Folia Morphol. Vol. 70, No. 2, pp. 61–67 Copyright © 2011 Via Medica R E V I E W A R T I C L E ISSN 0015–5659 www.fm.viamedica.pl

Human classification: a new proposal

G.K. Paraskevas

Department of Anatomy, Medical School, Aristotle University of Thessaloniki, Greece

[Received 24 January 2011; Accepted 22 March 2011]

A high concern exists among physicians about surgically important ligaments such as cruciate and collateral ligaments of the , patellar , tibiofibular syndesmosis, collateral ligaments of the , and coracoclavicular ligament. However, the classification of the ligaments is insufficient in the literature, due to their origin from . A new classification is proposed, based on various parameters such as the macroscopic and microscopic features, the function and the nature of their attachment areas. (Folia Morphol 2011; 70, 2: 61–67)

Key words: ligaments, classification, Nomina Anatomica

INTRODUCTION connective tissue surrounding neurovascular bundles There was always some confusion concerning the or ducts as “true ligaments” [4]. classification of ligaments of the human body, presu- The “false ligaments”, could be subdivided in the mably due to their origin from the connective tissue following categories: that is considered a low quality tissue compared to oth- a) Splachnic ligaments, which are further subdivid- ers. Moreover, orthopaedists are focused only on surgi- ed into “peritoneal” (e.g. phrenocolic ligament), cally important ligaments. For these reasons there is an “pericardiac” (e.g. sternopericardial ligaments), absence of a well-designated classification system that “pleural” (e.g. suprapleural membrane), and subdivides the ligaments into subgroups according to “pure splachnic ligaments” (e.g. hyoglossus various parameters such as their relation to the membrane and phrenoesophageal ligament). capsule, their morphology, histological structure, and b) Neuronic ligaments that interconnect either sym- the nature of the original anatomical structure. metrical areas of the two halves of the central nervous system and consist of nerve fibres and DISCUSSION bodies of neurons (e.g. corpus callosum, fornix, In gross anatomy a ligament is considered an ana- anterior and posterior cerebral commissure, and tomical structure interconnecting two anatomical ele- white and grey commissure of spinal cord), which ments. We believe that the ligaments should be sub- represent thickenings of the dura mater of the divided into true and false ligaments. True ligaments spinal cord contributing to its support (e.g. den- should be defined as those which are found in the tate and coccygeal ligament). structures of the musculoskeletal system and they c) Cutaneous ligaments that are skin folds (e.g. an- should be named “motor or articular ligaments”, while terior and posterior commissure of large labia of false ligaments should be defined as those found apart the pudendum). from the musculoskeletal system. Pansky named the d) Arterial ligaments that form after transformation peritoneal folds “false ligaments” [8], while Healey et of embryonic vessels into connective tissue (e.g. al. depicted the peritoneal reflections as “false liga- ligament of Botallo, lateral umbilical ligaments, ments” and certain thickenings of the subperitoneal teres ligament of the liver).

Address for correspondence: Dr. G.K. Paraskevas, MD, PhD, Assist. Professor of Anatomy, Department of Anatomy, Medical School of Aristotle University of Thessaloniki, P.O. Box: 300, Postal Code: 54124, Thessaloniki, Greece, tel: +302310 999330, e-mail: [email protected]

