For the tartar sauce: In a small bowl, combine the mayonnaise, relish, hot sauce, salt, pepper, Cajun seasoning and vinegar. Cover and refrigerate for at least 30 minutes, or until ready to serve.
For the crab cakes: Meanwhile, in a large bowl, whisk together the melted butter, eggs, sour cream, parsley, lemon zest, lemon juice, hot sauce, Worcestershire sauce, Old Bay, capers, celery and salt. Gently fold in the crab and breadcrumbs. Form crab cakes by turning out 1/3 cup of the crab mixture for each cake onto a plate. Using the palm of your hand, lightly flatten the top to make patties.
In a large skillet over medium heat, heat the oil until shimmering, about 2 minutes. Cook the crab cakes in batches until brown and crispy, 4 to 5 minutes per side. Transfer to a paper-towel-lined plate to drain and sprinkle with salt. Serve with lemon wedges and a dollop of tartar sauce.
Panko breadcrumbs are Japanese breadcrumbs made with crustless bread--a lighter version of traditional crumbs, which are made using the crusts.