Thomas Mittlmeier

Comparison between sheep and human cervical spines: An anatomic, radiographic, bone mineral density, and biomechanical study

Study Design. The quantitative anatomic, radiographic, computerized tomographic, and biomechanical data of sheep and human cervical spines were evaluated. Objectives. To compare the anatomic, radiographic, computerized tomographic, and biomechanical data of human and sheep cervical spines to determine whether the sheep spine is a suitable model for human spine research. Summary of Background Data. Sheep spines have been used in several in vivo and in vitro experiments. Quantitative data of the normal sheep cervical spine are lacking, yet these data are crucial to discussion about the results of such animal studies. Methods. In this study, 20 fresh adult female Merino sheep cervical spines and 20 fresh human cadaver cervical spines were evaluated anatomically, radiographically, computerized tomographically, and biomechanically. Three linear and two angular parameters were evaluated on four digital radiographic views: anteroposterior, right lateral in neutral position, flexion, and extension. Quantitative computed tomography scans at the center of each vertebral body and 3 mm below both endplates were analyzed for bone mineral density measurements. Biomechanical testing was performed in flexion, extension, axial rotation, and lateral bending by a nondestructive stiffness method using a nonconstrained testing apparatus. Range of motion and stiffness of each motion segment were calculated. Additionally, 10 linear anatomic parameters of each vertebra were measured using a digital ruler. Results. Anterior and mean disc space height in the sheep cervical spine increased constantly from C2–C3 to C6–C7, whereas middle disc space height decreased and posterior disc space height remained unchanged. Anterior and mean disc space height were significantly higher in sheep. In both sheep and human cervical spines, intervertebral angles were not significantly different. Standard deviations of bone mineral density in the human cervical spine were fourfold higher than in the sheep cervical spine, yet no significant differences were found in bone mineral density values between the two species. Range of motion differed significantly between the two species except in flexion–extension of C3–C4, C5–C6, axial rotation of C2–C3, and lateral bending of C2–C3, C3–C4, and C4–C5. Stiffness also was significantly different except in flexion–extension of C2–C3, C4–C5, C5–C6, and lateral bending of C2–C3, C3–C4, and C4–C5. Anatomic evaluation showed no difference in upper endplate parameters for C4 and C5. Conclusions. Although several differences were found between human and sheep cervical spines, the small intergroup standard deviations and the good comparability with the human spine encourage the use of the sheep cervical spine as a model for cervical spine research. On the basis of the quantitative data obtained in this study, the sheep motion segment C3–C4 seemed to be the most reliable model for the corresponding human motion segment.

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 stiffnessfor flexion extension and bending was highest for theHarms 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.

Prolonged Superficial Local Cryotherapy Attenuates Microcirculatory Impairment, Regional Inflammation, and Muscle Necrosis after Closed Soft Tissue Injury in Rats

Background Closed soft tissue injury induces progressive microvascular dysfunction and regional inflammation. The authors tested the hypothesis that adverse trauma-induced effects can be reduced by local cooling. While superficial cooling reduces swelling, pain, and cellular oxygen demand, the effects of cryotherapy on posttraumatic microcirculation are incompletely understood. Study Design Controlled laboratory study. Methods After a standardized closed soft tissue injury to the left tibial compartment, male rats were randomly subjected to percutaneous perfusion for 6 hours with 0.9% NaCL (controls; room temperature) or cold NaCL (cryotherapy; 8°C) (n = 7 per group). Uninjured rats served as shams (n = 7). Microcirculatory changes and leukocyte adherence were determined by intravital microscopy. Intramuscular pressure was measured, and invasion of granulocytes and macrophages was assessed by immunohistochemistry. Edema and tissue damage was quantified by gravimetry and decreased desmin staining. Results Closed soft tissue injury significantly decreased functional capillary density (240 ± 12 cm-1); increased microvascular permeability (0.75 ± 0.03), endothelial leukocyte adherence (995 ± 77/cm2), granulocyte (182.0 ± 25.5/mm2) and macrophage infiltration, edema formation, and myonecrosis (ratio: 2.95 ± 0.45) within the left extensor digitorum longus muscle. Cryotherapy for 6 hours significantly restored diminished functional capillary density (393 ± 35), markedly decreased elevated intramuscular pressure, reduced the number of adhering (462 ± 188/cm2) and invading granulocytes (119 ± 28), and attenuated tissue damage (ratio: 1.7 ± 0.17). Conclusion The hypothesis that prolonged cooling reduces posttraumatic microvascular dysfunction, inflammation, and structural impairment was confirmed. Clinical Relevance These results may have therapeutic implications as cryotherapy after closed soft tissue injury is a valuable therapeutic approach to improve nutritive perfusion and attenuate leukocyte-mediated tissue destruction. The risk for evolving compartment syndrome may be reduced, thereby preventing further irreversible aggravation.

