Orthotopic forelimb transplantation in a Yucatan minipig model: Anatomic and in vivo study

INTRODUCTION

Above elbow transplants represent 19% of the upper extremity transplants. Previous large-animal models have been too distal or heterotopic, did not use immunosuppression and had short survival. We hypothesize that an orthotopic forelimb transplant model, under standard immunosuppression, is feasible and can be used to address questions on peri-transplant ischemia reperfusion injury, and post-transplantation vascular, immunologic, infectious, and functional outcomes.

MATERIALS AND METHODS

Four forelimbs were used for anatomical studies. Four mock transplants were performed to establish technique/level of muscle/tendon repairs. Four donor and four recipient female Yucatan minipigs were utilized for in-vivo transplants (endpoint 90-days). Forelimbs were amputated at the midarm and preserved through ex vivo normothermic perfusion (EVNP) utilizing an RBC-based perfusate. Hourly perfusate fluid-dynamics, gases, electrolytes were recorded. Contractility during EVNLP was graded hourly using the Medical Research Council scale. EVNP termination criteria included systolic arterial pressure ≥115 mmHg, compartment pressure ≥30 mmHg (at EVNP endpoint), oxygen saturation reduction of 20%, and weight change ≥2%. Indocyanine green (ICG) angiography was performed after revascularization. Limb rejection was evaluated clinically (rash, edema, temperature), and histologically (BANFF classification) collecting per cause and protocol biopsies (POD 1, 7, 30, 60 and endpoint). Systemic infections were assessed by blood culture and tissue histology. CT scan was used to confirm bone bridging at endpoint.

RESULTS

Animals 2, 4 reached endpoint with grade 0-I rejection. Limbs 1, 3 presented grade III rejection on days 6, 61. CsA troughs averaged 461 ± 189 ng/mL. EVNLP averaged 4.3 ± 0.52 h. Perfusate lactate, PO2 , and pH were 5.6 ± 0.9 mmol/L, 557 ± 72 mmHg and 7.5 ± 0.1, respectively. Muscle contractions were 4 [1] during EVNLP. Transplants 2, 3, 4 showed bone bridging on CT.

CONCLUSION

We present preliminary evidence supporting the feasibility of an orthotopic, mid-humeral forelimb allotransplantation model under standard immunosuppression regimen. Further research should validate the immunological, infectious, and functional outcomes of this model.

Lymphatic Mapping with Contrast-enhanced Ultrasound for Lymphaticovenous Anastomosis Surgery: How We Do It

Lymphaticovenous anastomosis (LVA) surgery is an effective surgery for the treatment of lymphedema in the extremities. Indocyanine green lymphography is the reference standard for visualizing lymphatics for LVA surgery, but it has several limitations; most notably, superficial dermal congestion can mask deeper lymphatic vessels. To overcome the limitations, we add contrast-enhanced ultrasound (CEUS) lymphography. We have previously reported that CEUS lymphography can identify lymphatic vessels for LVA surgery that indocyanine green lymphography does not. Here, we describe how we perform CEUS lymphography, including workflow, technique, and documentation. Before informed consent, the patient must be screened for possible adverse reactions to microbubbles. The procedure involves multiple intradermal injections of the microbubble agent at various sites along the extremity. After each injection, imaging for microbubble uptake by lymphatic vessels is performed using an ultrasound scanner with contrast-specific software. We use sulfur hexafluoride lipid-type A microspheres (Lumason/SonoVue; Bracco Suisse SA), but we are investigating the performance of other Food & Drug Administration-approved microbubble agents for CEUS lymphography. Having a systematic approach to marking the skin can mitigate the hindrance of marking over ultrasound coupling gel. Another benefit of CEUS lymphography is the rapid identification of neighboring veins compatible in size and location for anastomosis. We hold regular scheduled multidisciplinary meetings for coordination of care, discussion of outcomes, quality assurance, and ongoing innovation.

