Management of achilles tendon rupture in the small animal (Proceedings)

The Achilles tendon is the common calcaneal tendon and is most commonly injured by laceration in both dogs and cats.2 Chronic injuries are increasing in frequency and therefore will also be discussed here. The common calcaneal tendon is really three separate tendons including the superficial digital flexor tendon, gastrocnemius tendon, and the common tendon of the biceps femoris, gracillis, and semitendinosus muscles.3 The gastrocnemius tendon is the largest component and inserts on the proximal dorsal surface of the calcaneus. It functions to focus ground reaction forces through the tibia's long axis in both flexion and extension.4 The muscles of the common tendon insert predominantly on the tibia but all send continuations of the crural fascia to insert on the calcaneus. The superficial digital flexor tendon passes from deep to the gastrocnemius muscle proximally, medial to the gastrocnemius tendon, then superficial to the tendon with two insertions onto the lateral and medial surfaces of the calcaneus and continues distally to the phalanges.4

Acute injuries to the common calcaneal tendon are most commonly due to lacerations and have occurred within the last 48 hours prior to presentation. Subacute injuries have occurred at any time between 2 and 21 days and chronic injuries are older than 21 days.1 With chronic progressive or intermittent injuries resulting in progressive damage, onset of the disease is often difficult to ascertain. The severity of the rupture of the tendon has been classified as type I (complete disruption, plantegrade stance), type IIa (musculotendinous rupture, tarsal hyperflexion), type IIb (ruptured tendon but paratenon intact, tarsal hyperflexion), type IIc (gastrocnemius tendon rupture but semitendinosus intact, flexed hock with excessive digit flexion), type III (tendinosis or peritendinitis, normal stance).2 Chronic injuries are more problematic to treat and may carry a poorer prognosis since tendon and muscular contracture develops along with fibrous scar tissue at the ruptured tendon ends. The most common area for tendon rupture along the length of the tendon in humans and small animals is within 2 to 6 cm of the calcaneal insertion.5 This is also the area of tendon with the poorest blood supply and therefore the least likely to heal primarily without interposing inferior scar tissue.5 Re-establishment of a blood supply across the defect is important since all of the blood supply to the distal third of the tendon arises from the calcaneal bone.1,6

The pathogenesis of subacute or chronic injuries not associated with laceration of the tendon is not well understood. Avulsion fractures can occur in dogs less than 2 years of age due to immature bone in the calcaneous.1 Progressive rupture of the Achilles tendon can develop over time with injury to the gastrocnemius component most commonly affected.2 Suspected initiators of such chronic ruptures have included steroid and fluoroquinolone administration.5,7 These drugs have not been definitively proven causes of rupture in clinical small animals. Experimentally, fluoroquinolones can cause a decrease in collagen and elastin in tendons and articular cartilage of growing dogs most likely due to magnesium antagonism since most of the tendon and cartilage changes are similar to dogs with magnesium deficiency.8 Most veterinary cases are in large breed, active dogs and may be related to chronic repetitive injury during exercise.1

Whatever the insiting cause, diagnosis is made on physical examination and confirmed with radiography and ultrasound. Examination may reveal changes in posture with hock hyperflexion, with or without excessive digit flexion, and potentially a plantigrade stance. Palpation of the tendon may reveal thickening, thinning, or a normal sized tendon. Pain in the tendon or proximal muscle groups may be present as well. Radiographs may indicate an osteophytic reaction at the calcaneus to calcific deposits in the superficial digital flexor tendon just proximal to the calcaneus. The deposits are likely related to increased force placed on the superficial digital flexor tendon with rupture of the gastrocnemius tendon.1,9 Ultrasonography findings may include signs of hemorrhage, fiber disruption, and scar tissue formation.9,10 The contralateral limb may also be examined at the same time as the affected tendon since bilateral disease may be present.10 Normal tendon diameter as seen on transverse ultrasound images has been established at 2.4 to 3.2 mm.11

