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Digital extensor tendon lacerations in horses: A retrospective evaluation of 22 cases
Reviewed
DIGITAL EXTENSOR TENDON LACERATIONS IN HORSES: A RETROSPECTIVE EVALUATION OF 22 CASES Nicolai Jansson, DVM, PhD
SUMMARY
Hospital records of 22 horses referred to the Royal Veterinary and Agricultural University (RVAU) of Copenhagen between January 1, 1990 and December 31, 1993 for treatment of digital extensor tendon lacerations were reviewed, and follow-up information on final outcome was collected to determine whether any injury or treatment factors could be associated with the outcome. Mean age of the horses was 5.2 years (range, 1 to 20 years), and follow-up time ranged from 1 to 5 years after injury. In 21 (95 %) of the horses, injury involved the hind limbs. Eleven (50 %) horses returned to their original or intended level of use. Eighteen (82 %) horses had no signs of lameness. There was no statistically significant correlation between outcome and elapsed time from injury to treatment, type of injury, treatment variables, or wound healing in the present study, and these findings support previous reports. It was concluded that horses with digital extensor tendon lacerations had a favorable prognosis for return to riding soundness and a fair prognosis for return to their original or intended level of use. Tendon suturing and primary wound healing did not improve the prognosis.
INTRODUCTION Traumatic severance of the digital extensor tendons is Author's address: Section of Large Animal Surgery, Department of Clinical Studies, The Royal Veterinary and Agricultural University, BLilowsvej 13, DK1870 Frederiksberg C, Denmark. Present address: Department of Clinical Sciences, College of Veterinary Medicine, Comell University, Ithaca, New York 14853 Volume 15 Number 12,1995
relatively common in horses as a result of wounds in the dorsal metatarsal/metacarpal region. 1~ These wounds occur most frequently in the proximal part of the metatarsal region in the hind limb, but they also occur in the forelimb between the fetlock and carpus. 1,3 Wire cuts are the major cause of these injuries, 1-3 but other sharp objects may also be implicated. 5 Usually, these wounds are characterized by extensive soft tissue damage with exposure of the underlying bone. 4 The periosteum is commonly stripped from the bone, which may lead to development of a bone sequestrum and subsequent surgical removal. ~9 Formation of a bone sequestrum is a major cause of delayed healing of distal limb wounds in the horse. 9 Although horses without digital extensor tendon function may drag the toe or knuckle over at the fetlock when walking, they are usually able to bear full weight on the limb. 10 Despite the fact that the ends of the severed tendons are not amenable to suturing in many cases of digital extensor tendon lacerations, the prognosis for future athletic soundness seems to be favorable. 1-3'5'8'1~Attempts to suture severed extensor tendons have been discouraged, 12-1a and it has been stated that such endeavors can in fact delay the healing of these wounds. 1~ Others have suggested that the tendon ends may be sutured in cases with minimal wound contamination. 1-s In a recent study, no association was found between final outcome and tendon suturing in horses with digital extensor tendon lacerations? 1 In wounds healing by second intention, extensor tendon function is restored by formation of a bridge of fibrous tissue between the severed ends. 8,14 When treating severed digital extensor tendons, it seems to be of importance that extension of the digits is maintained during the healing period, and this can be achieved by cast or splint bandage application, or corrective shoeing. 4'as'Is External support to the limb of 4 to 6 537
weeks duration has been recommended. 2 The purpose of the present study is to evaluate the results obtained in 22 horses treated for digital extensor tendon lacerations, and to determine whether specific injury or treatment factors influence the outcome.
