Sinding-Larsen-Johansson (SLJ) syndrome is a traction apophysitis of the inferior pole of the patella in skeletally immature athletes, the patellar counterpart of Osgood-Schlatter disease.
It typically presents at 10 to 13 years, slightly younger than Osgood-Schlatter disease, more often in boys and in jumping and running sports. It is usually self-limiting and settles with skeletal maturity.
The main hazard is missing a patellar sleeve avulsion fracture, an acute injury that can disrupt the extensor mechanism and needs urgent orthopaedic assessment.
The proximal patellar tendon attaches to the inferior pole of the patella. In the skeletally immature, the chondro-osseous junction there is weaker than the tendon, so repeated traction in jumping and running causes microtrauma at the bone rather than within the tendon.
Rapid growth adds to the load: bone lengthens faster than the quadriceps, raising traction at the inferior pole. The result is irregularity and fragmentation on imaging, and occasionally small separated bony fragments.
Patellar sleeve avulsion is a different injury. A sudden eccentric contraction, such as landing from a jump, tears the cartilaginous sleeve from the inferior pole. A small bony fragment on X-ray may be the only sign of a much larger cartilage injury, and the extensor mechanism is often disrupted.
The extensor mechanism has 2 traction apophyses:
In a skeletally mature athlete, pain at the inferior pole is patellar tendinopathy.
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