Since 1989 we have been using custom lateral-flare stems. Using this stem, its lateral flare can produce high proximal fit and less fit in distal part. Applying this automatic designing software to the average femoral geometries, we can make off the shelf high proximal fit stem (Revelation ®). Putting the off the shelf stem, the original center of the femoral heads were well reproduced. But in DDH cases, severe deformities around hip sometimes make complicated difficulty for better functional reconstruction. They are high hip center such as Crowe II-IV, shortening of the femoral neck, high anteversion etc. DDH cases are well known to have higher anteversion than non DDH cases. There would be no definite explanations for it. The high anteversion would not always be harmful for the preoperative patients. But in some cases, osteophytes are observed at posterior side of the femoral head which make another sphere with different centre. We can guess that the patient's biomechanics had not been matched with the original anteversion. Then posterior osteophytes can correct inappropriate anteversion (self-reduction.) (Fig.1) In those patients, reduction of the anteversion by putting stems twisted into the canal or using modular stems are sometimes done by the surgeons' decision. Younger DDH cases can also be treated with THA, because of the complicated deformities or biomechanical disorders. Short stems are expected to reduce operative invasion and stress shielding then can reserve bone quality and quantity. From these point of view to improve the understanding of the characteristics of the DDH anteversion, and design a DDH oriented short stem could be one of good solution for those cases.
For the better understanding of the high anteversion 57 femora (mean anteversion: 34.4 deg.) were analyzed slice by slice. The direction of femoral head centre, lesser trochanter (LTR), linea aspera (aspera) just below LTR, aspera in the middle of the femur and aspera between the last 2 sections. All of the directions were assessed from PC line To clarify the meaning of the head osteophytes, 35 operated cases were analyzed the extent of the head osteophytes. According to the results, a DDH oriented short stem was designed.Introduction
Method
In DDH cases often have high anteversion. They also often have high hip center. THA for those cases sometimes requires subtrochanteric derotational/shortening osteotomy. To achieve good results of the surgery, accurate preoperative planning based on biomechanics of the high anteversion cases, method for accurate application of the plan, and stable fixation are very important. At ISTA 2008, we have reported that the location of the anteversion exist several centimeters below the lesser trochanter. Independently from the extent of anteversion, femoral head, grater trochanter, and lesser trochanter are aligned in the same proportion. We have also reported in 2007, in improper high anteversion cases, many cases grow osteophytes posterior side of femoral head to reduce it functionally. In 2014, we reported about development of the stem for subtrochanteric osteotomy. (ModulusR)[Fig.1] In the present study, we established systematic planning way for estimate proper derotation and shortening and apply it for the surgery. Leg alignment during walking were well observed. According to the CT, 3D geometry of the femur, anteversion in hip joint and its compensation by the osteophyte, and knee rotation were measured. It was divided into proximal part and distal part at several centimeter below the lesser trochanter. Adequate hip local anteversion was determined by local original anteversion – compensation if IR-ER can be done. Keeping that anteversion for the proximal part, distal part was rotated as knee towards front. Thus derotation angle was decided. Using 3D CAD (Magics®) proper size of Modulus R was selected and overlapping with canal was extracted then its center of gravity was calculated. This level is decided as the height of osteotomy to obtain equal fixation to both proximal and distal part.[Fig.2] If the derotation angle is less than 15 degree, modular neck adjustment was selected first. By trial reduction and motion test, according to the instability osteotomy was performed. In the high hip center cases, original hip center was reconstructed. Shortening length was determined not to make leg elongation more than 3cm. ModulusR were used for the replacement and fixation of the osteotomy.Introduction
Methods
Infection is one of the most severe comlications of the total arthroplasty. We sometimes encounter cases, which are very hard to finish repeated recurrence. Usage of steroids, immunosuppressants, and biologics would possibly effect to the incidence of the prosthetic infection and to the result of its treatment. Biologics have drastically decreased the number of the total arthoplasic patients, on the other hand, we must be more careful about the infectious conditions. For the infection two stage revision surgery; first removal and antibiotics cement spacer insertion then reimplantation later; is often chosen but sometimes one time antibiotics cement spacer cannot stop the infection and requires multi times spacer insertion. In those cases the dead spaces, poor blood supply and tight skin could be the cause of the recurrence. For these cases we had been performing musclo-cutaneal flap and successfully finish the infection. Our objectives are to review infection cases treated with musclo-cutaneal flap and compare with treatment without it. Methods: Since 2004 to 2013, 6 infection cases were treated. Our standard policy is 2-staged revision. In the first surgery, the prosthesis was removed and cement spacer was inserted. If no evidence of the remained infection was found reimplantation would be done in the second surgery. Otherwise debridement and cement spacer were repeated. In 3 cases, the infection could be finished without musclo-cutaneal flap but in 3 cases musclo-cutaneal flap was finally done then the infection was finished. The clinical courses were reviewed.Background