MATERIALS AND METHODS
Hospital records of all horses referred to the Royal Veterinary and Agricultural University (RVAU) of Copenhagen because of digital extensor tendon lacerations between January 1, 1990 and December 31, 1993 were reviewed. Data on signalment, medical history, type and location of the injury, treatment, wound healing, and complications were collected. The signalment included age, sex, and breed. The medical history concerned elapsed time from injury to treatment and was classified as either less or more than 24 hours between injury and treatment. Type of injury was classified as either total or partial tendon disruption. Treatment was categorized by presence or absence of tendon suturing, type and duration of medical therapy (antibiotics; nonsteroidal anti-inflammatory drugs), and type and duration of external support to the limb (cast; splint bandage). Wound debridement was not used as a treatment factor in the present study; all horses had their wounds debrided as part of the initial treatment. Wound healing was regarded as primary when the skin defect had healed at the time of skin suture removal. Complications were registered as presence or absence of bone sequestration at the injury site. Follow-up information was obtained by questionnaires sent to, and filled out by the owners. This information included statements on current use, present level of use, degree of lameness, and cosmetic appearance of the injury site. Based on this information, .the following categories of final outcome were used 11: 1. the horse returned to its original or intended level of use;
2. the horse could be ridden but did not return to its previous level of.use; 3. the horse was sound for breeding or pasture; 4. the horse was euthanatized before or after discharge from the RVAU because of the original injury. Young horses not yet in training and with no signs of lameness at the time of follow-up, were placed in category 2. Cosmetic appearance was categorized by presence or absence of white hair growth and/or visible swelling at the injury site. Correlations between outcome and medical history, type of injury, treatment variables, and wound healing were determined by use of Fisher's exact test for 2 x 2 tables (P<0.05). In this statistical test, category 1 was regarded as successful outcome, while categories 2, 3 and 4 were 538
collectively regarded as unsuccessful outcome.
RESULTS
Twenty-six horses, 7 males (6 stallions and 1 gelding) and 19 females met the criteria for inclusion in the study. The age of the horses ranged from 9 months to 20 years (mean, 5.0 years). Four horses were unavailable for follow-up leaving 22 horses which are dealt with in this study. Of the 22 horses for which adequate follow-up was available, 6 were male (5 stallions and 1 gelding) and 16 were female. The age ranged from 1 to 20 years (mean, 5.2 years), and the group consisted of 10 Warmbloods, 5 Ponies, 3 Standardbreds, 2 Mixed breeds, 1 Arabian, and 1 Thoroughbred. Follow-up time ranged from 1 to 5 years after injury. Eleven (50 %) horses returned to their original or intended level of use; one (5 %) horse was sound for riding at a level below its previous level of use; 6 (27 %) horses were not yet in training but with no signs of lameness; 2 (9 %) horses were sound for breeding; and 2 (9 %) horses were euthanatized before discharge from the RVAU because of the Original injury. Table 1. Treatment and injury variables, and outcome in 22 cases of digital extensor tendon lacerations. 1, return to original or intended level of use; 2, return to riding at a level below the original level of use; 3, sound for breeding or ~asture; 4, euthanatized after initiating treatment. Outcome category All horses (n=22) Time between injury and treatment: <24 hours (n=19) >24 hours (n=3) Type of injury: Total disruption (n= 18) Partial distruption (n=4) Location of injury: Hind limb (n=21) Forelimb (n=l) Tendon suturing: Sutured (n=l 1) Not sutured (n=l 1) Duration of antibiotic treatment: <5 days (n=9) >5 days (n=9) Duration of external support: <30 days (n=13) >30 days (n=9) Wound healing: Primary (n=5) Secondary (n=15) Evaluation not possible (n=2)
1 11
2 7
3 2
4 2
10 1
6 1
2 0
1 1
7 2 0 J_ 0
2 0
7 4
/
10 1
7 0
2 0
2 0
5 6
4 3
1 1
1 1
4 7
2 5
1 1
2 0
7 4
3 4
1 1
2 0
4 7 0
1 6 0
0 2 0
0 0 2
JOURNAL OF EQUINE VETERINARY SCIENCE
