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A5-week-old male domestic longhair cat weighing0.56 kg (1.2 lb; case 1) was examined at Angell

Animal Medical Center-Boston because of abnormal con-formation involving the hind limbs. The kitten’s parentswere known to be anatomically normal. The affected kit-ten was the only kitten in the litter and had been bornwith bilateral hind limb abnormalities that had neitherprogressed nor improved with age. No other physicalabnormalities were observed. The owner had researched“twisted leg disease” on the Internet and brought the kit-ten in for evaluation and possible treatment.

The only musculoskeletal abnormality observedduring the initial physical examination was severebilateral tarsal hyperextension such that the kitten boreweight on the cranial aspect of the tarsus (Figure 1).No palpable bone abnormalities were detected. Thetibiotarsal joints could be flexed to an angle of approx-imately 135° (typical angulation of the tarsus in stand-ing position), but the manipulation required sufficientforce to elicit signs of discomfort in the kitten. No neu-rologic deficits were observed.

Radiographs were not obtained because of the kit-ten’s age and the assumption that bone ossificationwould be incomplete. The kitten was sedated with oxy-morphone (0.03 mg/kg [0.013 mg/lb], SC), midazolam(0.3 mg/kg [0.13 mg/lb], SC), and propofol (2.0 mg/kg[0.9 mg/lb], IV) to facilitate examination and applica-tion of a splint to each hind limb. Fiberglass splintswere placed on the lateral aspect of each limb from themid-tibial level to the digits to maintain the tarsus inan appropriate weight-bearing position. The laterallyplaced splints were ineffective at maintaining limbs inthe proper position and were changed 1 week later sothat they were positioned on the cranial aspect of thelimbs. This method of splinting was also ineffective.The following week, full-cylinder fiberglass casts wereplaced on both hind limbs from the level of the proxi-mal portion of the tibia to the digits. Casts werechanged weekly to allow for growth. By the third weekafter cast application, the kitten was able to ambulatewhile wearing the casts (Figure 2). Pressure sores withpurulent discharge developed near the medial and lat-eral malleoli and were cleansed with a dilute chlorhex-idine solution and partially closed with skin staples.The kitten was treated with amoxicillin (22 mg/kg [10mg/lb], PO, q 12 h) for 7 days.

The cast on the kitten’s left hind limb was main-tained for 8 weeks, and the cast on the right hind limbwas maintained for 14 weeks. After final cast removal,the owner was instructed to perform physical therapyto increase the range of flexion of the tibiotarsal joints.This entailed forcing the kitten to walk on the hindlimbs by manually elevating the forelimbs and by pas-sive manipulation of each tarsal joint. Physical therapywas prescribed for a minimum of 3 to 4 times each day

Congenital tarsal hyperextension in three cats

Nicole J. Buote, DVM, and Catherine J. Reese, DVM, DACVS

Case Description—3 kittens were examined becauseof a malformation affecting the hind limbs, resulting inan inability to bear weight or ambulate normally. Clinical Findings—2 kittens were younger than 6weeks of age, and 1 was 4 months of age at thetime of initial examination. The congenital abnor-mality was characterized by severe tarsal hyperex-tension in which weight was borne on the cranialaspect of the tarsus, and the plantar surface of themetatarsus faced dorsally. In 2 kittens, the condi-tion affected both hind limbs, and in the older kitten,the condition was unilateral. In the 2 kittens inwhich radiographs were obtained, no bone abnor-malities were detected. Full-cylinder fiberglasscasts were applied and changed weekly to accom-modate growth. Owners administered physicaltherapy after final cast removal.Treatment and Outcome—Conservative manage-ment involving external coaptation and physical thera-py led to favorable results in all 3 cats. Clinical Relevance—Although further studies areneeded to determine the etiology of the disorder,affected kittens may be successfully treated with con-servative management. Owners should be committedto the necessity for returning cats for serial castchanges, care for pressure sores, and administration ofphysical therapy after cast removal. (J Am Med Assoc2006;228:1200–1203)

From Angell Animal Medical Center-Boston, 350 S Huntington Ave,Jamaica Plain, MA 02130. Dr. Buote’s present address is DallasVeterinary Surgical Center, 4444 Trinity Mills Rd, Ste 203, Dallas,TX 75287.

Address correspondence to Dr. Buote.

Figure 1—Photograph of a 5-week-old kitten that was exam-ined because of a congenital anatomic defect involving thehind limbs. Notice the severe tarsal hyperextension andinward metatarsal rotation resulting in weight being borne onthe cranial surface of the tarsi with the plantar surface of themetatarsi facing dorsally.