Objectives
Since 1989, we have been developing lateral flare stem. The concept of lateral flare stem is to deliver proximal part big enough to fill the proximal cavity that most of the cement stems can fill and most of the cementless stems cannot. Also having distal part polished, much less distal load transfer occurs than cement stem. Thus, we can expect high proximal load transfer to prevent stress shielding. To deliver lateral flare stem, straight insertion path cannot be available, as proximal lateral part to fill inside the greater throchanter collides to the greater trochanter. So 3-Dimension insertion path was calculated to deliver that part through the narrow made by neck osteotomy. The first generation of the lateral flare stem was custom made. The second generation was designed as an off-the-shelf stem from what we have learned by the experience of custom stems. With the third generation, the stem was shortened to achieve more proximal load transfer. Direct Anterior Approach (DAA) developed by Judet is one of less invasive hip approach. With a stem with straight insertion path, the extended line of proximal femoral axis should come out of the skin. To achieve this position, proximal end of the femur has to be fully pulled up. (Fig.1) Some of the cases would be able to be lifted up but some have difficulty. Using lateral flare stem with curved 3 dimensional insertion path, even the axis extension does not come out of the skin, it would be expected to be inserted. In the present study, 3D insertion path of the lateral flare short stem for DAA was analyzed. Preoperative CAT scan data were transferred to STL data by Mimics®. The procedures after that were done by Magics®. First, neck osteotomy was done, externally rotated, and mild extension that doesn't make the axis come out of the skin was added. Then insertion path was verified keeping the stem attached medial sidewall of the canal (Fig. 2). In actual case, skin translation and pelvis rotation was assessed by 3D scanner. (Fig. 3)Introduction
Materials and methods
During THA in lateral position, keeping accurate lateral position is very important for obtaining good cup position. We normally use two kinds of hip positioner, but sometimes we can only use universal positioner provided with operational table. The pelvic tilt can be changed by surgical procedures such as traction, dislocation, reduction and so forth. In the present study, pre-op and post-op pelvic tilt was assessed using Kinect (Xbox 360′s sensor) as 3D scanner. As a 3D scanner, “Kinect®” was used (Fig. 1) with scanning software “Artec Studio 9 ®”. First, accuracy of the scanning system was validated, then 6 postero-lateral approach hip replacement with lateral position surgery cases (Fig.2) (1 male and 5 female, average 55.5 y.o., average BMI 27.6, IMP® positioner: 3 cases, Kyocera positioner: 2 cases, universal fixator provided with surgical table: 1 case), one direct anterior approach case, and one supine antero lateral case (Fig. 3) were scanned pre and post operatively. Pelvic tilts were assessed using tableside rails or edges of positioner that is tightly fixed to the table, as the reference.Introduction
Materials and Methods
This study shows the radiographic results of total hip arthroplasty (THA) using the Revelation hip system® for hip joint disease. We performed THA for hip disease using the Revelation Hip System®. From July 2007 to May 2009, 30cases (35 hips) were available for this study. Radiographic evaluation was performed at the last follow-up. Evaluation items included the presence or absence of subsidence, spot welds, demarcation line, cortical hypertrophy and stress shielding. The stem was designed to be implanted without cement and to be combined to the femur bone at the proximal portion to avoid stress shielding. Zone of Gruen zone 1 was divided into 1A or 1B, above and below the outermost tip of the lateral flare of the stem.Objective
Methods
