Histologic anatomy of the triangular fibrocartilage The collagen arrangement of the triangular fibrocartilage complex was studied in 20 fresh cadaver wrists by means of standard and polarized light microscopy and scanning electron microscopy. The collagen fibers in the articular disk are arranged in undulating sheets oriented at oblique angles to each other. The fibers of the radioulnar ligaments are oriented longitudinally from the radial origin to the ulnar insertion. The origin of the articular disk from the radius is characterized by thick fibers 1 to 2 mm in length radiating from the radius into the articular disk. Five specimens were also injected with india ink. The radioulnar ligaments and the peripheral 15% to 20% of the articular disk arc well vascularized, whereas the central 80% of the articular disk is avascular. (J IIAl'n SURG 1991;16A:I084-J100.)
Larry K. Chidgey, MD, Paul C. Dell, MD, Edward S. Bittar, MD, PhD, and Susan S. Spanier, MD, Gainesville, Fla.
Pathologic conditions involving the triangular fibrocartilage complex (TFCC) have been well documented as a cause of ulnar wrist pain.!" In both diagnosis and treatment, a thorough understanding of the normal anatomy of this complex region of the wrist is fundamental. This includes not only the gross anatomy (at the macroscopic level) but also the fine structure (at the microscopic level). An understanding of the functional anatomy is especially strengthened by a study of the collagen fiber arrangement. Collagen fibers withstand tensile stress and arrange themselves along tension lines within connective tissue. Study of the meniscus in the knee has shown a hoop arrangement of collagen fibers with radially oriented reinforcing fibersv" and has contributed to an understanding of the pathomechanics of meniscal tears . Similarly, study of the collagen fiber arrangement in articular cartilage has contributed to an understanding of normal load transfer in joints and the patterns of joint surface degenerative changes. 7-9 Our study examines the
From the University of Florida , Department of Orthopaedics, Gainesville, Fla. Received for publication April 2, 1991; accepted in revised form April 24, 1991. No benefits in any form have been received .or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Larry K. Chidgey, MD, University of Florida, College of Medicine, Department of Orthopaedics, Bolt )·246, JHM Health Center, Gainesville, FL 32610 . 3/1/30880
1084
TilE JOURNAL OF llANO SURGERY
fine structural anatomy of the TFCC with special attention to the collagen fiber arrangement.
Materials and methods A total of20 fresh cadaver wrists were used. Eighteen of the wrists were from adults (age range, 23 to 52 years) and two were from children (IO and 13 years of age). Specimens were excluded if disease of the TFCC was noted on direct inspection or if bone disease was detected radiographically. Fourteen specimens (12 adults, 2 children) were studied with the light microscope and three with the electron microscope. In five specimens the vascular anatomy was studied by means of india ink injection. Two of the india ink-injected specimens were also sectioned and studied with the light microscope. Before sectioning, the surface structure was examined in six (four adults and two children) of the 14 light microscopy specimens by the split-line technique." When cartilage is pricked with a sharp, round pin, the corresponding defect in the surface layer is typically not a round hole but a longitudinal split. The direction of the split is characteristic for a particular area of cartilage and is reproducible. If the pin is charged with india ink, the split is stained and easily visible. The direction of the split is believed to correspond to the orientation of the superficial arrangement of the collagen fibers, with the split representing a separation between adjacent fiber bundles. This technique has been applied most commonly to hyaline articular cartilage in the hip and knee." 10. II With the radiocarpal joint disarticulated, multiple split lines were made in the artie-
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
Fig. 1. India ink-stained split lines of scaphoid fossa (SF) of radius are oriented primarily in flexion/extension direction. Split lines of the lunate fossa (LF) have a similar orientation radially, but ulnarly they radiate out from the base of the fossa. In the adult, the split lines of the central area of the TFCC where it originates from the radius (arrow) are oriented almost 90 degrees to the split lines of the lunate fossa of the radius. Peripheral to this central area the split lines form a series of arches originating from the dorsal and palmar ulnar aspects of the radius and arch toward the ulnar insertion.
p 1m r Fig. 2. Split lines in immature specimens flow smoothly from lunate fossa (LF) into TFCC without abrupt change in direction seen in adult. (Arrow indicates site of origin of TFCC from the radius).
1085
1086
The Journal of HAND SURGERY
Chidgey et al.
Fig, 3. Whcn viewed from the distal radioulnar joint side. the split lines of the sigmoid notch (SN) are oriented along the frontal plane. An abrupt change in split-line orientation occurs at the area of origin of the TFCC (black arrow); the central area lines are oriented in the dorsal/palmar direction, and the peripheral lines arch toward thc ulnar insertion . The ulnar head (UH) has been rellected to the right of the photograph to visualize the undersurface of the TFCC. D. Dorsal; P, palmar.
"
~
...
~ r
, .
t
Fig. 4. Section from central articular disk area of TFCC has high collagen matrix/cell ratio. Sections from other areas of the TFCC have a similar matrix/cell ratio. Fibers of elastin (stained black with Verhoeff's stain) arc sparsely scattered throughout {arrows}. (Original magnification X 16.)
ular surface of the radius and the TFCC. The distal ulna was then cut just proximal to the distal radioulnar joint and pivoted away from the radius to open up the distal radioulnar joint. Multiple split lines were made in the radial and ulnar articular surfaces of the distal part of the radioulnar joint as well as the proximal surface of the TFCC. Of the 14 specimens studied with the light microscope, 12 were sectioned serially and stained with hematoxylin and eosin for study by standard and polarized light microscopy. Seven of these specimens were sectioned in the transverse plane, three in the sagittal plane, and two in the frontal plane. Two specimens were sectioned and stained with Verhoeff 's stain for elastin; one was sectioned in the transverse plane and one in the frontal plane. Three specimens were examined with the scanning electron microscope (SEM) to further define the collagen patterns. Specimens were fixed in 2% glutaraldehyde for 2 hours and then dehydrated through serial concentrations of ethanol. Dehydration was followed by freeze-fracturing in liquid nitrogen, immersion in hexamethyldisilazane, and critical-point drying. The fracture surfaces were then sputter-coated with gold and examined with the SEM at 20 kV. Five of the specimens were injected with india ink before sectioning to delineate the vascularity. The brachial artery was cannulated above the elbow, and ap-
Vol. 16A, No.6 November 1991
Histologic anatomy of trial/gular fibrocartilage
1087
Fig. 5. A, Area ofTFCC outlined wherc histologic section was taken , representing junction between dorsal radioulnar ligament and articular disk . B, Transverse histologic section of junction between dorsal radioulnar ligament (top half of photograph) and articular disk (bottom half of photograph) . (Polarized light. Orig inal magnification x 16.)
proximately 3000 ml of a 40%/60% mixture of india ink and normal saline solution was injected. The TFCC was then removed in two of the specimens, sectioned, and stained with hematoxylin and eosin . The other three specimens were cleared by the Spalteholz technique." Results Surface structure. When viewed from the radio carpal joint side, the split lines of the scaphoid fossa of the radius are oriented primarily in the flexion 1extension direction (Fig . I). Split lines of the lunate fossa have a similar orientation radially, but ulnarlyjhey have a sunburst or radiating pattern out from the base of the fossa . In the adult , the split lines of the central area of the TFCC, where it originates from the radius, are oriented almost 90 degrees to the split lines of the lunate fossa of the radius. Moving out from this central area , the split lines form a series of arches that originate from the dorsal and palmar ulnar aspects of the radius. The split-line pattern in immature specimens appears to be
different from that in the adult, although only a small number of immature specimens (1/ = 2) have been studied (Fig. 2). The split lines flow smoothly from the lunate fossa into the TFCC without the abrupt change in direction seen in the adult . When viewed from the distal radioulnar joint side , the split lines of the sigmoid notch are oriented along the frontal plane (Fig. 3). An abrupt change in splitline orientation once again occurs at the area of origin of the TFCC; the central area lines are oriented in the dorsal/palmardirection wherea s the lines bordering the central area arch toward the ulnar insertion. On the distal radioulnar joint side, as on the radiocarpal side, the immature specimens have a smoother transition between the radius articular cartil age and the TFCC than do the adult specimens. Light microscopy. Hematoxylin and eosin-stained sections of the TFCC show a high collagen matrix 1cell ratio (Fig. 4). Compared to the adjacent articular cartilage of the distal radius, there is also a high col-
The Journal of 1088
Chidgey et af.
