Biomedical subjects

J Ménétrey

Publications and source records attributed to J Ménétrey.

13 recordsLinked to original sources

PubMed2005

Anatomy of the anterior cruciate ligament.

The anterior cruciate ligament (ACL) is a band of dense connective tissue which courses from the femur to the tibia. The ACL is a key structure in the knee joint, as it resists anterior tibial translation and rotational loads. When the knee is extended, the ACL has a mean length of 32 mm and a width of 7-12 mm. There are two components of the ACL, the anteromedial bundle (AMB) and the posterolateral bundle (PLB). They are not isometric with the main change being lengthening of the AMB and shortening of the PLB during flexion. The ACL has a microstructure of collagen bundles of multiple types (mostly type I) and a matrix made of a network of proteins, glycoproteins, elastic systems, and glycosaminoglycans with multiple functional interactions. The complex ultrastructural organization and abundant elastic system of the ACL allow it to withstand multiaxial stresses and varying tensile strains. The ACL is innervated by posterior articular branches of the tibial nerve and is vascularized by branches of the middle genicular artery.

Anterior Cruciate Ligament↗

PubMed2005

[Patella dislocation].

Patella dislocation is a classical injury affecting teenagers. In 2/3 of cases, it occurs in sports activities. It is often a benign trauma which happens in a patello-femoral dysplasia context, leading to dislocation and reccurence if nothing is done to correct the defaults. Radiographic and scanner examinations allow to measure the dysplasia parameters and think about its correction. With MRI documentation, capsulo-ligamentous and cartilaginous lesions can be identified and their surgical repair can be discussed. When the dislocation occurs in a normal anatomical context, conservative therapy is still indicated.

Adolescent↗

PubMed2002

Medial meniscectomy in patients over the age of fifty: a six year follow-up study.

PURPOSE: Meniscectomy in the older patient remains a controversial topic. The aim of our study is to assess the mid-term outcome of arthroscopic partial medial meniscectomy in patients over fifty years of age and attempt to retrospectively identify symptoms and/or findings on examination which can differentiate between non-degenerative medial meniscal tears versus degenerative meniscal changes. MATERIALS AND METHODS: Thirty-two patients over the age of fifty who had undergone arthroscopic medial partial meniscectomy, were reviewed. The average age was 60 (51-74 yrs) and the average follow-up was six years (3-7 yrs). Based upon the intra-operative findings, patients were divided into two groups: (1) non-degenerative meniscal tears (NDM; n = 12) and (2) degenerative meniscal changes (DM; n = 20). Our outcome measurements were with the HSS knee score, a satisfaction score, and weight-bearing X-rays. RESULTS: In the NDM group, eleven patients were rated excellent or good, and one was rated poor. In the DM group, three patients were rated as excellent or good, eight as fair, and nine as poor. The HSS score was 97 +/- 4.6 for the NDM group and 85 +/- 9.5 for the DM group. The average satisfaction score was 9.2 +/- 0.7 (very satisfied) for the NDM group and 5.8 +/- 2.6 (fairly satisfied) for the DM group. There was no significant difference between the NDM and the DM groups with regards to pre-operative symptoms and signs, except for the McMurray sign, which was found to be positive in 83% of NDM cases versus 25% of DM cases (sensitivity = 83%). Using only these data, the McMurray sign was 67% specific for NDM. CONCLUSIONS: Arthroscopic medial meniscectomy in older patients provides 90% good results six years after a non-degenerative meniscal tear, but only 20% of good results after a degenerative meniscal tear. However, based on this study, neither symptoms nor physical examination are able to differentiate between traumatic meniscal tears and degenerative meniscal changes in older patients. A positive McMurray's sign favors the diagnosis of a traumatic tear. However, a specificity of this test of only 67% as shown in our data questions its utility in clinical decision-making.

Age Factors↗

PubMed2001

Structure of the EMAPII domain of human aminoacyl-tRNA synthetase complex reveals evolutionary dimer mimicry.

The EMAPII (endothelial monocyte-activating polypeptide II) domain is a tRNA-binding domain associated with several aminoacyl-tRNA synthetases, which becomes an independent domain with inflammatory cytokine activity upon apoptotic cleavage from the p43 component of the multisynthetase complex. It comprises a domain that is highly homologous to bacterial tRNA-binding proteins (Trbp), followed by an extra domain without homology to known proteins. Trbps, which may represent ancient tRNA chaperones, form dimers and bind one tRNA per dimer. In contrast, EMAPII domains are monomers. Here we report the crystal structure at 1.14 Angstroms of human EMAPII. The structure reveals that the Trbp-like domain, which forms an oligonucleotide-binding (OB) fold, is related by degenerate 2-fold symmetry to the extra-domain. The pseudo-axis coincides with the dyad axis of bacterial TtCsaA, a Trbp whose structure was solved recently. The interdomain interface in EMAPII mimics the intersubunit interface in TtCsaA, and may thus generate a novel OB-fold-based tRNA-binding site. The low sequence homology between the extra domain of EMAPII and either its own OB fold or that of Trbps suggests that dimer mimicry originated from convergent evolution rather than gene duplication.