Masculinizing chest wall gender-affirming surgery: Clinical outcomes of 73 subcutaneous mastectomies using the double-incision and semicircular incision techniques

Masculinizing chest wall gender-affirming surgery is an important element in the treatment of gender dysphoria. In this study, we report an institutional series of subcutaneous mastectomies and aim to identify the risk factors for major complications and revision surgery. A retrospective review of consecutive patients who underwent primary masculinizing top surgery via subcutaneous mastectomy at our institution through July 2021 was performed. Demographics and clinical characteristics were recorded as well as major complications and revision surgeries. Time-to-event analyses were performed to assess predictors of major complications and revision surgery. Seventy-three consecutive patients (146 breasts) were included. The mean age and the mean body mass index were 25.2 ± 7 years and 27.6 ± 6.5 kg/m2, respectively. The mean follow-up time was 7.9 ± 7.5 months. None of the patients had a history of chest wall radiation or breast surgery. Double incision with free nipple grafting was the most common technique (n = 130, 89%), followed by periareolar semicircular incision (n = 16, 11%). The mean resection weight was 524.7 ± 377.7 g. Concomitant suction-assisted lipectomy was performed in 48 (32.9%) cases. The rate of major complications was 2.7%. Revision surgery was performed in 8 (5.4%) cases. Concomitant liposuction was significantly associated with a lower rate of revision surgery (p = 0.026). Masculinizing chest wall gender-affirming surgery is a safe procedure with a low rate of revision. Concomitant liposuction significantly reduced the need of revision surgery. Future studies utilizing patient-reported outcomes are still required to better assess the success of this procedure.

The Anatomic Feasibility of a Functional Chimeric Flap in Complex Abdominal Wall Reconstruction

BACKGROUND

Dynamic and functional abdominal wall reconstruction (FAWR) remains a complex challenge. The ideal flap should have a minimal donor-site morbidity and cover a large surface area with motor and sensory capabilities. The goal was to investigate the feasibility of using a free chimeric flap with anterolateral thigh (ALT) and rectus femoris (RF) components pedicled only on the motor nerve branch.

METHODS

Ten fresh cadavers were dissected with a designed chimeric thigh flap including ALT and RF flaps. Anterolateral thigh was designed and raised with the lateral femoral cutaneous nerve integrated, and the descending branch of the lateral circumflex femoral artery was preserved. Rectus femoris was elevated and the common pedicle was dissected up to the femoral origin. Accompanying motor nerve branches were carefully dissected to their femoral origin.

RESULTS

Twenty RF flaps were dissected and 9 were harvested as a true chimeric flap with ALT. The mean number of neurovascular bundles associated with RF flap was 2.11 ± 0.47, and the mean primary motor nerve average length was 9.40 ± 2.42 cm. The common vascular bundle in all 9 chimeric flaps was ligated, and the flap was rotated toward the abdomen pedicled only by primary motor nerve of the RF muscle. Nerve length was adequate for reach up to xiphoid area in all 20 flaps.

CONCLUSIONS

This study demonstrates the feasibility of the chimeric ALT/RF muscle free flap pedicled only by the motor nerve branch, with adequate flap rotation. Even with the limitations in a live patient, this flap would be an excellent option for FAWR in the right patient.

Metabolic Profiling of Skeletal Muscle During Ex-Vivo Normothermic Limb Perfusion

INTRODUCTION

Ex vivo normothermic limb perfusion (EVNLP) provides several advantages for the preservation of limbs following amputation: the ability to maintain oxygenation and temperature of the limb close to physiological values, a perfusion solution providing all necessary nutrients at optimal concentrations, and the ability to maintain physiological pH and electrolytes. However, EVNLP cannot preserve the organ viability infinitely. We identified evidence of mitochondrial injury (swelling, elongation, and membrane disruption) after 24 hours of EVNLP of human upper extremities. The goal of this study was to identify metabolic derangements in the skeletal muscle during EVNLP.

