Knee pain manifests through various aetiologies, including injuries to cartilage, ligaments, tendons, muscles, and bones, as well as inflammatory conditions such as bursitis, gout, and rheumatoid arthritis. Some of other contributing factors may include patellofemoral pain syndrome, Osgood-Schlatter disease, cancer, or referred pain from the hip joint or lumbar spine.
Among these, osteoarthritis stands out as a very common cause, exhibiting a significant increase in prevalence in Australia with a 126% rise from 1990 to 2019.
Management of symptomatic knee osteoarthritis typically commences with conservative measures such as rest, cold packs, anti-inflammatory medications, physiotherapy, assistive devices, weight loss and TENS machine. When these methods fall short of providing adequate relief, more intensive treatments, including surgical interventions and interventional pain procedures, come into consideration.
Interventional pain techniques for knee osteoarthritis encompass a range of approaches:
Intra-articular steroid injection: This outpatient procedure, facilitated by anatomical landmarks or imaging guidance (ultrasound, x-ray, CT), reduces inflammation within the joint, offering short-term pain relief, generally for few weeks. Some of the studies demonstrated a pain reduction up to 24 weeks. The evidence suggests good pain relief with the use of intra-articular steroid injection, but only for short duration. Repeated injection of steroid may lead to cartilage volume loss; hence caution should be exercised with repeat injections.
Platelet-rich plasma (PRP) injection: PRP injections, gaining popularity in recent years, have shown varied results in studies, with some suggesting only comparable pain reduction to placebos, while others indicate significant improvements in pain and function. In this process, the patient’s blood (around 10ml) is centrifuged. The separated plasma, which contains platelets, other cells, cytokines and growth factor, is then injected into the joint space. The theory behind it is that PRP promotes cell proliferation and accelerates healing process via concentrated growth factors and proteins. Consensus about volume of the blood and frequency of the injection is still required. PRP is commonly used in knee pain from OA, meniscus and ligament injuries.
Visco-supplementation: Hyaluronic acid (HA) is a naturally occurring glycosaminoglycan and is a component of cartilage and synovial fluid. It can stimulate chondrocyte metabolism, synthesis of cartilage matrix and reduce inflammation. By injecting HA into the joint, HA aims to enhance synovial fluid viscosity, to act as a lubricant and a shock absorber. Cochrane reviews in 2006 found HA to be effective in managing knee pain from osteoarthritis.
Genicular rhizotomy: This technique targets chronic knee pain such as osteoarthritis or persistent pain post knee replacement surgery, which are unresponsive to conservative treatments. Rhizotomy works by ablating sensory nerves around the knee joint preventing the transmission of pain signal from knee to the central nervous system. Main targeted nerves are superior medial, superior lateral and inferior medial genicular nerves. Recent studies highlighted additional nerves that can be targeted for enhanced pain relief.
In clinical practice, the selection of nerves for rhizotomy is based on patient history and examination findings. Combining X-ray with ultrasound technique can help with precise needle placement to gain a better result from this procedure. It is worth noting that rhizotomy is a technique and can be performed in different ways – thermal rhizotomy, cryo-rhizotomy, pulsed or cooled radiofrequency ablation.
While novel techniques such as stem cell, amniotic fluid therapy and geniculate artery embolisation offer potential, further research is necessary to establish their efficacy and safety.
It’s important to acknowledge the risks associated with interventional injections, including infection, bleeding, nerve injury, exacerbation of pain, and steroid side effects. Hence, while interventional pain procedures represent significant advancements in managing chronic knee pain, providing targeted relief and functional improvement for individuals with debilitating joint conditions, their application requires a balanced assessment of risks and benefits to ensure optimal patient outcomes and should be offered once the conservative managements fail to provide a satisfactory pain relief.
Key messages
- Injections for knee pain can be considered after exhausting conservative treatments
- Intra-articular hyaluronic acid, steroid and PRP injections can provide a period of pain relief
- Genicular rhizotomy is an advanced pain procedure that can provide a long-term pain reduction.
– References available on request
Author competing interests – nil