International
International Orthopaedics (SICOT) (1992) 16:363 - 368
Orthopaedics © Springer-Verlag 1992
The healing of flexor tendons in chickens N. A. Siddiqi, Y. Hamada, and A. Noryia Yamanashi University School of Medicine, Japan
Summary. The healing offlexor tendons was studied in chickens using transmission electron microscopy. After resecting the flexor sheath between the proximal and distal pulleys in zone II, the profundus tendon was severed and sutured. Intermittent passive motion was carried out 35 times daily immediately afterwards. The chickens were sacrificed at 3, 6 and 9 weeks. In vivo healing was shown to be much more rapid than in in vitro studies. There was marked proliferation of endoplasmic reticulum and phagocytosis at 3 weeks, collagen synthesis at 6 weeks and remodelling at 9 weeks. Healing was by a combination of extrinsic and intrinsic mechanisms. Rgsumfi. Le processus de cicatrisation des tendons fldchisseurs a dtd dtudid chez le poulet en utilisant la microscopie dlectronique. Le modOle de plaie tendineuse a dt6 r6alisd par suture du tendon fldchisseur profond sectionnd, aprds rdsection de la gaine entre les poulies distale et proximale, en zone II. Une mobilisation passive intermittente a dtd entreprise immddiatement apr6s la rdparation, au rythme de 35 fois par jour. Les poulets ont dtd sacrifi6s ~t la troisiOme, sixiOme et neuviOme semaine et on a dtudid les modifications cellulaires au niveau de la zone suturde. Les Msultats montrent que la cicatrisation est plus rapide in vivo qu'in vitro. On a observd gt trois semaines une prolifdration marqude du rdtinaculum endoplasmique dans les cellules de l' endotendon et une phagocytose par des cellules de type pdriphdrique, gt six semaines une synthOse du collagone et~ neuf semaines un remodelage du collagOne.
Reprint requests to: N. A. Siddiqi, Department of Orthopaedics, Yamanashi Medical College, 1110 Shimokato, Nakakoma gun, Tamahocho, Yamanashi,Japan 409- 438
La cicatrisation tendineuse est une combinaison de mdcanismes de reconstruction extrinskques et intrinskques.
Introduction Flexor tendons are dynamic organs. Experiments have shown that they have an intrinsic potential for repair, and do not depend on extrinsic cells for healing [1, 2, 3, 4, 7, 8, 9, 10, 11]. The repair process after injury is explained by the proliferation of epitenon cells which act as macrophages and phagocytose debris at the suture site, while epitenon cells proliferate and secrete collagen to bridge the gap [8]. Manske et al. have reported that external healing with peripheral adhesions does not appear to be an essential part of the repair process, and that if the suture site is protected from the invasion of peripheral tissues, the tendon could heal by an intrinsic mechanism [8]. In our experimental model adhesions were diminished by intermittent passive motion started immediately after operation and healing was studied by transmission electron microscopy.
Material and methods Fifteen white adult female Leghorn chickens weighing an average of 1.2 kg were chosen for the experiment. Pentobarbital l ml/kg body weight was given intramuscularlyfor anaesthesia. A zig-zag plantar incision was made starting fi'om zone 11I and extending to the distal interphalangeal joint. The flexor tendon sheath was excised between the proximal and distal pulleys in zone II. The profundus tendon was then exposed by resecting sublimis and severed proximal to the vinculum longus. The severed tendon was repaired by Tsuge's technique using 5-0 nylon suture. The toes were placed in a plaster cast for 3 weeks,
364
N.A. Siddiqi et al.: Healing of flexor tendons in chickens
Fig. 1. Transmission electron microscopy (TEM) of normal chicken's tendon with epitenon cells (arrows) on the surface. Original magnification (OM) x 7000 Fig. 2. TEM of normal chicken' s tendon with endotenon cells (arrows) in between the collagen bundles. OM x 7000
but intermittent passive motion was carried out through a window made to allow access to the digit which had been operated on. Manual mobilisation of the interphalangeal and metacarpophalangeal joints from full extension to full flexion was carried out 35 times a day. The plaster was removed after 3 weeks and unrestricted movement allowed. The animals were divided into 3 groups; 5 were sacrificed at 3 weeks, 5 at 6 weeks, and 5 at 9 weeks. The specimens were removed and washed for several days in sodium cacodylate buffer (pH 7.4), followed by dehydration through a graded series of ethanol and propylene oxide. They were then embedded in Epon 312; thin sections stained in uranyl acetate and lead citrate were examined with a JEM-100SX electron microscope (JEOL Co Ltd, Japan).
