRB- antihistamine -RRB- , prednisolone -LRB- corticosteroid -RRB- and ranitidine -LRB- histamine H2-receptor antagonist -RRB- . He also received fluid , mannitol and furosemide . By the next morning he had haemoptysis and had produced 400 ml of dark urine . On examination , the patient was drowsy , pale , icteric and cyanosed and had approximately one hundred and fifty red and swollen sting marks all over the body . Systemic examination revealed polyphonic wheezes and crepitations at the base of the right lung . Investigations are shown in Table 1 . The onset of the oliguric phase was at 12 hours postenvenomation . Chest radiograph showed right basal consolidation . He died on the 8th day following admission despite aggressive therapy with medication , blood transfusions , assisted ventilation , and 16 cycles of dialysis . CASE 2 A 40-year-old forest guard was attacked by a swarm of wasps . He presented with approximately twenty-five sting marks in exposed areas of face , throat , hands and legs -LSB- Fig. 1 -RSB- . The patient was treated in the primary health centre with rubbing of saliva and papaya slices over the sting marks and referred to teaching hospital almost 24 hours after being stung . He developed anuria and had not passed any urine the previous night . On examination , the patient had a rapid pulse , unrecordable blood pressure , icterus , an urticarial rash in exposed parts of the face , legs and hands , facial puffiness , and a swollen left ankle and right knee joint . The rest of the physical examination was unremarkable . Investigations are shown in Table 1 . He was treated with oxygen , salbutamol , chlorpheniramine , cyproheptadine , prednisolone and ranitidine . His hepatic and renal function improved gradually with fluid challenge , furosemide , mannitol , bicarbonate infusion , dopamine , and 12 cycles of dialysis in 3 weeks ' time . OBSERVATION DISCUSSION Wasp stings are well-known causes of toxic and hypersensitivity reactions . Direct toxicity is rare , but has been reported in cases when a very large amount of venom is injected . Immediate hypersensitivity reactions , such as bronchospasm in the first case and an urticarial rash in the second , are known to occur . In our report , both reactions responded to steroids and antihistaminics . The second patient had swollen joints indicating serum sickness-like reaction in a sensitized individual . Wasp venom contains toxic melittin , apamine , phospholipases A1 , hyaluronidase , acid phosphatase , histamine , and degranulating peptide mastoparan -LRB- 4 -RRB- . These components have direct and indirect cytotoxic -LRB- hepatic , renal and myocyte membrane -RRB- , hemolytic , neurotoxic and vasoactive properties , which can cause intravascular haemolysis and rhabdomyolysis -LRB- 5 , 6 -RRB- . Wasp venom can cause ARF by several mechanisms , which include ATN , acute interstitial nephritis , pigment nephropathy resulting from rhabdomyolysis -LRB- myoglobinuria -RRB- or intravascular haemolysis -LRB- haemoglobinuria -RRB- and hypotension caused by an anaphylactic reaction -LRB- 7 , 8 -RRB- . Previously rhabdomyolysis and renal ischemia were thought to be main causes of nephropathy . Sakhuja et al had postulated that direct toxic injury could be one of the possible mechanisms of ARF following wasp poisoning -LRB- 9 -RRB- . Many cases of rhabdomyolysis-associated ARF have been published , but those due to wasp stings are rare . The wasp venom has deleterious effect on renal tubules and glomeruli -LRB- albuminuria , haematuria and ARF -RRB- , red blood cells -LRB- haemolysis , reticulocytosis , unconjugated hyperbilirubinaemia -RRB- , muscles -LRB- rhabdomyolysis , elevated creatinine phosphokinase and lactate dehydrogenase , myoglobinuria -RRB- and liver -LRB- elevated transaminases , hypoalbuminaemia and prolonged prothrombin time -RRB- -LRB- 10 -RRB- . Kularatne et al had described similar multi-organ failure with high mortality following wasp poisoning owing to direct toxic effect -LRB- 11 -RRB- . In the first case we presented , the patient had myalgia , indicating muscle injury as evidenced by elevated CPK , LDH and AST and myoglobinuria -LRB- 728 ng/ml -RRB- . He also had intravascular haemolysis and