Pain at the bottom of the kneecap in active, growing children
SLJ disease causes pain at the bottom tip of the kneecap in growing children, typically in late elementary to middle school ages.
It is similar to Osgood-Schlatter disease but the pain location is slightly different — at the kneecap itself rather than below it.
Repeated jumping and sprinting cause cumulative micro-damage to the still-soft growth center at the kneecap's lower end.
The growth center (apophysis) at the bottom of the kneecap hasn't fully hardened
The strong pull of the quadriceps through the patellar tendon stresses the kneecap's lower tip
High training volume accumulates repetitive stress at the growth center
Micro-damage accumulates in the growth center, causing pain and swelling
Mild cases improve within a few weeks; higher training loads may require 1–3 months, and stubborn cases can take longer. SLJ usually settles on its own by the time growth is complete, and with a step-by-step approach to activity modification and rehabilitation, most young athletes return to sport without lasting effects. Return-to-sport criteria include: pain-free at rest and during jogging, able to do 10 single-leg squats without pain, and stable landing form. Surgery is almost never needed.