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Item type:Publication, Access status: without files , Migration and cyclic motion of a new short-stemmed hip prosthesis : a biomechanical in vitro study(Elsevier, 2006-10-01); ; ; ; Background: Uncemented, short-stemmed hip prostheses have been developed to reduce the risk of stress shielding and to preserve femural bone stock. The long-term success of these implants is yet uncertain. Prerequisite for osseointegration is sufficient primary stability. In this study the cyclic motion and migration patterns of a new short-stemmed hip implant were compared with those for two clinically successful shaft prostheses. Methods: The prostheses were implanted in paired fresh human femura and loaded dynamically (gait cycle) with increasing load (max 2100 N) up to 15,000 cycles. Relative displacements between prosthesis and bone were recorded using a 3D-video analysis system. Findings: The short stem displayed a biphasic migration pattern with stabilisation at maximum load. Initial migration was predominantly into varus and was greater than that for the shaft prostheses. Failure occurred in cases of poor bone quality and malpositioning. Cyclic motion of the short prosthesis was less than that for the shaft prostheses. Surface finish showed no effect. System stiffness for the new stem was lower than for the shaft prostheses. Interpretation: The new stem tended to migrate initially more than the shaft prostheses, but stabilised when cortical contact was achieved or the cancellous bone was compacted sufficiently. Bone quality and correct positioning were important factors for the short stem. The lower cyclic motion of the new stem should be favourable for bony ingrowth. The lower system bending stiffness with the new implant indicated a more physiological loading of the bone and should thereby reduce the effects of stress shielding.Publicationtype: Journal Article17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Comparison of total hip replacements cup orientation and position using different navigation systems and the conventional manual technique(Springer, 2005-11-01); ; ; Background. Aim of this in-vitro study was to compare the hip cup placement for total hip replacement when using different navigation systems compared with the traditional, non-navigated technique. Methods. Five different navigation systems were used: the CT-less systems Navitrack™, Orthopilot™ and Surgetics Station™, as well as the CT-based Navitrack™ and VectorVision™. Three different surgeons carried out five cup implantations using all navigation systems and the manual approach on a surgery dummy. Cup orientation (inclination and anteversion) and the cup position (achieved cup center) were determined with a coordinate measuring machine. Results. In the manual group the variability of the cup orientation was higher in comparison and hardly influenced by the surgeon. Navigation was identified as a significant factor for smaller deviations from planned inclination and anteversion angles (p<0,001 for both). Cup position was not affected by surgeon in the manual group (p=0,966). Compared with manual technique, the cup misplacement vector was significantly smaller in the CT-Navitrack group (p<0,001) but higher in the Navitrack (CT-less) and VectorVision group (p<0,001). Conclusions. The use of computer navigation will help the surgeon to orientate the acetabular component more accurately but not necessarily with regard to cup positioning.Publicationtype: Journal Article6 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Abrasive water jet cutting as a new procedure for cutting cancellous bone : in vitro testing in comparison with the oscillating saw(Wiley, 2004-11-15); ; 12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Comparison of the THR-Cup-Orientation using different navigation systems(International Society for Computer Assisted Orthopaedic Surgery, 2004-06-18); ; ; 4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The water jet as a new tool for endoprosthesis revision surgery : an in vitro study on human bone and bone cement(IOS Press, 2003-12-30); ; ; Dierk, OliverIn revision surgeries of endoprostheses, the interface between implant and bone cement or bone must be loosened. Conventional tools have many disadvantages because of their size and limited range. Taking advantage of the selective and athermic cutting process, a plain water jet is already used in order to cut soft tissues. This study investigates the possibilities of both a plain and an abrasive water jet as cutting tools for revision surgery. Samples of the mid-diaphysis of human femora and bone cement (CMW3) were cut with a plain water jet (PWJ) and an abrasive water jet (AWJ) at two different jet-to-surface angles (30°, 90°) and at five different pressure levels (30, 40, 50, 60, 70 MPa). For a PWJ a selective pressure range was identified, where only bone cement was cut. Injecting a bio-compatible abrasive (lactose) to the jet stream resulted in significantly higher cut depths in both materials. Material removal in bone was significantly less at the smaller jet-to-surface angle for both techniques. No clear selectivity between bone and bone cement was observed for application of the AWJ. However, the material removal rate was significantly higher for bone cement than for bone at all pressure levels. The results indicate that an AWJ might be an alternative tool for cement removal. The possibility for localised cutting at interfaces could be an advantage for revision of a non-cemented prosthesis.Publicationtype: Journal Article10 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Load shift-total hip replacement : numerical and clinical evaluation of a new concept of adaptive stem fixation(Thieme, 2003-11-01); ; ; ; Aim: The new load-shift fixation concept pursues the goal of an adaptive change of geometrical characteristics of the in-situ hip replacement. In this study a preclinical and clinical evaluation was performed. Methods: By three-dimensional, dynamic finite element calculation the biomechanical properties of the prosthesis were analyzed in the early postoperative and long-term configuration. By clinical (20 ± 10 months) and radiological (18 ± 10 months) follow-up of a first series of implants (n = 20) the primary functional status of the prosthesis was examined in vivo. Results: The preclinical results revealed that the metaphyseal micromotions are reduced significantly with the diaphyseal fit of the stem postoperatively. By absorption of a biodegradable element (spreader) integrated into the tip of the stem a change of stem geometry associated with loss of the diaphyseal fit occurs. This results in a complete shifting of load transmission into the metaphyseal area. In the clinical situation the postoperative Harris hip score averaged 92.9 ± 10.5 points. Only in two patients did reversible episodes of thigh pain occur. The radiological analysis of bone remodeling phenomena pointed to a physiological load transmission. There was no evidence of loosening or osteolysis. On radiology, stem tapering could be demonstrated. Conclusion: On the basis of these promising preclinical and early clinical results the innovative load-shift prosthesis should now be further evaluated in prospective long-term studies.Publicationtype: Journal Article6 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Comparison of robotic-assisted and manual implantation of a primary total hip replacement : a prospective study(Wolters Kluwer Health, 2003-08-01); ; Background: Robotic-assisted total hip replacement has become a common method of implantation, especially in Europe. It frequently has been postulated that robotic reaming would result in an improved clinical outcome due to the better fit of the prosthesis, but that has never been demonstrated in a prospective study, to our knowledge. The purpose of this study was to compare robotic-assisted implantation of a total hip replacement with conventional manual implantation. Methods: One hundred and fifty-four patients scheduled for total hip replacement were randomly assigned to undergo either conventional manual implantation of an S-ROM prosthesis (eighty patients) or robotic-assisted implantation of such a prosthesis (seventy-four patients). The five-axis ROBODOC was used for the robotic-assisted procedures. Preoperatively as well as at three, six, twelve, and twenty-four months after surgery, the scores according to the Harris and Merle d'Aubigné systems and the Mayo clinical score were determined. Radiographs made at these intervals were analyzed for evidence of loosening, prosthetic alignment, and heterotopic ossification. Results: Thirteen (18%) of the seventy-four attempted robotic implantations had to be converted to manual implantations as a result of failure of the system. The duration of the robotic procedures was longer than that of the manual procedures (mean and standard deviation, 107.1 ± 29.1 compared with 82.4 ± 23.4 minutes, p < 0.001). Limb-length equality (mean discrepancy, 0.18 ± 0.30 compared with 0.96 ± 0.93 cm, p < 0.001) and varus-valgus orientation of the stem (mean angle between the femur and the shaft of the prosthesis, 0.34° ± 0.67° compared with 0.84° ± 1.23°, p < 0.001) were better after the robotic procedures. At six months, slightly more heterotopic ossification was seen in the group treated with robotic implantation. The group treated with robotic implantation had