Results T h e t e n d o n is c o m p o s e d o f two types o f cells or fibrocytes, b l o o d vessels, nerves and c o l l a g e n bundles. T h e cells lying on the surface o f the t e n d o n are called epitenon cells (Fig. 1) and those b e t w e e n the collagen bundles are e n d o t e n o n cells (Fig. 2). T r a n s m i s s i o n electron m i c r o s c o p y s h o w e d that at 3 weeks, the e n d o t e n o n cells had increased in n u m ber. T h e r e was also an increase in granular endop l a s m i c r e t i c u l u m cells with dilated cisternae and studded e x o c y t o t i c vesicles in the c y t o p l a s m . This
N. A. Siddiqi et al.: Healing of flexor tendons in chickens
365
Fig. 3. TEM of repair site at 3 weeks. The active fibroblasts show a significant increase in granular endoplasmic reticulum with dilated cisternae (rER), studded exocytotic vesicles, vacuoles (V) and mitochondria (M). OM x 14000 Fig. 4. TEM showing active flbroblasts at 3 weeks. There is an increase of granular endoplasmic reticulum (rER), lipid droplets (L), autophagic vacuoles (V) and
mitochondria(M). OM x 7000
evidence of fibroblastic activity is in preparation for collagen synthesis (Fig. 3). In some cells immature collagen synthesis could be seen. Mitochondria were increased in number and size, and had become more rounded in appearance. The nucleus was bigger with a ruffled membrane. The epitenon-like cells at the suture line resembled macrophages. Their cytoplasm was filled with autophagic vacuoles, lysosomes and lipid droplets (Fig. 4). Many membranous ruffles, indicating cell locomotion, were found. The findings suggest that the epitenon cells have changed into scavenger
cells and have migrated from the surface of the tendon to the suture site. At 6 weeks, the phagocytic fibroblasts had decreased, whereas collagen secretion predominated. There was marked synthesis of immature collagen fibrils which could be seen streaming into the extracellular areas (Fig. 5). The epitenon-like cells on the surface around the suture site also showed synthesis of collagen, thus bridging the gap (Fig. 6). The collagen fibres were now more organised and running in a longitudinal direction, parallel to the more mature fibres. The fibroblasts in the epitenon showed
366
N.A. Siddiqi et al.: Healing of flexor tendons in chickens
Fig. 5. TEM of repair site at 6 weeks. Metabolically active fibroblasts within the endotenon show marked secretion of extracellular new collagen fibrils in the extracellular matrix (arrows)in various stages of polymerisation. OM x 14 000. Fig. 6. TEM at 6 weeks of the surface of the tendon at the repair site. There m'e metabolically active epitenon-like cells lining the surface and marked secretion of collagen in the suture gap as well as on the surface. OM x 14000
marked secretion of collagen and a large number of exocytotic vesicles containing immature collagen. At 9 weeks, maturation of the collagen fibres was present and the number o f active epitenon-like cells had decreased. The cells now had a spindle-shaped nucleus lined by a thin layer of cytoplasm with long processes which resembled normal epitenon cells in a resting phase (Fig. 7). Proliferation of new blood vessels and capillaries was also be seen around the suture site.
