S. Geis

Stem cell-based tissue-engineering for treatment of meniscal tears in the avascular zone.

Meniscal tears in the avascular zone have a poor self-healing potential, however partial meniscectomy predisposes the knee for early osteoarthritis. Tissue engineering with mesenchymal stem cells and a hyaluronan collagen based scaffold is a promising approach to repair meniscal tears in the avascular zone. 4 mm longitudinal meniscal tears in the avascular zone of lateral menisci of New Zealand White Rabbits were performed. The defect was left empty, sutured with a 5-0 suture or filled with a hyaluronan/collagen composite matrix without cells, with platelet rich plasma or with autologous mesenchymal stem cells. Matrices with stem cells were in part precultured in chondrogenic medium for 14 days prior to the implantation. Menisci were harvested at 6 and 12 weeks. The developed repair tissue was analyzed macroscopically, histologically and biomechanically. Untreated defects, defects treated with suture alone, with cell-free or with platelet rich plasma seeded implants showed a muted fibrous healing response. The implantation of stem cell-matrix constructs initiated fibrocartilage-like repair tissue, with better integration and biomechanical properties in the precultured stem cell-matrix group. A hyaluronan-collagen based composite scaffold seeded with mesenchymal stem cells is more effective in the repair avascular meniscal tear with stable meniscus-like tissue and to restore the native meniscus.

Contrast enhanced ultrasound (CEUS) and time intensity curve (TIC) analysis in compartment syndrome: First results

OBJECTIVE Purpose of this study was to monitor changes of microcirculation in acute compartment syndrome using contrast enhanced ultrasound (CEUS) and to assess the modified perfusion with a special quantification software. METHODS 8 patients with trauma of the lower limb or the upper extremity were enrolled after acute compartment syndrome was diagnosed clinically and by intracompartmental pressure measurement. The qualitative analysis of the corresponding compartment was assessed using B-scan mode and CEUS simultaneously. CEUS was performed using a multifrequence probe (6-9 MHz, LOGIQ E9 GE) after a i.v. bolus injection of 2 × 2.4 ml contrast agent (SonoVue(®), Bracco, Italy). Digital raw data were stored as cine loops up to 2 minutes. Retrospectively semiquantitative perfusion analysis was performed using time intensity curve analysis and the quantification software QONTRAST(®). RESULTS 6 out of 8 patients had to be operated due to clinical symptoms and to a pressure perfusion gradient lower than 30 mm Hg. 2 out of 8 were treated conservatively. In all patients haematomas were seen in B-scan mode. No necrosis could be detected. In the TIC analysis low levels of time to peak (20.0 ± 12.1) and area under the curve (118.4 ± 87.8) were observed in acute compartment syndrome. Similarly results have been obtained using the perfusions parameter PEAK (11.1 ± 5.7), time to PEAK (14.7 ± 9.7), regional blood volume (257.1 ± 192.6), and regional blood flow (12.1 ± 6.5) in QONTRAST(®) perfusion software. CONCLUSION CEUS may be capable of differing between acute compartment syndrome and imminent compartment syndrome.

TTP (time to PEAK) and RBV (regional blood volume) as valuable parameters to detect early flap failure

