A novel accessory muscle in the flexor compartment of anterior forearm inserting into the tenosynovium of the flexor pollicis longus.

A common variant of accessory muscles in the anterior forearm is the Gantzer's muscle (GM). GM arises as a muscle belly from flexor digitorum superficialis (FDS) or ulnar coronoid process to merge distally with the flexor pollicis longus (FPL) muscle. In the present case report, we describe a novel accessory muscle in the flexor compartment of the forearm. The proximal attachment was tendinous and came from three sources: FDS muscle, ulnar coronoid process, and the medial aspect of the proximal radius. The distal tendon of the novel accessory muscle ran parallel to FPL, passed through the carpal tunnel, and entered the palmar aspect of the hand. In the hand, the tendon thinned out and blended with the tenosynovium of the FPL, contributing to the sheath around the FPL tendon. This accessory muscle of the FPL is comparable to the frequently documented GM; however, the present case exhibited fundamental nuances that distinguish it from the previously described iterations of the GM in the following ways: 1) The novel accessory muscle is tendinous from its proximal origin and throughout the upper one-third of the forearm, and one component of its origin arose from the medial aspect of the radius. GMs with an origin on the radius have not been previously reported. 2) In the middle one-third, the tendinous proximal attachment transitioned to a muscle belly that passed through the carpal tunnel and entered the hand. 3) In the hand, the novel tendon widened, thinned, and merged with the tenosynovium of the FPL. Accessory muscles are a common finding in the anterior forearm during cadaveric dissection. In patients, they can be the cause of neuropathies due to compression of the anterior interosseous nerve. Awareness of variations is also important for clinicians who examine the forearm and hand, as well as hand surgeons.

Pointing in a different direction: a case of bilateral absence of extensor indicis.

Understanding anatomical variations as well as normal anatomy of the muscles and tendons of the hand is vital for successful clinical evaluation and surgery. A number of extensor muscle and tendon variations have been reported in the literature, including duplication, triplication, and absence. We report a rare anatomical variation that includes bilateral absence of the extensor indicis (EI) muscles and bilateral duplication of the extensor digitorum (ED) tendon to the second digit in the forearm of an 83-year-old male cadaver during routine upper limbs dissection. In the present case, only three muscles were present in the deep compartment: extensor pollicis longus (EPL), extensor pollicis brevis (EPB), and abductor pollicis longus (APL) with bilateral absence of EI. The reported prevalence of bilateral absence of EI muscle and tendon ranges from 0.5% to 3.5%. The prevalence of an additional index tendon arising bilaterally from the ED muscle belly is 3.2% of the population. Extension of the index finger is governed by the actions of EI and ED. However, the four tendons of ED are linked to each other by juncturae tendinum, restricting independent extension of the digits in certain postures, e.g. when the hand is fisted. With fisted hand, EI controls extension of the index finger. Clinically, EI tendons are used for tendon reconstruction procedures to restore function to the hand and thumb after trauma or tendon rupture. This report highlights the importance of anticipating anatomical variations and conducting pre-operative evaluations to confirm the presence of EI when planning tendon transfer procedures.

Novel, bilateral, two-bellied muscles span the extensor forearm, thenar eminence to insert on the proximal phalanx of the thumb: clinical and embryological significance.

Muscle and tendon variations in the forearm, wrist and hand are commonly reported in the anatomical and surgical literature. They are frequently the source of inflammatory conditions such as de Quervain's tenosynovitis or carpal tunnel syndrome. During academic dissection, a cadaver presented with bilateral, additional muscles running parallel to the abductor pollicis longus muscles (APL) in the extensor compartment of the forearm. Both additional muscles had two bellies, one proximal and one distal, with an intervening tendon. The proximal bellies were separate and distinct from the adjacent APLs. The tendons traversed the first dorsal compartments with the tendons of the APLs and the extensor pollicis brevis muscles (EPB). The distal bellies lay adjacent to the abductor pollicis brevis (APB) muscles in the thenar compartments, and inserted onto the volar base of the proximal phalanges of the thumbs. Following a thorough search of the literature, we determined that these additional muscles constitute a previously unreported variation. This report details the variation, compares it with other reported variations, presents the related embryology, and reviews the significance of this variation as it relates to inflammatory conditions and surgical procedures.

Bilateral duplicated internal jugular veins: case study and literature review.

