As with any knee replacement, a sequential treatment regime starting with conservative measures and ending with the total knee replacement must be firmly established to show a clear primary or secondary procedure indication. The main aim of the article is to convert those who believe that TKA provides little or no benefit to patients with pain behind the knee. No specific surgical detail will be discussed as that can be found elsewhere in general or patellofemoral TKA references. The duration of the study referred to in all examples was at least 18 months.
Overview of Total Knee Arthroplasty
Patients with arthritis within the knee causing pain in the back of the knee respond well to total knee arthroplasty. People usually call this knee replacement surgery, however there are lots of different kinds of arthroplasties for diverse conditions. Total knee arthroplasty is considered the best and may comprise of resurfacing damaged cartilage with metal and plastic, or implanting artificial cartilage. The total knee arthroplasty is major surgery that consists of resurfacing the patella (knee cap). This is usually done when the patient has end stage changes of the patella cartilage. This kind of surgery is not the scope of this paper, however patients with bilateral facet changes of the patella from arthritis will also respond to this procedure. Total knee arthroplasty has been shown to be greatly successful in eliminating pain in the back of the knee related to indirect hamstring overload. This is due to the restoration of more usual sagittal plane motion at the knee. Total knee arthroplasty entails using metal and plastic to resurface the ends of the bones forming the knee joint. Time of healing varies depending on the patient. Usually healing is complete in three to 12 months, but thorough healing of the bone takes about a year. Post-operatively, the patient will require a well-structured therapy programme. This should restore normal gait pattern and muscle balance around the knee and also improve knee motion. This is usually a successful method to resolving knee pain in the back of the knee.
Causes of Pain in the Back of the Knee
The pain of isolated PCL insufficiency would be at the back of the knee with a feeling of instability or giving way. This is usually pain with recent or old injury, and often the pain is activity-related. Osteoarthritis may affect PCL insufficiency knees where there may be pain from more diffuse disease but it is difficult to be certain if the pain is from the arthritis and thus would be a relative indication for surgery at the same time as complex cartilage reconstruction. Early isolated PCL disease without arthritis is a rare condition seen more often in young athletes. They may well respond to PCL reconstruction, and the decision for TKA is unusual unless secondary arthritis develops. Osteophyte impingement is a cause of pain with specific activities as during sitting in a deep armed chair, or climbing steps. It is posteriorly located at the level of the joint line. A small fragment may be intra-articular and cause symptoms of locking or catching.
The most common reason people seek the advice of a knee specialist occurs when they have pain in the back of the knee. The cause of pain in the back of the knee is multifactorial. It may be related to the knee joint itself or be referred pain from more proximal in the thigh or below in the shin. There may or may not be accompanying swelling or instability. Pain in the back of the knee may be acute onset, and chronically become more severe. Conditions discussed in this essay are those that are most effectively treated with total knee arthroplasty (TKA).
Diagnosis and Evaluation
The physical examination often follows on from the history and is targeted to confirming or refuting the diagnosis. An effusion or swelling within the knee can obliterate the symptoms of the lesion and therefore aspiration or arthrocentesis may be a diagnostic as well as a therapeutic measure. A needling sensation and pain relief with aspiration will confirm that the swelling was responsible for the patient’s pain. Other tests specific to diagnoses are beyond the scope of this essay.
The medical history is an important part of the evaluation and often provides the most valuable information regarding the cause of the patient’s knee pain. Important points in the medical history often include an injury, an unusual twisting or wrenching motion of the knee, changing of position of pain i.e. kneeling, squatting and recent infection. These suggestive points will lead the physician to the most likely diagnoses. It is important to distinguish pain in the back of the knee vs. pain in the front of the knee as there are different structures and different pathologies responsible for the pain. Pain in the back or posterior aspect of knee is likely to involve the hamstrings, the ligaments within the joint or a cyst emanating from the joint. Pain felt at the back of the knee but coming from the lower back is likely a referred pain and the pathology is in the lower back. Cotton and Ride’s article on clinical examination of the posterior cruciate ligament is a paper which may be of interest.
