THE ANATOMICAL RECORD 267:242–251 (2002) Functional Gliding Spaces of the Dorsal Side of the Human Hand PETRA THURMÜLLER,* MARKUS SCHUBERT, HOLGER BADE, HANS-PETER NOTERMANS, JUTTA KNIFKA, AND JÜRGEN KOEBKE Department of Anatomy, University of Cologne, Cologne, Germany ABSTRACT The clinical and functional importance of gliding spaces of the hand (e.g., their role in the spread of infection or as a consideration in reconstructive surgery) has been repeatedly emphasized. However, only a few studies have provided details regarding the connective tissue spaces in the metacarpal region of the dorsal side of the human hand. The aim of the present study was to analyze the morphology and elucidate the anatomic relation of functional gliding spaces in the metacarpal region on the dorsal side of the human hand in order to provide a better understanding of function, and of clinical disorders and their treatment. To delineate these spaces we used a plastic (Acrifix 90威) injection method. Twenty fixed and unfixed cadaver hands were subcutaneously injected with Acrifix 90威 (a methacrylate) into the metacarpophalangeal transitional region and into the tendon sheaths of the extensor muscles. Different colors were used to distinguish one injected plastic solution from another. The spreading pattern of the injected medium was analyzed by careful dissection. To delineate the exact bordering structures and the topography of the injected spaces, two hands were plastinated using the E12/E6 technique (von Hagens et al., Anat Embryol 1987;175:411– 421), and one hand was injected and embedded in Technovit 7100威 for histological investigations. Injecting the plastic into the metacarpophalangeal transitional region of fingers II–IV in a disto-proximal direction, the solution spreads along the surface of the separate extensor tendons. It then coalesces 1–2 cm proximal to the injection points to form a continuous plastic plate, which protrudes between and on top of the previous injected tendon sheaths. In no case was a communication between the paratendinous tissue and the tendon sheaths observed. Laterally, the injected solution is delimited at the radial side of the extensor tendon of the second finger and at the ulnar side of the extensor tendon of the fourth finger. Using the described technique at the fifth finger yields a plastic plate that extends from the injection point to the tendon sheath. However, in two specimens a connection between the plastic injected into the tendon sheath of the fifth finger, and the distal injected solution was observed. Anat Rec 267:242–251, 2002. © 2002 Wiley-Liss, Inc. Key words: anatomy; extensor apparatus; paratendinous connective tissue; tendon sheath With respect to its connective tissue architecture, the dorsal side of the hand can be contrasted with the palm. The connective tissue surrounding the extensor apparatus forms loose structured layers, providing the dorsal connective tissue body with a high degree of mobility (Schmidt and Lanz, 1992). On the dorsal side of the human hand the extensor tendons are not covered by tendon sheaths in their metacarpal part, but are surrounded by a multilamellary paratendinous connective tissue (Bade et al., 1992), which is considered to have a specialized gliding function for the tendons. The importance of the paratenon to the supple movement of the extensor tendons is made obvious by pathological alterations such as the paratendonitis crepitans that results from mechanical overloading or direct trauma. Moreover, insufficient posttraumatic © 2002 WILEY-LISS, INC. and postoperative regenerative processes or adhesions of the paratenon often lead to secondary functional disturbance of neighboring tendinous elements of the dorsal extensor apparatus. Contributing to frictionless motility *Correspondence to: Petra Thurmüller, Institut II für Anatomie der Universität zu Köln, Joseph-Stelzmann-Stra␤e 9, D-50931 Köln, Germany. Fax: ⫹49-221-4785318. E-mail: Petra.Thurmueller@uni-koeln.de Received 21 October 1999; Accepted 14 March 2002 DOI 10.1002/ar.10113 Published online 10 June 2002 in Wiley InterScience (www.interscience.wiley.com). GLIDING SPACES OF THE DORSAL SIDE OF THE HAND during tendon movement, (Feneis, 1935; Lang, 1960; Dykyj and Jules, 1991; Rauber/Kopsch, 1998) the paratendinous connective tissue is rich in blood vessels and is important to the vascular supply of the metacarpal part of the extensor tendons between the distal end of the tendon sheaths and the metacarpophalangeal joints (Lang, 1960; Bade et al., 1992). The clinical and functional importance of gliding and connective tissue spaces has been repeatedly emphasized, e.g., as regards their role in spread of infection and as a consideration in reconstructive surgery. However, only a few studies have investigated the connective tissue spaces (Mason and Koch, 1930; Kanaval, 1939; Anson et al., 1945; Landsmeer, 1976; Bade et al., 1994) at the dorsal side of the human fingers or hand. Kanaval (1939) used injection experiments to demonstrate the morphology of tissue spaces. He correlated