Joint Trauma in Small Animals
Rupture of the cranial cruciate ligament is most frequently due to excessive trauma and a possibly weakened ligament secondary to degeneration, immune-mediated diseases, or conformational defects (straight-legged dogs). Plasmacytic-lymphocytic synovitis is sometimes diagnosed concurrently with ligament injury, but it remains unclear whether it is a cause or effect of the joint instability. Stable (nonsurgical) joints with an early or mild condition can be treated with steroids or an NSAID. Most injuries involve a midsubstance tear (mature dog), although bone avulsion (immature dog) at the origin of the ligament is possible. Instability of the stifle joint after rupture of the cranial cruciate ligament can lead to medial meniscal injury, joint effusion, osteophytosis, and joint capsule fibrosis.
Clinical signs involve lameness, pain, medial joint swelling, effusion, crepitation, excessive cranial laxity of the proximal tibia relative to the distal femur (drawer sign, or positive compression test), and increased internal tibial rotation. Partial cranial crucial ligament tears are characterized by a reduced cranial laxity, usually more pronounced in flexion. Medial meniscal injury may be identified by a clicking sound during locomotion or flexion and extension. A tibial compression test (flexion of the hock and cranial displacement of the tibial tuberosity) can also be used to demonstrate laxity of the cranial cruciate ligament. Radiography reveals joint effusion and signs of degenerative joint disease in chronic injuries. Arthrocentesis may reveal mild cellular increases and hemarthrosis. Arthroscopy can confirm the diagnosis but requires specialized equipment.
Treatments include medical and surgical therapies. Weight reduction, controlled physical therapy, and NSAIDs alleviate pain and discomfort from inflammation and degenerative joint disease. Surgical stabilization of the stifle joint is recommended for active dogs. Extracapsular techniques include fascial suturing, fabella to tibial tuberosity imbrication sutures, cranial transposition of the fibular head, leveling of the tibial plateau, tibial tuberosity advancement, and synthetic grafts. Intracapsular techniques include fascia lata or patellar tendon grafts sutured over the top of the lateral femoral condyle. Medial meniscal injury requires removal of damaged avascular tissue. Postoperative physical therapy is critical for clinical recovery. Prognosis after surgery is good.
Traumatic fractures frequently involve the shoulder, elbow, carpal, hip, stifle, and tarsal joints. In immature animals, the weakness of the physis compared with adjacent bones, ligaments, and joint capsule predisposes this area to injury. A Salter-Harris classification scheme (I-V) is often used to describe the location of the fracture relative to the physis and joint. Specific common sites of injury include the greater tubercle and condyle of the humerus, distal ulnar physis, and the head and condyles of the femur. The humeral condyle is also frequently injured in mature Spaniel breeds and characterized by Y or T fracture configurations. This may be related to incomplete ossification and vascularity of the bone.
Clinical signs of joint fractures include lameness, pain, and joint swelling. Chronic injuries may be characterized by angular limb deformities if the injury affected an open growth plate. Radiography and CT are useful in delineating the fracture.
The goal of joint fracture treatment is stable anatomic reconstruction to maintain joint congruency and joint and limb functions. Internal fixation with pins, wires, or screws is performed to achieve stable fixation. Prognosis for recovery is good if proper surgical technique has been used and joint trauma has not been excessive.
This hyperextension injury secondary to falls or jumps produces excessive force on the carpus, which leads to collapse of the proximal, middle, and/or distal joints secondary to tearing of the palmar carpal ligaments and fibrocartilage. Clinical signs include lameness, carpal swelling, and a characteristic plantigrade stance. External splints or casts may be attempted in mild cases, although surgical treatment is usually required to restore limb function. Surgery involves fusion (arthrodesis) of the affected joints using a bone plate and screws, pins and wires, or external skeletal fixation. A cancellous bone graft is used to enhance bone union, and postoperative support is necessary. Prognosis for recovery is good.
Traumatic dislocation of the hip is most frequently a craniodorsal displacement of the femoral head relative to the acetabulum. Clinical signs include lameness, pain during manipulation of the hip joint, and a shortened limb due to dorsal displacement of the femur. Radiography is useful in confirming the luxation and delineating the presence of other fractures in the femoral head or acetabulum. Treatment involves either closed manipulation and postoperative slings to maintain the reduction or open surgical stabilization using sutures or toggle pins. Femoral head and neck resection or total hip replacement can be performed after failed reductions. Prognosis for recovery is usually excellent.