The diagnosis of synovial crepitus syndrome should be made by the exclusion method, which gradually excludes other knee pathologies, such as knee extension device injury, patellofemoral arthritis, and meniscal injury. However, because its clinical manifestations are more similar to other knee pathologies, the differential diagnosis is more difficult and requires comprehensive history and sign analysis. (1) Differentiation between crepitus syndrome and knee extension device injury: the former has a longer course, mostly starting in adolescence, with intermittent onset of symptoms and gradual aggravation; the latter has a history of excessive physical activity or exercise, with onset in all age groups. Comparison of clinical findings: in the former, striae can be palpated on the patellar rim with pressure pain, and the pressure pain is reduced or disappears when the knee extension device is tense, while in the latter, swelling and pressure pain can be palpated on the knee extension device around the patella, and there is no relief when it is tense; in the former, the patellar grinding test can be felt as a flicking of the striae between the patellofemoral joint and pain, while the latter can be negative; in the former, the patellar twitch test is positive, while the latter is mostly negative. Although both squat test results are positive, the former mostly produces pain between 30° and 60°. (2) Differentiation between crepitus syndrome and patellofemoral arthropathy: the former is mostly symptomatic since adolescence and can lead to patellofemoral arthropathy in those with a long history; the latter has a high age of onset. In terms of clinical symptoms, the pain symptoms are very similar, but the former has frequent crisp popping sounds, while the latter has no popping sounds, and the latter has a rubbing sound; the former may have mild joint swelling intermittently, while the latter has no joint swelling when not accompanied by other diseases. Clinical examination reveals that although the results of both patellar compression and patellar grinding tests can be positive, the former can be palpated with patellar rim strips of pressure pain, and the patellofemoral joint can be felt as strips of flicking during patellar grinding, while the latter is only patellar pressure pain, and the patellofemoral joint feels rough and uneven during patellar grinding. (3) Differentiation between crepitus syndrome and meniscal injury: the former has a history of excessive exercise and may not have a clear history of trauma, while the latter has a history of acute trauma. Clinical symptoms, the former pain is mostly chronic dull pain, light only discomfort location can be in the suprapatellar or above the joint line; the latter in the acute phase of trauma pain is obvious, can be relieved when it turns old, but every time after the strangulation lock aggravated, the location of the medial-lateral joint space. The former has a variety of crisp popping sounds, which can be “babbling”, short “thump” and “crackling”, etc., located in the patellofemoral joint in front of the knee; the latter is a low, muffled sound. The former is frequently “pseudo” strangulation, only the popping sensation, do not need to unlock; the latter occasionally strangulation, not easy to unlock, or even unable to unlock themselves. (4) Crepitus syndrome and subpatellar fat pad inflammation: this disease is due to pathological hypertrophy of the subpatellar fat pad and the extrusion of the patellofemoral joint to produce congestion, edema and other inflammatory reactions caused by pain, when the knee joint is straightened fat pad by the patellofemoral joint extrusion caused by pain, the pressure point in the subpatellar fat pad.