Discussion Our electron microscope studies were designed to show tendon healing when intermittent passive motion was carried out resulting in decreased adhesion formation. The gap was completely filled and bridged with newly formed collagen at 9 weeks. Thus, tendon cells are able to differentiate and synthesise collagen at the time of repair. The healing of tendon in vivo goes through three phases:
N. A. Siddiqi et al.: Healing of flexor tendons in chickens
367
Fig. 7. TEM at 9 weeks illustrating collagen bundles in different phases of maturation confirming the remodelling phase. Proliferation of endoplasmic reticulum could not be seen in the cytoplasm of the endotenon indicating a less active phase. OM × 7000 Fig. 8. TEM at 9 weeks illustrating new vasculature in the endotenon around the suture site (arrow). OM × 7000
(1) Proliferative phase. The changes described above at 3 weeks suggested that the cells were preparing for collagen synthesis, although collagen secretion was minimal at this time. The proliferation of the endoplasmic retinaculum is more important than phagocytosis which is seen during repair at other sites in the body. (2) Collagen secretion phase. This was apparent at 6 weeks, but the collagen fibres were not yet orientated longitudinally. Collagen was present in both intra- and extracellular forms.
(3) Maturation and remodelling phase. This seemed to begin from 7 to 9 weeks, but differed from animal to animal. The new collagen bundles were arranged longitudinally along the old bundles. Fibroblasts were mostly inactive metabolically, reduced in size, with a thin layer of cytoplasm and an oval nucleus; some active fibroblasts were also present. Mass et al. reported that the intrinsic healing process might be too slow to allow healing of large human flexor tendons in tissue culture [9]. Gilberman et al. also suggested that in culture experiments
368
[
N. A. Siddiqi et al.: Healing of flexor tendons in chickens
]
Tendon trauma -
-
Release of chemicals
}
Receptors stimulation
mesenchymalcells
Perivascular Epitenon cells Endotenorl cells Synov al ca s
HeaIirlgtactors Helperceils
[ Proliferation and
Maturation and remodelling
Healing complete
Blood Synowial ltuld
Maturation factor
Collagen synthesis
~
1
multiplication of cells Phagocytes s
I
Fig. 9. Diagram showing the mechanism of tendon healing after injury
the endotenon cells are not able to fill the suture gap completely. Therefore repair proceeds more slowly, and sometimes in a less regulated manner than in in vivo experiments [3]. Manske et al. stated that progressive filling of the injured site and bridging of the defect by mature collagen fibres could not be achieved in in vitro experiments [8]. This is in contrast to our experimental work where complete healing with mature collagen synthesis readily occurred. We assume that healing begins as soon as the tendon is injured (Fig. 9) and some chemical substances are released which ultimately stimulate the four basic cells which are involved in healing, namely the perivascular mesenchymal cells (parent cells), the epitenon cells, the endotenon cells, and the synovial cells. Multiplication of the epitenon and endotenon occurs. The endoplasmic reticulum proliferates with the formation of vacuoles, so that these cells can perform the two important functions of phagocytosis at the suture site and collagen synthesis. It therefore seems that some other humoral factors, present in blood or synovial fluid, are needed for tendon healing. Furthermore, extrinsic cells may also be necessary. Our studies suggest that extrinsic fibroblasts reach the suture site and accelerate the process. The exact nature and action of these helper cells is not clearly understood, but they seem to be essential. They are absent in tissue culture of tendons, where the proliferation of tenocytes is slow and less marked. In vivo the endotenon cells show marked collagen synthesis, which is less and is delayed in vitro. This again suggests that the helper cells or healing factors are very important for the intrinsic healing process.
In the final stage, it seems that factors are released which result in maturation of the newly-formed collagen, the ceils recognise that healing is complete and synthesis is stopped. It is not yet understood which cells release these factors. Remodelling of collagen takes place in time and almost normal tendon is formed at the site of repair. This study supports the concept that there is an intrinsic healing process in tendon repair, but it seems that in clinical practice healing occurs by extrinsic repair. Direct invasion of extrinsic peripheral fibroblasts suppress intrinsic healing, but the mechanism is not known [8]. The invasion results in peritendinous adhesions which frequently occur after hand injuries. Intrinsic healing alone seems not to be sufficient for complete healing, and there may be an additional factor, or helper cells, needed for rapid healing in vivo.
Acknowledgements. The authors wish to express gratitude to Dr Akira Kawaoi, Professor of Pathology-II, Dr Kobayashi for their guidance and academic advice, and to Mrs Mikiko Yoda for her kind assistance.