Amino Acid Sequence↗

PubMed2001

The structural GDP/GTP cycle of human Arf6.

The small GTP-binding protein Arf6 coordinates membrane traffic at the plasma membrane with aspects of cytoskeleton organization. This function does not overlap with that of other members of the ADP-ribosylation factor (Arf) family, although their switch regions, which are their major sites of interaction with regulators and effectors, have virtually identical sequences. Here we report the crystal structure of full-length, non-myristoylated human Arf6 bound to GTPgammaS. Unlike their GDP-bound forms, the active forms of Arf6 and Arf1 are very similar. Thus, the switch regions are discriminatory elements between Arf isoforms in their inactive but not in their active forms, a property that may generalize to other families of small G proteins. This suggests that GTP-bound Arfs may establish specific interactions outside the switch regions and/or be recognized in their cellular context rather than as isolated proteins. The structure also allows further insight into the lack of spontaneous GTPase activity of Arf proteins.

ADP-Ribosylation Factor 1↗

PubMed2000

Structure of Arf6-GDP suggests a basis for guanine nucleotide exchange factors specificity.

Arf6 is an isoform of Arf that localizes at the periphery of the cell where it has an essential role in endocytotic pathways. Its function does not overlap with that of Arf1, although the two proteins share approximately 70% sequence identity and they have switch regions, whose conformation depends on the nature of the guanine nucleotide, with almost identical sequences. The crystal structure of Arf6-GDP at 2.3 A shows that it has a conformation similar to that of Arf1-GDP, which cannot bind membranes with high affinity. Significantly, the switch regions of Arf6 deviate by 2-5 A from those of Arf1. These differences are a consequence of the shorter N-terminal linker of Arf6 and of discrete sequence changes between Arf6 and Arf1. Mutational analysis shows that one of the positions which differs between Arf1 and Arf6 affects the configuration of the nucleotide binding site and thus the nucleotide binding properties of the Arf variant. Altogether, our results provide a structural basis for understanding how Arf1 and Arf6 can be distinguished by their guanine nucleotide exchange factors and suggest a model for the nucleotide/membrane cycle of Arf6.

ADP-Ribosylation Factor 1↗

PubMed1999

Structure of the small G protein Rap2 in a non-catalytic complex with GTP.

We report a novel crystal form of the small G protein Rap2A in complex with GTP which has no GTPase activity in the crystal. The asymmetric unit contains two complexes which show that a conserved switch I residue, Tyr 32, contributes an extra hydrogen bond to the gamma-phosphate of GTP as compared to related structures with GTP analogs. Since GTP is not hydrolyzed in the crystal, this interaction is unlikely to contribute to the intrinsic GTPase activity. The comparison of other G protein structures to the Rap2-GTP complex suggests that an equivalent interaction is likely to exist in their GTP form, whether unbound or bound to an effector. This interaction has to be released to allow the GAP-activated GTPase, and presumably the intrinsic GTPase activity as well. We also discuss the definition of the flexible regions and their hinges in the light of this structure and the expanding database of G protein structures. We propose that the switch I and switch II undergo either partial or complete disorder-to-order transitions according to their cellular status, thus defining a complex energy landscape comprising more than two conformational states. We observe in addition that the region connecting the switch I and switch II is flexible in Rap2 and other G proteins. This region may be important for protein-protein interactions and possibly behave as a conformational lever arm, as characterized for Arf. Taken together, these observations suggest that the structural mechanisms of small G proteins are significantly driven by entropy-based free energy changes.

Crystallography, X-Ray↗

PubMed1998

Structure of the Sec7 domain of the Arf exchange factor ARNO.

Small G proteins switch from a resting, GDP-bound state to an active, GTP-bound state. As spontaneous GDP release is slow, guanine-nucleotide-exchange factors (GEFs) are required to promote fast activation of small G proteins through replacement of GDP with GTP in vivo. Families of GEFs with no sequence similarity to other GEF families have now been assigned to most families of small G proteins. In the case of the small G protein Arf1, the exchange of bound GDP for GTP promotes the coating of secretory vesicles in Golgi traffic. An exchange factor for human Arf1, ARNO, and two closely related proteins, named cytohesin 1 and GPS1, have been identified. These three proteins are modular proteins with an amino-terminal coiled-coil, a central Sec7-like domain and a carboxy-terminal pleckstrin homology domain. The Sec7 domain contains the exchange-factor activity. It was first found in Sec7, a yeast protein involved in secretion, and is present in several other proteins, including the yeast exchange factors for Arf, Geal and Gea2. Here we report the crystal structure of the Sec7 domain of human ARNO at 2 A resolution and the identification of the site of interaction of ARNO with Arf.

ADP-Ribosylation Factor 1↗

PubMed1998

[Acute compartment syndrome in the post-traumatic leg].

