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Purpose: Dynamic hip screw (DHS) insertion for the fixation of lateral femoral neck fractures is an accepted surgical treatment method. A computer-assisted planning and navigation system based on 2D fluoroscopy has been developed for guidewire insertion in order to perform screw placement. The image acquisition process was supported by a radiation-saving procedure called "zero-dose C-arm navigation". The aim of this study was to evaluate this new system., Materials and Methods: In the context of a sawbone study, we inserted dynamic hip screws. The procedure was performed under navigation control and in the conventional technique in 12 sawbones. Both procedures were performed in an open and closed technique., Results: The computer-assisted technique significantly reduced the number of intraoperative fluoroscopic images (open technique: -8.1 ± 0.5; p < 0.001 - closed technique: -12.3 ± 3.7; p < 0.001) and the number of guidewire passes (open technique: -1.3 ± 1.2; p < 0.05 - closed technique: -1.5 ± 1.2; p < 0,05). There was no difference with respect to precision in both groups. The operation time was significantly longer in the navigation-assisted groups (open technique: + 14.6 ± 5.4 min; p < 0.001 - closed technique: + 13 ± 3 min; p < 0.001)., Conclusion: The addition of computer-assisted planning and surgical guidance supported by "zero-dose C-arm navigation" may be useful for the fixation of lateral femoral neck fractures by the DHS as it reduces the amount of fluoroscopic images and requires fewer drill tracks. Further studies with the goal of reducing the operation time are necessary., (© Georg Thieme Verlag KG Stuttgart · New York.)

Background: The efficiency and success of computer-assisted fluoroscopic navigation systems mainly depend on the quality of the process of image acquisition: obtaining the correct view of anatomic structures, relative orientation of multiplanar X-ray images and the necessary amount of radiation dose. These systems may be optimised by using a system called zero-dose c-arm navigation (ZDCAN). We investigate whether the available computer-assisted systems may be used to navigate the c-arm before image acquisition to obtain X-ray images with maximised accuracy and minimal radiation exposure., Methods: Based on position data of an optical tracking system combined with statistical deformable bone models, ZDCAN is able to generate a real-time preview of expected X-ray images of the lower extremities without using radiation. We performed a cadaver study on six full-body specimens comparing the zero-dose approach to conventional positioning of the c-arm in order to evaluate efficiency and accuracy. Eight users acquired two perpendicular X-ray images of the hip, the knee and the femoral diaphysis., Results: The number of X-ray images required to get a satisfying picture could be reduced to seven using the zero-dose approach; the conventional approach needed 11 images. The mean time did not differ significantly. Regarding the image quality, using ZDCAN quasi-orthogonality could be reached while the conventional approach showed a large variation of the relative orientation., Conclusion: Using ZDCAN, the amount of radiation can be reduced by requiring less X-ray images as well as reaching better accuracy., (© Georg Thieme Verlag KG Stuttgart · New York.)

Introduction: Despite controversial discussions, hip resurfacing at the moment seems to be the most bone-sparing surgical procedure of the femoral bone when implanting hip endoprostheses. Main risks are septic and aseptic loosening and necroses of the coxal end of the femoral bone mainly influenced by the periprosthetic allocation of bone cement. Because of a lack of radiation transparency of the hip resurfacing implant, this cement allocation cannot be sufficiently evaluated by common radiological procedures. A pilot study was conducted to describe and validate the macromechanical interdigitation of bone cement with spongy bone of anatomic specimens compared to artificial bone models and to evaluate whether artificial bones may be used for further interdigitation studies of different implantation techniques., Methods: Plastic models of polyoxymethylene (POM) according to the inside geometry of the Metasul Durom hip prosthesis were implanted on ex vivo femora (n = 14) versus artificial bone models (n = 24) (Sawbones) of three different spongy densities (0.16; 0.20; 0.32 g/cm(3)) (each n = 8) in a clinically standardised surgical procedure and reproduced by highly resolving computed tomography. Afterwards a computer-based analysis of the cement allocation was accomplished., Results: It could be shown that the Sawbones of the lower spongy densities (0.16 and 0.20 g/cm(3)) were similar to the ex vivo femora regarding the bone penetration of cement. No significant differences could be shown regarding interdigitation. According to our data, both groups of Sawbones may be used for further studies., (Georg Thieme Verlag KG Stuttgart, New York.)