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for 10-minute periods until normal limb position andrange of motion in the tarsus were observed. One yearafter the initial examination, the owner reported thatthe cat was using both hind limbs well, although theright limb was still disfigured. The owner acknowl-edged discontinuing physical therapy 1 month afterthe last appointment.

A 4-week-old female domestic shorthair kittenweighing 0.63 kg (1.4 lb; case 2) was surrendered tothe Angell hospital shelter. The kitten was the only kit-ten in the litter and was the offspring of a mother-sonmating. Physical examination revealed severe tarsalhyperextension in both hind limbs. The kitten was ableto drag itself with the forelimbs but could not bearweight on the hind limbs.

The kitten was sedated, and full-cylinder fiberglasscasts were placed at the level of the proximal portion ofthe tibia and molded such that the tarsal joints weremaintained in a weight-bearing position (approx 135°).Meloxicam (0.1 mg/kg [0.045 mg/lb], SC) was admin-istered for analgesia. Casts were changed every 7 to 10days to accommodate growth. Between visits, the ownerobserved the kitten to be ambulatory while wearing thecasts. A pressure sore that developed on the left tarsuswas managed with cleansing and administration ofamoxicillin (22 mg/kg, PO, q 12 h) for 7 days.

Six weeks after the first cast was applied, the castslipped off the right hind limb, and the owner wasinstructed to perform physical therapy. At a recheckexamination 1 week later, the cat was using the right hindlimb well and improvement was observed in the positionof the right tarsus. The tarsus had a decreased range ofmotion (range of flexion, 90°), but the cat was able toproperly bear weight on the paw. The cast on the left limbwas removed, and physical therapy was continued onboth hind limbs. Radiographs of both hind limbs wereobtained at 10 weeks of age, and no skeletal abnormalitieswere observed. The cat was examined every 2 weeks forthe next 6 weeks, and improvement was evident at eachvisit. Sixteen weeks after the initial examination, the cathad a slightly noticeable decrease in flexibility of the lefttarsus but was otherwise ambulating normally (Figure 3).

A 4-month-old male kitten (case 3), which hadbeen adopted from an animal shelter 1 month earlier,was examined. The kitten had been surrendered to theshelter with a female littermate that was clinically nor-mal. Severe tarsal hyperextension in the left hind limbwas observed with the kitten bearing weight on thecranial surface of the tarsus. The right hind limb wasanatomically normal. Radiographs of the affected limbrevealed no skeletal abnormalities. After sedation, afiberglass cast was placed on the left hind limb fromthe mid-tibial level to the digits. In this kitten, evenwith sedation, it was not possible to reduce the tarsalhyperextension to 180° of angulation without inducingsigns of pain. A single dose of meloxicam (0.1 mg/kg,SC) was administered after application of the cast.

The cast was changed every 7 days. While the kit-ten was sedated, the tarsal joint was progressivelyflexed prior to cast reapplication until a weight-bearingangle of approximately 135° was achieved. The catambulated well between visits while wearing the cast.After 4 weeks of casting, the tarsus remained at a 135°angle. The cast was removed at this time, and theowner initiated physical therapy. The kitten was exam-ined 3 times during the next 2 months, and use of thelimb progressively improved. Although the cat walkedon the plantar aspect of the paw appropriately, the tar-sus remained in an extended position. At that time, thetarsus could be flexed to an angle of approximately 90°without causing signs of discomfort.

DiscussionCongenital hyperextension of the tarsus occurs

infrequently in cats and has not been reported in theveterinary literature to our knowledge. The commoncalcanean tendon is composed of 5 structures, mostimportantly the superficial digital flexor tendon andtendon of the gastrocnemius muscle. Other contribut-ing structures are the tendons of the biceps femoris,gracilis, and semitendinosus muscles. Disruptions ofthe tendons can lead to various clinical signs includingplantigrade stance, curling toes, swelling over the tar-sus, and severe lameness; methods of diagnosis and

Figure 2—Photograph of the same kitten as in Figure 1 after 5weeks of wearing full-cylinder fiberglass casts. Notice that thelimbs are positioned such that the tarsus is maintained in an appro-priate degree of angulation and the kitten is able to ambulate.

Figure 3—Photograph of a kitten in which casts had beenapplied for 6 weeks. Notice the approximately normal hind limbstance with proper weight bearing on the plantar surface of thepaws, although the tarsus remains extended.

