In 1887 he earned his medical doctorate from Friedrich Wilhelm University with a dissertation on scoliosis titled Zur Pathologie und Therapie der Skoliose, and afterwards remained in Berlin as an assistant to Julius Wolff (1836-1902). He received his habiltation in 1898, and two years later founded a private clinic. In 1908 he became an associate professor in Berlin.
In Berlin, Joachimsthal performed important experimental studies involving the physiological effects of orthopedic procedures. In 1907 he was co-editor of the Zeitschrift für Orthopädische Chirurgie, and in 1910 founded the Berlin Orthopedic Society. In 1905 he published a highly regarded textbook on orthopedic surgery called Handbuch der Orthopädischen Chirurgie.