it provides rigid fixation and allows early mobilization , ensuring that fixation failure of patellar fractures is rare . however , when this complication does arise , advanced fixation methods are often needed for successful management . to the best of our knowledge , only a few investigators have reported fixation failures , and no one has specifically addressed the details of treating a fixation failure . we present our experience with , and good results of , patellar fracture revision using 2 tension bands in each of 6 patients who sustained fixation failure of a repaired patellar fracture . the study protocol was approved by the ethics committee of shanghai sixth people s hospital affiliated to shanghai jiao tong university . between march 2010 and march 2013 , 4 men and 2 women with failed fixation patellar fractures were treated in our department . the mechanism of the primary injury was a fall in 5 cases and a motor vehicle accident in 1 . one patient suffered multiple fractures at the time of the primary injury . according to the ao classification , there were 3 c1 type fractures , 1 c2 type fracture , and 2 c3 type fractures . the mean interval between injury and the primary operation was 4 days ( range 28 days ) . each patient underwent internal fixation with a modified anterior tension band ( matb ) supplemented with cerclage wiring . except for 1 referred patient , the average time to fixation failure was 11.8 weeks ( range 619 weeks ) postoperatively . all failures were caused by tensioned cable sliding past the tip of the kirschner wires ( k - wires ) ( figure 1 ) . the mean time between the primary and revision operations was 16.2 months ( range 263 months ) ( table 2 ) . the surgical procedure was explained to the patients , and written informed consents were obtained before the surgery . after anesthesia was administered , the patient was placed in the supine position . fibrous tissue at the fracture site was cleared until we could see fresh cancellous bone . an iliac bone graft was inserted and packed into the fracture site when a significant bony defect was encountered . the fracture was reduced and temporarily fixed using point reduction forceps . we then inserted 2 2.5-mm kirschner ( k)-wires distally from the proximal pole of the patella through the fracture site and the cortex of the distal fragment . a stab incision was made at each end of the k - wires to expose the surface of the bone . two stainless steel wires ( 0.8465 mm ) were looped around the k - wires separately in a figure - eight manner . we tightened the loops to make them cling to the anterior surface of the patella and twisted the steel wires at the insertions in the k - wires . cerclage wiring was then performed using a cable or a stainless steel wire . the knee was flexed and extended to check the stability of the fixation and to determine if there was any abnormal movement . intraoperative fluoroscopy was used to ensure that the hardware was properly placed and the articular surface was not displaced . the proximal ends of the k - wires were bent posteriorly and cut , leaving a 6-mm length . we then drew the other ends of the k - wires so the proximal ends attached to the upper surface . postoperatively , patients were allowed to perform active and passive range of motion ( rom ) within 30 degrees in the first 6 weeks . after that , full rom was allowed according to the situation of fracture healing . in the setting of a tenuous fixation or an osteoporotic patient , immobilization in a cast fibrous tissue at the fracture site was cleared until we could see fresh cancellous bone . an iliac bone graft was inserted and packed into the fracture site when a significant bony defect was encountered . the fracture was reduced and temporarily fixed using point reduction forceps . we then inserted 2 2.5-mm kirschner ( k)-wires distally from the proximal pole of the patella through the fracture site and the cortex of the distal fragment . a stab incision was made at each end of the k - wires to expose the surface of the bone . two stainless steel wires ( 0.8465 mm ) were looped around the k - wires separately in a figure - eight manner . we tightened the loops to make them cling to the anterior surface of the patella and twisted the steel wires at the insertions in the k - wires . the knee was flexed and extended to check the stability of the fixation and to determine if there was any abnormal movement . intraoperative fluoroscopy was used to ensure that the hardware was properly placed and the articular surface was not displaced . the proximal ends of the k - wires were bent posteriorly and cut , leaving a 6-mm length . we then drew the other ends of the k - wires so the proximal ends attached to the upper surface . postoperatively , patients were allowed to perform active and passive range of motion ( rom ) within 30 degrees in the first 6 weeks . after that , full rom was allowed according to the situation of fracture healing . in the setting of a tenuous fixation or an osteoporotic patient , immobilization in a cast all patients were followed up for an average of 52 months ( range 3167 months ) after the revision . it takes into consideration factors such as rom , pain , ability to return to work , muscle atrophy , use of aids , effusion , instability of the knee , and ability to climb stairs . of a maximum score of 30 points , an excellent outcome is 2830 points , good 2027 points , and poor < 20 points . at the last follow - up of our patients , the bostman knee scores were 28 points in 3 patients and 27 points in the other 3 . no complications ( e.g. , infection ) were detected ( table 3 ; figure 2 ) . the tension band technique has been the most commonly used method for treating patellar fractures , including comminuted ones . although the incidence of fixation failure is low , it is still a major postoperative complication . reported a higher rate of re - displacement , with 22% of fractures becoming displaced by 2 mm . neither the fracture type nor the presence of an