Harvesting local cylinder autograft from adjacent vertebral body for anterior lumbar interbody fusion: surgical technique, operative feasibility and preliminary clinical results

Autogenous iliac crest has long served as the gold standard for anterior lumbar arthrodesis although added morbidity results from the bone graft harvest. Therefore, femoral ring allograft, or cages, have been used to decrease the morbidity of iliac crest bone harvesting. More recently, an experimental study in the animal showed that harvesting local bone from the anterior vertebral body and replacing the void by a radio-opaque beta-tricalcium phosphate plug was a valid concept. However, such a concept precludes theoretically the use of posterior pedicle screw fixation. At one institution a consecutive series of 21 patients underwent single- or multiple-level circumferential lumbar fusion with anterior cages and posterior pedicle screws. All cages were filled with cancellous bone harvested from the adjacent vertebral body, and the vertebral body defect was filled with a beta-tricalcium phosphate plug. The indications for surgery were failed conservative treatment of a lumbar degenerative disc disease or spondylolisthesis. The purpose of this study, therefore, was to report on the surgical technique, operative feasibility, safety, benefits, and drawbacks of this technique with our primary clinical experience. An independent researcher reviewed all data that had been collected prospectively from the onset of the study. The average age of the patients was 39.9 (26-57) years. Bone grafts were successfully harvested from 28 vertebral bodies in all but one patient whose anterior procedure was aborted due to difficulty in freeing the left common iliac vein. This case was converted to a transforaminal interbody fusion (TLIF). There was no major vascular injury. Blood loss of the anterior procedure averaged 250 ml (50-350 ml). One tricalcium phosphate bone plug was broken during its insertion, and one endplate was broken because of wrong surgical technique, which did not affect the final outcome. One patient had a right lumbar plexopathy that was not related to this special technique. There was no retrograde ejaculation, infection or pseudoarthrosis. One patient experienced a deep venous thrombosis. At the last follow up (mean 28 months) all patients had a solid lumbar spine fusion. At the 6-month follow up, the pain as assessed on the visual analog scale (VAS) decreased from 6.9 to 4.5 (33% decrease), and the Oswestry disability index (ODI) reduced from 48.0 to 31.7 with a 34% reduction. However, at 2 years follow up there was a trend for increase in the ODI (35) and VAS (5). The data in this study suggest that harvesting a cylinder of autograft from the adjacent vertebral body is safe and efficient. Filling of the void defect with a beta-tricalcium phosphate plug does not preclude the use of posterior pedicle screw stabilization.

Biomechanical Evaluation of the Stabilizing Function of Three Atlantoaxial Implants Under Shear Loading: A Canine Cadaveric Study

OBJECTIVE: To compare the biomechanical properties of a ventral transarticular lag screw fixation technique, a new dorsal atlantoaxial instability (AAI) clamp, and a new ventral AAI hook plate under sagittal shear loading after transection of the ligaments of the atlantoaxial joint. STUDY DESIGN: Cadaveric biomechanical study. ANIMALS: Canine cadavers (n = 10). MATERIALS AND METHODS: The occipitoatlantoaxial region of Beagles euthanatized for reasons unrelated to the study was prepared leaving only ligamentous structures and the joint capsules between the first 2 cervical vertebrae (C1 and C2). The atlanto-occipital joints were stabilized with 2 transarticular diverging positive threaded K-wires. The occipital bone and the caudal end of C2 were embedded in polymethylmethacrylate and loaded in shear to a force of 50 Newtons. The range of motion (ROM) and neutral zone (NZ) of the atlantoaxial joint were determined after 3 loading cycles with atlantoaxial ligaments intact, after ligament transection, and after fixation with each implant. The testing order of implants was randomly assigned. The implants tested last were subjected to failure testing. RESULTS: All stabilization procedures decreased the ROM and NZ of the atlantoaxial joint compared to transected ligament specimens. Only stabilization with transarticular lag screws and ventral plates produced a significant reduction of ROM compare to intact specimens. CONCLUSION: Fixation with transarticular lag screws and a ventral hook plate was biomechanically similar and provided more rigidity compared to dorsal clamp fixation. Further load cycling to failure tests and clinical studies are required before making clinical recommendations.

