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Tim Pohlemann

Publications and source records attributed to Tim Pohlemann.

9 recordsLinked to original sources
PubMed2007

A new in vitro wound model based on the co-culture of human dermal microvascular endothelial cells and human dermal fibroblasts.

BACKGROUND INFORMATION: Different in vitro models, based on co-culturing techniques, can be used to investigate the behaviour of cell types, which are relevant for human wound and soft-tissue healing. Currently, no model exists to describe the behaviour of fibroblasts and microvascular endothelial cells under wound-specific conditions. In order to develop a suitable in vitro model, we characterized co-cultures comprising NHDFs (normal human dermal fibroblasts) and HDMECs (human dermal microvascular endothelial cells). The CCSWMA (co-culture scratch wound migration assay) developed was supported by direct visualization techniques in order to investigate a broad spectrum of cellular parameters, such as migration and proliferation activity, the differentiation of NHDFs into MFs (myofibroblasts) and the expression of endothelin-1 and ED-A-fibronectin (extra domain A fibronectin). The cellular response to hypoxia treatment, as one of the crucial conditions in wound healing, was monitored. RESULTS: The comparison of the HDMEC-NHDF co-culture with the respective mono-cultures revealed that HDMECs showed a lower proliferation activity when co-cultured, but their number was stable throughout a period of 48 h. NHDFs in co-culture were slightly slower at proliferating than in the mono-culture. The MF population was stable for 48 h in the co-culture, as well as in NHDF mono-culture. Co-cultures and HDMEC mono-cultures were characterized by a slower migration rate than NHDF mono-cultures. Hypoxia decreased both cell proliferation and migration in the mono-cultures, as well as in the co-cultures, indicating the general suitability of the assay. Exclusively, in co-cultures well-defined cell clusters comprising HDMECs and MFs formed at the edges of the in vitro wounds. CONCLUSIONS: On the basis of these results, the CCSWMA developed using co-cultures, including HDMECs, NHDFs and MFs, proved to be an effective tool to directly visualize cellular interaction. Therefore, it will serve in the future to evaluate the influence of wound-healing-related factors in vitro, as shown for hypoxia in the present study.

Actins↗
PubMed2006

Erythropoietin (EPO): EPO-receptor signaling improves early endochondral ossification and mechanical strength in fracture healing.

Beyond its role in the regulation of red blood cell proliferation, the glycoprotein erythropoietin (EPO) has been shown to promote cell regeneration and angiogenesis in a variety of different tissues. In addition, EPO has been indicated to share significant functional and structural homologies with the vascular endothelial growth factor (VEGF), a cytokine essential in the process of fracture healing. However, there is complete lack of information on the action of EPO in bone repair and fracture healing. Therefore, we investigated the effect of EPO treatment on bone healing in a murine closed femur fracture model using radiological, histomorphometric, immunohistochemical, biomechanical and protein biochemical analysis. Thirty-six SKH1-hr mice were treated with daily i.p. injections of 5000 U/kg EPO from day 1 before fracture until day 4 after fracture. Controls received equivalent amounts of the vehicle. After 2 weeks of fracture healing, we could demonstrate expression of the EPO-receptor (EPOR) in terminally differentiating chondrocytes within the callus. At this time point EPO-treated animals showed a higher torsional stiffness (biomechanical analysis: 39.6+/-19.4% of the contralateral unfractured femur) and an increased callus density (X-ray analysis (callus density/spongiosa density): 110.5+/-7.1%) when compared to vehicle-treated controls (14.3+/-8.2% and 105.9+/-6.6%; p<0.05). Accordingly, the histomorphometric examination revealed an increased fraction of mineralized bone and osteoid (33.0+/-3.0% versus 28.5+/-3.6%; p<0.05). Of interest, this early effect of the initial 6-day EPO treatment had vanished at 5 weeks after fracture. We conclude that EPO-EPOR signaling is involved in the process of early endochondral ossification, enhancing the transition of soft callus to hard callus.

Animals↗
PubMed2005

Different cell cycle responses of wound healing protagonists to transient in vitro hypoxia.