haemoglobinuria . Toxic pigments might have caused nephropathy resulting in ARF . The alternative mechanism of ARF postulated was direct nephrotoxicity by massive wasp venom . Zhang R et al. -LRB- 12 -RRB- reported for the first time that acute tubulointerstitial nephritis could lead to ARF in wasp sting cases . In the second case we present , the patient had eosinophiluria , indicating interstitial nephritis . He recovered fully with the mentioned treatment . He did not report taking any medication which might have had nephrotoxic side-effects , and no other causes of ATN could be found . Ultrasound abdomen was unremarkable . Kidney biopsy revealed proximal peritubular necrosis and eosinophilic infiltration . Hence it can be hypothesized that the ATN was caused by a hypersensitivity reaction to the wasp venom . CONCLUSION Wasp stings pose a great environmental hazard in Nepal and early recognition of anaphylactic shock , hepatic or renal dysfunction , rhabdomyolysis or haemolysis and rapid transport to hospital are essential steps of management to avoid fatalities . ARF due to toxic or pigment nephropathy and tubulointerstitial nephritis should be considered in any oliguric and azotemic patient following wasp attack .

O B I O B I I O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I I O O O O O O O O O O O O O O O O O O O B O O O O O B I I O O O O O O O O O B I O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B I O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

wasp envenomation
rhabdomyolysis
interstitial nephritis
acute renal failure
nepal


Effects of a contoured articular prosthetic device on tibiofemoral peak contact pressure : a biomechanical study Many middle-aged patients are affected by localized cartilage defects that are neither appropriate for primary , nor repeat biological repair methods , nor for conventional arthroplasty . This in vitro study aims to determine the peak contact pressure in the tibiofemoral joint with a partial femoral resurfacing device -LRB- HemiCAP ® , Arthrosurface Inc. , Franklin , MA , USA -RRB- . Peak contact pressure was determined in eight fresh-frozen cadaveric specimens using a Tekscan sensor placed in the medial compartment above the menisci . A closed loop robotic knee simulator was used to test each knee in static stance positions -LRB- 5 ° / 15 ° / 30 ° / 45 ° -RRB- with body weight ground reaction force -LRB- GRF -RRB- , 30 ° flexion with twice the body weight -LRB- 2tBW -RRB- GRF and dynamic knee-bending cycles with body weight GRF . The ground reaction force was adjusted to the living body weight of the cadaver donor and maintained throughout all cycles . Each specimen was tested under four different conditions : Untreated , flush HemiCAP ® implantation , 1-mm proud implantation and 20-mm defect . A paired sampled t test to compare means -LRB- significance , P ≤ 0.05 -RRB- was used for statistical analysis . On average , no statistically significant differences were found in any testing condition comparing the normal knee with flush device implantation . With the 1-mm proud implant , statistically significant increase of peak contact pressures of 217 % -LRB- 5 ° stance -RRB- , 99 % -LRB- dynamic knee bending -RRB- and 90 % -LRB- 30 ° stance with 2tBW -RRB- compared to the untreated condition was seen . No significant increase of peak contact pressure was evaluated with the 20-mm defect . The data suggests that resurfacing with the HemiCAP ® does not lead to increased peak contact pressure with flush implantation . However , elevated implantation results in increased peak contact pressure and might be biomechanically disadvantageous in an in vivo application . Introduction In 50 % of the patients undergoing routine arthroscopy , articular cartilage defects are detected -LSB- 6 -RSB- . The majority of cartilage lesions are observed in patients over the age of 40 years -LSB- 6 , 11 -RSB- . Approximately 20 % of these lesions were categorized as full thickness cartilage defects -LRB- Grade IV -RRB- -LSB- 6 -RSB- . The average defect size in 1,000 knee arthroscopies was 2.1 cm2 with 42 % of these defects being between 2 to 4 cm2 in area -LSB- 11 -RSB- . Location of the lesions are predominantly on the medial femoral