Introduction
The tarsus of dogs and cats is less frequently affected by disease or injury when compared to other joints. Ligament injury resulting in instability or luxation of one of the tarsal joint rows is probably the most common condition encountered in the tarsus of dogs and cats. Fractures of tarsal bones are less common. They can accompany ligament injures.
Osteochondrosis (OC) of the talus represents the most common disease of the tarsal joint. It typically occurs in young large breed dogs. The tarsal joints are also frequently involved with immune-mediated polyarthritis. Dogs and cats with bilateral tarsal pain and joint effusion, especially when in conjunction with carpal pain and joint effusion should therefore undergo arthrocentesis and cytology of the synovial fluid to diagnose or rule out polyarthritis.
Osteochondrosis of the Talus
Osteochondrosis (OC) of the talus is usually found in young (5-7 months) large breed dogs, although some dogs are only presented when older. Rottweilers are overrepresented. The lesions are more commonly located on the medial aspect of the talus (80%) than on the lateral aspect (20%). Clinical signs include a standing position with an extended hock, pain on flexion of the tarsus, crepitation, and palpable joint effusion. Both tarsal joints should be radiographed to rule out bilateral OC, which has been described to occur in approximately 40% of cases. The OC lesions are not always readily seen on radiographs and both an extended and flexed lateral view, an extended caudocranial view, a flexed craniocaudal view, and 45° oblique views may have to be obtained.1 The presence of degenerative joint disease in large breed dogs displays a high level of suspicion for OC, even if the OC lesion itself cannot be identified radiographically. Advanced imaging modalities, such as CT-scan, allow better visualization of the exact location and the extent of the OC lesion.2
When the loose cartilage flaps dislodge and float freely within the synovial fluid the condition is called osteochondrosis dissecans (OCD). The free cartilage fragments can grow and mineralize in the synovial fluid. They can also dislodge into the tendon sheath of the deep digital flexor muscle, which has a connection with the tarsal joint.3 Mineralized fragments then become radiographically visible in the soft tissues caudoproximal to the tarsal joint.
Treatment typically consists in removal of the loose cartilage flap, which should result in filling of the defect with fibrocartilage. The surgical approach is selected based on the location of the lesion on the medial or lateral trochlear ridge of the talus4,5: the plantaromedial approach exposes the plantar aspect of the medial trochlear ridge of the talus, which is the most common site for tarsal OC. The dorsomedial approach exposes the dorsal aspect of the medial trochlear ridge of the talus. The dorsolateral approach allows access to the dorsal, and the plantarolateral approach to the plantar aspect of lateral trochlear ridge of the talus. Arthroscopy has been used in recent years both to diagnose and to treat OC of the talus. It is less invasive than an open approach, but fragments cannot always be removed. Arthroscopic fragment removal was only possible in one to two thirds of cases because the fragments were too large in the others.2,6
Dogs generally improve after surgery although minor gait abnormalities may remain. Degenerative joint disease typically progresses. The time to reach maximal function after surgery has been described to be 30 days.7 Osteochondrosis of the lateral aspect of the talus seems to have the better prognosis than OC of the medial trochlear ridge of the talus.7
Displacement of the Superficial Digital Flexor Tendon
Displacement of the superficial digital flexor tendon (SDFT) at the level of the calcaneus is a rare condition that has been described in dogs,8 and in one cat.9 Shetland Sheepdogs seem to be overrepresented. The tendon of the superficial digital flexor muscle is part of the Achilles tendon. It normally passes over the calcaneus where it is attached both medially and laterally to insert on the palmar aspect of the middle phalanges. Rupture of the tendinous attachment of the SDFT to the calcaneus can result in lateral (more often) or medial displacement of the SDFT. Affected animals usually present with an acute lameness and a swelling over the calcaneus. Surgery involves repositioning of the tendon and reconstruction of its attachment to the calcaneus. Augmentation of the repair with an encircling wire has also been described.10
Ligament Injuries of the Tarsus
Ligament injuries can affect the tarsocrural, the intertarsal or the tarsometatarsal joints, resulting in instability or luxation. Stress radiographs may be needed to confirm the diagnosis and evaluate the exact location of the instability. Stress radiographs are performed under general anesthesia and include valgus and varus stress views, and often hyperextension and hyperflexion stress views. A good knowledge of the complex tarsal anatomy is necessary to be able to assess the injuries and to make a treatment choice.
Tarsocrural Instability and Luxation
Tarsocrural instability results from injury of the joint capsule and the collateral ligaments. Collateral ligament sprains occur most commonly on the medial side, and cause medial (valgus) instability. Medial or lateral instability is sometimes also caused by an avulsion fracture of the medial or lateral malleolus, which are the attachment sites of the collateral ligaments. Surgical repair is advised in the presence of clinically and radiographically evident joint instability. It involves repair of ruptured collateral ligaments and/or stabilization of fractured malleoli. Suturing of the shredded ligaments is not always possible or strong enough, and a ligament prosthesis is therefore applied in most cases. This can be done using a screw and figure-of-eight suture technique or a tunnel technique.11 A splinted bandage is usually applied for 3-4 weeks postoperatively.
