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Eqrtiue vet. J. (1992) 24 ( 5 ) 35 1-356

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Five cases ot gastrocnemius tendinitis in the horse 1

SUE J. DYSON AND LISA KlDD Equine Clinical Unit, Animal Health Trust, PO Box 5, Newmarket, Suffolk, CB8 7DW, UK.

Summary The normal gastrocnemius tendon may contain some muscular tissue proximally. This results in a patchy echogenicity ultrasonographically where it lies caudal or lateral to the superficial digital flexor tendon (SDFT). When it has assumed a position dorsal (cranial) to the SDFT the gastrocnemius tendon has a more uniform echogenicity and its margins are well defined. Five horses had lameness associated with lesions identified ultrasonographically in the gastrocnemius tendon in the latter region. Lameness ranged from mild to severe and was characterised by reduced hock flexion, lowered arc of foot flight, shortened length of the cranial phase of the stride and in some horses a reduced duration of weight bearing during the caudal phase of the stride. Lameness was variably accentuated by flexion of the proximal or distal limb joints of the lame limb. Perineural analgesia of the tibial and fibular nerves or the tibial nerve alone substantially improved the lameness. All horses remained lame 2-3 months after initial examination, with minimal change in the ultrasonographic appearance of the lesion(s). Introduction THE gastrocnemius muscle arises by two heads which terminate in the mid-tibia1 region in a common tendon. The gastrocnemius tendon

lies caudal to the superficial digital flexor tendon (SDFT),and then lateral and ultimately dorsal (cranial), inserting on the plantar aspect of the tuber calcaneus (Getty 1975). The superficial digital flexor and gastrocnemius tendons are separated by a bursa which extends to the mid-tarsal level. A small bursa also lies cranial to the insertion of the gastrocnemius on the tuber calcaneus. There may be communication between these bursae (Sack and Habel 1977). To the authors' knowledge gastrocnemius tendinitis has not previously been documented in the horse although rupture of the gastrocnemius tendon (Valdez, Coy and Swanson 1982) or muscle (Pascoe 1975; Sprinkle, Swerczeck and Crowe 1985; Shoemaker et a1 1991) has been recorded. The purposes of this paper are to describe the normal ultrasonographic features of the gastrocnemius tendon and the clinical and ultrasonographic features of 5 cases of gastrocnemius tendinitis.

Materials and methods Clinical investigation

The horses were referred to the Equine Clinical Unit of the Animal Health Trust between March and June 1991 for lameness investigation (Table I). A comprehensive clinical examination was performed at rest, moving in hand on a hard surface, and on the lunge on soft and hard surfaces (Table 2). Perineural and intraarticular analgesia of the lame limb was ultimately performed in

TABLE 1: Hlstory of horses wlth gastrocnemlus tendlnitls

Horse

Age (years)

Breed

Sex

Duration of lameness (weeks)

Occupation ~~

History

~

1

9

TB

G

R( PtoP)

7'

2

14 7

X TB

G

3

M

SJ E

8 2t

4

7

TB

G

D

1

5

7

X

G

GP

8

Sudden onset lameness after rough trailer ride and training gallop. Kept in work while receiving treatment with phenylbutazone; lameness deteriorated associated with the development of localised swelling Lame when bought in from field Performance deteriorated; refused several times before exacerbation of previously extremely subtle lameness Lame day after working for first time in deep going Sudden onset lameness

~~

TB = Thoroughbred; X = crossbred; G = gelding; M = mare; R (PtoP) = Racing (point to point); SJ = show jumping; E = eventing; D = dressage; GP = general purpose. 'Gluteal muscle atrophy at time of onset of problem indicative of more chronic problem. Radiographic evidence of degenerative joint disease of tarsometatarsal joint. tprevious sudden onset lameness 8 months after stop and fall cross country. Pain localised to hock region by local analgesia but no diagnosis reached. Rested 3.5 months and improved following resumption of work but subsequently deteriorated

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Fig 1 : Enlargement in the region of the gastrocnt ,mius tendon (Horse 2 ) I

Fig 3: "Capped" appearance oj the hock of Horse 5 . Note also the enlargement in the region of the AchiIles tendon Fig 2 : Enlargement of the bursa between gastrocnemius and superficial digital flexor tendons medially and laterally (Horse I )

performed using a linear scanner (DSL 300, Diagnostic Sonar), and a 7.5 MHz transducer, both with and without a stand off (Kitecko, 3M). The caudal or plantar soft tissues in the tibia1 and metatarsal regions were examined after fine clipping and washing of the limbs and liberal application of a coupling gel. Normal study

all cases (Table 3). Radiographic examination of the tarsus and proximal metatarsus was performed in Horses 1 4 and included dorsoplantar, lateromedial, dorsolateral-plantaromedial oblique, plantarolateral-dorsomedial oblique and flexed dorsoplantar views. An ultrasonographic examination of both hindlimbs was

An ultrasonographic examination of the gastrocnemius tendons of

5 clinically normal horses was performed. 'hvo additional horses were humanely destroyed for reasons other than hind-limb lameness. The cms of both hindlimbs of one horse was dissected with particular attention being paid to the gastrocnemius muscle,

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TABLE 2: Cllnlcal features

Degree of lameness at trot

Horse

At rest

1

Atrophy L gluteals. "Capped" hock; firm soft tissue swelling involving bursa between SDfT and gastrocnemius. Difficult to assess gastrocnemius

2-3

2

Atrophy L gluteals. Slight enlargement of gastrocnemius and localised heat (increased after exercise). Hyperextension of metatarsophalangeal joints +Swelling medial aspect immediately proximal to tuber calcis; medial and lateral margins less well defined compared to contralateral limb Slight enlargement of distal aspect of gastrocnemius and slight heat Enlargement of region of gastrocnemius and SDfT. Heat. "Capped hock

t .5-2

3

4 5

Gait characteristics Shortened duration of weight bearing caudal phase of stride; decrease in hock flexion; lowered arc of foot flight; tendency to land toe first; slight decrease in length of cranial phase of stride Marked asymmetry of hindquarters Slightly shortened cranial phase of stride. Decrease in hock flexion

Effect of flexion tests on lameness Distal limb Proximal limb N/C

Increase

Increase

Large increase

Large increase

Increase