condyle -LSB- 6 , 11 -RSB- . Clinical and experimental studies have shown that a relationship exists between larger defect size and degeneration of the articular surface . Linden et al. -LSB- 19 -RSB- demonstrated that the presence of a significant chondral defect is associated with a much higher incidence of osteoarthritis than occurs in the general population . Hughston et al. -LSB- 13 -RSB- showed that larger osteochondral defects are associated with a poorer clinical outcome than smaller defects . The treatment for articular cartilage defects offers a great variety of options depending on the severity of the damage . The main factors to be considered are the patient age , the size of the lesion , the location of the defect , and further damage to the joint . Biological repair techniques , such as autologeous chondrocyte transplantation , osteochondral transplantation -LRB- OATS , Mosaicplasty -RRB- and marrow stimulation techniques are proposed for the treatment of localized cartilage defects in younger patients with a normal weight bearing axis and no further damage to the joint -LSB- 3 , 8 -RSB- . However , many middle aged patients are affected by localized cartilage damage and are neither fit for biological repair methods , nor for traditional resurfacing techniques such as unicompartimental or total joint replacement . A contoured articular prosthetic unicondylar femoral resurfacing prosthesis -LRB- HemiCAP ® , Arthrosurface Inc. , Franklin , MA , USA -RRB- was developed to offer a treatment option among the currently used modalities . It is intended for use as a partial resurfacing device of the femoral condylar surface of the knee when only one compartment is affected by posttraumatic , degenerative disease or necrosis associated with large unstable articular defects with significant subchondral bone exposure . However , it is unknown if the femoral resurfacing device leads to increased peak contact pressure to the opposing biological structures such as meniscus and articular cartilage of the tibial plateau . The purpose of our study was to determine peak contact pressures in the medial compartment of human cadaveric knees under different loading conditions comparing the normal articular surface to flush and proud HemiCAP ® implantation and defect . Based on the experimental study , biomechanical device safety on opposing structures can be assessed and a guideline might be given to the clinician for prosthetic implantation while avoiding potentially damaging effects . Materials and methods Knee joints A total of eight fresh-frozen knee cadaver specimens -LRB- 3 pairs , 2 single -RRB- were used for data collection in this study . The specimens were obtained from donors , who consented in writing during their lifetime to the use of their body for research and education . The average age of the seven male and one female specimen was 71 years -LRB- range 61 -- 81 -RRB- with an average weight of 71 kg -LRB- range 62 -- 85 -RRB- . Specimens were selected after inspection of the medial compartment according to the following criteria : Intact femorotibial cartilage , intact meniscus , and intact collateral and cruciate ligaments . Thirteen specimens were excluded following these criteria . Another six specimens were excluded due to specimen failure during the testing procedure : The reason for exclusion was fracture of the femur or tibial plateau -LRB- 2 specimens -RRB- , rupture of the anterior cruciate ligament -LRB- 2 specimens -RRB- or rupture of the patella tendon -LRB- 2 specimens -RRB- . All specimen failures were female human cadaver knees . Technology A specially designed knee simulator was used for this study -LRB- Fig. 1 -RRB- . Similar to in vivo conditions , the main system composed of artificial muscle , force transducer sensor , the joint angle detection and the ground reacting force form a closed loop . The ground reaction force is adjustable according to the donor 's weight . The knee simulator consists of a loading frame -LRB- MTS 858 Bionix , MTS Systems , Eden Prairie , MN , USA -RRB- with a long stroke main actuator driven by a hydraulic pump unit -LRB- MTS 505.11 silent flow -RRB- to simulate body weight and the vertical hip displacement in the