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Ligaments passing over or located adja- 2) Intracapsular ligaments. In our opinion, these cent to them are called “motor or articular liga- ligaments are divided into the following sub- ments”. It is difficult to determine the total num- categories: ber of “motor ligaments”, because of the incon- a) Intracapsular extra-articular ligaments. These li- stant existence of most of them (e.g. the intra-ar- gaments line the inner surface of the fibrous cap- ticular sternocostal ligaments are usually located sule without extending into the articular space. at the second sternocostal joint, the costotransverse This group includes the three glenohumeral li- ligaments of the eleventh and twelfth are ru- gaments (superior, middle, inferior), which be- dimentary, while the oblique chord may be dupli- come most prominent when viewed from inside. cated or even absent). Furthermore, there are nu- b) Intracapsular intra-articular ligaments. These li- merous bundles of connective tissue (ligaments) not gaments are located within the articular cavity listed in Nomina Anatomica [19]. We consider that and are classified as follows: i) Totally intra-ar- it is more convenient to record the total number of ticular ligaments, totally surrounded by the ar- motor ligaments which are found in Nomina Ana- ticular . This group includes tomica, and their number was estimated at approxi- the round ligament of the , the mately 745. intra-articular ligaments of the head of the ribs, In classic anatomical textbooks, the “motor liga- and the intra-articular sternocostal ligaments. ments“ are classified as: ii) Partial intra-articular ligaments, surrounded A) Accessory ligaments. These ligaments are local partially by articular synovial membrane, such thickenings of the fibrous capsule and contri- as the cruciate ligaments. bute to the articular surface restraining. These li- B) Interosseous ligaments. These are short and gaments are flexible enough to allow normal joint strong ligaments, covering the narrow spaces movement. Simultaneously, these ligaments are formed between the opposite surfaces of adjacent inflexible and they can be ruptured in extreme bones, thus greatly reducing their mobility. These distension. In our opinion, the “accessory liga- ligaments are located in synovial joints ( and ments” may be further subdivided into extracap- tarsal joints), synarthroses (inferior tibiofibular syn- sular and intracapsular. desmosis, interosseal membranes of the 1) Extracapsular ligaments. There are two groups: and tibia), and amphiarthroses (). a) Periarticular or distal extracapsular ligaments. C) Independent ligaments. These ligaments, may These ligaments are cylindrical or strip-like be subdivided into the following two categories: thickenings of the fibrous capsule that in 1) Motor ligaments not participating in joint some way have been detached from the cap- function. These ligaments belong mainly to sule, migrating into adjacent areas (e.g. co- the periarticular ligaments (e.g. lumbocostal racohumeral ligament). ligaments), the interosseous ligaments (e.g. b) Proximal extracapsular ligaments. These li- interspinal ligaments), and the syndesmoses gaments are usually band-like thicknesses of (e.g. interosseous membrane of forearm). The the fibrous capsule, which are distinct from most prominent feature of these ligaments the fibrous capsule and are attached in close is that they do not participate, or participate proximity to sites of capsule attachment (e.g. to a lesser extent, in the movements of the medial collateral ligament of the knee). Ro- neighbouring joint. The term “independent gers subdivided the extracapsular ligaments ligament” is used with respect to the joint into extrinsic ligaments that are not in con- capsule, not the joint function [3, 11]. tact with the and intrinsic liga- 2) Ligaments forming fibro-osseal foramina or ments that are in contact with the capsule obstructing foramina. These ligaments are and are capsular thickenings [11]. In the 7th subdivided into two categories: edition of Nomina Anatomica the ligaments a) Proper ligaments that connect two different are classified as: “Extracapsular ligaments” areas of the same bone (usually bridge bony which are far apart from the capsule, “cap- notches). This category includes the thyroid sular ligaments” that are thickenings of the membrane, the inguinal ligament, the ilio- fibrous capsule, and “intracapsular liga- pectineal ligament, the superior and inferior ments” that are found interior to the joint transverse ligaments of the scapula, the trans- capsule [19]. verse ligament of the , the trans-