References 1. Furlow LT (1976) The role of tendon tissue in tendon healing. Plast Reconstr Surg 57:39-49 2. Gelberman RH, Vande Berg JS, Lundborg GN, Akeson WH (1983) Flexor tendon healing and restoration of the gliding surface. J Bone Joint Surg [Am] 65:70-80 3. Gelberman RH, Manske PR, Akeson WH, Woo SL-Y, Lundborg G, Amiel D (1986) Flexor tendon repair. J Orthop Res 4:119-128 4. Gelberman RH, Manske PR, Vande Berg JS, Lasker PA, Akerson WH (1984) Flexor tendon repair in vitro: a comparative histological study of the rabbit, chicken, dog, and monkey. J Orthop Res 2:39-48 5. Ishii S, Umeda H (1987) Role of tendon in healing: A morphological study in vitro and in vivo. In: Hunter JM, Schneider LH, Mackin EJ (eds) Tendon surgery in the hand. The Mosby, New York, pp 79 - 85 6. Lindsay WK, Thomson HG (1959) Digital flexor tendons: An experimental study. Br J Plast Surg 12:289-316 7. Lundborg G, Rank F (1978) Experimental intrinsic healing of the flexor tendons based upon synovial fluid nutrition. J Hand Surg 3:21-31 8. Manske PR, Gelbe1~nan RH, Vande Berg JS, Lesker PA (1984) Intrinsic flexor-tendon repair. J Bone Joint Surg [Am] 66:385-396 9. Mass DP, Tuel R (1989) Human flexor tendon participate in the in vitro repair process. J Hand Surg 14:64-71 10. Schepel SJ (1987) Intrinsic healing of flexor tendons in primates. In: Hunter JM, Schneider LH, Mackin EJ (eds) Tendon surgery in the hand. Mosby, New York, pp 61-66 11. Umeda H (1978) An experimental study on the intrinsic healing mechanisms of digital flexor tendons. J Jpn Orthop Assoc 52:917-929
International Orthopaedics (SICOT) (1992) 16:363 - 368
Orthopaedics © Springer-Verlag 1992
The healing of flexor tendons in chickens N. A. Siddiqi, Y. Hamada, and A. Noryia Yamanashi University School of Medicine, Japan
Summary. The healing offlexor tendons was studied in chickens using transmission electron microscopy. After resecting the flexor sheath between the proximal and distal pulleys in zone II, the profundus tendon was severed and sutured. Intermittent passive motion was carried out 35 times daily immediately afterwards. The chickens were sacrificed at 3, 6 and 9 weeks. In vivo healing was shown to be much more rapid than in in vitro studies. There was marked proliferation of endoplasmic reticulum and phagocytosis at 3 weeks, collagen synthesis at 6 weeks and remodelling at 9 weeks. Healing was by a combination of extrinsic and intrinsic mechanisms. Rgsumfi. Le processus de cicatrisation des tendons fldchisseurs a dtd dtudid chez le poulet en utilisant la microscopie dlectronique. Le modOle de plaie tendineuse a dt6 r6alisd par suture du tendon fldchisseur profond sectionnd, aprds rdsection de la gaine entre les poulies distale et proximale, en zone II. Une mobilisation passive intermittente a dtd entreprise immddiatement apr6s la rdparation, au rythme de 35 fois par jour. Les poulets ont dtd sacrifi6s ~t la troisiOme, sixiOme et neuviOme semaine et on a dtudid les modifications cellulaires au niveau de la zone suturde. Les Msultats montrent que la cicatrisation est plus rapide in vivo qu'in vitro. On a observd gt trois semaines une prolifdration marqude du rdtinaculum endoplasmique dans les cellules de l' endotendon et une phagocytose par des cellules de type pdriphdrique, gt six semaines une synthOse du collagone et~ neuf semaines un remodelage du collagOne.
Reprint requests to: N. A. Siddiqi, Department of Orthopaedics, Yamanashi Medical College, 1110 Shimokato, Nakakoma gun, Tamahocho, Yamanashi,Japan 409- 438
La cicatrisation tendineuse est une combinaison de mdcanismes de reconstruction extrinskques et intrinskques.