Physical Examination and Medical History
Histiocytic reaction, foreign body and/or particle disease are poor clinical diagnoses and a confirmation of the clinical suspicion is necessary. The recognition of osteolysis adjacent to a well-fixed prosthesis has a major impact on patient treatment. The use of metal-backed porous coated patellar components in TKAs is an attempt to decrease the incidence of polyethylene wear and osteolysis which have been problems with conventional patellar designs. A practical diagnostic test is the use of a lateral radiograph of the knee with the patella tangentially pointed to aid in the visualization of patellar osteolysis. Ultra high molecular weight polyethylene debris has also been shown to induce a foreign body granulomatous reaction that clinically and radiographically resembles infection. A characteristic feature of osteolysis of the tibia or femur around the knee prosthesis is pain or loosening of the TKA in a previously asymptomatic individual.
Knee aspiration is often necessary to adequately differentiate infection from aseptic failure in the TKA. The ESR and quantitative CRP have been shown to be sensitive tests to aid in the diagnosis of infection. Subsequent discussion regarding the actual numbers of these tests varies and is dependent on the form of arthroplasty and the status of the patient’s general medical health. Available evidence would suggest that levels in the range of 35 for ESR and 10 or 1 mg/dl for CRP have been shown to accurately diagnose infection.
Physical examination A major determinant in the clinical examination of a patient with a TKA is the clinical indication for the implant. In patients with apparent failure of a TKA with gross loosening and bone loss, the physical findings may be obvious. However, in the patient with pain and swelling but without an obvious history of acute injury, the dilemma is to exclude or intentionally confirm the possibility of infection. Periprosthetic joint infection can mimic some of the manifestations of mechanical failure with pain and effusion. The physical examination should be directed toward an accurate differentiation of these problems. A systematic approach to this problem using specific tests for infection has been recommended.
Imaging Tests for Knee Evaluation
The typical findings of patients with pain localized to the back of the knee and without significant arthritis are degenerative changes within a meniscus and a cyst in relation to the meniscal tear. An MRI scan is the best test to assess damage to the menisci, as it can show both the inner and outer edges of the meniscus. It is also good for detecting a tear of the ligament or a cartilage defect on the bone surface. In the case of a suspected meniscal cyst, which is relatively rare, an ultrasound examination can be very effective in making the diagnosis, and this can be followed by MRI to assess the nature of the damage to the meniscus. The best test to show a Baker’s cyst is an ultrasound, but an MRI is usually done as this can also assess the underlying cause such as a meniscal tear.
Imaging tests are an important part of the evaluation of knee pain. X-rays are usually taken to look for arthritis, a common cause of pain in the back of the knee. Patients with arthritis typically have a narrowing of the space within the joint and bony spurs around the joint. X-rays are also useful to look for other causes of pain, such as a tibial stress fracture or a loose body in the joint. Rarely, special x-ray views or an MRI scan are needed to look for a stress fracture. MRI is the best test for a loose body, although a large loose body can be seen on a plain x-ray. It is also useful to assess the extent of damage to the cartilage or ligaments, although it may show abnormalities that are not actually causing the patient’s pain.
Other Diagnostic Procedures
Looking beyond the knee: It is important to realize that pain localized to the back of the knee is not uncommonly referred from the lumbar spine. It may also be referred from a Baker’s cyst, particularly if there is associated swelling. A careful history and physical examination should help differentiate between these causes of pain. Often the quality of the pain, back pain with radiation down the leg versus a sharp catch in the knee, may be the only guide. If in doubt, nerve conduction studies and a CT scan of the lumbar spine may be helpful. The latter investigation will also show up any arthritic change in the facet joints, another potential source of referred pain to the knee. Finally, one must consider the possibility of referred pain from a more distal source. An ultrasound examination of the leg should pick up a Baker’s cyst and clinically this may be suspected if the knee pain is accompanied by a feeling of ‘giving way’ or locking. In cases of referred pain from symptomatic varicose veins or peripheral vascular disease, treatment should be directed at the primary cause of the pain.
