11.1.1 Cause

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  Osteoarthritis, rheumatoid arthritis, or trauma.

11.1.2 Presentation

An effusion may be visible or detected on clinical examination. The patient may be able to describe an initiating traumatic event or change in activity which precipitated an exacerbation of pain and swelling. However, in the patient with osteoarthritis the patient may be unable to describe any such mechanism.

11.1.3 Equipment

See Table  11‑1.

11.1.4 Anatomical Considerations

The safest and easiest technique is to use a lateral to medial approach immediately proximal to the superior edge of the patella. The clinician need not worry about any major blood vessels or nerves if this technique is used and excellent needle visualization is obtained for both aspiration if needed and injection.

11.1.5 Procedure

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  Supine with the knee flexed approximately 20 degrees.

  
  
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  Transducer placed in the transverse plane over the suprapatellar recess.

  
  
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  Needle introduced lateral to medial in long axis to the transducer.

  
  
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  Aim for the suprapatellar recess between the quadriceps tendon or quadriceps fat pad (superficial) and prefemoral fat (deep).

Note: Medial/lateral patellar gliding can improve identification of the suprapatellar recess.

11.1.6 The Aspiration/Injection

See Fig.  11‑1 and Fig.  11‑2.

11.1.7 Notes

In the case of trauma the possibility of a fracture should be excluded before an injection is considered. This is particularly the case in the elderly or osteoporotic patient who may sustain a fracture in return for a relatively innocuous injury. In the case of the younger patient consider a meniscal injury, ligamentous damage, or osteochondral lesion prior to injection.

In addition as in any corticosteroid injection infection or reactive arthritis should be considered when presented with an effused knee for which the patient can describe no significant initiating trauma.

If no effusion is present in the suprapateller region it may be easier to give the injection into the medial margin of the patellofemoral joint. In this case, the probe is placed in the transverse plane over the patella and medial patella femoral joint. The needle is introduced in line with the probe at a 45 degree angle deep to the patella.

In the case of an osteoarthritic knee with no clear effusion consider injection of a hyaluronan rather than a corticosteroid.

11.2.1 Cause

Spontaneous and insidious onset. The Baker’s cyst is often related to an underlying osteoarthritis of the knee joint. In the case of a semimembranosus bursa onset may follow a history of repetitive sporting activity such as repeated deep squatting during powerlifting.

11.2.2 Presentation

Swelling in the popliteal fossa may be quite large. More subtle swellings may only be seen on ultrasound.

11.2.3 Equipment

See Table  11‑2.

11.2.4 Anatomical Considerations

A Baker’s cyst is a synovial fluid–filled herniation through the posterior wall of the knee joint capsule. The cyst can usually be seen to originate deeply from the posterior aspect of the joint extending between the tendon of the medial gastrocnemius medially and the tendon of semimembranosus laterally in transverse imaging. Smaller swellings may represent a distension of the semimembranosus bursa in which case there may be no clear extension more deeply.

11.2.5 Procedure

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  The patient is positioned in prone with the knee supported on a pillow.

  
  
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  The transducer is placed in the anatomical sagittal plane.

  
  
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  The needle is introduced in a line progressing from inferior to superior in the long axis of the transducer.

  
  
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  Fluid is aspirated from the bursa.

  
  
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  If injection is also required, the needle may be left in place and a fresh syringe connected with the injectable drug.

  
  
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  Injection is given as a bolus.

11.2.6 The Aspiration/Injection

See Fig.  11‑3 and Fig.  11‑4.

11.2.7 Notes

Identify the popliteal artery, veins, and tibial nerve which should be seen medial to the swelling. The cyst/bursa may be lobulated and require that the different parts are targeted. In the case of the semimembranosus bursa corticosteroid injection may follow aspiration.

It should be noted that a Baker’s cyst is often related to an underlying osteoarthritis of the knee joint. In such cases treatment should be directed at the osteoarthritis as the predisposing factor.

When imaging the popliteal fossa, an accessory fabella (Latin for little bean) may be noted lying within the medial or lateral gastrocnemius tendon. This small sesamoid bone is a normal variant present in 10 to 30% of patients. Rarely there may be two to three of these bones (fabella bi or tripartite). The fabella rarely causes problems unless the patient’s occupation or sport involves repeated end-range flexion and heavy loading of the knee such as required in powerlifting or weightlifting. In this case guided injection around the fabella may be of both diagnostic and therapeutic benefit.

Although relatively rare, a popliteal artery aneurysm should always be excluded with the use of Doppler imaging. Popliteal artery aneurysms are the most common true peripheral aneurysm occurring more frequently than femoral artery aneurysm but less frequently than abdominal aortic aneurysm.

11.3.1 Cause

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  Commonly overuse.

  
  
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  Often related to long distance running or fell running.

11.3.2 Presentation

The patient describes pain over the lateral aspect of the knee which may be diffuse in nature but on palpation centered over the lateral femoral condyle. If the bursa is inflamed, there may be a palpable swelling.

11.3.3 Equipment

See Table  11‑3.

11.3.4 Anatomical Considerations

The bursa lies deep to the iliotibial band over the lateral femoral condyle of the femur. In its normal state it is not visible on ultrasound.

11.3.5 Procedure

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  The patient is positioned in side lying with the symptomatic side up and knee flexed to 20 degrees and supported on a pillow.

  
  
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  The transducer is placed in the anatomical coronal plane so that it lies longitudinally over the iliotibial band at the level of the lateral femoral condyle.

  
  
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  The needle is introduced from a superior to inferior line in the long axis of the transducer.

  
  
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  The needle tip should be positioned between the iliotibial band and the lateral femoral condyle.

11.3.6 The Injection

See Fig.  11‑5 andFig.  11‑6.

11.3.7 Notes

Inflammation and distension of the bursa is unusual. More commonly the bursa itself cannot be seen on imaging, but the iliotibial band appears thickened suggesting a more chronic condition. If this is the case, a higher-volume injection may be given with up to 10 mL to help stretch and free any adhesions.

As always the patient should be assessed in regard to any muscle imbalance or tightness of the iliotibial band itself. In addition, gait analysis should be considered if foot position is considered an issue.

11.4.1 Cause

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  Most commonly overuse.

  
  
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  Often related to long-distance running.

11.4.2 Presentation

The patient describes pain over the superior medial aspect of the tibia at the insertion of the tendons of sartorius, semitendinosus, and gracilis (pes anserine tendons). There may be some pain on resisted knee flexion. More commonly the only clinical finding is pain to direct palpation. If the bursa is inflamed, there may be a visible swelling.

11.4.3 Equipment

See Table  11‑4.