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verse humeral ligament, the transverse liga- The distinction between ment of the , and the pterygospinous liga- ligaments and membranes ment. It is possible for a “proper ligament” There is a great deal of confusion in anatomical to participate in the formation and function literature regarding the determination of an ana- of a , like the transverse ligament tomical structure either as a ligament or as a mem- of the atlas and the acetabulum. brane. The following report of the famous Cana- b) Ligaments interconnecting two or more bones. dian anatomist J. Grant is characteristic “…this struc- These ligaments are extended between two ture is a membrane, called cricothyroid ligament” or more bones, bridging various bony notch- [1]. Searching for the “motor membranes”, refer- es, thus transforming them into foramina or ring to the last edition of Nomina Anatomica [19], canals containing vessels and nerves. Exam- we estimated there to be 34 in number. The follow- ples of this category include the transverse liga- ing criteria have been established in the present work ment of the wrist joint, the ischiospinal and in order to classify a “ligamentous structure” as ischiotuberal ligaments, the posterior atlanto- a membrane: 1) A thin and broad lamina of connec- occipital membrane, and the transverse tive tissue. 2) Covering the interossei spaces, in which perineal ligament. one dimension is longer than the other. 3) Obstruc- tion of a circular or oval foramen by a lamina of Classification of the motor ligaments connective tissue. 4) Exclusion of the various above- according to their morphology mentioned “morphological” types of ligaments with According to their shape the “motor ligaments” the exception of oval and a few quadrangular liga- are classified as follows: ments. At this point it is worthwhile reporting that a) Band-like ligaments: Most “motor ligaments” both the flava ligaments and the nuchal ligaments belong here (e.g. lateral collateral ligament of are membranes and not ligaments. the knee joint). b) Cylindrical ligaments (e.g. teres ligament of the Functions of ligaments femoral head). Despite the great interest of anatomists and sur- c) Quadrangular ligaments: These ligaments may geons regarding ligament functions, limited atten- be confused with the band-like ligaments; in tion has been paid in classical anatomical textbooks band-like ligaments one dimension is larger than regarding this issue. The chapters concerning such the other (e.g. sternoclavicular ligaments). an issue are, according to our considerations, inade- d) Triangular ligaments (e.g. of the quately organised and designated [1, 3, 6, 7, 12, 20]. ankle joint). Here we attempt to provide a more organised e) Trapezoid ligaments (e.g. trapezoid ligament of classification of the ligament functions. the acromioclavicular joint). a) Joint capsule reinforcement, resulting in great- f) Rhomboid ligaments (e.g. costoclavicular ligament). er stability of articular surfaces. This function g) Conoid ligaments (e.g. conoid ligament of the is mostly performed by “accessory ligaments”. acromioclavicular joint). The following ligaments beyond their “rein- h) Radiate ligaments (e.g. radiate sternocostal liga- forcement action” appear to have purely “sup- ments). portive action” as well: the annular ligament i) Bifurcated ligaments, are bifurcated to small liga- of the radius, the intra-articular ligaments of mentous bands (e.g. lateral collateral ligament the heads of the ribs, the intra-articular ster- of the joint). nocostal ligaments, the teres ligament of the j) Annular ligaments, which are circular (e.g. an- femoral head, the cruciate ligaments, Lisfranc’s nular ligament of the radius). ligament, and the interosseal membranes of k) Cruciate ligaments, that correspond to ligaments the forearm and tibia. from which perpendicular fibrous bands arise b) Reduction of the extreme mobility of articulat- forming a cross-like shape (e.g. cruciate ligament ing bones in synovial joints (e.g. the anterior cru- of the atlas). ciate ligament prevents the extreme anterior dis- l) Ellipsoid or circular ligaments are usually mem- placement of the tibia in the knee joint). branes which obliterate foramina (e.g. thyroid c) Maintenance of the track of movement in synovial membrane). joints (e.g. the collateral ligaments in the elbow joint m) Arcuate ligaments (e.g. arcuate popliteal ligament). and in the phalangophalangeal joints restrain the