the anatomical findings with his own clinical experience in relation to the spread of infections following penetrating injuries. Mason and Koch (1930) placed their emphasis on the dorsal side of the metacarpophalangeal transitional region of the long fingers, which deserves special attention because infections within these areas can spread not only on the dorsal side of the fingers but also on the dorsal side of the hand. They attempted to examine tissue spaces using injections of a barium sulfate gelatin solution in fingers of human cadavers, and analyzed the specimens by subsequent dissection and radiographs to determine the dispersion of the solution. Nevertheless, the morphology of connective tissue spaces, and their relationship to the extensor apparatus and the tendon sheaths remain unclear. Because these are potential spaces, they are often difficult to dissect and therefore require special techniques for demonstration purposes. In the present study, we used a plastic injection method previously described by Schubert et al. (1994) for delineation of these capillary spaces, and analyzed the macroscopic topography and morphology of the connective tissue spaces on the dorsal side of the human hand, with preparation and plastination of the injected specimens. To obtain detailed information about this topographically and morphologically complex gliding system, which consists of multilamellary paratendinous connective tissue and the tendon sheaths of the extensor apparatus, we used the Technovit 7100威 (Kulzer GmbH, Wehrheim, Germany) resin embedding technique for histological investigations. Special attention was given to the small transition region of these gliding spaces. Bade et al. (1994) and Schubert et al. (1996) investigated gliding spaces at the dorsal side of the human finger using plastic injections, and described very constant spaces. Bade et al. (1995) examined the dorsal connective tissue body of the human finger and described a deep lamellar system that covers the aponeurosis dorsalis of the human finger. This system of collagen lamellae separates the dorsal connective tissue from the dorsal aponeurosis. Furthermore, Bade et al. (1995) showed that the internal side of the deep lamellar system is covered by a synovial-like epithelium. These results identified the spaces between the dorsal hood and the deep lamellar system as gliding spaces. Schubert et al. (1996) reported that in some cases the gliding spaces at the dorsal side of the fingers expand on the dorsal side of the human hand. Kanaval (1939) injected a barium sulfate mixture into the dorsal side of the hand and found that the solution dispersed widely. The aim of the present study was to analyze the exact morphology, expansion, and anatomical relation of functional gliding spaces on the 243 Fig. 1. Schematic representation of the injection sites (a and b) marked by dots. dorsal side of the human hand to provide an anatomical basis for a better understanding of their function, and of clinical disorders and their treatment. MATERIAL AND METHODS Sixteen fixed and unfixed hands were injected with a plastic solution at predefined points (Fig. 1a and b) and the dispersion of the injected medium was analyzed by subsequent dissection. The injection was performed immediately proximal to the metacarpophalangeal joints II–V (Fig. 1a) with disto-proximal direction of dispersion. Prior to this, an injection into the tendon sheath of the m. extensor digitorum and the m. extensor indicis was performed (Fig. 1b) with proximo-distal dispersion of the injected plastic solution. Acrifix 90威 (Röhm GmbH, Darmstadt, Germany) was used as the injection plastic. Acrifix 90威 is a plastic based on acrylic acid and is used industrially as a plexiglas glue. We used Acrifix 90威 in the mixture (see Table 1). To avoid artifacts, the injection points were dissected in a T-shape, with the horizontal bar oriented in the direction of dispersion. An open pouch was formed in the dispersion direction. The plastic was injected at these points and was allowed to flow slowly into the capillary spaces. In order to distinguish between the plastic solutions injected at various locations, different colors were used. The injection was performed by a threaded, guided injection apparatus (Schlüter, 1961). The injection pressures were controlled by leaving an air bubble in the injection system as a useful pressure indicator. This facilitated the use of low injection pressures (Schubert et al., 1994). Following the 244 THURMÜLLER ET AL. TABLE 2. TABLE 1. Injection mixture Catalyst 20威 Thinner Acrifix 90威 Coloring (Röhm GmbH 8076/8075) % 3 1–3 93–95 1 Injection plastic Parts Biodur E20威 Biodur E2威 Biodur AT 10威 Coloring (Röhm GmbH 8076/8075) 100 42 20 2 TABLE 3. Infiltration solution injection, the hand was placed in a position that allowed the plastic to drain slowly into the capillary spaces. Two unfixed hands were examined by the technique of block-plastination, which allowed the production of 1-mmthick serial sections using a diamond wire saw (type 6234, Fa. Well). The