RADIOLOGY: Imaging Utility of the Knee

Ultrasound offers high-spatial resolution imaging of

The extensor mechanism of the knee is a superficial structure which can be reliably interrogated with ultrasound.

Correlation with radiographs is routinely recommended at the time of ultrasound. Radiographic review of quadriceps and patella tendon outlines, ossification/ mineralisation within tendons and osseous pathology at tendon attachments improves ultrasound interpretation.

Intra articular structures such as the cruciate ligaments, menisci and cartilage cannot be accurately assessed with ultrasound and the modality offers limited evaluation of the medial collateral ligament and lateral collateral structures. Assessment of these structures are best

• Quadriceps and patella tendon tears and tendinosis

• Prepatellar and infrapatellar bursitis

• Paediatric/adolescent entities of Sinding Larsen Johansson and Osgood Schlatter syndromes

• Popliteal cyst (Baker's cyst)

Fig. 1: Normal extensor mechanism anatomy https://radiologykey.com/imaging-of-the-knee

Fig. 2a. Proximal patella tendinosis and tendon tear: Tendon thickening with loss of the normal fibrillar architecture and a fluid filled tear defect

Fig. 2c. MRI confirms a fluid filled tear deficit of the proximal patella tendon

Fig. 2b. Intratendinous neovascularity of tendinosis Fig. 3. Full thickness quadriceps tendon tear defect with the distal stump remaining attached to the superior pole of the patella

Fig. 4a. Osgood Schlatter’s: Tibial tubercle irregularity with fragmented mineralization within the distal patella tendon

Fig. 4b. Osgood Schlatter’s: Distal patella tendon thickening, echogenic tibial tubercle irregularity and echogenic mineralization within the distal patella tendon

Fig. 4c. Osgood Schlatter’s: Intratendinous hyperaemia and echogenic mineralization within the distal patella tendon

Fig. 5a. Sinding Larsen Johansson: Corticated ossification within the substance of the patella tendon and separate from the inferior pole of the patella, consistent with remote traction injury of the osteotendinous junction

Fig. 5b. Sinding Larsen Johansson: Echogenic ossification within the substance of the patella tendon and separate from the inferior pole of the patella, consistent with remote traction injury of the osteotendinous junction Fig. 6a. Prepatella bursitis: Increased prepatellar soft tissue density

Fig. 6b. Prepatella bursitis: Adventitial prepatellar bursal fluid

Fig. 7a. Baker’s cyst interposed between the semimembranosus and medial head of gastrocnemius tendons

Fig. 7b. MRI equivalent demonstrating the Baker’s cyst

1. Pathological entities of the extensor mechanism of the knee can be reliably interrogated with ultrasound due to the high spatial resolution of superficial structures

2. Radiographic correlation improves ultrasound interpretation

3. Intra articular and collateral structures are best characterized with MRI

Author Dr David Dow

Musculoskeletal Radiologist

Auckland Radiology Group