Nineteen of the 22 horses were referred and treated within 24 hours of injury, and of these 10 returned to their previous or intended level of use (Table 1). Three horses were referred and treated more than 24 hours after injury, and one of these had a successful outcome. There was no statistically significant correlation between outcome and time between injury and treatment (<24 hours and >24 hours). Eighteen horses had total disruption of the involved digital extensor tendon (long digital extensor tendon in hind limbs; common digital extensor tendon in forelimbs), while 4 horses suffered only a partial tendon disruption. Seven of the horses with total tendon disruption and all of the horses with partial tendon disruption returned to their original or intended level of use. Outcome and injury type (total/partial tendon disruption) did not correlate statistically (P = 0.09) below the chosen significance level (p < 0.05) In 21 of the horses, the injury was located in the hind limb, and only one horse had the injury located in the forelimb. Ten of the horses with hind limb injury and the horse with the forelimb injury returned to their previous or intended level of use. Eleven horses had their tendons sutured, and of these 5 returned to their original or intended level of use. Six tendons were sutured with #2 polyglycolic acid a, 4 tendons were sutured with #2 stainless steeP, and for one horse information on suture material was not available. Eleven horses did not have their tendons sutured, and of these 6 had a successful outcome. In 8 horses, the skin was sutured without tendon suturing. There was no statistically significant correlation between outcome and tendon suturing. All horses were administered preoperative systemic antibiotics, and in 9 horses this treatment was continued for 5 days or less postoperatively, while in 13 horses it was continued for more than 5 days postoperatively. Mean duration of antibiosis for all horses was 5.7 days (range, 1 to 13 days). Of the 9 horses receiving less than or equal to 5 days of antibiotic treatment, 4 returned to their original or intended level of use. Of the 13 horses treated for more than 5 days, 7 had such an outcome. Outcome and duration of antibiosis (<5 days and >5 days) were not statistically correlated. Nonsteroidal anti-inflammatory drugs (phenylbutazone or flunixin meglumine) were used in 13 horses for a mean of 3.6 days (range, 1 to 7 days). Casts were used on 6 horses for an average of 20.7 days (range, 1 to 35 days), and in 11 horses, external support by splint bandages was used for an average of 26.2 days (range, 1 to 40 days). In 3 horses, a cast was used initially and subsequently replaced by a splint bandage (mean immobilization time, 36.3 days; range, 21 to 52 days). Two horses had no external support to the limb. aDexon, Davis and Geck Inc. bKruse AIS, Denmark
Volume 15 Number 12,1995
In 13 of the horses, duration of external support was less than or equal to 30 days, and of these, 7 returned to their previous or intended level of use. Of the 9 horses in which the external support was maintained longer than 30 days, 4 had a favorable outcome. There was no statistical correlation between outcome and duration of external support (<30 days and >30 days). Of the 2 horses that had no external support to the limb, one had partial tendon disruption and a favorable outcome, whereas the other had total tendon disruption and an unsuccessful outcome. In 5 horses, primary healing of the wounds was obtained, and of these 4 returned to their original or intended level of use. The wounds of 15 horses healed by second intention, and 7 had a favorable outcome. In the 2 horses that were euthanatized before discharge from the RVAU, information on wound healing was not available. No statistical correlation was found between outcome and wound healing (primary/secondary). Only one horse developed a bone sequestrum of the cannon bone at the injury site. In 3 of the horses, the owners stated that no signs of the original injuries could be seen at the time of follow-up, and in two of these, primary wound healing had taken place. In 13 horses, white hair growth and/or chronic swelling at the injury site were reported, and in only one of these, primary wound healing had occurred. In 5 horses, follow-up information on cosmetic appearance was not available, including the 2 horses that had been euthanatized before discharge from the RVAU.
