犬の膝蓋骨脱臼：膝蓋骨がずれたとき
膝蓋骨脱臼は間歇性の跛行を引き起こす一般的な整形外科疾患です。重症度分類、治療法、手術の適応について学びましょう。
A luxating patella is one of the most common orthopedic conditions in dogs, especially toy and small breeds. It occurs when the kneecap (patella) slides out of its normal groove at the end of the thigh bone. Some dogs skip or hop on three legs momentarily before the kneecap pops back into place. While mild cases may only cause occasional discomfort, severe luxation can lead to arthritis and cruciate ligament injuries if left untreated. (Source: VCA Hospitals)
- Most common in toy and small breeds (Maltese, Chihuahua, Pomeranian, French Bulldog)
- Medial luxation (inward slip) accounts for most cases in small dogs
- Four severity grades from mild (Grade I) to permanent dislocation (Grade IV)
- Intermittent 'skipping' gait is the hallmark sign owners notice
- Surgery is highly successful when performed before arthritis develops
- Approximately 50% of affected dogs have both knees involved
What Is a Luxating Patella?
The patella (kneecap) sits under the patellar ligament, which connects the thigh muscles to the shinbone. During normal movement, the patella slides smoothly in a groove (trochlear groove) at the end of the femur. In medial luxation (the most common type in small breeds), the patella slips to the inside of the leg. This often happens because the dog has a bowlegged structure where the patellar ligament attaches too far inward on the tibia. Lateral luxation (slipping to the outside) is more common in medium to large breeds and can cause more significant mobility issues.
Severity Grades
Veterinarians grade luxating patella from I to IV based on severity. Grade I: the patella can be manually pushed out of its groove but pops back immediately when released. Grade II: the patella occasionally pops out on its own and stays out until the leg is extended and rotated. Grade III: the patella is out most of the time but can be manually pushed back in. Grade IV: the patella is permanently dislocated and cannot be repositioned. Higher grades carry greater risk of arthritis and cruciate ligament injury.
Recognizing the Signs
The classic sign is a 'skip' in the dog's step or temporary three-legged lameness that resolves suddenly. Owners may see their dog kick the affected leg backward to hyperextend the knee and snap the kneecap back into place. With medial luxation, some dogs develop a characteristic 'knock-kneed' stance. Over time, repeated luxation stretches supporting tissues, making recurrence easier and more frequent. If left untreated, chronic luxation leads to cartilage damage, arthritis, and increased risk of cruciate ligament tears.
Treatment Options
Grade I cases are often managed conservatively with weight management, joint supplements, and anti-inflammatory medications as needed. Grades II through IV typically benefit from surgical correction. Common surgical techniques include tibial tuberosity transposition (repositioning the ligament attachment), trochleoplasty (deepening the femoral groove), and soft tissue imbrication (tightening loose tissues around the knee). The prognosis is excellent if surgery is performed before arthritis or cruciate injury occurs, with most dogs regaining full use of the leg. If arthritis is already present, ongoing management with anti-inflammatories, joint supplements, and weight control may be needed.
- Intermittent skipping or hopping on three legs
- Sudden temporary lameness that resolves quickly
- Kicking the leg backward to 'snap' the kneecap back
- Knock-kneed stance or pivoting gait
- Persistent limping after a skip episode
- Swelling around the knee joint
RVC
RVC's orthopedic team can grade your dog's luxating patella through physical examination and X-rays. We offer both conservative management for mild cases and surgical correction for more severe grades. Early intervention prevents arthritis and cruciate ligament damage. To schedule an orthopedic assessment, call +853 6677 6611.
+853 6677 6611