Knee joint effusion has been shown to cause a reflex inhibition of the quadriceps musculature. However, the effect of effusion on knee joint proprioception has not been thoroughly investigated. This issue is further clouded by the debate surrounding the role of the muscle spindle and joint mechanoreceptors in providing afferent feedback to the central nervous system. This case study examines the effects of a chronic effusion on knee joint proprioception. Possible suggestions for the results are discussed, and areas for further study are offered.