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PURPOSE OF THE STUDY The current study aimed to investigate the intra- and inter-observer reliability of the Ellman classification system in partialthickness rotator cuff tears through magnetic resonance imaging (MRI) scans instead of arthroscopic views. MATERIAL AND METHODS Pre-operative MRI scans of 45 patients, with confirmed partial-thickness rotator cuff rupture in previous arthroscopic surgeries (performed by the senior author), were obtained from Picture Archiving and Communication Systems records. The observers (n=8) were asked to categorize MRI scans according to Ellman's classification of location and grade. There were four orthopedic surgeons less experienced in rotator cuff operations in the first group and four more experienced orthopedic surgeons in the second group. They were asked to re-evaluate the MRI scans six weeks later, without access to their previous answers. Reliability evaluation was performed within and among the groups. It was also evaluated if the surgeon's experience increased the reliability of the classification. Fleiss kappa coefficient was used for the inter-observer reliability and Cohen kappa coefficient for the intra-observer reliability, and post hoc analysis was performed. RESULTS When all observers were examined in the inter-observer evaluation, it was seen that there was moderate agreement in the first location evaluation (κ=0.414); however, there was fair agreement in all other evaluations in both groups (κ=0.339- 0.383-0.337, respectively). When all observers were examined in the mean intra-observer evaluation, it was seen that there was substantial agreement in both evaluations (κ=0.795-0.721, respectively). DISCUSSION A classification system must be valid, reliable, and reproducible. It should establish a standard terminology for both surgeons and researchers. The correct identification of the tear configuration is crucial for selecting the correct repair technique. In our study, in which we evaluated the Ellman classification, which is frequently used in arthroscopic diagnosis, we investigated its intra-observer and inter-observer reliability on MRI scans. Although the mean intra-observer evaluation results were substantial agreement (κ=0.795-0.721, respectively), inter-observer evaluation results were fair agreement (κ=0.339- 0.383-0.337, respectively) except for the first location evaluation (κ=0.414). CONCLUSIONS Although intra-observer reliability was satisfactory, the Ellman system used in the classification of partial-thickness rotator cuff tears was not found to be useful by using only MRI views because of fair inter-observer reliability except for the first location evaluation, which was moderate agreement. Key words: partial, rotator cuff, tear, Ellman classification, reliability, validity.

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Bisphosphonates are commonly used in the treatment of osteoporosis. Long-term use without drug holiday causes the risk of atypical fractures. Subtrochanteric and femoral stress fractures are among the frequently described complications. In our case report; a stress fracture of the scapular spine, a previously undescribed adverse effect of bisphosphonates, is presented. Key words: bisphosphonates, scapular spine, stress fracture, drug holiday.

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PURPOSE OF THE STUDY Pauwels classification system is widely used to classify the femoral neck fractures. Even its widely usage there are severals debates about its reliability. After the femoral neck fracture occured the lower extremity rotates externally and this external rotation deformity could lead to misevaluation of Pauwels angle at the initial radiographs. The purpose of our study is to investigate whether the reliability of Pauwels classification increases after reduction of femoral neck fractures. MATERIAL AND METHODS Two power point presentation was prepared with 117 slides that include antero-posterior radiographs of each femoral neck fracture. The first one included preoperatively taken radiographs and the second one included early postoperatively taken radiographs. Eight observers evaluated these radiographs and they classified the fractures according to Pauwels classification system. After 3 months, the order of the slides were changed for each presentation and the observers were asked to evaluate the radiographs again. Intraclass correlation coefficient values were calculated for evaluation of inter- and intra-observer reliability. RESULTS The mean intra-observer agreement of preoperative evaluation was 0.406 (0.071-0.626) and the interobserver agreements were 0.263 (0.197-0.342) and 0.359 (0.287-0.447), respectively. The intra-observer agreement of postoperative evaluation was 0.508 (0.393-0.757), inter-observer agreements were 0.427 (0.353-0.509) and 0.431 (0.356-0.513), respectively. According to preoperative and postoperative evaluations, 6 of 8 observers' intra-observer agreements were found to be increased and the remaining 2 decreased. Interobserver reliability was improved from poor to fair-good values after evaluating the reducted fracture radiographs. DISCUSSION Femoral neck fractures(FNF) are common and anatomical reduction and internal fixation are preferred as a treatment option in young people and patients have good bone quality. Pauwels classification system is used for classify the FNF based on the shearing angle of the fracture line. As this angle increases, the fracture becomes unstable and nowadays stronger fixation devices are preferred for unstable fractures. Therefore, misevaluation of the fracture can lead to wrong treatment method selection. Non-optimal X-rays taken in the emergency rooms may cause misinterpretation of femoral neck fractures according to Pauwels classification system. We hypothized that the reliability of this classification system could be improved after reduction of the fracture. CONCLUSIONS Our study showed that classifying the femoral neck fracture according to Pauwels classification system is more confidential after the reduction, however we can not state that it's reliability is adequate. Key words: femoral neck fracture, Pauwels classification, reliability, inter-observer, intra-observer.

