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Study Design: Benchtop biomechanics study examining kinematic effects of progressive resection in a human cadaveric spine model., Objective: To determine the effects of posterior longitudinal ligament (PLL) resection, unilateral and bilateral foraminotomy, and laminectomy on cervical intervertebral rotation and translation after cervical disc arthroplasty (CDA)., Summary of Background Data: Although the clinical results after CDA have been studied, there remain unanswered questions regarding the surgical techniques used at the time of device insertion. For example, it is unclear whether a surgeon should retain or resect the PLL and uncinate processes at the time of primary surgical intervention. Further, the effect of a subsequent posterior decompression (foraminotomy or laminectomy) on the stability of a motion segment containing a disc arthroplasty is unknown., Methods: Three-dimensional intervertebral motion was measured by biplanar videography in human cadaveric spines at C4-C5 or at C5-C6 subjected to a 1.5-Nm moment applied to induce motion in the sagittal plane. Coupled motions were not constrained. After measuring intact spine motion, disc arthroplasty with bilateral ventral foraminotomy was performed without PLL resection. Sequentially, rotations and translations were measured after PLL resection, unilateral foraminotomy, bilateral foraminotomy, and laminectomy., Results: CDA with bilateral ventral foraminotomy increased sagittal rotation by 0.4 degrees (16%) compared with the intact spine. The addition of PLL resection increased rotation by 0.5 degrees (14% increase). Unilateral and bilateral foraminotomy had negligible effects on sagittal rotation or anteroposterior (AP) translation. Laminectomy resulted in an additional sagittal plane rotation of 2 degrees. The sagittal-plane interverterbal rotation resultant after all interventions was 6 degrees , with 1.5 mm of AP translation occurring only., Conclusion: Given that a greater degree of motion was seen with PLL resection combined with ventral foraminotomy, we recommend that PLL resection be performed when performing CDA. In our benchtop model, unilateral and bilateral posterior foraminotomies were not associated with the creation of significant sagittal rotational or AP translational instability.

Background: To compare the stability achieved using two 6.5-mm screws versus two or four 3.5-mm screws for the fixation of a unicondylar distal femur fracture., Methods: A fracture model was created in femoral synthetic composite bones to simulate a lateral femoral condyle fracture (AO/OTA 33-B1). Fixation was performed using three different types of screw constructs: 1) two 6.5-mm cancellous screws inserted using the lag technique, 2) two 3.5-mm cortical screws inserted using the lag technique, and 3) four 3.5-mm cortical screws, with two inserted using the lag technique and two as position screws. After reduction and fixation, the constructs were axially loaded in a material-testing machine. Main outcome measurements were the mean load required to displace the osteotomy site 1 and 2 mm as well as the mean stiffness of the different fixation methods., Results: The 6.5-mm construct required 56% more load to displace the osteotomy fragment 1 mm than the two 3.5-mm construct required (p < 0.0001), and 40% more load than the four 3.5-mm construct required (p < 0.0001). At loads that caused 2 mm of osteotomy displacement, these differences increased to 62% (p < 0.0001) and 48% (p < 0.0001), respectively. The mean loads needed to displace the osteotomy site were 28% higher for 1 mm of displacement (p = 0.003) and 27% higher for 2 mm of displacement (p = 0.03) for the four 3.5-mm screw construct compared with those needed for the two 3.5-mm group. The mean stiffness for the 6.5-mm group (1312.5 N/mm) was significantly higher than for the four 3.5-mm construct (784.2 N/mm; p < 0.0001) and the two 3.5-mm screw construct (409.4 N/mm; p < 0.0001). The difference in stiffness between the 3.5-mm groups was significant as well (p < 0.0001)., Conclusion: Stabilization of a unicondylar distal femur fracture with two 6.5-mm cancellous screws provides the most rigid and stable fixation. If small fragment screws are used, a minimum of four 3.5-mm cortical screws should be used to approximate the mechanical stability of two 6.5-mm screws.

Background: This study was designed to evaluate the effect of donor hyperosmolarity secondary to diabetes insipidus, an almost universal occurrence among brain-dead patients, on hepatic function., Methods: In vitro (isolated liver perfusion) and in vivo (hyaluronic acid and indocyanine green uptake, arterial ketone body ratio, orthotopic liver transplantation) experiments were conducted using Brattleboro rats, with hereditary hypothalamic diabetes insipidus, and Sprague-Dawley rats, with normal pituitary function. ATP content and recovery after cold preservation were measured during the perfusion., Results: Cold-preserved livers from hyperosmolar rats were observed to have elevated hepatic enzyme release and decreased bile production compared with normosmolar controls. Moreover, in these livers, the recovery of ATP after cold preservation was completely absent. Transmission electron microscopy of liver biopsies collected from hyperosmolar rats demonstrated profound ultrastructural changes, particularly in the mitochondria, that were not evident in the biopsies from normosmolar rats. All the experimental groups demonstrated similar hyaluronic acid uptake, whereas indocyanine green uptake was markedly impaired in the hyperosmolar group, suggesting that hepatocyte and not sinusoidal endothelial cell function is adversely affected by hyperosmolarity. The arterial ketone body ratio was profoundly compromised by chronic and, to an even greater degree, by acute hyperosmolarity. Survival after transplantation using hyperosmolar donors was not affected in this study., Conclusions: These results are an important step toward understanding the mechanism whereby brain death, a complicated pathophysiologic phenomenon, adversely affects the hepatic allograft.