Jean-Luc Kahn

Effects of freezing/thawing on the biomechanical properties of human tendons.

Abstract Numerous biomechanical studies using osteoarticular complex need frozen cadaveric specimens. Some of these studies deal with the resistance of the tendinous structures, for example the resistance of some autografts, such as the patellar ligament and the semitendinosus and gracilis tendons for reconstruction of the anterior cruciate ligament. The aim of this study was the in-vitro evaluation of the mechanical modifications induced by freezing/thawing on human tendons. The long head of the biceps brachii tendon was used as the reference. Eight pairs of tendons of the long head of the biceps brachii were taken from eight fresh cadavers. After drawing lots, one was tested immediately, the other was deep-frozen and then thawed. With an Instron material-testing machine, we performed a relaxation test and a uniaxial tensile test, to estimate the ultimate tensile failure and the elastic modulus of each pair of tendons. Freezing had no influence on the tendinous relaxation, but altered significantly the ultimate tensile failure and Young’s modulus of the tendons.

A plea for the use of drawing in human anatomy teaching

Descriptive human anatomy constitutes one of the main parts of the educational program of the first part of the medical studies. Professors of anatomy have to take into account the exponential evolution of the techniques of morphological and functional exploration of the patients, and the trend to open more and more the contents of the lectures of anatomy to clinical considerations. Basically, teaching requires a series of descriptive and educational media to set up, in front of the student, the studied structures and so to build the human body. More generally, lectures in morphological sciences try to develop three types of knowledge: declarative, procedural, and conditional. Traditionally in France “basic or first” anatomy is taught in amphitheater and in big groups by building each structure or region on a blackboard with colored chalk that allows a relief stake of certain structures and builds in two dimensions a three-dimensional organization. Actually, the blackboard is and stays for us an excellent media of non-verbal expression.

Determination of the external forces applied to the mandible during various static chewing tasks

The purpose of this study is to determine the external forces that are brought to bear on the mandible during 14 masticatory tasks, exerted in three defined mandibular positions. A static two-dimensional mandibular model is presented, taking into account projections in the sagittal plane of the forces exerted by six muscle groups and the joint reaction force. In calculating these external forces, two working hypotheses are adopted: the existence of a linear relationship between cross-sectional surface of the muscle and its maximum force of contraction, and the existence of a linear relationship between the electrical signal emitted by a muscle and the force the muscle then develops. Our first results are provided and compared with data from the literature. Individual variations recorded in the measurement of the different parameters involved in the equilibrium equations are such that they must be taken into account in the calculation of the forces. Moreover, the functional value of the muscles appears to be closely dependent on the mandibular position with which they are associated, which is not brought out in earlier studies. Finally, intra-joint action proves to be intense, although its direction varies according to the mandibular position and the type of exercise performed.

Le rameau transverse de la branche dorsale du nerf ulnaire : anatomie et rapports avec les voies arthroscopiques du poignet: Quarante-cinq dissections

