Most patients are very happy with their function and pain relief post knee replacement however a small percentage experience ongoing pain. Associated symptoms include knee cap pain, stiffness, instability and swelling. Physical examination should exclude referred pain (spine/ hip/ vascular insufficiency), chronic regional pain syndrome (CRPS – characterised by skin changes, stiffness and intolerance to light touch), knee instability and extensor mechanism dysfunction. If you have ongoing issues post knee replacement useful investigations include an XR, blood tests (CRP/ ESR), joint aspirate (for white cell count) and a nuclear medicine scan (SPECT – CT). These tests can identify problems with your joint replacement which include
- Component malposition
- Loose cement
The above physical examination and investigations can identify a problem which usually can be fixed with revision surgery.
A second group exists where the above physical examinations and investigations are normal however patients still experience pain and dissatisfaction with the knee replacement. This group of patients has been colloquially referred to in the Orthopaedic literature as the ‘looks good, feels bad’ knee replacement. They have often been told by their surgeon that there is nothing wrong with their knee replacement and that they are in the 20% of patients who are unhappy with their knee replacement for unknown reasons. A CT scan with the Perth protocol applied can assess the rotation of the components within the knee. There is now evidence that malrotation of the femoral and tibial components (excess internal rotation) may result in pain, stiffness and instability and that correction of this results in improvement in pain and function which is comparable to revision surgery for loosening (a traditional indication for revision surgery). I have provided links to published data below.
Taking this concept further, most surgeons state they aim for a ‘balanced’ knee replacement. This means they aim for equal pressure in both the medial and lateral compartments of the knee throughout the range of motion of the knee. I am currently researching the concept of relative malrotation of the femoral component. This is a new topic with no published research. Relative malrotation of the femur can occur with a small inaccuracy of the tibial cut. For example 4 degrees of internal rotation of the femur is established threshold for revision surgery. However if the tibia is cut obliquely at 2 degrees (valgus) and the femur is internally rotated 2 degrees the effect on asymmetrical joint pressure is the same.
The third group of patients have no malrotation or relative malrotation but ongoing pain, stiffness and instability. Unequal joint pressure may still exist which can be detected with the use of a wireless smart trial insert (Verasense) which allows the knee ligaments to be released until equal pressure is achieved.
My current algorithm is to perform the above investigations with a CT scan (Perth protocol). If your prosthesis is malrotated in absolute or relative terms I would discuss the pros and cons of revision surgery. My preference is to use the Legion revision system as it allows the use of Verasense (smart sensor) which can optimise pressure and outcome in knee replacement surgery. Remember that knee revision is major surgery and complications do rarely occur. Please follow this link for the risks associated with knee revision surgery.
In summary, if you have the misfortune of a ‘looks good, feels bad’ knee replacement
- Give your knee a good 12 month trial of physiotherapy and muscle strengthening
- If pain persists see your treating surgeon
- If needed, request a second opinion from a surgeon with an interest in knee revision
- Many of these knees can be improved with revision surgery if malrotation is present
- Remember that other causes of pain and dissatisfaction exist and not every knee can be improved with revision surgery