I agree with the recommendation of Essentials of Musculoskeletal Care as a basic book for PCPs. It is well formatted and easy to read. It covers a lot of different conditions.
Delee & Drez's Orthopaedic Sports Medicine: Principles and Practice (2 Volume Set) (Hardcover) by Jesse Delee (Editor), David Drez (Editor), Mark D. Miller (Editor) is one of the main reference text used by orthopaedists for sports. It is a comprehensive reference geared toward orthopaedic surgeons, but useful for all.