Diagnosis

Diagnostic measures include clinical and physical examinations as well as imaging procedures such as magnetic resonance imaging (MRI) and X-rays. In the clinical examination, a test can be used to check the “Zohlen’s sign”, which is specific for retropatellar arthrosis. Here, the patient lies on his back with his legs stretched out.

The examiner grasps the patella with one hand and carefully moves it downwards towards the lower leg and fixes it there. He then asks the patient to tense his thigh muscle, i.e. the quadriceps. This causes the patella to move back up again.

This is called a positive soles sign if the test causes friction and pain. This then speaks for a retropatellar arthrosis. The x-ray, which is basically used for diagnostics, allows a classification of the radiologically recognizable arthrotic changes.

Based on the stages, the therapeutic procedure can be planned. However, it should be noted that especially in the early stages, the clinical picture cannot match the radiological findings. The joint space narrowing, osteophytic marginal attachments, subchondral sclerosing and pseudocysts are the signs of arthrosis, i.e. also of retropatellar arthrosis, that are recognizable in the radiograph.

MRI can also be used to diagnose retropatellar arthrosis, although X-rays are preferred. The advantages of MRI are the very detailed and high-resolution imaging of the articular cartilage and the fact that there is no radiation exposure. The stage classification of retropatellar arthrosis, which can be primary or secondary, is used to assess cartilage damage, since arthrosis is a degenerative change in the joint cartilage.The classification according to “Outerbridge” describes the extent to which joint wear has progressed.

At a certain stage, the degeneration extends beyond the cartilage, so that the bone can also be affected.

Stage 0: no cartilage damage visible
Stage 1: surface of the cartilage still relatively intact and if, only the slightest changes in the form of cracks
Stage 2: Surface damaged, structural cartilage damage
Stage 3: Cartilage damage already deep and clearly visible
Stage 4: Cartilage completely destroyed and bone is also exposed.

Apart from the classification according to “Outerbridge”, the classification into 4 stages can also be done in the context of imaging diagnostics. In the so-called “Kellgren-Lawrence-Score”, radiological signs of osteoarthritis are used to define the severity of the disease.

These include subchondral sclerosis, joint space narrowing and osteophyte formation. It is important to know that the correlation between the stages and the actual feeling of illness or limitation of the patient is not identical.

Stage 1: mild subchondral sclerosis
Stage 2: Slightly irregular joint surface, slight narrowing of the joint space and formation of osteophytes
Stage 3: Joint surface highly irregular, joint space narrowing and osteophyte formation
Stage 4: Joint completely destroyed