Pain is the most important indication for joint replacement surgery and although surgery is successful in a vast majority of patients, some continue to have persisting pain. As per research evidence, approximately 9% after hip and 20% after knee replacement have an unfavourable pain outcome. 20% implies 1 in 5 patients, a significant number. Despite the high prevalence, the condition remains under acknowledged and can be rightly addressed as a silent epidemic.

Persistent pain not only has an adverse impact on the quality of life but often leaves patients confused or blaming themselves for the pain or the decision to go ahead with surgery. It can have an impact on mobility, general health, mood, sleep and lead to functional limitation with social isolation. When no obvious cause is found, the problem may be downplayed leading to the dissatisfaction, frustration, anger, tension or breakdown of the doctor–patient relationship, promoting doctor shopping. Somewhat ironically, persisting pain can sometimes be a consequence of surgery that was performed to alleviate pain.

Risk Factors for Persisting Pain after Knee Replacement

Persisting pain may have more than one reason, with a wide range of factors influencing the outcomes. It is important to know about these as some of them are modifiable. 

Some of the known risk factors include

• Poor mental Health including major depression, anxiety
• Catastrophization (Constant worrying and exaggerated negative orientation towards pain experience)
• Presence of other chronic pain conditions
• Surgical factors include infection, instability, implant loosening or failure, alignment problems with the implant (misalignment), soft-tissue impingement, nerve injury and extensor mechanism problems (patellar malt racking and non-resurfaced patella) 
• Severe preoperative pain. Some studies have linked poorly controlled pain after the operation to increased chance of developing chronic pain whereas other studies have found insufficient evidence. 
• High number of comorbidities (other medical problems). Pre-existing heart disease has been found to be an independent risk factor for pain at 5 years after knee replacement. The peripheral edema (swelling), sedentary lifestyle/ reduced engagement with physical therapy may contribute to increased pain levels. 
• Young age and female gender 

Pain Assessment

Most patients with persisting pain after the replacement surgery would return to the operating surgeon for a reassessment. Sometimes a second opinion from another surgeon is sought. Careful assessment in required to identify the problem and this involves detailed history, clinical examination (including the spine, hip and knee), psychological exploration, review of preoperative images & operative records, new investigations (serological, radiological and microbiological), assessing response to treatments and joint aspiration/ diagnostic injections if indicated. Sometimes despite extensive evaluation and best attempts using all modern technology at our disposal, the cause of pain cannot be identified. In such cases a trial of conservative therapy including pain relieving medications and physical therapy is often suggested. 

Management Of Persisting Knee Pain After Knee Replacement Surgery

Treatment of chronic pain after knee replacement is challenging. It requires a multidisciplinary team approach with input from orthopaedic surgeon, pain physician, physiotherapist, psychologist and many others. The aim is generally improvement in function and quality of life. Once the cause of persisting pain is known the treatment can be directed accordingly. 

Anatomically the cause of pain may be located 

• Extra articular (outside the knee joint at a distant site such as spine)
• Peri articular (around the joint) such as tendinitis (tendon problem), bursitis (inflammation of bursa) 
• Intra articular (inside the joint) such as joint instability, loosening of implant, issues related to size/type of implant, infection, osteolysis (loss of bone), kneecap problems 

How Can A Pain Physician Help ?

A pain specialist plays an important role in management of persistent pain and this includes

• Identifying the type /source of pain. This is especially relevant when issues with implant have been excluded and surgery is not required/not possible. Diagnostic joint injections can help differentiate whether the pain is coming from inside the joint or from an external source. If required, some joint fluid can be aspirated (removed) at the same time to evaluate for infection. Similar injections can be used to identify pain sources around the joint by trigger point injections, nerve blocks etc.
• Regulating pain medications. This is an essential component of overall management, best performed by professionals who are aware of all options and their limitations. Pain physicians are more familiar with use of stronger pain killers and some options such as capsaicin & Lidocaine patches as they use it more often. Sometimes small changes in medications can make a huge difference in the pain levels.
• Treating nerve pain. Nerve pain after knee replacement often goes unrecognized and may be responsible for persisting pain in approximately 6%-13% of patients. Typically, it presents with electrical shock like or burning sensation, numbness or altered sensitivity, although it can also present as an aching sensation associated with stiffness. Sometimes thickening of the nerve (neuromas) can be a source of persistent pain. 

Infrapatellar branch of the saphenous nerve. This is a small nerve running from the inner to the outer side of the knee below the kneecap. An injury to this nerve or a neuroma can be a common cause of persistent knee pain. Pain physicians can treat this successfully in an overwhelming majority of patients with nerve blocks, radiofrequency or cryoablation procedures. 

• Nerve blocks are offered if nerves are suspected to be the pain generator. A simple OPD performed procedure can often help identify the pain source and provide prolonged relief. 
• Pulsed Radiofrequency can be performed as a day case in an attempt to prolong the pain relief, in case the effect of the nerve block is short lasting. This is similar to nerve block but uses special needles and a radiofrequency machine to interfere with the pain signals being transmitted to the brain. 
• Cryoablation. This specialised technique involves application of cold to cause temporary disruption of the nerves ability to transmit pain signals without causing permanent nerve damage. 