Biomechanical evaluation of different angle-stable locking plate systems for mandibular surgery

PURPOSE To compare the initial stability and stability after fatigue of three different locking systems (Synthes(®), Stryker(®) and Medartis(®)) for mandibular fixation and reconstruction. METHOD Standard mandible locking plates with identical profile height (1,5 mm), comparable length and screws with identical diameter (2,0 mm) were used. Plates were fixed with six screws according a preparation protocol. Four point bending tests were then performed using artificial bone material to compare their initial stability and failure limit under realistic loading conditions. Loading of the plates was performed using of a servo hydraulic driven testing machine. The stiffness of the implant/bone construct was calculated using a linear regression on the experimental data included in a range of applied moment between 2 Nm and 6 Nm. RESULTS No statistical difference in the elastic stiffness was visible between the three types of plate. However, differences were observed between the systems concerning the maximal load supported. The Stryker and Synthes systems were able to support a significantly higher moment. CONCLUSION For clinical application all systems show good and reliable results. Practical aspects such as handling, possible angulation of screw fixation, possibility of screw/plate removal, etc. may favour one or the other plating system.

Effect of an intervertebral disk spacer on stiffness after monocortical screw/polymethylmethacrylate fixation in simulated and cadaveric canine cervical vertebral columns.

OBJECTIVE To determine the biomechanical effect of an intervertebral spacer on construct stiffness in a PVC model and cadaveric canine cervical vertebral columns stabilized with monocortical screws/polymethylmethacrylate (PMMA). STUDY DESIGN Biomechanical study. SAMPLE POPULATION PVC pipe; cadaveric canine vertebral columns. METHODS PVC model-PVC pipe was used to create a gap model mimicking vertebral endplate orientation and disk space width of large-breed canine cervical vertebrae; 6 models had a 4-mm gap with no spacer (PVC group 1); 6 had a PVC pipe ring spacer filling the gap (PCV group 2). Animals-large breed cadaveric canine cervical vertebral columns (C2-C7) from skeletally mature dogs without (cadaveric group 1, n = 6, historical data) and with an intervertebral disk spacer (cadaveric group 2, n = 6) were used. All PVC models and cadaver specimens were instrumented with monocortical titanium screws/PMMA. Stiffness of the 2 PVC groups was compared in extension, flexion, and lateral bending using non-destructive 4-point bend testing. Stiffness testing in all 3 directions was performed of the unaltered C4-C5 vertebral motion unit in cadaveric spines and repeated after placement of an intervertebral cortical allograft ring and instrumentation. Data were compared using a linear mixed model approach that also incorporated data from previously tested spines with the same screw/PMMA construct but without disk spacer (cadaveric group 1). RESULTS Addition of a spacer increased construct stiffness in both the PVC model (P < .001) and cadaveric vertebral columns (P < .001) compared to fixation without a spacer. CONCLUSIONS Addition of an intervertebral spacer significantly increased construct stiffness of monocortical screw/PMMA fixation.

Population-based design of mandibular fixation plates with bone quality and morphology considerations

In this paper we present a new population-based implant design methodology, which advances the state-of-the-art approaches by combining shape and bone quality information into the design strategy. The method may enhance the mechanical stability of the fixation and reduces the intra-operative in-plane bending which might impede the functionality of the locking mechanism. The computational method is presented for the case of mandibular locking fixation plates, where the mandibular angle and the bone quality at screw locations are taken into account. The method automatically derives the mandibular angle and the bone thickness and intensity values at the path of every screw from a set of computed tomography images. An optimization strategy is then used to optimize the two parameters of plate angle and screw position. The method was applied to two populations of different genders. Results for the new design are presented along with a comparison with a commercially available mandibular locking fixation plate (MODUS(®) TriLock(®) 2.0/2.3/2.5, Medartis AG, Basel, Switzerland). The proposed designs resulted in a statistically significant improvement in the available bone thickness when compared to the standard plate. There is a higher probability that the proposed implants cover areas of thicker cortical bone without compromising the bone mineral density around the screws. The obtained results allowed us to conclude that an angle and screw separation of 129° and 9 mm for females and 121° and 10 mm for males are more suitable designs than the commercially available 120° and 9 mm.

