Risks / Complications

Knee arthroscopy is a relatively safe procedure. However, there are potential associated risks and various (reasonably rare) complications that can occur. The decision as to whether or not to go ahead with any kind of knee surgery should be based very much on an assessment of the balance of potential benefits (related to how severe your symptoms are) vs the potential risks, as well as considering the time required for appropriate rehab and recovery after any surgery.

The potential risks of knee arthroscopy surgery are:-

  • infection
  • nerve or blood vessel damage
  • blood clots
  • ongoing knee symptoms



The risk of infection from a knee arthroscopy is very small indeed, and is in the region of about 1 in 1000. Small, minor, superficial infection in the skin from the surgical scars can rarely occur, but these can normally be treated easily with a short course of antibiotic tablets. Deep infection, actually affecting the inside of the knee joint (septic arthritis) is thankfully extremely rare, but if it does occur then it can be very serious. Patients with a septic arthritis will present normally a few days after surgery with severe pain in the knee, generalised tender swelling on the joint, the knee will be hot and red, the knee is very painful to move and it is painful to weight bear, and patients feel severely ill. Anyone suspecting an infection in their knee joint should seek medical attention immediately, as this is a surgical emergency — if there is septic arthritis then the patient will need to have the fluid/pus aspirated from their knee, they will need to be started on intravenous antibiotics and they will need a repeat arthroscopy to washout all of the pus from the joint. [It is NOT appropriate to treat a septic arthritis with antibiotics alone, without actually washing out the knee joint properly.]

Septic arthritis in a joint can often have serious long-term consequences. Infection in a joint often causes damage to the cartilage in the joint, increasing the future risk of secondary osteoarthritis developing in the joint in the future. Also, infection in joints or bones often has the nasty habit of recurring and flaring up again at some stage in the future. As discussed, however, thankfully the risk of serious infections from knee arthroscopy are very small indeed.


Nerve / blood vessel damage

Knee arthroscopy is performed via small (1/2 cm) incisions through the skin at the front of the knee (normally two but sometimes three incisions). All of the important and major nerves and blood vessels are round the back of the knee. Therefore, the risk of any nerve or blood vessel damage from knee arthroscopic surgery is tiny.

There are, however, a few potential exceptions to this. First, there is a small but important nerve called the Common Peroneal Nerve, that comes from round the back of the knee, across to the outer (lateral) side and which then wraps around the fibular neck (just below the outer side of the knee). Therefore any surgery specifically around the outer side of the knee (such as a posterolateral corner ligament reconstruction or surgery around the fibular head) does run the potential risk of damage to the Common Peroneal Nerve. The Common Peroneal Nerve supplies the muscles on the front and outer side of the shin that pull the foot/ankle upward/backwards. Therefore, any damage to this nerve can cause temporary or even sometimes permanent damage to this nerve, which can result in what is called a ‘foot drop’, which is where a patient will end up with a high-stepping gait and their foot will slap down hard as they take a step, which may necessitate the use of orthotics.

Another specific nerve at potential risk from surgery to the knee is the saphenous nerve on the inner (medial) distal (lower) thigh and its infra patellar branch, which passes just below the front of the knee. These nerves can be damaged during ACL reconstruction surgery, particular if the medial hamstring tendons are being harvested from the patient’s own leg to use as the graft for the ACL reconstruction. Damage to these nerves can cause patches of numbness at the front of the shin (but without this affecting any of the leg muscles at all).

Finally, one further specific instance where the risk of neuromuscular damage is larger than the tiny risk normally associated with knee arthroscopy is if the back of the knee is opened up at all. This is where all the major nerves or blood vessels are situated. Therefore, any surgery where access to the back of the knee is required has to be performed through reasonably large incisions, specifically so that all of the nerves and blood vessels can be clearly seen, identified and protected, to try and minimise the risk of damage.


Blood clots

Thankfully, the risk of developing a blood clot is also very rare after knee arthroscopy surgery. A blood clot in the veins of the calf is called a Deep Vein Thrombosis (DVT). Most calf DVTs are small and extend upwards from below, but do not extend any higher than the knee. Bigger above-knee DVTs are less common but can be more serious. Potentially, bits of blood clots from a DVT (particularly above-knee DVTs) can break off, pass up in the circulation and can get lodged in the blood vessels of the lungs, and this is called a Pulmonary Embolus (a PE). PEs can cause chest pain and shortness of breath, and can even in rare instances be fatal.

The risk of a DVT from an arthroscopy is very small. Some surgeons use tourniquets when performing their knee surgery (for knee arthroscopies and for knee replacements). However, Mr McDermott does not use tourniquets for any of his surgery, as he feels that they can cause increased damage to the muscles and thus increased post-operative pain, one can see potential bleeding (and therefore stop it) during an actual operation without a tourniquet (rather than only finding out after the operation, once a tourniquet has been removed), and also avoiding the use of tourniquets probably also decreases the risk of a DVT.

Some patients have blood disorders that make them naturally more prone to clotting and to developing DVTs. If there is a past history or a family history of DVT then it is sensible to see a Consultant Haematologist to have ones blood tested to exclude any underlying genetic/enzyme clotting condition. If any patient is considered to be at increased DVT risk then there are various different anti-coagulant drugs that can be given that thin the blood, to reduce the risks of a clot.

After surgery, most patients are given special anti-DVT TED stockings to wear. However, the most important thing is for patients to keep moving and to mobilise as much as possible, as quickly as possible after any surgery. Even if a patient is advised to avoid weight-bearing, they can still keep their feet/ankles wiggling regularly, to keep the circulation going and reduce the potential risk of a DVT.


Ongoing knee symptoms

Before going ahead with any kind of surgery, every patients should always enquire of their surgeon what the anticipated likely success rates might be for their surgery.

For example, the short term success rate for trimming of a meniscal cartilage tear (partial meniscectomy) is very high indeed – close to 100% (although in the longer term, the more meniscal tissue is lost the bigger the future risk of arthritis in the knee). The success rate for a meniscal repair healing up is approximately 90% at best. The success rate for ACL reconstructions is about 95%. The success rate for meniscal transplantation (at 5-year follow-up) is about 85%. The success rate for articular cartilage grafting is about 80% (at 5-year follow-up).  Therefore, it should be appreciated that there is no such thing as a guaranteed successful outcome with any kind of surgery (and any surgeon who says otherwise is either stupid, mad or dishonest!) – which is why it is so very important that all aspects of any potential surgery should be discussed properly and in full with your surgeon prior to you actually making any decisions about whether or not to go ahead with any particular specific operation.

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Written by Mr Ian McDermott Consultant Knee Surgeon, London

Last updated 4-5-17