Introduction Flexor tendons are dynamic organs. Experiments have shown that they have an intrinsic potential for repair, and do not depend on extrinsic cells for healing [1, 2, 3, 4, 7, 8, 9, 10, 11]. The repair process after injury is explained by the proliferation of epitenon cells which act as macrophages and phagocytose debris at the suture site, while epitenon cells proliferate and secrete collagen to bridge the gap [8]. Manske et al. have reported that external healing with peripheral adhesions does not appear to be an essential part of the repair process, and that if the suture site is protected from the invasion of peripheral tissues, the tendon could heal by an intrinsic mechanism [8]. In our experimental model adhesions were diminished by intermittent passive motion started immediately after operation and healing was studied by transmission electron microscopy.
Material and methods Fifteen white adult female Leghorn chickens weighing an average of 1.2 kg were chosen for the experiment. Pentobarbital l ml/kg body weight was given intramuscularlyfor anaesthesia. A zig-zag plantar incision was made starting fi'om zone 11I and extending to the distal interphalangeal joint. The flexor tendon sheath was excised between the proximal and distal pulleys in zone II. The profundus tendon was then exposed by resecting sublimis and severed proximal to the vinculum longus. The severed tendon was repaired by Tsuge's technique using 5-0 nylon suture. The toes were placed in a plaster cast for 3 weeks,
364
N.A. Siddiqi et al.: Healing of flexor tendons in chickens
Fig. 1. Transmission electron microscopy (TEM) of normal chicken's tendon with epitenon cells (arrows) on the surface. Original magnification (OM) x 7000 Fig. 2. TEM of normal chicken' s tendon with endotenon cells (arrows) in between the collagen bundles. OM x 7000
but intermittent passive motion was carried out through a window made to allow access to the digit which had been operated on. Manual mobilisation of the interphalangeal and metacarpophalangeal joints from full extension to full flexion was carried out 35 times a day. The plaster was removed after 3 weeks and unrestricted movement allowed. The animals were divided into 3 groups; 5 were sacrificed at 3 weeks, 5 at 6 weeks, and 5 at 9 weeks. The specimens were removed and washed for several days in sodium cacodylate buffer (pH 7.4), followed by dehydration through a graded series of ethanol and propylene oxide. They were then embedded in Epon 312; thin sections stained in uranyl acetate and lead citrate were examined with a JEM-100SX electron microscope (JEOL Co Ltd, Japan).
Results T h e t e n d o n is c o m p o s e d o f two types o f cells or fibrocytes, b l o o d vessels, nerves and c o l l a g e n bundles. T h e cells lying on the surface o f the t e n d o n are called epitenon cells (Fig. 1) and those b e t w e e n the collagen bundles are e n d o t e n o n cells (Fig. 2). T r a n s m i s s i o n electron m i c r o s c o p y s h o w e d that at 3 weeks, the e n d o t e n o n cells had increased in n u m ber. T h e r e was also an increase in granular endop l a s m i c r e t i c u l u m cells with dilated cisternae and studded e x o c y t o t i c vesicles in the c y t o p l a s m . This
N. A. Siddiqi et al.: Healing of flexor tendons in chickens
365
Fig. 3. TEM of repair site at 3 weeks. The active fibroblasts show a significant increase in granular endoplasmic reticulum with dilated cisternae (rER), studded exocytotic vesicles, vacuoles (V) and mitochondria (M). OM x 14000 Fig. 4. TEM showing active flbroblasts at 3 weeks. There is an increase of granular endoplasmic reticulum (rER), lipid droplets (L), autophagic vacuoles (V) and
mitochondria(M). OM x 7000
evidence of fibroblastic activity is in preparation for collagen synthesis (Fig. 3). In some cells immature collagen synthesis could be seen. Mitochondria were increased in number and size, and had become more rounded in appearance. The nucleus was bigger with a ruffled membrane. The epitenon-like cells at the suture line resembled macrophages. Their cytoplasm was filled with autophagic vacuoles, lysosomes and lipid droplets (Fig. 4). Many membranous ruffles, indicating cell locomotion, were found. The findings suggest that the epitenon cells have changed into scavenger
cells and have migrated from the surface of the tendon to the suture site. At 6 weeks, the phagocytic fibroblasts had decreased, whereas collagen secretion predominated. There was marked synthesis of immature collagen fibrils which could be seen streaming into the extracellular areas (Fig. 5). The epitenon-like cells on the surface around the suture site also showed synthesis of collagen, thus bridging the gap (Fig. 6). The collagen fibres were now more organised and running in a longitudinal direction, parallel to the more mature fibres. The fibroblasts in the epitenon showed
366
N.A. Siddiqi et al.: Healing of flexor tendons in chickens
