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N P Haas

Publications and source records attributed to N P Haas.

At least 19 recordsLinked to original sources
PubMed2002

Comparison of BMP-2 and combined IGF-I/TGF-ss1 application in a sheep cervical spine fusion model.

Growth factors have proven to promote spine fusion. However, no comparative evaluation of growth factors in spinal fusion has yet been performed. The purpose of this study was to compare the efficacy and safety of combined IGF-I and TGF-ss1 application with BMP-2 application and autologous cancellous bone graft at an early time point in a sheep cervical spine fusion model. Thirty-two sheep underwent C3/4 discectomy and fusion. They were divided into four groups, according to their treatment: group 1, titanium cage ( n=8); group 2, titanium cage filled with autologous cancellous iliac crest bone grafts ( n=8); group 3, titanium cage coated with a poly-(D,L-lactide) (PDLLA) carrier including BMP-2 (5% w/w) ( n=8); group 4, titanium cage coated with a PDLLA carrier including IGF-I (5% w/w) and TGF-ss1 (1% w/w) ( n=8). Blood samples, body weight and temperature were analysed. Radiographic scans were performed pre- and postoperatively and after 1, 2, 4, 8 and 12 weeks. At the same time points, disc space height and intervertebral angle were measured. After 12 weeks, the animals were killed and fusion sites were evaluated using functional radiographic views in flexion and extension. Quantitative computed tomographic scans were performed to assess bone mineral density, bone mineral content and bony callus volume. Biomechanical testing was carried out and the values for range of motion, and neutral and elastic zone were determined. Histomorphological and histomorphometrical analysis were performed and polychrome sequential labelling was used to determine the time frame of new bone formation. The results showed that, in comparison to the group treated with the cage alone (group 1), the cage plus BMP-2 group (group 3) and the cage plus IGF-I and TGF-ss1 group (group 4) demonstrated a significantly higher fusion rate in radiographic findings, a higher biomechanical stability, a more advanced interbody fusion in histomorphometrical analysis, and an accelerated interbody fusion on fluorochrome sequence labelling. In comparison to the bone graft group (group 2), the BMP-2 (group 3) and IGF-I/TGF-ss1 group (group 4) showed significantly less residual motion on functional radiographic evaluation, higher bone mineral density of the callus and higher biomechanical stability in extension, rotation and bending. The BMP-2 group showed significantly less residual motion on functional radiographic evaluation and higher intervertebral bone matrix formation on fluorochrome sequence labelling at 9 weeks in comparison to the IGF-I/TGF-ss1 group. In contrast, the IGF-I/TGF-ss1 group showed a significantly higher bone mineral density of the callus than the BMP-2 group. In comparison to the autologous cancellous bone graft group, both growth factors (BMP-2 and combined IGF-I and TGF-ss1) significantly improved the biomechanical results of interbody fusion. No systemic side effects were observed for either growth factor. On the basis of these preliminary results, it would appear that combined IGF-I/TGF-ss1 application yields equivalent results to BMP-2 application at an early time point in anterior sheep cervical spine fusion.

Animals↗
PubMed2002

A new electrochemically graded hydroxyapatite coating for osteosynthetic implants promotes implant osteointegration in a rat model.