MATERIALS AND METHODS

Fourteen human upper extremities were procured from organ donors after family consent. Seven limbs underwent EVNLP for an average of 41.6 ± 9.4 hours, and seven contralateral limbs were preserved at 4°C for the same amount of time. Muscle biopsies were performed at 24 hours of perfusion, both from the EVNLP and control limbs. Perturbations in the metabolic profiles of the muscle during EVNLP were determined via untargeted liquid chromatography-mass spectrometry (MS) operated in positive and negative electrospray ionization modes, over a mass range of 50 to 750 Da. The data were deconvoluted using the XCMS software and further statistically analyzed using the in-house statistical package, MetaboLyzer. Putative identification of metabolites using exact mass within ±7 ppm mass error and MS/MS spectral matching to the mzCloud spectral library were performed via Compound Discoverer v.2.1 (Thermo Scientific, Fremont, CA, USA). We further validated the identity of candidate metabolites by matching the fragmentation pattern of these metabolites to those of their reference pure chemicals. A nonparametric Mann-Whitney U-test was used to compare EVNLP and control group spectral features. Differences were considered significantly different when P-value < 0.05.

RESULTS

We detected over 13,000 spectral features of which 58 met the significance criteria with biologically relevant putative identifications. Furthermore we were able to confirm the identities of the ions taurine (P-value: 0.002) and tryptophan (P-value: 0.002), which were among the most significantly perturbed ions at 24 hours between the experimental and control groups. Metabolites belonging to the following pathways were the most perturbed at 24 hours: neuroactive ligand-receptor interaction (P-values: 0.031 and 0.036) and amino acid metabolism, including tyrosine and tryptophan metabolism (P-values: 0.015, 0.002, and 0.017). Taurine abundance decreased and tryptophan abundance increased at 24 hours. Other metabolites also identified at 24 hours included phenylalanine, xanthosine, and citric acid (P-values: 0.002, 0.002, and 0.0152).

DISCUSSION

This study showed presence of active metabolism during EVNLP and metabolic derangement toward the end of perfusion, which correlated with detection of altered mitochondrial structure, swelling, and elongation.

A meta-analysis of functional outcomes in rat sciatic nerve injury models

INTRODUCTION

Rat sciatic nerve injury (PNR) is the most utilized model in studies on peripheral nerve regeneration. However, large animal models are increasingly favored based on the assumption that nerve regeneration in rodents achieves more favorable outcomes than in humans. The purpose of this meta-analysis was to investigate which rat PNR models are more stringent and should be used before utilizing large animal experimentation.

METHODS

A PRISMA-guided meta-analysis of the English literature regarding functional outcomes in rat peripheral nerve injury models was conducted. Outcomes of five basic scenarios: (1) transected nerve/negative control, (2) transection with primary microsurgical repair, (3) isogenic/autologous grafts, (4) acellular-allogenic grafts, and (5) limb transplantation were compared to sciatic nerves without any intervention/positive control. Outcomes were compared using Sciatic Functional Index (SFI). Log-based projections were generated and evaluated using mean squared error (MSE), one-way-ANOVA, and Tukey-HSD post-hoc analysis.

RESULTS

In total, 167 articles met the inclusion criteria. The earliest manifestations of motor recovery were encountered in the transection and primary repair group (p <.0005). There was a significant difference in recovery time and degree of recovery between all surgical models (p <.0005). At 24 weeks, the SFI in hindlimb transplantation group was significantly worse than all other groups (-74.07 ± 2.74, p <.0005). Autografts smaller than 10 mm recovered sooner than autografts longer than 10 mm (p = .021) and autografts recovered faster than allografts.

CONCLUSION

This meta-analysis does not support the belief that neuro-regeneration is exceptional in transection models. These models remain adequate to provide translatable information and should initially be used in investigational studies.