New means in spinal pedicle hook fixation. A biomechanical evaluation

Pedicle hooks which are used as an anchorage for posterior spinal instrumentation may be subjected to considerable three-dimensional forces. In order to achieve stronger attachment to the implantation site, hooks using screws for additional fixation have been developed. The failure loads and mechanisms of three such devices have been experimentally determined on human thoracic vertebrae: the Universal Spine System (USS) pedicle hook with one screw, a prototype pedicle hook with two screws and the Cotrel-Dubousset (CD) pedicle hook with screw. The USS hooks use 3.2-mm self-tapping fixation screws which pass into the pedicle, whereas the CD hook is stabilised with a 3-mm set screw pressing against the superior part of the facet joint. A clinically established 5-mm pedicle screw was tested for comparison. A matched pair experimental design was implemented to evaluate these implants in constrained (series I) and rotationally unconstrained (series II) posterior pull-out tests. In the constrained tests the pedicle screw was the strongest implant, with an average pull-out force of 1650 N (SD 623 N). The prototype hook was comparable, with an average failure load of 1530 N (SD 414 N). The average pull-out force of the USS hook with one screw was 910 N (SD 243 N), not significantly different to the CD hook's average failure load of 740 N (SD 189 N). The result of the unconstrained tests were similar, with the prototype hook being the strongest device (average 1617 N, SD 652 N). However, in this series the difference in failure load between the USS hook with one screw and the CD hook was significant. Average failure loads of 792 N (SD 184 N) for the USS hook and 464 N (SD 279 N) for the CD hook were measured. A pedicular fracture in the plane of the fixation screw was the most common failure mode for USS hooks.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of theoretical fixation stability of three devices employed in medial opening wedge high tibial osteotomy: a finite element analysis.

BACKGROUND Medial open wedge high tibial osteotomy is a well-established procedure for the treatment of unicompartmental osteoarthritis and symptomatic varus malalignment. We hypothesized that different fixation devices generate different fixation stability profiles for the various wedge sizes in a finite element (FE) analysis. METHODS Four types of fixation were compared: 1) first and 2) second generation Puddu plates, and 3) TomoFix plate with and 4) without bone graft. Cortical and cancellous bone was modelled and five different opening wedge sizes were studied for each model. Outcome measures included: 1) stresses in bone, 2) relative displacement of the proximal and distal tibial fragments, 3) stresses in the plates, 4) stresses on the upper and lower screw surfaces in the screw channels. RESULTS The highest load for all fixation types occurred in the plate axis. For the vast majority of the wedge sizes and fixation types the shear stress (von Mises stress) was dominating in the bone independent of fixation type. The relative displacements of the tibial fragments were low (in μm range). With an increasing wedge size this displacement tended to increase for both Puddu plates and the TomoFix plate with bone graft. For the TomoFix plate without bone graft a rather opposite trend was observed.For all fixation types the occurring stresses at the screw-bone contact areas pulled at the screws and exceeded the allowable threshold of 1.2 MPa for at least one screw surface. Of the six screw surfaces that were studied, the TomoFix plate with bone graft showed a stress excess of one out of twelve and without bone graft, five out of twelve. With the Puddu plates, an excess stress occurred in the majority of screw surfaces. CONCLUSIONS The different fixation devices generate different fixation stability profiles for different opening wedge sizes. Based on the computational simulations, none of the studied osteosynthesis fixation types warranted an intransigent full weight bearing per se. The highest fixation stability was observed for the TomoFix plates and the lowest for the first generation Puddu plate. These findings were revealed in theoretical models and need to be validated in controlled clinical settings.

