Outcome following surgical repair of achilles tendon

246 © 2006

Brief Communication Schattauer GmbH

Outcome following surgical repair of achilles tendon rupture and comparison between postoperative tibiotarsal immobilization methods in dogs 28 cases (1997–2004) C. Nielsen, G. E. Pluhar Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota, USA Summary

Surgical treatment of Achilles tendon rupture in dogs is generally associated with a favourable outcome, although the recovery time to best function is relatively long at 20.2 weeks. Dogs with injuries of less than 21 days duration may have a better functional outcome. When comparing external fixator application to splint or cast management, initial tibiotarsal immobilization method does not significantly affect the complication rate, duration of immobilization, recovery time, or functional outcome.

Keywords

Achilles tendon, surgery – tendon, joint immobilization Vet Comp Orthop Traumatol 2006; 19: 246–9

Vet Comp Orthop Traumatol 4/2006

Introduction The Achilles (common calcaneal) tendon is made up of three structures: the tendons of the gastrocnemius and superficial digital flexor, and the common tendon of the biceps femoris, gracilis, and semitendinosus. Rupture of one or more components is a disabling injury in dogs, and surgical repair is the generally accepted recommendation for effective return to function. In dogs the injury is generally classified according to the age of the injury (acute vs. chronic), and the degree of tendon involvement (partial vs. complete) (1). Partial rupture, with one or more tendon components intact, is reportedly more common in dogs (2). Following surgical repair, in order to counteract large tensile forces during healing, immobilization of the tibiotarsal joint is recommended. Primary tenorrhaphy using different suture patterns has been described (3–5). Augmentation methods have been used when the length or integrity of tendon is insufficient (6, 7). Several methods of joint immobilization have been advocated, including the application of a transarticular external skeletal fixator (TESF) (8, 9), placement of a calcaneo-tibial bone screw (10), and various configurations of splints and casts (1, 5). These small case series also provide the only published evaluation of outcome following Achilles tendon repair in dogs, and, to date none of the studies has compared the associated complications and functional outcome of different methods of initial joint immobilization.

We hypothesized that immobilization with TESF would result in longer surgical time and greater cost of surgery, but would lead to a quicker return of function with fewer complications compared to external coaptation. In addition, we hypothesized that the overall long-term function after recovery would be the same for both groups, with most dogs regaining excellent to normal function of the limb. The purpose of the study reported herein was to provide information regarding recovery and longterm outcome after surgical management of Achilles tendon rupture in a large group of dogs, and to compare immobilization with TESF to standard external coaptation using splints or casts.

Methods, results, and discussion The medical records of all dogs that underwent surgical Achilles tendon repair at the University of Minnesota between 1997 and 2004 were reviewed. Follow-up information regarding post-operative management and final outcome was obtained by reviewing the medical record, and contact with the referring veterinarian and client interview. The length of time to best function from surgery was estimated to the nearest number of weeks, and functional outcome score was assigned on a scale from one to six (1 representing normal function with no residual lameness, and 6 representing severe lameness preventing regular use of the limb or

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Received December 1, 2005 Accepted March 13, 2006

247 Achilles repair in 28 cases

arthrodesis of the tibiotarsal joint), from a combination of these follow-up methods. Based on their initial immobilization method, the dogs were divided into two treatment groups. Descriptive statistics were calculated for the continuous variables for both the overall population and individually for each treatment group. Proportions were calculated for discrete variables. The two sample t-tests was used to compare continuous variables between treatment groups. The Chi-Square test was generally used to compare discrete variables between treatment groups, with Fisher’s Exact test substituted where necessary due to small cell counts. The correlation coefficient between duration of injury and recovery time was calculated. Two sample t-tests were carried out in order to compare the mean injury duration by functional outcome score group and mean recovery time by tendon rupture type (partial or complete). Functional outcome score was categorized into two groups for analysis of association with other data, with the first group including scores of 1 or 2 and the second group including all scores of 3 or higher. For all of the tests, significance was set at a p-value of 21 days). The mean time from injury to surgery was 85 days (range 1 to 772 days), with a median of 26 days. One dog had had the injured tendon unsuccessfully repaired, on two separate occasions, at another clinic, and two dogs had had the injured tendon unsuccessfully repaired once previously at the same institution. Details of any ongoing conservative management were not available for the dogs with chronic injury and without previous surgery. During the operations, complete rupture of all tendon com-