hands were arterially perfused with physiological saline solution and a plastic solution was injected at defined injection points (Fig. 1) by the technique described above. The contents of the injection plastic are shown in Table 2. It was necessary to use an acetone-insoluble injection medium to prevent the injected substance from being dissolved by the acetone dehydration bath. After the plastic was hardened, the hands were fixed with a 4% formaldehyde solution via the radial artery and placed in a formaldehyde solution for 14 days. The hands were plastinated using the E6威/E12威 technique (von Hagens, 1985/1986), which consists of three steps (described in detail by Schubert et al., 1996): 1) dehydration and fat removal, 2) forced impregnation, and 3) hardening. Histological Investigations Another unfixed hand was arterially perfused with physiological saline solution and injected with plastic at defined injection points (Fig. 1) using Biodur E20®/E2® as the injection solution. After hardening of the plastic, the hand was fixed via the radial artery with a 4% formaldehyde solution. After fixation, the hand was frozen to –25°C and cut into 1-cm-thick slices with a diamond wire saw (type 6234, Fa. Well). The slices were placed in a formaldehyde solution for 14 days. Dehydration and fat removal of the specimens was performed in acetone baths of increasing concentrations (90%, 98%, and 99%). The tissue slices were decalcified using EDTA, and the calcium remnants of the bone were examined radiographically. The embedding technique (Technovit 7100威) had to be modified to handle these large specimens. The preinfiltration step was not used, and the specimens were put directly into the infiltration solution (see Table 3). During acetone extraction and infiltration, the specimens were kept in a vacuum environment for 3 hr. To prevent elevation of temperature caused by heat of reaction in such large objects, the Harder II (10 ml/100 ml infiltration solution; Heraeus Kulzer, Wehrheim, Germany) was mixed with the infiltration solution at –25°C. The polymerization was initiated at –25°C. Step by step the polymerization was continued at slowly increasing temperatures, and it reached room temperature in 14 days. After hardening, sections (5–10 m thick) were made using a hard microtome. The sections were stained with toluidine blue. Another hand was treated in the described manner, without injection of plastic. Technovit 7100威 (GMA with Co-Catalyst XLC) Harder I (Dibenzoylperoxid) 100 ml 1g RESULTS Topography and Morphology of the Gliding Tissue Spaces of the M. extensor digitorum and the M. extensor indicis, Analyzed by Injection and Subsequent Dissection Injection of the plastic solution into the metacarpophalangeal transition region of fingers II–IV in disto-proximal direction led to a dispersion of the solution on the surface of the extensor tendons (Fig. 2). The solution spread along the surface of the extensor tendons, and then coalesced to form a continuous plastic plate 1–2 cm proximal to the injection points. This plate protruded between and over the previously injected tendon sheaths of the M. extensor digitorum and the M. extensor indicis. In no case was a communication between the plastic solution injected into the multilamellary paratendinous connective tissue and the plastic solution injected into the tendon-sheaths observed. Laterally, the injected solution was delimited at the radial side of the extensor tendon of the second finger and at the ulnar side of the extensor tendon of the fourth finger (Fig. 2). The dorsal surface of the plastic plate was covered by an always demonstrable connective tissue membrane. This membrane forms a roof for the gliding compartment, which is occupied by the extensor tendons and their enveloping coats and separates the loose, areolar, subcutaneous tissue of the dorsum of the hand from the delineated gliding spaces. This connective tissue membrane is non-fatty and very strong, and contains clearly visible fibers that contribute to its appearance as a weaker aponeurosis. It dips at the ulnar side of the extensor tendon of the fourth finger and at the radial side of the extensor tendon of the second finger volarwards to become continuous with the equivalent infratendinous membrane, which itself forms the palmar surface of the gliding tissue spaces of the M. extensor digitorum and the M. extensor indicis. These marginal attachments of both connective tissue membranes can be regarded as the cause of the precise bordering of the injected plastic plate at the ulnar and the radial side of these tendons. In no case did the injected plastic plate reach the extensor tendon of the first or the fifth finger. Around the free edges of the second and fourth extensor tendons, the infratendinous and supratendinous layers are not distinct. Conjoined, they become continuous with the connective tissue of the extensor tendon of the first and fifth fingers. In the proximal direction, the supratendinous connective tissue membrane is in close contact with the tendon sheaths and continues