Influence of screw augmentation in posterior dynamic and rigid stabilization systems in osteoporotic lumbar vertebrae: a biomechanical cadaveric study.

STUDY DESIGN Biomechanical cadaveric study. OBJECTIVE To determine whether augmentation positively influence screw stability or not. SUMMARY OF BACKGROUND DATA Implantation of pedicle screws is a common procedure in spine surgery to provide an anchorage of posterior internal fixation into vertebrae. Screw performance is highly correlated to bone quality. Therefore, polymeric cement is often injected through specifically designed perforated pedicle screws into osteoporotic bone to potentially enhance screw stability. METHODS Caudocephalic dynamic loading was applied as quasi-physiological alternative to classical pull-out tests on 16 screws implanted in osteoporotic lumbar vertebrae and 20 screws in nonosteoporotic specimen. Load was applied using 2 different configurations simulating standard and dynamic posterior stabilization devices. Screw performance was quantified by measurement of screwhead displacement during the loading cycles. To reduce the impact of bone quality and morphology, screw performance was compared for each vertebra and averaged afterward. RESULTS All screws (with or without cement) implanted in osteoporotic vertebrae showed lower performances than the ones implanted into nonosteoporotic specimen. Augmentation was negligible for screws implanted into nonosteoporotic specimen, whereas in osteoporotic vertebrae pedicle screw stability was significantly increased. For dynamic posterior stabilization system an increase of screwhead displacement was observed in comparison with standard fixation devices in both setups. CONCLUSION Augmentation enhances screw performance in patients with poor bone stock, whereas no difference is observed for patients without osteoporosis. Furthermore, dynamic stabilization systems have the possibility to fail when implanted in osteoporotic bone.

Evaluation of a Novel Screw Position in a Type III Distal Phalanx Fracture Model: An Ex Vivo Study

OBJECTIVE: Mechanical evaluation of a novel screw position used for repair in a type III distal phalanx fracture model and assessment of solar canal penetration (SCP). STUDY DESIGN: Experimental study. SAMPLE POPULATION: Disarticulated equine hooves (n = 24) and 24 isolated distal phalanges. METHODS: Hooves/distal phalanges cut in a sagittal plane were repaired with 1 of 2 different cortical screw placements in lag fashion. In group 1 (conventional screw placement), the screw was inserted halfway between the proximal border of the solar canal (SC) and the subchondral bone surface on a line parallel to the dorsal cortex, whereas in group 2, the screw was inserted more palmar/plantar, where a perpendicular line drawn from the group 1 position reached the palmar/plantar cortex. Construct strength was evaluated by 3-point bending to failure. SCP was assessed by CT imaging and macroscopically. RESULTS: Screws were significantly longer in group 2 and in forelimbs. Group 2 isolated distal phalanges had a significantly more rigid fixation compared with the conventional screw position (maximum point at failure 31%, bending stiffness 41% higher). Lumen reduction of the SC was observed in 13/52 specimens (all from group 2), of which 9 were forelimbs. CONCLUSIONS: More distal screw positioning compared with the conventionally recommended screw position for internal fixation of type III distal phalangeal fractures allows placement of a longer screw and renders a more rigid fracture fixation. The novel screw position, however, carries a higher risk of SCP

Surgical exposures and options for instrumentation in acetabular fracture fixation: Pararectus approach versus the modified Stoppa.