Hydroxyapatite (HAP) is widely used as an osteoconductive coating for orthopedic implants. So far standard coating methods like plasma spraying produce a relatively thick coating layer (>30 microm). In addition, the chemical structure of the HAP may be altered because of the heating throughout the coating process. This may have negative effects on the coating stability, implant fixation, and induction of bone formation. The relatively thick layer may detach from the implant with the risk of wear debris. In the present study the potential of a newly developed HAP coating of implants on osteointegration was investigated in a rat model. The coating method, based on an electrochemical process, is applied in a graded manner and results in a biodegradable HAP coating with a thickness of approximately 2 mum. Coated versus uncoated titanium Kirschner wires (1.4-mm diameter) were inserted into the medullary cavity of the right femora of 5-month old female Sprague Dawley rats (n=36) in a retrograde fashion. Throughout an experimental period of 2 months the osteointegration was traced radiologically. After this time the animals were sacrificed and the implant integration was tested biomechanically with the use of a push-out test. To analyze the bone-implant interface, histological sections (80 mum) were investigated with an image analyzing system. The biomechanical testing revealed a significantly higher implant fixation in the group treated with the HAP-coated implant (shear strength: 27.8 +/- 6.7 MPa) compared to control (shear strength: 8.08 +/- 3.4 MPa). The histological analyses demonstrated a better ingrowth of the implants in the HAP group with significantly more direct bone-implant contacts compared to the control group. The results demonstrate that the HAP coating promotes implant osteointegration in a rat model.

Animals↗
PubMed2002

[Experimental fusion of the sheep cervical spine. Part I: Effect of cage design on interbody fusion].

INTRODUCTION: There has been a rapid increase in the use of interbody fusion cages as an adjunct to spondylodesis, although experimental data are lacking. A sheep cervical spine interbody fusion model was used to determine the effect of different cage design parameters (endplate-implant contact area, maximum contiguous pore) on interbody fusion. MATERIAL AND METHOD: IN VITRO EVALUATION: 24 sheep cadaver specimens (C2-C5) were tested in flexion, extension, axial rotation, and lateral bending with a nondestructive flexibility method using a nonconstrained testing apparatus. Four different groups were examined: (1) control group (intact) ( n=24), (2) autologous tricortical iliac crest bone graft ( n=8), (3) Harms cage ( n=8), and (4) SynCage-C ( n=8). IN VIVO EVALUATION: 24 sheep underwent C3/4 discectomy and fusion: group 1: autologous tricortical iliac crest bone graft ( n=8), group 2: Harms cage filled with autologous cancellous iliac crest bone grafts ( n=8), and group 3: SynCage-C filled with autologous cancellous iliac crest bone grafts ( n=8). Radiographic scans were performed pre- and postoperatively and after 1, 2, 4, 8, and 12 weeks, respectively. At the same time points, disc space height (DSH), height index (HI), intervertebral angle (IVA), and endplate angle (EA) were measured. After 12 weeks the animals were killed and fusion sites were evaluated using biomechanical testing in flexion, extension, axial rotation, and lateral bending. Additionally, histomorphological and histomorphometrical analyses were performed. RESULTS: Over a 12-week period the cage groups showed significantly higher values for DSH, HI, IVA, and EA compared to the bone graft. In vivo stiffness was significantly higher for the tricortical iliac crest bone graft and Harms cage than in vitro stiffness. However, there was no difference between in vitro and in vivo stiffness of the SynCage-C. Histomorphometrical evaluation showed a more progressed bone matrix formation in the Harms cage group than in both other groups. CONCLUSION: The parameter endplate-implant contact area was not able to determine subsidence of cages. In contrast, the maximum contiguous pore of a cage significantly correlates with interbody bone matrix formation inside the cage. Additionally, there was no correlation between in vitro and in vivo stiffness of interbody fusion cages. Therefore, biomechanical in vitro studies are not able to determine in vivo outcome of fusion cages. Animal experimental evaluations of interbody fusion cages are essential prior to clinical use.

Animals↗
PubMed2002

[Computer assisted pelvic and acetabular surgery. Clinical experiences and indications].

CT based navigation has been used in spine surgery since 1994. Several clinical studies could show an increase in precision compared to the conventional technique and thus nowadays the navigated pedicle screw placement is a routine procedure in many hospitals. Based upon the experience in spine surgery the CT based navigation module was used for percutaneous screw fixations in minimally displaced pelvic ring and acetabular fractures. After preclinical experimental trials the C-arm navigation was used for 19 screw fixations. The postoperative control of the screw position was performed with postop. X-ray and CT. Overall 23 of the 24 screws were placed correctly. In one SI screw the postoperative CT could reveal a ventral cortex perforation of the sacrum without any clinical symptoms. Based upon this limited clinical experience we see the indication for CT based navigation in minimally displaced acetabular fractures or in SI screw fixations in case of sacral dysplasia. The C-arm based navigation with adequate image quality is our method of choice for SI screw fixation in traumatic or degenerative instabilities, especially if reduction maneuvers are necessary.