DISCUSSION
The results presented here are in agreement with previous reports on the prognosis for digital extensor tendon lacerations in horses. 1-s,~,1~ Eleven of the 22 horses (50 %) in the present study returned to their original or intended level of use, while one horse was sound for riding at a level below its previous level of use, and 6 horses were not yet in training but with no signs of lameness. This gives a total of 18 horses (82 %) with no signs of larneness at the time of follow-up. The more favorable prognosis for digital extensor tendon lacerations, compared with digital flexor tendon lacerations has been attributed to the different biomechanical functions of the tendons, s Digital extensor tendons have no primary weight-supporting function, and their main function is to oppose flexion of the fetlock joint during the swing phase of the stride and to provide extension of the digital joints~prior to impact with the ground. 16 The 6 horses that were not yet in training at the time of follow-up in the present study, were all placed in outcome category 2 (Table 1). This was done to avoid overestimating the success rate of treatment for digital extensor tendon lacerations. On the other hand, it is important to be aware 539
that at least some of these 6 horses eventually can be expected to reach their intended level of use (outcome category 1). Two horses were sound for breeding, and in one of these the lameness was diagnosed to originate at the injury site, presumably caused by adhesions between the extensor tendon and periosteum. The two horses that were euthanatized encountered complications related to the original injury; in one of these, pain was severe and could not be controlled by medical treatment, and in the other, vascular supply to the distal limb was compromised. A previous report revealed no statistical correlation between outcome and tendon suturing in 15 horses treated for digital extensor tendon lacerations,11 and these findings are in accordance with the results of this study. Although the present study failed to show a statistical correlation between outcome and type of injury, it is clear from the data that all of the 4 horses with partial tendon disruption had a successful outcome, hereby indicating a more favorable prognosis for partial disruption, compared with total disruption of the extensor tendon. The present study also showed no statistical correlation between outcome and duration of antibiosis (<5 days and >5 days) or duration of external support to the affected limb (<30 days and >30 days). It is difficult to make conclusions based on these findings, but they indicate that external support can be limited to approximately 4 weeks and that postoperative antibiosis should be of relatively short duration, of course depending on the individual case. Another method of maintaining extension of the digits is corrective shoeing by application of a shoe with an extended toe, 1'4'12'1sand the use of this type of shoe may shorten the duration of external support to the limb. Bone sequestration did not seem to be a major problem in the present study, with only one horse developing a bone sequestrum of the dorsal metatarsal bone. Baxter a found that 4 of 8 horses with digital extensor, tendon lacerations developed bone sequestra, and Belknap et al., 5 reported that sequestrum formation/osteitis was a problem in 10 of 49 cases. In this study, time between injury and treatment (<24 hours and >24 hours) did not correlate with outcome. In addition, no correlation could be determined between wound healing (primary/secondary) and outcome. These findings agree with the general view that most digital extensor tendon lacerations can be allowed to heal by second intention. 1-3,5,1~ Three of the horses in the present study had no visible scarring at the time of follow-up, while 13 had white hair growth and/or chronic swelling at the injury site. In none of the horses was the cosmetic appearance unacceptable to the owner. In a previous report, 5 of 8 horses treated for digital extensor tendon lacerations had cosmetically acceptable scars. 8 Information based on owner statements regarding cosmetic appearance of the injury site is insuffi540
cient and conclusions are difficult to make. However, the relatively high incidence of white hair growth and/or chronic swelling at the injury site reflects the relatively high number of horses in which healing by second intention took place. In conclusion, the results presented here indicate that horses with digital extensor tendon lacerations have a favorable prognosis for return to riding soundness and a fair (50%) prognosis for return to their original or intended level of use. Tendon suturing and primary wound healing do not seem to influence the outcome.
REFERENCES
