**Core Concept**
The obturator nerve is responsible for innervating the adductor muscles of the thigh, which are essential for hip joint adduction. Damage to this nerve can result in muscle weakness and pain in the affected area.

**Why the Correct Answer is Right**
The obturator nerve originates from the lumbar plexus (L2-L4) and travels through the obturator canal to innervate the adductor longus, adductor brevis, adductor magnus (adductor part), and gracilis muscles. These muscles are crucial for hip joint adduction, and their dysfunction can lead to pain and weakness in the knee and hip joint. The obturator nerve also provides sensory innervation to the medial aspect of the thigh and the knee joint.

**Why Each Wrong Option is Incorrect**
**Option B:** The tibial nerve is primarily responsible for innervating the muscles of the posterior compartment of the leg, including the gastrocnemius and soleus muscles, which are involved in plantarflexion of the foot.

**Option C:** The femoral nerve is responsible for innervating the muscles of the anterior compartment of the thigh, including the quadriceps femoris, which are essential for knee extension.

**Option D:** The saphenous nerve is a sensory nerve that provides innervation to the medial aspect of the leg and foot, but it is not involved in the motor function of the hip joint.

**Clinical Pearl / High-Yield Fact**
The obturator nerve is often damaged during hip arthroplasty or dislocation, leading to weakness and pain in the affected limb. It is essential to identify and address obturator nerve dysfunction in patients with hip joint pathology.

**✓ Correct Answer: A. Obturator nerve**