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movement occurring around the joints securing the rior atlanto-occipital membrane that forms (with the movement around the transverse of the joint). groove for the vertebral artery) a foramen for the d) Saving of muscular energy (e.g. the anterior liga- passage of that artery. ments of the joint, which stretch passively k) Carrier of a nutrient artery for an articulated bone during extension, maintaining the body such as the teres ligament of the femoral head weight, thus reducing the expended energy of (that contains the acetabular artery for the vas- the corresponding muscles). This group includes cular supply of the femoral head) and the the and the flavae ligaments, scapholunate ligaments (that contain arteries for which save “muscular energy” due to their elas- the vascular supply of the lunate). tic fibres. These ligaments reveal their “muscular l) Diffusion of the articular fluid in articular surfa- energy” during extension. ces, as happens with the intra-articular ligaments e) Attachment area for the muscles. Typical exam- and especially with the teres ligament of the fe- ples are the nuchal ligament, the interossei mem- moral head [14]. branes of the forearm and the tibia, and the sty- lohyoid ligament [6]. Classification based on ligament histological structure f) Transmission of muscular energy an example be- ing the case of the interosseous membrane of a) Collagen fibres. The majority of ligaments and es- the forearm and the thyrohyoid membrane [16]. pecially those of the musculoskeletal system con- g) Harmonisation and control of mobility of the con- sist of dense fibrous connective tissue. This fact nected anatomical structures, as happens in the case makes these ligaments soft, inelastic and flexible. of the transverse ligament of the knee joint, the deep Only if they are subject to continuous tension may portion of the medial collateral ligament of the knee the collagen fibres be lengthened. Their direction, joint, the anterior and posterior meniscofemoral liga- however, in the joint fibrous capsule and capsular ments, and the interclavicular ligament. ligaments is such that inhibition of collagen fibre h) Protection of the adjacent structures, as occurs distension is possible. Exceptions are the sacroiliac in the case of the intervertebral discs which are ligaments and the intervertebral discs that lie un- protected by the posterior longitudinal ligament, der continuous bodyweight tension. the radiate ligament, and the intra-articular liga- b) Collagen and elastic fibres. In this group of liga- ment of the head of the . Similarly, the spi- ments the elastic fibres dominate providing the nal cord is protected (from the dens of axis in ligaments with an ability of elastic restoration case of fracture) by the cruciate ligament, while to the initial length after distension. These liga- the flexor tendons are protected (reduce of fric- ments are yellowish, a fact that explains the tion) from the underneath located palmar liga- term “” which are located be- ments of the metacarpophalangeal and phalan- tween the vertebral arches. Other examples of gophalangeal joints [3]. Finally, the subclavian “elastic ligaments“ belonging to the group of vessels and the brachial plexus are protected from “splachnic ligaments” are the following: the cri- the stronger (compared to the anterior) poste- cothyroid ligament or elastic cone, the poste- rior sternoclavicular ligament, and the is rior cricoarytenoid ligament, the ligaments of protected from the stronger (compared to the tympanic ossicles [6], and the thyroepiglottic anterior) posterior sternal membrane [12]. and the hyoepiglottic ligament [20]. i) Support of tendons track, as happens in the case c) Collagen and smooth muscular fibres. This group of the retinacular ligaments of the wrist and ankle of ligaments includes mainly the “splachnic liga- joints, the transverse humeral ligament, the deep ments”, such as the teres ligament of the uterus transverse metacarpal ligaments, and the short and that contains smooth muscular fibres derived from long vincula of the flexor tendons of digits. the outer and middle layers of the muscular coat of j) Formation of foramina, canals, or spaces for the the uterus, the proper ligament of the ovary, and passage of vessels and/or nerves. That is achieved the cremaster ligament-muscle of the duodenum. not only with the presence of the “proper ligaments” d) Collagen and striated muscular fibres. These liga- but with the presence of other “accessory ligaments” ments are also splachnic ligaments. Basic repre- as well, such as the sphenomandibular ligament that sentatives of the category include the median cre- creates (with the mandibular condyle) a space for master ligament of the pharynx and the cremas- the passage of the maxillary artery and the poste- ter ligament of the duodenum.

