Is intrathoracic rib plate fixation advantageous over extrathoracic plating? A biomechanical cadaveric study.

BACKGROUND: The high morbidity following surgical interventions on the chest wall because of large incisions often prevents surgeons from operative rib fracture treatment. Minimally invasive approaches to the intrathoracic side of the rib could allow for smaller incisions with lower morbidity while maintaining stability of fixation. The aim of this study was to explore the biomechanical competence of intrathoracic versus extrathoracic plating in a human cadaveric rib fracture model and investigate the effect of plating using two versus three screws per fracture fragment. METHODS: Twenty pairs of fresh-frozen human cadaveric ribs from elderly female donors aged 82.4 ± 7.8 years were used. First, the stiffness of each native rib was calculated via nondestructive (2 N-5 N) biomechanical testing under two loading conditions: ramped two-point bending and combined ramped tensile bending with torsional loading. Second, the ribs were fractured under three-point bending with their intrathoracic side put under tensile stress. Third, specimens were assigned to four groups (n = 10) for either intrathoracic or extrathoracic plating with two or three screws per fragment. Following instrumentation, all ribs were dynamically tested over 400,000 cycles under combined sinusoidal tensile bending with torsional loading (2 N-5 N at 3 Hz). Finally, all specimens were destructively tested under ramped two-point bending. RESULTS: Following instrumentation and cyclic testing, significantly higher construct stiffness was observed for intrathoracic vs. extrathoracic plating under anatomical loading conditions (p ≤ 0.03). No significant differences were detected for implant subsidence after plating with two or three screws per fragment (p ≥ 0.20). CONCLUSION: This study demonstrates significantly higher construct stiffness following intrathoracic over extrathoracic plating, thus indicating superior plate support of the former. In the clinical context, using only two instead of three screws per fragment not only could maintain stability of fixation but also decrease surgery time and costs, and allow for smaller incisions with lower morbidity. LEVEL OF EVIDENCE: Therapeutic/Care Management; Level V.

Chronic stress impairs recall of extinction of conditioned fear.

Chronic restraint stress produces retraction of apical dendrites of pyramidal neurons in medial prefrontal cortex. To begin to examine the functional significance of this dendritic reorganization, we assessed the effects of chronic restraint stress on a prefrontally mediated behavior, extinction of conditioned fear. After bar press training to obtain a baseline of activity against which to measure freezing, rats were either unstressed or stressed via placement in a plastic restrainer (3 h/day for 1 week). After an additional day of bar press training, rats underwent fear conditioning and extinction. Rats received five habituation trials to a 30-s tone (4.5 kHz, 80 db) followed by seven pairings of tone and footshock (500 ms, 0.5 mA). One hour later, rats received tone-alone extinction trials to criterion. The next day, rats received 15 additional extinction trials. Percent freezing was assessed during all phases of training. Stress did not significantly affect unconditioned responding to tone, acquisition of conditioned fear, or initial extinction, but significantly increased freezing on extinction day 2. Thus, consistent with the regressive dendritic changes seen in medial prefrontal cortex, one week of restraint stress specifically impaired recall of extinction, a pattern of deficits typical of animals with impaired medial prefrontal function.