Background: The most essential improvement of modern hip resurfacing arthroplasty is the metal-on-metal bearing as well as the integration of a procedure for the exact and repeatable positioning of the femoral component through a specific mechanical alignment instrument. Nevertheless, the main reasons for early implant failure are mal-positioning of the femoral component and notching of the femoral neck during femoral head preparation., Materials and Methods: In the context of an in vitro study, in each case six DUROM-Hip resurfacing prostheses were implanted in artificial femora with the prosthesis-specific mechanical alignment instrument, as well as under navigation control. The aim of the study was to evaluate the functionality and accuracy of a computer-assisted planning and navigation system on the basis of a navigation module library from Surgitaix AG (Aachen, Germany), as well as a comparison with the prosthesis-specific mechanical alignment instrument., Results: The main angulation error between planning and navigation of the stem-shaft angle was 0.2+/-1.2 degrees for the navigation system and 6.5+/-4.1 degrees for the mechanical alignment instrument, the main anterior offset error was 1.2+/-1.2 mm vs. -0.83+/-4.1 mm. The mean time for all five planning and navigation steps was 17+/-1.2 min vs. 14+/-0.8 min. The main distance error between planning and navigation was 1.9+/-0.6 mm for the navigation system, and 5.3+/-2.4 mm for the mechanical alignment instrument. Femoral notching was not observed for navigational or conventional positioning., Conclusion: The computer-assisted fluoroscopic planning and navigation system for hip resurfacing showed, within the scope of this in vitro study, first promising experiences. The system approves a practicable planning with a high accuracy in implementation. Nevertheless, the potential benefit has to be evaluated in further clinical studies, especially from the perspective of a possible integration of this navigation system into the clinical workflow. Further studies should consider a fluoroscopy-assisted range of motion assessment under consideration of an additional cup-module to enhance the postoperative range of motion after hip resurfacing procedures.

Introduction: Resurfacing arthroplasty represents an alternative method to total hip replacement especially for the young and active patient. The main reasons for early implant failure are mal-positioning of the femoral component and notching of the femoral neck during femoral head preparation., Material and Methods: In the context of a cadaver study of formalin-fixed cadaveric full body specimens 6 DUROM -Hip-Resurfacing prosthesis have been implanted under navigation control. The aim of the study was an evaluation of the functionality and accuracy of the computer-assisted planning and navigation system on the basis of a navigation module library from Surgitaix AG Aachen, Germany., Results: The main angulation error between planning (135.2 +/- 3.6 degrees ) and navigation (136.2 +/- 2.8 degrees ) was 1.9 +/- 1.1 degrees , the main anterior offset error between planning (2.2 +/- 1.3 mm) and navigation (2.7 +/- 2.3 mm) was 1.2 +/- 1.9 mm. The main distance error between planning and navigation was 2.7 +/- 1.3 mm. The mean time for all five planning and navigation steps was 20.2 +/- 2.5 min. Against the background of a acetabular bone-saving approach in all 6 cases the smallest possible femoral component could be implanted., Conclusion: The computer-assisted fluoroscopic planning and navigation system for hip resurfacing showed within the scope of this cadaver study first promising results. The system approaches a practicable intraoperative planning with a high accuracy in operative implementation. Nevertheless, the potential benefit has to be evaluated in further clinical studies, especially from the perspective of a possible integration of this navigation system into the clinical work-flow. Further studies should consider a fluoroscopic-assisted range of motion assessment under consideration of an additional cup-module to enhance the postoperative range of motion after hip resurfacing procedures.

Aim: Computer-assisted cement removal out of the femoral medullary canal requires the exact definition of the plug's shape within a 3D coordination system. Aiming at a sufficiently precise reconstruction based on segmentation of just a few 2D X-ray images a special mathematic procedure is needed for automatic surface interpolation. The geometric specification of the resulting virtual model should take into account the characteristic geometry of the navigated tools in order to achieve the best possible removal., Method: Studies were performed on anatomic specimens of entire human femora, that underwent cemented THA before being cut every 5 mm. The cross-sections were scanned at the high resolution of 600 dpi. Segmentation of the cement was performed with the help of a virtual deformable template and was both used for simulation of X-ray projections from various points of view and for validation of the reconstructed 3D model. By this means systematic errors such as those possible during X-ray acquisition, tracking or segmentation could be avoided and the precision of the procedure could be measured exclusively., Results: With increasing number of X-rays the distance from the reconstructed 3D model to the original could continuously be reduced. Using only two x-rays a maximum error was measured with 6.5 mm, whereas 5 pictures taken from different angles showed to be enough to ensure an error below 1 mm in the distal part of the femur. By the use of 6 or more pictures no significant improvement could be attained., Conclusion: The innovative procedure is essential for future 2D image-based fluoroscopic navigation of PMMA removal and bears the options of computer-controlled and robotic material working, respectively.

