The management of patients with painful total knee replacement.

Toms AD, Mandalia V, Haigh R and Hopwood, B. J Bone Joint Surg. 2009;91-B:143-150.

This is the editor's interpretation of a paper published in the orthopaedic literature in 2009 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original it is easy to ask your librarian to obtain a reprint for you from any medical library.


The authors address the problem of distressing pain in patients who have had total knee replacement but in whom investigations have revealed no obvious cause for the pain.

The authors discuss the most common causes of pain persisting after total knee replacement, and the investigations - clinical evaluation, blood tests, diagnostic imaging and microbiological analysis - used to try and unravel the problem.

They stress that such pain must be investigated early, and that it is important to involve a pain specialist. The investigating team also needs to be multidisciplinary, involving clinicians from various disciplines and including the family doctor. Tackling the problem early may avoid anxiety and depression, together with the health problems that may accompany these symptoms. The authors feel that a pain clinic offers the best environment, as generally longer appointment slots allow for for detailed investigation.

While investigations are underway, analgesics need to be adequate. After the initial pain of the knee replacement has been covered with pain killers (analgesics), if pain persists it is likely that the routine post-op prescriptions have ended, and physiotherapy may also have ended, so continuing and increasing pain may lead to inactivity and stiffness of the joint. The World Health Organisation (WHO) have published an 'analgesic ladder' - a stepwise progression of pain management - to help clinicians manage the patients pain adequately while investigations are continuing.

Analgesic Ladder

  • mild pain - paracetamol 1g 4-6 hourly (max 8 tabs a day)
  • moderate pain - paracetamol 1g 4-6 hourly (max 8 tabs a day), + codeine 30-60mg 4-6 hourly, +/- ibuprofen 400mg 6-8 hourly if no contra-indications (or other non-steroidal anti-inflammatory).
  • severe pain - moderate pain - paracetamol 1g 4-6 hourly (max 8 tabs a day), + an appropriate opioid (eg morphone, fentanyl, oxycodone), +/- ibuprofen 400mg 6-8 hourly if no contra-indications (or other non-steroidal anti-inflammatory)

The authors go on to discuss several possible causes of persistent pain after total knee replacement, and the KNEEguru suggests that you try and obtain the original article to read about these in detail. Briefly their list includes -

Neuropathic pain

This is 'nerve' pain, experienced as increased skin sensitivity or even decreased skin sensitivity. This may respond to locally-applied cream (eg capsaicin) or plasters (eg local anaesthetics like lignocaine). Local massage of scars may be helpful. If the pain persists then anti-depressant medication may work on brain chemistry to diminish the experience of pain, but may also help to control the emotional aspects of anxiety and low mood. The next tool in the doctor's armamentariam is strangely enough the anti-convulsant drugs Gabapentin and Pregabalin, which may be effective on the pain pathways.

Painful neuroma

A neuroma is a little knot of painful nerve tissue that may occur in the scar tissue. Diagnosis can be confirmed by anaesthetising the local area and seeing if the pain goes away. Surgery may be necessary to remove the neuroma, but they may also resolve on their own with time.

Complex regional pain syndrome

'Full-blown' CRPS is uncommon after total knee replacement, but the disorder itself certainly occurs fairly commonly. The 'syndrome' - ie a collection of symptoms that tend to occur together - may include neuropathic pain, numbness, skin mottling, and a whole variety of bizarre signs and symtoms. Management involves early and adequate analgesia while efforts are made to break the sequence of events by careful physiotherapeutic exercise under the guidance of pain care specialists.

Infection

Infection in a knee replacement requires treatment, but the seriousness of the infection and the extent of the treatment is determined by whether the infection is superficial or deep. Antibiotics will be required, but surgery will depend on the extent and nature of the infection. The authors refer to other publications that discuss this important and complex matter (including - Toms AD, Davidson D, Masri BA, Duncan CP. The management of peri-prosthetic infection in total joint arthroplasty. J Bone Joint Surg [Br] 2006;88-B:149-55).

Instability

The authors distinguish between 'feelings' of instability - due to weak muscles, inability to fully straighten the knee, or the patella not tracking properly - and true measurable instability due to mechanical things like the ligaments being too loose. These mechanical things may have been inadequately sorted out during the surgery, but also sometimes mechanical stretching of ligaments may occur after the surgery for various reasons.

Again the topic is complex, and the management will depend on the exact nature of the instability. Surgery may be necessary in some cases but the authors make a point of encouraging correction of aggravating factors such as losing weight, optimising footware, and paying attention to problems with the hip and the spine.

Problems with the extensor mechanism

The authors flag up the 'extensor mechanism' as commonly being at the root of persistent pain after total knee replacement. By 'extensor mechanism' they mean the anatomical structures that work together to straighten the knee - the quadriceps muscle, its tendon above the patella, the patella itself, the patellar tendon below the patella, and the attachment of the whole to the front of the tibia bone via the bony prominence known as the tibial tubercle.

Extensor mechanism problems might include -

Stiffness

The authors of this article point out that there are a number of possible causes of painful stiffness after total knee replacement. The pre-existing arthritis and bony deformity may be an issue, technical errors during surgery may result in mechanical stiffness, and infection and complex regional pain syndrome may lead to stiffness. They recommend that the physiotherapist work closely with a pain specialist to try and determine the contribution of these factors to postoperative stiffness.

Uncontrolled pain itself may result in stiffness as the patient guards the knee from full movement, allowing a build up of sticky adhesions within the joint cavity. These adhesions can mature into internal scarring, and require surgical release, so it is important that this complication is avoided by early pain relief, adequate physiotherapy and manipulation under anaesthesia (MUA) where indicated. MUA itself carries a risk of damaging other structures, and the authors suggest that timing is important and that 6 weeks post op is probably the best time to consider an MUA for painful stiffness. Surgery for painful stiffness may be considered at 3-6 months, and the procedure involves freeing adhesions or internal scars, and especially freeing the posterior cruciate ligament if it is caught up in scar tissue. Usually the surgery can be done arthroscopically ('keyhole') but if the knee is very stiff it may be safer to do a conventional open operation.

Impingements

Impingements may cause pain when structures become nipped or crushed by the new prosthesis. The authors refer to a previous publication of theirs (Mandalia V, Eyres K, Schranz P, Toms AD. Evaluation of patients with a painful total knee replacement. J Bone Joint Surg [Br] 2008;90-B:265-71) where they discuss assessment of such problems , and in particular -

Recurrent haemarthrosis

Bleeding inside the joint (haemarthrosis) may be a consequence of overgrowth of joint lining - one of the causes of impingement - and the blood itself can irritate and aggravate the pain.

 

Wrapping up their paper, the authors emphasise that the investigation and management of the persistently painful knee after total knee replacement requires a multi-disciplinary approach. They stress that it is important to adequately manage the pain during the period of investigation. In those patients where there are no immediate indications for surgery, they have found that most patients find their pain settles if given time and adequate pain management and revision surgery should not be rushed into on the basis of pain alone.

 

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