• Other specialist interventions used to provide pain relief include

• Radiofrequency Ablation of Genicular nerves. Knee joint is supplied by many nerves and these are collectively addressed as genicular nerves. This procedure involves an initial diagnostic test whereby a small amount of local anaesthetic is injected close to these nerves. If this produces effective pain relief then one proceeds with the radiofrequency ablation. In radiofrequency ablation special types of radio waves are used to create a heat lesion around the nerves interrupting the transmission of pain signals to the brain. These nerves are approached with help of needles placed under x-ray and ultrasound guidance with no requirement for any surgical incisions. This is a safe, non-surgical procedure performed as a day case under local anaesthesia.
• Cooled Radiofrequency Ablation. Cooled Radiofrequency treatment is a minimally invasive treatment performed on a day care basis under local anaesthesia. The treatment aims to deactivate the nerves responsible for transmitting pain signals from the painful knee. It involves placing needles close to these nerves under x-ray or ultrasound guidance followed by heating of nerves to reduce the pain signals being transmitted. It differs from conventional Radiofrequency (described earlier) as it has water circulating through the device and can create a larger treatment area increasing the chances of success. Normal activities can generally be resumed soon after the procedure. 

• Spinal Injections – All nerves supplying the knee joint originate from the spine and interventions targeted on these (such as pulsed radio frequency of dorsal root ganglion) can help reduce the pain.
• Identifying your needs and directing you to other experienced professionals (such as physiotherapists, occupational therapists, psychologists) as required. 

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Chronic knee pain troubles a significant number of people worldwide. It is a common problem amongst the aging population, and can indeed be very painful and debilitating, sometime even confining individuals to the bed. The most common cause of knee pain in elderly is osteoarthritis (OA), a condition where the cartilages of the knee joint have worn out due to wear and tear. This results in friction between the bones of the joint during movement which results in pain. The impact is more in overweight and obese because of the extra load on the knees. The risk of knee OA in overweight women is nearly 4 times and in overweight men is 5 times greater. It is not just the mechanical factors which promote OA in obesity but also the co-existence of disordered glucose and lipid metabolism and the highly metabolic and inflammatory environments have a significant role.

What can be done for chronic knee pain?

Initial management involves lifestyle modification, supplements, simple pain killers and physiotherapy. It is estimated that an extra Kg of weight exerts a force of nearly three to six times across the knee while walking. Thus, weight loss is an important modifiable factor in the treatment of knee OA which the affected individual can drive. Various studies have demonstrated that weight loss improves both pain and function in obese subjects with knee OA.

Local injections are considered depending on the severity of problem and other factors such as age, functional status etc. When the pain and discomfort is severe your doctor may offer you the option of undergoing a knee replacement surgery. This involves removal of the worn out part of joint, shaping the ends of the bone and placing a metal implant. This reconstruction of the knee joint allows for smooth, pain free movement for most individuals. However some, even following the rehabilitation process, continue to experience pain.

For those who are

• Not keen on the replacement surgery or
• Not fit to have one or
• Continue to have pain after knee replacement surgery

Cooled Radiofrequency is an alternative treatment. Details about this treatment can be found in the Knee pain section of the website and in old blogs.

What causes continued pain following surgery?

The causes of knee pain following replacement surgery can be located inside the joint (intra articular causes) or outside the joint (extra articular causes).

The intra articular causes include:

• Knee joint instability
• Loosening of the implant
• Infection of the bone or the joint space
• Problems related to the kneecap (patella)
• Osteolysis (loss of bone)
• Issues related to size or type of implant

It is important to rule out the extra articular causes when a patient complains of persistent knee joint pain following surgery, because they can have serious consequences if they are missed.

The extra articular causes include:

• Localized knee problems such as tendinitis and bursitis
• Pain radiating from the nearby joints/body parts such as spine, hip and ankles
• People who have ongoing psychological illnesses will also tend to experience longer postoperative pain
• Nerve injuries/ problems

The focus of a recent research in Oxford, UK has been weather the knee replacement should be done earlier and not as a last resort. The authors suspected that long term persisting knee pain can lead to changes in the nervous system (nerves, spinal cord and brain) which can be responsible for persisting pain even if the original cause is corrected.

Diagnosing the problem:

You doctor will go through multiple steps in order to evaluate the pain you are experiencing. This process includes, taking a detailed history of the pain, such as when what type of pain you are experiencing and when you experience it the most. Then your doctor will go on to examine the knee, which will help him/her to further narrow down on probable causes & identify problems such as stiffness, swelling, and issues with alignment of the joint.

You will be asked to undergo investigations such as, X-ray, MRI, blood tests including inflammatory markers such as CRP and ESR etc.

How to manage this condition?

Depending on the cause of your pain, you doctor may suggest a variety of treatment plans. On some occasions pain relief medication may help to control the pain, and even get rid of it completely. Physiotherapy is another option which has proven to be effective in managing pain following knee replacement surgery. Nerve blocks are sometimes offered if nerves are suspected to be the pain generator. Cooled Radiofrequency of the nerve supplying the knee can help in reducing or resolving your pain issues. Sometimes repeat surgery such as revision knee replacement is required If.

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