HAND SURGERY
Fig. 6. A, Area outlined where histologic section was taken, representing origin of dorsal radioulnar ligament from radius. B, Transverse histologic section of radial origin of dorsal radioulnar ligament demonstrating longitudinal orientation of collagen fibers. (Polarized light. Original magnification x 16.)
lagen I ground substance ratio within the articular disk region of the TFCC. Fibers of elastin are sparsely scattered throughout, with no difference in concentration of elastin fibers in different regions of the TFCC (Fig. 4).
Examination of histologic sections under polarized light enhances visualization of the collagen fibers. Although not well delineated in gross specimens or in sections stained with hematoxylin and eosin , under polarized light a clear distinction between the dorsal and
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
1089
Fig. 7. A, Area outlined where histologic section was taken. representing origin of articular disk from radius. B, Transverse histologic section of radial origin of articular disk. Short, thick fibers extend from the radius (left side of photograph) into the articular disk (right side of photograph). (Polarized light. Original magnification x 16.)
palmar radioulnar ligaments can be made from the more central articular disk (Fig. 5). The radioulnar ligaments are formed by longitudinally oriented collagen fiber bundles originating from the dorsal and palmar aspects of the sigmoid notch of the radius and insert onto the
ulna (Fig. 6). The area of origin of the central articular disk has thick collagen bundles projecting from the radius into the TFCC for I to 2 mm (Fig. 7). On transverse sections, the more central aspects of the articular dis!.:: appear to bp .nade up of short, randomly
1090
The Journal of HAND SURGERY
Chidgey et al.
A
Fig. 8. A, Area outlined where histologic section was taken, representing central area of articular disk . B, Transverse histologic section of central area of articular disk. Collagen fibers appear short in length and are going in multiple directions. C, Transverse histologic section through articular disk, which cut through both very superficial layer (SL) and deeper layer (DL). The superficial layer of fibers has a more oriented pattern than the deeper layer. (Polarized light. Original magnification x 16.)
oriented collagen fiber bundles (Fig. 8, A and B). These bundles have an average width of up to 0.25 mm and appear banded . The periodicity of these bands ranges from 10 to 30 !J. in length along the bundle. Transverse sections taken through the very superficial layers of the TFCC have a much more oriented pattern (Fig. 8, C). The collagen fibers can be followed for 5 to 10 rnm, and the pattern corresponds to that produced by the india ink split lines (an arched pattern) . This agrees with the findings in studies of articular cartilage by the split-line technique in which the split-line patterns corresponded only to the superficial collagen fiber arrangement. 13 The fiber bundles can be followed for greater dis-
tances in the frontal section than in the transverse sections. The fibers of the articular disk appear to form a wave pattern that is more prominent on the frontal sections than on the sagittal sections (Figs. 9 and 10). Interspersed with bundles sectioned in profile are bundles sectioned closer to right angles and are thus viewed end on. The wave pattern on the frontal sections is much more pronounced in the immature specimens than in the adult specimens (Fig. II). The distinction between the superficial layer and the deeper fibers is also better defined in the immature specimens . This superficial layer averages 100 !J. in thickness and is much better defined at the radiocarpal joint surface than at the distal radioulnarjoint surface. Even in young adults,
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
1091
Fig. 9. A, Area outlined where histologic section was taken, representing central area of articular disk sectioned in frontal plane. B, Frontal histologic section of central area of articular disk. Collagen fibers can be followed for greater distances than on transverse sections and appear to form a wave pattern. RC jt, Radiocarpal joint space. (Polarized light. Original magnification x 2.5.)
there is histologic evidence of early fibrillation of the superficial layer on the distal radioulnar joint side, although this is not seen on gross inspection. Ulnarly, in the frontal sections the collagen fiber bun-
dles coalesce into a more parallel orientation and group themselves into two main bundles (Fig. 12). The bundles on the distal radioulnar joint side tum more proximally to continue as an insertion into the ulnar aspect
1092
Chidgey et al.
A Fig. 10. A, Area outlined where histologic section was taken, representing central area of articular disk sectioned in sagittal plane. B, Sagittal histologic section of central area of articular disk. Collagen fibers are oriented more horizontally than on the frontal sections but still appear to form a wave pattern. RC jt, Radiocarpal joint space. (Polarized light. Original magnification x 2.5.)
Fig. 11. Frontal histologic section of articular disk of immature specimen with radial attachment to left of photograph. Wave pattern of collagen fibers is more pronounced than in the adult. Superficial layer is also better defined in the immature specimens and averages 100 f-l. in thickness (between arroll's). RC it. Radiocarpal joint space. (Polarized light. Original magnification x 2.5.)
Histologic anatomy of triangular fibrocartilage
1093
Fig. 12. A, Area outlined where histologic section was taken, representing ulnar insertion area of TFCC sectioned in frontal plane. B, Frontal histologic section of ulnar insertion area of TFCC. Collagen fibers have a parallel orientation. Fibers in the lower portion of the photograph tum proximally and radially to insert into the ulnar head (UH). Distally, the ulnar styloid (US) is completely encompassed by the insertion of collagen fibers. Loose, vascular connective tissue separates these two areas of ulnar insertion (arrow). (Polarized light..Original magnification, X 2.5.)
of the ulnar head. This area of insertion into the ulnar head is separated by vascular loose connective tissue from the more distal fibers, which insert into the ulnar styloid. The ulnar styloid is completely encompassed
by the insertion of collagen fibers. Fibers continue distally to blend intimately with the sheath of the extensor carpi ulnaris (ECU) tendon and into the ulnar carpus. Fibers of the ulnocarpal ligaments blend intimately with
1094
Chidgey et al.
Fig. 13. Fibers of palmar ulnocarpal ligament (UC fig) interdigitate with palmar radioulnar ligament (RU fig). Some ulnocarpal ligament fibers can be traced into the peripheral aspects of the articular disk. (Polarized light. Original magnification, X 16.)
The Journal of HAND SURGERY
Fig. 14. Scanning electron micrograph of central area of articular disk. Collagen fibers are arranged in undulating sheets, which are layered at various angles to each other. (ArrolVs indicate direction of two different sheets oriented at 90 degrees to each other.) (Original magnification x 450.)
Fig. 15. Scanning electron micrograph of dorsal radioulnar ligament. The collagen fibers are arranged in bundles oriented in a parallel fashion and have a much more subtle, undulating pattern than the collagen fiber sheets of the central articular disk. (Original magnification x 450.)