ponents was found in 12 dogs (42.8%) and partial rupture, with one or more intact components, was found in 16 dogs (57.1%); this difference is not statistically significant. All of the dogs had mid-substance tendon tears, without any calcaneal avulsion injuries being described. All of the tendons were repaired with a three-loop pulley, locking loop, or Bunnell-Meyer suture pattern, or a combination of these patterns, using nonabsorbable, monofilament suture. Due to small cell counts, meaningful comparisons regarding outcome could not be made between suture patterns. The mean follow-up time considering all methods of contact was 111 weeks (range 5 to 271 weeks). The length of time reported by only having been evaluated by a veterinarian was 43 weeks (range 0 to 196), with 25 dogs having at least eight weeks of follow-up by this method. All of the dogs had some method of tibiotarsal immobilization applied at the time of surgery. A calcaneo-tibial screw was placed in one dog and supplemented by a splint; a splint or full cast was placed in 11 dogs, and a type II transarticular external skeletal fixator (TESF) with positive-profile pins in both the tibia and metatarsals was placed in 16 dogs. The type of TESF connecting bars (acrylic, metal, or carbon fibre) was not consistently available. Of the 12 dogs with a splint or cast placed, there were six with a lateral splint, one with a cranial splint, one with a full cast, one with a bi-valved cast, and the remainder had splints of unspecified type. The degree of support was decreased incrementally in all dogs after surgery, following a variable time course, and all of the dogs were transitioned to a soft, padded bandage prior to complete removal of coaptation. The mean duration that some type of coaptation was maintained for the 23 dogs with this information available was 10.1 weeks (range 5.7 to 21.9 weeks). Complications were generally attributable to the coaptation method rather than to the surgical repair. Details of the surgical failure were not available for the one dog that had undergone two previous surgeries elsewhere. Of the two dogs that each underwent a previous surgical repair at the VMC, one dog had splint breakage four days post-operatively and the other had breakage of the acrylic TESF connecting bars eight days post-operatively.

These complications resulted in failure of the primary tendon repair in both dogs. Considering only the final surgery on the affected tendon for all 28 dogs to maintain independence of samples, 13 had complications recorded. Five dogs had major complications, including metatarsal fracture secondary to TESF pins (n=1), metatarsal osteomyelitis secondary to TESF pins (n=2), broken fixator bar and loss of TESF pin that did not result in tendon failure but required a surgical revision of the TESF (n=1), and excessive tendon laxity after healing (n=1). Eight dogs had minor complications, including superficial infection of the TESF pin tracts (n=2), bandage-induced dermatitis or wounds (n=4), swelling and skin impingement againstTESF clamps (n=1), and splint breakage that did not result in tendon failure (n=1). The mean time to best function from the date of surgery for the 21 dogs with this information available was 20.2 weeks (range 8 to 48.3 weeks). The mean functional outcome score at the time of best function for 23 dogs with this information available was 1.9 (range 1 to 5). The mean recovery time to best function for dogs with a partial tendon rupture was not significantly different from those with a complete tendon rupture (p = 0.800).There was no significant association between tendon rupture type (partial vs. complete) and functional outcome score group (1 or 2 vs. 3 to 6) (p = 0.692). When the dogs were divided by initial coaptation type, there were 16 dogs in the TESF group and 11 dogs in the splint/cast group (Tables 1, 2). The two treatment groups were not significantly different with regard to gender distribution, body weight, time from injury to surgery, or injury type (partial vs. complete rupture).The mean age in the TESF group was 4.98 years (range 0.7 to 10.1 years), which was less than the mean age in the splint/cast group of 7.56 years (range 5.1 to 9.3 years); this difference was statistically significant (p = 0.007). The mean surgical time in the TESF group was 116 minutes (range 50 to 310 minutes), which was significantly longer than the mean surgical time in the splint/cast group of 66 minutes (range 35 to 115 minutes) (p = 0.009). The overall cost of the initial visit including surgery in the TESF group was US$ 1,539 (range US$ 994 to US$ 2,419), which



248 Nielsen, Pluhar

Table 1 Comparison of descriptive statistics by treatment group (initial coaptation method) for continuous variables. Note that one dog was treated with a calcaneo-tibial screw for coaptation and is not included in either treatment group.