mechanical axis of the lower limb . Ankle joint simulation is performed with a hinge joint with one free motion axis . The possible rotation during the movement occurs in the artificial hip joint as if standing with fixed shoe contact . A load transducer is fixed between the mounting plate and ankle joint to detect the vertical ground reacting force -LRB- U3 load cell , Hottinger-Baldwin , Darmstadt , Germany -RRB- . Two smaller actuators apply loads , which simulate the quadriceps force . The tendons of the quadriceps muscle are attached to customized curved cryo-clamps , which avoid patella tilting . These cryo-clamps are connected to a waterproof force transducer -LRB- SSM-AJ 500 , Interface , Scottsdale , AZ , USA -RRB- and connected to an artificial muscle -LRB- Fluidic muscle MAS , Festo , Esslingen , Germany -RRB- . The mathematical model shows that the properties of this fluidic muscle is comparable with a skeletal muscle -LSB- 28 -RSB- . Fig. 1Schematic drawing of the knee simulator that was used for this study A 0.1 mm thin electronic pressure measuring sensor -LRB- K-scan 4000 , Tekscan , Boston , MA , USA -RRB- was placed in the medial compartment above the menisci and fixed with sutures in a manner that no displacement was possible . The sensor consists of load-sensing regions oriented in a grid with 1.27 mm spacing between rows and columns . Each region is referred to a sensel with piezo-resistive pigments to determine the total compressive load within that region . The size of the sensor is 28 × 33 mm with 62 sensels/cm2 . The K-scan sensor was successfully used in comparable applications by several authors -LSB- 18 , 21 , 25 , 31 -RSB- . The HemiCAP ® implant -LRB- Arthrosurface Inc. , Franklin , MA , USA -RRB- is a contoured articular prosthetic -LRB- CAP -RRB- unicondylar femoral resurfacing prosthesis consisting of two components , a fixation component and an articular component , that mate together via a taper interlock to provide stable and immobile fixation of the implant and stress-bearing contact at the bone/prosthetic interface . The fixation component is a modified titanium cancellous screw with a tapering distal tip , a full-length cannulation , and a proximal female taper bore . The articular component is a dome-shaped component manufactured of a Cobalt -- Chromium -- Molybdenum alloy with titanium plasma spray coverage on the underside for bony in-growth . Each diameter comes in a variety of incremental offset sizes which correspond to the superior/inferior and medial/lateral radius of curvatures at the implant site . The size of the implant used in this study was 20 mm in diameter with different offset sizes , matching the individual specimen joint curvature . Testing protocol The specimens were aligned using a fixed laser beam to achieve correct alignment in the mechanical axis of the lower limb . The mechanical axis was defined by a line through the center of the head of the artificial hip joint , the center of the knee joint and the center of the hinge joint representing the artificial ankle . For calibration of the sensor the ankle hinge joint was secured with two aluminum plates perpendicular to the ground . Thereby the knee was fixed in full extension . Each sensor was individually preconditioned and calibrated intra-articulary with a two-point calibration method at 700 and 1,500 N according to manufacturer 's guidelines . Definitions of the correct angles of the actual knee position were adjusted with a custom-made goniometer and by the displacement-controlled main rod . During the test cycles the cadaver were sprayed with saline solution to prevent dehydration . The specimens were tested in four different conditions : -LRB- 1 -RRB- Untreated knee , -LRB- 2 -RRB- Flush HemiCAP ® -LRB- 20 mm -RRB- implanted in the central weight bearing area of the medial femoral condyle , -LRB- 3 -RRB- 1 mm proud implantation to adjacent cartilage , -LRB- 4 -RRB- 20 mm defect -LRB- Fig. 2a -- d -RRB- . Each knee was tested in static knee stance positions -LRB- 5 ° , 15 ° , 30 ° , 45 ° -RRB- with body weight ground reaction force , 30 ° flexion with two times body weight ground reaction force and during a knee-bending dynamic cycle -LRB- 10 cycles -RRB- with