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
...
.
1095
...
-
.. . ...
Fig. 16. Radioulnar ligaments and peripheral 15% to 20% of articular disk are well vascularized, (Histologic section of dorsal radioulnar ligament ; vessels filled with black india ink. Original magnification X 16.)
Fig. 17. Vessels in peripheral region of articular disk form arcades at junction of peripheral 20% (upper right of photograph) and central 80% (lower left of photograph) of articular disk. The vessels arc more dense along the ulnar aspects of the articular disk (where this section was made). (Original magnification x 8.)
the dorsal and palmar radioulnar ligament fibers in addition to sending some fibers into the more central articular disk (Fig. 13). Scanning electron microscopy. Scanning electron microscopy has added further insight into the collagen fiber arrangement within the TFCC. Histologic sections
represent a two-dimensional perspective of this threedimensional structure; SEM adds a three-dimensional perspective. The groups of collagen fibers in the central portion of the articular disk, which appear to represent bundles or cords on light microscopy sections , actually represent fibers arranged in sheets (Fig. 14). The sheets
The Journal of 1096
HAND SURGERY
Chidgey et af.
,.
Fig. 18. Section through central area of articular disk after vascular injection of india ink. No vessels could be identified in this region. (Original magnification x 16.)
Fig. 19. In addition to extrinsic contribution of blood vessels to peripheral aspects ofTFCC, vessels enter TFCC through foveal area of ulnar head (stained black with india ink). DRUJ, Distal radioulnar joint. (Original magnification x 8.)
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
1097
Fig. 20. Wave pauern of articular disk collagen fibers as suggested by Hofmann." In the frontal plane, fibers make relatively steep angles radially and become more horizontal ulnarly (solid line). In the sagittal plane, fibers course in a wave pattern from dorsal to palmar (dashed line). This creates an interweaving of fibers similar to that found in a wicker basket.
have an undulating or crimped pattern. The distance between the peaks and troughs of the waves within these sheets ranges from 10 to 30 1-1. This corresponds to the periodic banding of the collagen observed under polarized light . The sheets arc arranged in layers at various angles to each other. Some are at oblique angles, and others are at 90-degree angles. Freeze-fracturing allows examination of these sheets over a distance of only several millimeters within the midsubstance of the TFCC. These sheets vary in width up to 0.25 mm or more. The dorsal and palmar radioulnar ligaments have collagen fibers arranged in bundles that arc oriented in a parallel fashion (Fig. 15). These bundles have a much more subtle undulating pattern than the collagen fiber sheets of the central articular disk . The distance between the peaks of the radiouln ar ligament waves is approximtely twice that found in the articular disk. Vascular study. The specimens injected with india ink demonstrate vessels entering the peripheral aspects of the TFCC. The dorsal and palmar radioulnar ligaments are well vascularized, as is the peripheral 15% to 20% of the articular disk (Fig. 16). The vessels in the peripheral regions of the articular disk form arcades or blind loops, which are more dense on the ulnar aspect
of the disk (Fig. 17). The more central area of the disk is avascular (Fig. 18). No blood vessels can be identified entering the articular disk from the radius. In addition to the vessels entering from the peripheral aspects of the TFCC, another important vascular contribution is through the foveal area of the ulnar head (Fig. 19). Vessels can be demonstrated coming from the interosseous aspects of the ulnar head and entering the TFCC at its site of insertion. These branches from the ulnar head also contribute blood vessels to the loose connective tissue (ligamentum subcrucntum) found between the ulnar head and the ulnar styloid insertion sites of the TFCC. Discussion Kauer, 14 using serial histologic sections, has reviewed the embryonic and fetal development of the TFCC. In the earliest stages, the TFCC is represented by a mesenchyrnal cell mass between the ulnar edge of the developing radius and the styloid process of the ulna (still in contact with the triquetrum). The withdrawal of the ulnar styloid process from the triquetrum corresponds with the development of the prestyloid recess (an invagination of the radiocarpal joint). Two insertion areas develop into the ulna-the ulnar aspect of the ulnar
1098
Chidgey et
at.
The Journal of HAND SURGERY
Fig. 21. Collagen fiber arrangement is very different between fibrocartilaginous articular disk (A) and hyaline cartilage of articular surface of distal radius (8). In the distal radius cartilage, fibers are arranged longitudinally and directed from the subchondral bone out to the articular surface (arrow indicates direction from subchondral bone out to the articular surface) with oblique interconnections between adjacent fibrils. (Scanning electron micrograph. Original magnification X 3000.)
head and the styloid process. The area between the two insertion sites is filled with vascular loose connective tissue, which represents the anterior aspect of the prestyloid recess. Henle" has called this area of loose connective tissue the ligamentum subcruentum. In addition to the development of other areas of insertion into the ulna carpus, the sheath of the ECU tendon develops as a part of the fibrous system of the TFCC. This deep layer of the antebrachial fascia is separated from the superficial layer. These two layers have also been referred to as the ECU subsheath and the extensor retinaculum, respectively." This embryologic study emphasizes the ECU tendon sheath as part of the TFCC. Hofmann 17 examined the collagen arrangement in the central area of the TFCC by means of polarized light microscopy. He identified a central pattern of short,
multidirectional fibers and suggested that these represent much longer fiber bundles passing in and out of the plane of section. Hofmann suggested that in the frontal plane the individual bundles course in a sine wave pattern, making relatively steep angles radially and becoming more horizontal ulnarly (Fig. 20). In the sagittal plane, fibers course in a similar wave pattern in a dorsal to palmar direction. With fiber bundles arrayed in both the frontal and sagittal planes, an interweaving of fibers similar to that found in a wicker basket is created. Scanning electron microscopy shows that the collagen fibers in the articular disk arc arranged in sheets instead of cords. The length of these sheets and the course that they outline through the articular disk substance cannot be determined with this technique. There-
Vol. 16A, No.6 November 1991
fore we cannot confirm that these fibers course the entire length of the TFCC. The small undulations or crimping within the individual sheets of collagen fibers (10 to 30 Jl. in length) should not be confused with the larger waves suggested by Hofmann, which course the entire thickness of the TFCC (1 to 3 mm). An undulating or crimped pattern of collagen fiber bundles has been found in tendon. This pattern is similar to that found in the collagen fiber sheets of the articular disk and the fiber bundles of the radioulnar ligaments." When tendon is exposed to physiologic loads, the collagen bundles are stretched into a more parallel pattern. Once the loads are removed from tendon, the crimped pattern returns. It has been suggested that these crimps in the fiber bundles have a shock-absorbing function when sudden stresses are applied to the tendon." The collagen pattern under physiologic loads within the TFCC has not been examined, so it is premature to postulate a shock-absorbing function forthe undulations within this area. There is a dramatic contrast in the collagen arrangement of the fibrocartilaginous articular disk as compared with the hyaline cartilage of the articular surface of the distal radius (Fig. 21). Like articular cartilage elsewhere in the body, the collagen arrangement within the distal radius cartilage demonstrates a longitudinal arrangement of fibers directed from the subchondral bone out to the articular surface with oblique interconnections between adjacent fibrils.": 19.20 With ground substance filling the interspaces, this creates a three-dimensional meshwork of fibrils well suited biomechanically to serve in a compression mode." Although no study has measured the forces within the articular disk during radiocarpal loading and forearm rotation, studies have shown that compressive loads are transmitted across the articular disk to the ulna" and that the dorsal and palmar radioulnar ligaments are under tension during full supination and full pronation." The collagen arrangement of the articular disk is suggestive of a structure experiencing tension and shear forces in addition to compressive loads. The fiber patttem in the two immature specimens was different from that in the adult specimens. Conclusions cannot be drawn from observations in only two specimens, and further study will be needed to define age-related differences in the collagen fiber arrangement. No histochemical studies of the TFCC have been published. The collagen types, as well as the composition of the ground substance, are as yet undefined. The extrinsic and internal blood supply of the TFCC has been examined by Thiru-Pathi et a1.2~ The TFCC