Non-Surgical Treatment Options
As the baby boom generation continues to age, the demand for treatment for pain of back of knee in patients over 65 years will continue to increase. Age is not the only factor contributing to this increase, as the indications for TKA have expanded over the years to include a variety of conditions that lead to disability and pain. With the success of total hip arthroplasty and allowing patients to lead active lives, the demand for relief from knee pain due to the desire to continue many work and leisure activities is necessary to enjoy a good life. Many patients experience varying degrees of pain in the back of the knee joint. This can be due to a variety of causes including: Baker’s cyst, intraarticular pathology where the patient localizes pain to the back of the knee or simply referred pain from degeneration of the patellofemoral joint or one of the tibiafemoral compartments. These patients desire relief from their pain in order to continue or return to an active lifestyle. There is no gold standard to the surgical treatment of pain in the back of the knee joint. Many attempts can be made to manage symptoms non-surgically, with different modalities aimed at different pathology. Given the often times degenerative nature of the knee conditions and the patients age, many are not keen on immediate surgical intervention for what they perceive is a relatively minor problem. Non-surgical treatments include medications, bracing, steroid injections, aspiration and rest. This population of patients in today’s economic climate is increasingly being influenced by the cost of medical care. It is now important to consider cost effectiveness of treatments and the resulting quality adjusted life years as compared to surgery. Having said that, with the continuing improvement of TKA as a reliable and effective surgical option for knee arthritis, the threshold for the influence of cost and what patients are willing to undergo as previously mentioned above is likely to change.
Medications for Pain Management
High risk of complications with knee surgery may prompt some patients to try NSAIDs. They are highly effective at reducing pain from inflammatory conditions and are popular with arthritis sufferers. Unfortunately, their effect on PFP is moderate at best and must be weighed against increased risk of gastrointestinal bleeding, interference with fracture healing, and creation of adverse renal conditions. Due to these circumstances, NSAIDs are generally not a preferred long-term option for PFP, but a short controlled trial may achieve positive results for some patients.
Paracetamol is the most commonly used analgesic and is generally well tolerated. It has few side effects and can be used long-term with appropriate monitoring. If paracetamol is ineffective or inappropriate, stronger opioid-based narcotics such as codeine or tramadol could be used. Opioids are highly effective painkillers; however, their use is limited by numerous side effects, including drowsiness, constipation, and addiction. The decision to use opioids should not be taken lightly, and patients should be made aware of their potential negative effects.
Patients with chronic pain in the back of the knee, unrelieved by non-surgical methods, may require medications. The three most common drug groups used to alleviate knee pain are analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), and intra-articular corticosteroids. Unfortunately, no medications are specifically targeted to relieve the pain of PFP, and the response to all medications is variable. With this in mind, it is logical to start with the safest drug group, simple analgesics.
Physical Therapy and Exercise
When attempting to treat chronic pain at the back of the knee in patients with end-stage knee OA, exercise is recommended as a method to ease pain. In terms of exercise, muscle strengthening has shown to improve pain and function greatly compared to OTC medication. Specifically, the quadriceps muscles are paramount to knee joint health. Weak quadriceps muscles have been shown to be a strong risk factor for developing knee OA and also an accelerant. Additionally, strong quadriceps muscles decrease pain and increase function. Concentric and eccentric training have been shown to improve pain and function in knee OA patients by increasing quadriceps strength. Although concentric training is effective, eccentric training, although shown to be effective, is difficult to implement because it has been noted to cause muscle soreness and increased knee joint pain during activity. Other types of exercise such as aerobic exercise tend to have a lower effect size in comparison to strength training, but are nonetheless beneficial and should not be disregarded. Finally, it is worth noting that prolonged rest is detrimental to knee OA as it causes increased weakness of the quadriceps muscles and stiffness of the knee joint.