body weight ground reaction force . The setting of ground reaction force to be achieved during the trial was adjusted to the living body weight of the donator of the cadaver -LRB- e.g. 70 kg ∼ 700 N -RRB- . The loading rate for exploring the dynamic contact pressures was 0.1 Hz/s . Fig. 2Different testing conditions -LRB- a Untreated ; b Flush ; c 1 mm ; d Defect -RRB- Operative technique All specimens were released at their femoral fixation during preparation of a new testing condition . The exact position was marked and recorded to maintain specimen position in the knee simulator across all testing conditions . The position of the sensor did not change during the preparation . All procedures were performed by the same investigator -LRB- CB -RRB- . The medial femoral condyle was exposed by a medial parapatellar incision . The knee was flexed to 90 ° to expose the central weight-bearing portion . A drill guide was used to place a pin perpendicular to the joint surface representing the center of the defect . The center of the defect was determined by measuring the condylar width and bisecting the distance . The cannulated instrumentation set ensured that the vertical axis was maintained throughout the procedure . After drilling a pilot hole , the fixation component was inserted . A contact probe determined the radius of curvature in two planes . With a matching reamer , the site for the implantation was prepared and a sizing trial with corresponding offsets inserted . The selected device was oriented in the correct planes and connected to the anchoring screw with a tapered lock . In order to allow for careful removal of the articular component , the guide wire was initially drilled through the condyle and remained inside the cannulated screw during the trial . After testing with flush implantation -LRB- Fig. 2b -RRB- , the device was removed with the guide wire . The anchoring screw was elevated with a counter-clockwise quarter turn representing 1 mm and the device re-inserted for positioning 1 mm above the adjacent cartilage -LRB- Fig. 2c -RRB- . Defect condition was tested after removing the guide wire and device leaving a 20-mm osteochondral defect of 3 -- 4 mm depth -LRB- Fig. 2d -RRB- . Data analysis Data were obtained using I-Scan software 4.23 -LRB- Tekscan , Boston , MA , USA -RRB- . Peak contact pressure was assessed and recorded as the highest value at each stance position and during the dynamic knee-bending cycle . Mean , median and standard deviation values were evaluated using MS-Excel 2003 -LRB- Microsoft Inc. , Redmond , WA , USA -RRB- and SPSS 11.0 -LRB- SPSS Inc. , Chicago , IL , USA -RRB- . For statistical analysis a paired sampled t test to compare means -LRB- significance , P ≤ 0.05 -RRB- was used . Results Continuous data were obtained at every trial . No difference in the quality of data collection was seen comparing the stance positions or dynamic testing . The highest mean peak contact pressures were noted with the implant being 1 mm proud -LRB- Fig. 3 ; Table 1 -RRB- . Statistically significant increase of peak contact pressures of 217 % -LRB- 5 ° stance ; P ≤ 0.004 -RRB- , 99 % -LRB- dynamic knee bending ; P ≤ 0.02 -RRB- and 90 % -LRB- 30 ° stance with 2tBW ; P ≤ 0.03 -RRB- compared to the untreated condition was seen . Average results of 45 ° static testing demonstrated only slightly higher values compared to the other testing positions , indicating that the implant was non-weight bearing and lost contact to the sensor at this position -LRB- Fig. 3 ; Table 1 -RRB- . Fig. 3Mean peak contact pressures with one standard deviationTable 1Peak contact pressures at different testing conditionsTesting positionTesting conditionPeak contact pressure -LRB- Mpa -RRB- Mean difference to untreated -LRB- % -RRB- P value5 ° Untreated3 .09 ± 0.86 -LRB- 3.05 , 1.92 -- 4.86 -RRB- N/AN/AFlush3 .98 ± 2.19 -LRB- 3.59 , 2.15 -- 9.02 -RRB- 29NS1 mm proud9 .80 ± 4.37 -LRB- 9.36 , 4.70 -- 18.37 -RRB- 217 ≤ 0.004 Defect3 .35 ± 1.39 -LRB- 3.39 , 1.90 -- 5.83 -RRB- 8NS15 ° Untreated3 .01 ± 0.81 -LRB- 2.95 , 2.01 -- 4.11 -RRB- N/AN/AFlush3 .69 ± 1.79 -LRB- 3.89 , 1.38 -- 7.06 -RRB- 23NS1 mm proud 9.19 ± 9.27 -LRB- 5.87 , 2.10 -- 30.49 -RRB- 205NSDefect2 .94 ± 1.07 -LRB- 2.84 , 1.69 -- 5.09 -RRB- − 2NS30 ° Untreated3 .18 ± 0.94 -LRB- 3.52 , 1.46 -- 4.26 -RRB- N/AN/AFlush2 .89 ± 0.85 -LRB- 3.02 , 1.03 -- 3.83 -RRB- − 9NS1 mm proud 7.07 ± 5.97 -LRB- 5.24 , 1.03 -- 19.81 -RRB- 122NSDefect3 .31 ± 1.06 -LRB- 3.11 , 2.05 -- 5.34 -RRB- 4NS45 ° Untreated4 .77 ± 1.85 -LRB- 4.23 , 2.66 -- 7.90 -RRB- N/AN/AFlush4 .96 ± 2.02 -LRB- 4.18 , 2.79 -- 7.92 -RRB- 4NS1 mm proud 5.79 ± 2.76 -LRB- 5.54 , 2.01 -- 11.82 -RRB- 21NSDefect4 .94 ± 1.81 -LRB- 4.65 , 2.05 -- 7.54 -RRB- 4NSDynamicUntreated5 .84 ± 2.12 -LRB- 5.14 , 3.85 -- 9.82 -RRB- N/AN/AFlush6 .02 ± 2.05 -LRB- 5.21 , 3.46 -- 8.97 -RRB- 3NS1 mm proud 11.61 ± 6.39 -LRB- 10.50 , 6.22 -- 25.46 -RRB- 99 ≤ 0.02 Defect5 .68 ± 1.76 -LRB- 5.11 , 3.76 -- 8.24 -RRB- − 3NS30 ° 2tBWUntreated6 .57 ± 2.31 -LRB- 6.01 , 4.09 -- 11.15 -RRB- N/AN/AFlush6 .05 ± 1.40 -LRB- 5.82 , 4.68 -- 8.97 -RRB- − 8NS1 mm proud 12.49 ± 8.02 -LRB- 9.67 , 5.83 -- 30.49 -RRB- 90 ≤ 0.03 Defect7 .38 ± 4.68 -LRB- 5.31 , 4.75 -- 17.70 -RRB- 12NSValues given as mean ± SD -LRB- median , range -RRB- NS not significant On average , comparison of the untreated normal knee with flush device implantation demonstrated neither statistically significant differences in peak contact pressure during the dynamic knee-bending cycle nor static testing -LRB- 5 ° , 15 ° , 30 ° , 45 ° -RRB- or two times body weight GRF at 30 ° static testing -LRB- Table 1 -RRB- . Six out of eight specimens demonstrated similar peak contact pressures in both testing conditions , two specimens showed a noticeable increase in peak contact pressures -LRB- flush device implantation -RRB- averaging 29 % during 5 ° static testing and 23 % in 15 ° static testing . Data evaluation of the two respective trials with outlying measurements demonstrated edge loading at the border of the implant to the adjacent cartilage -LRB- Figs. 4b , 5b -RRB- . Fig. 4Peak contact pressure at 15 ° static knee stance position with single body weight of specimen No. 2 . The color represents the spectrum of pressures -LRB- high pressure-red ; low pressure-blue -RRB- . From left to right the different testing conditions are displayed -LRB- a Untreated , b Flush , c 1 mm proud , d Defect -RRB- . Marked increase of peak contact pressure at the edge of the implant to the adjacent cartilage is demonstrated -LRB- b -RRB- Fig. 5Picture of specimen No. 2 before testing with flush implantation of the device in front view -LRB- a -RRB- and top view -LRB- b -RRB- . The arrow indicates the area of peak contact pressure displayed in Fig. 4b No significant increase of peak contact pressures was evaluated with the 20-mm osteochondral defect . However , average increase by 8 % -LRB- 5 ° stance -RRB- and 12 % -LRB- 30 ° stance with 2tBW -RRB- were found compared to untreated-condition -LRB- Table 1 -RRB- . Furthermore , maximum values were higher compared to untreated condition -LRB- except 45 ° stance position and dynamic testing cycle -RRB- . Discussion The patient aged over 40 years with a full thickness chondral or osteochondral defect reflects a serious problem for the orthopedic surgeon . Considered as being too old for biological repair of the defect , primarily the patients are mostly managed with conservative , non-surgical treatment including weight reduction , physical therapy to increase and support musculature , unloading braces and medications such as NSAID 's , intraarticular injections -LRB- Corticosteroids , Hyaluronic acid , etc. -RRB- and dietary supplements . However , conservative treatment at best ameliorates the symptoms . Biomechanical studies have shown that untreated osteochondral defects may result in increased contact pressures -LSB- 4 , 7 , 17 -RSB- . Animal models proved that untreated osteochondral defects undergo progressive degenerative changes -LSB- 5 , 14 -RSB- . Whereas smaller defects might have the capacity for healing -LSB- 5 -RSB- , it was shown that larger defects resulted in resorption of the osseous walls of the defect , the formation of a large cavitary lesion , and the collapse of the surrounding articular cartilage and subchondral bone as well as to degeneration of the opposing tibial articular surface -LSB- 5 , 14 -RSB- . A `` threshold '' effect for localized full thickness defects was