Ilistologic anatomy of triangular fibrocartilage
1099
receives its blood supply from the dorsal and palmar radiocarpal branches of the ulnar artery as well as from the dorsal and palmar branches of the anterior interosseous artery. Our findings confirm good vascularity in the peripheral radioulnar ligaments as well as in the peripheral 20% of the articular disk. As in the study by Thiru-Pathi et aI., 24 no vessels could be demonstrated in the more central area and no vessels were seen entering the articular disk from the radial attachment. Palmer has developed a classification system for TFCC injuries that deals with injuries involving the entire TFCC. Within the subcategory of lesions involving the central articular disk, we have documented several recurring tear patterns. 25 Thus far, five different tear patterns of the articular disk have been identified.. The most common (61 % of tears) is a linear tear originating from the radiopalmar angle and extending dorsally for a variable distance. Tears have always been located several millimeters from the ulnar edge of the radius. The second most common tear (23%) is a central, irregular, stellate lesion . The third tear pattern (6%) has been found in patients with rheumatoid arthritis. These tears are very large and centrally located, completely obliterating the articular disk. The fourth type of tear (6%) extends palmarly from the radiodorsal angIe. As in the first type of tear, it has always been located several millimeters from the margin of the radius. The fifth type of tear has been found in only 2% of wrists; these characteristically are short , ulnar-dorsal linear tears that parallel the dorsal radioulnar ligament. Of the five types of articular disk tear in our study, types I, 4, and 5 were believed to represent traumatic tears, while types 2 and 3 were thought to be degenerative tears. Type 2 and 3 tears characteristically were irregular and frayed along the tear margin, suggesting chronicity. Patients with type I, 4, and 5 tears had histories of trauma and a tear pattern that was linear with minimal fraying at the tear margin. Two of the three traumatic tear patterns that we found arthroscopically were within 2 mm from the ulnar edge of the radius. The location of the tears suggested that they occurred between the junction of the short, radially oriented fibers and the remainder of the articular disk. These short, thick fibers, 1 to 2 mm in length, may prevent direct avulsion of the articular disk from the radius.
Summary Histologic examination of the TFCC reveals parallel, longitudinally oriented collagen fibers peripherally whereas the more central articular disk is made up of
BOO
The Journal of HAND SURGERY
Chidgey et al.
interweaving obliquely oriented sheets of collagen fibers. This arrangement suggests a peripheral region subjected to tensile loads between the region of origin from the radius and the area of insertion into the ulna. The fiber orientation in the central region is more compatible with a structure subjected to multidirectional stresses. The articular disk origin from the radius is reinforced by collagen bundles projecting out from the radius for I to 2 mm. Many traumatic tears are oriented parallel to the radial origin of the TFCC and are located approximately I to 2 mm from the site of origin. This corresponds to the junction of the short, radially oriented fibers and the remainder of the articular disk. The inner 80% of the articular disk is avascular, as is its radial attachment. Traumatic tears in this region would have a low healing potential unless some method of introducing additional vascularity, such as reattachment through drill holes in the radius to allow neovascularization of this otherwise avascular region, were undertaken. REFERENCES I. Palmer AK. The distal radioulnar joint: anatomy, biomechanics, and triangular fibrocartilage complex abnormalities. Hand Clin 1987;3:31-40. 2. Menon J, Wood VE, Schoene HR, Frykman GK, Hohl JC, Bestard EA. Isolated tears of the triangular fibrocartilage of the wrist: results of partial excision. J HAND SURG 1984;9A:527-30. 3. Palmer AK. Triangular fibrocartilage complex lesions: a classification. J HAND SURG 1989;14A:594-606. 4. Imbriglia JE, Boland DS. Tears of the articular disc of the triangular fibrocartilage complex and results of excision of the articular disc. J HAND SURG 1983;8: 620. 5. Aspden RM, Yarker YE, Hukins DWL. Collagen orientations in the meniscus of the knee joint. J Anat 1985;140:371-80. 6. Bullough PG, Munuera L, Murphy J, Weinstein AM. The strength of the menisci of the knee as it relates to their fine structure. J Bone Joint Surg 1970;52B:564-70. 7. Broom ND. Abnormal softening in articular cartilage. Arthritis Rheum 1982;25:1209-16. 8. Bullough P, Goodfellow J. The significance of the fine structure of articular cartilage. J Bone Joint Surg 1968;50B:852-7. 9. Broom ND. Further insights into the structural principles
10.
I I.
12. 13.
14. 15.
16.
17. 18.
19. 20.
21.
22. 23.
24.
25.
governing the function of articular cartilage. J Anat 1984;139:275-94. O'Connor P, Bland C, Bjelle A, Gardner DL. Production of split patterns on the articular cartilage surface of rats. J PathoI 1980;130:15-21. Meachim G, Denham D, Emery IH, Wildinson PH. Collagen alignments and artificial splits at the surface of human articular cartilage. J Anat 1974;118:101-18. Gelberman RH, Menon J. The vascularity of the scaphoid bone. J HAND SURG 1980;5:508-13. O'Connor P, Bland C, Gardner DL. Fine structure of artificial splits in femoral condylar cartilage of the rat: a scanning electron microscopic study. J Pathol 1980;132:169-79. Kauer JMG. The articular disc of the hand. Acta Anat 1975;93:590-605. Henle J. Handbuch der Banderlehre des Menschen. In: Handbuch der systematischen Anatomie des Menschen. vol. 1. Braunschweig: Vieweg, 1856. Palmer AK, Skahen JR, Werner FW, Glisson RR. The extensor retinaculum of the wrist: an anatomical and biomechanical study. J HAND SURG 1985; lOB:I I. Hofmann S. Der Bau des Discus Articularis Articulationis Radio-ulnaris Distalis. Anat Anz 1959; I06: 173-85. Diamant J, Keller A, Baer E, Lilt M, Arridge RGC. Collagen; ultrastructure and its relation to mechanical properties as a function of ageing. Proc R Soc Lond 1972;180:293-315. Minn RJ, Steven FS. The collagen fibril organization in human articular cartilage. J Anat 1977;123:437-57. Broom ND, Marra DL. Ultrastructural evidence for fibrilto-fibril associations in articular cartilage and their functional implication. J Anat 1986;146:185-200. Broom ND, Marra DL. New structural concepts of articular cartilage demonstrated with a physical model. Connect Tissue Res 1985;14:1-8. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin OrthopI984;187:26-35. Af Ekenstam F, Hagert CoG. Anatomical studies on the geometry and stability of the distal radioulnar joint. Scand J Plast Reconstr Surg 1985;19:17-25. Thiru-Pathi RG, Ferlic DC, Clayton ML, McClure DC. Arterial anatomy of the triangular fibrocartilage of the wrist and its surgical significance. J HAND SURG 1986;IIA:258-63. Chidgey LK, Dell PC, Bittar E, Spanier S, Hermansdorfer JD. Tear patterns and collagen arrangement in the triangular fibrocartilage. J HAND SURG 1990;15A: 826.
