In general, the best way to know if physical therapy is working is that you will see a gradual improvement in symptoms and function over time.
It is important to keep in mind that many patients with hip dysplasia have lived for decades with hip instability and that this can cause a lot of muscle and movement compensations over time. Re-training muscles to fire properly and teaching your body how to maintain postures and move in new patterns can take a lot of time. Be patient with the process and discuss strategies with your PT to help know if you are progressing in the right direction.
As a patient it is easy to get impatient with the process of recovery and feel like it takes forever. You may go through phases or rapid improvement and other phases of slower improvement during the treatment or recovery process. Keeping a diary or calendar of your symptoms or rehab progress can be helpful. Your PT can also be a great resource for maintaining perspective on recovery since he or she will be documenting your session activities and progress towards your goals on a regular basis. It’s important to keep your focus on the “big picture” goals and outcomes, but don’t forget to appreciate and celebrate the smaller milestones along the way!