BACKGROUND Free flap transplantation is used more and more frequently in order to cover extensive wound defects. The basic prerequisite for successful flap salvage after flap failure is a short time interval from failure until revision. For this reason many different flap monitoring systems have been tested over the last years. OBJECTIVE The aim of the experiment was to detect critical capillary perfusion using contrast enhanced ultrasound. Quantitative analysis should be performed by a special perfusion software (QONTRAST; Bracco, Italy) appraising digital raw data of contrast enhanced ultrasound (CEUS). Additionally diverse risk factors for free flap transplantation were determined. METHODS Thirty-one patients were examined after free flap transplantation during the first 72 hours after operation. CEUS was performed with a linear transducer (6-9 MHz, LOGIQ E9/GE) and a bolus injection of 2.4 ml of contrast agent (SonoVue, Bracco, Italy). Operation and examination were performed by either an experienced plastic surgeon or an experienced ultrasound examiner. Depth dependent capillary perfusion was analysed and quantitative perfusions analysis was performed using the perfusions software QONTRAST (Bracco, Italy). Eleven revisions had to be performed: 7 due to haematoma and 4 due to superficial necrosis. RESULTS Reduced capillary perfusion was seen in all 11 complications using CEUS. Significant difference comparing the no complication and the complication group was observed using TTP (time to PEAK) and RBV (regional blood volume) quantitative analysis. Mean RBV was 922.1 ± 150.9 in the no complication and 303.0 ± 53.9 in the complication group (p = 0.001). Mean TTP was 37.6 ± 3.8 in the no complication and 21.3 ± 3.4 in the complication group (p = 0.006). Tendency to higher complication rate was seen in older male patients with vascular or malignant primary disease. CONCLUSION In this clinical trial, capillary perfusion after free flap transplantation as well as detection of vascular complications was demonstrated using CEUS. Quantitative perfusions analysis could be performed and flap viability could be assessed easily.

Post-operative monitoring of tissue transfers: Advantages using contrast enhanced ultrasound (CEUS) and contrast enhanced MRI (ceMRI) with dynamic perfusion analysis?

BACKGROUND The immediate evaluation of microvascular tissue flaps with respect to microcirculation after transplantation is crucial for optimal monitoring and outcome. The purpose of our investigation was to evaluate the clinical value of contrast-enhanced ultrasound (CEUS) and contrast-enhanced MRI (ceMRI) for monitoring the integrity of tissue flaps in plastic surgery. METHODS To this end, we investigated 10 patients (47 ± 16 a) between postoperative day 7 and 14 who underwent flap surgery in order to cover tissue defects in various body regions. For CEUS we utilized the GE LOGIQ E9 equipped with a linear transducer (6-9 MHz). After application of 2.4 ml SonoVue, the tissue perfusion was detected in Low MI-Technique (MI < 0.2). The perfusion curves were quantitatively analyzed using digital video sequences (QONTRAST, Bracco, Italy) regarding peak % and relative blood flow (RBF). Furthermore, we investigated all tissue flaps using contrast-enhanced MRI (Magnetom Symphony TIM, Siemens) with a 3D-VIBE sequence and a time resolution of 7s. Thus, the transplants were completely captured in all cases. As perfusion parameters, the positive enhancement integral (PEI) as well as the maximum intensity projection time (MIP-time) were collected. For comparison of both applications, all parameters were displayed in color-coded resolution and analyzed by three independent readers. Depending on the flap thickness, 1-3 regions of interest (ROI) were investigated. Each ROI measured 1 × 3 cm. RESULTS The subcutaneous ROI-1 showed a significantly lower rating regarding RBF in the ceMRI compared to CEUS (Mann-Whitney Rank-Sum test, p < 0.05). ROI-2 and -3 did not show any significant differences between the two applications. The frequency distribution showed good accordance in both modalities. Both imaging techniques detected 1 partial flap necrosis within the random area of cutaneous and subcutaneous layers, 1 hematoma as well as 1 insufficient perfusion over all tissue layers. After subsequent reoperation, graft loss could be prevented. CONCLUSION At present, both technologies provide an optimal assessment of perfusion in cutaneous, subcutaneous and muscle tissue layers, whereby the detection of fatty tissue perfusion is currently more easily detected using CEUS compared to ceMRI.