A rare bilateral duplication of the internal jugular vein (IJV) was discovered during cadaveric dissection. From each jugular foramen, a single IJV descended to the level of the hyoid bone then divided into medial and lateral veins. The medial IJVs traveled in the carotid sheath; the lateral IJVs coursed posterolateral to the sheath across the lateral cervical region (posterior triangle) of the neck. On the right side, medial and lateral IJVs entered the subclavian vein separately. C2-C3 anterior rami and the suprascapular artery passed between the medial and lateral IJVs. The right external jugular vein passed aberrantly between the heads of the sternocleidomastoid muscle (SCM) into the subclavian vein anterior to the lateral IJV. On the left side, the medial IJV drained into a large bulbous jugulovertebrosubclavian (JVS) sinus that received six main vessels. The lateral IJV diverged posterolaterally toward the border of the trapezius muscle, received the transverse cervical vein, and then turned sharply anteromedially to drain into the JVS sinus. The lateral IJV also gave an aberrant additional large vein that passed laterally around the omohyoid muscle before entering the JVS sinus. The left external jugular vein paralleled the anterior border of SCM before passing posterolaterally to terminate in the JVS sinus. Jugular vein anomalies of this magnitude are very rare. Determining the frequency of multiple IJVs is hampered by inconsistent terminology. We suggest that IJV duplication differs from fenestration anatomically and, potentially, developmentally. Criteria for characterizing IJV duplication and fenestration are proposed. The mechanism of development and the clinical significance of multiple IJVs are discussed.

Astrocyte-derived monocyte-chemoattractant protein-1 directs the transmigration of leukocytes across a model of the human blood-brain barrier.

The migration of leukocytes across the blood-brain barrier (BBB) into the central nervous system is critical in the pathogenesis of central nervous system inflammatory diseases. The production of chemokines, such as monocyte-chemoattractant protein-1 (MCP-1), by endothelial cells (EC) and astrocytes may initiate and amplify this process. Using a coculture of human EC and astrocytes to model the BBB, we demonstrated that exogenous MCP-1 induces the transmigration of monocytes in a dose-dependent manner. TNF-alpha, IFN-gamma, or IL-1beta treatment of cocultures also induced significant migration of monocytes that correlates with the induction of MCP-1 protein. TGF-beta, previously shown to induce MCP-1 expression in astrocytes, but not in EC, caused migration of monocytes across cocultures, but not across EC grown alone. Monocytes and lymphocytes transmigrated across cytokine-treated cocultures in greater numbers than across EC alone. Astrocytes were the main source of cytokine-induced MCP-1, supporting a role for astrocytes in facilitating leukocyte transmigration. A blocking Ab to MCP-1 inhibited MCP-1- and cytokine-induced transmigration of monocytes by 85-90%. Cytokine treatment of cocultures also resulted in the transmigration of activated, CD69-positive lymphocytes. The MCP-1-mediated transmigration of monocytes across cocultures was blocked using an Ab to ICAM-1 and inhibited by 55% using an Ab to E-selectin. These data suggest a central role for astrocyte-derived MCP-1 in directing the migration of monocytes and lymphocytes across the BBB.

Different roles for fibronectin in the generation of fore and hind limb precartilage condensations.

Fibronectin expression and spatiotemporal distribution were examined in relation to the distinctive patterns of mesenchymal condensation and chondrogenesis seen in high-density serum-free cultures of chicken wing and leg bud precartilage cells. More fibronectin protein was produced on a per cell basis by leg than by wing mesenchyme, both in freshly isolated tissue and during the prechondrogenic condensation period in culture, where the difference was twofold. The quantitative difference in fibronectin expression in freshly isolated wing and leg mesenchyme was also seen at the level of total and poly (A)+ RNA. During the condensation phase, fibronectin was distributed in the wing and leg mesenchymal cultures in a way that prefigured the eventual distribution of cartilage in these cultures: in wing cultures condensations were broad and flat, and rich in diffusely organized fibronectin; in leg cultures, condensations were compact and spheroidal, and contained abundant deposits of fibronectin. In addition, the leg condensations were connected by long fibronectin-rich fibers. Transient treatment with TGF-beta early during the culture period led to increase in fibronectin production and expansion of condensations in both wing and leg cultures. Leg mesenchyme was more responsive to transforming growth factor-beta than wing mesenchyme with respect to fibronectin production, and this was reflected in a greater enhancement of cartilage formation in later cultures. Treatment of cultures with monoclonal antibody 304 directed against the amino-terminal heparin-binding domain of fibronectin inhibited condensation formation and reduced chondrogenesis in wing mesenchyme, but left these two processes unchanged in leg mesenchyme, despite disruption by the antibody of the leg-specific fibronectin fibers. These studies indicate that for both wing and leg mesenchyme the morphology, extent, and spatiotemporal regulation of precartilage condensation and subsequent chondrogenesis closely parallels the deposition of fibronectin. But whereas the interaction between cells and fibronectin in wing bud mesenchyme is mediated in part by the protein's amino-terminal domain, this domain does not appear to be involved in analogous interactions in leg bud mesenchyme.