Tarsocrural luxations are caused by trauma to multiple ligaments. Several combinations of injuries are possible. A common one is rupture of the medial collateral ligament, fracture of the lateral malleolus, and disruption of the distal tibiofibular ligament. Tarsocrural luxations always need to be treated surgically. The joint is reduced and the collateral ligaments/malleolus are repaired as mentioned above. A transarticular external fixator is commonly used for postoperative joint immobilization. Type II constructs should be used to avoid premature pin loosening.12 The external skeletal fixator is usually left in place for approximately 4 weeks.
Tarsocrural injuries are not uncommonly associated with shearing injuries. Surgical stabilization then has to be delayed until the presence of healthy granulation tissue indicates the wound to be free of infection. The wound is usually left to heal by second intention and temporary joint immobilization is performed with a splinted bandage or a transarticular external fixator. Fibrous periarticular tissue, which is formed during immobilization by a transarticular external skeletal fixator, can result in sufficient joint stability to obviate the need for specific ligament replacement.
Intertarsal and Tarsometatarsal Instability and Luxation
With intertarsal and tarsometatarsal instabilities or luxations it is important to determine if the dorsal or the plantar ligaments are disrupted. Plantar intertarsal or tarsometatarsal ligament injuries are more disabling than dorsal ligament injuries, because the plantar side is under tension during weight bearing. Plantar instabilities occur more commonly in the dog. They are usually located at the level of the calcaneoquartal joint, and the tarsometatarsal joint. Primary ligament repair is not feasible due to the large tensile forces. These injuries are treated by partial tarsal arthrodesis.
Dorsal instabilities are more frequently seen in cats than in dogs. Because the short dorsal ligaments are not under tensile stress during weight bearing, fibrous healing of the periarticular tissue results in restoration of functional joint stability if the affected joint is temporarily immobilized. Locking plates13 are ideal implants for internal immobilization of dorsal instabilities, but standard miniplates or a tension band fixation using screws or pins and a figure-of-eight wire/suture across the lesion can also be used. The prognosis is excellent.
Luxation of the base of the talus is another intertarsal injury that can be seen in dogs and cats. It is a debilitating injury if left untreated because it interrupts axial loading between the talus and the central tarsal bone. Luxation of the base of the talus has a good prognosis with internal splinting using a positional screw from the base of the talus into the calcaneus, or using locking plates or mini-plates applied across the dorsal surface of the talocentral joint.
Fractures of the Tarsal Bones
Fractures can involve any of the tarsal bones, but tend to affect the talus, the calcaneus, the central tarsal, and the fourth tarsal bone. They are sometimes associated with ligament injuries. Especially fractures of the calcaneus, the central tarsal bone, and the fourth tarsal bone occur more commonly in racing and working dogs than in pet dogs or cats.
Tarsal Arthrodeses
Arthrodeses are salvage procedures that are only performed if other means of treatment are not able to restore an acceptable and pain-free joint function. An arthrodesis involves debridement of the hyaline cartilage, application of a bone graft, and a stable fixation, usually with a bone plate. In the tarsus either a pantarsal or a partial tarsal arthrodesis can be performed, depending on the localization of the lesion. Postoperative immobilization of the tarsus is recommended after both pantarsal and partial tarsal arthrodesis. High postoperative complication rates of up to 75% have been described with tarsal arthrodeses, and they are more common with pantarsal than with partial tarsal arthrodesis.15
Pantarsal Arthrodesis
Indications for pantarsal arthrodesis include comminuted fractures of the tibiotalar joint surface, tarsocrural luxations with destruction of the joint surfaces, severe shearing injuries with destruction of the joint surfaces, chronic pain associated with severe osteoarthritis, and other conditions of the tarsocrural joint that result in permanent pain and dysfunction. Pantarsal arthrodesis has classically been performed with dorsal plating. Because a dorsal plate is positioned on the biomechanically weak compression side of the limb, it is prone to failure. The addition of an intramedullary pin has been shown to improve stability and fatigue life of the plate.16 The intramedullary pin is inserted in a normograde fashion (from proximal) into the tibia and is crossing the tibiotarsal joint. Medial plating has been evaluated in the last few years and is considered biomechanically superior to dorsal plating.17 Postoperative external coaptation is usually required for approximately 6 weeks. Complications of pantarsal arthrodesis include failure to fuse, implant or fixation failure, infection, skin necrosis, and bandage related complications.
Partial Tarsal Arthrodesis
The most common indications for partial tarsal arthrodesis are injuries to the plantar ligaments of the intertarsal and tarsometatarsal joints, where the tarsocrural joint is intact. A pin and tension band wire technique, bone plates, and external skeletal fixation have been used. The only indication for a pin and tension band wire technique is a plantar intertarsal instability of the proximal intertarsal joint. Bone plates are the best implant for partial tarsal arthrodesis. They are usually applied laterally, but can also be applied medially, especially for fusion of the tarsometatarsal joint row. External coaptation should not exceed 4 weeks for partial tarsal arthrodesis in order to preserve function of the tarsocrural joint.
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