1. Mcllwraith CW: Traumatic problems of tendons and ligaments. In: Stashak TS, ed. Adams'lameness in horses. 4th ed. Philadelphia: Lea & Febiger, 1987;463-479. 2. Stashak TS: Traumatic division of the digital extensor tendons of the fore- and hind limb. In: Stashak TS, ed. Adams' lameness in horses. 4th ed. Philadelphia: Lea & Febiger, 1987: 764. 3. Stashak TS: Management of wounds associated with tendons, paratendons, and tendon sheaths. In: Equine Wound Management. Philadelphia: Lea & Febiger, 1991;238-257. 4. Watkins JP: Treatment principles of tendon disorders. In: Auer JA, ed. Equine surgery. Philadelphia: WB Saunders Company, 1992;916-924. 5. Belknap JK, Baxter GM, Nickels FA: Extensor tendon lacerations in horses: 50 cases (1982-1988). J Am Vet Med Assoc 1993; 203:428-431. 6. Moens Y, Verschooten F, De Moor A, Wouters L: Bone sequestration as a consequence of limb wounds in the horse. Vet Radiol 1980;21:40-44. 7. Booth LC, Feeney DA: Superficial osteitis and sequestrum formation as a result of skin avulsion in the horse. Vet Surg 1982;11:2-8. 8. Baxter GM: Retrospective study of lower limb wounds involving tendons, tendon sheaths or joints in horses, in Proceedings Am Assoc Equine Pract 1987;33:715-728. 9. Firth EC. Bone sequestration in horses and cattle. Aust Vet J 1987;64:65-69. 10. Wyn-Jones G: Tendon injuries. In: Equine lameness. Oxford: Blackwell Scientific Publications, 1988;224-236. 11. Foland JW, Trotter GW, Stashak TS, et al: Traumatic injuries involving tendons of the distal limbs in horses: a retrospective study of 55 cases. Equine Vet J 1991 ;23:422-425. 12. Selway SJ: Diseases of the tendons. In: Mansmann RA, McAIlister ES, eds. Equine Medicine and Surgery. 3rd ed. Santa Barbara: American Veterinary Publications, 1982; 1071-1088. 13. Turner A-q. ~urgery of tendons and ligaments in large animals. In: Jen'~n ~sn n- PB, ed. The Practice of Large Animal Surgery. PhiladeL~h,5:~WB Saunders Company, 1984:917-929. 14. Fackelm~ ~E: The nature of tendon damage and its repair. Equine V~t ii -1973;5:141-149. 15. Flecker I:~',,-,Wagner PC: Therapy and corrective shoeing for equine tendon disorders. Compend Contin Educ Pract Vet 1986;8:970-976. 16. Rooney JR: Passive function of the extensor tendons of the fore and rear limbs of the horse. J Equine Vet Sci 1987; 7:2930.
JOURNAL OF EQUINE VETERINARY SCIENCE
DIGITAL EXTENSOR TENDON LACERATIONS IN HORSES: A RETROSPECTIVE EVALUATION OF 22 CASES Nicolai Jansson, DVM, PhD
SUMMARY
Hospital records of 22 horses referred to the Royal Veterinary and Agricultural University (RVAU) of Copenhagen between January 1, 1990 and December 31, 1993 for treatment of digital extensor tendon lacerations were reviewed, and follow-up information on final outcome was collected to determine whether any injury or treatment factors could be associated with the outcome. Mean age of the horses was 5.2 years (range, 1 to 20 years), and follow-up time ranged from 1 to 5 years after injury. In 21 (95 %) of the horses, injury involved the hind limbs. Eleven (50 %) horses returned to their original or intended level of use. Eighteen (82 %) horses had no signs of lameness. There was no statistically significant correlation between outcome and elapsed time from injury to treatment, type of injury, treatment variables, or wound healing in the present study, and these findings support previous reports. It was concluded that horses with digital extensor tendon lacerations had a favorable prognosis for return to riding soundness and a fair prognosis for return to their original or intended level of use. Tendon suturing and primary wound healing did not improve the prognosis.
INTRODUCTION Traumatic severance of the digital extensor tendons is Author's address: Section of Large Animal Surgery, Department of Clinical Studies, The Royal Veterinary and Agricultural University, BLilowsvej 13, DK1870 Frederiksberg C, Denmark. Present address: Department of Clinical Sciences, College of Veterinary Medicine, Comell University, Ithaca, New York 14853 Volume 15 Number 12,1995
relatively common in horses as a result of wounds in the dorsal metatarsal/metacarpal region. 1~ These wounds occur most frequently in the proximal part of the metatarsal region in the hind limb, but they also occur in the forelimb between the fetlock and carpus. 1,3 Wire cuts are the major cause of these injuries, 1-3 but other sharp objects may also be implicated. 5 Usually, these wounds are characterized by extensive soft tissue damage with exposure of the underlying bone. 4 The periosteum is commonly stripped from the bone, which may lead to development of a bone sequestrum and subsequent surgical removal. ~9 Formation of a bone sequestrum is a major cause of delayed healing of distal limb wounds in the horse. 9 Although horses without digital extensor tendon function may drag the toe or knuckle over at the fetlock when walking, they are usually able to bear full weight on the limb. 10 Despite the fact that the ends of the severed tendons are not amenable to suturing in many cases of digital extensor tendon lacerations, the prognosis for future athletic soundness seems to be favorable. 1-3'5'8'1~Attempts to suture severed extensor tendons have been discouraged, 12-1a and it has been stated that such endeavors can in fact delay the healing of these wounds. 1~ Others have suggested that the tendon ends may be sutured in cases with minimal wound contamination. 1-s In a recent study, no association was found between final outcome and tendon suturing in horses with digital extensor tendon lacerations? 1 In wounds healing by second intention, extensor tendon function is restored by formation of a bridge of fibrous tissue between the severed ends. 8,14 When treating severed digital extensor tendons, it seems to be of importance that extension of the digits is maintained during the healing period, and this can be achieved by cast or splint bandage application, or corrective shoeing. 4'as'Is External support to the limb of 4 to 6 537
weeks duration has been recommended. 2 The purpose of the present study is to evaluate the results obtained in 22 horses treated for digital extensor tendon lacerations, and to determine whether specific injury or treatment factors influence the outcome.