The logic and clinical applications of blocking screws.

In 1999, Krettek et al. introduced the concept of placing screws around an intramedullary nail (so-called Poller screws)1,2. These screws were used in association with interlocking nailing of tibial fractures with either proximal or distal fragments to facilitate alignment and to prevent late loss of alignment. Krettek et al. recommended placing one screw proximally and one distally on the concave side of the displacement. These screws were thought to work by narrowing the medullary canal in the metaphysis to provide a tight mechanical fit for the intramedullary nail. Similarly, Biewener et al. employed the sequential placement of Kirschner wires to guide an intramedullary nail with a good central position into a distal short fragment3. This procedure was called the “pallisade method.” To clarify the mechanical effect of such screws and to provide a better understanding of their placement, a mechanical model was designed. ### Description of the Model The model has long and short rectangular Lucite plates that represent the diaphysis and metaphysis of a long bone, respectively (Fig. 1). Aluminum frames are fixed to these Lucite plates to represent the cortex. The plates have matching convex surfaces at the metaphyseal-diaphyseal junction so that they can rotate on one another to simulate angular misalignment. A rubber band can be used to connect the short and long cortical segments in order to model unbalanced muscle forces, which cause axial malalignment. Three different inserts can be used to fill the end of the short segment. These inserts provide either a central entry portal, an eccentric entry portal, or a central zone into which the “nail” can be embedded. The nail is an opaque plastic bar that can be introduced into the medullary cavity from either the metaphyseal or the diaphyseal portion of the model. Holes on both sides of the nail …

IGF-I and TGF-β1 Application by a Poly-(D, L-Lactide)-Coated Cage Promotes Intervertebral Bone Matrix Formation in the Sheep Cervical Spine

STUDY DESIGN A sheep cervical spine interbody fusion model was used to determine the effect of combined insulin-like growth factor-I (IGF-I) and transforming growth factor-beta-1 (TGF-beta1) applied by a poly-(D,L-lactide) (PDLLA)-coated cage. OBJECTIVES The purpose of this study was to determine the effect of a new PDLLA carrier system, and to evaluate the effect of combined IGF-I and TGF-beta1 application in a sheep cervical spine model. SUMMARY AND BACKGROUND DATA Growth factors such as bone morphogenic protein-2 have been shown to promote spine fusion and to overcome the disadvantages of an autologous bone graft. The optimum growth factor for promoting spinal fusion and the optimum method for delivering such growth factors are still a matter of discussion. METHOD In this study, 32 sheep underwent C3-C4 discectomy and fusion: Group 1 (autologous tricortical iliac crest bone graft; n = 8), Group 2 (titanium cage; n = 8), Group 3 (titanium cage coated with a PDLLA carrier; n = 8), and Group 4 (titanium cage coated with a PDLLA carrier including IGF-I [5% w/w] and TGF-beta1 [1% w/w; n = 8). Blood samples, body weight, and body temperature were analyzed. Radiographic scans were performed before and after surgery, then at 1, 2, 4, 8, and 12 weeks, respectively. At the same time points, the disc space height, intervertebral angle, and lordosis angle were measured. After 12 weeks, the animals were killed, and fusion sites were evaluated using functional radiographic views of the animals in flexion and extension. Quantitative computed tomographic scans were performed to assess bone mineral density, bone mineral content, and bony callus volume. Biomechanical testing of the motion segment C3-C4 was performed in flexion, extension, axial rotation, and lateral bending. The stiffness, range of motion, neutral zone, and elastic zone were determined. Histomorphologic and histomorphometric analysis was performed, and polychrome sequential labeling was used to determine the time frame of new bone formation. RESULTS There were no differences between the groups in terms of blood counts, body weight, and temperature. Over a 12-week period, cage Groups 2 to 4 showed significantly higher values for the intervertebral angle than for the bone graft. Functional radiographic assessment showed significantly lower residual flexion-extension movement in Group 4 than in any other group. The PDLLA-coated cages with IGF-I and TGF-beta1 showed significantly higher values for bone mineral density, bone mineral content, and bony callus volume. The average stiffness in rotation and bending was significantly higher, and the range of motion, neutral zone, and elastic zone in rotation were significantly lower in Group 4 than in any other group. Although only one animal in Group 4 demonstrated solid bony fusion after 12 weeks, histomorphometric evaluation showed a more progressed bone matrix formation in the group that had PDLLA-coated cages with IGF-I and TGF-beta1 than in any other group. Polychrome sequential labeling showed accelerated intervertebral bone matrix formation in Group 4. CONCLUSIONS The findings showed that PDLLA coating of cervical spine interbody fusion cages as a delivery system for growth factors was effective. Although IGF-I and TGF-beta1 application by a PDLLA-coated interbody cage was not able to achieve solid bony fusion during the 12-week follow-up period, these growth factors significantly increased the results of interbody bone matrix formation. Additional longer-term studies are required to determine whether combined IGF-I and TGF-beta1 application leads to a successful spinal fusion.