Variable Age (yrs)

*

Weight (kg)

TESF Group Total = 16

Splint/Cast Group Total = 11

Entire Population Total = 28

N

Mean (Std Dev)

N

Mean (Std Dev)

N

Mean (Std Dev)

16

004.98 (2.99)

11

0007.56 (1.56)

28

0005.90 (2.81)

16

035.6 (10.3)

11

0032.1 (12.4)

28

0033.81 (11.09)

Duration of Injury (days)

16

082.9 (190.4)

11

0095.9 (117.4)

28

0085.11 (159.86)

Total Cost (2005 US $)*

16

1538.9 (353.0)

11

1189.9 (235.8)

28

1391.77 (346.25)

Surgery Length (min)*

16

116.3 (63.1)

11

0065.5 (25.9)

28

0094.29 (55.94)

Total Coaptation Time (wks)

14

009.96 (3.25)

09

0010.3 (4.58)

23

0010.10 (3.73)

Overall Recovery Time (wks)

12

022.4 (13.3)

09

0017.4 (8.5)

21

0020.26 (11.52)

Functional Outcome Score

13

001.69 (0.85)

10

0002.20 (1.32)

23

0001.91 (1.08)

Follow-up Available (wks)

16

115.5 (80.2)

11

0113.9 (73.8)

28

0110.91 (77.56)

*= Statistically significant (p < 0.05) differences between treatment groups.

was significantly more than the mean cost in the splint/cast group of $1,190 (range US $774 to US$ 1,479) (p = 0.008). Although all of the dogs with major complications were in the TESF group, there was no difference in the proportion of dogs with reported complications (minor, major, or overall) between the two groups. There was not any significant difference between groups, with respect to total duration of coaptation nor recovery time to ‘best function’. The correlation coefficient between the duration of injury and recovery time to best function was not statistically significant (p

= 0.243). The mean duration of injury for dogs in the favourable outcome score group (scores 1 or 2) was 50.2 days. Although this period was much shorter than the mean of 259.6 days for dogs in the unfavourable outcome score group (scores 3 to 6), the difference was not significantly different (p = 0.193). However, when comparing the functional outcome score groups by injury chronicity classification, there was a trend for a higher proportion of dogs with acute and subacute injuries in the favourable outcome score group compared to those with chronic injuries (p = 0.085).

TESF Group Total = 16

Splint/Cast Group Total = 11

Entire Population Total = 28

N (Percent)

N (Percent)

N (Percent)

Gender

16 Total

11 Total

28 Total

FS

06 (37.5 %)

04 (36.4 %)

10 (35.7 %)

M

03 (18.8 %)

02 (18.2 %)

06 (21.4 %)

MC

07 (43.8 %)

05 (45.5 %)

12 (42.9 %)

Tendon Rupture Type

16 Total

11 Total

28 Total

Complete

09 (56.3 %)

03 (27.3 %)

12 (42.9 %)

Partial

07 (43.8 %)

08 (72.7 %)

16 (57.1 %)

Complications

16 Total

11 Total

28 Total

Major

05 (31.3 %)

00 (0.0 %)

05 (17.9 %)

Minor

03 (18.8 %)

05 (45.5 %)

08 (28.6 %)

None reported

08 (50.0 %)

06 (54.6 %)

15 (53.6 %)

*= Statistically significant (p < 0.05) differences between treatment groups.


Table 2 Comparison of descriptive statistics by treatment group (initial coaptation method) for discrete variables. Note that one dog was treated with a calcaneo-tibial screw for coaptation and is not included in either treatment group.

The animals in this study were predominantly young adult to middle-aged largebreed dogs, consistent with previous reports (2, 5, 9). Contrary to a previous article (1), there was not any significant difference in the proportion of complete vs. partial tendon injuries. Despite a wide range of injury duration, the tendon was surgically repaired within three weeks of injury in 50% of the dogs. The results support our hypothesis that the outcome following surgical repair of Achilles tendon rupture in dogs is favourable irrespective of either the method of repair or initial joint immobilization. Most of the dogs (78%) with complete follow-up available had returned to an acceptable level of function with a function outsome score of 1 or 2. Complications were seen in 15 of 28 dogs (46%) and were generally related to the immobilization method rather than to the tenorrhaphy. Immobilization details and recovery time following surgical repair of Achilles tendon rupture have previously been reported in small case series. The total duration of postoperative joint immobilization ranged from five to nine weeks and recovery time ranged from seven weeks to 12 months in the 19 dogs in these studies (5, 7–9). In all but one study (8) the method of joint immobilization was modified to provide decreased support before complete removal. While recovery time is difficult to compare between the studies, due to different methods of assessment and follow-up intervals, our mean duration of joint immobilization of 10 weeks and mean recovery time to best function of 20 weeks (five months) compares well to the previously reported clinical outcomes. The complication rate following surgical repair of Achilles tendon ruptures in dogs has not been specifically reported. Previous case series (7–9) describe 15 repairs in 14 dogs that had initial joint immobilization via external fixator and five dogs that had initial joint immobilization via a cranial half cast (5). One report (8) of six dogs does not describe any complications. In the remaining three reports (5, 7, 9) of 14 total repairs, two major and two minor complications are attributed to external skeletal fixation, and four major and three minor complications are attributed to casting or splinting. Both of the types of complications seen and our