into Fig. 2. Acrifix mold of the paratendinous connective tissue space occupied by the extensor tendons (blue color) and the previously injected synovial tendon sheaths (yellow color) following injection (see the injection points marked with dots a and b in Fig. 1) and dissection. Fig. 4. Multilamellary paratendinous connective tissue space (red color) of the M. extensor digitorum and the M. extensor indicis in the region of the middle of the metacarpus (Technovit 7100姞, toluidine blue, 7 m, ⫻7, line 1 (Fig. 3)). The enlargement of this section shows the localization of the injection medium between the supratendinous (arrowheads) and infratendinous (arrows) membranes bordered laterally by a thin lamella at the free edges of the fourth (IV) and second (II) extensor tendons. The division of the paratendinous connective tissue space into lesser spaces by intertendinous networks of loose connective tissue is shown. Fig. 5. Transverse section through the common tendon sheath of the M. extensor digitorum, lying immediately under the retinaculum extensorum (Technovit 7100姞, toluidine blue, 7 m, ⫻5, line 5 (Fig. 3)). The extensor tendons are completely surrounded by the yellow injected tendon sheath (arrow), which is closely adherent to the retinaculum extensorum without any loose intervening connective tissue of the paratenon. The tendon sheath of the M. extensor carpi radialis brevis is marked by an arrowhead. 246 THURMÜLLER ET AL. the retinaculum extensorum and the fascia antebrachii. Distally, the supratendinous connective tissue membrane fuses with the capsular tissue of metacarpophalangeal joints II–IV, with the periosteum on either side of each extensor tendon and with the infratendinous membrane at the clefts between metacarpal bones II–III and III–IV, to form a crenated margin at each of the interdigital concavities. The described fusion of the supra- and infratendinous membranes forms a definite circumscribed compartment, which contains the extensor tendons. This structural detail of the connective tissue body of the M. extensor digitorum and the M. extensor indicis was seen in all specimens examined, except in two cases. In these two cases the injected solution became continuous with the paratendinous apparatus of the fingers and lay upon the dorsal aponeurosis between the dorsal hood and a covering membrane. This membrane covers the dorsal aponeurosis and separated the solution from the subcutaneous tissue. After the supratendinous connective tissue membrane and the plastic plate were removed, some particles of the injected plastic solution remained between the fascicle of the tendons. Dissection of the fifth finger and the respective tendon showed that the injected solution surrounded the tendon completely. The injected plastic and the tendon were completely covered by a thin connective tissue membrane. Proximally, the solution protruded onto the previous injected tendon sheath. However, in two cases it appeared that the two different injected spaces communicated. Topography and Morphology of the Gliding Tissue Spaces of the M. extensor digitorum and the M. extensor indicis, Analyzed by Injection and Plastination Transverse sections of the dorsum of the hand displayed a definite circumscribed paratendinous gliding space formed by the described supra- and infratendinous membranes, and confirmed the results regarding the morphology of the gliding tissue spaces of the M. extensor digitorum and the M. extensor indicis established by injection and preparation. The tendons of the M. extensor digitorum and M. extensor indicis, with their surrounding tissue (which envelops each tendon and stretches between the extensor tendons over the intermetacarpal spaces), divide this connective tissue space incompletely into two spaces lying on the dorsal and palmar surfaces of the tendons. The dorsal aspect of the described space is subdivided by a vertical lamella, which continues from the palmar side of the supratendinous membrane to the infratendinous membrane at the ulnar side of the third extensor tendon. This vertical lamella separates the paratendinous connective tissue space into lesser spaces—a closed space for the extensor tendon of the fourth finger, and a common space for the extensor tendons of the second and third fingers. At the radial side of the second, and the ulnar side of the fourth extensor tendon, the injected solution followed the supratendinous membrane to the conjunction with the infratendinous membrane. Therefore, a thin layer of plastic solution reached the palmar side of the extensor tendons. However, this thin solution did not continue to form a continuous plastic plate, so that the palmar side of the extensor tendon of the third finger was never covered by the injected plastic solution. Fig. 3. Topographic localization of the histologically investigated cross sections in the region of the metacarpus and carpus, marked by lines 1–5. Histological Investigations of Injected Specimens The topographic localization of the histologically investigated cross sections in the region of