Győrfi, Gyula

Kiss, László

Lőrincz, Ádám

Manó, Sándor

Szabó, János

Biomechanica Hungarica

DEA University of Debrecen Electronic Archive

31Biomechanica Hungarica V. évfolyam, 1. számORIGINAL ARTICLESIntroductionThe replacement of the dysplatic acetabulum is a surgically demanding procedure. One of the most important aspects is the reconstruc-tion of the supero-lateral defect of the ace-tabulum.1–5During the development of the Intraosseal Structural Graft (ISG) technique our research group also worked on the surgical instruments required during the operation. During the procedure in the cranial quadrant of the ace-tabulum a proximally hinged cortico-spon-gious plate is fashioned that is opened laterally and a wedge shaped graft made from the fem-oral head is impacted. This is stabilized by 1-2 cortical screws with washers (Figure 1).AbstractThe authors report on the development of special surgical instruments required for the new Intraosseal Structural Graft (ISG) technique in case of dysplastic acetabular replacement pres-ently under introduction at our Institute. One of novelties of procedure is the development of a proximally hinged cortico-spongious plate in the cranial quadrant of the acetabulum that is opened laterally. The instruments were developed, tested, and modifi ed based on experiments on 14 3D models and 19 cadaver hips. For the cortico-spongious plate a 1 and 3 step method was developed and the prototypes of the chisels required were made. The open the bone block laterally a threaded device was planned and developed. Based on the experiments the 1 step method was discarded, because the device used for opening the bone block laterally proved diffi cult, and so it was not further developed. The instruments required for the 3 step method was fi nalized and since than 2 successful opera-tions were performed with them. With the aid of these special surgical instruments the ISG technique is easier, quicker and safer to perform. Keywords: hip dysplasia, prosthesis, graft, special chiselsINSTRUMENT DEVELOPMENT FOR ACETABULAR ROOF PLASTY IN CASE OF DYSPLASTIC ACETABULAR REPLACEMENTJános Szabó, Sándor Manó, Ádám Lőrincz, Gyula Győrfi , László KissDepartment of Orthopaedic Surgery, Medical and Health Science Center, University of Debrecenszabojan@med.unideb.huFigure 1. Schematic drawing of the ISG techniqueBiomechanica Hungarica V. évfolyam, 1. szám32ORIGINAL ARTICLESMethods and materialsIn the ISG technique there are two surgical steps which can be made easier if special instruments are at our disposal. During the development of the instruments it was a basic requirement that they should be simple, easy to use, and economical. 1.  The preparation  of the cortico-spongious blockPrior to development morphological examina-tions were performed on 3D models in order to determine the parameters of the instru-ments. It can be seen on the cranial to caudal sections in the supra-acetabular region that the iliac crest thins towards the cranial direc-tion. This is most prominent at dorsal plane of the acetabulum (Figure 2 white arrows).Following this we measured the thickness of the pelvic wall in 4 places in the supra-acetab-ular region where the proximal hinged cortico-spongious plate is planned to be made (Figure 3). The plate is calculated to be 4 3 cm. The thick ness measurements were made at the rim of the acetabulum and 4 cm cranial to it. Fourteen pelvic models were used that cover the most frequently sizes occurring during hip replacement surgery (Table 1). It can be seen that the thinnest part of the pelvis in this area is the proximal-dorsal point. The lowest value was 10 mm, which means that the bone block at this point cannot be thicker than this. Figure 2. The supra-acetabular region on the horizontal sections of the right hip. The white arrows show the thinning of the pelvis33Biomechanica Hungarica V. évfolyam, 1. számORIGINAL ARTICLESNo. Cup Distal Proximalventral dorsal ventral dorsal1 46 19 31 16 112 48 19 33 13 123 48 15 37 15 134 50 22 45 21 145 50 13 26 14 136 50 23 47 19 157 52 15 40 17 108 52 23 47 19 159 54 22 25 19 1010 54 16 34 17 1711 54 17 30 15 2112 54 22 43 15 1113 58 20 33 17 1514 60 24 38 11 19Two ideas were examined for the instrument development. Both were tested on models and cadaver experimentations. During the devel-opment great emphasis was taken to protect the gluteal muscles and to avoid pelvic perfo-ration.  