249 Achilles repair in 28 cases

overall complication rate of 46% were similar to these studies in aggregate. The prognosis for functional recovery following surgical repair of Achilles tendon ruptures in dogs has not been shown to be associated with chronicity of the injury. In this study there was a wide range of times from injury to surgery, with one dog presented for evaluation more than two years after the injury. There was not any association between chronicity of injury and recovery time in this study, but a favourable outcome was more likely in dogs with injuries that were less than three weeks old. The marginal significance of this finding indicates that if the same relationship held in a study with a larger sample size, the result would likely be statistically significant. The finding that less chronic injuries may have a better prognosis for the quality of functional outcome fits with our clinical impressions. In this retrospective study, the initial coaptation method was selected based on ‘surgeon preference’and was likely affected by patient factors such as personality and activity level, which are difficult to quantify. The dogs in the splint/cast group were significantly older than those in the TESF group, and this may represent a bias towards less active dogs when selecting this type of coaptation. Other patient factors such as breed and body weight were not different between the two groups. There were not any clear differences in outcome between treatment groups in this study. Using a TESF for initial immobilization resulted in significantly longer surgical time and greater initial cost when compared to using a splint or cast. There are additional costs associated with either immobilization method such as follow-up visits

for bandage care and radiographs, which could not be accounted for in this study because many dogs were seen elsewhere for bandage and other follow-up care. Contrary to our hypothesis, the TESF did not provide a quicker return to function. While there was a trend towards better functional outcome score in the TESF group, this difference was not statistically significant There were several limitations to our current study. It was retrospective in design, which limits the inferences that can be made from the results and may introduce bias or unknown associations. Prospective studies are preferred, but are logistically difficult particularly with a relatively uncommon injury. There was not an objective outcome assessment measure such as goniometric posture evaluation or computer-aided gait analysis. Although this is common in veterinary studies, it weakens the consistency of results and makes comparisons to previous or future studies more difficult. Data regarding coaptation management, functional outcome score, and recovery time were often gathered from records of the referring veterinarian or from client interview. The relatively small number of cases limits the significance of the study and makes it difficult to draw broad conclusions. However, compared to the few, small case series that currently comprise the veterinary literature on Achilles tendon injuries in dogs we feel that this study provides important clinical information regarding the treatment and outcome of this disabling injury. Acknowledgement We would like to extend our thanks to Cynthia Davies from the Biostatistics Consulting Laboratory, University of Minnesota School of Public Health, for assistance with statistical testing.

References

1. King M, Jerram R. Achilles tendon rupture in dogs. Compend Cont Ed Pract Vet 2003; 25: 613–21. 2. Rivers BJ, Walter PA, Kramek B et al. Sonographic findings in canine common calcaneal tendon injury. Vet Comp Orthop Traumatol 1997; 10: 45–53. 3. Moores AP, Comerford EJ, Tarlton JF et al. Biomechanical and clinical evaluation of a modified 3-loop pulley suture pattern for reattachment of canine tendons to bone.Vet Surg 2004; 33: 391–7. 4. Moores AP, Owen MR, Tarlton JF. The three-loop pulley suture versus two locking-loop sutures for the repair of canine Achilles tendons. Vet Surg 2004; 33: 131–7. 5. Guerin S, Burbidge H, Firth E et al. Achilles tenorrhaphy in five dogs: A modified surgical technique and evaluation of a cranial half cast. Vet Comp orthop Traumatol 1998; 11: 205–10. 6. Shani J, Shahar R. Repair of chronic complete traumatic rupture of the common calcaneal tendon in a dog, using a fascia lata graft: Case report and literature review. Vet Comp Orthop Traumatol 2000; 13: 104–8. 7. Sivacolundhu RK, Marchevsky AM, Read RA et al. Achilles mechanism reconstruction in four dogs. Vet Comp Orthop Traumatol 2001; 14: 25–31. 8. Morshead D, Leeds EB. Kirschner-Ehmer apparatus immobilization following Achilles tendon repair in six dogs. Vet Surg 1984; 13: 11–4. 9. deHaan JJ, Goring RL, Renberg C et al. Modified transarticular external skeletal fixation for support of Achilles tenorrhaphy in four dogs. Vet Comp Orthop Traumatol 1995; 8: 32–5. 10. Reinke JD, Mughannam AJ, Owens JM. Avulsion of the gastrocnemius tendon in 11 dogs. JAAHA 1993; 29: 410–8.