Larry K. Chidgey, MD, Paul C. Dell, MD, Edward S. Bittar, MD, PhD, and Susan S. Spanier, MD, Gainesville, Fla.
Pathologic conditions involving the triangular fibrocartilage complex (TFCC) have been well documented as a cause of ulnar wrist pain.!" In both diagnosis and treatment, a thorough understanding of the normal anatomy of this complex region of the wrist is fundamental. This includes not only the gross anatomy (at the macroscopic level) but also the fine structure (at the microscopic level). An understanding of the functional anatomy is especially strengthened by a study of the collagen fiber arrangement. Collagen fibers withstand tensile stress and arrange themselves along tension lines within connective tissue. Study of the meniscus in the knee has shown a hoop arrangement of collagen fibers with radially oriented reinforcing fibersv" and has contributed to an understanding of the pathomechanics of meniscal tears . Similarly, study of the collagen fiber arrangement in articular cartilage has contributed to an understanding of normal load transfer in joints and the patterns of joint surface degenerative changes. 7-9 Our study examines the
From the University of Florida , Department of Orthopaedics, Gainesville, Fla. Received for publication April 2, 1991; accepted in revised form April 24, 1991. No benefits in any form have been received .or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Larry K. Chidgey, MD, University of Florida, College of Medicine, Department of Orthopaedics, Bolt )·246, JHM Health Center, Gainesville, FL 32610 . 3/1/30880
1084
TilE JOURNAL OF llANO SURGERY
fine structural anatomy of the TFCC with special attention to the collagen fiber arrangement.
Materials and methods A total of20 fresh cadaver wrists were used. Eighteen of the wrists were from adults (age range, 23 to 52 years) and two were from children (IO and 13 years of age). Specimens were excluded if disease of the TFCC was noted on direct inspection or if bone disease was detected radiographically. Fourteen specimens (12 adults, 2 children) were studied with the light microscope and three with the electron microscope. In five specimens the vascular anatomy was studied by means of india ink injection. Two of the india ink-injected specimens were also sectioned and studied with the light microscope. Before sectioning, the surface structure was examined in six (four adults and two children) of the 14 light microscopy specimens by the split-line technique." When cartilage is pricked with a sharp, round pin, the corresponding defect in the surface layer is typically not a round hole but a longitudinal split. The direction of the split is characteristic for a particular area of cartilage and is reproducible. If the pin is charged with india ink, the split is stained and easily visible. The direction of the split is believed to correspond to the orientation of the superficial arrangement of the collagen fibers, with the split representing a separation between adjacent fiber bundles. This technique has been applied most commonly to hyaline articular cartilage in the hip and knee." 10. II With the radiocarpal joint disarticulated, multiple split lines were made in the artie-
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
Fig. 1. India ink-stained split lines of scaphoid fossa (SF) of radius are oriented primarily in flexion/extension direction. Split lines of the lunate fossa (LF) have a similar orientation radially, but ulnarly they radiate out from the base of the fossa. In the adult, the split lines of the central area of the TFCC where it originates from the radius (arrow) are oriented almost 90 degrees to the split lines of the lunate fossa of the radius. Peripheral to this central area the split lines form a series of arches originating from the dorsal and palmar ulnar aspects of the radius and arch toward the ulnar insertion.
p 1m r Fig. 2. Split lines in immature specimens flow smoothly from lunate fossa (LF) into TFCC without abrupt change in direction seen in adult. (Arrow indicates site of origin of TFCC from the radius).
1085
1086
The Journal of HAND SURGERY
Chidgey et al.
Fig, 3. Whcn viewed from the distal radioulnar joint side. the split lines of the sigmoid notch (SN) are oriented along the frontal plane. An abrupt change in split-line orientation occurs at the area of origin of the TFCC (black arrow); the central area lines are oriented in the dorsal/palmar direction, and the peripheral lines arch toward thc ulnar insertion . The ulnar head (UH) has been rellected to the right of the photograph to visualize the undersurface of the TFCC. D. Dorsal; P, palmar.
"
~
...
~ r
, .
t
Fig. 4. Section from central articular disk area of TFCC has high collagen matrix/cell ratio. Sections from other areas of the TFCC have a similar matrix/cell ratio. Fibers of elastin (stained black with Verhoeff's stain) arc sparsely scattered throughout {arrows}. (Original magnification X 16.)
ular surface of the radius and the TFCC. The distal ulna was then cut just proximal to the distal radioulnar joint and pivoted away from the radius to open up the distal radioulnar joint. Multiple split lines were made in the radial and ulnar articular surfaces of the distal part of the radioulnar joint as well as the proximal surface of the TFCC. Of the 14 specimens studied with the light microscope, 12 were sectioned serially and stained with hematoxylin and eosin for study by standard and polarized light microscopy. Seven of these specimens were sectioned in the transverse plane, three in the sagittal plane, and two in the frontal plane. Two specimens were sectioned and stained with Verhoeff 's stain for elastin; one was sectioned in the transverse plane and one in the frontal plane. Three specimens were examined with the scanning electron microscope (SEM) to further define the collagen patterns. Specimens were fixed in 2% glutaraldehyde for 2 hours and then dehydrated through serial concentrations of ethanol. Dehydration was followed by freeze-fracturing in liquid nitrogen, immersion in hexamethyldisilazane, and critical-point drying. The fracture surfaces were then sputter-coated with gold and examined with the SEM at 20 kV. Five of the specimens were injected with india ink before sectioning to delineate the vascularity. The brachial artery was cannulated above the elbow, and ap-
Vol. 16A, No.6 November 1991
Histologic anatomy of trial/gular fibrocartilage
1087
Fig. 5. A, Area ofTFCC outlined wherc histologic section was taken , representing junction between dorsal radioulnar ligament and articular disk . B, Transverse histologic section of junction between dorsal radioulnar ligament (top half of photograph) and articular disk (bottom half of photograph) . (Polarized light. Orig inal magnification x 16.)
proximately 3000 ml of a 40%/60% mixture of india ink and normal saline solution was injected. The TFCC was then removed in two of the specimens, sectioned, and stained with hematoxylin and eosin . The other three specimens were cleared by the Spalteholz technique." Results Surface structure. When viewed from the radio carpal joint side, the split lines of the scaphoid fossa of the radius are oriented primarily in the flexion 1extension direction (Fig . I). Split lines of the lunate fossa have a similar orientation radially, but ulnarlyjhey have a sunburst or radiating pattern out from the base of the fossa . In the adult , the split lines of the central area of the TFCC, where it originates from the radius, are oriented almost 90 degrees to the split lines of the lunate fossa of the radius. Moving out from this central area , the split lines form a series of arches that originate from the dorsal and palmar ulnar aspects of the radius. The split-line pattern in immature specimens appears to be
different from that in the adult, although only a small number of immature specimens (1/ = 2) have been studied (Fig. 2). The split lines flow smoothly from the lunate fossa into the TFCC without the abrupt change in direction seen in the adult . When viewed from the distal radioulnar joint side , the split lines of the sigmoid notch are oriented along the frontal plane (Fig. 3). An abrupt change in splitline orientation once again occurs at the area of origin of the TFCC; the central area lines are oriented in the dorsal/palmardirection wherea s the lines bordering the central area arch toward the ulnar insertion. On the distal radioulnar joint side, as on the radiocarpal side, the immature specimens have a smoother transition between the radius articular cartil age and the TFCC than do the adult specimens. Light microscopy. Hematoxylin and eosin-stained sections of the TFCC show a high collagen matrix 1cell ratio (Fig. 4). Compared to the adjacent articular cartilage of the distal radius, there is also a high col-
The Journal of 1088
Chidgey et af.
