Why is my total knee replacement still painful?

By Mr Nikhil Shah, consultant trauma and orthopaedic surgeon at Wrightington Hospital, Lancashire

[A TOTAL KNEE REPLACEMENT is generally a successful operation to improve the pain and function associated with end stage arthritis of the knee joint. It involves resection or excision of the arthritic surface of the tibia and femur, and in many cases the patella (the kneecap), and replacing that with artificial prosthetic joint components made of metal – commonly cobalt-chrome or titanium – and plastic. The National Joint Registry of the United Kingdom and various other registries have shown excellent longevity and prosthetic survival at follow-up periods of 20-25 years.

However, despite the good long-term success of total knee replacements, many patients who undergo the operation remain subjectively dissatisfied with their end result. The orthopaedic literature would suggest that the percentage of patients who are unhappy with their total knee replacement can vary from 20 to 25%. That can be noticed even with otherwise technically well-performed surgical procedures. The percentage of dissatisfied patients is found to be much greater (30-40%) in certain high-risk patient groups.

In other words, the objective parameters by which a knee can be assessed by the surgeon remain satisfactory, but the patient is unhappy with the result. That outcome can be measured by various subjective assessments that are referred to as patient reported outcome measures (PROMs). Over the past few years there has been an increased emphasis on recording the PROMS, to help determine whether a patient is satisfied or not with the total knee replacement that they undergo. Such outcome measures also show the discrepancy between what patients perceive to be a good result from surgery, as opposed to what surgeons define as a good result.

The usual symptoms that patients complain of when they are unhappy with their total knee replacements are wide ranging, but include pain or discomfort, stiffness or reduced movement, instability or a feeling of wobbliness, pain or unpleasant sensations on the side of the surgical scar, or sounds and noises (clicking, clunking etc) coming from the knee joint among others. Often that is associated with functional problems such as difficulty in walking longer distances, an inability to kneel, difficulty in climbing stairs etc. A common reason for dissatisfaction is the failure to meet the patient’s expectations from the surgery.

There are various causes why someone may be disappointed with the result of their knee replacement. One of the most important aspects of performing this type of surgery is patient selection. A good indication for a total knee replacement is a patient in an older or elderly age group who has severe end stage knee arthritis, associated with symptoms of significant pain which interfere with the quality of life.

It is important that the symptoms reported by the patient correlate with the clinical examination findings noted by the surgeon and that in turn correlates with the x-ray findings of severe arthritis. It is well recognised that total knee replacements offered in arthritis of lesser severity in patients who have otherwise well-preserved function and who do not have significant pain levels are associated with subjectively inferior outcomes. One must exercise caution in offering surgery where the symptoms are atypical or do not correlate with the signs and x-rays.

It is important to ensure that pain is actually emanating from the knee joint itself. Pain that is referred from the spine or the hip joint to the knee, or pain due to vascular or neurogenic claudication, can make it difficult to determine the exact source of pain. That pitfall is not uncommonly seen in some patients, where it is retrospectively identified that the pain was coming from a different area.

Certain other patient groups are also found to be at higher risk of developing subjectively poorer outcomes following total knee replacements. That group includes patients who are of a younger age group. Often, the expectations of younger patients from their knee replacements are much greater than elderly or low demand patients, although that is increasingly changing with very active older age group patients also expecting their knee replacement to give them high levels of activity. If those expectations cannot be met, then that leads to subjective dissatisfaction.

Other risk factors include patients who have had several previous surgical procedures on their knee joint before undergoing a total knee replacement. Recent studies have also identified a raised body mass index into bracket obesity to be a risk factor for subjective dissatisfaction following total knee replacements. Similarly, neuropathic pain may rarely occur due to a condition called complex regional pain syndrome. That condition is quite difficult to treat. In every case it is important to identify certain treatable or surgically correctable causes of a painful knee replacement before labelling the knee as an unhappy one. Those causes include prosthetic joint infection or loosening. Infection after total knee replacement can be quite difficult to diagnose in many patients, especially when it is low grade. A thorough and meticulous approach towards taking a comprehensive history, performing a clinical examination and obtaining appropriate radiological and serological investigations is required to diagnose infection. Loosening of the total knee replacement, although uncommon, can also be quite difficult to diagnose and the x-ray findings may be quite subtle. Arthrofibrosis is a constitutionally influenced condition characterised by formation of internal scar tissue inside the knee, which leads to stiffness. That often leads to the patient being quite disappointed.

Managing expectations and educating the patient are key factors in satisfaction after total knee replacements. It is very important to counsel the patient carefully about the benefits and risks of the procedure and the possible outcomes. A detailed and frank discussion of those aspects at the time of the first consultation and in subsequent consultations is extremely important in educating the patients about realistic outcomes. That dialogue is an important part of the overall consent process.

Occasionally patients may state after surgery that they did not fully understand the implications of undergoing a total knee replacement. That can sometimes lead to a breakdown of the doctor/patient relationship. Not only is it important to provide a detailed explanation of the potential risks and complications, but also to ensure that the patient has understood the consequences of those complications should they materialise. It is also important that pain after total knee replacement is a recognised non-negligent complication: just because a total knee replacement has not turned out quite the way the patient wanted it to, that is not synonymous with breach of duty. q www.yourexpertwitness.co.uk 43 43