Assistive Devices and Orthotics
Assistive devices and orthotics come in a variety of different options. When it comes to assistive devices, the use of a cane can offload weight from the affected knee and place it in the upper extremity. Canes are easy to use because they are simply gripped in the hand. However, the effectiveness of the cane depends on the strength and correctness of usage. Patients first need to be instructed on which side to hold the cane and which side the cane should be used on. They should then be instructed to place the cane on the same side as the affected knee and then step through with the normal leg at the same time as the cane. If the usage is done incorrectly, it will be uncomfortable and non-beneficial. Unloading braces may also be beneficial. These braces can shift the load away from the affected knee to the normal or less affected knee. The braces aim to reduce pain and slow the progression of knee osteoarthritis. The expected result is the preservation of function and delay of TKA. However, the overall effectiveness of offloading braces have not been shown to be more beneficial compared to consistent patient education.
Lifestyle Modifications
It is important that patients understand the impact of lifestyle on their knee pain and work with their physicians to identify and implement beneficial changes. Losing weight may help diminish pain and may also help improve function and increase the tolerable walking distance. Nutritional advice in the form of a weight loss program could form part of the treatment plan. The relative benefits of different weight loss methods in improving symptoms and function prior to knee replacement require further exploration. A home-based, self-directed program of instruction in lifestyle modification, with monthly telephone contact, can improve function and decrease knee pain in overweight, over 55-year-old adults with knee OA. Changes in body weight and psychosocial determinants of function may mediate the intervention effect on physical function. High adherence to this lifestyle intervention combined with weight loss can significantly reduce pain and increase function in older adults with knee OA. This would suggest that weight loss is likely to be beneficial for those with mild to moderate knee OA, particularly if it is possible to combine weight loss with exercise as a means of improving both aerobic capacity and muscle strength. Weight loss would be of most benefit if it resulted in a long-term maintenance of a lower body weight.
Surgical Treatment Options
There are several surgeries available in treating pain in the back of the knee. All procedures aim at diminishing pain, improving function, and increasing quality of life. Total knee arthroplasty (TKA) is a common treatment for pain in the back of the knee. It also has the most predictable long-term success rate of 85-90%. TKA is a surgical procedure whereby the diseased knee joint is replaced with artificial material. The knee is a hinge joint that has three parts. The thighbone (femur) meets the shinbone (tibia) at the knee. The patella (kneecap) rides on the femur. The three parts of the knee are separated by two discs (menisci). The joint is surrounded by ligaments, which provide static stability, and muscles provide dynamic stability. Articular cartilage, which is a pearly white covering that coats the end of each bone, provides a smooth gliding surface for joint motion. The distal end of the femur and the proximal end of the tibia are covered with articular cartilage. There is also articular cartilage on the underside of the patella. This surface is durable and can withstand heavy loads. It is this joint that can be affected by trauma or some systemic rheumatologic disorders to cause pain in the back of the knee. Often, this is a result of significant loss of articular cartilage. TKA can be performed when there is severe pain and disability resulting in significant loss of function and quality of life. This is usually a last resort for people aged greater than 55-60 years old. Sometimes it is indicated for people with fractures around the knee joint or a high tibial osteotomy with persistent pain. The number of TKAs performed for isolated pain in the back of the knee is on the rise, although it is still difficult to confirm whether the pain is a result of significant loss of articular cartilage at the knee joint.