1. a) One step conceptThe U shaped chisel would make it possible to develop the cortico-spongious block in one step (Figure 4).The one step concept Benefi ts: – quick; –  simple, no need to reconcile each step; – less soft tissue damage.Disadvantages: –  hard to control, therefore the probability of pelvic perforation increases;  –  due to the length of the chisel great force is needed; –  because of different sized acetabula a series is required.1. b) Three step conceptTwo chisels are required. The T shaped rasp-chisel (Figure 5) is used for the frontal cut while the fl at rasp-chisel (Figure 6) is used to make the horizontal osteotomy. Figure 3. The points of thickness measurements Table 1. The thickness of the bone in the four measured points in relation to the size of the acetabular cup (mm)Figure 4. The U shaped chisel and its use on a model and in cadaver examinationsBiomechanica Hungarica V. évfolyam, 1. szám34ORIGINAL ARTICLESThe horizontal blade of the T instrument guides the chisel on the exterior cortical of the pelvis. This way the detachment of the gluteal muscles is less traumatic, and by choosing the proper width of the vertical blade pelvic perfo-ration can be avoided. Based on model exami-nations taking into consideration the perios-teal coverage the width of the vertical blade was chosen to be 10 mm. The length of the cranial direction chiseling is 30 mm in case the implanted acetabular cup is under 50 mm and 40 mm if it is larger. For the sagittal plane chiseling we developed the instrument shown in Figure 6. The tip of the chisel is asymmetric this directs the head of the instrument towards the external cortical bone. In this manner it decreases the risk of pelvic perforation. The three step conceptBenefi ts: –  the shape and size of the graft is adaptable; –  the individual steps require less force; –  the work is easier to control.Disadvantages:  –  slower, the individual steps require more planning; –  greater soft tissue damage;  –  the instruments because of left and right versions are more expensive.Modifi cationsThe basic concept was to design the instru-ments based on available models and to test these prototypes on similar models and cadav-ers. Since all the work phases were performed Figure 5. The T shaped rasp-chisel and its use on a model and in cadaver examinationsFigure 6. The fl at rasp-chisel and its use on a model and in cadaver examinations35Biomechanica Hungarica V. évfolyam, 1. számORIGINAL ARTICLESby our team – including the prototype manu-facturing – we had the chance to modify or discard every concept. Figure 7 shows the fi rst prototype series. During the cadaver experimentation using the fi nal prototypes we realized that the 45 degree angle between the shaft and the head of the chisel although allows good reach of the supra-acetabular region; this also decreases the amount of force that can be applied. To solve this problem we modifi ed the instruments by making the distal third bayonet shaped with a 30-30 degrees break (Figure 8–9).The modifi cations solved the problems with the applied force, but new problems arose. The blade of the U chisel was so long that even after modifi cation large force was required to pass through the subchondral bone. Also due to its size and shape it was diffi cult to maneu-ver the instrument in the acetabulum, and the cortico-spongious block frequently became entrapped into the head of the chisel and dur-Figure 8. The modifi ed T chiselFigure 7. The fi rst prototypesFigure 9. The modifi ed U chiselBiomechanica Hungarica V. évfolyam, 1. szám36ORIGINAL ARTICLESing removal it broke the proximal hinge. Examining these results we discarded the one step concept. During the modifi cation of the fl at chisel the head was also modifi ed. The new sharp design makes it easier to begin and control the oste-otomy (Figure 10). Though the asymmetric sharp end, due to good experience was main-tained. The bayonet redesign of the T instrument besides increasing the amount of force that can be applied also made the ventral approach easier. Dorsally there was serious diffi culty with the proximal femur. This problem was solved by bending the shaft of the chisel 30-30 degrees in the frontal and saggital plane (Fig-ure 11). It can be seen from the fi gure that this modifi cation allows for better aiming in the dorsal proximal direction. Unfortunately this requires a left and a right version of the instru-ment. Based on the fi nal and tested prototype plans were drawn up as can be seen in Figure 12 and the fi nal version of the chisels was manufac-tured by a company (Figure 13).2.  