Patrick Kluger

Computer-assisted surgery in posterior instrumentation of the cervical spine: an in-vitro feasibility study.

Abstract Transarticular C1/2 screws are widely used in posterior cervical spine instrumentation. The use of pedicle screws in the cervical spine remains uncommon. Due to superior biomechanical stability compared to lateral mass screws, pedicle screws can be used, especially for patients with poor bone quality or defects in the anterior column. Nevertheless there are potential risks of iatrogenic damage to the spinal cord, nerve roots or the vertebral artery associated with both posterior cervical spine instrumentation techniques. Therefore, the aim of this study was to evaluate whether C1/2 transarticular screws as well as transpedicular screws in C3 and C4 can be applied safely and with high accuracy using a computer-assisted surgery (CAS) system. We used 13 human cadaver C0-C5 spine segments. We installed 1.4-mm Kirschner wires transarticular in C1/2, using a specially designed guide, and drilled 2.5-mm pedicle holes in C3 and C4 with the assistance of the CAS system. Hole positions were evaluated by palpation, CT and dissection. Forty-eight (92%) of the 52 drilled pedicles were correctly positioned after palpation, imaging and dissection. The vertebral artery was not injured in any specimen. All of the 26 C1/2 Kirschner wires were placed properly after imaging and dissection evaluations. No injury to vascular or bony structures was observed. C1/2 transarticular screws as well as transpedicular screws in the cervical spine can be applied safely and with high accuracy using a CAS system in vitro. Therefore, this technique may be used in a clinical setting, as it offers improved accuracy and reduced radiation dose for the patient and the medical staff. Nevertheless, users should take note of known sources of possible faults causing inaccuracies in order to prevent iatrogenic damage. Small pedicles, with a diameter of less than 4.0 mm, may not be suitable for pedicle screws.

Load-displacement properties of the normal and injured lower cervical spine in vitro

Abstract The objective of this study was to determine which discoligamentous structures of the lower cervical spine provide significant stability with regard to different loading conditions. Accordingly, the load-displacement properties of the normal and injured lower cervical spine were tested in vitro. Four artificially created stages of increasing discoligamentous instability of the segment C5/6 were compared to the normal C5/6 segment. Six fresh human cadaver spine segments C4-C7 were tested in flexion/extension, axial rotation, and lateral bending using pure moments of ± 2.5 Nm without axial preload. Five conditions were investigated consecutively: (1) the intact functional spinal unit (FSU) C5/6; (2) the FSU C5/6 with the anterior longitudinal ligament and the intertransverse ligaments sectioned; (3) the FSU C5/6 with an additional 10-mm-deep incision of the anterior half of the anulus fibrosus and the disc; (4) the FSU C5/6 with additionally sectioned ligamenta flava as well as interspinous and supraspinous ligaments; (5) the FSU C5/6 with additional capsulotomy of the facet joints. In flexion/extension, significant differences were observed concerning range of motion (ROM) and neutral zone (NZ) for all four stages of instability compared to the intact FSU. In axial rotation, only the stage 4 instability showed a significantly increased ROM and NZ compared to the intact FSU. For lateral bending, no significant differences were observed. Based on these data, we conclude that flexion/extension is the most sensitive load-direction for the tested discoligamentous instabilities.

Biomechanical evaluation of a new modular rod-screw implant system for posterior instrumentation of the occipito-cervical spine: in-vitro comparison with two established implant systems

Abstract Posterior instrumentation of the occipito-cervical spine has become an established procedure in a variety of indications. The use of rod-screw systems improved posterior instrumentation as it allows optimal screw positioning adapted to the individual anatomic situation. However, there are still some drawbacks concerning the different implant designs. Therefore, a new modular rod-screw implant system has been developed to overcome some of the drawbacks of established systems. The aim of this study was to evaluate whether posterior internal fixation of the occipito-cervical spine with the new implant system improves primary biomechanical stability. Three different internal fixation systems were compared in this study: the CerviFix System, the Olerud Cervical Rod Spinal System and the newly developed Neon Occipito Cervical System. Eight human cervical spine C0/C5 specimens were instrumented from C0 to C4 with occipital fixation, transarticular screws in C1/C2 and lateral mass or pedicle screws in C3 and C4. The specimens were tested in flexion/extension, axial rotation, and lateral bending using pure moments of ± 2.5 Nm without axial preload. After testing the intact spine, the different instrumentations were tested after destabilising C0/C2 and C3/C4. Primary stability was significantly increased, in all load cases, with the new modular implant system compared to the other implant systems. Pedicle screw instrumentation tended to be more stable compared to lateral mass screws; nevertheless, significant differences were observed only for lateral bending. As the experimental design precluded any cyclic testing, the data represent only the primary stability of the implants. In summary, this study showed that posterior instrumentation of the cervical spine using the new Neon Occipito Cervical System improves primary biomechanical stability compared to the CerviFix System and the Olerud Cervical Rod Spinal System.

