Late MRI-detected patellar sleeve fracture: A case report
This is a detailed report of a case and a review of literature concerning the patellar sleeve fracture. The diagnosis of this type of fracture is often missed in the emergency room, which the mentioned case also stresses.

An 11-year-old boy, arrived at the accident and emergency department unable to bare any weight on his left leg. He explained that the same day he had been jumping on a trampoline when a sudden onset of pain and swelling occurred to his left knee, after landing on fully extended legs. The patient’s mother described the injury as a ‘dislocation of the femur close to the tibia’ immediately after the trauma.

The boy was of moderate adiposity, (70 kilograms), but otherwise healthy with no medical history and no recognized hypermobility, (Beighton scale 0), or use of steroids. Initial examination revealed diffuse swelling and extreme pain when trying to bear weight or when passive or active mobilization of the knee was attempted. Plain radiographs of the knee in accident and emergency department showed a high riding patella and calcifications according to the patella tendon. No fracture was seen.

A three-day ambulatory control revealed persistent swelling and global tenderness around the anterior aspect of the knee. The patient’s mobility decreased from 0 to 30 degrees and he was unable to perform a straight-leg raise. An ultrasound (US) examination revealed a likely avulsion and a small partial tearing of the ligamentum patella. There was no rupture of the quadriceps ligament.

For comparison, the right knee was also US-scanned and changes compatible with Sinding Larsen-Johansson syndrome were detected. Based on the US-verified avulsions, the patient was diagnosed with minor avulsions of the patella, and therefore, treated conservatively with a hinged knee brace for six weeks with gradual unlocking from 0 to 90 degrees, and allowance of full (weight) support.

Following the removal of the knee brace and six weeks of intensive physiotherapy, the patient still had pain-complaints and a 20 degree extension defect. Clinically, the patella was still high riding and a subsequent MRI scan revealed osseous avulsion of the inferior pole of the patella with division of ligamentum patella, an infrapatellar sleeve fracture. Subsequently, a subacute open surgical reduction and fixation of the patella as done, using a cerclage and fiberwire sutures.

This case was coincidentally examined in the emergency department three years following the sleeve fracture. The patient had been lifting weights and suddenly felt a similar onset of pain to the left knee as three years beforehand. A normal plain radiograph of the affected knee and a normal examination, apart from a little distinct soreness of the patella ligament, ruled out a re-rupture or fracture.

A five-year follow-up examination revealed that the patient was still complaining of soreness and swelling around the distal part of the patellar ligament. Based on an objective examination and normal radiologic imaging, the patient was treated with a methylprednisolone and bupivacaine blockade on suspicion of chronic irritation of the patellar ligament. At a six-year follow-up, the patient had no complaint.

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