HAND SURGERY
Fig. 6. A, Area outlined where histologic section was taken, representing origin of dorsal radioulnar ligament from radius. B, Transverse histologic section of radial origin of dorsal radioulnar ligament demonstrating longitudinal orientation of collagen fibers. (Polarized light. Original magnification x 16.)
lagen I ground substance ratio within the articular disk region of the TFCC. Fibers of elastin are sparsely scattered throughout, with no difference in concentration of elastin fibers in different regions of the TFCC (Fig. 4).
Examination of histologic sections under polarized light enhances visualization of the collagen fibers. Although not well delineated in gross specimens or in sections stained with hematoxylin and eosin , under polarized light a clear distinction between the dorsal and
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
1089
Fig. 7. A, Area outlined where histologic section was taken. representing origin of articular disk from radius. B, Transverse histologic section of radial origin of articular disk. Short, thick fibers extend from the radius (left side of photograph) into the articular disk (right side of photograph). (Polarized light. Original magnification x 16.)
palmar radioulnar ligaments can be made from the more central articular disk (Fig. 5). The radioulnar ligaments are formed by longitudinally oriented collagen fiber bundles originating from the dorsal and palmar aspects of the sigmoid notch of the radius and insert onto the
ulna (Fig. 6). The area of origin of the central articular disk has thick collagen bundles projecting from the radius into the TFCC for I to 2 mm (Fig. 7). On transverse sections, the more central aspects of the articular dis!.:: appear to bp .nade up of short, randomly
1090
The Journal of HAND SURGERY
Chidgey et al.
A
Fig. 8. A, Area outlined where histologic section was taken, representing central area of articular disk . B, Transverse histologic section of central area of articular disk. Collagen fibers appear short in length and are going in multiple directions. C, Transverse histologic section through articular disk, which cut through both very superficial layer (SL) and deeper layer (DL). The superficial layer of fibers has a more oriented pattern than the deeper layer. (Polarized light. Original magnification x 16.)
oriented collagen fiber bundles (Fig. 8, A and B). These bundles have an average width of up to 0.25 mm and appear banded . The periodicity of these bands ranges from 10 to 30 !J. in length along the bundle. Transverse sections taken through the very superficial layers of the TFCC have a much more oriented pattern (Fig. 8, C). The collagen fibers can be followed for 5 to 10 rnm, and the pattern corresponds to that produced by the india ink split lines (an arched pattern) . This agrees with the findings in studies of articular cartilage by the split-line technique in which the split-line patterns corresponded only to the superficial collagen fiber arrangement. 13 The fiber bundles can be followed for greater dis-
tances in the frontal section than in the transverse sections. The fibers of the articular disk appear to form a wave pattern that is more prominent on the frontal sections than on the sagittal sections (Figs. 9 and 10). Interspersed with bundles sectioned in profile are bundles sectioned closer to right angles and are thus viewed end on. The wave pattern on the frontal sections is much more pronounced in the immature specimens than in the adult specimens (Fig. II). The distinction between the superficial layer and the deeper fibers is also better defined in the immature specimens . This superficial layer averages 100 !J. in thickness and is much better defined at the radiocarpal joint surface than at the distal radioulnarjoint surface. Even in young adults,
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
1091
Fig. 9. A, Area outlined where histologic section was taken, representing central area of articular disk sectioned in frontal plane. B, Frontal histologic section of central area of articular disk. Collagen fibers can be followed for greater distances than on transverse sections and appear to form a wave pattern. RC jt, Radiocarpal joint space. (Polarized light. Original magnification x 2.5.)
there is histologic evidence of early fibrillation of the superficial layer on the distal radioulnar joint side, although this is not seen on gross inspection. Ulnarly, in the frontal sections the collagen fiber bun-
dles coalesce into a more parallel orientation and group themselves into two main bundles (Fig. 12). The bundles on the distal radioulnar joint side tum more proximally to continue as an insertion into the ulnar aspect
1092
Chidgey et al.
A Fig. 10. A, Area outlined where histologic section was taken, representing central area of articular disk sectioned in sagittal plane. B, Sagittal histologic section of central area of articular disk. Collagen fibers are oriented more horizontally than on the frontal sections but still appear to form a wave pattern. RC jt, Radiocarpal joint space. (Polarized light. Original magnification x 2.5.)
Fig. 11. Frontal histologic section of articular disk of immature specimen with radial attachment to left of photograph. Wave pattern of collagen fibers is more pronounced than in the adult. Superficial layer is also better defined in the immature specimens and averages 100 f-l. in thickness (between arroll's). RC it. Radiocarpal joint space. (Polarized light. Original magnification x 2.5.)
Histologic anatomy of triangular fibrocartilage
1093
Fig. 12. A, Area outlined where histologic section was taken, representing ulnar insertion area of TFCC sectioned in frontal plane. B, Frontal histologic section of ulnar insertion area of TFCC. Collagen fibers have a parallel orientation. Fibers in the lower portion of the photograph tum proximally and radially to insert into the ulnar head (UH). Distally, the ulnar styloid (US) is completely encompassed by the insertion of collagen fibers. Loose, vascular connective tissue separates these two areas of ulnar insertion (arrow). (Polarized light..Original magnification, X 2.5.)
of the ulnar head. This area of insertion into the ulnar head is separated by vascular loose connective tissue from the more distal fibers, which insert into the ulnar styloid. The ulnar styloid is completely encompassed
by the insertion of collagen fibers. Fibers continue distally to blend intimately with the sheath of the extensor carpi ulnaris (ECU) tendon and into the ulnar carpus. Fibers of the ulnocarpal ligaments blend intimately with
1094
Chidgey et al.
Fig. 13. Fibers of palmar ulnocarpal ligament (UC fig) interdigitate with palmar radioulnar ligament (RU fig). Some ulnocarpal ligament fibers can be traced into the peripheral aspects of the articular disk. (Polarized light. Original magnification, X 16.)
The Journal of HAND SURGERY
Fig. 14. Scanning electron micrograph of central area of articular disk. Collagen fibers are arranged in undulating sheets, which are layered at various angles to each other. (ArrolVs indicate direction of two different sheets oriented at 90 degrees to each other.) (Original magnification x 450.)
Fig. 15. Scanning electron micrograph of dorsal radioulnar ligament. The collagen fibers are arranged in bundles oriented in a parallel fashion and have a much more subtle, undulating pattern than the collagen fiber sheets of the central articular disk. (Original magnification x 450.)
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
...
.
1095
...
-
.. . ...
Fig. 16. Radioulnar ligaments and peripheral 15% to 20% of articular disk are well vascularized, (Histologic section of dorsal radioulnar ligament ; vessels filled with black india ink. Original magnification X 16.)
