الفهرس 
Physiology of Knee PainOnly 14 pages are availabe for public view
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Abstract
Total knee arthroplasty is a major orthopedic surgery that is usually followed by moderate to severe postoperative pain. The management of that pain should gain much more concern and to be dealt with in a way different from any other postoperative pain. Not only the patient’s relief and satisfaction are the reasons for that different management, but also because the degree of that pain massively influences the surgical outcome of the procedure. Very early mobilization of patients undergoing total knee arthroplasty with passive and active movement at the knee joint has direct impact on reducing the incidence of delayed postoperative joint stiffness, motion range limitation and residual delayed joint pain. Moreover, the rates of total knee arthroplasty in UK and United States have been rising during the last decade and are expected to continue rising in the next ten years.
The appropriate postoperative pain management after total knee arthroplasty can’t be achieved without full understanding of the terms of knee pain physiology which involve transduction, transmission, modulation and perception. This type of knowledge allows the enhancement of the ability to alter and block acute pain sensation at its different levels of conduction.
Not less important by any mean is the brief knowledge of the pharmacology of drugs used in the postoperative period for pain control. Opioids, especially morphine, remain the corner stone of this process despite the great development in regional pain block methods with local anaesthetics and their adjuvants which also include opioids. However, opioids preparations and routes of administration have been developed and can be used in the process of postoperative pain management such as transdermal controlled-release fentanyl patch and extended release epidural morphine. But it remains undeniable that the adverse effects of opioids of such as respiratory depression, nausea and vomiting are still a strong barrier against administration of high doses of opioids sufficient for patient satisfaction postoperatively with such severe pain as after total knee replacement. Moreover, these adverse effects stand also against the targeted early mobilisation and activity required by the patient after surgery.
Non-opioid analgesics vary widely in their efficacy, pharmacodynamics and side effects. However, they are all the same concerning that they are not effective enough in producing analgesia postoperatively individually. They can be simultaneously with intravenous opioids or regional neuraxial or nerve block, to reduce either the narcotic dose or the local anaesthetic concentration. Examples of that are: the injection of ketorolac (NSAID) at the incision site in combination with local anesthesia, COX-2 inhibitors for postoperative pain management, paracetamol which is a valuable part of any multimodal analgesia regimen, ketamine, clonidine and dexmedetomidine either intravenously or as a local anaesthetic adjuvant have all proved to reduce postoperative opioid consumption and consequently their adverse effects. It was also proved that all of them improved patient satisfaction.
Patient controlled analgesia pumps are the most recent techniques concerning intravenous opioid administration. The most recent pumps are designed to ensure safety by auto shut-off systems and alarm system to guard against inadverent administration of high doses of opioids. In addition, it was noticed that PCA facilitate early ambulation, reduce respiratory complications and improved patient satisfaction. Alternative routes other than the intravenous route for PCA were adopted to make use the success achieved by PCIA. These routes include PCEA with continuous infusion and demand dose system, PCA via a peripheral nerve catheter and fentanyl HCl patient-controlled transdermal system. However, frequent adjustments to optimize relief or minimize the opioid-associated side effects or increasing the likelihood of the use of large doses of opioids remain against the idea of using PCA systems individually. Other methods of regional pain management can aid in avoiding high opioid dose associated side effects.
Regional approaches in the pursuit of optimum management of postoperative pain after total knee replacement is now of common use. It includes mainly two groups. These are neuroaxial epidural analgesia and peripheral nerve blocks. Epidural analgesia can be used either for epidural opioid administration or for neuroaxial nerve block via local anaesthetics. Single dose of extended release epidural morphine (EREM) produced better analgesia than PCIA during the first 48 hour but with the same side effects. On the other side neuroaxial epidural block via local anaesthetics still have some drawbacks as motor block with high concentrations of local anaesthetics, risk of patient falling during movement and the unwanted bilateral limbs block. These drawbacks are against the fact that patients undergoing total knee arthroplasty should practice very early mobilization and activity. In addition anticoagulation drugs protocols followed by elderly patients undergoing this surgical procedure or adopted by most orthopedic surgeons postoperatively are very strong barriers against epidural catheter application to avoid spinal hematomas.
Four peripheral nerves arising from the lumbar plexus and passing in direct relation to the fascia iliaca are responsible for sensory and pain sensation at the knee joint. These are femoral, sciatic, obturator and latera femoral cutaneous nerve. The modern ultrasound techniques rendered peripheral nerve blocks more accuracy, more reliability and fewer complications in the field of pain management and analgesia. The most important of which is the femoral nerve block which can be accompanied by catheter insertion to produce a continuous femoral nerve block. However, when it’s performed individually residual pain at the knee joint is usually noticed. That’s why sciatic nerve blocks are added to CFNB or to 3 in 1 block which involve the obturator and lateral femoral cutanuous nerve with the femoral nerve. Lumbar plexus block is of limited use in clinical practice due to two main causes. These are dificulty in the technique which makes small number of anaesthetics who are skilled to do it and the risk of retroperitoneal hematomas and main vessel and nerve injury.
Each mode of analgesia postoperatively after total knee arthroplasty has its advantages and side effects. This was the fact that forced anaesthetists to adopt the idea of multimodal analgesia. Variable methods and interventions are used in combination with each other to achieve adequate levels of pain control that helps to reach the patient’s satisfaction and relief with minimal side effects. For example, the use of single dose EREM with CFNB, or the use of PCIA with neuroaxial epidural block, or the use of combined CFNB and sciatic nerve block with intravenous opioids. All these multimodal regimens are targeting to avoid high dose opioid associated side effects, motor block associated with high concentrations of local anaesthetics, risky interventions with hazards to patient’s safety or patient suffering from any residual pain.