PURPOSE OF THE STUDY We conducted an anatomic study of the transverse branch of the dorsal ulnar nerve to describe its morphology and position in relation to arthroscopic exploration portals. MATERIAL AND METHODS Forty-five non-side-matched anatomic specimens of unknown age and gender were preserved in formol. The dorsal branch of the ulnar nerve was identified and dissected proximally to distally in order to reveal the different terminal branches. The morphometric analysis included measurement of the length and diameter of the transverse branch and measurement of wrist width. We also measured the smallest distance between the transverse branch and the ulnar styloid process, and between the branch and usual arthroscopic portals (4-5, 6R, 6U) in the axis of the forearm. RESULTS The transverse branch was inconstant. It was found in 12 of the 45 dissection specimens (27%). In two-thirds of the specimens, the branch ran over less than 50% of the wrist width, tangentially to the radiocarpal joint. Mean nerve diameter was 1 mm. It was found 5-6 mm from the ulnar styloid process and was distal to it in 83% of the specimens. The dissections demonstrated two anatomic variants. Type A corresponded to a branch running distally to the ulnar styloid process, parallel to the joint line (10/12 specimens). Type B exhibited a trajectory proximal to the ulnar styloid process, crossing the ulnar head (2/12 specimens). The relations with the arthroscopic portals (4-5, 6R, 6U) showed that the mean distance from the branch to the portal was 3.75 mm for the 4-5 portal (distally in 11/12 specimens), 3.68 mm for the 6R portal (distally in 10/12 specimens), and 4.83 mm for the 6U portal (distally in 7 specimens and proximally in 5). DISCUSSION To our knowledge, there has been only one report specifically devoted to this transverse branch. Two other reports simply mention its existence. According to the literature, the transverse branch of the dorsal ulnar nerve occurs in 60-80% of the cases. We found two anatomic variations different than those described in the literature. Based on our findings and data reported previously, we propose a new classification, describing two main types. In Type 1, the transverse branch arises proximally to the ulnar styloid process;type 1A and type IB are described in relation to the direction of the branch. In Type II, the branch arises distally to the ulnar styloid process;type IIA and type IIB again being described in relation to the direction of the branch. On the tangential trajectory over the radiocarpal joint, the morphometric data show a zone of risk described by a rectangle measuring 10 mm wide (6 mm distal and 4 mm proximal to the ulnar styloid process) and covering 50% of the wrist width. The relations with arthroscopic portals describe a zone of risk corresponding to a 5-7 mm radius circle centered on the portals (4-5, 6R, 6U), which includes 83% of the transverse branches.Resume Le but de ce travail etait de definir l’anatomie morphologique du rameau transverse de la branche dorsale du nerf ulnaire, et de definir ses rapports avec les voies d’abord arthroscopiques du poignet (4-5, 6R et 6U), a partir 45 dissections de pieces anatomiques. Le rameau transverse est variable dans son existence oscillant entre 80 % des cas selon la litterature et 27 % pour notre etude (12 fois sur 45). Selon notre etude, il presente un diametre moyen de 1 mm et un trajet tangentiel a l’articulation radio-carpienne. Deux fois sur 3, il parcourt moins de 50 % de la largeur du poignet. Dans 83 % des cas, il est situe a 5-6 mm en distalite du processus styloide ulnaire. Il existe ainsi une zone a risque schematisee par un rectangle de largeur de 10 mm sur 50 % de la largeur du poignet, centre sur le processus styloide ulnaire, en regard de l’interligne articulaire radio-carpien. Deux types de variations anatomiques, differentes de celles deja publiees, ont ete observees. Le rameau transverse est situe a proximite des voies d’abord arthroscopiques 4-5, 6R et 6U. Les resultats de notre etude anatomique soulignent l’existence d’une zone a risque schematisee par un cercle centre sur chaque voie d’abord, de 5 a 7 mm de rayon incluant 83 % des rameaux transverses. Afin d’eviter une complication nerveuse, il faut avoir a l’esprit l’anatomie de la branche dorsale du nerf ulnaire, l’existence de ces zones a risques et une parfaite connaissance des voies d’abord. Ce respect des structures nerveuses est d’autant plus important que cette region anatomique de la face dorsale du poignet peut etre utilisee comme lambeau pedicule pour la chirurgie reconstructrice.

Biomechanics of open Bankart and coracoid abutment procedures in a human cadaveric shoulder model.

The specific aims of this experiment were (1) to develop a clinically relevant model of anteroinferior shoulder dislocation in the apprehension position to compare the biomechanics of the intact anterior capsuloligamentous structures, and (2) to evaluate the initial strength of an open Bankart and of a coracoid abutment procedure. Fifteen shoulders from deceased donors were used. For the intact shoulders, mean peak load was 486 N, and stiffness was 26,7 N/mm. For the Bankart repair, the mean peak load was 264 N, and mean stiffness was 14.1 N/mm. Transosseous repairs failed by suture pullout through soft tissues. For the coracoid abutment repair, the mean peak load was 607 N and stiffness was 25.57 N/mm. This study reveals that the biomechanical performance of the Bankart and coracoid abutment repairs fails to reproduce the properties of the natural intact state.

New findings on intermetacarpal fat pads: anatomy and imaging

Many studies have focused on the functional importance of the gliding structures of the hand. These structures are clinically important in reconstructive surgery and mechanically essential for an efficient hand grasp. The aims of this study were to first review the intermetacarpal space and then focus on its fatty tissue, the intermetacarpal fat pad. This study used dissections and histological analysis of fetal and adult hands and CT scans of adult hands. The intermetacarpal fat pads are well-defined adipose structures located between the heads of the second, third, fourth and fifth metacarpal bones. They are located in spaces defined by the palmar fascia and its deep expansions. These spaces are closed distally but open proximally into the tunnels surrounding the flexor tendons (Legueu and Juvara canals). The pads are composed of non-mobilizable fat; they protect the neurovascular pedicles of the fingers. They may act with the palmar skin to mitigate compressive and shear forces during gripping. Finally they may be involved in neurological symptoms if their size is increased by any trauma or inflammatory process.