a better Mayo clinical score at six and twelve months and a better Harris score at twelve months; however, by twenty-four months, no difference was found between the groups with regard to any of the three scores. Dislocation was more frequent in the group treated with robotic implantation: it occurred in eleven of the sixty-one patients in that group compared with three of eighty in the other group (p < 0.001). Recurrent dislocation and pronounced limping were indications for revision surgery in eight of the sixty-one patients treated with robotic implantation compared with none of the seventy-eight (excluding two with revision for infection) treated with manual insertion (p < 0.001). Rupture of the gluteus medius tendon was observed during all of the revision operations. Conclusions: The robotic-assisted technology had advantages in terms of preoperative planning and the accuracy of the intraoperative procedure. Disadvantages were the high revision rate; the amount of muscle damage, which we believe was responsible for the higher dislocation rate; and the longer duration of surgery. This technology must be further developed before its widespread usage can be justified. Level of Evidence: Therapeutic study, Level I-1a (randomized controlled trial [significant difference]). See Instructions to Authors for a complete description of levels of evidence.Publicationtype: Journal Article4 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Use of a water jet for synovectomy : in vitro study of feasibility(Thieme, 2003-05-01); ; Rentzsch, ReemtAim: The selectivity of a water jet (WJ) is already used with clinical advantage in the surgery of liver, brain, kidney and herniated lumbar discs. The aim of the present study was to determine whether a WJ can be used for synovectomy without damaging the joint capsule and the cartilage. Method: 60 human cadaver knee specimens (67 ± 14 years) were dissected into synovial and cartilage samples. They were randomly assessed to four pressure groups (pw = 3; 6; 9; 12 MPa) and three jet surface angles (β = 30; 60; 90°) The nozzle diameter was dD= 0.12 mm, the stand off distance of the jet was s = 10 mm with a feed rate of Vv = 2 mm/s. The acquired parameters were depth of the cuts, histological layer, and change of the samples thickness. Result: There was a correlation of the cutting depth and the pressure (pw), whereas the jet-surface angle (β) showed no correlation. The synovial layer of the cut likewise correlated with the pressure. At pw = 6 MPa the stratum subsynoviale could be cut selectively without damaging the fibrous capsule or the cartilage. The increase of the samples thickness was caused by an interstitial oedema. Conclusion: The different mechanical properties of the joint capsule and the stratum subsynoviale lead to the selective cutting of the water jet. Since the joint capsule was not damaged, the feasibility of WJ synovectomy has been proven. The device can be used for synovectomy in parts of the joint that are not visible as well as in very small joints.Publicationtype: Journal Article8 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The pulsed water jet for selective removal of bone cement during revision arthroplasty(De Gruyter, 2003); ; ; 9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Pelvic girdle reconstruction based on spinal fusion and ischial screw fixation in a case of aneurysmal bone cyst(Hindawi Publishing Corporation, 2003-01-01); ; ; ; A case of lytic lesion of the pelvis in a 23-year-old woman is presented. A biopsy led to the diagnosis aneurysmal bone cyst(ABC). Due to the histologically very aggressive growth of the tumor, a low malignant osteosarcoma could not be excluded.In an initial operation the tumour, affecting the sacrum, the iliac crest and the lower lumbar spine was resected. Temporaryrestabilisation of the pelvic ring was achieved by a titanium plate. The histological examination of the entire tumourconfirmed the diagnosis ABC. After 6 months, the MRI showed no recurrence. The observed tilt of the spine to the operatedside on the sacral base prompted a second surgical procedure: a transpedicular fixation of L5 and L4 was connected via benttitanium stems to the ischium, where the fixation was achieved by two screws. This construction allowed the correction of thebase angle and yielded a stable closure of the pelvic ring. The patient has now been followed for 6 years: the bone grafts havebeen incorporated and, in spite of radiological signs of screw loosening in the ischium, the patient is fully rehabilitated andfree of symptoms. Pedicle screws in the lower spine can be recommended for fixation of a pelvic ring discontinuity.Publicationtype: Journal ArticleScopus© Citations 4 364 378