total knee arthroplasty ( tka ) is an effective treatment for knee joint diseases such as osteoarthritis and rheumatoid arthritis .
the perfect reconstruction of lower limb alignment plays a very important role in the outcomes of knee joint replacement , and can affect both symptom relief and the life time of the prosthesis . the traditional method for a correctional osteotomy
is to use the lower - extremity weight - bearing full - length x - ray to determine the osteotomy location and the angle of the coronal plane . as the accuracy of measuring the joint center with two - dimensional ( 2d ) images can not be guaranteed , the preoperative osteotomy position and angle planning with these images are imprecise .
the angle of the sagittal and transverse plane depends on the surgeon 's experience . a prolonged operative time and poor accuracy
the clinical applications of three - dimensional ( 3d ) measurement and operative simulation have gradually increased . in our study , calibrated lower - extremity weight - bearing full - length x - rays and computed tomography ( ct ) scans of the knee were collected . the statistical shape model ( ssm ) technique
was used to synthesize a 3d model of the knee from the x - ray .
a 3d model of the lower limb can be generated with the use of the 3d knee model created using the ssm technique along with ct scans .
after the hip and ankle centers were determined on the dual plane x - ray , the relative positional relationship between the two joint centers and the 3d knee model was measured . using this method ,
a preoperative analysis can be conducted on the basis of weight - bearing function , avoiding the significant radiation exposure due to ct scan .
the 3d - printed osteotomy guide plate from the digitally designed model was applied to the tka .
this clinical trial received permission from the ethics committee of guizhou provincial people 's hospital , and all patients and their families signed informed consents .
a total of 42 cases of osteoarthritis in patients who previously underwent a unilateral tka at guizhou provincial people 's hospital from october 2014 to june 2015 were enrolled in our study . of these patients ,
the involved knee was on the left in 20 cases , while 22 were on the right .
the eligibility criteria included : ( 1 ) unilateral tka ; ( 2 ) varus deformity of the operative knee ; ( 3 ) osteoarthritis of the operative knee .
exclusion criteria included : ( 1 ) severe comorbidities that may prolong hospitalization time ; ( 2 ) severe osteoporosis ; ( 3 ) the patient declined to participate in the research .
patients were divided into two groups : a guide plate group ( gpg , 21 cases ) , and a traditional surgery group ( tsg , 21 cases ) , using the random number table method . in gpg patients ,
preoperative thin slice ct scans of the knee were obtained using the siemens 64 row spiral ct ( siemens , munich , germany ) .
the scanning voltage was 130 kv , the scanning thickness was 1 mm , and the matrix was 512  512 .
digital imaging and communications in medicine format ct data were imported into simpleware 7.2 ( simpleware ltd . , exeter , uk ) to reconstruct the 3d stereolithography format knee model .
calibrated weight - bearing full - length dual plane knee x - ray images were obtained [ figures 1 and 2 ] .
3d knee models were synthesized from calibrated dual plane images with ssm of the knee and registration .
the automatic registration of the 3d knee model from the ct scan and from the ssm technique can be obtained digitally [ figure 3 ] .
registration between the three - dimensional model synthesized from calibrated x - ray and three - dimensional model from computed tomography .
( c ) the lateral film after registration . the hip center ( center of the synthesized sphere ) and the ankle center ( center of the talar articular surface ) were determined . through the position relationship between the centers , points on the calibration device and the x - ray source , the relative spatial relationship between the two central points and the 3d model of the knee joint was determined .
the central point of the distal femur was defined as the midpoint of the whiteside line .
the central point of the proximal tibia was defined as the center of the tibial intercondylar eminence .
the femoral anatomic axis was defined as the connection between the central point of the distal femur and the medullary cavity center 10 cm above the knee joint space .
the femoral mechanical axis was defined as the connection between the central point of the distal femur and the central point of the femoral head .
the mechanical axis of the tibia was defined as the connection between the central point of the proximal tibia and the central point of the ankle joint .
prosthetic models were obtained by 3d scanning the nexgen lps ( zimmer biomet , warsaw , indiana , usa ) with the laser - re ( serein precision machinery company , shenzhen , china ) .
the femoral distal osteotomy valgus angle was the angle measured between the femoral anatomy and the mechanical axis , while the osteotomy thickness was 9 mm from the lowest point of the medial femoral condyle . through the simulated operation
the osteotomy line of the anterior and posterior condyles was parallel to the surgical transepicondylar axis ( stea ) [ figure 4 ] .
the proximal tibial osteotomy line was perpendicular to the mechanical axis on the coronal plane , and was 7 posterior slope on the sagittal plane resulting from the design of the prosthesis .
the thickness of the proximal tibial osteotomy was 10 mm from the highest point of the lateral tibial condyle .