described with rim concentration around the lesion becoming a factor for defects greater than 10 mm in diameter -LRB- 0.79 cm2 -RRB- -LSB- 7 -RSB- . Defect repair is therefore regarded crucial to prevent or delay progressive degenerative joint destruction . However , unicompartimental or total knee arthroplasty represent procedures of final resort for some of the affected patients . The HemiCAP ® resurfacing prosthesis -LRB- Arthrosurface Inc. , Franklin , MA , USA -RRB- offers an interim or alternative treatment strategy for the middle-aged patient with a full thickness cartilage defect . However , effects of a metallic implant articulating with intact opposing tibial articular cartilage and meniscus remain largely unanswered to date . An experimental study assessing the functional and biological response to its use in a goat model resulted in good clinical outcomes . One year after implantation , gross necropsy and histologic data implied the biocompatibility and functionality of the implant . No ongoing degenerative joint disease was apparent -LSB- 15 -RSB- . Macroscopic and histological analysis showed that the cartilage around the implant was largely intact although some focal fraying and erosion and limited meniscal damage was observed . The opposing tibial plateau cartilage surface was generally intact but exhibited some focal erosions of variable depth -LSB- 15 -RSB- . The outcome was substantially better by comparison to other reported experimental animal studies in goats with untreated full-thickness defects -LSB- 14 , 29 -RSB- . A patellar resurfacing prosthesis resulted at an average of 8.1 years in 71 % good or excellent cases with no progressive degenerative changes in the non-resurfaced apposing femoral articular cartilage as long as 16 years -LSB- 9 -RSB- . A successful clinical outcome with a metallic distal femoral prosthesis articulating directly against the menisci and proximal tibial plateau over 30 years was documented in a case report -LSB- 12 -RSB- . Our results revealed significant increase of peak contact pressures with the implant being proud to the surrounding cartilage compared to the untreated condition with an average maximum increase of 217 % and 205 % at 5 ° and 15 ° stance compared to untreated knees . Results in a biomechanical model using osteochondral plugs for the treatment of osteochondral defects demonstrated increased contact pressures up to 57 % compared to intact condition in elevated or angled plugs with an edge placed higher than the adjacent cartilage -LSB- 16 , 17 -RSB- . Thus , increased peak contact pressures may suggest biomechanical disadvantages and may cause damage to opposing structures . Several in vitro studies have shown increased chondrocyte apoptosis and matrix deformation after peak stress loading of bovine and human articular cartilage -LSB- 2 , 20 , 22 , 23 -RSB- . However , quantitative thresholds above which elevated pressure is detrimental are not defined yet . Flush implantation showed no statistical increase of peak contact pressures compared to untreated . However , in two specimens we found marked increase of peak contact pressures at the edge of the implant . Evaluation of the pictures of the specimen after the trial showed that the implant did not appear to be proud to the adjacent cartilage in the front view -LRB- Fig. 5a -RRB- . However , in the top view it seemed that the implant was in level with the adjacent cartilage or even slightly elevated at the point of increased peak contact pressure -LRB- Fig. 5b -RRB- . Reduced quality of the adjacent cartilage directly next to the measured peak contact pressure might have lead to less resistive cartilage capacity allowing for edge loading . Thus , it appears to be crucial to have healthy surrounding cartilage around the implant and to spend special care during the implantation process so that the implant is not elevated above the adjacent cartilage at any point . Koh et al. -LSB- 16 -RSB- showed in their biomechanical study , that slightly recessed osteochondral grafts with the highest edge placed flush to neighboring cartilage demonstrated nearly normal contact pressures , whereas elevated angled grafts produced increased contact pressures . Our results