the metacarpus and carpus is marked by lines 1–5 in Fig. 3. The paratendinous connective tissue of the M. extensor digitorum and the M. extensor indicis is characterized by the above-described supra- and infratendinous membranes, which formed the dorsal and palmar borders of the red-injected connective tissue body (Fig. 4). The supratendinous membrane is highly populated with fibrocytes. Their cytoplasm often displayed metachromatic granules in the toluidine-blue stain as a sign of increased activity. The fibrocytes form a loose layer at the dorsal border of the depicted gliding space. At the ulnar side of the extensor tendon of the fourth finger and at the radial side of the extensor tendon of the second finger, a thin connective tissue lamella originates from the inner surface of the supratendinous membrane, dips volarwards, and fuses with the infratendinous membrane, resulting in a clearly defined gliding space containing the extensor tendons (Fig. 4). Between the supratendinous and infratendinous membrane, the intertendinous spaces of the extensor tendons are filled by a loose network of fatty areolar connective tissue, which contains many small vessels and separates the connective tissue body into lesser spaces. Connecting the several extensor tendons, small vessels could be seen coursing through these areolar sleeves toward the tendons at frequent, regular intervals. Between the fourth and third extensor tendons, the loose intertendinous connective tis- GLIDING SPACES OF THE DORSAL SIDE OF THE HAND sue is adherent to the supra- and infratendinous membranes, whereas the connective tissue network between the third and second extensor tendons is in close contact with the infratendinous membrane. The expansion of the injected plastic solution (red color) demonstrated that these differences in the intertendinous connective tissue body led to a closed gliding space for the extensor tendon of the fourth finger, and a common gliding space for the extensor tendons of the second and third fingers (Fig. 4). The adhesions of the intertendinous connective tissue lamellae with the infratendinous membrane to both sides of the extensor tendon of the third finger explain why the injected plastic solution was never seen at the palmar side of this tendon, whereas at the free sides of the extensor tendons of the second and fourth fingers the injected solution followed the supratendinous membrane and expanded on the palmar surface of the tendons (Fig. 4). The injection of the plastic solution into the tendon sheaths (yellow color) of the M. extensor digitorum and the M. extensor indicis, 1 cm proximal of the retinaculum extensorum, showed that their morphology is not uniform throughout their entire course. Only in their proximal aspect, under the retinaculum extensorum, were the tendons completely enclosed by the yellow injected tendon sheaths (Fig. 5). Distally, after splitting of the common synovial sheath of the M. extensor digitorum and the M. extensor indicis into the separate recesses at the distal margin of the retinaculum extensorum, the synovial tendon sheaths continue only on the dorsal aspect of the respective tendon with a size comparable to that of a bursa, and do not surround the entire tendon surface (Fig. 6). The distal termination of the synovial tendon sheaths appeared as small clefts surrounded by the paratendinous connective tissue of the extensor tendons. The transitional region of the injected tendon sheaths (yellow color) and the injected multilamellary, paratendinous connective tissue space (red color) of the M. extensor digitorum and M. extensor indicis showed a close engagement of these two different gliding spaces. In any case, they are completely separated by connective tissue lamellae. The distal termination of the tendon sheath of the fourth finger is enclosed by the supratendinous membrane and is located at the dorsal aspect of the paratendinous connective tissue without contact with the respective tendon (Fig. 7). The gap between the tendon sheath and the tendon is filled by the paratendinous connective tissue (red color). In the proximal direction, the synovial tendon sheath becomes adherent to the dorsal aspect of the tendon, so that the tendon of the fourth finger is partially surrounded by the clearly defined paratendinous connective tissue (red color) and the synovial tendon sheath (yellow color) (Fig. 6). The distal recesses of the tendon sheath of the third and second fingers lie immediately on the dorsal surface of the respective tendon. Their size is comparable to that of a bursa covered by a thin layer of paratendinous connective tissue (Figs. 6 and 8). As observed at the fourth finger, the tendons of the third and second fingers are also, in a proximal direction, surrounded more and more completely by the respective tendon sheath. The tendons of the M. extensor digitorum and the M. extensor indicis are enclosed by their tendon sheaths only in their proximal part, immediately beneath and under the retinaculum extensorum (Fig. 5). At this point, the tendon sheath is closely