Autotransfusion-bacterial contamination during hip arthroplasty and efficacy of cefuroxime prophylaxis : A randomized controlled study of 40 patients

40 patients undergoing primary hip arthroplasty, given autologous processed blood transfusion, were randomized a receive no antibiotic prophylaxis (group A, n 20) or cefuroxime (1.5 g single injection; group B, n 20). Bacterial contamination at various steps in the autotransfusion procedure was assessed in liquid and solid culture media. The operation field and the wound drainage blood were never contaminated either of the groups but some of the suction tips were. Parts of the Vacufix blood collection bags of group A contained bacteria, but none in group B. Processed red blood cell concentrates in both groups showed bacterial growth. Greater blood loss did not increase the contamination rate in general. Isolated bacteria included the species Staphylococcus epidermidis, coagulase-negative staphylococci and Propionibacteria in both groups, but with different cell counts. In addition, Corynebacterium bovis et minutissimum and Moraxelle were identified in group A. In conclusion, autologous blood transfusion was a safe procedure. If contamination occurred, the bacterial count was low, and the bacteria of low pathogenicity. Antibiotic prophylaxis with cefuroxime reduced this contamination of suction tips and collection bags and limited the transfer of autologous blood products.

Biomechanical evaluation of a newly developed monocortical expansion screw for use in anterior internal fixation of the cervical spine. In vitro comparison with two established internal fixation systems.

STUDY DESIGN The primary biomechanical stability of anterior internal fixation of the cervical spine obtained with a new monocortical expansion screw in vitro was evaluated. OBJECTIVES To determine whether the anterior internal fixation of the spine obtained with the new monocortical expansion screw provides biomechanical stability comparable with that obtained with bicortical fixation. SUMMARY OF BACKGROUND DATA The anterior plate instrumentation used with bicortical screw fixation in the cervical spine provides a primary stability superior to that associated with monocortical screw fixation. However, bicortical screws have the potential to perforate the posterior cortex. Therefore, monocortical instrumentation systems were developed, but without the biomechanical stability associated with bicortical systems. A new expansion screw for monocortical fixation was developed to improve biomechanical stability of monocortical systems. METHODS Three different internal fixation systems were compared in this study: 1) H-plate with AO 3.5-mm bicortical screws, 2) cervical spine locking plate with monocortical screws, and 3) H-plate with the new monocortical expansion screws. Eight fresh human cadaver spine segments from C4 to C7 were tested in flexion-extension, axial rotation, and lateral bending using pure moments of +/- 2.5 Nm without axial preload. Five conditions were investigated consecutively: 1) intact spine; 2) uninstrumented spine with the segment C5-C6 destabilized; 3-5) instrumentation of the segment C5-C6 with the three implants mentioned above after removal of the disc and insertion of an interbody spacer. RESULTS Between bicortical and monocortical expansion screw H-plate fixation, no significant differences were observed in all load cases concerning range of motion and neutral zone. The neutral zone and range of motion were significantly larger for the cervical spine locking plate than for bicortical and monocortical expansion screw fixation in all load cases, except neutral zone for axial rotation versus bicortical screw fixation. The instrumented cases only had a significantly lower range of motion and neutral zone than the intact cases in extension-flexion, whereas for lateral bending and axial rotation no significant differences could be observed. Because the experimental design precluded any cyclic testing, the data represent only the primary stability of the implants. CONCLUSIONS In anterior instrumentation of the cervical spine using a H-plate, the new monocortical expansion screw provides the same biomechanical stability as the bicortical 3.5-mm AO screw and a significantly better biomechanical stability than the cervical spine locking plate. Therefore, the expansion screw may be an alternative to the bicortical fixation and does not involve the risk of penetration of the posterior vertebral body cortex.

In situ rigidity of a new sliding rod for management of the growing spine in Duchenne muscular dystrophy

STUDY DESIGN This biomechanical, in vitro laboratory study determined the static stiffness of a new telescoping rod and the axial motion of this implant during various loading conditions. OBJECTIVES To compare the stability of the new telescoping rod with the classic Luque instrumentation, and to determine whether the sliding rod elongates or contracts during spine motion. SUMMARY OF BACKGROUND DATA A new telescoping rod was developed to stabilize the spine in children with Duchenne muscular dystrophy and to provide capacity for spinal growth. METHODS The stability of 11 instrumented calf spines was determined in flexion, extension, lateral bending, and torsion to determine the stiffnesses of the spines instrumented with these two implants. The telescoping motion in the left and right rod was measured in the new rod system. RESULTS In flexion, the spines with the telescoping rods were stiffer than those with the Luque implant. However, no significant differences in the stiffness coefficients were found for extension, lateral bending, or torsion. The restoring force of the telescoping system was greater than that of the Luque system in all directions. All modes of loading produced an accommodating change of length in the construct. CONCLUSIONS The dynamic telescoping system provides stiffness comparable with that of established systems while allowing elongation during growth of the young patient.