PURPOSE OF THE STUDY: Compartment syndrome represents a clinical entity, whose diagnosis depends both on clinical findings as well as on measurement of the intracompartmental pressure. Physiopathology and clinical aspects of diagnosis and treatment of the acute compartment syndrome are discussed, based on the literature review and personal clinical experience. MATERIAL AND METHODS: We have based our experience on a series of 100 consecutive fractures of the leg, in which we studied mechanism of trauma, fractures localization, timing of surgery for fasciotomy and wound closure. RESULTS: The incidence of compartment syndrome was 8 per cent. Younger age (< 30 years), high energy trauma, or trauma occurring during physical activity appeared to increase the risk of occurrence. Localization of the fracture on the proximal, mid or distal thirds of the leg did not. DISCUSSION: The following aspects are discussed: 1) The perfusion pressure of a compartment is defined as the difference between the diastolic blood pressure and the intracompartmental pressure. 2) Fasciotomy is indicated whenever this value is inferior to 30 mmHg. 3) Failure to measure the pressure within 5 cm from the fracture site may cause underestimation of the compartment pressure. 4) Intramedullary nailing does not seem to increase the risk of compartment syndrome.

Compartment Syndromes↗

PubMed1997

Crystal structures of the small G protein Rap2A in complex with its substrate GTP, with GDP and with GTPgammaS.

The small G protein Rap2A has been crystallized in complex with GDP, GTP and GTPgammaS. The Rap2A-GTP complex is the first structure of a small G protein with its natural ligand GTP. It shows that the hydroxyl group of Tyr32 forms a hydrogen bond with the gamma-phosphate of GTP and with Gly13. This interaction does not exist in the Rap2A-GTPgammaS complex. Tyr32 is conserved in many small G proteins, which probably also form this hydrogen bond with GTP. In addition, Tyr32 is structurally equivalent to a conserved arginine that binds GTP in trimeric G proteins. The actual participation of Tyr32 in GTP hydrolysis is not yet clear, but several possible roles are discussed. The conformational changes between the GDP and GTP complexes are located essentially in the switch I and II regions as described for the related oncoprotein H-Ras. However, the mobile segments vary in length and in the amplitude of movement. This suggests that even though similar regions might be involved in the GDP-GTP cycle of small G proteins, the details of the changes will be different for each G protein and will ensure the specificity of its interaction with a given set of cellular proteins.

Amino Acid Sequence↗

PubMed1997

[Isolated dislocation of the elbow].

GOALS OF THE STUDY: To analyse the results of non surgical management of isolated dislocation (without any fractures) of the elbow in adult. MATERIAL AND METHODS: We reviewed with an average follow up of 36 months 22 patients (22 elbows) who had been treated conservatively after a first episode of posterior dislocation of the elbow. RESULTS: Nineteen patients (86%) reported an excellent or a good subjective result, although 64% suffered occasionally from pain. None had presented a recurrent dislocation. At physical examination, 27% had a restricted extension of the elbow of 10 degrees and more, and 27% had some kind of chronic laxity. Fifty percent had modifications visible on the X-rays. We found no correlation between laxity and duration of immobilization. At contrary, patients who were immobilized for a longer time than 3 weeks suffered more often of a painful restricted extension of the elbow. DISCUSSION: Conservative management of posterior dislocation of the elbow has a good prognosis. Occasional pain and chronic laxity are often present but well supported. Early mobilization decreases the risk of permanent limited extension of the elbow.

Adolescent↗

PubMed1992

[Study of the type of physical effort exerted by competition in Supercross].

The authors draw up a tentative account of the physiological load a pilot bears during a Supercross event. Examination of heart frequency and blood lactate concentration curves during a series of races shows that this sport is not only highly stressful, but demands by the same token a muscular effort which has to be taken into account. Muscular work is of the mixed type, both aerobic and anaerobic, the share of the latter being of moderate importance, as it depends mainly on the technical proficiency of the driver.

Adolescent↗

PubMedDate not supplied

Subtalar subluxation in ballet dancers.

Ankle injuries frequently occur in dancers. Among these injuries, only a few cases of talar subluxation have been reported in the literature. In our series, we diagnosed and treated 25 subtalar subluxations over a 1-year period in the Ballet Béjart Lausanne company. The subluxations occurred after a grand plie on pointes or at the landing of a jump on demi-pointes, without any mechanism of ankle sprain. The dancer usually noted a sudden and sharp pain in the talonavicular joint and hindfoot with a feeling of "forward displacement" of the foot. At palpation, the talonavicular ligament, the anterior talofibular ligament, and the posteromedial part of the subtalar joint were painful. A limitation of the ankle extension and a clear hypomobility of the subtalar joint were noted. Under the effect of shearing forces on the midtarsal joint, a posteromedial subtalar subluxation occurred. Treatment consisted of a manipulation that reduced the subluxation. Continuous taping, which locks the talonavicular joint in the anterior direction, was recommended for 6 weeks. Dancing could be resumed in a swimming pool after 2 weeks, and on the ground after 3 to 4 weeks. We found that subluxation could recur, and that it could eventually become chronic.

Adult↗