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e) Fatty tissue. This group includes ligaments that g) Interclavicular ligament. This ligament is consi- contain either lobuli of fatty tissue or organised dered to be a homologous structure with the fatty masses as fat pads. The first sub-group in- wish-bones of birds [1]. cludes the interosseous sacroiliac ligament, while Classification according to original the second sub-group the fat pad of the larynx. anatomical structure f) Bursa elements. This category, also, includes the “splachnic ligaments”, such as the thyrohyoid a) Capsular ligaments. This category includes the membrane in which the infrahyoid bursa is en- majority of the ligaments of the musculoskeletal closed. However, a “motor ligament”, the costo- system. These ligaments are thickenings of the clavicular ligament, also belongs to that catego- fibrous capsule making it strong enough to bet- ry. An interposing bursa is presented between ter stabilise the articular surfaces. These liga- the two component layers of that ligament [2]. ments, which are inelastic and inflexible and can g) Collagen fibres and cartilaginous elements. This rupture easily on great distension, are called “ac- cessory ligaments” [7]. group includes all ligaments consisting of col- b) Bursal ligaments. Some retinacular ligaments, lagen fibres and cartilaginous elements, which such as the dorsal ligament of the wrist joint and form an articular cartilage in contact with a bony the laciniate ligament, are expansions of the un- surface. Examples are the transverse ligament of derlying fibrous tendon sheath [15]. the atlas, the annular ligament of the radius, the c) Tendinous ligaments. Some ligaments are formed plantar calcaneonavicular ligament, the interossei by the tendinous fibre expansions of adjacent ligaments of the upper row of carpal bones, and muscles. Basic representatives of that group are the annular ligament of the stapedius. the following ligaments: 1) Patellar ligament. This Classification concerning origins ligament is an expansion of the tendon of the from remnant or atrophic organs quadriceps femoris muscle. 2) Retinacular liga- ments of the patella. Similarly, these bearing liga- a) Apical or cremaster ligament of the atlas. This ments of the patella are formed by expansions ligament, which arises from the tip of the axis of the quadriceps tendon. 3) Transverse hume- dens and is inserted into the middle third of the ral ligament. This ligament, which transforms the anterior border of magnum foramen, is either bicipital groove into a fibrosseous canal, is a remnant of an or a remnant formed by the convergence and fusion of the of a whole called the pre-axis. This is tendinous fibres of the subscapular muscle or, supported by the fact that this ligament is in the rare cases in which this muscle is absent, crossed by notochords and in its middle portion the transverse humeral ligament is constituted cartilaginous elements are found. These elements from the tendinous fibres of the latissimus dorsi are thought to be an intervertebral disc remnant. and major pectoral muscle [14]. It has been sug- b) External internal intercostal membranes. These gested that the transverse humeral ligament con- membranes represent the anterior edge of the stitutes a capsular thickness [6]. 4) Coracohumer- external intercostal muscles and the posterior al ligament. This is thought to be an expansion edge of the internal intercostal muscles, corre- of the tendon of the minor pectoral muscle [14]. spondingly, that have become atrophic. d) Periosteal ligaments. These ligaments are thick- c) Preurethral ligament. This ligament is considered enings of the periosteum. Typical examples of to be a remnant of the ischiopubic muscle. such ligaments are the anterior and posterior d) Ligament of the coccyx. This ligament is consi- pubic ligament formed by the periosteum of the dered to be a remnant anatomical structure from pubic bones, and the lacunar ligament, which is the phylogenetic development [5]. a thickening of the pectineal periosteum [10]. e) Ligamentum teres of the femoral head. This is e) Fascial ligaments. These ligaments are thicken- considered either to be a remnant of the pubo- ings of the fascia, as occurs in the case of the femoral muscle, which in reptiles is located out- oblique chord that is thought to be a thickening side the joint cavity [15], or a remnant of the of the supinator fascia [1]. Similarly, the retina- pectineus muscle [13]. cular ligaments of the wrist and ankle joint are f) Intertransverse ligaments. These ligaments are thickenings of the fascia of the forearm and ti- considered as atrophic portions of the intertrans- bia or parts of the intermuscular septa, as oc- verse muscles [9]. curs in the case of the nuchal ligament.