Surgical treatment is preferred over conservative medical management in cases of complete gastrocnemius tendon rupture since recurrence is common in conservatively treated cases.2,12 The method of repair used is often dependent upon the surgeon's preference and many procedures exist in human and veterinary surgery. In both human and small animal cases, primary repair of the tendon is performed and most commonly involves one of two different suture techniques: the three-loop pulley or the locking-loop suture pattern. Both patterns have superior strength over other patterns used in the past but the locking loop may have improved resistance to gap formation with loading of the tendon.13 A gap of less than 3 mm allows strength and stiffness to increase with a decrease in repair failure during the first 6 weeks following surgery.14 A modified three-loop suture pattern has been adapted for use with tendon avulsions and suture is passed through a bone tunnel in the calcaneous.15 In chronic cases, many veterinary reports recommend removing the interposing fibrous scar tissue to increase the strength of healing and to provide a successful outcome.1,2,10 A recent report of 6 human cases used the interposing mature scar tissue in the repair of the Achilles tendon and had a successful outcome.16 It is unknown if repair in dogs using scar tissue would be acceptable, however, excessive resection of scar tissue resulting in gap formation will impact negatively on healing. All sutures involved in the primary repair are recommended to be nonabsorbable monofilament suture in order to allow gliding motion along the suture but sustain re-apposition of the tendon ends for at least 3 weeks.2

Augmentation of the primary repair is controversial. Acute lacerations or injuries of less than 48 hours duration usually are not augmented at the time of surgery. Subacute or chronic lacerations are most often augmented with various implants or tissues intended to remain permanently at the repair site. Examples of synthetic implants include bone plates, carbon fiber, and polypropylene mesh.10,12 These implants carry the risk of significant foreign body reactions, infection, or self-mutilation by the patient. Biological implants include free fascia lata graft, porcine small intestinal submucosa, or in humans, pattern flaps of the peroneus, plantaris, and gastrocnemius muscles.5,12,17-19 The free grafts have the advantage of easy of implantation without the requirement of a large surgical approach with the attending morbidity but their main disadvantage is that they lack a blood supply and therefore, time is required for ingrowth of vasculature with delayed healing. Pattern flaps have the advantage of an immediate blood supply to the area of tendon repair and may facilitate earlier rehabilitation of the limb to stimulate healing of the tendon. Injection of the tendon repair with concentrated platelet gel has been advocated to speed healing post-operatively, however, it is ineffective without early controlled rehabilitation.20 Porcine small intestinal submucosa has been used experimentally in dogs and facilitates complete tendon healing within 90 days of the surgically created Achilles tendon defect.21 Use of porcine small intestinal submucoa in clinical cases of chronic calcaneal tendon injuries in dogs has not been reported. Some surgeons do not advocate the use of augmentation in dogs regardless of the chronicity of the injury since there is no definitive evidence that augmentation of a primary repair is more successful than primary end to end repair alone.2,5

Protection of the repair early in the healing process is a must. Additional support can be from casts, external skeletal fixators, splints, calcaneal-tibial bone screws, or a Rudy boot (external fixator attached to a boot distally). All of these methods provide relief of tension on the repair for 3 weeks to 3 months.2,22 Immobilization for longer than 4 weeks will result in deleterious effects on the joints, some of which can be permanent.23 In addition, early mobilization of the joint improves the healing process and augments the tensile strength of the tendon repair.20,24,25 The average length of time that some form of immobilization is needed is about 10 weeks, however, most surgeons decrease the amount of support incrementally over that time.22 Complications as a result of the immobilization following surgery occur in up to 46% of cases and can include infection, failure of the repair, fracture of bones involving screws or fixator pins, cast sores, and excessive tendon laxity.22 Some surgeons prefer rigid immobilization following tendon repair with an external skeletal fixator while others rely on casts or splints to allow some early mechanical loading of the repair. No study has shown a better functional outcome with one method over the other.2,6,22 Clearly the repair must be protected from excessive force, however, the earlier the return to some load-bearing the more likely the repair will be successful.