Acetabulum↗
PubMed2002

Recombinant species-specific growth hormone increases hard callus formation in distraction osteogenesis.

The effect of growth hormone (GH) on secondary fracture healing and callus formation has been demonstrated in several previously investigated animal models. The aim of this study was to investigate and quantify the effects of GH on bone regenerates in a distraction osteogenesis model. In 20 mature female Yucatan micropigs, the tibia and fibula were osteotomized, stabilized with an external fixator, and distracted at 2 mm/day for 10 days after a 4 day latency period. The regenerates were allowed to consolidate for 10 days. Micropigs in the study group (ten animals) received a daily injection of 100 microg per kilogram body weight of recombinant porcine growth hormone (r-pGH). Micropigs in the control group (ten animals) received sodium chloride as placebo. After killing on day 25, a quantitative histomorphometrical analysis of the formed callus and the adjacent cortical bone was performed and the results of polychrome in vivo labeling were assessed. The regenerates of the r-pGH-treated animals showed a significantly larger callus area but no change in callus structure. We found islands of cartilage tissue in the regenerates of both groups; the calli from the control group exhibited a higher fraction of cartilage compared with the r-pGH group, but this was not significant. Quantification of the fluorescent in vivo labeling revealed that the distraction gap in GH-treated group showed significant ossification even during distraction. These results demonstrate that growth hormone can accelerate the maturation of the regenerate in distraction osteogenesis without changing the callus microstructure. This may prove to be a useful clinical tool for shortening the healing time in limb lengthening and bone segment transport.

Animals↗
PubMed2002

Insulin-like growth factor-1 and transforming growth factor-beta1 accelerates osteotomy healing using polylactide-coated implants as a delivery system: a biomechanical and histological study in minipigs.

Stimulation of bone healing and bone formation through local application of growth factors from implants may improve the clinical outcome in fracture treatment. Previous studies demonstrated a high mechanical stability of a thin poly(D,L-lactide) (PDLLA) coating on metallic implants that can withstand the process of intramedullary insertion. Following an initial peak, 80% of incorporated insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta1 (TGF-beta1) were released continuously, within 42 days. The goal of the present study is evaluation of the coated implants on fracture healing in a large animal model. A midshaft osteotomy (1 mm gap) of the right tibia of Yucatan minipigs was stabilized with uncoated vs. coated titanium interlocking nails (5 mm). X-ray examinations and blood analyses (including IGF-1 and IGF-binding proteins) were performed, and body weight and body temperature were taken throughout the experiment. After 28 days, both tibiae were dissected for mechanical torsional testing and histomorphometric analyses. No differences were found in the blood analyses, body weight, or temperature due to the coating or the incorporated growth factors between the groups. X-ray examinations revealed a faster consolidation of the osteotomy in the growth factor-treated group. Biomechanical testing showed a significantly higher torsional stiffness and maximum load. Progressive remodeling was observed in the histological and histomorphometric analyses with a larger callus volume in the growth factor group compared with the control groups. We conclude that local application of growth factors from a biodegradable PDLLA coating of intramedullary implants accelerates bone healing in a large animal model without systemic side effects.

Animals↗
PubMed2002

Bone morphogenetic protein-2 coating of titanium implants increases biomechanical strength and accelerates bone remodeling in fracture treatment: a biomechanical and histological study in rats.

