Why it's Hard for Doctors to Find the Cause
It's an exciting time in orthopaedic surgery and total joint replacement surgery is considered one of the most successful and rewarding procedures performed. Although total knee replacement (TKR) is an effective operation for end-stage arthritis of the knee, studies have shown that nearly 20 percent of patients have persistent symptoms after this procedure. The work-up of painful TKR includes clinical evaluation, radiographic imaging, and in some cases microbiological analysis.
However, it is not uncommon that there is no obvious underlying cause of the pain. In such a situation, a plan of management should be made and agreed upon with the patient. On some occasions it is important to involve a pain specialist early, specifically for the prevention of a chronic pain syndrome. While narcotic medicines may be used for short-term pain relief, the side effects and addictive nature makes this intervention a poor choice for sustained use.
Currently, there is a movement toward opiate-free joint replacement surgery, which has already been instituted in many countries around the world. Patient education is of utmost importance, and most joint centers have moved toward a pre-operative educational program.
While there are many potential causes of persistent postoperative joint pain within the first two years following replacement, the most common are instability, infection and arthrofibrosis (stiffness). Arthrofibrosis has many causes and is often a product of dense scar tissue formation likely caused by immobility and increased ligamentous and tendinous stress.
Interestingly, although x- rays are a highly emphasized part of the work-up, they will actually show limited information regarding any of the three common causes of pain and failure. The clinical exam and history are crucial to the evaluation. You can send me a patient's x-rays that show perfect component position and alignment and yet the patient may be miserable, while another patient with mal-positioned implants does do not experience any pain at all. I need to see them, hear their story and examine their joint.
Instability in the early post-operative period may be due to uncorrected pre-operative ligamentous imbalance, improper intra-operative ligamentous balancing, mismatch of the flexion-extension gap, surgeon injury to the ligaments during surgery or pre-existing neuromuscular pathology. However, late instability can occur secondary to mal-alignment leading to progressive stretching of the ligaments, wear of polyethylene, loosening of the component and collapse. Patients can go undiagnosed for years. Unless you have examined thousands of knees, some ligamentous instability can be very difficult to detect.
An often unrecognized problem with pain total knee replacements is impingement syndromes. A few examples of this include; popliteus tendon impingement, patella clunk and fabellar impingement. While most of these may be treated with anti-inflammatories and conservative treatment, if non-operative treatment fails, surgery may be warranted.
Metal sensitivity, also known as allergy, has gained a lot of interest over the past decade. Attention was first noticed in early failure of metal on metal articulations in the hip. Unfortunately, a universally accepted test for predicting sensitivity with a high degree of specificity has not been developed. Metal sensitivity can occur around any metal implant containing cobalt, chromium and nickel; however it appears that some patients are more vulnerable to this than others. Some implant companies have begun either using alternative metals or coatings. All materials will eventually wear and fail. Synthetic materials have no ability to repair themselves from damage. Other potential sensitivities include methymethacrylate bone cement, which also does not have an accepted screening to test to identify ask risk patients. Patients with high levels of cobalt and chromium in their blood have expressed concerns about heart, kidney and neurologic problems. In these circumstances, I have referred them to specialists in these areas to exclude other etiologies.
As the US moves toward opiate free, outpatient joint replacement, long acting local analgesics and peripheral nerve blocks are becoming more and more popular. Our surgical instrumentation continues to improve and our understanding of how to prevent future problems continues to advance. Pain management has become an essential part of the team approach to joint replacement. Patients experiencing postoperative problems following knee replacement are encouraged to contact a specialist.
Herrick J. Siegel, MD is an Associate Professor of Orthopaedic Surgeon at UAB Medical Center.