Classic history and presentation: Patients often present with pain and swelling at the inferior pole of the patella, which is exacerbated with activities such as running and jumping. SLJD may present unilaterally or bilaterally. Point tenderness at the inferior pole of the patella is noted on physical examination and is sometimes accompanied by x-ray evidence of fragmentation or calcification of the inferior patellar pole.
Prevalence: SLJD is relatively rare and often misdiagnosed as Osgood-Schlatter disease (OSD). Incidence of radiographic abnormalities at the inferior pole of the patella is reported to be 2%-5% in healthy adolescents. However, it is difficult to assess the true incidence of disease since all patients with radiographic abnormalities do not present with symptoms of the disease. It is historically seen in adolescent males between the ages of 10 and 14 years who are regularly involved in athletics. However, similar rates may be observed in girls due to the rise in female athletic participation over the past few decades.
Risk factors: Risk factors include participation in sports that involve running and jumping, such as football, soccer, basketball, volleyball, and gymnastics.
Pathophysiology: Pathogenesis is similar to that of OSD, and the two disorders can sometimes occur simultaneously. The underlying pathophysiology is poorly understood but believed to be caused by repetitive microtrauma associated with traction of the patellar tendon on the developing patella.
Grade / classification system: Medlar and Lyne have proposed 4 radiographic stages of SLJD:
- Stage I – normal patellar findings
- Stage II – irregular calcification at the inferior pole of the patella
- Stage III – progressive coalition of the calcification
- Stage IV-A – incorporation of calcification within the patella
- Stage IV-B – calcified mass separate from the patella