Grade one is the best - if there is such a thing. Hopefully with a joint supplement and no jumping, it will never get any worse.
Your Dad is pretty handy, isn't he? Get him to make you a set of stairs for Lexi to get on and off the couch!
You might want to consult an orthopedic specialist for a second opinion.
Here is some information from the Bhe Jei website:
Luxated Patellas
(slipping stiffles - knees)
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Luxated patellas or "slipped stifles" are a common orthopedic problem in small dogs. Dogs classified as small (such as Maltese) are much more likely to be affected as larger breed dogs. Luxated patellas are more common in female dogs. No research has yet identified the reason for this higher incidence in females, however researchers feel it could possibly be related to X-linked sex genes or hormonal influences.
Patellar luxation is a dislocation of the kneecap (patella). The kneecap may dislocate toward the inside (medial) or outside (lateral) of the leg, or may move in both directions. It may result from injury or congenital (present at birth) deformities. Both legs maybe affected. The most common luxation is medial patellar luxation in small breeds, such as the Maltese. This type of luxation is mainly a congenital or developmental condition. It is graded on a scale of 1 to 4, with grade 4 being most severe.
The crippling effects of patellar luxation are related to the severity and duration of the luxation. The milder forms, especially in small breeds, show little or no signs, and only minimal treatments required. Severe cases cause more intense pain, with limping. Grade 1 luxations may respond well to anti-inflammatory therapy and restricted exercise. These may or may not progress to worsening grades. Grades 2 through 4 luxations tend to require surgical corrections. The worse the luxations the more reconstructive surgery required to provide a functional joint.
Many techniques are available depending on the severity of the condition. Treatment ranges from rest (decreasing your pet's activity for 1-2 weeks) to surgical reconstruction of the knee joint. Treatment is based upon the severity of signs and your pet's age, breed and weight. Obesity complicates surgery and convalescence. A weight-reduction program may be required in conjunction with treatment. Satisfactory results are usually obtained if the joint degeneration has not progressed too far. Once the condition is repaired, most affected Maltese will make satisfactory recovery.