Characteristics of an extended internal fixation system for polysegmental transpedicular reduction and stabilization of the thoracic, lumbar, and lumbosacral spine

Abstract The Kluger internal fixator, with its artificial fulcrum outside the operative site, had to be extended for multisegmental use. Three different prototypes, called Central Bar (CB), Double Bar I (DB I) and Double Bar II (DB II) were designed, which were fully compatible with the existing reduction system. To evaluate the ability of these newly developed systems to provide primary stability in a destabilized spine, their stiffness characteristics and stabilizing effects were investigated in multidirectional biomechanical stability tests and compared with those of the clinically well-known Cotrel-Dubousset (CD) system. The investigations were performed on a spine tester using freshly prepared calf spines. The model tested was that of an intact straight spine followed by a defined three-column lesion simulating the most destabilizing type of injury. Pure moments of up to 7.5 Nm were continuously applied to the top of each specimen in flexion/extension, left/right axial rotation, and left/right lateral bending. Segmental motion was measured using a three-dimensional goniometric linkage system. Range of motion and stiffness within the neutral zone were calculated from obtained load-displacement curves. The DB II attained 112.5% (P = 0.26) of the absolute stiffness of the CD system in flexion and enhanced its stability in extension by up to 144.3% (P = 0.004). In axial rotation of the completely destabilized spine, this system achieved 183.3% of the stiffness of the CD system (P < 0.001), and in lateral bending no motion was measured in the most injured specimens stabilized by the DB II. The DB I, which was the first to be designed and was considered to provide high biomechanical stability, did not attain the stiffness standard set by the CD system in either flexion/extension or axial rotation of the most injured spine. The study confirms that it is worthwhile to evaluate in vitro the biomechanical properties of a newly developed implant before its use in patients, in order to refine weak construction points and help to reduce device-related complications and to better evaluate its efficacy in stabilizing the spine.

The treatment of spondylolistheses with segmental reduction and interbody fusion by means of an internal fixator

SummaryIn spondylolisthesis with an indication for fusion and with a slipping of more than 50 % at least a partial reposition should be reached in general because the incidence of pseudarthrosis would increase with a fusion in situ and a large disturbance of the spinal statics would persist. Hereby with almost all methods an enlarged operative morbidity and often a longer fusion range has to be taken in account compared to the fusion in situ. Therefore, in smaller slippages the fusion in situ will be favoured because the disturbance of the statics is not so important, that such an effort combined with such methods is necessary. If the operation method with small spondylolisthesis and pseudospondylolisthesis allows the reposition without much effort and if the operative morbidity in comparison with the fusion in situ is not higher, then it is reasonable to fuse the cases with a spondylolisthesis Meyerding grade 1 and 2 in the anatomic corrected position too. Because the spinal fixator we use fills out these criteria we combine the correction of the position with the fusion also in cases of small spondylolisthesis. The incidence of neurologic complications correlates with the amount of the reposition distance and can be caused by preforaminal or extraforaminal lesions. The reduction of small malpositions could only produce preforaminal lesions. Using the spine fixator with its reposition instruments linked outside the wound and with its uninhibited access to the segment and to the preforaminal neural structures during the whole repositioning these lesions can be avoided.ZusammenfassungBei Spondylolisthesen mit einem Gleitweg von über 50 % wird bei gegebener Indikation zur Fusion allgemein wenigstens eine Teilreposition angestrebt, da bei einer Fusion in situ die Pseudarthroserate erhöht wäre und weil eine erhebliche Störung der Wirbelsäulengesamtstatik persistieren würde. Dafür muß bei fast allen Methoden eine gegenüber der Fusion in situ erheblich erhöhte operative Belastung und oft eine Ausdehnung der Fusionsstrecke in Kauf genommen werden. Bei geringeren Gleitwegen wird daher die Fusion in situ empfohlen, weil hier die Störung der Statik nicht so ausgeprägt ist, daß sie den bei solchen Methoden großen Aufwand der Reposition erzwingt. Wenn aber ein Operationsverfahren bei geringen Spondylolisthesen und Pseudospondylolisthesen die Reposition ohne nennenswerten Mehraufwand gestattet und wenn dabei das operative Risiko gegenüber der Fusion in situ nicht erhöht ist, dann ist es naheliegend, auch Olisthesen der Grade Meyerding I und II in der anatomischen Korrekturstellung zu fusionieren. Weil der von uns angewendete Wirbelsäulenfixateur diese Kriterien erfüllt, führen wir die Stellungskorrektur auch bei der Fusion geringgradiger Olisthesen durch. Das Auftreten neurologischer Komplikationen korreliert mit der Größe des Repositionsweges, und es kann durch präforaminale und durch extraforaminale Läsionen begründet sein, bei geringen Fehlstellungen spielen nur präforaminale Ursachen eine Rolle. Durch den beim Wirbelsäulenfixateur wegen des nach außen verlagerten Repositionsinstrumentars unbehinderten Zugang zum Segment und zu den präforaminalen neuralen Strukturen während des gesamten Repositionsvorganges können diese Schäden zuverlässig vermieden werden.