The prognosis for surgical treatment of Achilles tendon rupture in dogs has been deemed excellent by many authors.2,6,12 The patient may achieve a stable functional hind limb following repair but return to normal function is less likely. One study found that the average functional outcome was 1.9 on a scale of 1 (normal) to 6 (non-weight bearing).22 A study from New Zealand determined that only 7 out of 10 dogs return to full or substantial levels of work following healing and 29% of those have moderate persistent lameness.26 In humans, a degree of reduced function is not unexpected, and these patients unlike dogs, are plantegrade and may place less force on the Achilles mechanism.27,28

New methods to enhance and speed healing of tendon repairs are being investigated. Low energy shock wave therapy may enhance neovascularization of the bone-tendon junction in dogs.29 Ultrasound therapy may be able to accelerate healing and tendon maturation in dogs as well.30 While no clinical studies exist, future developments and methods of postoperative care in the future may improve the functional outcome in small animals with Achilles tendon injuries.

References

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11. Lamb CR, Duvernois A. Ultrasonographic anatomy of the normal canine clacaneal tendon. Vet Radiol Ultrasound 2005;46:326-330.

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13. 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;33:131-137.

14. Gelberman RH, Boyer MI, Brodt MD, et al. The effect of gap formation at the repair site on the strength and excursion of intrasynovial flexor tendons. J Bone Joint Surg Am 1999;81:975-982.

15. 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.

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19. Garabito A, Martinez-Miranda J, Sanchez-Sotelo J. Augmented repair of acute Achilles tendon ruptures using gastrocnemius-soleus fascia. International Orthop 2005;29:42-46.

20. Virchenko O, Aspenberg P. How can one platelet injection after tendon injury lead to a stronger tendon after 4 weeks? Acta Orthop 2006;77:806-812.

21. gilbert TW, Stewart-akers AM, Simmons-Byrd A, et al. Degradation and remodeling of small intestinal submucosa in canine Achilles tendon repair. J Bone Joint Surg Am 2007;89-A:621-630.

22. Nielsen C, Pluhar GE. Outcome following surgical repair of achilles tendon rupture and comparison between post-operative immobilization methods in dogs. Vet Comp Orthop Traumatol 2006;19:246-249.

23. Haapala J, Arokoski JP, Hyttinen MM, et al. Remobilization does not fully restore immobilization induced articular cartilage atrophy. Clin Orthop Relat Res 1999:218-229.

24. Enwemeka CS. Functional loading augments the initial tensile strength and energy absorption capacity of regenerating rabbit Achilles tendons. Am J Phys Med Rehabil 1992;71:31-38.

25. Murrell GA, Lilly EG, 3rd, Goldner RD, et al. Effects of immobilization on Achilles tendon healing in a rat model. J Orthop Res 1994;12:582-591.

26. Worth AJ, Danielsson F, Bray JP, et al. Ability to work and owner satsifaction following surgical repair of common calcaneal tendon injuries in working dogs in New Zealand. N Z Vet J 2004;52:109-116.

27. Mullaney MJ, McHugh MP, Tyler TF, et al. Weakness in end-range plantar flexion after Achilles tendon repair. Am J Sports Med 2006;34:1120-1125.

28. Kangas J, Pajala A, Ohtonen P, et al. Achilles tendon elongation after rupture repair: a randomized comparison of 2 postoperative regimens. Am J Sports Med 2007;35:59-64.

29. Wang CJ, Huang HY, Pai CH. Shock wave-enhanced neovascularization at the tendon-bone junction: an experiment in dogs. J Foot Ankle Surg 2002;41:16-22.

30. Saini NS, Roy KS, Bansal PS, et al. A preliminary study on the effect of ultrasound therapy on the healing of surgically severed achilles tendons in five dogs. J Vet Med A Physiol Pathol Clin Med 2002;49:321-328.