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Carboxypeptidase T (CPT) from Thermoactinomyces vulgaris (EC 3.4.17.18) has a broad substrate specificity, the mechanism of which remains unclear. It cleaves off arginine residues by 10, and lysine residues by 100 times worse than hydrophobic leucine residues despite the presence of negatively charged Asp260 at the bottom of the primary specificity pocket. To study the relationship between the structure and specificity the 3D structure of CPT in complex with the stable transition state analog N-sulfamoyl-l-lysine (SLys) was determined in which the S-atom imitates the sp3-hybridized carbon in the scissile-bond. Crystals grown in microgravity has the symmetry of space group P6322. The present complex structure was compared with the previously reported complex structure of CPT and N-sulfamoyl-L-arginine (SArg). The location/binding of SLys in the active site of CPT very closely resembled that of SArg, and the positively charged N-atom of SLys was at the same position as the corresponding positively charged N-atom of SArg. The SLys complex is stabilized by the hydrogen bond between the nitrogen atom and OH-group of Thr257. The contact areas of the residues Tyr255, Leu211, and Thr262 with SLys were reduced in comparison with the same of SArg. This difference in bonding of SArg and SLys side chains in the primary specificity pocket induces shifts differences within the catalytic center (especially Tyr255-O20 and S18-Arg129 N1 gap) that may influence the enzyme's catalytic reaction. Therefore, this information may be useful for the design of carboxypeptidases with improved selectivity towards Arg/Lys for biotechnological applications.

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The carboxypeptidase T (CPT) from Thermoactinomyces vulgaris has an active site structure and 3D organization similar to pancreatic carboxypeptidases A and B (CPA and CPB), but differs in broader substrate specificity. The crystal structures of CPT complexes with the transition state analogs N-sulfamoyl-L-leucine and N-sulfamoyl-L-glutamate (SLeu and SGlu) were determined and compared with previously determined structures of CPT complexes with N-sulfamoyl-L-arginine and N-sulfamoyl-L-phenylalanine (SArg and SPhe). The conformations of residues Tyr255 and Glu270, the distances between these residues and the corresponding ligand groups, and the Zn-S gap between the zinc ion and the sulfur atom in the ligand's sulfamoyl group that simulates a distance between the zinc ion and the tetrahedral sp3-hybridized carbon atom of the converted peptide bond, vary depending on the nature of the side chain in the substrate's C-terminus. The increasing affinity of CPT with the transition state analogs in the order SGlu, SArg, SPhe, SLeu correlates well with a decreasing Zn-S gap in these complexes and the increasing efficiency of CPT-catalyzed hydrolysis of the corresponding tripeptide substrates (ZAAL > ZAAF > ZAAR > ZAAE). Thus, the side chain of the ligand that interacts with the primary specificity pocket of CPT, determines the geometry of the transition complex, the relative orientation of the bond to be cleaved by the catalytic groups of the active site and the catalytic properties of the enzyme. In the case of CPB, the relative orientation of the catalytic amino acid residues, as well as the distance between Glu270 and SArg/SPhe, is much less dependent on the nature of the corresponding side chain of the substrate. The influence of the nature of the substrate side chain on the structural organization of the transition state determines catalytic activity and broad substrate specificity of the carboxypeptidase T.

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The crystal structures of carboxypeptidase T (CpT) complexes with phenylalanine and arginine substrate analogs - benzylsuccinic acid and (2-guanidinoethylmercapto)succinic acid - were determined by the molecular replacement method at resolutions of 1.57 Å and 1.62 Å to clarify the broad substrate specificity profile of the enzyme. The conservative Leu211 and Leu254 residues (also present in both carboxypeptidase A and carboxypeptidase B) were shown to be structural determinants for recognition of hydrophobic substrates, whereas Asp263 was for recognition of positively charged substrates. Mutations of these determinants modify the substrate profile: the CpT variant Leu211Gln acquires carboxypeptidase B-like properties, and the CpT variant Asp263Asn the carboxypeptidase A-like selectivity. The Pro248-Asp258 loop interacting with Leu254 and Tyr255 was shown to be responsible for recognition of the substrate's C-terminal residue. Substrate binding at the S1' subsite leads to the ligand-dependent shift of this loop, and Leu254 side chain movement induces the conformation rearrangement of the Glu277 residue crucial for catalysis. This is a novel insight into the substrate selectivity of metallocarboxypeptidases that demonstrates the importance of interactions between the S1' subsite and the catalytic center.

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Molecular modeling was addressed to understand different substrate-binding modes and clarify the role of two positively charged residues of the penicillin G acylase active site - ßR263 and αR145 - in binding of negatively charged substrates. Although the electrostatic contribution to productive substrate binding was dominated by ßR263 rather than αR145, it was found that productive binding was not the only possible mode of substrate placement in the active site. Two extra binding modes - nonproductive and preproductive - were located by means of molecular docking and dynamics with binding affinities comparable with the productive one. A unique feature of nonproductive and preproductive complexes was that the substrate's acyl group did not penetrate the hydrophobic pocket, but occupied a patch on the protein interface spanning from ßR263 to αR145. Nonproductive and preproductive complexes competed with each other and productive binding mode, giving rise to increased apparent substrate binding. Preproductive complex revealed an ability to switch to a productive one during molecular dynamics simulations, and conformational plasticity of the penicillin G acylase active site was shown to be crucial for that. Nonproductive binding observed at molecular modeling corresponded well with experimentally observed substrate inhibition in penicillin acylase catalysis. By combining estimated free energies of substrate binding in each mode, and accounting for two possible conformations of the penicillin G acylase active site (closed and open) quantitative agreement with experimentally measured K(M) values was achieved. Calculated near-attack conformation frequencies from corresponding molecular dynamics simulations were in a quantitative correlation with experimental k(cat) values and demonstrated adequate application of molecular modeling methods.

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