In THA of DDH cases, sometimes shortening and/or derotational subtrochanteric osteotomy is required, for cases with high hip center and/or high anteversion. Initial fixation is one of the most important problems after subtrochanteric osteotomy. To prevent rotational displacement V-osteotomy or step osteotomy is often used. Even though until the osteotomy part unites, additional fixation is required. When a stem with distal load transfer was used body weight can be transferred to healthy part, so early full weight bearing should be expected. However, the muscles around hip joint can pull up proximal part, so it would be possible osteotomy part to be split. When a stem with proximal load transfer, body weight would be loaded on non united osteotomy part. So full weight bearing could sometimes be postponed. A stem that has both proximal and distal load transfer, and has facility for prevent rotation, those situations would possibly be simply solved. Lima (Italy) has a proximal load transfer conical stem with fins “Modulus” and a distal load transfer conical stem “Revision.” Combining these two stems, a stem as explained prior was designed. In the present study, applicability of the stem for cases such as subtrochanteric osteotomy was assessed. The stem geometry data were provided by the maker. Forty CAT scan DICOM data, 12 male, 28 female, 58+/−13.8 Y.O. were transferred to STL geometry data using Mimics®. Then using Magics® fit studies were done. For each femur, most suitable size of conventional “Modulus” and double conical stem “Modulus R” were selected to have tight fit making greater trochanter top height as head center height, then the area where stem core attaches to the inside surface of the canal were determined.Introduction
Materials and Methods
Patient specific surgical guide (PSSG) is a relatively new technique for accurate total knee arthroplasty (TKA), and there are many reports supporting PSSG can reduce the rate of outlier in the coronal plane. We began to use PSSG provided by Biomet (Signature®) and have reported the same results. Before using Signature, we performed TKA by modified gap technique (parallel cut technique) to get the well balanced flexion gap. Signature is the one of the measured resection technique using the anatomical landmarks as reference points on the images of CT or MR taken before surgery. We usually measure the center gap width and gap balance during operation with the special device “knee balancer”(Fig. 1) that can be used on patella reposition. After cutting all of the bone with Signature, gap balance in the extension position was very good but the gap balance was shown slight lateral opening in the 90 degrees flexion position. So we have changed the surgical procedure. We use Signature for cutting only distal femur and proximal tibia to get extension gap and apply the modified gap technique to decide the rotation of the femoral component (Signature with modified gap technique). The purpose of this study is to compare the gap balance between the two techniques. From November, 2012 through March, 2014, 50 CR type TKA (Vanguard Knee®, Biomet) in osteoarthritis patients were performed using Signature. 25 TKA were performed using only Signature (group S) and other 25 TKA were done using Signature with modified gap technique (group SG). After all osteotomies of femur and tibia were completed, applying femoral trial, center gap width and gap balance (plus means lateral opening angle) were measured using knee balancer with respect to 30 degrees of the knee flexion angle from zero to 120 degrees (Fig. 2).Introduction
Materials & Methods
We have been developed lateral flare stem and have been using it since 1989. It was custom stem at first. After being experienced, using the same software, off-the-shelf version lateral flare stem (Revelation) was developed in 1996 in the U.S. We could start using it since 2001 in our country. Lateral flare stems are designed to reproduce physiological proximal load transfer lateral side as well as medial side. It was obtained by having bigger and more accurate proximal part with lateral flare. The design is optimized by matching with 3D insertion path. Using many custom stems including different length and off-the-shelf standard stems, we have come to feel that as for this high proximal fit and load transfer design, it is not necessary to having long distal part and sometimes it is harmful to obtain good proximal load transfer in some situation such as type A (champagne flute) canal. So we have developed short version of the stem. Many makes of the hip stems have included short stems recently. Some aimed to improve easier insertion, some aimed to improve the volume of residual bone quantity. We have aimed to improve proximal fit expecting more proximal and more physiological load transfer to the femur. Our objectives are to comare standard stem and short stem from biomechanical aspect and clinical aspect.Introduction
Objectives
Massive defect of the acetabular bone is one of the severe situation in the hip arthroplasty. Installation of cup supporter or acetabular reinforcement device is one of the important method as well as big cup and bone graft etc. Preparing the device to be suitable shape is very important and installing it at the very position where the shaping was intended is also very important to obtain a stable condition for the arthroplasty. When we use navigation system, the device must be programmed in. But it is impossible to programme a device we have bended by ourselves into the system. If we can use a navigation system for such devices for those cases, we can expect better installation. We can fit the device on the patient's bone during the surgery of course; which is the ordinary procedure fot it; but it requires much time and tissue damage maybe with less accurate fitting. Two primary and three revision total hip arthroplasty cases with severe acetabular bone defect were treated with this method. First we have made chemical wood model for each case and bended the cup supporter on it. (Fig. 1) Then CAT scan of the model and the bended device on it were taken. Then the coordinate system of DICOM data set of the patient's original pelvis and the second DICOM data set i.e. the bended prosthesis were unified using MIMICS (Materialize, Belgium.) An STL format geometry data file of the bended device was extracted and merged into original DICOM dataset. Thus we could obtain a DICOM data set we call “predicted post-op DICOM.” During the surgery, a navigation system was used based on the predicted DICOM data.Introduction
