Strain energy density as a rupture criterion for the kidney: impact tests on porcine organs, finite element simulation, and a baseline comparison between human and porcine tissues.

High-velocity (up to 25 m/s) impact tests were performed on pig kidneys to characterize failure behavior at deformation rates associated with traumatic injury. Cylindrical tissue samples (n = 45) and whole perfused organs (n = 34) were impacted using both falling weights and a high-velocity pneumatic projectile impactor. Impact energy was incrementally increased until visible rupture occurred. The strain energy density failure threshold fell between 25 and 60 kJ/m3 for excised porcine tissue samples, and between 15 and 30 kJ/m3 for whole, perfused organs. The relationship between localized failure in whole organ impacts and tissue level failure thresholds observed in cylindrical tissue samples was explored using a detailed finite element model of the human kidney. The model showed good correlation between experimentally observed injury patterns and predicted strain energy density distributions within the renal parenchyma. Finally, to facilitate interpretation of the porcine renal impact results with regard to human trauma, quasi-static compression test results of freshly excised human kidney cortex samples (n = 30) were compared against similar tests on pig kidneys. Human tissues failed at Lagrange strain levels similar to porcine tissue (63+/-6.3%), but at 52% lower Lagrange stress (116+/-28 kPa), and 35% lower strain energy density (17.1+/-4.4 kJ/m3). Thus conservative interpretation of porcine test results is recommended.

Strain-rate dependent material properties of the porcine and human kidney capsule.

This study was performed to characterize the mechanical properties of the kidney capsular membrane at strain-rates associated with blunt abdominal trauma. Uniaxial quasi-static and dynamic tensile experiments were performed on fresh, unfrozen porcine and human renal capsules at deformation rates ranging from 0.0001 to 7 m/s (strain-rates of 0.005-250 s(-1)). Single stroke, dynamic tests were performed on samples of porcine renal capsule at strain-rates of 0.005 s(-1) (n = 33), 0.05 s(-1) (n = 17), 0.5 s(-1) (n = 38), 2 s(-1) (n = 10), 4 s(-1) (n = 10), 50 s(-1) (n = 21), 100 s(-1) (n = 18), 150 s(-1) (n = 17), 200 s(-1) (n = 10), and 250 s(-1) (n = 17). Due to limited availability of human tissues, only quasi-static tests were performed (0.005 s(-1), n = 25). Porcine renal capsule properties were found to match the material properties of human capsular tissue sufficiently well such that porcine tissue material can be used as a human test surrogate. The apparent elastic modulus and breaking stress of the porcine renal capsule were observed to increase significantly with increasing strain-rate (p < 0.01). Breaking strain was inversely related to strain-rate (p < 0.01). The effect of increasing strain-rate on material properties diminished appreciably at rates exceeding 150 s(-1). Empirically derived mathematical models of constitutive behavior were developed using a hyperelastic/viscoelastic Ogden formulation, as well as a Cowper-Symonds law material curve multiplication.

Measurement and prediction of thermal behavior and acute assessment of injury in a pig model of renal cryosurgery.

PURPOSE: To analyze in vivo end temperatures and histologic injury in a standardized cryo-iceball using a porcine kidney model in order to establish the threshold temperature for tissue ablation. To evaluate the ability to predict end temperatures using a thermal finite element model. MATERIALS AND METHODS: A single freeze/thaw cryolesion was created in five pig kidneys and the temperature history recorded. End temperature was calculated using a thermal finite element model. The threshold temperature for tissue injury was established by directly correlating end temperature and histologic injury. RESULTS: Reproducible geometry and temperature profiles of the cryo-iceball were found. End temperature could be accurately predicted through thermal modeling, and correlation with histologic injury revealed a threshold temperature of -16.1 degrees C for complete tissue ablation. CONCLUSION: Thermal modeling may accurately predict end temperature within a cryo-iceball. Provided threshold temperatures for tissue destruction are known, modeling may become a powerful tool in cryosurgery, improving the assessment of damage in normal and malignant tissue.