according to the design above and the operative simulation , the hole position of the nonheaded screw and the size of the prosthesis were determined .
the base of the guide plate was reverse engineered in accordance with the shape of the distal femur and proximal tibia . the screw hole and the base
the digital design was created using geomagic ( 3d systems , valencia , ca , usa ) . in the reverse design stage of the base , the more shape characteristic bone surface was selected to be the attachment area for the guide plate to obtain a better match for the installation .
the guide plate was 3d - printed with the polylactic acid material using a 3d printer ( 3d systems company , rock hill , south carolina , usa ) .
after the operative exposure , the guide plates were attached to the bony surface where the articular cartilage was removed to determine the position of the nonheaded screw for the distal femoral , anterior and posterior condylar , and proximal tibial osteotomy devices .
postoperative radiographs were obtained to verify the alignment of the reconstruction [ figure 6 ] .
the nonhead screws positions were determined according the guide plates in order to locate the osteotomy devices .
( a ) the guide plate determined the positions of the nonhead screws in the proximal tibia .
( b ) the nonhead screws determined the positions of the proximal tibial osteotomy divices .
( c ) the guide plate determined the positions of the nonhead screws in the distal femur .
( d)the nonhead screws determined the positions of the anterior and posterior condylar osteotomy divices .
postoperative coronal femoral / tibial angles and the angle between posterior condylar osteotomy surface and the surgical transepicondylar axis .
( a ) the postoperative coronal femoral / tibial angles were 90. ( b ) the postoperative angle between posterior condylar osteotomy surface and the surgical transepicondylar axis was 0. in the tsg , the angle between the femoral anatomic and mechanical axis was measured preoperatively using a weight - bearing full - length lower - extremity x - ray .
the valgus angle for the distal femoral osteotomy was chosen using the closest available angle on the surgical instruments .
the intramedullary alignment guide was applied to the femur while the extramedullary alignment guide was applied to the tibia .
obtained data were statistically analyzed using spss 16.0 ( ibm , armonk , ny , usa ) .
a t - test was applied to assess for differences between groups , with p < 0.05 considered significant .
the operation time was 49.0  10.5 min for gpg , and 62.0  9.7 min for tsg .
the coronal femoral angle , coronal tibial angle , posterior tibial slope , and the angle between the posterior condylar osteotomy surface and the stea were 89.2  1.7 , 89.0  1.1 , 6.6  1.4 , and 0.9  0.3 in gpg , and 86.7  2.9 , 87.6  2.1 , 8.9  2.8 , and 1.7  0.8 in tsg , respectively .
the hospital for special surgery knee scores 3 months after surgery were 83.7  18.4 after gpg and 71.5  15.2 after tsg , respectively .
statistically significant differences were found between all previously noted comparisons [ table 1 ] . comparing the outcomes of the gpg and the tsg hss : hospital for special surgery
; gpg : guide plate group ; tsg : traditional surgery group ; stea : surgical transepicondylar axis .
an accurate osteotomy and the reconstruction of the normal alignment of the lower limbs are key to obtaining a good curative effect .
there is significant anatomic variation of the knee joint , especially in the southwest part of china .
the knee joint prosthesis and the matching operative instruments are designed with the anatomic characteristics of the european and american knee joint in mind .
there may therefore be a large error when using conventional osteotomy instruments in east asia , resulting in poor alignment of the lower limb , early component loosening , pain , activity limitation , and other complications .
the traditional surgical osteotomy is based on the measurement of the weight - bearing full - length lower - extremity x - ray and the intra / extramedullary alignment guides .
this increases the potential risk of infection , bleeding , and fat embolism in the traditional intramedullary alignment guide - based surgery .
hafez et al . digitally designed and 3d printed the osteotomy guide plate for a tka for the first time , which can effectively avoid the fat embolisms that often result from the placement of the intramedullary alignment guide .
uses digital technology to control the axial alignment of total knee arthroplasties , but they needed a ct of the full - length lower limb .
zhang et al . synthesized a 3d joint model from hip , knee , and ankle cts and a weight - bearing full - length x - ray .