MATERIALS AND METHODS
Hospital records of all horses referred to the Royal Veterinary and Agricultural University (RVAU) of Copenhagen because of digital extensor tendon lacerations between January 1, 1990 and December 31, 1993 were reviewed. Data on signalment, medical history, type and location of the injury, treatment, wound healing, and complications were collected. The signalment included age, sex, and breed. The medical history concerned elapsed time from injury to treatment and was classified as either less or more than 24 hours between injury and treatment. Type of injury was classified as either total or partial tendon disruption. Treatment was categorized by presence or absence of tendon suturing, type and duration of medical therapy (antibiotics; nonsteroidal anti-inflammatory drugs), and type and duration of external support to the limb (cast; splint bandage). Wound debridement was not used as a treatment factor in the present study; all horses had their wounds debrided as part of the initial treatment. Wound healing was regarded as primary when the skin defect had healed at the time of skin suture removal. Complications were registered as presence or absence of bone sequestration at the injury site. Follow-up information was obtained by questionnaires sent to, and filled out by the owners. This information included statements on current use, present level of use, degree of lameness, and cosmetic appearance of the injury site. Based on this information, .the following categories of final outcome were used 11: 1. the horse returned to its original or intended level of use;
2. the horse could be ridden but did not return to its previous level of.use; 3. the horse was sound for breeding or pasture; 4. the horse was euthanatized before or after discharge from the RVAU because of the original injury. Young horses not yet in training and with no signs of lameness at the time of follow-up, were placed in category 2. Cosmetic appearance was categorized by presence or absence of white hair growth and/or visible swelling at the injury site. Correlations between outcome and medical history, type of injury, treatment variables, and wound healing were determined by use of Fisher's exact test for 2 x 2 tables (P<0.05). In this statistical test, category 1 was regarded as successful outcome, while categories 2, 3 and 4 were 538
collectively regarded as unsuccessful outcome.
RESULTS
Twenty-six horses, 7 males (6 stallions and 1 gelding) and 19 females met the criteria for inclusion in the study. The age of the horses ranged from 9 months to 20 years (mean, 5.0 years). Four horses were unavailable for follow-up leaving 22 horses which are dealt with in this study. Of the 22 horses for which adequate follow-up was available, 6 were male (5 stallions and 1 gelding) and 16 were female. The age ranged from 1 to 20 years (mean, 5.2 years), and the group consisted of 10 Warmbloods, 5 Ponies, 3 Standardbreds, 2 Mixed breeds, 1 Arabian, and 1 Thoroughbred. Follow-up time ranged from 1 to 5 years after injury. Eleven (50 %) horses returned to their original or intended level of use; one (5 %) horse was sound for riding at a level below its previous level of use; 6 (27 %) horses were not yet in training but with no signs of lameness; 2 (9 %) horses were sound for breeding; and 2 (9 %) horses were euthanatized before discharge from the RVAU because of the Original injury. Table 1. Treatment and injury variables, and outcome in 22 cases of digital extensor tendon lacerations. 1, return to original or intended level of use; 2, return to riding at a level below the original level of use; 3, sound for breeding or ~asture; 4, euthanatized after initiating treatment. Outcome category All horses (n=22) Time between injury and treatment: <24 hours (n=19) >24 hours (n=3) Type of injury: Total disruption (n= 18) Partial distruption (n=4) Location of injury: Hind limb (n=21) Forelimb (n=l) Tendon suturing: Sutured (n=l 1) Not sutured (n=l 1) Duration of antibiotic treatment: <5 days (n=9) >5 days (n=9) Duration of external support: <30 days (n=13) >30 days (n=9) Wound healing: Primary (n=5) Secondary (n=15) Evaluation not possible (n=2)
1 11
2 7
3 2
4 2
10 1
6 1
2 0
1 1
7 2 0 J_ 0
2 0
7 4
/
10 1
7 0
2 0
2 0
5 6
4 3
1 1
1 1
4 7
2 5
1 1
2 0
7 4
3 4
1 1
2 0
4 7 0
1 6 0
0 2 0
0 0 2
JOURNAL OF EQUINE VETERINARY SCIENCE