Evaluation of hyperbaric oxygen therapy for free flaps using planar optical oxygen sensors. Preliminary results

OBJECTIVES This study was designed to determine if a) hyperbaric oxygen increases the tissue oxygenation of free flaps and b) verification of this effect is possible by using a recently validated and innovative method for two-dimensional pO₂ measurement (Luminescence lifetime imaging = LLI). METHODS Six patients with a free parascapular flap transplanted to the lower limb received hyperbaric oxygen (HBOT) therapy. The HBOT regimen consisted of treatment over 90 minutes with 100% O₂ (FiO₂ 1.0) at 240 kPa (Marx-Schema). The transcutaneous oxygen partial pressure (ptcO₂) was measured over the entire flap with the use of luminescence lifetime imaging (LLI) before and 30, 60, 120 minutes after treatment. The LLI is based on the oxygen dependent quenching of phosphorescence of the indicator dye platinum (II)-octaethyl-porphyrin implemented in a polystyrene sensor foil. RESULTS In all six free flaps we could find a significant increase of tissue oxygen over the entire flap in form of increased R-values as well as subsequently calculated absolute ptcO₂ values over a period of 120 min after hyperbaric therapy. The ptcO₂ values increased significantly from 42.59 ± 1.11 Torr before to 81.14 ± 5.95 Torr after hyperbaric treatment (p < 0.001). Even after 2 hours the ptcO₂ values were significantly higher (83.45 ± 13.80 Torr) compared with values prior to HBOT (p < 0.006). CONCLUSIONS The findings of this study demonstrated an increase of oxygen supply over the entire flap after hyperbaric oxygen therapy.

Transcutaneous pO2 measurement during tourniquet-induced venous occlusion using dynamic phosphorescence imaging.

A sufficient oxygen supply in skin grafts requires a functioning microcirculation. Venous occlusion impairs the microcirculation and is therefore a major threat of healing. Luminescence life time imaging (LLI) enables the non-invasive and two-dimensional assessment of the transcutaneous oxygen partial pressure (p(tc)O2). In the current trial this new device was applied for monitoring of venous congestion. A tourniquet on the upper arm was inflated up to 40-50 mmHg and released after 10 min in eight healthy volunteers. The p(tc)O2 was measured at the lower arm every minute prior to, during and up to 10 min after cuff occlusion (40 degrees C applied skin temperature) using LLI of platinum(II)-octaethyl-porphyrin immobilized in a polystyrene matrix. For validation the polarographic Clark electrode technique was applied in close proximity and measurement was performed simultaneously. p(tc)O2 measurements prior to (Clark: 50.68+/-5.69 mmHg vs. LLI: 50.89+/-4.96 mmHg) and at the end of the venous congestion (Clark: 16.41+/-4.54 mmHg vs. LLI: 23.82+/-3.23 mmHg) did not differ significantly using the Clark electrode vs. LLI. At the initial congestion respectively reperfusion phase the Clark electrode measured faster decreases respectively increase of p(tc)O2 due to oxygen consumption of this method. This experimental trial demonstrates the applicability of LLI to quantify the p(tc)O2 under changing venous blood flow. The use of planar transparent sensors allows the non-invasive generation of two-dimensional maps of surface pO2 what makes this method particular suitable for monitoring of skin grafts.

Contrast enhanced ultrasound (CEUS) – an unique monitoring technique to assess microvascularization after buried flap transplantation

OBJECTIVE Incidence of patients requiring complex soft tissue or osseous reconstruction has dramatically increased. However most of the monitoring systems have limitations in tissue penetration and are not able to detect microvascular complications after transplantation of so-called buried-flaps, that have no contact to the surface.Aim of the study was to assess contrast enhanced ultrasound (CEUS) as monitoring tool after buried flap transplantations. METHODS 20 patients were examined after buried flap transplantation using CEUS. Quantitative perfusion analysis (TIC) was performed with an integrated perfusion software using stored cine-loops. Two perfusion-parameters, time to PEAK (TtoPk) and area under the curve (Area), were evaluated using TIC analysis. RESULTS Minor complications were observed in 3 patients. In these patients a delayed contrast agent wash-in and wash-out was observed. Additionally the perfusion values TtoPk (sec.) and Area (relative Units) were clearly different in the patients with minor complications: TtoPk: 32.0 sec; Area 425.5 rU (without complication), TtoPk: 38.6 sec.; Area: 18.3 rU (wound healing disturbance) and TtoPk: 14.4 sec.; Area: 105.9 rU (hematoma). CONCLUSION As CEUS can assess microvascularization almost depth-independent, CEUS is an unique method to assess global flap perfusion after buried flap transplantation.

