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Inferior dislocated patella locked by a loose body
  1. Yunhao Qin and
  2. Jiong Mei
  1. Department of Orthopedics, Shanghai Sixth People's Hospital, Shanghai, China
  1. Correspondence to Dr Yunhao Qin; yunhao_qin{at}

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Inferior patellar dislocation is rare in clinical practices.1 A 57-year-old man presented to the emergency department after slipping while cleaning the floor in the knee sitting position. He reported he suddenly slipped forward during the initiation of standing. Trauma evaluation revealed no intracranial, intrathoracic or intrabdominal injuries. He kept the left knee in flexion and had severe pain while extension. Lateral radiographs and CT scans of the left knee showed the patellar was locked by a loose body (figure 1). He underwent the peripheral nerve block of the lower left limb. The patellar was unlocked by being pushed to the distal end while slowly extending the knee. The post-reduction radiographs revealed the left patellar restored to normal position (figure 2). The patient accepted a knee brace for temporary fixation and was recommended further surgical intervention.2 However, the patient decided not to take the surgery and then was asked for a regular follow-up. Currently, the patient has returned to daily life.

Figure 1

(A) Lateral radiograph of the left knee, (B) lateral CT scan of the left knee and (C) axial CT scan of the left knee. All figures demonstrated an inferior dislocated patella locked by a loose body (yellow arrows).

Figure 2

(A) Anteroposterior radiograph of the left knee and (B) lateral radiograph of the left knee. Both figures demonstrated the patellar restored to normal position after manual reduction.

The origination of loose body remains controversial. Common causes of knee loose bodies are injuries to cartilage, osteoarthritis and inflammatory. In this case, the patient was a retired worker and was diagnosed with osteoarthritis 10 years ago. He reported no locking or catching of his knee in the past 10 years.

Learning points

  • Inferior patellar dislocation affects patients with osteoarthritis and osteophytes.

  • Peripheral nerve block and manual reduction are appropriate therapy for an inferior dislocated patellar.



  • Contributors YQ provided the image. YQ and JM revised the manuscript. YQ wrote the manuscript and treated the patient.

  • Funding This case report was supported by the National Natural Science Foundation of China (8190090238, to YQ).

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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