Anaesthesia for knee surgery: spinal, general and nerve blocks

Who decides, and how

Your anaesthetist is a specialist doctor who looks after you from before the operation until you are comfortable in recovery. The surgeon and anaesthetist plan together, but the anaesthetic itself is the anaesthetist's decision, made with you.

At the pre-anaesthetic assessment you will be asked about heart and lung conditions, diabetes, sleep apnoea, previous anaesthetics, family reactions to anaesthesia, allergies, loose teeth and the medicines you take, particularly blood thinners. The choice depends on the operation, how long it is expected to take, your back, your health and your own preference. Share any worries; anxiety is common and the team is used to it.

Spinal anaesthesia

A spinal anaesthetic is an injection of local anaesthetic into the lower back, which numbs you from roughly the waist down for a few hours. You sit or lie curled on your side, the skin is numbed first, and a very fine needle is used. Most people feel pressure rather than sharp pain.

You can stay awake, or you can have sedation so that you are drowsy and relaxed, and many patients remember little of the operation. Because you keep breathing on your own, many people wake up clearer, feel less sick and can eat sooner. While it wears off, the legs feel heavy and you may find it hard to pass urine for a while.

General anaesthesia

With a general anaesthetic you are fully asleep. The medicines are given through a cannula in your hand or arm, and once you are asleep a breathing tube or airway device keeps your airway open. You will not feel or remember anything until you wake in the recovery room.

General anaesthesia may be chosen when a spinal is not suitable, for example because of certain blood thinners, back surgery or problems with the spine, or for longer operations, or simply because you prefer it. Afterwards a sore throat, nausea and drowsiness for the rest of the day are common and usually settle quickly.

Nerve blocks and local anaesthetic

A nerve block is an injection of local anaesthetic near the nerves supplying the knee, usually guided by ultrasound in the thigh. It does not replace the main anaesthetic; it adds pain relief that can last many hours after surgery. The surgeon may also inject local anaesthetic into the knee and wound at the end of the operation.

While a block is working, the leg may feel numb, heavy or weak. That is expected, but it means you must not try to walk without help, because the knee can buckle suddenly. Start your regular pain tablets before the block wears off, often during the first night, so the pain does not catch you off guard.

What you will feel on the day

• A small needle to place the cannula, and stickers and a cuff to monitor your heart, blood pressure and oxygen.
• Oxygen through a light mask or small tubes under the nose.
• With a spinal, warmth and tingling in the legs, then numbness; you may feel pulling or vibration during surgery but should not feel pain.
• A screen that keeps the operation out of view, and often music or quiet conversation.
• On waking, a nurse checking your pain, nausea and the feeling in your legs.

Theatres are kept cool, so ask for a warm blanket. If anything feels uncomfortable at any point, say so; the anaesthetist can adjust things straight away.

Risks, in balanced terms

Modern anaesthesia is generally safe for most healthy patients, but no anaesthetic is without risk. Common and usually short-lived effects include nausea, shivering, itching, a sore throat, drowsiness and difficulty passing urine.

Less common problems include a headache after a spinal, which usually eases with rest, fluids and simple treatment, and a lingering patch of numbness or tingling after a nerve block, which in most patients recovers over weeks to months. Serious complications such as severe allergic reactions, nerve damage or heart and lung problems are rare. Your own risk depends on your health, so your anaesthetist will discuss what applies to you. Smoking, uncontrolled diabetes, obesity, sleep apnoea and heart or lung disease raise the risk, and improving them before surgery helps.