Hand-assisted laparoscopic bilateral nephrectomy.

Open bilateral nephrectomy in renal transplant patients may be indicated for various reasons and is associated with a significant rate of morbidity and mortality. Laparoscopic bilateral nephrectomy may favorably influence postoperative recovery but is technically difficult. This case report is the first description of hand-assisted laparoscopic bilateral nephrectomy. We believe this technique significantly shortens the operative time, increases the safety of the procedure, and assures the patient the benefits of minimal invasive surgery in terms of postoperative pain and recovery.

The higher injury risk of abnormal kidneys in blunt renal trauma.

OBJECTIVE: To investigate the vulnerability of abnormal kidneys in blunt trauma, and to determine clinical features which enable identification of patients at risk of renal abnormality, hence modifying their management. MATERIAL AND METHODS: The medical records of 120 patients with blunt renal trauma were reviewed. Presence of pre-existing renal abnormalities, clinical symptoms, contrast study findings, associated injuries and the estimated impact velocity were recorded. RESULTS: Pre-existing renal abnormalities were found in 23 patients (19%). Patients with renal abnormalities had a lower rate of associated trauma to other abdominal organs, a lower Injury Severity Score (ISS) and their kidneys were more frequently injured by low velocity impacts. Of the patients with normal kidneys requiring surgery, hemodynamics and/or severity of the renal lesions triggered the operative indications in all cases, whereas most (57%) of the abnormal kidneys were operated because of their underlying renal pathology. CONCLUSION: Patients at risk for harbouring renal pathology are characterized by the association of monotrauma, macroscopic hematuria and low impact velocity. In this clinical setting, contrast studies should be generously indicated, since the management of abnormal kidneys unmasked by trauma is, to a large extent, dependent on the type of pathology.

[The conservative treatment of major kidney injuries]. / Le traitement conservateur du traumatisme rénal majeur.

The choice of treatment (surgical or conservative) for major renal trauma still remains controversial. The objective of this study was to compare the results of patients with major renal trauma (grade III and IV) primarily treated by surgical intervention (1980-1992) with those in patients mainly treated conservatively (1992-1995). Between 1980 and 1995, 83 patients with major renal trauma were hospitalized at our institution. Our results show a higher nephrectomy rate of 44% in the case of primary surgical intervention compared to conservative management (27%). The outcome of twenty-two patients treated conservatively was analyzed prospectively with repeated radiological imaging, blood pressure profiles, and renal function assessment by means of MAG 3 renal scintigraphy. No patient developed renovascular hypertension and the relative function of the traumatized kidney was greater than 40% in 95% of patients. In conclusion, our results confirm a lower nephrectomy rate in the case of conservative management without any increase of the immediate or long-term morbidity. Major renal trauma (grade III, IV) can therefore be effectively treated by conservative management and primary surgical repair is only indicated in patients with hemodynamic instability, persistent hematuria and associated visceral injuries.

Force transmission and stress distribution in a computer-simulated model of the kidney: an analysis of the injury mechanisms in renal trauma.

Injury mechanisms in renal trauma were investigated by analyzing the stress distributions within a two-dimensional computer-simulated model of the kidney. In biomechanics, damage to biological tissue is primarily caused by stresses resulting in tissue deformation beyond recovery limits. Segmental surface force was applied to the model and the resulting stress distributions were analyzed. Maximum stress concentrations were found at the periphery of the kidney model. Stresses were caused by the combined effect of the applied force and the reaction generated by the liquid-filled inner compartment as a function of its hydrostatic pressure. Maximum stress concentrations corresponded to typical injury sites observed clinically. Our findings suggest that a similar mechanism may play a crucial role in renal trauma. Renal injuries as well as the higher trauma susceptibility of hydronephrotic kidneys and renal cysts could thus be explained. The role of computer models in injury biomechanics research is discussed.