Journal of Orthopaedic Raeurch 13138-142 The Journal of Bone and Joint Surgery, lnc 0 1995 Orthopaedic Research Society

Short Communication

Growth of Severed Flexor Tendons in Chickens

Naoki Nishijima, Keiji Fujio, and Takao Yamamuro

Department of Orthopaedic Surgery, Fuculty of Medicine, Kyoto University, Kyoto, Japan

Summary: To examine tendon growth in both the distal and proximal portions of severed tendons, we investigated the growth of severed flexor tendons within the fibro-osseous tunnel in young chickens. When the tendon was severed at the proximal site in the sole, dynamic tension applied by the muscle was lost. Growth in the distal tendon was retarded considerably, although passive tension initially was maintained through the residual vincula and later by adhesion to the chiasma of adjacent flexors. When the tendon was severed at the insertion, passive tension from the extensors was lost. Proximal tendon growth con- tinued if active tension was maintained through the residual vincula. If not, the tendon was markedly shortened and degenerated. Maintaining normal tension may be the most important factor in longitudinal tendon growth.

Currently, there is considerable clinical interest in the influence of tension on tendon growth. Pedi- atric issues include whether a lengthened tendon will grow at a rapid rate, a lacerated tendon will sub- sequently grow (l) , and a contracted or shortened tendon can be corrected with a splint. In addition, flexor tendon injury in children occurs most fre- quently within the fibro-osseous tunnel. There also is interest in the mechanisms of deformity of the ends of a severed tendon within the fibro-osseous tunnel and whether end-to-end tenorrhaphy is pos- sible to treat long-standing laceration of the flexor tendon.

To examine tendon growth in both the distal and proximal portions of severed tendons and to deter- mine the influence of tension on tendon growth, we investigated the longitudinal growth of severed flexor tendons in young chickens by marking the tendon along its length and observing the dis-

Received September 14,1993; accepted March 29,1994. Address correspondence and reprint requests t o N.

Nishijima at 9-21 Konoe-choe, Yoshida, Sakyo-ku, Kyoto, 606 Japan.

tance between the marks at various stages during growth.

MATERIALS AND METHODS The flexor digitorum profundus tendon of the right

third digit of 50 male White Leghorn chickens was marked during the first week after birth. In the pres- ent study, growth of severed tendons was measured for 20 weeks after surgery, as previously reported (4). Briefly, surgery was performed under general anes- thesia (thiamylal sodium 0.3-0.6 pg injected intramus- cularly into wing muscles) and tourniquet control, with use of a surgical microscope and aseptic tech- niques. For skin sutures, marking, and closure of the fibro-osseous sheath after marking, 10.0 nylon su- tures (diameter, 25 pm) were used (Fig. 1).

Experiment 1: Growth After Proximal Injury In this experiment, tendon growth within the

fibro-osseous tunnel was observed in 25 chickens after the tendon had been severed through an open- ing at the proximal site in the sole (5.0 mm distal to the bifurcation of the flexor digitorum profundus tendon of the right third digit) within 1 week after

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GROWTH OF SEVERED FLEXOR TENDONS IN CHICKENS 139

hatching. The marks were placed near the insertion zone on the distal portion of the lacerated tendon; one mark was placed at the insertion of the third vinculum and the other was placed 5.0 mm distal to it (Fig. 1). Five chickens each were killed immediately after surgery and at 5,10,15, and 20 weeks following surgery, and the distance between the marks was measured. The distance from the insertion to the distal mark also was measured. As a control, the left tendon in each chicken was marked at the same lo- cations but was not severed. The portion of the ten- don from the proximal stump to the bifurcation also was examined.

Experiment 2: Growth After Distal Injury In this experiment, tendon growth within the fibro-

osseous tunnel was observed in 25 chickens after the flexor digitorum profundus tendon of the right third digit had been severed at the insertion within 1 week after birth. The marks were placed on the same loca- tion as already described (proximal portion of the lacerated tendon) (Fig. 1). Five chickens each were killed immediately after surgery and at 5 , 10,15, and 20 weeks after surgery. Each left tendon was used as a control. The distance between the bifurcation and the proximal mark also was measured.

RESULTS Experiment 1: Growth After Proximal Injury

Retardation of tendon growth was noted in the distal portion, the end of which usually adhered to

the flexor digitorum superficial tendon at the chi- asma. The difference between the growth of the sev- ered tendon and that of the control tendon became more pronounced with time.