Small volume hypertonic hydroxyethyl starch reduces acute microvascular dysfunction after closed soft-tissue trauma

A major pathway of closed soft-tissue injury is failure of microvascular perfusion combined with a persistently enhanced inflammatory response. We therefore tested the hypothesis that hypertonic hydroxyethyl starch (HS/HES) effectively restores microcirculation and reduces leukocyte adherence after closed soft-tissue injury. We induced closed soft-tissue injury in the hindlimbs of 14 male isoflurane-anaesthetised rats. Seven traumatised animals received 7.5% sodium chloride-6% HS/HES and seven isovolaemic 0.9% saline (NS). Six non-injured animals did not receive any additional fluid and acted as a control group. The microcirculation of the extensor digitorum longus muscle (EDL) was quantitatively analysed two hours after trauma using intravital microscopy and laser Doppler flowmetry, i.e. erythrocyte flux. Oedema was assessed by the wet-to-dry-weight ratio of the EDL. In NS-treated animals closed soft-tissue injury resulted in massive reduction of functional capillary density (FCD) and a marked increase in microvascular permeability and leukocyte-endothelial cell interaction as compared with the control group. By contrast, HS/HES was effective in restoring the FCD to 94% of values found in the control group. In addition, leukocyte rolling decreased almost to control levels and leukocyte adherence was found to be reduced by approximately 50%. Erythrocyte flux in NS-treated animals decreased to 90 +/- 8% (mean SEM), whereas values in the HS/HES group significantly increased to 137 +/- 3% compared with the baseline flux. Oedema in the HS/HES group (1.06 +/- 0.02) was significantly decreased compared with the NS-group (1.12 +/- 0.01). HS/HES effectively restores nutritive perfusion, decreases leukocyte adherence, improves endothelial integrity and attenuates oedema, thereby restricting tissue damage evolving secondary to closed soft-tissue injury. It appears to be an effective intervention, supporting nutritional blood flow by reducing trauma-induced microvascular dysfunction.

Erythropoietin Improves Functional and Histological Recovery of Traumatized Skeletal Muscle Tissue

Apart from its hematopoietic effect, erythropoietin (EPO) is known as pleiotropic cytokine with anti‐inflammatory and anti‐apoptotic properties. Here, we evaluated for the first time the EPO‐dependent regeneration capacity in an in vivo rat model of skeletal muscle trauma. A myoblast cell line was used to study the effect of EPO on serum deprivation‐induced cell apoptosis in vitro. A crush injury was performed to the left soleus muscle in 80 rats treated with either EPO or saline. Muscle recovery was assessed by analysis of contraction capacities. Intravital microscopy, BrdU/laminin double immunohistochemistry and cleaved caspase‐3 immunohistochemistry of muscle tissue on days 1, 7, 14, and 42 posttrauma served for assessment of local microcirculation, tissue integrity, and cell proliferation. Serum deprivation‐induced myoblast apoptosis of 23.9 ± 1.5% was reduced by EPO to 17.2 ± 0.8%. Contraction force analysis in the EPO‐treated animals revealed significantly improved muscle strength with 10–20% higher values of twitch and tetanic forces over the 42‐day observation period. EPO‐treated muscle tissue displayed improved functional capillary density as well as reduced leukocytic response and consecutively macromolecular leakage over day 14. Concomitantly, muscle histology showed significantly increased numbers of BrdU‐positive satellite cells and interstitial cells as well as slightly lower counts of cleaved caspase‐3‐positive interstitial cells. EPO results in faster and better regeneration of skeletal muscle tissue after severe trauma and goes along with improved microcirculation. Thus, EPO, a compound established as clinically safe, may represent a promising therapeutic option to optimize the posttraumatic course of muscle tissue healing.