adherent to the supratendinous membrane and the retinaculum extensorum, without any loose intervening con- 247 nective tissue of the paratenon. Distally, the tendon sheaths lose their intimate connection with the supratendinous membrane; thus the paratendinous connective tissue is situated between the top of the sheath and the supratendinous membrane. DISCUSSION Different methods for analyzing the morphology and topography of connective tissue spaces have been reported in the literature. Anson et al. (1945) studied the dorsal layers of the hand exclusively by careful dissection of several specimens to demonstrate regional differences in texture and attachment. Kanaval (1939) based his observations on injection studies using a barium sulfate solution injected in the dorsal connective tissue body. He used different injection pressures and completed his studies with the examination of 1-cm-thick cross sections through the metacarpus. Mason and Koch (1930) used a gelatin barium solution and documented the expansion of the injection mass with x-rays. By combining the injection and GMA-embedding techniques, it has been possible to analyze connective tissue spaces of capillary character and their bordering structures in greater detail. The applied method of combined injection and plastination used by Bade et al. (1994) and Schubert et al. (1996) to analyze gliding spaces nearly closes the gap between macroscopic and microscopic observations. To identify even single collagen fibers bordering the injected spaces, we have introduced a combination of injection and histological embedding which has made it possible to investigate even the small transitional region of the extensor tendon sheaths and the multilamellary paratendinous connective tissue body in detail. A frequent criticism of injection techniques is that injection itself destroys fine connective tissue structures and leads to erroneous results. Using the described technique we have been able to show that the injected solution spread along very fine collagen lamella without destroying them. The clinical and functional importance of connective tissue spaces has been repeatedly commented upon, especially as regards their role in the spread of hemmorhage or infection (Mason and Koch, 1930; Kanaval, 1939; Grodinsky and Holyoke, 1941; Anson et al., 1945; Rieger and Brug, 1992; Schubert et al., 1996). The connective tissue spaces on the palmar side of the human hand have been extensively investigated by Garlock (1924), Kanaval (1939), Grodinsky and Holyoke (1941), and Flynn (1942). However, only a few studies have analyzed the connective tissue body in the metacarpal region of the dorsal side of the human hand (Mason and Koch, 1930; Kanaval, 1939; Anson et al., 1945; Landsmeer, 1976). Mason and Koch (1930), Kanaval (1939), and Landsmeer (1976) described a dorsal subcutaneous space lying on the dorsal surface of the extensor tendons. Mason and Koch (1930) and Landsmeer (1976) observed a defined compartmentalization of the subcutaneous space by fascial structures. Kanaval (1939) described an extensive area of loose tissue without defined boundaries in which pus can spread over the entire dorsum of the hand. Kanaval made his observations by means of injection experiments employing a high degree of injection force to obtain expansion of the injection mass equally over the entire dorsum of the hand. In the present study we demonstrated the dorsal multilamellary, paratendinous connective tissue space of the extensor tendons to be a gliding space of 248 THURMÜLLER ET AL. clearly defined pattern. This space is separated from the subcutaneous fat by the supratendinous membrane, which was previously described by Anson et al. (1945), who named this membrane the “supratendinous fascia.” They showed by subsequent dissection that this membrane forms the roof of a compartment containing the extensor tendons. The bottom of this extensor compartment is formed by the infratendinous membrane. At the free edges of the second and the fourth extensor tendons, the two membranes fuse and complete a close extensor compartment. We demonstrated that the extensor tendons occupying this compartment are surrounded by a definite gliding space. Anson et al. (1945) described a subsequent division of the extensor compartment into a supra- and infratendinous part, defined by the extensor tendons and their intertendinous fascia, which enclosed the tendons and attached medially and laterally to the compartment wall. In our study, we demonstrated that the tendons are not enclosed by an intertendinous fascia, but are surrounded by a loose network of fatty areolar connective tissue. This tissue fills the intertendinous spaces and contains many small vessels, separating the connective tissue body into lesser spaces, but it does not attach to the compartment walls laterally. Therefore, the supra- and infratendinous spaces are not completely separated. Schubert et al. (1996) identified a connective tissue space lying between the dorsal hood and a bordering membrane of the human finger. He