Polyploidization is a process present in cells of many different human tissues. Since it is also prominent in human wound healing in vivo and in vitro, we focused on the influence of hypoxia on the cells' proliferation and polyploidization response. The proliferation response of two major cell types, involved in human wound healing, human dermal microvascular endothelial cells (HDMEC) and normal human dermal fibroblasts (NHDF) was quite similar in the in vitro setup: proliferation significantly decreased under the influence of 18 h of hypoxia and was reinitiated after 72 h of reoxygenation. The cells' response concerning their tendency towards the development of polyploidy was different: NHDF did not generate any polyploid cells, which stands in contrast to former in vitro studies with human wound-derived fibroblasts, but HDMEC were characterized by the presence of both mononuclear and binuclear tetraploid cells. The number of tetraploids was downregulated during hypoxia and increased during reoxygenation, accompanied by proliferation onset. The immunomicroscopic survey of HDMEC opened up a cell cycle model, which might be useful in the future to evaluate cell cycle modulations leading to polyploidy without the need to apply any additional cell cycle inhibitors.

Cell Cycle↗
PubMed2005

[Internal fixation of sacroiliac joint disruption].

OBJECTIVE: Stabilization of the completely disrupted sacroiliac (SI) joint with two three-hole DC plates. INDICATIONS: Definitive treatment of the posterior pelvic ring in type C injuries (AO classification) with complete SI joint disruption, transiliac or transsacral fracture-dislocation of the SI joint with an insignificant, small fragment. Emergency stabilization of the SI joint following a laparotomy. CONTRAINDICATIONS: Poor general health of patient. Local soft-tissue damage. Rotationally unstable type B pelvic injuries. SURGICAL TECHNIQUE: Supine. Anterolateral approach to the iliac crest. Subperiosteal detachment of the iliac muscle. Debridement of the SI joint and reduction under direct vision. Stabilization of the SI joint with two three-hole DC plates inserted at an angle of 70-90 degrees. POSTOPERATIVE MANAGEMENT: Partial weight bearing on the injured side at 15 kg for 8-12 weeks with two forearm crutches. Implant removal 6-12 months after injury provided ankylosis has not occurred. RESULTS: In 27 patients with disruption of the SI joint consistent with a type C injury, the average displacement of the affected SI joint was 16 mm (8-30 mm). Complications relating to the osteosynthesis occurred as a deep infection in one patient, originating from a concomitant acetabular osteosynthesis. Iatrogenic nerve damage (lateral femoral cutaneous nerve) was present in two patients. 16 patients were followed up using radiologic techniques (pelvic, possibly inlet and outlet views, computed tomography). 13 SI joints healed in anatomic position. The malalignments observed were relatively slight (2-4 mm). There was no secondary implant failure. Almost all patients (n = 14) showed posttraumatic changes of the SI joint (osteophytes, arthrosis, ankylosis).

Adolescent↗
PubMed2005

[A simple supraacetabular external fixation for pelvic ring fractures].

OBJECTIVE: Closed reduction and maintenance of pelvic ring injuries by external stabilization. INDICATIONS: Emergency management of unstable type B and type C pelvic ring fractures. Definitive treatment of type B injuries. Definitive treatment of the anterior pelvic ring in type C injuries with transpubic instability after posterior internal stabilization. Adjunct stabilization of internal fixation. Stabilization of pelvic ring fractures in children. CONTRAINDICATIONS: Poor general condition. Local soft-tissue damage. Local infection. SURGICAL TECHNIQUE: Bilateral percutaneous insertion of Schanz screws into the supraacetabular area of iliac bone. Closed reduction and stabilization of the pelvic ring by compression and application of a connecting rod under image intensification. POSTOPERATIVE MANAGEMENT: Depending on the patient's condition and the degree of pelvic instability, a change to an open procedure may become necessary. Mobilization of the patient with partial weight bearing (one fifth of body weight) on the side of the injured posterior pelvic ring using forearm crutches, irrespective of the degree of stability of the pelvis. RESULTS: Retrospective analysis of 64 supraacetabular external fixator applications to stabilize the anterior pelvic ring in 20 type B and 44 type C injuries. Iatrogenic lesions of the lateral femoral cutaneous nerve: 4.5%; all sensory disturbances completely reversed within 1 year. No pin site infection. In two patients (3%) primary perforation of the Schanz screw into the small pelvis not necessitating any treatment. No secondary displacements of the anterior or posterior pelvic ring in type B injuries nor for type C injuries, sacral fractures associated with fractures of the pubic ramus. One pseudarthrosis of the pubic and ischial rami requiring surgical treatment.