Bone morphogenetic protein-2 (BMP-2), a member of the transforming growth factor (TGF)-beta superfamily, is known to be a very potent osteoinductive growth factor. The purpose of this study was to investigate the effect of BMP-2 (5% [w/w], 50 microg on each nail), locally released from poly(D,L-lactide) (PDLLA)-coated intramedullary implants, on fracture healing. A closed fracture of the right tibia of 5-month-old Sprague-Dawley rats (n = 64) was intramedullary stabilized with uncoated vs. BMP-2-coated titanium Kirschner wires. X-ray examinations (posteroanterior and lateral) were performed throughout the experiment. At 28 and 42 days after fracture, the animals were killed and both tibiae were dissected for biomechanical torsional testing. For histological and histomorphometric evaluation, 5 microm sections were obtained, stained with Safranin-O/light green and von Kossa, and examined using an image analysis system. The radiological results demonstrated progressed callus consolidation in the BMP-2-treated groups compared with the uncoated groups at both timepoints. Histomorphometric evaluation showed progressed callus remodeling with significantly increased mineralization and less cartilage of the periosteal callus. Due to the BMP-2 treatment, increased mineralization of the cortices was detected at 28 and 42 days after fracture. Biomechanical testing revealed significantly elevated maximum load and torsional stiffness in the BMP-2-treated groups compared with controls at both timepoints. The results clearly demonstrate that local application of BMP-2 from PDLLA-coated implants is feasible and significantly accelerates fracture healing. Local administration of growth factors from coated implants could reduce clinical problems in fracture treatment without opening of the fracture, implantation of further devices, or injection with the risk of infection or side effects caused by other carriers.

Animals↗
PubMed2002

Treatment of complex acetabular fractures through a modified extended iliofemoral approach.

OBJECTIVES: To assess the rate of anatomic reconstructions as well as approach-related morbidity and complications in the treatment of complex acetabular fractures through a modified extended iliofemoral approach. DESIGN: Prospective clinical study. SETTING: Level I trauma center, University Hospital. PATIENTS: Inclusion criteria were as follows: (a) associated acetabular fracture or transverse fracture with comminuted roof area stated as not sufficiently reconstructable through a single approach, and (b) age between sixteen and sixty-five years. A total of forty-nine patients with fifty complex acetabular fractures could be included out of the series of ninety-six acetabular fractures treated operatively from August 1992 to February 1996. Open reduction and internal fixation of complex acetabular fractures through the modified extended iliofemoral approach were performed. RESULTS: In 80 percent of the fifty fractures the reduction was anatomic with a remaining displacement of less than or equal to one millimeter, in eight cases there was a persistent displacement of two millimeters, and two fractures had a poor result with a three-millimeter displacement. Complications included 8 percent loss of reduction, 13 percent heterotopic ossification grade 3, and 4 percent avascular femoral head necrosis. At the two-year follow-up there were 74 percent good or excellent radiographic and clinical results. Two patients had already been reoperated with total hip replacement, and the two patients with femoral head necrosis are currently scheduled for arthroplasty. CONCLUSIONS: The modified extended iliofemoral approach proved to be appropriate to achieve anatomic reduction in complex acetabular fractures. The high rate of approach-related morbidity has to be considered carefully and may lead to a decreased incidence of extended approaches.

Acetabulum↗
PubMed2002

Osseous integration of hydroxyapatite grafts in metaphyseal bone defects of the proximal tibia (CT-study).

