Lumbar Disc Herniation: This condition can cause sciatica on one side and, due to pain or neurological deficits, lead to limping on the opposite side as a compensatory mechanism. Hip instability might be perceived due to altered gait mechanics.

Lumbar Spondylosis or Spondylolisthesis: These conditions can cause sciatica and lead to an abnormal gait, resulting in limping. Hip instability could be related to the altered biomechanics of the lower back and pelvis.
Piriformis Syndrome: This condition can cause sciatica due to compression of the sciatic nerve by the piriformis muscle. It might lead to limping and could contribute to the feeling of hip instability due to pain and altered gait.
Trochanteric Bursitis: While primarily causing hip pain, severe cases could lead to limping and might be perceived as hip instability. However, the presence of sciatica would need another explanation, possibly co-existing conditions.

Cauda Equina Syndrome: A serious condition that requires immediate medical attention, characterized by low back pain, sciatica, and potentially neurological symptoms like bladder or bowel dysfunction. Limping and perceived hip instability could be part of the presentation.
Spinal Infection (e.g., Abscess or Osteomyelitis): Infections in the spine can cause severe back pain, sciatica, and systemic symptoms. Limping and hip instability could be secondary to pain and neurological deficits.
Spinal Tumor: Tumors in the spine can cause back pain, sciatica, and neurological symptoms. They are less common but critical to diagnose early.

Arteriovenous Malformation (AVM) of the Spine: A rare condition that could cause back pain, sciatica, and potentially lead to neurological deficits, limping, and perceived hip instability.
Ehlers-Danlos Syndrome: A genetic disorder affecting connective tissue, which could lead to joint instability, including the hip, and potentially cause sciatica through various mechanisms, including spinal instability or nerve compression.