What are the preferred techniques for knee joint injections, comparing the lateral approach and superior approach?

Knee Joint Injection Techniques: Lateral vs Superior Approach

For knee joint injections, the lateral approach is generally preferred over the superior approach due to higher accuracy rates, better anatomical access, and lower risk of complications.

Anatomical Considerations and Accuracy

• The superolateral approach to the knee joint has the highest pooled accuracy rate of 91% (95% CI 84% to 99%) compared to other approaches, making it the preferred technique for knee injections 1.
• The medial patellofemoral angle is significantly higher than the lateral patellofemoral angle in both healthy knees and knees with effusion, suggesting that the medial approach provides a larger joint opening for injection 2.
• Successful aspiration of synovial fluid helps confirm proper needle placement within the joint, which is more consistently achieved with lateral approaches 1.

Technique Comparison

Lateral Approach

• Involves insertion of a needle 1 cm above and 1 cm lateral to the superior lateral aspect of the patella at a 45-degree angle 3.
• Requires needle insertion of approximately 1 to 1½ inches, followed by aspiration aided by local compression 3.
• The anterolateral approach targeting the lateral femoral condyle requires a significantly shorter needle depth (3.0 ± 0.8 cm) compared to the medial condyle approach (5.0 ± 0.8 cm), making it technically easier 4.

Superior Approach

• While less commonly recommended in guidelines, the superior approach involves accessing the suprapatellar pouch.
• May be more challenging due to the anatomical constraints and potential for quadriceps tendon injury 5.
• Less evidence supports its routine use compared to lateral approaches 1.

Safety Considerations

• The lateral approach has fewer reported complications compared to medial approaches, with the medial approach showing a mildly higher number of bruises (p = 0.034) 6.
• Saphenous nerve injury has been reported following medial knee joint injection, particularly in obese patients where anatomical landmarks are obscured 7.
• The risk of septic arthritis following intra-articular procedures is very low (0.035%), but proper aseptic technique should always be maintained regardless of approach 1.

Imaging Guidance

• For difficult cases or when targeting specific compartments, ultrasound guidance is recommended to improve accuracy 5.
• Ultrasound guidance improves accuracy in delivery of intra-articular therapies, though clinical outcomes are similar to landmark-guided approaches 1.
• The accuracy of intra-articular injection depends on the joint and practitioner skills; imaging guidance is particularly recommended for joints that are difficult to access due to factors including site, degree of deformity, and obesity 1.

Clinical Outcomes

• Both medial and lateral approaches show statistically significant improvement in pain scores and functional outcomes when used for hyaluronic acid injections, without significant differences between approaches 6.
• The choice between lateral or medial approach ultimately depends on the operator's skill and experience, though the lateral approach appears to have fewer local side effects 6.

Procedural Recommendations

• Obtain informed consent, explaining the procedure, potential benefits, side effects, and post-injection care 1.
• Prepare an optimal setting: clean, quiet, private, well-lit room with the patient positioned appropriately on an adjustable examination table 1.
• Thoroughly clean and disinfect the skin with antiseptic solution before injection 5.
• Offer local anesthesia explaining pros and cons; options include topical anesthetics, subcutaneous infiltration, or intra-articular injection 5.
• Ensure availability of equipment for aseptic procedures and resuscitation equipment nearby, as vasovagal reactions occur in approximately 2.6% of procedures 1.

Pitfalls to Avoid

• Proceeding without proper aseptic technique, which increases infection risk 1.
• Failing to consider imaging guidance for difficult cases, especially in obese patients where landmarks are obscured 7.
• Using the medial approach in obese patients where the risk of saphenous nerve injury is increased 7.
• Expecting long-term relief from injections without implementing a comprehensive rehabilitation program 8.