Leukoreduction in ex vivo perfusion circuits: comparison of leukocyte depletion efficiency with leukocyte filters

BACKGROUND

Leukodepletion of whole blood-based perfusates remains a challenge in experimental models of ex vivo perfusion. This study investigated the leukoreduction efficacy of the commonly used LeukoGuard LG Arterial and BC2 Cardioplegia filters.

METHODS

Eleven liters of washed porcine blood was used to evaluate the filtration efficiency of LG (n = 6) and BC2 (n = 5) filters. Filter efficacy was tested by passing 1 L of washed blood through each filter. Complete blood count was performed to detect a reduction of white blood cells, red blood cells, and hemoglobin concentration.

RESULTS

The BC2 Cardioplegia filter showed a significant reduction in white blood cell count (13.16 ± 4.2 × 10³ cells/μL pre-filtration, 0.62 ± 0.61 cells/μL post-filtration, p = 0.005), red blood cell count (9.18 ± 0.16 × 10⁶ cells/μL pre-filtration, 9.02 ± 0.16 × 10⁶ cells/μL post-filtration, p = 0.012) and hemoglobin concentration (15.89 ± 0.66 g/dL pre-filtration, 15.67 ± 0.83 g/dL post-filtration, p = 0.017). Platelet reduction in the LG filter group was statistically significant (13.23 ± 13.98 × 10³ cells/μL pre-filtration, 7.15 ± 3.31 × 10³ cells/μL post-filtration, p = 0.029), but no difference was seen in the BC2 group. There was no significant difference in white blood cell count in the LG filter group (10.12 ± 3.0 × 10³ cells/μL pre-filtration, 10.32 ± 2.44 × 10³ cells/μL post-filtration, p = 0.861).

CONCLUSION

Our results suggest that the LG filter should not be used in ex vivo perfusion circuits for the purpose of leukodepletion. The BC2 filter can be used in EVP circuits with flow rates of less than 350 mL/min. Alternatively, perfusate may be leukodepleted before perfusion.

Extended ex vivo normothermic perfusion for preservation of vascularized composite allografts

Ischemia and reperfusion injury remains a significant limiting factor for the successful revascularization of amputated extremities. Ex vivo normothermic perfusion is a novel approach to prolong the viability of the amputated limbs by maintaining physiologic cellular metabolism. This study aimed to evaluate the outcomes of extended ex vivo normothermic limb perfusion (EVNLP) in preserving the viability of amputated limbs for over 24 hours. A total of 10 porcine forelimbs underwent EVNLP. Limbs were perfused using an oxygenated colloid solution at 38°C containing washed RBCs. Five forelimbs (Group A) were perfused for 12 hours and the following 5 (Group B) until the vascular resistance increased. Contralateral forelimbs in each group were preserved at 4°C as a cold storage control group. Limb viability was compared between the 2 groups through assessment of muscle contractility, compartment pressure, tissue oxygen saturation, indocyanine green (ICG) angiography and thermography. EVNLP was performed for 12 hours in group A and up to 44 hours (24-44 hours) in group B. The final weight increase (-1.28 ± 8.59% vs. 7.28 ± 15.05%, P = .548) and compartment pressure (16.50 ± 8.60 vs. 24.00 ± 9.10) (P = .151) were not significantly different between the two groups. Final myoglobin and CK mean values in group A and B were: 875.0 ± 325.8 ng/mL (A) versus 1133.8 ± 537.7 ng/mL (B) (P = .056) and 53 344.0 ± 16 603.0 U/L versus 64 333.3 ± 32 481.8 U/L (P = .286). Tissue oxygen saturation was stable until the end in both groups. Infra-red thermography and ICG-angiography detected variations of peripheral limb perfusion. Our results suggest that extended normothermic preservation of amputated limbs is feasible and that the outcomes of prolonged EVNLP (>24 hours) are not significantly different from short EVNLP (12 hours).