BACKGROUND As an alternative to the modified Stoppa approach, the Pararectus approach is used clinically for treatment of acetabular fractures involving the anterior column. The current study assessed the surgical exposure and the options for instrumentation using both of these approaches. METHODS Surgical dissections were conducted on five human cadavers (all male, mean age 88 years (82-97)) using the modified Stoppa and the Pararectus approach, with the same skin incision length (10cm). Distal boundaries of the exposed bony surfaces were marked using a chisel. After removal of all soft-tissues, distances from the boundaries in the false and true pelvis were measured with reference to the pelvic brim. The exposed bone was coloured and calibrated digital images of each inner hemipelvis were taken. The amount of exposed surface using both approaches was assessed and represented as a percentage of the total bony surface of each hemipelvis. For instrumentation, a suprapectineal quadrilateral buttress plate was used. Screw lengths were documented, and three-dimensional CT reconstructions were performed to assess screw trajectories qualitatively. Wilcoxon's signed rank test for paired groups was used (level of significance: p<0.05). RESULTS After utilization of the Pararectus approach, the distances from the farthest boundaries of exposed bone towards the pelvic brim were significantly higher in the false but not the true pelvis, compared to the modified Stoppa approach. The percentage (mean±SD) of exposed bone accessible after utilizing the Pararectus approach was 42±8%, compared to 29±6% using the modified Stoppa (p=0.011). In cadavers exposed by the Pararectus approach, screws placed for posterior fixation and as a posterior column screw were longer by factor 1.8 and 2.1, respectively (p<0.05), and screws could be placed more posteromedial towards the posterior inferior iliac spine or in line with the posterior column directed towards the ischial tuberosity. CONCLUSION Compared to the modified Stoppa, the Pararectus approach facilitates a greater surgical access in the false pelvis, provides versatility for fracture fixation in the posterior pelvic ring and allows for the option to extend the approach without a new incision.

Surgical dislocation of the hip for the fixation of acetabular fractures

Surgical dislocation of the hip in the treatment of acetabular fractures allows the femoral head to be safely displaced from the acetabulum. This permits full intra-articular acetabular and femoral inspection for the evaluation and potential treatment of cartilage lesions of the labrum and femoral head, reduction of the fracture under direct vision and avoidance of intra-articular penetration with hardware. We report 60 patients with selected types of acetabular fracture who were treated using this approach. Six were lost to follow-up and the remaining 54 were available for clinical and radiological review at a mean follow-up of 4.4 years (2 to 9). Substantial damage to the intra-articular cartilage was found in the anteromedial portion of the femoral head and the posterosuperior aspect of the acetabulum. Labral lesions were predominantly seen in the posterior acetabular area. Anatomical reduction was achieved in 50 hips (93%) which was considerably higher than that seen in previous reports. There were no cases of avascular necrosis. Four patients subsequently required total hip replacement. Good or excellent results were achieved in 44 hips (81.5%). The cumulative eight-year survivorship was 89.0% (95% confidence interval 84.5 to 94.1). Significant predictors of poor outcome were involvement of the acetabular dome and lesions of the femoral cartilage greater than grade 2. The functional mid-term results were better than those of previous reports. Surgical dislocation of the hip allows accurate reduction and a predictable mid-term outcome in the management of these difficult injuries without the risk of the development of avascular necrosis.

Obesity, age, sex, diagnosis, and fixation mode differently affect early cup failure in total hip arthroplasty: a matched case-control study of 4420 patients

Studies about the influence of patient characteristics on mechanical failure of cups in total hip replacement have applied different methodologies and revealed inconclusive results. The fixation mode has rarely been investigated. Therefore, we conducted a detailed analysis of the influence of patient characteristics and fixation mode on cup failure risks.

Internal fixation of symphyseal disruption resulting from childbirth

To investigate the clinical and radiographic results after operative treatment of complete symphyseal disruption resulting from childbirth and to evaluate residual pain and implant failure in relation to the timing of surgery.

Mesh shrinkage and pain in laparoscopic ventral hernia repair: a randomized clinical trial comparing suture versus tack mesh fixation

Mesh fixation during laparoscopic ventral hernia repair can be performed using transfascial sutures or metal tacks. The aim of the present study is to compare mesh shrinkage and pain between two different techniques of mesh fixation in a prospective randomized trial.