Fig. 17. Vessels in peripheral region of articular disk form arcades at junction of peripheral 20% (upper right of photograph) and central 80% (lower left of photograph) of articular disk. The vessels arc more dense along the ulnar aspects of the articular disk (where this section was made). (Original magnification x 8.)
the dorsal and palmar radioulnar ligament fibers in addition to sending some fibers into the more central articular disk (Fig. 13). Scanning electron microscopy. Scanning electron microscopy has added further insight into the collagen fiber arrangement within the TFCC. Histologic sections
represent a two-dimensional perspective of this threedimensional structure; SEM adds a three-dimensional perspective. The groups of collagen fibers in the central portion of the articular disk, which appear to represent bundles or cords on light microscopy sections , actually represent fibers arranged in sheets (Fig. 14). The sheets
The Journal of 1096
HAND SURGERY
Chidgey et af.
,.
Fig. 18. Section through central area of articular disk after vascular injection of india ink. No vessels could be identified in this region. (Original magnification x 16.)
Fig. 19. In addition to extrinsic contribution of blood vessels to peripheral aspects ofTFCC, vessels enter TFCC through foveal area of ulnar head (stained black with india ink). DRUJ, Distal radioulnar joint. (Original magnification x 8.)
Vol. 16A, No.6 November 1991
Histologic anatomy of triangular fibrocartilage
1097
Fig. 20. Wave pauern of articular disk collagen fibers as suggested by Hofmann." In the frontal plane, fibers make relatively steep angles radially and become more horizontal ulnarly (solid line). In the sagittal plane, fibers course in a wave pattern from dorsal to palmar (dashed line). This creates an interweaving of fibers similar to that found in a wicker basket.
have an undulating or crimped pattern. The distance between the peaks and troughs of the waves within these sheets ranges from 10 to 30 1-1. This corresponds to the periodic banding of the collagen observed under polarized light . The sheets arc arranged in layers at various angles to each other. Some are at oblique angles, and others are at 90-degree angles. Freeze-fracturing allows examination of these sheets over a distance of only several millimeters within the midsubstance of the TFCC. These sheets vary in width up to 0.25 mm or more. The dorsal and palmar radioulnar ligaments have collagen fibers arranged in bundles that arc oriented in a parallel fashion (Fig. 15). These bundles have a much more subtle undulating pattern than the collagen fiber sheets of the central articular disk . The distance between the peaks of the radiouln ar ligament waves is approximtely twice that found in the articular disk. Vascular study. The specimens injected with india ink demonstrate vessels entering the peripheral aspects of the TFCC. The dorsal and palmar radioulnar ligaments are well vascularized, as is the peripheral 15% to 20% of the articular disk (Fig. 16). The vessels in the peripheral regions of the articular disk form arcades or blind loops, which are more dense on the ulnar aspect
of the disk (Fig. 17). The more central area of the disk is avascular (Fig. 18). No blood vessels can be identified entering the articular disk from the radius. In addition to the vessels entering from the peripheral aspects of the TFCC, another important vascular contribution is through the foveal area of the ulnar head (Fig. 19). Vessels can be demonstrated coming from the interosseous aspects of the ulnar head and entering the TFCC at its site of insertion. These branches from the ulnar head also contribute blood vessels to the loose connective tissue (ligamentum subcrucntum) found between the ulnar head and the ulnar styloid insertion sites of the TFCC. Discussion Kauer, 14 using serial histologic sections, has reviewed the embryonic and fetal development of the TFCC. In the earliest stages, the TFCC is represented by a mesenchyrnal cell mass between the ulnar edge of the developing radius and the styloid process of the ulna (still in contact with the triquetrum). The withdrawal of the ulnar styloid process from the triquetrum corresponds with the development of the prestyloid recess (an invagination of the radiocarpal joint). Two insertion areas develop into the ulna-the ulnar aspect of the ulnar
1098
Chidgey et
at.
The Journal of HAND SURGERY
Fig. 21. Collagen fiber arrangement is very different between fibrocartilaginous articular disk (A) and hyaline cartilage of articular surface of distal radius (8). In the distal radius cartilage, fibers are arranged longitudinally and directed from the subchondral bone out to the articular surface (arrow indicates direction from subchondral bone out to the articular surface) with oblique interconnections between adjacent fibrils. (Scanning electron micrograph. Original magnification X 3000.)
head and the styloid process. The area between the two insertion sites is filled with vascular loose connective tissue, which represents the anterior aspect of the prestyloid recess. Henle" has called this area of loose connective tissue the ligamentum subcruentum. In addition to the development of other areas of insertion into the ulna carpus, the sheath of the ECU tendon develops as a part of the fibrous system of the TFCC. This deep layer of the antebrachial fascia is separated from the superficial layer. These two layers have also been referred to as the ECU subsheath and the extensor retinaculum, respectively." This embryologic study emphasizes the ECU tendon sheath as part of the TFCC. Hofmann 17 examined the collagen arrangement in the central area of the TFCC by means of polarized light microscopy. He identified a central pattern of short,
multidirectional fibers and suggested that these represent much longer fiber bundles passing in and out of the plane of section. Hofmann suggested that in the frontal plane the individual bundles course in a sine wave pattern, making relatively steep angles radially and becoming more horizontal ulnarly (Fig. 20). In the sagittal plane, fibers course in a similar wave pattern in a dorsal to palmar direction. With fiber bundles arrayed in both the frontal and sagittal planes, an interweaving of fibers similar to that found in a wicker basket is created. Scanning electron microscopy shows that the collagen fibers in the articular disk arc arranged in sheets instead of cords. The length of these sheets and the course that they outline through the articular disk substance cannot be determined with this technique. There-
Vol. 16A, No.6 November 1991
fore we cannot confirm that these fibers course the entire length of the TFCC. The small undulations or crimping within the individual sheets of collagen fibers (10 to 30 Jl. in length) should not be confused with the larger waves suggested by Hofmann, which course the entire thickness of the TFCC (1 to 3 mm). An undulating or crimped pattern of collagen fiber bundles has been found in tendon. This pattern is similar to that found in the collagen fiber sheets of the articular disk and the fiber bundles of the radioulnar ligaments." When tendon is exposed to physiologic loads, the collagen bundles are stretched into a more parallel pattern. Once the loads are removed from tendon, the crimped pattern returns. It has been suggested that these crimps in the fiber bundles have a shock-absorbing function when sudden stresses are applied to the tendon." The collagen pattern under physiologic loads within the TFCC has not been examined, so it is premature to postulate a shock-absorbing function forthe undulations within this area. There is a dramatic contrast in the collagen arrangement of the fibrocartilaginous articular disk as compared with the hyaline cartilage of the articular surface of the distal radius (Fig. 21). Like articular cartilage elsewhere in the body, the collagen arrangement within the distal radius cartilage demonstrates a longitudinal arrangement of fibers directed from the subchondral bone out to the articular surface with oblique interconnections between adjacent fibrils.": 19.20 With ground substance filling the interspaces, this creates a three-dimensional meshwork of fibrils well suited biomechanically to serve in a compression mode." Although no study has measured the forces within the articular disk during radiocarpal loading and forearm rotation, studies have shown that compressive loads are transmitted across the articular disk to the ulna" and that the dorsal and palmar radioulnar ligaments are under tension during full supination and full pronation." The collagen arrangement of the articular disk is suggestive of a structure experiencing tension and shear forces in addition to compressive loads. The fiber patttem in the two immature specimens was different from that in the adult specimens. Conclusions cannot be drawn from observations in only two specimens, and further study will be needed to define age-related differences in the collagen fiber arrangement. No histochemical studies of the TFCC have been published. The collagen types, as well as the composition of the ground substance, are as yet undefined. The extrinsic and internal blood supply of the TFCC has been examined by Thiru-Pathi et a1.2~ The TFCC