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S management for these disorders are well known.1-6

Talocalcaneal luxation, which results in similar clinicalsigns to those observed in the cats of this report, hasbeen reported in companion animals.7 A search of theInternet revealed many nonveterinarian-hosted sites inwhich “twisty-leg cats” or “twisted limbs” in cats werediscussed; however, a literature search disclosed nopeer-reviewed reports describing the condition.8

An anatomically similar condition (ie, clubfoot ortalipes equinovarus) has been described in Caucasianhuman infants. The structural abnormalities in affectedinfants are similar to those described in the kittens ofthis report. In humans, physical examination findingsinclude the ankle and heel being positioned in equinus(severe flexion at ankle joint) and varus (heel pointedlaterally) configurations, with the front part of the footsupinated (internal rotation) and with metatarsusadductus and calf-muscle atrophy.9 In affected humans,the defect occurs in both legs approximately 50% of thetime and is present at birth. The defect is thought toarise from 3 etiologies. Postural clubfoot develops as aresult of intrauterine molding and may be self-correctingor respond to conservative treatment. In other infants,the condition is linked with neurogenic or teratogeniccauses and in association with other neuromuscular dis-orders (eg, spina bifida and arthrogryposis).10-14 Most(75%) cases in humans are of unknown etiology,although a genetic relationship involving a single autoso-mal dominant gene has been proposed.

Breeding histories were not available for the cats ofthe present report, so determination of a genetic com-ponent to the disease was not possible. Two cats weresingleton kittens, which should have allowed for morespace in the uterus and a decreased likelihood ofintrauterine malpositioning. Neither concurrent con-genital defects nor neurologic deficits were observed inany of the cats. A primary muscular cause could not beruled out because muscle biopsy was not performed inany of the cats, but such information would be of inter-est in future studies.

The treatment of choice in humans is initiation ofcasting shortly after birth. Other treatments investigat-ed have included methods of soft tissue release (ie,posterior, medial, or plantar tenotomy procedures), aswell as application of malleable splints and taping.15-17

However, casting has the best outcome and is the leastinvasive. In the present study, cats responded favorablyto conservative treatment that included external coap-tation followed by physical therapy. Strict owner adher-ence to cast care measures and a long-term commitmentto returning cats on a weekly basis for reevaluation andcast changes are necessary. The only complicationobserved in the cats of this study was development ofpressure sores associated with the casts, but cleansing,administration of antimicrobials, and skin staplingyielded good outcomes in each instance. Although cast-ing can be challenging in pediatric veterinary patients,initiation of proper tarsal positioning and stretching ofthe musculotendinous unit of the common calcaneantendon at as young an age as possible appeared to beimportant. The soft tissues of the third and oldest catwere more difficult to manipulate, necessitating thatstretching be staged. Two of the cats had signs of pain

during recovery from sedation after application of thefirst cast, presumably as a result of stretching of thecommon calcanean tendon and other soft tissues. Itappears that treatment of this condition should be ini-tiated as early as possible to take advantage of thefavorable fibroelastic properties of soft tissues in andaround the joint in young kittens.

A cast was maintained in the first cat for 8 to 14weeks; the final outcome in that cat was not as cos-metically favorable or functional in 1 of the affectedlimbs as it was in the other. Failure of the owner tocontinue rigorous physical therapy beyond 4 weeksafter cast removal may have played a role in this out-come. Casts were applied for 6 weeks in the secondcat, followed by 10 weeks of physical therapy. Finaloutcome in that cat was a near-normal range of tarsalmotion and function in both hind limbs. In the thirdcat, casts were applied for only 4 weeks and physicaltherapy was performed for 8 weeks; that cat had sub-stantial improvement in positioning and use of thelimb. Other possible treatments such as tenotomy ofthe common calcanean tendon and external skeletalfixation were unnecessary. Additionally, the age ofthe kittens would likely preclude the use of externalskeletal fixation because of the absence of bonedevelopment. External skeletal fixation alone wouldalso have been difficult in the third cat because theproper weight-bearing angle could not be achieved atthe first visit. Surgical correction would likely bereserved for cats that did not respond to conservativemanagement.

Physical therapy was considered essential to thepositive outcome in the cats of this report. In oldercats, staged stretching at the time of cast applicationsmay be necessary, in addition to physical therapy for anextended period of time. In humans, corrections can bemade with casting and physical therapy in children asold as 2 to 3 years of age. Study of a larger number ofcats will be necessary to ascertain differences in treat-ment protocols, outcomes, possible causes, incidence,and prognosis.

References1. McNicholas WT, Wilkens BE, Barstad RD. Luxation of the

superficial digital flexor tendon in a cat. J Am Anim Hosp Assoc 2000;36:174–176.

2. Johnson AL, Hulse DA. Ligament injury of the tarsus. In:Fossum TW, ed. Small animal surgery. 2nd ed. St Louis: Mosby, 2002;1143–1150.

