Prevention
It is important the surgeon is aware of the cause of pain and takes the following steps to prevent it.
1. The operation is reserved for bone on bone arthritis
2. The surgeon must be meticulous with the technique, particularly relating to the tibia:
(a) The tibial component should be supported all around its periphery by cortical bone
(b) Care should be taken to avoid overhang, impingement, medial or deep tibial resection
3. The patient should be warned before surgery that early pain is common and, if it occurs, they should restrict their activity. The pain almost always settles spontaneously, but this may take a year.
Investigation
Radiographs are the most useful investigation: Ideally, an AP radiograph aligned with the tibial component (screened) should be obtained. This should be compared to the postoperative screened view. Physiological radiolucencies must be ignored as they are not a source of pain (Gulati et al, 2009). If femoral component loosening is suspected, lateral views at 0° and 90° should be obtained and examined carefully to determine if there is movement of the component (see Fig. 11.9) (Monk et al, 2009).
Radionuclide bone scans are not helpful and are often misleading. They are likely to be ‘hot’ for many years even if the patient is asymptomatic. If the pain is lateral, an MRI scan is useful as it may identify a meniscal tear. An ultrasound guided aspiration can be helpful to exclude infection.
Arthroscopy has a limited use in the management of these patients. This should not be undertaken before a year but can be useful if lateral meniscal lesions, cement loose bodies, impingement or chondral flaps in the PFJ are suspected.
Treatment of unexplained pain
The temptation for early revision should be avoided. We believe that, in general, the threshold for revision is too low. As a result, many patients are revised early for unexplained pain in all national registries. In most patients revised for unexplained pain, the pain does not improve. For example, in our retrieval study 75% of patients who were revised to TKA and had no mechanical problems identified at operation had no improvement in symptoms (Psychoyios et al, 1998).
Patients should be treated conservatively as their pain tends to settle spontaneously. We recommend that patients should be warned that they are likely to have some pain for three to six months and that there is a small chance it may take one or even two years to fully settle. If patients have pain we advise them to decrease their level of activity and use a walking stick. If the pain is focal it is worth trying a steroid injection. If the pain persists beyond six months and the patient is becoming anxious, it is worth requesting a second opinion from a surgeon who is experienced with the OUKA, as they will tend to reassure the patient which is very helpful.