Hossein Ghofrani

Psoas muscle architectural design, in vivo sarcomere length range, and passive tensile properties support its role as a lumbar spine stabilizer.

Study Design. Controlled laboratory and cross-sectional study designs. Objective. To determine psoas major (PM) muscle architectural properties, in vivo sarcomere-length operating range, and passive mechanical properties. Summary of Background Data. PM is an important hip flexor but its role in lumbar spine function is not fully understood. Several investigators have detailed the gross anatomy of PM, but comprehensive architectural data and in vivo length-tension and passive mechanical behaviors have not been documented. Methods. PM was isolated in 13 cadaver specimens, permitting architectural measurements of physiological cross-sectional area (PCSA), normalized fiber length (Lf), and Lf:muscle length (Lm) ratio. Sarcomere lengths were measured in vivo from intraoperative biopsies taken with the hip joint in flexed and extended positions. Single-fiber and fiber bundle tensile properties and titin molecular weight were then measured from separate biopsies. Results. Architecturally, average PCSA was 18.45 ± 1.32 cm2, average Lf was 12.70 ± 2 cm, and average Lf: Lm was 0.48 ± 0.06. Intraoperative sarcomere length measurements revealed that the muscle operates from 3.18 ± 0.20 &mgr;m with hip flexed at 10.7° ± 13.9° to 3.03 ± 0.22 &mgr;m with hip flexed at 55.9° ± 21.4°. Passive mechanical data demonstrated that the elastic modulus of the PM muscle fibers was 37.44 ± 9.11 kPa and of fiber bundles was 55.3 ± 11.8 kPa. Conclusion. Analysis of PM architecture demonstrates that its average Lf and passive biomechanical properties resemble those of the lumbar erector spinae muscles. In addition, PM sarcomere lengths were confined to the descending portion of the length-tension curve allowing the muscle to become stronger as the hip is flexed and the spine assumes a forward leaning posture. These findings suggest that the human PM has architectural and physiologic features that support its role as both a flexor of the hip and a dynamic stabilizer of the lumbar spine.

An evaluation of fracture stabilization comparing kyphoplasty and titanium mesh repair techniques for vertebral compression fractures: is bone cement necessary?

Study Design. In vitro biomechanical investigation using human cadaveric vertebral bodies. Objective. To evaluate differences in biomechanical stability of vertebral compression fractures (VCFs) repaired using an expandable titanium mesh implant, with and without cement, as compared with standard balloon kyphoplasty. Summary of Background Data. Vertebral augmentation, either in the form of vertebroplasty or kyphoplasty, is the treatment of choice for some VCFs. Polymethylmethacrylate, a common bone cement used in this procedure, has been shown to possibly cause injury to neural and vascular structures due to extravasation, embolization, and may be too rigid for an osteoporotic spine. Therefore, suitable alternatives for the treatment of VCFs have been sought. Methods. Individual vertebral bodies from 5 human cadaveric spines (from T4 to L5) were stripped of all soft tissues, and compressed at 25% of the intact height using methods previously described. Vertebral bodies were then randomly assigned to the following repair techniques: (1) conventional kyphoplasty, (2) titanium implant with cement, (3) titanium implant without cement. All vertebral bodies were then recompressed at 25% of the repaired height. Yield load, ultimate load, and stiffness were recorded and compared in these groups before and after treatment. Results. There were no differences in biomechanical data between intact groups, and between repaired groups. In all 3 treatment groups, yield load and ultimate load of repaired vertebrae were similar to that of intact vertebrae. However, the stiffness following repair was found to be statistically less than the stiffness of the intact vertebral body (P < 0.05 for all comparisons). Conclusion. Based on the biomechanical data, the titanium mesh implant with or without cement was similar to polymethylmethacrylate fixation by kyphoplasty in the treatment of VCFs. Avoiding the adverse effects caused by using cement may be the main advantage of the titanium mesh implant and warrants further study.

A retrospective review of long anterior fusions to the sacrum

BACKGROUND CONTEXT In the setting of tumor, infection, or trauma, a corpectomy of the L5 vertebral body may be necessary. However, the space has an irregular trapezoidal shape, and the failure to account for this may lead to improper fitting of the titanium cages or the allograft struts when performing a reconstruction. PURPOSE The purpose of this study was to evaluate the failure rate of implants used to reconstruct the anterior lumbar spine when an L5 corpectomy has been performed. METHODS A retrospective review of the medical records and radiographs of 19 consecutive patients undergoing an L5 corpectomy and anterior spinal fusion was performed. The radiographs were reviewed for implant failure and successful fusions. RESULTS Cases included osteomyelitis (13), fractures (4), and tumor (2). Anterior reconstruction was performed with a straight cylindrical titanium cage in six cases, allograft in six cases, iliac crest bone graft (ICBG) in two cases, and cages with lordosis built into the cage or end plates in five cases. In the six straight cylindrical titanium cages, four cases had displaced anteriorly, necessitating revision surgery. In the other two cases, both had poor fixation to the sacrum and developed nonunions. In the six reconstructed with allograft, all three fibular struts developed nonunions. In the three reconstructed with humeral or femoral allograft, all patients formed a solid fusion. In the patients reconstructed with ICBG, one formed a nonunion, whereas the other one formed a solid fusion. In the cages with lordosis built into the cage or end plates, all five developed solid fusions. CONCLUSIONS A corpectomy of L5 resulting in an irregular trapezoidal shape must be accounted for when performing the reconstruction. Use of straight cylindrical cages or allograft with small footprints may lead to an increased rate of failure. When performing the reconstruction, adding approximately 20° to 30° of lordosis to the construct may create a better fit and increase stability and result in an improved fusion rate. If using allograft, using a larger graft with greater end plate contact may also improve fusion rates.

NO pathway and phosphodiesterase inhibitors in pulmonary arterial hypertension

Nitric oxide (NO) is constitutively produced in the lung by NO-synthases. The main cellular sources of lung NO production are the vascular endothelium and the airway epithelia [1, 2]. Adaptation of the perfusion distribution to well ventilated areas of the lung (ventilation/perfusion (V/Q) matching) is mainly regulated by local NO production [3, 4]. NO- synthase activity is regulated on transcriptional and post-translational redox-based modulation level [5]. The common signaling pathway of endogenous vasodilators, such as nitric oxide, prostaglandins, and natriuretic peptides, engage cyclic nucleotides (cAMP and cGMP). The enzymatic source of these second messengers are mainly adenylate-and guanylate-cyclases [6]. PDEs represent a superfamily of enzymes, with PDE1 through PDE11 being currently known, that inactivate cyclic AMP and cyclic GMP, with different tissue distribution and substrate specificities [6, 7]. Depending on their selective profile, PDE inhibitors differentially regulate the activity of cAMP and/or cGMP. Thus, they might be offered as therapeutic tools to augment and prolong prostanoid-and NO-related vascular effects. The efficacy of this approach has been proven in various experimental studies [8, 9]. The most important cyclic GMP degrading phosphodiesterase – PDE5 – is abundantly expressed in lung tissue [7]. The selective PDE5 inhibitor sildenafil has been approved for the treatment of erectile dysfunction [10]. Documented use in numerous otherwise healthy individuals and patients with a variety of underlying diseases sildenafil displayed an excellent safety profile [11].