PURPOSE OF THE STUDY: The purpose of the study was the examination of the osseous integration of hydroxyapatite grafts used for the filling of metaphyseal bone defects in tibia head fractures. MATERIAL: Four patients with lateral tibia plateau fractures AO-type B3 (12) were included in the study. Patients were treated by arthroscopically assisted reduction and percutaneous screw fixation. The metaphyseal bone defects were filled with prepared solid hydroxyapatite graft blocks (Endobon Fa. Merk Darmstadt, Germany). In all of the patients a CT study for the osseous integration of hydroxyapatite grafts used for the filling of metaphyseal bone defects in tibial head fractures was performed. Measurements of density were performed of the implant region, the periimplant region, the distant periimplant region and the fibula bone. Follow-up CT examinations of these specific regions were performed 6 and 12 months postoperative. RESULTS: In all cases an increase of density of the hydroxyapatite graft after 6 months and 12 months follow-up was detected. The periimplant region showed in all cases a decrease of density. A progressive decrease of the periimplant and the distant cancellous tibial bone region was also detectable after 6 and 12 months post-op. A similar decrease of density was visible in the region of the cancellous bone of the fibula. In the interface region a direct bone formation between the hydroxyapatite graft and the adjected cancellous bone was visible in all cases during follow-up. CONCLUSION: The increase of density of the hydroxyapatite grafts and the direct bone formation in the interface region between the hydroxyapatite graft and the adjacent cancellous bone are clear radiomorphological signs for an osteointegration of hydroxyapatite grafts in the metaphyseal region.

Adult↗
PubMed2001

Biomechanical comparison of cervical spine interbody fusion cages.

STUDY DESIGN: An in vitro biomechanical study of cervical spine interbody fusion cages using a sheep model was conducted. OBJECTIVES: To evaluate the biomechanical effects of cervical spine interbody fusion cages, and to compare three different cage design groups. SUMMARY AND BACKGROUND DATA: Recently, there has been a rapid increase in the use of cervical spine interbody fusion cages as an adjunct to spondylodesis. These cages can be classified into three design groups: screw, box, or cylinder designs. Although several comparative biomechanical studies of lumbar interbody fusion cages are available, biomechanical data for cervical spine constructs are lacking. Additionally, only limited data are available concerning comparative evaluation of different cage designs. METHODS: In this study, 80 sheep cervical spines (C2-C5) were tested in flexion, extension, axial rotation, and lateral bending with a nondestructive stiffness method using a nonconstrained testing apparatus. Three-dimensional displacement was measured using an optical measurement system (Qualysis). Complete discectomy (C3-C4) was performed. Cervical spine interbody fusion cages were implanted according to manufacturers' information. Eight spines in each of the the following groups were tested: intact, autologous iliac bone graft, two titanium screws (Novus CTTi; Sofamor Danek, Koln, Germany), two titanium screws (BAK-C 8 mm; Sulzer Orthopedics, Baar, Switzerland), one titanium screw (BAK-C 12 mm; Sulzer Orthopedics), carbon box (Novus CSRC; Sofamor Danek), titanium box (Syncage; Synthes, Bochum, Germany), titanium mesh cylinder (Harms; DePuy Acromed, Sulzbach, Germany), titanium cylinder (MSD; Ulrich, Ulm, Germany), and titanium cylinder (Kaden; BiometMerck, Berlin, Germany). The mean apparent stiffness values were calculated from the corresponding load-displacement curves. Additionally, cage volume and volume-related stiffness was determined. RESULTS: After cervical spine interbody fusion cage implantation, flexion stiffness increased, as compared with that of the intact motion segment. On the contrary, rotation stiffness decreased after implantation of a cervical spine interbody fusion cage, except for the Novus CSRC, Syncage, and Kaden-Cage. If two screws were inserted (Novus CTTi and BAK-C 8 mm), there was no significant difference in flexion stiffness between screw and cylinder design groups. If one screw was inserted (BAK-C 12 mm), flexion stiffness was higher for cylinder designs (P < 0.05). Extension and bending stiffness were always higher with cylinder designs (P < 0.05). Volume-related stiffness for flexion extension and bending was highest for the Harms cage (P < 0.05). There was no difference for rotation volume-related stiffness between Harms and Syncage. CONCLUSIONS: The biomechanical results indicate that design variations in screw and cylinder design groups are of little importance. In this study, however, cages with a cylinder design were able to control extension and bending more effectively than cages with a screw design.

Animals↗
PubMed2001

Biodegradable poly(D,L-lactide) coating of implants for continuous release of growth factors.

