The surgery has no adverse effects in the long term. The main goal of this treatment is to allow the patient to return to his previous physical state and engage in sports activities without any limitations.
Certainly, the lengthened bone is a healing tissue at the beginning, but after full consolidation, it should have all the features and endurance of the original bone. In fact, the lengthened bone should have a harder consistency than the original one. So, by all means, it won’t be weaker.