Correspondence to: Dr. Cheri Nielsen Pet Emergency & Speciality Center of Marin 900 E. Francisco Blvd, Ste C San Rafael, CA 94901 USA Phone: +1 415 456 7372 E-mail: [email protected]



250 © 2006

Case Report Schattauer GmbH

Deep digital flexor tendon shortening as a treatment for distal interphalangeal joint hyperextension in a 2-year-old mare G. Kelmer, J. Kramer Equine Section, Department of Veterinary Medicine and Surgery, Veterinary Medicine Teaching Hospital, College of Veterinary Medicine, University of Missouri Columbia, Columbia, Missouri, USA Summary

Shortening of the deep digital flexor tendon was performed by tenotomy, overlapping and anastomosis. The procedure was performed on a two-year-old Quarter Horse Mare with distal interphalangeal joint hyperextension with subluxation and metatarsophalangeal joint hyperextension. These problems originated from damage to the digital flexor tendons, presumably due to previous distal limb trauma. The procedure markedly improved the mare’s level of comfort, degree of ambulation and limb conformation. Two years following surgery the mare was comfortable at pasture.

Keywords

Tendon shortening, equine, distal interphalangeal joint, deep digital flexor tendon Vet Comp Orthop Traumatol 2006; 19: 250–4


Case report A two-year-old Quarter Horse Mare was admitted to the Veterinary Medicine Teaching Hospital (VMTH) College of Veterinary Medicine, University of Missouri for a sixmonth-old injury to the left hind limb. The original injury had been a puncture wound to the plantar aspect of the distal limb just proximal to the coronary band. The mare received minimal medical attention at the time of injury. Shortly thereafter she developed diffuse swelling and severe lameness of the affected limb. At that time medical therapy consisted of oral antimicrobials and phenylbutazone. During the weeks following the injury the mare’s lameness gradually improved, but during this time period at stance, the affected toe was gradually elevated off the ground, indicating potential rupture of the deep digital flexor tendon (DDFT) with resultant distal interphalangeal (coffin) joint hyperextension. In addition, the metatarsophalangeal (fetlock) joint was gradually sinking towards the ground, indicating loss of support from either the superficial digital flexor tendon (SDFT) or the suspensory apparatus resulting in fetlock hyperextension. Further treatment included short-limb cast application for approximately four weeks. Following cast removal, several attempts were made to place an elevated heel shoe but the mare kept pulling it off and eventually was left unshod. However, her level of lameness did not improve and the coffin and fetlock joints hyperextension continued to deteriorate. She was reported to be uncomfortable in pasture with a reluctance to move. Approximately six months following the original injury the mare arrived to the VMTH for evaluation and treatment.