confirm the observation concluding that slightly recessed implantation should be considered if flush implantation can not be accomplished . Defect situation in our study did not result in significant increase of peak contact pressures . Rim stress concentration has been described by several authors in their biomechanical models evaluating the contact pressures in full thickness cartilage defects -LSB- 4 , 5 , 7 , 16 , 17 , 26 -RSB- . However , results were uncertain whether the peak contact pressure increases at the rim of the defect . Whereas Koh et al. -LSB- 17 -RSB- reported average increase of peak contact pressure by 23 % compared to the untreated condition , Raimondi et al. -LSB- 26 -RSB- and Nelson et al. -LSB- 24 -RSB- found no elevated contact stresses at the rim of the defect . These different observations might be caused by the different deformation of defect rims under a given load , especially in larger defects than in smaller defects . The relationship of defect size to the condylar surface may be also a factor -LSB- 7 -RSB- . The methodology concerning the model -LRB- animal or human being cadaver -RRB- , the experimental setup -LRB- loading mechanics , dynamic or static , etc. -RRB- and the pressure-sensitive sensor and performance of the trial have also to be considered . Limitations of this study have to be considered and include the following . -LRB- 1 -RRB- This is a human cadaver study and biomechanical model . Only approximation of the living system can be achieved . However , the pre-selection of the applied load by the ground reaction force gave the opportunity to load the specimens with the known body weight of the donor , and thus better approximate the forces that occur in the living system -LSB- 30 -RSB- . Furthermore , the knee bending dynamic measurement may have provided a more accurate reproduction of physiologic weight-bearing activity . However , the complexity of weight-bearing motions including all the muscle groups for knee motion could not be reproduced . Applied forces were too high for female human cadaver knees resulting in a high specimen 's failure rate . -LRB- 2 -RRB- Peak contact pressures were determined by an electronic pressure sensitive sensor . The reliability of the K-scan sensor was verified in several studies -LSB- 10 , 18 , 21 , 31 -RSB- . In comparison to other measuring devices -LRB- Fuji Photo Film -RRB- , the Tekscan K-sensor proved to be superior -LSB- 10 , 27 -RSB- . Limitations of the sensor include the thickness -LRB- 0.1 mm -RRB- , its sensitivity to temperature changes , its disposition for crinkling and the establishment of the position -LSB- 1 -RSB- . Although the position of the sensor was accurately secured , a small amount of displacement and crinkling could not be excluded . A certain amount of loss of sensitivity during the different testing conditions and imprecise calibration due to the different surface materials -LRB- metal on cartilage , cartilage on cartilage -RRB- have to be considered . Some drop of data point was observed at some specimen . However , peak contact values seemed not to be affected . -LRB- 3 -RRB- Stable , reproducible ground reaction force in full extension could not be established by the simulator . The quadriceps tendon could not be adequately tensioned in this position . -LRB- 4 -RRB- Implantation of the device was performed in the central weight-bearing area . Results might be different for the implantation in different areas of the medial femoral condyle or lateral condyle . In conclusion , the data suggest that resurfacing with the HemiCAP ® with flush implantation does not lead to significantly increased peak contact pressure . However , elevated implantation results in significantly increased peak contact pressure and might be biomechanically disadvantageous in an in vivo application . Further research is necessary to evaluate the effects of the prosthetic device on contact pressures after loss of meniscus function and in longer continuous dynamic testing .

O O O O B I I O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O B I O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

osteochondral defect
tibiofemoral joint
articular prosthetic device
peak contact pressure