Jingfa Liu | PubMed Health

PubMed2006

Structure optimization in a three-dimensional off-lattice protein model.

We studied a three-dimensional off-lattice AB model with two species of monomers, hydrophobic (A) and hydrophilic (B), and present two optimization algorithms: face-centered-cubic (FCC)-lattice pruned-enriched-Rosenbluth method (PERM) and subsequent conjugate gradient (PERM++) minimization and heuristic conjugate gradient (HCG) simulation based on "off-trap" strategy. In PERM++, we apply the PERM to the FCC-lattice to produce the initial conformation, and conjugate gradient minimization is then used to reach the minimum energy state. Both algorithms have been tested in the three-dimensional AB model for all sequences with lengths 13 < or = n < or = 55. The numerical results show that the proposed methods are very promising for finding the ground states of proteins. In several cases, we renew the putative ground states energy values.

Algorithms↗

PubMed2004

[Experimental study of posterior pedicle screw placement on atlas].

OBJECTIVE: To assess the possibility of placing the posterior pedicle screw on atlas. METHODS: Twenty human cadaver specimens were used to insert pedicle screws in atlas, through the posterior arch or the pedicle of C1 into the lateral mass. The screw entry point was on the posterior surface of C1 posterior arch and at the intersection of the vertical line through the center of C2 inferior articular process and the horizontal line at least 3 mm below the superior rim of the C1 lamina. The screw of 3.5 mm in diameter was placed in a direction of 10 degrees medial angle and 5 dgrees upward angle. After placement of C1 pedicle screw, the distance from C1 screw entry point to the medial-lateral midpoint of C1 pedicle, the maximum length of screw trajectory and the actual screw trajectory angles were measured. The direction of screw penetrating through the cortical of C1 pedicle or lateral mass and the injuries to the vertebral artery and spinal cord were observed. RESULTS: Forty pedicle screws were placed on atlas, the mean distance from C1 screw entry point to the medial-lateral midpoint of C1 pedicle was (2.20 +/- 0.42)mm, the maximum length of screw trajectory averaged (30.51 +/- 1.59)mm, and the actual screw trajectory angle measured (9.7 +/- 0.67)degrees in a medial direction and (4.6 +/- 0.59)degrees in a upward direction. Only 1 screw penetrated the upper cortical bone of the atlas pedicle because the upward angle was too large, and 8 screws were inserted so deep that the inferior cortical bone of the C1 lateral mass was penetrated. But no injuries to the vertebral artery and spinal cord were observed. CONCLUSION: C1 posterior pedicle screw fixation is quite accessible and safe, but the surgeons should pay attention to the angle and the depth of the screw placement.

Adult↗

PubMed2002

[Mosaicplasty osteochondral grafting to repair cartilaginous defects under arthroscopy].

OBJECTIVE: To study mosaicplasty a as method of autogenous osteochondral transplantation in the treatment of cartilaginous defects. METHODS: The technique involves obtaining small cylindrical grafts from the non-weight bearing periphery of the femur at the patellar femoral joint, and transporting them to the prepared recipient site by arthroscopy. RESULTS: Fifteen patients with defects cartilaginous received mosaicptasty osteochondral grafting. Follow up for 12 to 21 months (mean 15 months) showed good results. CONCLUSION: The treatment is indicated for patients with focal cartilaginous defects under the age of 45.

Adult↗