3. Piermattei DL, Flo GL. Fractures and other orthopedicinjuries of the tarsus, metatarsus, and phalanges. In: Brinker,Piermattei, and Flo’s handbook of small animal orthopedics and fracturerepair. 3rd ed. Philadelphia: WB Saunders Co, 1997;607–655.

4. Mughannam A, Reinke J. Avulsion of the gastrocnemiustendon in three cats. J Am Anim Hosp Assoc 1994;30:550–556.

5. Leonard CA, Tilson M. Feline lameness. Vet Clin North AmSmall Anim Pract 2001;31:143–163.

6. Earley TD. Carpal and tarsal injuries. In: Bojrab MJ, ed.Current techniques in small animal surgery. 3rd ed. Philadelphia: Lea& Febiger, 1990;871–883.

7. Macias C, McKee WM, May C. Talocalcaneal luxation withplantar displacement of the head of the talus in a dog and a cat. Vet Rec2000;147:743–745.

8. Veterinary Information Network. Message BoardArchives—Club Feet, Kitten. Available at: www.vin.com/Members/SearchDB/boards/b0150000/b0148054.htm. Accessed May 16, 2005.

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9. Scherl SA. Common lower extremity problems in children.Pediatr Rev 2004;25:52–61.

10. Dennis RR. The foot. In: Rudolph CD, Rudolph AM, eds.Rudolph’s pediatrics. 21st ed. New York: McGraw-Hill Book Co,2003;2425–2426.

11. Thompson GH. The foot and toes. In: Behrman RE, JensonHB, Kliegman RM, eds. Nelson textbook of pediatrics. 17th ed.Philadelphia: Saunders, 2004;2254–2261.

12. Musculosketal Part II. In: Netter FH, ed. The CIBA collection ofmedical illustrations. Vol 8. New Jersey: CIBA Geigy Corp, 1990;93–94.

13. Beaty JH. Congenital anomalies of lower extremity. In:

Canale ST, ed. Campbell’s operative orthopedics. 10th ed. St Louis:Mosby, 2003;988–1006.

14. Dimeglio A, Dimeglio F. Clubfoot. In: Fitgerald RH, KauferH, Malkani AL, eds. Orthopedics. St Louis: Mosby, 2002;1475–1489.

15. Herzenberg JE, Radler C, Bor N. Ponseti versus traditional meth-ods of casting for idiopathic clubfoot. J Pediatr Orthop 2002;22:517–521.

16. Souchet P, Bensahel H, Themar-Noel C, et al. Functionaltreatment of clubfoot: a new series of 350 idiopathic clubfeet withlong-term follow-up. J Pediatr Orthop B 2004;13:189–196.

17. eMedCenter. Congenital club foot. Available at: emedcen-ter.org/pages/default.asp?NavID=309. Accessed May 17, 2005.

Selected abstract for JAVMA readers from the American Journal of Veterinary Research

Objective—To evaluate the effects of deracoxib and aspirin on serum concentrations of thyroxine (T4),3,5,3'-triiodothyronine (T3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) in healthy dogs.Animals—24 dogs.Procedure—Dogs were allocated to 1 of 3 groups of 8 dogs each. Dogs received the vehicle used forderacoxib tablets (PO, q 8 h; placebo), aspirin (23 to 25 mg/kg, PO, q 8 h), or deracoxib (1.25 to 1.8mg/kg, PO, q 24 h) and placebo (PO, q 8 h) for 28 days. Measurement of serum concentrations of T4, T3,fT4, and TSH were performed 7 days before treatment (day –7), on days 14 and 28 of treatment, and 14days after treatment was discontinued. Plasma total protein, albumin, and globulin concentrations weremeasured on days –7 and 28.Results—Mean serum T4, fT4, and T3 concentrations decreased significantly from baseline on days 14and 28 of treatment in dogs receiving aspirin, compared with those receiving placebo. Mean plasmatotal protein, albumin, and globulin concentrations on day 28 decreased significantly in dogs receivingaspirin, compared with those receiving placebo. Fourteen days after administration of aspirin wasstopped, differences in hormone concentrations were no longer significant. Differences in serum TSHor the free fraction of T4 were not detected at any time. No significant difference in any of the analyteswas detected at any time in dogs treated with deracoxib.Conclusions and Clinical Relevance—Aspirin had substantial suppressive effects on thyroid hor-mone concentrations in dogs. Treatment with high dosages of aspirin, but not deracoxib, should be dis-continued prior to evaluation of thyroid function. (Am J Vet Res 2006;67:599–603)

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April 2006

Effects of deracoxib and aspirin on serum concentrations of thyroxine, 3,5,3'-triiodothyronine, free thyroxine, and thyroid-stimulating hormone in healthy dogs

David L. Panciera et al

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