Materials and Methods
This study shows the radiographic results of total hip arthroplasty (THA) using Revelation stem ® (Djo surgical USA) for hip joint disease. We removed cases which we couldn't follow up, the remaining of the patients who had undergone a primary THA July 2007 to December 2009 in our institution using Revelation hip stem® and 58 cases-65 hips (14 men and 44 women) were possible for progress observation on this study, and radiographic evaluation was done at the time of the last observation. The preoperative diagnosis of the hip included osteoarthritis (OA) in 40 patients, idiopatic, necrosis of the hip in 13 patients, Rheumatoid arthritis (RA) in 4 patients, and femoral head fracture in 1 patient. Three patients had undergone femoral head replacement (FHA) and 55 patients had undergone THA. At the time of the last evaluation, spot welds were detected in 63 hips (97%) in zone1 and 7. Demarcation lines, which indicates movement of the stem, were detected in zone3,4,5, but not in the proximal of the stem. Stress shielding were observed in 32 joints, according to Engh's classification, first degree were 27 joints and second degree were 5 joints. Cortical hypertrophy were detected in 13 joints. The revelation stem features a lateral overhang structure (lateral flare) and the stem has an expanded proximal geometry allowing the device to rest on both medial and lateral cortices at the metaphyseal level. Above all the stem has anterior overhand structure (trapezoidal structure). The medullary cavity occupation rate is made to increase by these structures. Above all, the stability of the stem is increased by a proximal portion by three point support. The distal stem is tapered and polished, which prevents the stress loading to a distal portion of the device. Stress shielding more than the third degree is not detected, and spots welds were detected in the proximal of the stem. These facts indicate that the concept of this stem, transmit loading to the femur bone, at the proximal portion of the stem, would be achieved.
In total hip arthroplasty, preoperative planning is almost indispensable. Moreover, 3-dimensional preoperative planning became popular recently. Anteversion management is one of the most important factors in preoperative planning to prevent dislocation and to obtain better function. In arthritic hip patients osteophytes are often seen on both femoral head and acetabulum. Especially on femoral head, osteophytes are often seen at posterior side and its surface creates smooth round contour that assumes new joint surface. (Fig. 1). We can imagine new femoral head center tracing that new joint surface. In the present study, the posterior osteophytes are compared in osteoarthritic patients and other patients.INTRODUCTION
OBJECTIVES
Navigation system has been used for very accurate surgery. It can also be useful for preoperative planning. A surgeon can understand whole surgery, plan the surgery and perform the surgery three dimensionally and accurately. But the planning procedures should be installed before everything is started. When the surgery will be done in an ordinary method, the surgeon would not find particular difficulties. But in sometimes the surgeon can have unordinary situation such as massive defect that should be treated with acetabular enforcement device and bone grafted. Using postoperative DICOM data which is predicted by preoperative planning using 3D CAD software, we will be able to use the navigation system for those cases with difficulties that is not supported. To establish a method to use a navigation system using preoperative planning data that is processed by our 3D CAD software which is not supported by the navigation system itself, including device preparation using plastic models.Introduction
Objectives
Dislocation following total hip arthroplasty is one of the most common complications, occurring in 1% to 5% of all cases. Several causes for dislocation have been suggested that
Mismatching of cup positioning and stem anteversion Impingement between cup and neck of stem prosthesis. Most often positioning of the stem is anatomically predetermined, while the orientation of the cup is much more flexible. Since July 2005, stem first method has been applied for all cases. During this method, canal preparation and stem trial was done first, and then cup orientation was determined according to the stem direction and impingement. For the bigger cups 34mm or 38mm heads were applied in this series. In the present study dislocation ratio was compared to cup first method. In the stem fist group (SF), the following procedures were done consequently.