open fracture affects the final results . during fracture management , technical errors , noncompliance , and unknown items are the 3 main factors that lead to fixation failure . some authors advocate using less prominent material , such as cannulated screws , non - absorbable polyester and second generation non - absorbable suture , to reduce the risk of re - operation [ 1517 ] . an additional cerclage wire for a tension band was not correlated with fixation failure . in a multivariate regression analysis , kadar et al . found that a history of diabetes significantly increased the risk of a second operation , including hardware removal , debridement , and revision surgery . technical errors have been attributed to improper placement of the hardware , to which surgeons should pay attention during fixation . in our series , all 6 patients exhibited improper placement of the tension band . the tension bands were all passed posterior to the k - wires but did not cling to the insertions , capturing only soft tissue . this allowed the loops to sling around the tips of the k - wires during early mobilization . the soft tissue between the insertion and the wire weakened the efficiency of the tension band , converting tension into compression ( figure 1b ) . this led to a prolonged union process during which the wire kept moving around the k - wires . after the loops slipping out of the k - wires , the tension band failed . once this happened , the other hardware could not provide enough stability , and fracture re - displacement was inevitable ( figure 1c ) . to make it worse , the migration of loops may result in more soft - tissue irritation which would lead to metallic hypersensitivity . that would increase the risk and cost of medical care . to the best of our knowledge , little research on treatment recommendation or data has specifically addressed the fixation failure of patellar fractures . in this series , we revised re - displaced fractures by a two - tension - band technique . because of the quadriceps and the patellar tendon , it is difficult to ensure that the tension wire clings to the insertions of all the ends of the k - wires . using our technique , 2 wires are looped separately around a single k - wire through stab incisions . this ensures that the wires cling to the k - wires and bone at the insertions of the k - wires . in the previous single - tension - band construct , once the slipping happened in any of the k - wire tips , the whole construct failed . instead of 1 tension band , we used 2 tension bands . all patients returned to their normal daily activities with full extension and an average range of flexion of 147.5 ( 135155 ) . previous biomechanical studies of various tension bands were invariably done on cadavers with a simple transverse osteotomy , which does not simulate the reality of clinical practice . also , all of the studies were performed in a load - to - failure condition and ignored cyclic loading , which is more practical . therefore , those studies reported wide variations to the extent that they have drawn opposite conclusions [ 7,914 ] . to resolve these limitations and obtain accurate measurements of interfragmentary compression , john et al . performed a study on wooden models they found that incorporating a horizontal figure - eight pattern with 4 strands crossing the fracture site , and tensioning the wire with 2 twists at the corner of the tension band , improved interfragmentary compression by 63% compared with the vertical mabt with a single twist . the improvement was achieved by increased number of wire strands passing across the fracture site , and had nothing to do with the materials used . it is composed of 2 figure - eight oriented tension bands and has 4 strands passing through the fracture site . placing the twists at the insertions of k - wires decreases losses due to friction and plastic deformation caused by the wire sliding around the k - wires . we believe that our technique provides more secure fixation than does that designed by john et al . . however , our aim was to report our experience and present a new alternative treatment technique in management of fixation failure of patellar fracture . the fixation failure of patellar fracture has been attributed to technical errors , most commonly involving improper placement or insufficient band wire tension . the two- tension - band technique can resolve these problems , and it provides secure fixation .
backgroundfailed patellar fracture fixation is rare , and is usually attributed to technical errors . 
 there are no specific details available on how to address this problem . 
 we present our two - tension - band technique for fixing patellar fractures.material/methodsbetween march 2010 and march 2013 , 4 men and 2 women with failed fixation patellar fractures were treated in our department . 
 their average age was 34 years ( range 2349 years ) . 
 the initial fracture type was c1 in 3 , c2 in 1 , and c3 in 2 , according to the ao classification . 
 the initial fracture patterns included 3 transverse and 3 comminuted fractures . 
 there were no open fractures . 
 all patients underwent internal fixation with a modified anterior tension band ( matb ) supplemented with cerclage wiring . 
 all failures were caused by tension bands sliding past the tip of the kirschner wires . 
 the mean time between the primary and revision operations was 16.2 months ( range 263 months ) . 
 we revised the fractures by two - separate - tension - band technique.resultsthe mean follow - up was 52 months ( range 3167 months ) . 
 all patients healed radiographically without complications at an average of 14.7 weeks ( range 820 weeks ) . 
 the bostman knee score was excellent in 3 and good in 3 . 
 all patients regained full extension and the mean range of flexion was 147.5 ( 135155).conclusionsuse of this two - tension - band technique can avoid technical errors and provide more secure fixation . 
 we recommend it for both primary and revision surgery of patellar fractures .