During x-ray based navigation a number of errors causes distortions in the output image. These errors lead to a fail position of the surgical instrument relative to the patients anatomy. To minimize these influences and to develop dewarping techniques an exact error source identification is necessary. This paper examines the mechanical shift of the x-ray source relative to the image intensifier. Therefore three measurement methods will be used: an optical tracking system, a x-ray opaque probe and the integrated laser cross of the C-arm. The results of this examination show a notable shift of the C-arm geometry. However, no hysteresis effects could be found.

The main objective of the MINARO project (Minimal Invasive NAvigation and RObotics) is the development of a modular intraoperative planning system for fluoroscopy based total hip revision surgery. Especially the distal cement removal can be a challenging problem. To avoid exhaustive x-ray imaging a navigation system should be used, nevertheless, the three-dimensional shape of the bone cement remains unclear. Our approach in the MINARO-project is to reconstruct the real shape of the bone cement by using just a few x-ray projections. First results show, that the reconstruction has an RMS-Error smaller than 0.5 mm using 6 x-ray projections.

Fifty-five patients totaling 98 hips afflicted by Dysplasia Capitis Femoris (DFC), monitored between 1960 and 1983, were analyzed. Mean follow-up: 8 years and 4 months (minimum 2 years, maximum 22 years and 2 months). Forty-three (78%) patients were males; fourteen (25%) were females. Non displayed any alteration in other osteoarticular segments. In 24 of the 98 affected hips it was possible to determine the exact radiological age appearance of the Epiphyseal Nucleus. Thirty-seven of the 55 patients had moderate signs and symptoms which were of short evolution. According to presence or absence of necrotic signs of the femoral epiphysis, two types of lesions were classified: Type 1: Pure Dysplasia Capitis Femoris (88 hips). Type 2: Dysplasia Capitis Femoris with unequivocal signs of necrosis (10 hips). Upon review of the 98 diseased hips, 80 (81.63%) had been fully repaired, while 18 (18.37%) were in reparatory stage. From the 80 fully healed hips, 56 were normal; 18 exhibited a Spherical Coxa Magna and 6 had a non-spherical epiphysis. As treatment concerns, patients with D.C.F. Type 1-A or Type 1-B only require observation and periodical control in addition to moderate restrictions in physical activities upon presence of symptomatic pain that is transitional. Patients with D.C.F. Type 2 must be treated as a classic case of Perthes Disease. Finally, a hypothesis of their etiopathogenis and its relationship to Perthes Disease is brought forth.

Unlabelled: 166 patients with congenital dislocation of the hip, ranging from 10 months to 5 years old, were operated between 1958 and 1971. 140 patients were women (84%) and 26 patients were men (16%). 96 patients had unilateral and 70 patients had bilateral dislocation; that makes a total of 236 dislocated hips. 61 patients with bilateral hip dislocation were operated simultaneously on both hips. All the patients were treated with adductor tenotomy and open reduction through Smith Petersen incision with section or elongation of the psoas tendon. The postoperative immobilization consisted in a period of one month pelvic toecast followed by 2 plaster casts with abduction rod during 3 to 5 months. The postoperatory follow-up ranged from 9 years to 26 years, 2 months; average 14 years, 5 months. The clinical evaluation comprises pain, hip mobility, gait and muscle power., Results: excellent 138 (59%); good 66 (28%); fair 29 (12%); and poor 3 (1%). The radiological evaluation considered: Mose; acetabular femoral head index; Wiberg's CD-angle; cervico-diaphysiary angle and radial quotient., Results: normal 5 (2%); excellent 44 (19%); good 78 (33%); subtotal 54%; fair 90 (38%), and poor 19 (8%). Complications (hips); infections 12 (5%); 3 of them deep ones (1%); residual subluxation 19 (8%); reluxation 1 (0.5%). Isquemic necrosis Grade II of Tönnis 31 (13%); Grade III 2 (1%) and Grade IV 1 (0.5%).