Pain and Impact of Chronic Pain on Function After Total Knee Replacements

INTRODUCTION:- A Total Knee Replacement (TKR) or arthroplasty (TKA) is a complex procedure that requires an Orthopedic Surgeon to make precise measurements and skillfully remove the diseased portions of the bone, in order to shape the remaining bone to accommodate the knee implant. Knee Replacement Surgery is most commonly performed in people with advanced osteoarthritis and should be considered when conservative treatments have been exhausted. Oncologic TKRs are different from the routine TKRs in a way that the former involves a wide local resection of the bone and soft tissues, ranging from 10 to 20 cm, resection of muscles like the head(s) of biceps femoris, the gastrocnemius muscle, the intermuscular septa, the joint capsule, etc. to ensure negative margins along with the complete resection of the tumour, followed by a reconstruction of almost the same length as that resected, to restore function.

The most common indication for doing oncologic TKR is Osteogenic Sarcoma (OGS) of and around the knee joint. The distal femur and proximal tibia are among the most common sites for primary bone tumor. OGS is the most common bone cancer in the world in children and adolescents, and the eighth-most common form of childhood cancer, accounting for 4% of all childhood cancers worldwide. In India, the incidence varies from 4.7% to 11.6%, where this malignancy is associated with significant morbidity and mortality. Additional treatment involves chemotherapy which further delays the healing and recovery of the patient.

Surgery is a known risk factor for development of Chronic Post Surgical Pain(CPSP) which as per the definition given by Macrae and Davies, is defined by

• Pain developing after a surgical procedure.
• Pain of at least 2 months' duration.
• Other causes of pain excluded (e.g.- malignancy, infection, etc.).
• Pain continuing from a pre-existing pain problem excluded.

CPSP is a well known risk factor in many surgeries like (but not exclusive of)-

• Mastectomy (Incidence of chronic pain = 11-57%)
• Amputation (30-85%)
• Inguinal hernia(5-63%)
• Cholecystectomy (3-50%)

CPSP develops after a surgical procedure or increases in intensity after the surgical procedure. Literature on TKR surgeries indicated for osteoarthritis, report that although many patients report a good outcome after their total knee replacement, at a time when recovery should have been achieved, about 10-34% of patients undergoing TKR for osteoarthritis report moderate to severe CPSP. In around 30% of patients with CPSP, the origin of CPSP might be neuropathic. Neuropathic pain is more severe and adversely affects the quality of life of patients. TKR on its own may cause neuropathic pain postoperatively due to local nerve damage, often to the infrapatellar branch of the saphenous nerve or due to local inflammation. Risk factors associated with the operation include increased duration of surgery and tourniquet time, revision surgery, TKA versus unicompartmental arthroplasty and intraoperative nerve damage. Oncologic TKRs are more extensive and include much morbid excisions, and consequently may be presumed to have a similar if not a greater incidence of CPSP. Some of the risk factors for CPSP include the following (but not exclusive of)-

• Pain, moderate to severe, lasting more than 1 month
• Repeat surgery
• Younger age (adults)
• Surgical approach with risk of nerve damage
• Neurotoxic chemotherapy

Preoperative pain is consistently found to be a predictor for persistent postsurgical pain, which might reflect an independent risk factor but could well be a manifestation of predisposing factors.

Tata Memorial Hospital, a tertiary cancer institute is a 629 bedded hospital and conducts approximately 6000 surgeries per year out of which approximately 100 TKRs are performed per year. Analgesia peri-operatively is provided by an epidural infusion of a combination of local anaesthetic and an opioid or intravenous opioids with non-steroidal anti-inflammatory analgesics and paracetamol as appropriate. Postoperatively, if inserted, epidural analgesia is continued for up to 3-4 days to help mobilization \& physiotherapy. In the absence of an epidural, around the clock analgesics with or without an opioid administered by means of an Intravenous Patient Controlled Analgesia (IVPCA) device is instituted. These patients are visited by the acute pain service team to address pain issues for the first 3 postoperative days or sometimes longer.