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Classification based on the number of joints d) Bone–skin. These ligaments are the homologues which a ligament passes through of the mimic muscles. This group includes the a) Ligaments passing over one joint. The majority anococcygeal ligament (tip of coccyx-skin of of the “motor ligaments” belong to this group. anus), the coccygeal ligament (tip of coccyx-skin b) Ligaments passing over two joints. This group of coccygeal fovea), and the cutaneous ligaments includes the following 15 ligaments: the lateral of the digits of Cleland (lateral sides of phalanx- collateral ligament of the knee joint (knee and skin over the phalangophalangeal joint) [18]. proximal tibiofibular joint), the calcaneotibial liga- e) Cartilage–cartilage. This group includes the in- ment (ankle and ), the calcaneofi- tercartilaginous ligaments (-cos- bular ligament (ankle and subtalar joint), the pal- tal cartilage), the transverse ligament of the ace- mar and dorsal radiocarpal ligament (wrist and tabulum (bridges the edges of the acetabular la- ), the palmar ulnocarpal ligament brum), and the transverse ligament of the knee (wrist and midcarpal joint), the interclavicular liga- joint (interconnecting the anterior edges of the ment (both the sternoclavicular joints), the late- lateral and medial ). ral collateral ligament of the elbow joint (hu- f) Ligament–ligament. This group includes the re- meroradial and proximal radioulnar joint), the flected ligament (extending between inguinal liga- apical ligament of the atlas (atlantoccipital and ment–linea alba), the superficial transverse atlantoaxial joint), the alar ligaments (atlanto- metacarpal (or metatarsal) ligaments (intercon- occipital and atlantoaxial joint), the cruciate liga- nect the longitudinal fascicles of the palmar or ment of the atlas (atlanto-occipital and atlanto- plantar aponeurosis), and the orbicular zone (at- axial joint), the tectorial membrane (atlanto-oc- tached to the fibrous capsule of the hip joint). cipital and atlantoaxial joint), the iliolumbar Classification based on various parameters ligament (lumbosacral and sacroiliac joint), the a) Simple or double ligaments. The majority of “mo- lumbocostal ligament (intervertebral and costo- tor ligaments” are double ligaments. The single li- vertebral joint), and the arcuate popliteal liga- gaments found in the last edition of Nomina Ana- ment (knee and proximal tibiofibular joint). tomica [19] are the following (33 in number): an- c) Ligaments passing over more than two joints. In terior and posterior atlanto-occipital membrane, this group four ligaments can be distinguished: anterior atlanto-occipital ligament, supraspinal li- the anterior longitudinal ligament (intervertebral gament, nuchal ligament, anterior and posterior lon- joints), the posterior longitudinal ligament (in- tervertebral joints), the supraspinal ligament (in- gitudinal ligament, anterior sacrococcygeal liga- terspinal syndesmoses), and the nuchal ligament ment, superficial and deep posterior sacrococcygeal (flava syndresmoses). ligament, cruciate ligament of the atlas, apical li- gament of the atlas, tectorial membrane, interspi- Classification according to the histological nal ligaments (16 in number), anterior and poste- structure of the attachment areas rior sternal membrane, interclavicular ligament, and of the ligaments the superior and inferior pubic ligaments. a) Bone–bone. This group includes the majority of b) Ligaments “acting” on vessels and nerves. Such “motor ligaments” (e.g. iliofemoral ligament). an action occurs in pathologic conditions in b) Bone–ligament. This group includes the iliopectineal which ligaments are thickened, compressing the ligament (extending between the iliopubic tubero- underlying vessel or nerve. This group includes sity and the inguinal ligament) and the lacunar liga- the superior and inferior ligament of the scapu- ment (extending between the superior ramus of the la, the transverse ligament of the wrist, and the pubic bone and the inguinal ligament). paraterminal ligaments that bridge the edges of c) Bone–cartilage. This group includes the anterior the distal phalanx permitting the passage of the and posterior radiate sternocostal ligaments (ster- proper palmar digital arteries and nerves [17]. num-costal cartilage), the intra-articular sterno- This group also includes the venosus ligament costal ligaments (–ostal cartilage), the cos- of the liver, which maintains the inferior vena toclavicular ligament (–costal cartilage), the cava within a groove of the posterior surface of glenohumeral ligaments (humeral tubercles–gle- the liver and ligament of Hey (superior margin noid labrum), and the meniscofemoral ligaments of the oval fossa), and the ligament of Burns (in- (intercondylar notch–). ferior margin of the oval fossa) that protect the