Fig. 5. TEM of repair site at 6 weeks. Metabolically active fibroblasts within the endotenon show marked secretion of extracellular new collagen fibrils in the extracellular matrix (arrows)in various stages of polymerisation. OM x 14 000. Fig. 6. TEM at 6 weeks of the surface of the tendon at the repair site. There m'e metabolically active epitenon-like cells lining the surface and marked secretion of collagen in the suture gap as well as on the surface. OM x 14000
marked secretion of collagen and a large number of exocytotic vesicles containing immature collagen. At 9 weeks, maturation of the collagen fibres was present and the number o f active epitenon-like cells had decreased. The cells now had a spindle-shaped nucleus lined by a thin layer of cytoplasm with long processes which resembled normal epitenon cells in a resting phase (Fig. 7). Proliferation of new blood vessels and capillaries was also be seen around the suture site.
Discussion Our electron microscope studies were designed to show tendon healing when intermittent passive motion was carried out resulting in decreased adhesion formation. The gap was completely filled and bridged with newly formed collagen at 9 weeks. Thus, tendon cells are able to differentiate and synthesise collagen at the time of repair. The healing of tendon in vivo goes through three phases:
N. A. Siddiqi et al.: Healing of flexor tendons in chickens
367
Fig. 7. TEM at 9 weeks illustrating collagen bundles in different phases of maturation confirming the remodelling phase. Proliferation of endoplasmic reticulum could not be seen in the cytoplasm of the endotenon indicating a less active phase. OM × 7000 Fig. 8. TEM at 9 weeks illustrating new vasculature in the endotenon around the suture site (arrow). OM × 7000
(1) Proliferative phase. The changes described above at 3 weeks suggested that the cells were preparing for collagen synthesis, although collagen secretion was minimal at this time. The proliferation of the endoplasmic retinaculum is more important than phagocytosis which is seen during repair at other sites in the body. (2) Collagen secretion phase. This was apparent at 6 weeks, but the collagen fibres were not yet orientated longitudinally. Collagen was present in both intra- and extracellular forms.
(3) Maturation and remodelling phase. This seemed to begin from 7 to 9 weeks, but differed from animal to animal. The new collagen bundles were arranged longitudinally along the old bundles. Fibroblasts were mostly inactive metabolically, reduced in size, with a thin layer of cytoplasm and an oval nucleus; some active fibroblasts were also present. Mass et al. reported that the intrinsic healing process might be too slow to allow healing of large human flexor tendons in tissue culture [9]. Gilberman et al. also suggested that in culture experiments
368
[
N. A. Siddiqi et al.: Healing of flexor tendons in chickens
]
Tendon trauma -
-
Release of chemicals
}
Receptors stimulation
mesenchymalcells
Perivascular Epitenon cells Endotenorl cells Synov al ca s
HeaIirlgtactors Helperceils
[ Proliferation and
Maturation and remodelling
Healing complete
Blood Synowial ltuld
Maturation factor
Collagen synthesis
~
1
multiplication of cells Phagocytes s
I
Fig. 9. Diagram showing the mechanism of tendon healing after injury
the endotenon cells are not able to fill the suture gap completely. Therefore repair proceeds more slowly, and sometimes in a less regulated manner than in in vivo experiments [3]. Manske et al. stated that progressive filling of the injured site and bridging of the defect by mature collagen fibres could not be achieved in in vitro experiments [8]. This is in contrast to our experimental work where complete healing with mature collagen synthesis readily occurred. We assume that healing begins as soon as the tendon is injured (Fig. 9) and some chemical substances are released which ultimately stimulate the four basic cells which are involved in healing, namely the perivascular mesenchymal cells (parent cells), the epitenon cells, the endotenon cells, and the synovial cells. Multiplication of the epitenon and endotenon occurs. The endoplasmic reticulum proliferates with the formation of vacuoles, so that these cells can perform the two important functions of phagocytosis at the suture site and collagen synthesis. It therefore seems that some other humoral factors, present in blood or synovial fluid, are needed for tendon healing. Furthermore, extrinsic cells may also be necessary. Our studies suggest that extrinsic fibroblasts reach the suture site and accelerate the process. The exact nature and action of these helper cells is not clearly understood, but they seem to be essential. They are absent in tissue culture of tendons, where the proliferation of tenocytes is slow and less marked. In vivo the endotenon cells show marked collagen synthesis, which is less and is delayed in vitro. This again suggests that the helper cells or healing factors are very important for the intrinsic healing process.