Upon presentation the mare appeared bright and alert. Physical examination findings included marked conformational abnormalities in the left hind limb (Fig. 1). The toe was elevated above the ground while the fetlock was moderately dropped. Both abnormalities were evident in a standing position and were exaggerated at walk. Initial assessment was suggestive of loss of distal limb flexor tendons support, secondary to previous trauma. Ultrasonographic evaluation revealed a diffuse central hypoechoic lesion consistent with extensive fiber damage to the affected DDFT (Fig. 2). The lesion extended from just proximal to the fetlock to just distal to the proximal interphalangeal (pastern) joint (13 cm in length). In addition, in the lesion’s periphery there was loss of fiber alignment. Similar but milder lesions were noticed in the SDFT (Fig. 2). Radiographs showed negative plantar angle and some dorsal displacement of the third phalanx, consistent with moderate coffin joint hyperextension and subluxation. Unfortunately, the lateral radiograph was obtained at incomplete weight bearing position hence the degree of coffin and fetlock joints hyperextension is underestimated (Fig. 3). Bony proliferation was evident at the abaxial and distal margins of both proximal sesamoid bones on the oblique views (not included). We believe that the latter abnormality was due to excessive strain on the suspensory apparatus, secondary to decreased fetlock support by the flexor tendons. The enthesiophytes at the abaxial surface indicates strain of the suspensory branches while the enthesiophytes at the distal margin indicates strain of the distal sesamoidean ligaments. At this stage primary diagnosis of coffin joint hyperextension due to DDFT laxity was confirmed. Treatment options considered included: an experimental DDFT shortening procedure (1),


Received July 25, 2005 Accepted April 25, 2006

251 Deep digital flexor tendon shortening

Fig. 1 The left hind limb of a 2-year-old mare showing hyperextension of the distal interphalangeal and the metatarsophalangeal joints.

coffin joint arthrodesis (2–5) or conservative management including corrective trimming and shoeing (6). Distal limb amputation (7, 8) and euthanasia on humane grounds were also considered. We felt that shortening of the DDFT would be the best option for the horse. Conservative management had been previously attempted with unsatisfactory results. Techniques for coffin joint arthrodesis have been reported but none has shown consistent positive results. Distal limb amputation was not opted for due to the age of the horse and the limited average survival time reported for the technique. Both coffin joint arthrodesis and distal limb amputation were considered valid options for a salvage that could be used if the tendon shortening procedure failed. Preoperatively, the mare received intravenous broad spectrum antimicrobials (gentamicin [6.6 mg/kg, q 24h] and potassium penicillin G [22,000 IU/kg, q 6h]) and phenylbutazone (4.4 mg/kg, q 12h). Surgery was performed under inhalation anesthesia in lateral recumbency with the affected limb uppermost. A 10 cm long incision was made at mid-metatarsal region, on the lateral aspect of the flexor tendons. The paratenon was incised longitudinally, and the DDFT was exposed and severed. The proximal and distal tendon edges were overlapped by 15 mm and sutured together using two pairs of horizontal mattress sutures in 90 degrees to each other (Fig. 4). Suturing was performed using a new generation braided polyblend suture (Fiber-Wirea). In order to reduce a

Fiber-Wire, Arthrex, Naples, FL, USA.

tension on the repair following closure, a short limb cast was applied with the dorsal cortices of the phalanges aligned. Recovery from anaesthesia was uneventful and the mare used the limb well in the early post-operative period. The following day the treatment regimen was changed to potentiated sulphonamides (trimethoprim sulphadiazine 15 mg/kg, q 12h) and phenylbutazone (2.2 mg/kg q 12h). Oral antibiotics were discontinued six days following surgery. Ten days after surgery phenylbutazone administration was reduced, to once daily, and continued for additional 30 days. After four weeks the cast was removed under general anaesthesia, due to cast sores a new cast was not applied. The limb was placed in a com-

Fig. 2 Ultrasonographic image of the plantar aspect of the fetlock, showing large hypoechoic areas in the deep digital flexor tendon (see vertical arrow) indicating severe structural damage. In addition, a noticeable hypoechoic lesion is noticed in the superficial digital flexor tendon (see horizontal arrow).

mercially made metal splint (Leg Saver Splintb). In addition, the skin sutures were removed and the surgical site appeared to be healing well. Five days following splint application the affected limb was shod with a Patten bar shoe, with approximately 4.5 centimeter heel elevation and 3.5 centimeter caudal heel extension. Heel elevation resulted in dorsal hoof angle of 75° and planb

Leg Saver Splint, Kimzey Inc., Woodland, CA, USA.

Fig. 3 Lateral-medial radiograph of the distal limb upon admission.



252 Kelmer, Kramer

tar hoof angle of approximately 25°. Over the next two weeks the mare was gradually weaned from the splint and was using the affected limb adequately. At the time of discharge, the mare’s limb posture was significantly improved. The toe was no longer elevated off the ground at a stance, fetlock hyperextension was still noted but to a lesser degree than prior to surgery. Over the months following discharge from the hospital the heel elevation and caudal extension were gradually reduced. Two years following surgery the mare is comfortable at pasture but still shows some degree of fetlock hyperextension when weight-bearing on the limb.