Nineteen of the 22 horses were referred and treated within 24 hours of injury, and of these 10 returned to their previous or intended level of use (Table 1). Three horses were referred and treated more than 24 hours after injury, and one of these had a successful outcome. There was no statistically significant correlation between outcome and time between injury and treatment (<24 hours and >24 hours). Eighteen horses had total disruption of the involved digital extensor tendon (long digital extensor tendon in hind limbs; common digital extensor tendon in forelimbs), while 4 horses suffered only a partial tendon disruption. Seven of the horses with total tendon disruption and all of the horses with partial tendon disruption returned to their original or intended level of use. Outcome and injury type (total/partial tendon disruption) did not correlate statistically (P = 0.09) below the chosen significance level (p < 0.05) In 21 of the horses, the injury was located in the hind limb, and only one horse had the injury located in the forelimb. Ten of the horses with hind limb injury and the horse with the forelimb injury returned to their previous or intended level of use. Eleven horses had their tendons sutured, and of these 5 returned to their original or intended level of use. Six tendons were sutured with #2 polyglycolic acid a, 4 tendons were sutured with #2 stainless steeP, and for one horse information on suture material was not available. Eleven horses did not have their tendons sutured, and of these 6 had a successful outcome. In 8 horses, the skin was sutured without tendon suturing. There was no statistically significant correlation between outcome and tendon suturing. All horses were administered preoperative systemic antibiotics, and in 9 horses this treatment was continued for 5 days or less postoperatively, while in 13 horses it was continued for more than 5 days postoperatively. Mean duration of antibiosis for all horses was 5.7 days (range, 1 to 13 days). Of the 9 horses receiving less than or equal to 5 days of antibiotic treatment, 4 returned to their original or intended level of use. Of the 13 horses treated for more than 5 days, 7 had such an outcome. Outcome and duration of antibiosis (<5 days and >5 days) were not statistically correlated. Nonsteroidal anti-inflammatory drugs (phenylbutazone or flunixin meglumine) were used in 13 horses for a mean of 3.6 days (range, 1 to 7 days). Casts were used on 6 horses for an average of 20.7 days (range, 1 to 35 days), and in 11 horses, external support by splint bandages was used for an average of 26.2 days (range, 1 to 40 days). In 3 horses, a cast was used initially and subsequently replaced by a splint bandage (mean immobilization time, 36.3 days; range, 21 to 52 days). Two horses had no external support to the limb. aDexon, Davis and Geck Inc. bKruse AIS, Denmark
Volume 15 Number 12,1995
In 13 of the horses, duration of external support was less than or equal to 30 days, and of these, 7 returned to their previous or intended level of use. Of the 9 horses in which the external support was maintained longer than 30 days, 4 had a favorable outcome. There was no statistical correlation between outcome and duration of external support (<30 days and >30 days). Of the 2 horses that had no external support to the limb, one had partial tendon disruption and a favorable outcome, whereas the other had total tendon disruption and an unsuccessful outcome. In 5 horses, primary healing of the wounds was obtained, and of these 4 returned to their original or intended level of use. The wounds of 15 horses healed by second intention, and 7 had a favorable outcome. In the 2 horses that were euthanatized before discharge from the RVAU, information on wound healing was not available. No statistical correlation was found between outcome and wound healing (primary/secondary). Only one horse developed a bone sequestrum of the cannon bone at the injury site. In 3 of the horses, the owners stated that no signs of the original injuries could be seen at the time of follow-up, and in two of these, primary wound healing had taken place. In 13 horses, white hair growth and/or chronic swelling at the injury site were reported, and in only one of these, primary wound healing had occurred. In 5 horses, follow-up information on cosmetic appearance was not available, including the 2 horses that had been euthanatized before discharge from the RVAU.