Total Knee Arthroplasty Procedure
One of the issues seen in osteoarthritis of the knee is in the early phase where the patient presents with anteromedial pain, which is often the chief complaint at the time of arthroplasty. This pain can also be felt in the anterolateral region. In what seems like a contraindication, patients who have primarily anteromedial pain can have a varus deformity secondary to medial compartment osteoarthritis. All of these patients will have markedly limited their functional activities. They are typically sedentary and avoid painful activities. But sometimes they have tried to use a cane, a knee brace or a shoe modification to try to unload their painful knee, realizing some relief of pain and improved stability. These patients are somewhat higher risk at the time of surgery, because the cane, brace or shoe modification are effective at relieving pain and may have given the patient the false impression that the disease is not severe. When patients progress to bone on bone arthritis, the options for medical management become very limited. When we see a patient with primarily anteromedial pain, even if it is part of a general endstage of disease in a varus knee, we will do a total knee arthroplasty. Indeed, a patient with anteromedial pain from a patellofemoral or medial compartment arthrosis can be effectively treated with an isolated patellofemoral or medial compartment prosthesis, we would still favour a total knee arthroplasty in that case, because the patient may subsequently develop lateral disease in the setting of the varus knee. Lateral disease in a knee with isolated medial or patellofemoral prostheses can be difficult to manage and may require revision to a total knee arthroplasty. Any patient with significant disease in more than one compartment should undergo a total knee arthroplasty.
Rehabilitation and Recovery
Rehabilitation managed by a physical therapist begins with simple exercises to move the new joint and increase its range of motion. The therapist has the patient move the new joint through its entire range, while sitting, standing, and lying down. Ankle pumps (alternately flexing and pointing the foot) help prevent blood clots and decrease swelling. The patient will learn positioning and transfer techniques and, within three to four days after surgery, will be able to walk with a walker or crutches. Patients who have their own homes typically can go home from the hospital after three to five days. Those who do not have home support or who are unsafe in their living situation will go to a skilled nursing facility or inpatient rehabilitation center. The goal during the first two to six weeks is steady progression. At two weeks, patients will see their surgeon for a wound check. They will also start outpatient physical therapy. Walking, stationary biking, and pool therapy are often recommended activities. At six weeks, patients usually take a week-long break from therapy to rest. Pain, swelling, and occasional aching may be present, but are usually not disabling. Established exercise routines should maintain or increase muscle strength and joint flexibility. With a return to full function as the end point, progress to higher level functional activities such as golf, hiking, and doubles tennis is common after three months. Note that it is important to differentiate between pain and exertional pain. Prolonged pain and swelling after activity may be a sign that certain activities should be modified, one activity to another (e.g. walking instead of running) in order to preserve the joint. This can be normal age-appropriate joint pain. On the other hand, abrupt onset of sharp pain during an activity may be a warning sign to immediately discontinue said activity in order to protect the joint. Noisy joints or crepitus do not appear to be a significant marker of improper activity and likely represent a normal sequela of joint stress, with inconsistent effectiveness of the activity in question. Activity modification is likely a never-ending process, with periodic re-evaluation of types of activities and their effects on the joint. Total knee replacement patients with postoperative activity levels that are unchanged are likely to have unsatisfactory outcomes compared to those who successfully change activity levels. Successful changes in activity can be considered as stemming from activity counseling and have been linked to a higher joint survival rate.
Potential Complications and Risks
Joint infection can occur in people with other medical problems, such as urinary tract infection or a skin infection. Medical attention for even minor infections will minimize the chance of the infection spreading to the knee joint. In the event of extensive joint infection, major surgery including removal of the prosthesis may be necessary. The infection is treated with antibiotics. Most frequently, the prosthesis can be re-implanted once the infection has been eradicated. High failure rates of the re-implanted prosthesis have been reported following treatment of periprosthetic joint infection with debridement and retention of components (DRC) or 1-stage exchange. Two-stage re-implantation has been recommended for treatment of the infected knee, resulting in infection eradication rates of greater than 90% and prosthesis survival rates of greater than 85% at 2 to 5 years following re-implantation. Step-wise treatment methods including aggressive initial treatment and utilizing a DRC strategy first are aimed at maximizing prosthesis survival. Prosthesis retention can be considered for low virulent infections such as chronic Propionibacterium acne periprosthetic joint infection.
Complications from total knee arthroplasty are not common, but they can occur. Almost all complications are minor and can be treated readily. Serious complications, such as joint infection, occur in less than 2% of patients. Chronic illnesses may increase the potential for complications. Poor health and functional impairment are the most important risk factors. It is extremely rare for an older person to have a complication from which they never recover.