STUDY DESIGN:- Prospective and Observational study

METHODS and MATERIALS:- After Institutional Review Board approval, adult patients scheduled for TKR surgeries will be enrolled into the study after obtaining their informed consent over a 24 month period. However, interim analyses of all cases who have completed the 6 month follow up as on 31st October, 2017 would be analyzed as part of the co- principle investigator's thesis. All consenting patients will be assessed for their pain preoperatively and for the first 3 post-operative days, and at 1, 4 and 6 months from the date of surgery. Pain scores will be assessed using the Numerical Rating Scale during the 3 days after surgery. Pain will be managed by the Acute Pain Service team as per the standard management protocols.

The Brief pain inventory (BPI), (short form with translations, obtained with permission from MD Anderson), which assesses the severity of pain and the impact of pain on daily functions will be administered to the patient in the language familiar to them, preoperatively, at 1, 4 and 6 months postoperatively. The BPI is a useful instrument to assess the severity of pain and impact of pain on daily functions in patients with pain from chronic diseases, conditions such as cancer, osteoarthritis and low back pain, or with pain from acute conditions such as postoperative pain. The short form comprises of nine questions related to the severity of pain, impact of pain on daily function, location of pain, pain medications and amount of pain relief in the past 24 hours or the past week. It has been widely used and validated in several languages the world over.

The Musculoskeletal Tumour Society Score (MSTS) evaluates the functional condition (impairment) after completed tumour treatment will be estimated at the end of 6 months from the date of surgery. It is calculated on the basis of a standardized physical examination by the physician. This clinical examination assesses six criteria and differs slightly between the upper and lower limb. For the lower limb, the components are pain, function, emotional acceptance of the treatment outcome, need for walking aids, walking and gait. For all criteria, the estimate is made from bad to very good with parallel awarding of points (0 to 5). There is thus a numerical value for each of the six criteria. These six values are added and divided by the maximum possible number of points (30). The percentage value is obtained by multiplying the calculated point value by 100.

The painDETECT questionnaire (PD-Q) is a quick, simple and reliable screening tool to identify the likelihood of a neuropathic pain component in patients with neuropathic pain. This questionnaire had been prepared by professionals and validated in various languages including Hindi and Marathi. Its sensitivity and specificity is higher than other screening questionnaires for neuropathic pain, including the Douleur Neuropathique 4 (DN4), Leeds Assessment of Neuropathic Symptoms and Signs (LANNS), and the Neuropathic Pain Questionnaire (NPQ) (Freynhagen et al 2006). The PD-Q has been used to identify neuropathic pain in patients with knee osteoarthritis (Ohtori et al 2012) and to identify sensory profiles in patients with diabetic neuropathy and postherpetic neuralgia (Baron et al 2009).This questionnaire will be administered tot he patients preoperatively , at 1, 4 and 6 months after surgery.

Details of postoperative chemotherapy and radiation will also be obtained from patient's notes and the electronic medical record. If the patient cannot follow up at the said intervals, the pain scores would be obtained telephonically and the BPI and PD-Q forms in prepaid envelopes would be given to them at discharge which they would have to duly fill in and post them to the given address at the appropriate intervals if they cannot visit the pain clinic. At the 6th month of follow up, they would be requested to visit the pain clinic for an assessment of MSTS score and completing the BPI and PD-Q.

MEASUREMENTS:-

• All demographic, preoperative, intraoperative and postoperative data would be collected by the investigators.
• Demographic data includes case no, age, sex, ASA (American Society of Anesthesiologists) grade.
• Preoperative variables include pain score, preoperative analgesics, duration of use, and the dose.
• Intraoperative variables include duration of surgery, tourniquet time, any nerve or muscle resection and length of bone resected.
• Postoperative variables include median average and worst pain score for the first 3 postoperative days , 1, 4 and 6 months after surgery.
• Analgesics administered postoperatively, dose \& dosing intervals, impact on daily functions as obtained from the BPI pre-operatively, 1, 4 and 6 months postoperatively.
• The painDETECT score to identify the neuropathic component of pain if any, preoperatively and at 1, 4 and 6 months after surgery.
• The MSTS score calculated by the physician and obtained from the patient's record at the 6th month after surgery.

STATISTICAL ANALYSIS:- The above mentioned data will be presented as mean (sd), median (range), and frequency (percentage). Categorical data will be analyzed using the Chi-square test or Fisher Exact test (for binary data). Continuous variables will be analyzed using paired t test or Wilcoxon signed rank test as per distribution of data. Repeated measure ANOVA will be used for pain score analysis. Pearson correlation coefficients will be used for association. p-value <0.05 will be considered statistical significant.