Towards Building a Multiscale Mechanical Model for the Prediction of Acute Subdural Hematomas

Acute subdural hematoma (ASDH) is a potentially devastating, yet curable, extra axial fluid collection within the subdural space situated between the skull and the cortex. It is often due to rupture of bridging veins crossing this subdural space, caused by the brain-skull relative motion. To be able to predict ASDH, a numerical model reflecting the mechanical properties of vascular walls is attractive. With this in mind, a suitable approach consists in modeling the material microstructure at different scales. In a former work [1, 2], R. Abdel Rahman studied the mechanical properties of the bridging veins – superior sagittal sinus junction when a human head is submitted to shock. This work showed the apparition of ASDH over a given value of head rotational acceleration. But lacks in the knowledge of microstructure and of the constituents mechanical properties were put forward in understanding the relations between material mechanical behavior and the apparition of ASDH. Therefore we chose to adopt a multiscale approach to model ASDH apparition. In the current work, several experimental observations have been set up to obtain a sufficient knowledge of the vein wall microstructure which was imprecisely documented to date. Stained thin slices of human brain were observed by optical microscopy. In addition, microtomography was used to assess the collagen fibers orientations. These observations allowed the identification of the different scales needed for modeling the microstructure. Many authors [3–6] deal with the mechanical behavior of vascular walls and of their various constituents but none of them consider multiple scales for modeling [7]. The next step of this work consists in improving the predictive capabilities of the existing model by going down the scales and taking microstructure into account. This methodology enabled the introduction of only physical parameters into the model, which is essential for future predictive capabilities. Finally, a failure criterion for the bridging veins taking into account the different scales has been created and is still being improved. It allows the evaluation of specific disease influence like collagen damage due to physiology. Besides it provides a prediction tool for ASDH useable for optimization of various shock absorbers.Copyright

The laryngeal fat body

AIM To describe the anatomy and topography of the laryngeal fat body and of the space it lies within. MATERIALS AND METHODS The study is carried out on series of histological sections of head and neck blocks from six foetuses and three newborns. Three adult necks were dissected, a fourth one analysed through sagittal median section. CT-Scan and MRI imaging complete the description. RESULTS The laryngeal fat body (LFB) lies within the pre-epiglottic (PE) space that stands in the median anterior part of the upper infrahyoid region, located just below the level of the hyoid bone. The walls of the PE space are: superior (base), anterior lateral right and left, posterior, inferior (apex). This space is divided into two compartments by a median septum. The LFB consists in a rather pure fat, structured in large polyhedral lobules. It shows no limiting capsule. DISCUSSION Dissection-based description of the PE space made in literature matches ours conducted on series of histological sections. All authors agree on the fat content of the space but some of them find a capsule around the LFB that we did not observe on our histological sections. CT-Scan and MRI imaging are accurate for analysis of these structures and of similar efficiency. The study of the LFB should be considered regarding the one of other fat bodies in the human body. CONCLUSION Anatomical knowledge of the PE space and its content, the LFB, is important, as alteration of their morphology is the early witness of neighbouring carcinological extension.

Arthroscopie complémentaire de l’ostéosynthèse du radius distal par abord antérieur

Resume A partir de 25 dissections de pieces anatomiques, nous avons analyse l’anatomie morphologique du systeme capsulo-ligamentaire de la face anterieure du poignet et mis en place deux nouvelles voies d’abord arthroscopiques radio-carpienne et radio-ulnaire. Les ligaments intrinseques et extrinseques du poignet ont ete reperes, et les soft-points ont ete repertories. Deux points d’introduction potentiellement utilisable en cas d’abord de la face anterieure du radius selon la voie de Henry ont ete systematiquement trouves : entre le ligament radio-lunaire et le ligament radio-scapho-capitatum sur le versant radial et entre le ligament radio-lunaire et le ligament ulno-lunaire. L’exploration arthroscopique a permis d’observer les ligaments scapho-lunaire, luno-triquetral, le complexe triangulaire, et l’ensemble de la surface articulaire radiale inferieure. A notre connaissance, aucune voie d’abord anterieure radiale n’a ete decrite pour l’arthroscopie. Cette voie d’abord nous semble interessante dans le cadre des fractures articulaires du radius distal necessitant une osteosynthese anterieure.PURPOSE OF THE STUDY Morphological and morphometric studies of the wrist ligaments are scarce. The radiocapitatum and scapholunate ligaments play a pivotal role in wrist stability. Classically, a posterior approach is used for arthroscopic procedures, but an anterior approach should be possible. We conducted a cadaver study to search for new anterior portals for wrist arthroscopy. MATERIAL AND METHODS Twenty-five formol-treated upper limbs were dissected. The classical anterior approach for open wrist surgery was executed. The different elements of the capsule-ligament system of the anterior aspect of the wrist were identified and labeled. The dissection was then extended to the ulna in search of soft points which were identified and evaluated. The different structures generally identified during wrist arthroscopy were noted. RESULTS Two potential portals were identified in all wrists: one between the radiolunate ligament and the radio-scapho-capitatum ligament on the radial aspect and one between the radio-lunate ligament and the ulno-lunate ligament. Arthroscopic exploration enabled observation of the scapho-lunate ligament, the luno-triquetral ligament, the triangular complex of the carpus, and the entire inferior aspect of the radial joint surface, with no risk of vessel or nerve injury because of the exposure allowed by the osteosynthesis approach. DISCUSSION Wrist arthroscopy is now accepted as a reliable technique not only for diagnostic purposes but also for therapeutic interventions for the treatment of fractures of the lower radius. Most of the arthroscopic portals described in the literature are posterior. The anterior portals described here do not involve any vascular or neurological risk since the radial approach is made under visual control by extension of the open anterior approach and on the ulnar side the noble structures are positioned medially to the ulnar flexor tendon of the carpus. This enables good triangulation necessary for the usual arthroscopic procedures. Finally, these portals have no supplementary morbidity which would be the case with percutaneous portals (injury to the medial nerve, the radial vasculonervous bundle, the radial flexor tendon). CONCLUSION These new arthroscopic portals are complementary to the anterior approach for open wrist surgery and enable a natural extension of joint exploration via both the radial and ulnar approaches described in this study.