In the final stage, it seems that factors are released which result in maturation of the newly-formed collagen, the ceils recognise that healing is complete and synthesis is stopped. It is not yet understood which cells release these factors. Remodelling of collagen takes place in time and almost normal tendon is formed at the site of repair. This study supports the concept that there is an intrinsic healing process in tendon repair, but it seems that in clinical practice healing occurs by extrinsic repair. Direct invasion of extrinsic peripheral fibroblasts suppress intrinsic healing, but the mechanism is not known [8]. The invasion results in peritendinous adhesions which frequently occur after hand injuries. Intrinsic healing alone seems not to be sufficient for complete healing, and there may be an additional factor, or helper cells, needed for rapid healing in vivo.
Acknowledgements. The authors wish to express gratitude to Dr Akira Kawaoi, Professor of Pathology-II, Dr Kobayashi for their guidance and academic advice, and to Mrs Mikiko Yoda for her kind assistance.
References 1. Furlow LT (1976) The role of tendon tissue in tendon healing. Plast Reconstr Surg 57:39-49 2. Gelberman RH, Vande Berg JS, Lundborg GN, Akeson WH (1983) Flexor tendon healing and restoration of the gliding surface. J Bone Joint Surg [Am] 65:70-80 3. Gelberman RH, Manske PR, Akeson WH, Woo SL-Y, Lundborg G, Amiel D (1986) Flexor tendon repair. J Orthop Res 4:119-128 4. Gelberman RH, Manske PR, Vande Berg JS, Lasker PA, Akerson WH (1984) Flexor tendon repair in vitro: a comparative histological study of the rabbit, chicken, dog, and monkey. J Orthop Res 2:39-48 5. Ishii S, Umeda H (1987) Role of tendon in healing: A morphological study in vitro and in vivo. In: Hunter JM, Schneider LH, Mackin EJ (eds) Tendon surgery in the hand. The Mosby, New York, pp 79 - 85 6. Lindsay WK, Thomson HG (1959) Digital flexor tendons: An experimental study. Br J Plast Surg 12:289-316 7. Lundborg G, Rank F (1978) Experimental intrinsic healing of the flexor tendons based upon synovial fluid nutrition. J Hand Surg 3:21-31 8. Manske PR, Gelbe1~nan RH, Vande Berg JS, Lesker PA (1984) Intrinsic flexor-tendon repair. J Bone Joint Surg [Am] 66:385-396 9. Mass DP, Tuel R (1989) Human flexor tendon participate in the in vitro repair process. J Hand Surg 14:64-71 10. Schepel SJ (1987) Intrinsic healing of flexor tendons in primates. In: Hunter JM, Schneider LH, Mackin EJ (eds) Tendon surgery in the hand. Mosby, New York, pp 61-66 11. Umeda H (1978) An experimental study on the intrinsic healing mechanisms of digital flexor tendons. J Jpn Orthop Assoc 52:917-929