Canal was prepared for the stem. Revelation lateral flare high proximal load transfer stem (DJO) was mainly selected. But for the case with high anteversion over 50 degrees, Modulas; conical distal load transfer stem with modular neck (Lima) was selected. According to the stem anteversion and neck length, cup position and orientation were determined. (For the cases with higher anteversion, less cup anteversion was selected, and for some cases higher cup position was selected. According to the cup size 28, 34, or 38 mm diameter neck was selected. From October 2002 to July 2008, there were 191 THA cases. There were 81 hips in Standard group and 109 hips in SF group. There were 63 females and 18 males in Standard group and 90 females and 19 males in SF group (p=0.41). Average age was 61.0(22–81) in Standard group and 60.2(29–89) in SF group (p=0.53). In Standard group, 64 were replaced for osteoarthritis, 15 for rheumatoid arthritis and two for avascular necrosis. In SF group, 86 were replaced for osteoarthritis, 17 for rheumatoid arthritis and six for avascular necrosis (p=0.53). As for Crowe’s classification, 61 type I, 18 type II and 2 type III were included in Standard group. And 88 type I, 15type II, 4 type III and 2 type IV were included in SF group (p=0.29). Average anteversion of femoral neck were 23.1(−2 to 70) degree in Standard group and 26.2(−4 to 65) degree in SF group measured with CAT scan (p=0.274). MoM bearing surfaces were used with 71 hips (87.7%) in Standard group and 100 hips (91.7%) in SF group (p=0.35). Only in SF group, big metal head were used in 24hips(22%) with 34mm and in 12hips(11%) as 38mm diameter. Average leg length difference between pre and post operation was 11.5mm(0 to 36) in Standard group and 8.0mm(−18 to 30) in SF group (p<
0.05). Average cup inclination was 43.2(25 to 84) degree in Standard group and 40.9 (22 to 66) degree in SF group (p<
0.05). Average cup anteversion was 8.2 degree (0 to 22.8) in Standard group and 7.1 degree (−12 to 30.5) in SF group (p<
0.05). Average operating time was 111.9min (67–150) in Standard group and 97.5min(60–162) in SF group (p<
0.05). Average intra operative hemorrhage was 744ml(10–2757) in Standard group and 487ml(10–1374) in SF group (p<
0.05). The dislocation rate was decreased from 3.7% (3/81 cases) in Standard group to 0.0% (0/109) in SF group. In conclusion our study suggested that Stem first method and utilization of big metal head would decrease the dislocation rate in primary cases. More bleeding from canal during accetabular reaming was expected. However less bleeding was observed in SF group.
Canal Flare Index, defined as the ratio of the intracortical width of the femur at a point 20mm proximal to the lesser trochanter and at the canal isthmus by Noble et al,; is considered to express the proximal femoral geometory, but it is usually measured by a plain A-P X-ray. Then it is thought the index is influenced by rotational position of the femur, so we made 3-D femoral model based on CAT scans and measured the canal flare index three dimensionally. Then the effect of observation from rotated direction was evaluated. CAT scans of 49 femurs (18 male, 31 female) were obtained from the pelvis to the feet. The average age was 60.4 years old ranging from 25 to 82. Forty nine femurs contained 22 osteoarthritis of hip joint, 12 trauma, 9 knee arthritis, 3 avascular necrosis of femoral head, 3 normal candetes. From those data, 3-D models of normal side were individually made for measuring the parameters. 3-D models were made using CAD software. We measured the canal flare index at which the femur posterior condyles were parallel to the plane, reproducing the situation to take A-P X-ray. After that, those 3-D models were rotated and investigated the difference of the value to study the effect of femur position. The canal flare index was between 2.8 and 6.6 with the average value at 4.65. The stovepipe (canal flare index<
3), the normal range (3~canal flare index<
4.7), the champagne flute (4.7~canal flare index), included 2%(1 femur), 61.2%(30 femurs), 36.7%(18 femurs), respectively. About the effect of rotation, we found the value of canal flare index was more sensitive to proximal femur rotation than the canal isthmus. The results of the canal flare index at the plane parallel to the posterior condyle line varied widely compared with the results at the position considering the anteversion. So it was suggested that the canal flare index at the patella front position does not represent the canal characteristics. It should be argued in 3-D space.