showed that, in some cases, an injected solution expanded in a proximal direction over the metacarpophalangeal joints on the dorsal aspect of the respective extensor tendon. In the present study, this kind of connection was found in only two cases. It is possible that the variability of the extent of the plastic plate on the respective tendon may be based on individual differences in connective tissue relationships. Usually, the distal border of the paratendinous connective tissue space of the extensor tendons is formed by a fusion of the supratendinous connective tissue membrane with the capsular tissue of metacarpophalangeal joints II–IV and with the periosteum on either side of each extensor tendon. According to generally accepted opinion (Staubesand, 1988; Platzer, 1989; Frick et al., 1992; Schmidt and Lanz, 1992; Rauber/Kopsch, 1998), tendon sheaths are closed chambers enveloping the respective tendon throughout the entire course of the tendon sheath. Based on the results of the present study, we have grounds to assert that this is not a common pattern for the morphology of the extensor tendon sheaths of the human hand. The tendons of the M. extensor digitorum and the M. extensor indicis are entirely surrounded by their common tendon sheath only in their proximal aspect under the retinaculum extensorum. Distally, the common tendon sheath divides into separate recesses, one for each tendon, which continue only on the dorsal aspect of the respective tendon. These recesses are comparable in size to a bursa, and terminate distally as small clefts surrounded by the paratendinous connective tissue. These results concerning the morphology of the extensor tendon sheaths provide a new model of the blood supply of the tendons in the transitional region of the paratendinous connective tissue and the tendon sheaths. While a good blood supply to the extensor tendons is observed in the extrasynovial region, provided by small vessels forming arcades between the loose paratendinous connective tissue (Bade et al., 1992), this situation was previously described as changing abruptly after entering the tendon sheaths (Edwards, 1946; Chaplin, 1973; Taylor and Townsend, 1979). Our study showed that the blood supply of the extensor tendons does not change abruptly in the transitional region of the gliding spaces, rather the part of extensor tendons lying in this region are partially nourished by the paratenon and by the tendon sheaths at the same time. The dorsal gliding space of the extensor tendons in the region of the metacarpal, described in this study, is one of the well-defined deep fascial spaces of the hand. Infection from local penetrating injuries is said to spread from an adjacent compartment or from hematogenous seeding (Hausman and Lisser, 1992). The dissemination of infection in preformed fascial spaces is predictable in that spread occurs through anatomic compartments and planes. The results of the current study provide an anatomic basis for the clinical observation of the pattern of spread of suppurative infections such as may occur following human bite wounds of the dorsal aspect of the hand (Mason and Koch, 1930; Faciszewski and Coleman, 1989). Faciszewski and Coleman (1989) described the mode of spread of infection resulting from bite wounds (clenched fist injury) over the metacarpophalangeal joints, which involved the whole extensor compartment within 1 week and necessitated extensive debridement. Infections of the closed spaces of the hand tend to produce more rapid tissue necrosis and abscess formation than those of the superficial areas of the hand (Glass, 1982). Treatment of established deep space infections requires both operative drainage and/or wound debridement, and intravenous antibiotics (Hausman and Lisser, 1992). The incision for operative drainage has to be placed in such a way as to give direct access to pus. It should create no additional Fig. 6. Transverse section through the transitional region of the multilamellary paratendinous connective tissue (red color) on the tendon sheaths of the extensor tendons of the third and fourth fingers (yellow color) (Technovit 7100姞, toluidin blue, 7 m, ⫻7, line 3 (Fig. 3)). The distal recess of the synovial tendon sheath of the third finger (III) lies on the dorsal aspect of the respective tendon, covered by a thin layer of paratendinous connective tissue, and does not surround their entire surface. The tendon of the fourth finger (IV) is partially surrounded by the paratenon (red color) and the synovial tendon sheath (yellow color). Fig. 7. Transverse section through the extensor tendon of the fourth finger in the region of the distal termination of the respective synovial tendon sheath (yellow color) (Technovit 7100姞, toluidine blue, 7 m, ⫻9, line 2 (Fig. 3)). The distal termination of the tendon sheath is enclosed by the supratendinous membrane (arrow) and lies on the dorsal aspect of the paratendinous connective tissue (red color) without contact to the respective tendon. Fig. 8. Transverse section through the transitional region of the multilamellary paratendinous connective tissue (red color) on the tendon sheath of the extensor tendon of the second finger (yellow color) (Technovit 7100姞, toluidine blue, 7 m, ⫻7, line 4 (Fig. 3)). The distal termination of the tendon sheath lies on the dorsal surface of the radial part of the extensor tendon of the second finger (II) covered by a thin layer of paratendinous connective tissue (red color). The synovial tendon sheath of the extensor tendon of the third finger (III) is marked by an arrow. 