Osteocutaneous free flaps: a critical analysis of quantitative evaluation of bone microcirculation with contrast-enhanced high resolution ultrasound (hrCEUS) and TIC analysis.

PURPOSE Osteocutaneous free flaps (OFF) are widely used to reconstruct large bone defects in trauma and cancer surgery. Currently no monitoring method is available to detect blood circulation around and inside the bone after transplantation. Therefore we used for the first time contrast-enhanced high-resolution ultrasound (hrCEUS) to gain evidence for the microcirculation of the transplanted bone. MATERIALS AND METHODS 15 patients transplanted with OFF because of large bone defects at different sites were examined postoperatively with hrCEUS with a high resolution linear probe (6-9 MHz, LOGIQ E9/GE) and a bolus injection of 2.4 ml of contrast agent (SonoVue®, Bracco, Italy). Operation and examination were performed by either an experienced plastic surgeon or an experienced ultrasound examiner. Microcirculation of the periost and bone was analyzed in different regions of interest (ROIs) and quantitative microcirculation analysis was performed using time intension curve analysis (TIC). We further analyzed clinical outcome of the patients in respect to revision-surgery, necrosis of the OFF and flap survival as well as viability on standard x-rays 2 months after surgery. RESULTS The most representative parameter by TIC analysis of hrCEUS were the area under the curve (AUC) and the time to peak (Ttop). The AUC of the periost and central part of the bone showed a high correlation (Pearsons r = 0.831). Mean AUC for the periost was 163.92 dB ± 49.44 and for the central part of the bone 70.42 dB ± 25.33. The Ttop of the periosteal ROI was 33.04 sec. ± 6.71 and the bone ROI 41.01 sec. ± 9.24. There was a high correlation of the Ttop of the periost and bone (Pearsons r = 0.937). One revision had to be performed due to haematoma and microcirculation defect of the distal part of the transplanted bone graft which was detected early by hrCEUS and the distal part of the avital bone could be removed timely. CONCLUSION For the first time we could show that hrCEUS is a reliable method to evaluate the viability of OFF. The AUC and Ttop seem to be a valuable parameter to detect the microcirculation around and inside the bone transplant.

Postoperative assessment of free skin flap viability by transcutaneous pO2 measurement using dynamic phosphorescence imaging

BACKGROUND Free flap transplantation is used more and more frequently in order to cover extensive wound defects. The basic prerequisite for successful flap salvage after flap failure is a short time interval from failure until revision. For this reason many different flap monitoring systems have been tested over the last years. But none of them has made the way into clinical routine. OBJECTIVE The aim of this clinical study was to study whether luminescence lifetime imaging (LLI) is an adequate method to assess flap viability during the postoperative period. In previous experiments LLI was proven to be a precise and non-invasive monitoring system for transcutaneous oxygen measurement. METHODS ptcO2 of 9 patients was detected during a postoperative period of 72 hours. In all cases the transplantation was performed by the same experienced surgeon. During the first 4 hours almost constant ptcO2 values were detected (53±0.7 mmHg). During the following time intervals ptcO2 values decreased and reached a more or less constant level after approximately 12 hours. The mean ptcO2 decreased from 53±0.7 mmHg to 39±1.0 mmHg. In one case an immediate decrease of ptcO2 below 10 mmHg was observed and a subsequently intervention was necessary to improve flap perfusion. CONCLUSION In this clinical trial, perfusion dynamics after free flap transplantation as well as the detection of vascular complications were demonstrated using LLI. Based on these data, LLI seems to be a sensitive and adequate monitoring system for the evaluation of free flap viability.

Recommendations for contrast enhanced ultrasound (CEUS) in free tissue transplant monitoring

Complications rates after free flap transplantation still amount up to 5% . Consequently a reliable monitoring system is of high importance in plastic and reconstructive surgery. The following guidelines provide an overview of the current opportunities for free flap planning and monitoring with ultrasound and in particular with contrast enhanced ultrasound.