Case of the Month #13: Persistent pain following total knee replacement

Differential diagnosis at this point:
1.    Persistent post-surgical pain
2.    CRPS post knee replacement
3.    Underlying infection or inflammatory process
4.    Loosening of the prosthesis, or malalignment
5.    Referred pain from the spine or right hip.

Prior to being referred to the Pain Clinic, Mrs B had been reviewed multiple times by her orthopaedic surgeon and indeed had even at her request had a second opinion.  From a radiological point of view, the prosthesis had been well placed and there were no signs of loosening.  She had undergone blood tests which ruled out an underlying infectious or inflammatory process.  She also had a nuclear bone scan which showed no signs to support loosening or underlying infection/inflammation. Both surgeons were in agreement that the prosthesis was well placed.
Mrs B had also had an MRI scan of the lumbar spine and an X-ray of the pelvis. The latter had shown well preserved hip joints. The MRI scan of the lumbar spine had shown an element of facet joint OA and some signs of disc dehydration commensurate with a patient of her age group. There was however no marked foraminal or central canal stenosis at any of the lumbar levels.

On examination of the knee joint, there was a well healed scar. The joint looked somewhat bulky but not overtly swollen.  There was no redness or abnormal sweating or shiny skin. Touching the skin around the scar and knee joint gently did not cause pain. She could extend the knee to nearly straight but could not flex it back fully.  She used a walking stick to walk, tending to list to the left in order not to fully weight bear on her painful knee.  Palpation of her low lumbar spine revealed tense paraspinal muscles and pain over the lower lumbar facet joints on the left-hand side.

Verbal rating scale pain score was 7 out of 10.
LANSS pain score 11
Pain Catastrophising Scale 34

Mrs B reported that she was concerned that she was unable to look after her husband who was 15 years her senior and depended on her to a greater extent.  Her grown up children lived far away and could not give her practical help. She relied more and more on neighbours for help and was worried about this. She reported that she slept poorly and was constantly worrying about what the future held in store for her and her husband. On a positive note, they did live in a single storey house with easy access and had no financial worries.

Mrs B reported that she was taking six Co-Codamol 30/500mg tablets in three divided doses and these did not help much and cause quite significant constipation. She had been taking Ibuprofen that she was purchasing over the counter.  With regards to her general health, she had no significant past medical history of note. She was not on any other medications.

Diagnosis:   Persistent pain following total knee replacement, 
                    Mechanical back pain, catastrophisation.