Local application of growth factors like insulin like growth factor-I (IGF-I) and transforming growth factor-beta 1 (TGF-beta1) from a biodegradable thin layer of poly(D,L-lactide) (PDLLA) coated implants could stimulate fracture healing. A new "cold coating technique" for metallic implants was established to produce a biodegradable coating with a high mechanical stability that provides a continuous release of incorporated growth factors. The properties of this bioactive coating were investigated in vitro and in vivo. Scanning electron microscope analysis revealed a coating thickness of in average 14.8 microm on titanium and 10.7 microm on steel wires. Intramedullary implantation and extraction experiments depicted a loss of PDLLA coating from titanium and steel implants of less than 5%. After explantation of the implants, the coating displayed a complete and regular layer without any defects of PDLLA uncovering the metallic surface. Smear tests demonstrate that the coating can be performed under sterile conditions. The PDLLA depicted a reduction of about 8% within 6 weeks in vitro and in vivo. The growth factors were incorporated in a stable form and demonstrated a loss of stability of less than 3% within 42 days and less than 5% within one year. In an elution experiment, 54% IGF-I and 48% TGF-beta1 were released within the first 48 h. After 42 days, 76% of IGF-I and 71% of TGF-beta1 were detected in the elution fluid by ELISA. Comparable results were obtained in the in vivo experiments after 42 days.

Animals↗
PubMed2001

[LISS--internal plate fixator].

The LISS DF (less invasive stabilisation system) is a new internal fixator for the operative treatment of distal femur fractures following the principles of minimally invasive surgery. The fixation of the implant is based on screws providing angular stability, which are inserted percutaneously guided by an aiming device. A large exposure of the fracture zone is not necessary. Between December 1996 and November 1998 a multicentre study were defined including finally 112 patients with 116 distal femur fractures treated with a LISS system. A follow up rate of 93% could be achieved, showing a fractures consolidation in 96% of all cases after 12 months. The results of the study showed a low rate of secondary bone grafting. The LISS system is a secure device for the treatment of all distal femur fractures including complex articular fractures types.

Adult↗
PubMed2001

[Mechanical comparison of biodegradable intervertebral lumbar cages].

INTRODUCTION: A biodegradable interbody cage for lumbar spine fusion would be able to solve several problems associated with the use of metallic cages. In a biomechanical in vitro study using human lumbar spines three different biodegradable poly(L-lactide-co-D,L-lacitide)(PLDLLA) cages were compared to metallic cages of the same design. MATERIAL AND METHOD: 40 human cadaver lumbar specimens (L3-S1) were tested in flexion, extension, rotation, and bending with a non-destructive flexibility method using a nonconstrained testing apparatus. Seven different groups were examined: (1) control group (intact) (n = 40); (2) unstable group (after discectomy L4/5) (n = 40), (3) autologous iliac crest bone graft (n = 8), (4) BAK-Cage (n = 8), (5) BIO-Cage 1 (PLDLLA) (n = 8), (6) BIO-Cage 2 (PLD-LLA/hydroxylapatite-buffer) (n = 8) and (7) BIO-Cage 3 (PLDLLA/hydroxylapatite particles of different size) (n = 8). Additionally, destructive compression tests of all implants were performed. RESULTS: In comparison to the intact motion segment all cages showed significantly lower range of motion (ROM) in all test modes (P < 0.01). There was no significant difference in stiffness values and ROM between BIO-Cages and metallic cages. Axial compression stiffness and failure load were significantly highest for metallic BAK-cages (P < 0.05). No significant difference for failure load was observed between BIO-cage 1 and the intact motion segment. However, in comparison to the intact motion segment failure load was significantly lower for BIO-cage 2 and 3 (P < 0.05). CONCLUSION: The results of this study are encouraging, because the biodegradable cages were able to limit lumbar spine motion similar to the metallic cages. Especially, the biodegradable PLDLLA cage consisting of pure polymer (BIO-Cage 1) showed adequate initial compression strength. However, further in vivo animal experiments are essential prior to the clinical application of biodegradable lumbar interbody fusion cages.

