Back Legs Immobile

Question
My gecko is about four inches long from head to the base of his tail, I've had him for four months. In the past week he has become increasingly sedentary to the point that he must be hand fed. He no longer uses his back legs and has become very unfriendly. His bone formation is fine and his jaw as strong, he bit me and held on for about a minute. I've confined him to a smaller habitat from the 25 gallon he shares with another gecko. He has no respiration issues as far as I can tell, and no hypocalcimic issues. He receives gutloaded crickets as well as waxworms and mealworms three times weekly. There is a dish of calcium for his access as well. The area around his rear legs is also thinning. Any answers would be great, thank you.

Answer
Hello Hans,

Well, what type of substrate are you using for the lining of the tank?  Sand, paper towels, tiles?
At his size, he needs to be fed daily since he is still growing.  If his muscle mass is thinning, then he sounds like he is not getting enough food intake.  
Great that you have calcium which is easily accessible to him.
How large are the crickets you are feeding him?  They should be smaller than the space between the eyes to avoid impaction.  
What are the temps in the tank for him?  Do you use an undertank heater in combination with a low wattage basking light?  There needs to be a basking or warm area on one end of the tank which reaches around 88-90 & a cooler end around 80 or so.
Can you post a picture of him?  Is the other gecko the same sex, or do you know the sex of either one of them?  Could it be an injury?

Tracie