250 THURMÜLLER ET AL. damage, it should be as limited as is expedient, and it should protect the subsequent function of the hand by ensuring that scars will heal with a minimum of deforming contracture (Linscheid and Dobyns, 1975; Glass, 1982). On this basis, an anatomic approach to the treatment of infections of the dorsal extensor compartment has much to recommend it. If the infection involves the whole extensor compartment, two linear incisions are preferred: one at the ulnar side of the extensor tendon of the fourth finger between the fourth and fifth metacarpals, and one at the radial side of the extensor tendon of the second finger over the second metacarpal (Burkhalter, 1989; Hausman and Lisser, 1992). The two-incision approach provides adequate soft-tissue coverage over the tendons, while permitting adequate drainage. Placement of the incisions at the ulnar and radial borders of the extensor compartment reduces the risk of tendon adhesions and impairment of function caused by healing scars. A midline incision directly over the extensor tendons is not recommended. The potential complications of this approach include extensor tendon dessication, injury to the junctura tendinum, ischemia due to injury of the loose paratendinous connective tissue, unsatisfactory wound healing, and formation of tendon adhesions (Jebson, 1998). If the infection of the dorsal extensor compartment is well localized, one longitudinal incision may be sufficient (Jebson, 1998). Injuries to the dorsal aspect of the hand with damage to underlying extensor tendons are associated with loss of the normally present “gliding mechanism” around these tendons (Biswas et al., 2001). Extensor tendon defects on the dorsum of the hand have been reconstructed secondarily by a combination of tendon transfer and tendon grafting beneath a flap previously placed to cover the soft-tissue defect (Campbell Reid, 1974). However, this results in tendon adhesions, and associated limitation of motion, with extension and flexion deficits in both the repaired and grafted tendons. Various authors have addressed this problem and emphasized the importance of reconstitution of the normal milieu for tendon gliding, with a well-lubricated gliding surface all around the tendons as a precondition for achieving optimum excursion (Hirase et al., 1991; Hirase and Kojima, 1994; Watanabe et al., 1996; Biswas et al., 2001). Hirase et al. (1991) first described a double-layered free temporal fascia flap as a tendon gliding surface to restore gliding function after avulsion or degloving injuries of the dorsum of the hand. By sandwiching the tendons between the layers of vascularized fascia, gliding surfaces were recreated, both superficial and deep to the exposed tendons, encouraging preservation of function. This clinical experience identifies the extensor space as a functional gliding compartment and emphasizes again the importance of detailed anatomical knowledge of connective tissue spaces on the dorsal side of the human hand as the basis for a better understanding of clinical disorders and their treatment. Evolutionary Considerations Comparative studies of the extensor assembly of the human hand and its evolutionary precursors suggest that progressive tendon fasciculation and individualization has occurred as a result of increased functional specialization (Landsmeer, 1987). A simple functional morphological pattern of the extensor apparatus consisting of a solid tendon plate over the metacarpal region is described as prevalent in reptiles, e.g., varanus and iguana. Perhaps this pattern subserves simple function and a stereotypical pattern of locomotion (Landsmeer, 1987). In opossum, at the dawn of mammalian eruption, the hand emerged with a more complex structure of the extensor assembly, including tendon fasciculation and a first tendency toward tendon individualization, which contributed to more specialized locomotion and the ability to grasp food (Landsmeer, 1979). Fasciculation and individualization of the extensor assembly in man and other primates (e.g., chimpanzees) has proceeded to the extent of individual finger recruitment and individual finger control, contributing to the adaptation of individual finger position to the shape of an object. The dorsal multilamellary paratendinous connective tissue space of the extensor tendons described in the current study is a gliding space of clearly defined pattern. It is partitioned into lesser spaces by loose networks of fatty areolar connective tissue. 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