Morphogenetic differences between fore and hind limb precartilage mesenchyme: relation to mechanisms of skeletal pattern formation.

Using a serum-free culture system, we have investigated morphogenetic differences between fore and hind limb precartilage mesenchymal cells derived from stages 21-26 chicken embryos. Across all stages, wing and leg cultures were intrinsically different in the amount and spatial organization of cartilage that they produced. By stage 24, leg cells began to produce a nodular pattern of cartilage while wing cells continued to produce sheets of cartilage. This pattern difference persisted throughout the later stages and was not due to differences in cell survival as judged by DNA content or to the presence of distinctive cell subpopulations in either tissue, as determined by flow cytometry. Chondrogenesis in wing and leg precartilage cell cultures was affected differently by 10% fetal bovine serum, TGF-beta 1 (1 ng/ml for 5 hr on the day after plating), and retinoic acid (5 ng/ml). In wing cultures, the extent of chondrogenesis was significantly enhanced by serum or by a combination of TGF-beta 1 and retinoic acid, but the cartilage pattern was not altered with any treatment. In leg cultures, the extent of chondrogenesis was enhanced by TGF-beta 1 alone, inhibited by retinoic acid alone, and the cartilage pattern was changed from nodular to sheet-like by treatment with TGF-beta 1. Wing and leg cultures also differed from each other in relative cohesivity and in condensation morphology and organization of fibronectin during the early phase of differentiation. Wing cells produced broad, flat condensations containing diffusely organized fibronectin, whereas leg cells elaborated an extensive network of long fibronectin-rich fibrils connecting very compact, fibronectin-rich condensations. These intrinsic and induced differences in fore and hind limb mesenchyme provide insight into the mechanisms that are common to the formation of all limb skeletal elements and those that distinguish skeletal elements from different limb regions and limb types.

Role of transforming growth factor-beta in chondrogenic pattern formation in the embryonic limb: stimulation of mesenchymal condensation and fibronectin gene expression by exogenenous TGF-beta and evidence for endogenous TGF-beta-like activity.

The possible role of TGF-beta-like molecules in skeletal pattern formation in the embryonic vertebrate limb was studied by analyzing the mechanism of enhancement of chondrogenesis in chick wing bud mesenchyme in vitro and testing for the presence and distribution of endogenous TGF-beta-like activity in this tissue. Transient exposure (3-6 hr) to TGF-beta 1 (1-2 ng/ml) on the day after plating resulted in a 1.5- to 2-fold enhancement of accumulation of Alcian blue (pH 1.0)-stainable extracellular matrix 5 days later. The enhancement of differentiation was preceded by an acceleration and an increase in the extent of precartilage condensation formation, visualized by Hoffman Modulation Contrast microscopy a day after TGF-beta treatment. In contrast, neither condensation nor subsequent chondrogenesis was stimulated by transient treatment with TGF-beta 1 on the day of plating. The effectiveness of a TGF-beta treatment regimen in enhancing chondrogenesis was correlated with its effectiveness in stimulating condensation formation. Exposures to the factor for 3-6 hr on the day after plating, which most consistently stimulated both condensation formation and chondrogenesis, also corresponded to a peak in the enhancement of the steady-state level of fibronectin mRNA (fourfold to eightfold over control levels) measured at the end of the treatment period. The elevation in fibronectin mRNA levels brought about by this treatment persisted throughout the period of condensation. Endogenous TGF-beta-like activity was detected in limb mesenchyme: extracts of freshly isolated and cultured limb tissues contained 6-25 pg TGF-beta-like activity per 1 x 10(6) cells by the Mv1Lu cell proliferation inhibition assay, and indirect immunofluorescence using a polyclonal antibody directed against a TGF-beta-related peptide indicated a patchy distribution of endogenous TGF-beta-like reactivity within a day after culture. These findings are discussed in relation to the "fibronectin prepattern" hypothesis for limb pattern formation.