3d alignment reconstruction and the determination of the femoral prosthetic valgus angle can be made using the preoperative design based on the 3d model of the lower limb . in this study ,
the measurement and reconstruction of the alignment was conducted under physiologic load to be more consistent with normal biomechanical characteristics .
however , it required a thin - cut ct scan of the three joints , which significantly increased the examination cost and the patient 's radiation exposure . in this study , the use of advanced 3d synthesis and 2d/3d registration technology allowed for the reconstruction of a weight - bearing 3d model of the lower limb , which was used to achieve an accurate 3d measurement of the coronal , sagittal and transversal plane , and to minimize medical expense and x - ray exposure .
our outcomes suggest that the customized guide plate can increase the accuracy of the operation , shorten operative times , and decrease the complications that can result from intramedullary alignment guide placement . in digital medical studies ,
the 2d/3d registration of image data is accurate and important . with the increased use of low - dose radiation imaging equipment in recent years
the construction of a 3d bone shape model plays an important role in both surgical navigation and image - based studies of the kinematics of the knee joint in vivo . in our study ,
the calibrated dual plane x - ray images were used to synthesize the ssm to conduct the feature - based registration of a 3d model from the ct .
although 2d/3d registration could be obtained by using a single plane x - ray , the accuracy of a single plane x - ray is far inferior to that of a dual plane x - ray .
li et al . used a dual fluoroscopic imaging system in a kinematic study of the knee joint in vivo .
van de velde et al . also took the attitude that the 3d model could be registered with a single plane x - ray , but overall accuracy of this approach is much lower than that obtained with the dual plane x - ray .
zhu and li held the view that in the 2d/3d registration , the accuracy gap in the synthesized distal femur model between single plane and dual plane x - rays is significant , while there is almost no gap between dual plane x - rays and mutual plane x - rays .
a number of studies have demonstrated that the irregularities in the 3d model created using a dual plane x - ray can be accepted in the medical field .
zhu et al . introduced a technique to predict the 3d model of the distal femur .
the deviation between the predicted 3d model and the model reconstructed from 3d medical images was < 0.2 mm .
wang et al . also applied the dual fluoroscopic image matching method in their study of in vivo spinal kinematics .
the average positional deviation was 0.2 mm , and the average angular deviation was 0.4. the repeatability was high .
indicated that the deviation between the distal femur model synthesized from dual plane x - rays and the 3d model reconstructed from the ct was < 1.68 mm .
they also created the surface shape model from calibrated x - rays to conduct feature - based registration .
this study is a preliminary evaluation of a digitally customized osteotomy guide plate for tka .
the limitation of an insufficient sample size in this study may result in unnecessary variation .
future work will also add a cartilage model to the bony knee 3d model to decrease variability and reduce the surgical task of removing the articular cartilage .
however , our findings suggest that the indications for a guide plate should be expanded , especially in cases of severe intra - or extra - articular deformity , given its customized and minimally invasive nature .
this work was supported by grants from special fund for culture of top young scientific talents in guizhou province ( no .
2011 - 30 ) , projects of science and technology of guizhou province ( no .
sy 3044 ) , fund of youth of guizhou provincial people 's hospital ( no .
this work was supported by grants from special fund for culture of top young scientific talents in guizhou province ( no .
2011 - 30 ) , projects of science and technology of guizhou province ( no . sy 3044 ) , fund of youth of guizhou provincial people 's hospital ( no .
gzsyqn 05 ) and medical scientific research foundation of guizhou province ( no . gzwjkj2015 - 1 - 018 ) .
 background : the conventional method can not guarantee the precise osteotomies required for a perfect realignment and a better prognosis after total knee arthroplasty ( tka ) . 
 this study investigated a customized guide plate for osteotomy placement in tkas with the aid of the statistical shape model technique using weight - bearing lower - extremity x - rays and computed tomography ( ct ) images of the knee.methods:from october 2014 to june 2015 , 42 patients who underwent a tka in guizhou provincial people 's hospital were divided into a guide plate group ( gpg , 21 cases ) and a traditional surgery group ( tsg , 21 cases ) using a random number table method . in the gpg group , 
 a guide plate was designed and printed using preoperative three - dimensional measurements to plan and digitally simulate the operation . 
 tsg cases were treated with the conventional method . 
 outcomes were obtained from the postoperative image examination and short - term follow-up.results:operative time was 49.0  10.5 min for gpg , and 62.0  9.7 min in tsg . the coronal femoral angle , coronal tibial angle , posterior tibial slope , and the angle between the posterior condylar osteotomy surface and the surgical transepicondylar axis were 89.2  1.7 , 89.0  1.1 , 6.6  1.4 , and 0.9  0.3 in gpg , and 86.7  2.9 , 87.6  2.1 , 8.9  2.8 , and 1.7  0.8 in tsg , respectively . the hospital for special surgery scores 3 months after surgery were 83.7  18.4 in gpg and 71.5  15.2 in tsg . 
 statistically significant differences were found between gpg and tsg in all measurements.conclusions:a customized guide plate to create an accurate osteotomy in tkas may be created using lower - extremity x - ray and knee ct images . 
 this allows for shorter operative times and better postoperative alignment than the traditional surgery . 
 application of the digital guide plate may also result in better short - term outcomes . 
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