Osteochondrosis of the primary ossification center of the patella is also called Kohler disease [navicular osteochondrosis is also called Kohler disease]. For sake of differentiation, some authors also term it as Kohler disease of the patella. It is a rare cause of knee pain in children between 5 and 9 years of age.
It affects the single knee usually but bilateral cases have been reported in the literature.
Kohler disease of the patella is a type of osteochondrosis.
Cause of Kohler Disease of Patella
The etiology of osteochondrosis of patellar ossification center remains unknown though growth spurt or strenuous sports activities have been suggested to be possible causes.
The secondary ossification center, at the distal pole, is more frequently involved. This entity is called Sinding Larsen Johansson syndrome.
The patella develops by endochondral ossification at primary and secondary ossification centers. Primary centers are in the proximal region and are responsible for longitudinal bone growth whereas secondary centers contribute to the spherical growth and are present distally.
Primary ossification occurs between 3 and 6 years old; secondary centers appear in early adolescence and close during early adulthood. That is why Sinding Larsen Johansson disease occurs in that age group.
Why osteochondrosis develops so rarely in the superior pole of the patella is unknown.
The patient generally presents with anterior knee pain which is worsened by activities. The proximal pole of the patella may or may not be tender. The range of motion of knee is usually normal. Patellar gliding is usually normal. Slight effusion may be present.
Generally not required. revealed normal erythrocyte sedimentation rate, C-reactive protein, and complete blood count.
X-rays of the knee may be entirely normal. Xray may show fragmentation and sclerosis of the primary ossification centres of the patella.
MRI of the left knee demonstrated fragmentation of the primary patellar ossification center with enhancement seen on this T1-w sequence.
Kohler disease of the patella, like other osteochondroses, is a self limiting condition. It mostly responds to conservative and symptomatic treatment. It may take up to two years to completely heal radiographically.
Treatment recommended is activity modification to relieve the knee of stress and avoiding irritating activities.
NSAIDs like ibuprofen or acetaminophen as needed may be used for control of pain.
Icing 2-4 times a day also helps to relieve the pain.
Immobilization by splint or cast may be the need for few cases.