MémoireArthroscopie complémentaire de l’ostéosynthèse du radius distal par abord antérieur: Bases anatomiques de nouvelles voies arthroscopiques antérieuresProposal for new anterior portals for wrist arthroscopic as a complementary approach to open anterior wrist surgery

Resume A partir de 25 dissections de pieces anatomiques, nous avons analyse l’anatomie morphologique du systeme capsulo-ligamentaire de la face anterieure du poignet et mis en place deux nouvelles voies d’abord arthroscopiques radio-carpienne et radio-ulnaire. Les ligaments intrinseques et extrinseques du poignet ont ete reperes, et les soft-points ont ete repertories. Deux points d’introduction potentiellement utilisable en cas d’abord de la face anterieure du radius selon la voie de Henry ont ete systematiquement trouves : entre le ligament radio-lunaire et le ligament radio-scapho-capitatum sur le versant radial et entre le ligament radio-lunaire et le ligament ulno-lunaire. L’exploration arthroscopique a permis d’observer les ligaments scapho-lunaire, luno-triquetral, le complexe triangulaire, et l’ensemble de la surface articulaire radiale inferieure. A notre connaissance, aucune voie d’abord anterieure radiale n’a ete decrite pour l’arthroscopie. Cette voie d’abord nous semble interessante dans le cadre des fractures articulaires du radius distal necessitant une osteosynthese anterieure.PURPOSE OF THE STUDY Morphological and morphometric studies of the wrist ligaments are scarce. The radiocapitatum and scapholunate ligaments play a pivotal role in wrist stability. Classically, a posterior approach is used for arthroscopic procedures, but an anterior approach should be possible. We conducted a cadaver study to search for new anterior portals for wrist arthroscopy. MATERIAL AND METHODS Twenty-five formol-treated upper limbs were dissected. The classical anterior approach for open wrist surgery was executed. The different elements of the capsule-ligament system of the anterior aspect of the wrist were identified and labeled. The dissection was then extended to the ulna in search of soft points which were identified and evaluated. The different structures generally identified during wrist arthroscopy were noted. RESULTS Two potential portals were identified in all wrists: one between the radiolunate ligament and the radio-scapho-capitatum ligament on the radial aspect and one between the radio-lunate ligament and the ulno-lunate ligament. Arthroscopic exploration enabled observation of the scapho-lunate ligament, the luno-triquetral ligament, the triangular complex of the carpus, and the entire inferior aspect of the radial joint surface, with no risk of vessel or nerve injury because of the exposure allowed by the osteosynthesis approach. DISCUSSION Wrist arthroscopy is now accepted as a reliable technique not only for diagnostic purposes but also for therapeutic interventions for the treatment of fractures of the lower radius. Most of the arthroscopic portals described in the literature are posterior. The anterior portals described here do not involve any vascular or neurological risk since the radial approach is made under visual control by extension of the open anterior approach and on the ulnar side the noble structures are positioned medially to the ulnar flexor tendon of the carpus. This enables good triangulation necessary for the usual arthroscopic procedures. Finally, these portals have no supplementary morbidity which would be the case with percutaneous portals (injury to the medial nerve, the radial vasculonervous bundle, the radial flexor tendon). CONCLUSION These new arthroscopic portals are complementary to the anterior approach for open wrist surgery and enable a natural extension of joint exploration via both the radial and ulnar approaches described in this study.