In the control tendons of the left third digit, the distance between the two marks increased (from 5.0 mm) to 8.4 -+ 0.5 mm at 5 weeks, 12.8 f 0.9 mm at 10 weeks, 14.4 2 1.1 mm at 15 weeks, and 14.9 ? 1.2 mm at 20 weeks. In the severed tendons of the right third digit, the mean distance between the two marks increased to 7.1 -C 0.6, 10.3 f 0.2,ll.O f 1.3, and 11.8 -+ 0.5 mm at the same time points, respec- tively (Fig. 2).

Tendon growth between the insertion and the dis- tal mark also was retarded, as shown by the mean distance between the marks. In the control, this dis- tance increased from 4.7 5 0.1 mm to 8.6 2 0.4 mm at 5 weeks, 11.2 t 1.0 mm at 10 weeks, 13.0 -+ 1.7 mm at 15 weeks, and 13.6 -+ 1.1 mm at 20 weeks. In the severed tendon, the distance increased from 4.7 ? 0.3 mm to 7.6 2 0.6, 9.8 -C 1.0, 10.4 -t 1.3, and 11.2 ? 0.8 mm at the same time points, respectively. These differences were statistically significant (p < 0.05 at 5 weeks and p < 0.005 at 10,15, and 20 weeks; Student's t test).

In proximal injuries, the distal portion of the sev- ered tendon (within the fibro-osseous tunnel) lacked dynamic tension with muscular contraction. The vincula in the severed tendon remained intact at 5, 10, 15, and 20 weeks. Passive tension initially was obtained with extension of the digit, due to the re-

Exp. 1

Exp. 2

FIG. 1. Experiment 1 (top): tendon growth after proximal injury. * = distance between the insertion and the distal mark. Experiment 2 (bottom): tendon growth after distal injury. ** = distance between the bifurcation and the proximal mark. V, = second vinculum, and V, = third vinculum.

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140 N. NISHIJIMA E T AL.

5 10 15 20

sidual vincula. However, after 10 weeks, the passive tension apparently was obtained firmly, due to scar- ring of the distal end of the severed tendon to the flexor digitorum superficialis tendon at the chiasma. rather than elastically, due to the vincula. These find- ings were confirmed in all chickens at dissection. The distal portion of thc severed tendon within the fibro- osseous tunnel showed no other substantial adhe- sion, even though it was slightly thinner than the control.

The proximal portion of the severed tendon (out of the fibro-osseous tunnel) lacked tension in the

Interval between Marks

mm I

Tendon growth between the bifurcation and the proximal mark also was retarded. In the control, this distance increased from 15.4 t 0.5 mm to 30.9 t 1.6 mm at 5 weeks, 44.8 t 3.6 mm at 10 weeks, 50.7 ? 2.3 mm at 15 weeks, and 49.1 -+ 3.9 mm at 20 weeks. In the severed tendon, the distance increased from 15.6 +- 0.4 mm to 24.2 % 3.2,38.5 ? 2.5,39.0 -+ 5.5, and 29.5 ? 13.8 mm at the same time points, respec- tively. These differences were statistically significant (p < 0.05 at 5,15, and 20 weeks and p < 0.005 at 10 weeks; Student’s t test).

With distal injuries, active flexion of the digit by

10 1 / / /‘ * *

I Weeks FIG. 2. Tendon growth bctwccn marks after proximal injury. The solid line indicates growth of the control tendon (left). and the broken line indicates growth of the lacerated tendon (right). The difference in tendon growth between the right and left tendons was statistically significant (p < 0.01; Student’s t test). The bars indicate the SD. V, = second vinculum, and V, = third vinculum.

sole, gradually degenerated, and disappeared by 10 weeks after surgery.

muscular contraction was demonstrated in the im- mediate postoperative period by movement of the

Experiment 2: Growth After Distal Injury digit after the chickens recovered from anesthesia. As long as the vincula near the end of the lacerated

In the control tendons of the left third digit, the tendon were intact, the flexor muscle could flex the mean distance between the two marks increased from 5.0 mm to 8.5 t 0.7 mm at 5 weeks, 12.2 t 0.8 mm at 10 weeks, 14.3 2 0.7 mm at 15 weeks, and 14.8 t 0.9 mm at 20 weeks. In the severed tendon of the right third digit, the distance between the two marks increased from 5.0 mm to 7.5 t 0.7,10.5 k 0.7, 9.8 -L 3.8, and 7.8 * 4.8 mm at the same time points, respectively (Fig. 3).

phalanx to which the vincula were attached. Ac- tive digital flexion also was observed at 5 and 10 weeks after operation. During the first 10 weeks, none of the lacerated tendons had ruptured vin- cula and the severed proximal end became rounded on the second vinculum without any adhesion to neighboring tissues. These findings were confirmed at dissection.

