Knee Joint Injection

Acute or chronic capsulitis

Causes and findings:
• Osteoarthritis, rheumatoid arthritis or gout
• Trauma
• Pain in knee joint
• Painful and limited: more passive flexion than extension with hard end-feel
• Possible effusion

Equipment:
Syringe - 5-10 ml
Needle - 21G 1.5 inches (40mm) green
Kenalog 40 - 40 mg
Lidocaine - 4 ml 1%-9 ml 0.5%
Total volume - 5-10 ml

Anatomy:
The knee joint has a potential capacity of approximately 120 ml in the average-sized adult. The capsule is lined with synovium, which is convoluted and so has a large surface area; in the large knee, therefore, more volume will be required to bathe all the surface. Plicae, which are bands of synovium, might exist within the joint and can also become inflamed. The suprapatellar pouch is a continuum of the synovial capsule and there are many bursae around the joint.

Technique:
• Patient sits with knee supported in extension
• Identify and mark medial edge of patella
• Insert needle and angle laterally and slightly upwards under patella
• Inject solution as bolus or aspirate if required

Aftercare:
The patient avoids undue weight-bearing activity for at least 1 week and is then given strengthening and mobilizing exercises to continue at home. One study indicated that total bed rest for 24 hours after injection in rheumatoid knees showed better results; however, the rest involved a hospital stay, which would not be cost effective.

Comments:
The injection will give temporary relief from pain and, provided the knee is not overused, this can last for some time. Repeat injections can be given at intervals of not less than 3 months with an annual X-ray to monitor joint degeneration. As with the hip joint, the patient might be awaiting surgery; the injection should not be given for at least 6 weeks prior to this.

Alternative approaches:
There are several ways to infiltrate or aspirate the knee joint - through the 'eyes of the knee', the supralateral approach into the suprapatella pouch just above the lateral pole of the patella, laterally at mid-point of patella or the medial approach as shown here. One study showed that there was more successful intra-articular placement using the lateral patella approach than through the 'eyes of the knee', but did not compare the lateral with this medial approach. The advantage of this approach is that there is normally plenty of space to insert the needle between the medial condyle and the patella, where even small amounts of effusion can be aspirated. The same approach can be used whether infiltrating or aspirating serous fluid or blood. For larger volumes, 40 mg Adcortyl, giving 4 ml of volume, might be the preferred steroid with less local anaesthetic. Hyalgen or similar substances can also be injected here but are more expensive than corticosteroids and do not appear to have longer-lasting benefits.