There is great overlap between anatomy and rehab (prior to doing residency, I did a PhD in Anatomical Sciences, and I know of at least 2 others who have as well).
Some topics to consider for a 20 page paper:
1. The process of nerve healing, both within the central and peripheral nerve systems. Could have sections discussing Wallerian degeneration, distinctions the Seddon and Sunderland classifications for nerve injury, and current studies attempting to regenerate nerves in the CNS (e.g., with activated macrophages)
2. A discussion of the kinetic chain in athletic and biomechanical performance. There is an emerging literature how biomechanical deficits in the pelvic girdle (e.g., weakness in external rotation and extension) can cause pathologies in other joint along the kinetic chain (e.g., patello-femoral syndrome, ACL tears, low back pain, sprained ankles)
3. A discussion of anatomical pain generators in the lower back (e.g., herniated disks, z-joint pain, discogenic pain, z-joint cysts, sacro-iliac pain, compression fractures, radiculopathies, myofascial pain, lumbar strains), with some emphasis on the nerve supply for each pain generator.
Any of these topics can easilly be searched using PubMed, and there are good reviews on both topics in some of our journals, like Physical Medicine and Rehabilitation Clinics of North America, or in the chapters on emedicine. They will help you develop a further love of anatomy and realize how much there is still to learn in its clinical applications to PM&R.