Ilistologic anatomy of triangular fibrocartilage
1099
receives its blood supply from the dorsal and palmar radiocarpal branches of the ulnar artery as well as from the dorsal and palmar branches of the anterior interosseous artery. Our findings confirm good vascularity in the peripheral radioulnar ligaments as well as in the peripheral 20% of the articular disk. As in the study by Thiru-Pathi et aI., 24 no vessels could be demonstrated in the more central area and no vessels were seen entering the articular disk from the radial attachment. Palmer has developed a classification system for TFCC injuries that deals with injuries involving the entire TFCC. Within the subcategory of lesions involving the central articular disk, we have documented several recurring tear patterns. 25 Thus far, five different tear patterns of the articular disk have been identified.. The most common (61 % of tears) is a linear tear originating from the radiopalmar angle and extending dorsally for a variable distance. Tears have always been located several millimeters from the ulnar edge of the radius. The second most common tear (23%) is a central, irregular, stellate lesion . The third tear pattern (6%) has been found in patients with rheumatoid arthritis. These tears are very large and centrally located, completely obliterating the articular disk. The fourth type of tear (6%) extends palmarly from the radiodorsal angIe. As in the first type of tear, it has always been located several millimeters from the margin of the radius. The fifth type of tear has been found in only 2% of wrists; these characteristically are short , ulnar-dorsal linear tears that parallel the dorsal radioulnar ligament. Of the five types of articular disk tear in our study, types I, 4, and 5 were believed to represent traumatic tears, while types 2 and 3 were thought to be degenerative tears. Type 2 and 3 tears characteristically were irregular and frayed along the tear margin, suggesting chronicity. Patients with type I, 4, and 5 tears had histories of trauma and a tear pattern that was linear with minimal fraying at the tear margin. Two of the three traumatic tear patterns that we found arthroscopically were within 2 mm from the ulnar edge of the radius. The location of the tears suggested that they occurred between the junction of the short, radially oriented fibers and the remainder of the articular disk. These short, thick fibers, 1 to 2 mm in length, may prevent direct avulsion of the articular disk from the radius.
Summary Histologic examination of the TFCC reveals parallel, longitudinally oriented collagen fibers peripherally whereas the more central articular disk is made up of
BOO
The Journal of HAND SURGERY
Chidgey et al.
interweaving obliquely oriented sheets of collagen fibers. This arrangement suggests a peripheral region subjected to tensile loads between the region of origin from the radius and the area of insertion into the ulna. The fiber orientation in the central region is more compatible with a structure subjected to multidirectional stresses. The articular disk origin from the radius is reinforced by collagen bundles projecting out from the radius for I to 2 mm. Many traumatic tears are oriented parallel to the radial origin of the TFCC and are located approximately I to 2 mm from the site of origin. This corresponds to the junction of the short, radially oriented fibers and the remainder of the articular disk. The inner 80% of the articular disk is avascular, as is its radial attachment. Traumatic tears in this region would have a low healing potential unless some method of introducing additional vascularity, such as reattachment through drill holes in the radius to allow neovascularization of this otherwise avascular region, were undertaken. REFERENCES I. Palmer AK. The distal radioulnar joint: anatomy, biomechanics, and triangular fibrocartilage complex abnormalities. Hand Clin 1987;3:31-40. 2. Menon J, Wood VE, Schoene HR, Frykman GK, Hohl JC, Bestard EA. Isolated tears of the triangular fibrocartilage of the wrist: results of partial excision. J HAND SURG 1984;9A:527-30. 3. Palmer AK. Triangular fibrocartilage complex lesions: a classification. J HAND SURG 1989;14A:594-606. 4. Imbriglia JE, Boland DS. Tears of the articular disc of the triangular fibrocartilage complex and results of excision of the articular disc. J HAND SURG 1983;8: 620. 5. Aspden RM, Yarker YE, Hukins DWL. Collagen orientations in the meniscus of the knee joint. J Anat 1985;140:371-80. 6. Bullough PG, Munuera L, Murphy J, Weinstein AM. The strength of the menisci of the knee as it relates to their fine structure. J Bone Joint Surg 1970;52B:564-70. 7. Broom ND. Abnormal softening in articular cartilage. Arthritis Rheum 1982;25:1209-16. 8. Bullough P, Goodfellow J. The significance of the fine structure of articular cartilage. J Bone Joint Surg 1968;50B:852-7. 9. Broom ND. Further insights into the structural principles
10.
I I.
12. 13.
14. 15.
16.
17. 18.
19. 20.
21.
22. 23.
24.
25.
governing the function of articular cartilage. J Anat 1984;139:275-94. O'Connor P, Bland C, Bjelle A, Gardner DL. Production of split patterns on the articular cartilage surface of rats. J PathoI 1980;130:15-21. Meachim G, Denham D, Emery IH, Wildinson PH. Collagen alignments and artificial splits at the surface of human articular cartilage. J Anat 1974;118:101-18. Gelberman RH, Menon J. The vascularity of the scaphoid bone. J HAND SURG 1980;5:508-13. O'Connor P, Bland C, Gardner DL. Fine structure of artificial splits in femoral condylar cartilage of the rat: a scanning electron microscopic study. J Pathol 1980;132:169-79. Kauer JMG. The articular disc of the hand. Acta Anat 1975;93:590-605. Henle J. Handbuch der Banderlehre des Menschen. In: Handbuch der systematischen Anatomie des Menschen. vol. 1. Braunschweig: Vieweg, 1856. Palmer AK, Skahen JR, Werner FW, Glisson RR. The extensor retinaculum of the wrist: an anatomical and biomechanical study. J HAND SURG 1985; lOB:I I. Hofmann S. Der Bau des Discus Articularis Articulationis Radio-ulnaris Distalis. Anat Anz 1959; I06: 173-85. Diamant J, Keller A, Baer E, Lilt M, Arridge RGC. Collagen; ultrastructure and its relation to mechanical properties as a function of ageing. Proc R Soc Lond 1972;180:293-315. Minn RJ, Steven FS. The collagen fibril organization in human articular cartilage. J Anat 1977;123:437-57. Broom ND, Marra DL. Ultrastructural evidence for fibrilto-fibril associations in articular cartilage and their functional implication. J Anat 1986;146:185-200. Broom ND, Marra DL. New structural concepts of articular cartilage demonstrated with a physical model. Connect Tissue Res 1985;14:1-8. Palmer AK, Werner FW. Biomechanics of the distal radioulnar joint. Clin OrthopI984;187:26-35. Af Ekenstam F, Hagert CoG. Anatomical studies on the geometry and stability of the distal radioulnar joint. Scand J Plast Reconstr Surg 1985;19:17-25. Thiru-Pathi RG, Ferlic DC, Clayton ML, McClure DC. Arterial anatomy of the triangular fibrocartilage of the wrist and its surgical significance. J HAND SURG 1986;IIA:258-63. Chidgey LK, Dell PC, Bittar E, Spanier S, Hermansdorfer JD. Tear patterns and collagen arrangement in the triangular fibrocartilage. J HAND SURG 1990;15A: 826.
