how do I grade patellar luxation in dogs and what grade warrants surgical intervention?

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Patellar luxation (PL) is graded on a 1–4 scale based on manual reducibility and spontaneous reluxation. Grade I: the patella can be manually luxated but spontaneously reduces when released. Grade II: the patella luxates on stifle flexion or manual manipulation and remains luxated until the stifle is extended or manually reduced. Grade III: the patella is continuously luxated but can be manually reduced. Grade IV: the patella is permanently luxated and cannot be manually reduced. 4 Surgical intervention is warranted for grade III and IV luxations, and is indicated for symptomatic grade II disease. For grade II medial patellar luxation (MPL) managed non-surgically in initially asymptomatic adult dogs, 50% subsequently develop chronic lameness or require surgery at an average of 15 months after initial presentation. 9 Early surgical treatment is recommended for higher-grade luxations, particularly in dogs with higher body weight, to prevent cartilage erosion and secondary osteoarthritis. 5 Cartilage damage is already prevalent at the time of surgical correction and increases with grade. In dogs surgically treated for MPL, patellar cartilage erosion is present in 47.6% of stifles and femoral trochlear erosion in 54.4%, with both increasing in prevalence and extent at higher grades. 5 Symptom duration is independently associated with the extent of cartilage erosion, reinforcing the case for early intervention rather than prolonged conservative management. 5 Surgical outcomes are grade-dependent. For grade II MPL in Pomeranians, surgical success is 100% with an overall recurrence rate of 10% across all grades combined. 6 For grade III MPL, recurrence occurs in approximately 11% of cases, rising to 36% for grade IV in the same population. 6 In small-breed dogs with grade IV MPL treated with trochlear block recession, tibial tuberosity transposition, and soft tissue techniques, no major or catastrophic complications were observed, though minor and major complications occur