DISCUSSION
The results presented here are in agreement with previous reports on the prognosis for digital extensor tendon lacerations in horses. 1-s,~,1~ Eleven of the 22 horses (50 %) in the present study returned to their original or intended level of use, while one horse was sound for riding at a level below its previous level of use, and 6 horses were not yet in training but with no signs of lameness. This gives a total of 18 horses (82 %) with no signs of larneness at the time of follow-up. The more favorable prognosis for digital extensor tendon lacerations, compared with digital flexor tendon lacerations has been attributed to the different biomechanical functions of the tendons, s Digital extensor tendons have no primary weight-supporting function, and their main function is to oppose flexion of the fetlock joint during the swing phase of the stride and to provide extension of the digital joints~prior to impact with the ground. 16 The 6 horses that were not yet in training at the time of follow-up in the present study, were all placed in outcome category 2 (Table 1). This was done to avoid overestimating the success rate of treatment for digital extensor tendon lacerations. On the other hand, it is important to be aware 539
that at least some of these 6 horses eventually can be expected to reach their intended level of use (outcome category 1). Two horses were sound for breeding, and in one of these the lameness was diagnosed to originate at the injury site, presumably caused by adhesions between the extensor tendon and periosteum. The two horses that were euthanatized encountered complications related to the original injury; in one of these, pain was severe and could not be controlled by medical treatment, and in the other, vascular supply to the distal limb was compromised. A previous report revealed no statistical correlation between outcome and tendon suturing in 15 horses treated for digital extensor tendon lacerations,11 and these findings are in accordance with the results of this study. Although the present study failed to show a statistical correlation between outcome and type of injury, it is clear from the data that all of the 4 horses with partial tendon disruption had a successful outcome, hereby indicating a more favorable prognosis for partial disruption, compared with total disruption of the extensor tendon. The present study also showed no statistical correlation between outcome and duration of antibiosis (<5 days and >5 days) or duration of external support to the affected limb (<30 days and >30 days). It is difficult to make conclusions based on these findings, but they indicate that external support can be limited to approximately 4 weeks and that postoperative antibiosis should be of relatively short duration, of course depending on the individual case. Another method of maintaining extension of the digits is corrective shoeing by application of a shoe with an extended toe, 1'4'12'1sand the use of this type of shoe may shorten the duration of external support to the limb. Bone sequestration did not seem to be a major problem in the present study, with only one horse developing a bone sequestrum of the dorsal metatarsal bone. Baxter a found that 4 of 8 horses with digital extensor, tendon lacerations developed bone sequestra, and Belknap et al., 5 reported that sequestrum formation/osteitis was a problem in 10 of 49 cases. In this study, time between injury and treatment (<24 hours and >24 hours) did not correlate with outcome. In addition, no correlation could be determined between wound healing (primary/secondary) and outcome. These findings agree with the general view that most digital extensor tendon lacerations can be allowed to heal by second intention. 1-3,5,1~ Three of the horses in the present study had no visible scarring at the time of follow-up, while 13 had white hair growth and/or chronic swelling at the injury site. In none of the horses was the cosmetic appearance unacceptable to the owner. In a previous report, 5 of 8 horses treated for digital extensor tendon lacerations had cosmetically acceptable scars. 8 Information based on owner statements regarding cosmetic appearance of the injury site is insuffi540
cient and conclusions are difficult to make. However, the relatively high incidence of white hair growth and/or chronic swelling at the injury site reflects the relatively high number of horses in which healing by second intention took place. In conclusion, the results presented here indicate that horses with digital extensor tendon lacerations have a favorable prognosis for return to riding soundness and a fair (50%) prognosis for return to their original or intended level of use. Tendon suturing and primary wound healing do not seem to influence the outcome.
REFERENCES
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