Discussion Coffin joint hyperextension is typically manifested in neonatal foals with congenital laxity of the DDFT and carries a favorable prognosis with conservative management (6). Treatment involves corrective trimming and in more severe cases caudal hoof extension. In most cases the deep digital flexor muscle gradually gains strength and normal limb conformation is attained within several weeks. Severe congenital distal limb hyperextension is uncommon and does not respond well to conservative management (1). Acquired coffin joint hyperextension is uncommon and presents typically secondary to DDFT rupture following navicular disease and neurectomy but has been reported secondary to enzymatic dissolution of the DDFT due to chronic sepsis in the digital flexors tendon sheath (DFTS) (4, 5, 13). These acquired cases typically present with severe conformational changes and achieving longterm comfortable ambulation may require surgical management. In the current case, conservative treatment had been attempted prior to referral but was unsuccessful and was unlikely to succeed due to the age of the horse and the structural damage to the DDFT. In this case, the history includes a penetrating wound at the plantar aspect of the distal limb, above the coronary band, followed by distal limb swelling, marked lameness and local pain reaction at the plantar aspect of the pastern region. The severe lameVet Comp Orthop Traumatol 4/2006

Fig. 4 Intra-operative photograph, showing overlapping of the proximal and distal ends of the Deep Digital Flexor Tendon.

ness, following such a small puncture wound is likely to be attributed to either synovial infection, a direct tendon penetrating injury or both. Sepsis of the DFTS commonly results from a penetrating injury (9, 10). Direct penetrating injuries leading to severe structural damage to the deep and superficial digital flexor tendons, without involvement of the DFTS, have been reported (11, 12). Additionally, chronic infection of the DFTS, occasionally results in infection of the tendon itself leading to structural damage and even complete rupture (9, 10, 13). The damage to the tendons, in cases of septic tendon sheath, results from enzymatic dissolution of collagen caused by bacteria as well as inflammatory cells (13, 14). The diffuse extensive hypoechoic lesion in the DDFT and to a lesser degree in the SDFT, found upon ultrasonographic examination indicated severe structural damage along most of the flexor tendons within the DFTS. It is possible that partial laceration of the DDFT and SDFT occurred at the original injury and further deterioration, including potentially complete rupture, resulted in hyperextension of the coffin and the fetlock joints. Since we evaluated the horse six months following the original injury we can only make assumptions as to the most likely aetiology. Considering the history, clinical

signs, radiographic and ultrasonographic findings it appears that the severe structural damage to the flexor tendons occurred at the time of the original injury or soon following it. The structural tendon damage was severe enough to cause marked loss of flexural function, resulting in coffin and fetlock joint hyperextension. Reported surgical treatment options for coffin joint hyperextension include: coffin joint arthrodesis and flexor tendon shortening. Surgical arthrodesis of the coffin joint has been described (2–5). The surgery poses significant technical difficulties. The approach offers limited exposure due to the need to cause minimal damage to the coronary band, while avoiding the hoof wall. The proximity of the surgical site to the contaminated sole leads to increased risk of infection that can be devastating (3, 4). Arthrodesis eliminates coffin joint range of motion and increases the load on adjacent joints, especially the pastern, and may potentially result in severe osteoarthritis (3, 4). In addition, arthrodesis at best resolves the coffin joint hyperextension without resolution of the fetlock hyperextension. Clinically the mare was admitted with two abnormalities, a dropped fetlock or moderate fetlock hyperextension and severe coffin joint hyperextension. These clinical problems are a manifestation of loss of normal DDFT and SDFT function. Thus, biomechanically, re-establishing tension in the DDFT by shortening appeared to be the most reasonable solution to the case. In humans, it was shown that tendon shortening, as the sole treatment or as an adjacent procedure, for chronic tendon rupture, provides good results and may offer a better outcome than joint arthrodesis (15–17). The primary limitation of tendon shortening is that healing of a flexor tendon typically occurs with gap healing which is counterproductive to the goal of shortening of the tendon. Even in ideal experimental conditions healing of appositionally sutured equine DDFT occurs with a gap (18). Extended external support to prevent loading of the tendon and to minimize gap formation is an essential part of post-operative management of equine flexor tendon tenorrhaphy (19). Tendon healing within the DFTS is limited. In experimental conditions, tenorrhaphy followed by pro-