One of the most important characteristic of the developmental dysplastic hip (DDH) is high anteversion in femoral neck. Neck-shaft angle is also understood to be higher (i.e. coxa-valga) in DDH femora. From this understanding many DDH intended stems were designed having larger neck shaft angle. According to the result of our prior study; reported in ISTA 2005 etc.; using computer 3-D virtual surgery of high fit-and-fill lateral flare stem into high anteversion patients, it was revealed that the geometry of proximal femur itself does not have big difference from normal femora but they are only rotated blow lessertrochanter. It is very important to know what anteversion is, and where anteversion is located, to design a better stem and to decide more proper surgical procedures for DDH cases with high anteversion. In the present study, the geometry of 57 femora was assessed in detail to reveal the geometry of anteversion and its location in the DDH femora. Fifty seven CAT scan data with many causes were analyzed. Thirty-two DDH, 3 Rheumatic Arthritis (RA), 2 metastatic bone tumors, 4 avascular necrosis (AVN), 1 knee arthritis, 12 injuries, and 3 normal candidates were included. Whole femoral geometries were obtained from CAT scan DICOM data and transferred to CAD geometry data format. All the following landmarks were measured its direction by the angle from posterior condylar line. The assessed landmarks were
anteversion, lesser trochanter, linea aspera at the middle of the femur, and two more (upper 1/6, 2/6 level of aspera) linea aspera directions were assessed between ii) and iii). All the directions were measured by the angle from the medial of the femur. The direction of anteversion and lesser trochanter were well correlated, (R=0.55, Y=0.56X−35) i.e. femoral head and lesser trochanter were rotated together. The direction of lesser trochanter and aspera in upper 1/6 section had no relation even they are located very close with only several cm distance, (R=−0.03, Y=−0.02X−88) i.e. however the lesser trochanter was rotated, the upper most aspera was located almost at the same direction (−87.5+/−7.58 degree). The direction of aspera at upper 1/6 and middle femur were strongly correlated. (R=0.63, Y=0.81X-22) i.e. they stay at the same direction. The results mean that the anteversion is a twist between normal proximal femur (from femoral head and lesser trochanter) and normal distal femur. The twist was located just blow lesser trochanter within several centimeter. The anteversion has been understood as the abnormal mutual position between femoral neck and femoral shaft. In high anteversion hips the neck shaft angle was also believed to be higher, so several DDH oriented stems have higher neck shaft angle i.e. coxa-valga geometries. It has been believed that the location of the anteversion was around neck part. This study revealed that the deformity was located in the very narrow part just below lesser trochanter. It has been discussed that DDH oriented stems should have fit to different canal geometries, but understanding the biomechanics of abnormal anteversion and its treatment should be more important.
Since 1993, we have been developing preoperative planning system based on CAT scan data. In early period it was used to decide cup diameter and orientation for Total Hip Arthroplasty (THA). It was done using hemisphere object locating proper position and orientation. According to our progress, we have started using it for custom stem designing, stem selection and stem size planning too since 1995. Since 2001, we have been using it for almost all THA cases. We also have started use it for any case we have question about 3D geometries. Since 2005 we started computer planed 2 staged THA after leg elongation for high riding hips and reported at ISTA 2007 too. Now our policy became that every tiny question we have, we shall analyze and plan preoperatively. In our population, the incidence of the developmental dysplastic hips is higher. The necks often have bigger anteversion, and less acetabular coverage. So we often use screws for cup fixation. The screw direction allowed in thin shell thickness is limited and less bone coverage makes good cup fixation difficult. With highly defected cases and with revision cases the situation is more difficult. In the present study, we have developed acetabular 3D preoperative planning method with screw direction, length, and for the cases with defect, cup supporter pre-shaping with models and prediction of the allograft volume. For the less defect cases, geometries of cup with screw holes were requested to the maker and were provided for us. Screws were attached perpendicular to each screw hole. Screw geometries have marks at every 5mm to plan proper length. The cup was located as much as closer to the original acetabular edge, keeping in the limit to avoid dislocation. Small space above the cup was accepted if anterior and posterior cup edge could be supported by original bone. Then the cup was rotated until we can obtain proper screw fixation. For the cases with severe defects, we use cup supporters and allografts. Cup supporters are designed to be bent and fit to the pelvis during the surgery. But to shape it a properly; for good coverage and strong support; is very difficult and takes long through the limited window with fatty gloves. And mean while we get more bleeding. The geometries were obtained by CAT scan of the devices. Then proper size was determined as cup size. Chemiwood model was made and proper size supporter was opened and bent preoperatively using the model. It was scanned again and compared to the pelvic geometry again. Using cluster cups, no dangerous screw was found as long as normal cup orientation was decided and screws were less than 30mm. Posterior screws were often too short then rotated anterior and found to have good fixation. Pre-bending could reduce surgical time remarkably. As long as we could know, no navigation system can control the cup rotation. But acetabular preoperative planning was very useful and could reduce operative invasion. It could be done easily without using navigation system.