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great saphenous vein from occlusion during flex- ples of this group are the costoxiphoid ligament ion of the thigh [4]. belonging to the radiate sternocostal ligament c) Ligaments and membranes perforated by vessels group, the posterior atlanto-occipital membrane and nerves. The interclavicular ligament, the sa- belonging to the flava ligament group, and the crotuberal ligament, the interosseous membrane lumbocostal ligament belonging to the anterior of the forearm and tibia, and the thyrohyoid costotransversal ligament group. membrane are classified in this group. k) Ligaments consisting of distinct bands. This group d) Ligaments altering their morphology with respect includes a great number of “motor ligaments” to age. There is probably only one ligament in such as the arcuate ligament of the wrist, the this group: the annular ligament of the radius. medial collateral ligament of the elbow, the co- This ligament, before the age of seven years old, racoclavicular ligament, and the lateral collate- has a cylindrical shape, but after this age forms ral ligament of the ankle, which are composed the shape of a frustrum with the larger basis di- of uni-layer bands of different directions. rected superiorly, which explains the higher inci- dence of proximal radioulnar joint dislocation in REFERENCES children [1]. 1. Basmajian JV (1975) Grant’s method of anatomy. th e) Ligaments affected by hormonal factors. A typi- 9 Ed. Williams & Wilkins Co, Baltimore. 2. Cave AJE (1961) The nature and morphology of the cal example is the influence of oestrogens on the costoclavicular ligament. J Anat, 95: 170–179. ligaments of the genital system of females and 3. Ellis H (1992) Clinical anatomy. A revision and applied in the “motor ligaments” of the female pelvis anatomy for clinical students. 8th Ed. Blackwell Scien- (pubic and sacrococcygeal ligaments). tific Publications, Oxford. f) Ligaments changing their strength with respect 4. Healey J, Hodge J (1990) Surgical anatomy, 2nd Ed. B.C. to sex. It is worth mentioning that the sacroiliac Decker Inc, Toronto. 5. Lippert H (1993) Anatomie, text und atlas. Auflage 6. and sacrococcygeal ligaments are more power- Urban & Schwarzenberg, Munchen. ful in males than females [6]. 6. McMinn R (1990) Last’s anatomy. 8th Ed. Churchill g) Ligaments constituting thickenings of other liga- Livingstone, New York. ments. Regarding the “motor ligaments”, the 7. Moore K (1992) Clinical oriented anatomy. 3rd Ed. anterior atlanto-occipital ligament being a thick- Williams & Wilkins, New York. th ening of the anterior atlanto-occipital membrane. 8. Pansky B (1992) Review of gross anatomy. 5 Ed. Mc Graw-Hill, New York. The majority of these ligaments belong to the 9. Paturet G (1961) Traite d’Anatomie humaine anatomie. group of “splachnic ligaments”. A typical exam- Vol. 1. Masson et cie editeurs, Paris. ple is the median cricothyroid ligament, which is 10. Platzer W (1984) Taschenatlas der Anatomie. Band 1. a thickening of the elastic cone and the thyro- Thieme Verlag, Struttgart. hyoid ligaments (median and lateral) that are 11. Rogers AW (1992) Textbook of anatomy. 5th Ed. thyrohyoid membrane densations. Churchill Livingstone, New York. 12. Romanes G (1991) Cunningham’s textbook of anato- h) Ligaments constituting expansions of other liga- my. 12th Ed. Oxford University Press, London. ments. Typical examples of this group are the nuchal 13. Savas A (1961) Human Anatomy, locomotor system. ligament, which is an expansion of the supraspinal Vol. 2. Kyriakides, Thessaloniki. ligament, and the tectorial membrane, which is an 14. Simkins C (1949) Functional human anatomy. W.C. expansion of the posterior longitudinal ligament. Brown Co, Iowa. i) Ligaments with multiple layers. The anterior and 15. Sklavounos G (1926) Human anatomy. Vol. 1. Tarouso- poulos, Athens. posterior longitudinal ligaments that consist of 16. Snell R (1981) Clinical anatomy, 2nd Ed. Brown & Co, a superficial and a deep layer, the medial col- Boston. lateral ligament of the knee and ankle joint con- 17. Soon P, Arnold M, Tracey D (1991) Paraterminal liga- sisting of a superficial and a deep layer, and ments of the distal phalanx. Acta Anat, 142: 339–346. the costoclavicular or rhomboid ligament con- 18. Stack HG (1973) The palmar fascia. Churchill Living- sisting of two cruciate bands; the anterior and stone, Edinburgh. 19. Terminologia Anatomia (1998) International anatomi- posterior band, belong to this group. cal terminology. 7th Ed. Thieme, Stuttgart. j) Ligaments belonging to the same ligamentous 20. Williams P, Warwick R, Dyson M, Bannister L (1989) Gray’s category but having a different term. Typical exam- anatomy. 37th Ed. Churchill Livingstone, Edinburgh.

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