253 Deep digital flexor tendon shortening

longed rehabilitation including six weeks in a short-limb cast, resulted in 50 mm gap at six months without direct healing between the proximal and the distal edges. Both DDFT edges adhered with fibrous tissue to the SDFT (20). In this case, in order to achieve optimized healing and to avoid sheath related complications, we transected the tendon at mid-metatarsal region, an area lacking a tendon sheath. The paratenon at this area provides adequate blood supply and thus promotes healing (21, 22). Among the techniques utilized in human studies were V-Y tenoplasty and a flap from the distal end of the proximal tendon, looped transversely through the distal end, turned back proximally and sutured upon itself and the proximal tendon. A modification of the latter technique could potentially be utilized in the DDFT. We projected that V-Y tensoplasty would not provide adequate shortening. A recent experimental study in horses showed tenorrhaphy using bioabsorbable plates to be superior to traditional three-loop-pulley technique. The plating technique would have eliminated the need to overlap the tendon edges and may be advantageous. However, so far the technique has only been reported on cadavers and the plates were not commercially available (23). We considered several techniques for tendon shortening (Fig. 5). Performing tenectomy followed by end to end anastomosis may result in a large gap formation that would negate the surgical goal (Fig. 5A). Tenectomy and longitudinal splitting of both DDFT and SDFT followed by individual anastomosis of each tendon unit (Fig. 5B) was performed by Fackelman et al. (1) but a follow-up was provided. Longitudinal splitting offers increased tendon surface area for healing but we preferred not to further weaken the tendon by longitudinal incisions. Folding the tendon upon itself and suturing while keeping it intact does not offer incised tendon surface areas that promotes healing (Fig. 5D). Tendon folding avoids the potential for achieving tendon elongation which is an inherent risk with all techniques that involve incising the tendon but results in excessive bulging that interferes with wound closure. Due to the weaknesses of the abovementioned techniques, transecting the DDFT followed by overlap-

Fig. 5 Illustration depicting several tendon shortening techniques: A) Tenectomy with simple appositional end-to-end anastomosis; B) Longitudinal transaction of both SDFT and DDFT followed by suturing the tendon strips end to end; C) Transverse tendon transaction followed by overlapping and suturing; D) Folding the tendon, overlapping and suturing without transecting.

ping the desired length to be shortened was the technique selected in the current case (Fig. 5C, Fig. 6). Typical suture materials used for equine tenorrhaphy include large diameter (# 2) absorbable or non-absorbable synthetic monofilament sutures (24, 25). In the current case we used a new generation synthetic non-absorbable braided polyblend suture (FiberWire). This suture was shown to have extreme durability and strength and compared favorably in cycling loading with equal size

Fig. 6 Illustration depicting the DDFT biplanar tenorrhaphy technique used with the tendon edges overlapping 15 mm. Two pairs of horizontal mattress sutures were placed in 90 degrees to one another. Bold and grey lines represent individual horizontal mattress sutures in the same plane, the grey is slightly narrower and shorter than the bold.

synthetic braided suture materials (26, 27). We felt that due to the known difficulty with achieving initial adequate strength in equine tenorrhaphy, using a mechanically superior material would be advantageous. The goal of the surgery was to salvage the mare for pasture soundness, prevent continuous conformational deterioration and to improve weight bearing on the affected limb. Complete resolution of clinical signs enabling athletic activity was not achieved in this mare. However, the mare was pasture sound two years following surgery and the owners were satisfied with the mare’s level of comfort and conformation. It is likely that shortening the tendon beyond 15 mm would have resulted in a better distal limb conformation. One factor that limited the degree of DDFT shortening was the resultant laxity of the superficial digital flexor tendon (SDFT). However, another potential consideration was concurrent shortening of the SDFT. Combined shortening of the flexor tendons was performed on a foal with severe congenital coffin joint hyperextension with no reported long term follow up (1). Shortening of the DDFT tendon in the horse as a treatment for distal limb hyperextension abnormalities is a novel approach. In the current case, positive results were attained by using this technique. We believe that in selected cases of DDFT laxity, DDFT shortening may be a viable option for salvaging the horse.



254 Kelmer, Kramer

Acknowledgements The authors thank Jason Cooley for providing excellent farriery support and Don Connor for providing excellent graphic support.

References

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