Vitamin D Increases Cellular Turnover and Functionally Restores the Skeletal Muscle after Crush Injury in Rats

Insufficient skeletal muscle regeneration after injury often impedes the healing process and is accompanied by functional deficiencies or pain. The aim of our study was to provide evidence that vitamin D improves muscle healing after muscle injury. Therefore, we used male rats and induced an injury of the soleus muscle. After crush injury, animals received either 8.3 mg/kg (332,000 IU/kg) body weight vitamin D or vehicle solution, s.c. After assessment of muscle force at days 1, 4, 14, and 42 after injury, sampling of muscle tissue served for analysis of proliferation, apoptosis, satellite cells, and prolyl-4-hydroxylase-β expression. Vitamin D application caused a significant increase in cell proliferation and a significant inhibition of apoptosis at day 4 after injury compared to control animals. The numbers of satellite cells were not influenced by the vitamin D application, but there was an increase in prolyl-4-hydroxylase-β expression, indicative of increased extracellular matrix proteins. This cellular turnover resulted in a faster recovery of contraction forces at day 42 in the vitamin D group. Current data support the hypothesis that vitamin D promotes the regenerative process in injured muscle. Thus, vitamin D treatment may represent a promising therapy to optimize recovery after injury.

Angular stable multiple screw fixation (Targon FN) versus standard SHS for the fixation of femoral neck fractures

OBJECTIVE Head-preserving fracture care especially for the elderly may be complicated by acetabular screw penetration, cut out, delayed union or femoral head necrosis. The following comparative study analyses whether a new angular stable device may overcome these shortcomings. MATERIAL AND METHODS The Targon FN plate (BBraun/Aesculap, Germany) employs up to four angular stable telescoping screws for the fixation of the head fragment. In a prospective study patients with displaced and undisplaced intracapsular femoral neck fractures where treated by closed reduction and fracture fixation using either the Targon FN implant or a standard sliding hip screw (SHS). Patients were followed up clinically, radiographically and via telephone at a mean of follow-up time of 15.5 months. RESULTS Fifty-two patients (mean age: 67 years) with femoral neck fractures were treated with either Targon FN (27 patients) or SHS (25 patients). Time for surgery did not differ within the two groups (56 min Targon FN vs. 55 min SHS). Eight patients with SHS (32%) and four patients (15%) with Targon FN experienced cut out of the lag screw and received hip replacement (p<0.05). Implant failure occurred after a mean of 1.8 months after SHS and 6.0 months after Targon FN implantation. Final radiographs revealed substantial subsidence in both groups (5.0mm Targon FN; 9.8mm SHS, p=0.055) with a clear trend to less subsidence for the Targon FN group. Furthermore, asymmetrical telescoping of the lag screws occurred in 30% (n=8), complete depletion of telescoping distance in 11% (n=3) in the Targon FN group. Functional assessment using the HHS assessment tool, however, presented with slightly better results for the SHS treatment (87.7 ± 13.9) when compared to Targon FN fixation (69.5 ± 14.5). CONCLUSIONS The study revealed less subsidence of the head fragment, lower cut out rate and a lower rate of conversion to hemiarthroplasty after Targon FN fixation in comparison to a standard SHS fixation in a small number of patients with hip fractures. However, this was not accompanied by functional limitations in the SHS group.

Continuous intra-arterial application of substance P induces signs and symptoms of experimental complex regional pain syndrome (CRPS) such as edema, inflammation and mechanical pain but no thermal pain.

Substance P is involved in nociception in both the peripheral nervous system and the CNS and has been documented to play a crucial role in the complex regional pain syndrome (CRPS). So far, however, most experimental animal models are restricted to the effect of neurokinin-1 receptor blockers to inhibit substance P and do not directly evaluate its action. Thus, this study was conducted to test the hypothesis that local application of substance P causes signs and symptoms of CRPS. For this purpose rats received a continuous infusion of either substance P or saline over 24 h delivered by a mini-osmotic pump connected to an intrafemoral catheter. Animals were analyzed at either day 1 (n=6, each group) or day 4 (n=5, each group) after start of infusion. Substance P application caused a significant and long-lasting decrease in paw withdrawal thresholds upon mechanical stimulation, while animals did not present with thermal allodynia at days 1 and 4 after onset of infusion. In addition, severe s.c. edema was observed in all animals receiving substance P. In vivo fluorescence microscopy of the extensor digitorum longus muscle of the affected hind paw revealed enhanced leukocyte-endothelial cell interaction with a significant rise in the number of leukocytes both rolling along and firmly adhering to the wall of postcapillary venules, while saline-exposed animals were free of this local inflammatory response. Muscle cell apoptosis, as assessed by in vivo bisbenzimide staining, terminal deoxynucleotidyl transferase nick end labeling analysis and caspase 3-cleavage, could not be observed in either of the animals. In summary, the present study indicates that substance P is responsible for neurogenic inflammation, including local cell response, edema formation and mechanical pain, while it seems not to contribute to the generation of thermal allodynia.