Absorbable Implants↗
PubMed2001

[Transoral atlanto-axial plate fixation in the treatment of a malunited dens fracture and secondary atlanto-axial instability].

INTRODUCTION: A case of a 22-year-old patient with a malunited dens fracture and secondary atlanto-axial instability is presented. The significant narrowing of the spinal canal due to the atlanto-axial instability was associated with anterior myelon compression and neurological deficit. METHODS: A transoral approach with odontoid resection and anterior atlanto-axial plate fixation was performed. With this technique the atlanto-axial subluxation was reduced and the myelon was decompressed. RESULTS: The postoperative course was uneventful. The follow-up showed a complete remission of the neurological deficit and a bony fusion of the atlanto-axial joints. CONCLUSIONS: The presented case illustrates the importance of an accurate initial diagnosis of the degree of instability and the need for short-term follow-up examinations. If atlanto-axial pseudarthrosis or malunion with anterior spinal cord compression occurs, a transoral procedure with odontoid resection and atlanto-axial plate fixation seems to be an excellent salvage procedure.

Adult↗
PubMed2001

[Navigation assisted by image conversion. An experimental study on pelvic screw fixation].

Within an experimental trial the new method of fluoroscopy based navigation was tested for percutaneous pelvic screw fixations. A regular C-arm was used and the navigation system developed by Medivision. In a first step appropriate C-arm projections were defined for five standardized screw positions. Then precision and fluoroscopy time of 60 screws in 6 artificial pelves were evaluated. For the sacroliacal screw in S1, S1 screw in S2, anterior column screw, posterior column screw and the supraacetabular ilium screw three to four appropriate projections were defined. These were all combinations of the known special pelvic views inlet/outlet and iliac/obturator. Using these standardized views the average fluoroscopy time was 6 seconds per screw. 51 screws (85%) were inserted correctly. In five cases there was a slight deviation without perforating the cortex, four times the cortex was perforated.

Acetabulum↗
PubMed2001

[Biomechanical study of angle-stable anterior atlanto-axial spondylodesis plate].

The optimum fixation method to achieve atlantoaxial fusion after odontoid resection is still subject to discussion. Isolated posterior surgical procedures for treatment of irreducible atlantoaxial kyphosis with spinal cord compression are associated with a high rate of morbidity and mortality. Transoral atlantoaxial plate fixation has been described by Harms as a fixation technique after odontoid resection. The purpose of this study was to compare biomechanically a new anterior atlantoaxial locking plate (AALP) with the Harms plate and the atlantoaxial transarticular screw fixation described by Magerl. Sixteen human cadaver craniocervical specimens were tested in flexion, extension, rotation, and bending with a nondestructive flexibility method using a nonconstrained testing apparatus. Five different groups were examined: (1) control group (intact) (n = 16), (2) unstable group (after dissection of the atlantoaxial ligaments and odontoidectomy) (n = 16), (3) Harms group (transoral atlantoaxial plate fixation) (n = 8), (4) AALP group (anterior atlantoaxial locking plate fixation) (n = 8), and (5) Magerl group (transarticular atlantoaxial screw fixation) (n = 16). Stiffness in any direction was significantly higher in the AALP specimens and those fixated with the Magerl method than in the Harms, control, or unstable specimens. The difference in stiffness between the AALP and Magerl reconstruction groups was not statistically significant. Experimentally, the AALP was significantly stiffer than the Harms plate. The AALP provided stiffness equal to transarticular screw fixation according to Magerl. A question that cannot be answered by this in vitro study concerns the level of rigidity required to obtain long-term stability and fusion by atlantoaxial fixation methods. However, it may be assumed that the more spinal motion is eliminated the greater the chance of definite spinal fusion. Therefore, it seems reasonable that the most reliable and rigid fixation method would be the method of choice.

Aged↗