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GROWTH OF SEVERED FLEXOR TENDONS IN CHICKENS 141

Interval between Marks

Inrn I 15 - T

I * I I I I I

5 10 15 20

I Weeks FIG. 3. Tendon growth between marks after distal injury. The solid line indicates growth of the control tendon (left), and the broken line indicates growth of the lacerated tendon (right). The difference in tendon growth between the right and left tendons was statistically significant at 10. 15, and 20 weeks (p < 0.05; Student’s f test). The bars indicate the SD. Vz = second vinculum, V, = third vinculum, and NS = not significant.

However, in two of the five chickens at 15 weeks and three of the five chickens at 20 weeks, the vincula were ruptured and the phalanx could not be flexed actively. At 15 weeks, the distance between the marks was 4.4 and 7.5 mm in the chickens with ruptured vincula, compared with 13.7 and 13.5 mm in the control tendons. After 20 weeks, in the digits with ruptured vincula, the distance between the marks was 3.0,5.1, and 5.1 mm, compared with 14.7, 13.8, and 14.1 mm in the control tendons. When the severed proximal end of the tendon with ruptured vincula had shrunk sufficiently to emerge from the fibro-osseous tunnel, it was markedly deformed (sin- uous and shortened).

Even after 1.5 weeks, a few severed proximal ends had adhered to a neighboring fibrous sheath or ten- don. The proximal tendon in the digits with intact vincula showed considerable growth. Actually, at 15 weeks, the distance between the marks was 13.2,11.0, and 13.0 mm, compared with 14.1,15.0, and 15.0 mm in the control tendons. At 20 weeks, the distance was 11.7 and 14.0 mm, compared with 15.7 and 15.9 mm in the control tendons.

In conclusion, lacerated tendons showed consid- erable growth when the vincula remained intact, whereas lacerated tendons became shortened when

the vincula ruptured. For this reason, the SD in- creased after 1.5 weeks.

DISCUSSION The mechanism of longitudinal growth in tendons

may be deposition of new collagenous tissue in the interstitium throughout its entire length (4). In the present study, the effect of tension on the longitudi- nal growth of flexor tendons was studied in chickens. In addition, whether the effect of dynamic or active tension on tendon growth differed from that of pas- sive tension also was investigated.

The growth of the lacerated tendon was less than that of an intact tendon, possibly because the tension on the tendon was present but reduced. The tendon that had lost all tension stopped growing.

Tension on the distal portion of the severed ten- don was produced chiefly by limb extension (i.e., passively without any dynamic tension). The distal portion of a severed tendon without dynamic ten- sion showed a retarded growth rate, and the end of the distal portion, remaining static, inevitably ad- hered to the surrounding tendons and the neigh- boring sheath. As long as the tendon remained covered by the fibro-osseous tendon sheath, it was less deformed.

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142 N. NISHIJIMA ET AL.

After it was severed at its insertion, the tendon continued to grow without much deformation if the vincula remained intact. Initially, the end, re- maining mobile through the elastic vincula, showed no adhesion within the fibro-osseous tunnel; how- ever, once the end emerged from the fibro-osseous tunnel, the tendon became markedly sinuous and shortened.

The synovial fluids in the synovial sheath may nourish the injured tendon (2,3), and the fibrous sheath may physically prevent the deformation of the injured tendon within the fibro-osseous tunnel. However, the residual tendon in the sole, which is

outside the fibro-osseous tunnel, degenerated rap- idly and disappeared.

REFERENCES 1 . Kang HJ, Park BM, Hahn SB, Kang ES: An experimental

study of healing of the partially severed flexor tendon in chickens. Yonsei M e d J 31:264-273, 1990

2. Manske PR, Lesker PA, Bridwell K: Experimental studies in chickens on the initial nutrition of tendon grafts. J Hand Surg 4:565-575,1979

3. Nishijima N, Ueba Y, Yamamuro T Growth of autografted tendons: an experimental study in vivo. J Hand Surg [Am] 13:234-237,1988

4. Nishijima N, Yamamuro T, Ueba Y Flexor tendon growth in chickens. J Orthop Res 12576-581,1994

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