The lateral bending  of the cortico-spongious blockA combined instrument was made to ease the lateral bending of the block (Figure 14).The gripping device rests on the acetabulum. The blade at the end of a threaded rod is inserted into the osteotomy. By lifting the han-Figure 10. The fi nal prototype version of the fl at chiselFigure 11. The fi nal prototype version of the T shaped chisel37Biomechanica Hungarica V. évfolyam, 1. számORIGINAL ARTICLESdle a lateral displacement of the cortico-spon-gious block occurs. The advantage of the device is that due the threaded nature the pro-cedure can be carried out gently and under good control. Since the grip is applied to the edge of the acetabulum during lateral dis-placement the fracture of the internal cortices can be avoided. By calibrating the shaft this device can also be used for measurement pur-poses.The prototype was encouraging during the model tests, but in the cadaver examination it proved to be diffi cult to use and uncontrollable so we gave up on further development. Numerous other instruments were tried, but the fl at chisel proved to be the most simplistic and reliable. Since the instrument has a rela-tively wide head there is no need to fear inter-nal cortical fracture. Figure 12. Plans of the fi nalized versionFigure 13. The fi nal version of the instrumentsFigure 14. The use of the instrument required for the lateral bending of the block on a modelBiomechanica Hungarica V. évfolyam, 1. szám38ORIGINAL ARTICLESResultsThe instruments were tested on 14 models and 19 cadavers and we used the fi nal version in 2 successful surgeries so far. The greatest result of our work was that the instruments were up to standard in the intraoperative setting (Figure 15). DiscussionThe Intraosseal Structural Graft (ISG) tech-nique belongs to the group of bulk bone graft techniques used during the replacement of dysplastic hips which presently is under clini-cal introduction at our Department. The oper-ation can be performed with the usually avail-able orthopaedic surgical instruments, but in order to make the proximally hinged graft preparation easier we decided to develop spe-cial instruments. The 3D model testing and cadaver experimentations and numerously modifi ed instrument set proved the success of the developmental work in the intraoperative setting. Figure 15. Intraoperative use of the fi nal version of the instrumentsREFERENCES1.  Ikeuchi M, Kawakami T, Kitaoka K, Okanoue Y, Tani T. Total hip arthroplasty with a sliding iliac graft for acetabular dysplasia. J Bone Joint Surg Br 2005 May;87(5):635–9.2.  Harris WH, Crothers O, Oh I. Total hip replace-ment and femoral-head bone-grafting for severe acetabular defi ciency in adults. J Bone Joint Surg Am 1977 Sep;59(6):752–9.3.  Hasegawa Y, Iwata H, Iwase T, Kawamoto K, Iwasada S. Cementless total hip arthroplasty with autologous bone grafting for hip dysplasia. Clin Orthop Relat Res 1996 Mar(324):179–86.4.  Yamaguchi T, Naito M, Asayama I, Shiramizu K. Cementless total hip arthroplasty using an auto-graft of the femoral head for marked aceta bular dysplasia: case series. J Orthop Surg (Hong Kong) 2004 Jun;12(1):14–8.5.  Feugier P, Fessy MH, Bejui J, Bouchet A. Acetabu-lar anatomy and the relationship with pelvic vas-cular structures. Implications in hip surgery. Surg Radiol Anat 1997;19(2):85–90.Dr. János Szabó Department of Orthopaedic Surgery, Medical and Health Science Center, University of DebrecenH–4032 Debrecen Nagyerdei krt. 98.Tel.: (+36) 52 255-815

Instrument development for acetabular roof plasty in case of dysplastic acetabular replacement

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Instrument development for acetabular roof plasty in case of dysplastic acetabular replacement

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