Acetabulum↗
PubMed2004

Clinical applications--pelvis.

Navigation procedures based on CT data were introduced into spinal surgery in 1994. Since then, the method has been used in other areas such as joint replacement, reconstructive surgery, and tumor surgery because of its high precision and reduced radiation exposure. The original CT-based spine module can be adjusted for pelvic surgery with the prerequisite that the positioning of the fragments is identical in CT and in the OR; otherwise a new dataset has to be acquired. Our experiences with CT-based navigation in pelvic surgery are explained on five percutaneous screw fixations and three tumor resections, including description of the technique. For modality-based navigation, the navigated procedure is performed in the CT suite with the advantage of immediate CT control of reduction quality and screw positioning. The technique is explained and illustrated on two cases. Fluoroscopy-based navigation has been used in trauma surgery since the late nineties. Since then, the method has been wide spread in the field of joint replacement and reconstructive surgery. Between June 2000 and December 2002, we performed 36 percutaneous screw fixations in the pelvis with postoperative x-ray and CT control. 35 of the 36 screws were placed correctly. In one screw, an anterior cortex perforation of the sacrum was seen in the CT without any neurological consequences. The Iso C 3-D fluoroscope has recently been approved for pelvic surgery. With the ability to reconstruct images, visualization of the acetabulum and the posterior pelvic ring, there is marked an improvement compare to conventional 2-D fluoroscopy. Thus, the field for navigation is also enhanced. Based on our clinical experiences, the indications for navigated techniques in pelvic and acetabular surgery are defined and illustrated.

Adult↗
PubMed2004

Pelvic emergency clamps: anatomic landmarks for a safe primary application.

The application of the pelvic clamp as a tool for emergency stabilization of unstable pelvic ring fractures has proved to be a life-saving procedure. Using correct technique, the pelvic clamp can be applied within a few minutes after the patient's admission. To avoid severe complications (eg, pin perforation into the pelvis) during the application, anatomic landmarks for the correct pin placement have to be defined. The surface landmarks that are presently recommended for the correct pin placement are not always reliably found due to deformation of the body surface caused by swelling and hematoma. Our experience with 43 emergency applications of the pelvic C-clamp showed that reliable anatomic landmarks on the bony surface of the innominate bone could be identified to ensure correct pin placement. The ideal insertion point of the pins is an anatomic region on the lateral cortex of the ileum, where an easily palpable "groove" is formed by angulations of the lateral cortex of the iliac wing. Being increasingly used as an entry point for percutaneous transiliosacral screw fixations of sacroiliac joint injuries and sacral fractures, this region, which is close to the sacroiliac joint, represents an ideal point for maximum compression of the posterior pelvic ring. With the described technique, this "groove" can be identified easily even in emergency situations by blunt palpation with an instrument, avoiding the time-consuming use of a fluoroscope in most cases.

Emergency Medical Services↗
PubMed2004

New indications for computer-assisted surgery: tumor resection in the pelvis.

The resection of recurrent malignant pelvic tumors was supported by a commercially available navigation system in three patients. Preoperatively three-dimensional images from the pelvis were obtained by computed tomography or magnetic resonance imaging to identify the tumor extension. During surgery navigated tools oriented the surgeon to excise the tumor with adequate virtual margins. Navigation was helpful for tumor identification in one patient with a recurrent presacral mesenchymal chondrosarcoma. In the other two patients the tumor resection in the bone was done with three-dimensional observation of the osteotomies in the sacrum. In all three patients the histopathologic analysis confirmed that the neoplasms were excised accurately within their margins. We think that computer-assisted surgery is a potential method to increase the accuracy of tumor resections.

Adult↗