Objective. The purpose of this investigation was to describe two sonographically guided popliteus tendon sheath injection techniques and determine their accuracy in a cadaveric model. Methods. A single experienced operator completed 24 sonographically guided popliteus tendon sheath injections, 12 using a longitudinal approach and 12 using a transverse approach relative to the tendon. The injection order was randomized, and all injections were completed with diluted colored latex. Coinvestigators blinded to the injection technique dissected each specimen and graded the colored latex location as accurate (in the sheath), accurate with overflow (within the sheath but also in other regions), or inaccurate (no latex in the sheath). Results. All 12 sonographically guided popliteus sheath injections using the longitudinal approach placed latex into the sheath. Eight of these injections (67%) also resulted in overflow into the knee joint. Ten of 12 transverse approach injections placed latex into the sheath (83%), with 7 of these (70%) also producing overflow into the knee joint. Two of 12 transverse injections (17%) placed latex only into the knee joint and were therefore inaccurate. Conclusions. Sonographic guidance can be used to inject the popliteus tendon sheath with a high degree of accuracy. Although the longitudinal approach is potentially more accurate, both approaches may result in injectate overflow into the knee joint, likely through the popliteus hiatus.