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The Knee Meniscus: Torn between Rehab or Surgery?

What Is A Meniscus?

Knee Pic

The meniscus is a piece a cartilage that sits in the knee between the bones of the thigh (femur) and the shin (tibia). Its made of a similar type of cartilage found in our ears (fibrocartilage) and is just as sturdy.

The meniscus acts as a shock absorber (suspension) in the knee and provides some stability too. When the meniscus is not working properly or has been injured or removed, more shock is transferred to the bones in the knee (and the smooth cartilage that lines those bones). This results in increased wear and tear and eventually osteoarthritis. People who have had meniscal surgery are 14 times more likely to develop osteoarthritis than people with a meniscus.

KEY POINTS:

  • The meniscus has no nerve supply. This means you can cut into the meniscus with a pair of scissors and feel NO pain
  • However, meniscal injuries can result in pulling on the lining of the knee (capsule) which is extremely sensitive to pain. The injury also stimulates inflammation which causes pain and swelling

Will My Meniscus Heal On Its Own?

The meniscus has some blood vessels at the very outer edge (see diagram). This blood supply (red zone) slowly fades away once we are older than 30 years old. For tissues to heal when they are injured they need to have a blood supply. So, most meniscal injuries have limited healing potential unless they are at the very outer edge and the patient is less than 30 years old.

What Symptoms Does A Meniscal Tear Give You?

  • Usually people will develop pain on the side of their knee (either the medial/inner or lateral/outer)
  • There may be an associated clicking/catching feeling
  • The pain can come on suddenly with a specific movement but in older people the pain usually comes on slowly with time
  • Some swelling of the knee may be present
  • The pain is irritated by twisting movements and squatting down
  • Major meniscal tears can lock your knee (stop it from straightening), these are known as bucket handle tears

How Does A Meniscus Get Injured?

A meniscal tear seen during arthroscopic surgery

The meniscus is usually injured when someone has a bent knee and changes direction. Often the movement that injures the meniscus is no different to any number of movements you would make throughout a day such as rising out of a chair and pivoting.

It is rarer to have meniscal injuries when you are less than 30 years old as the meniscus is healthy and strong. As we age, meniscal tears  become increasingly common as the meniscus wears down and erodes with time. For this reason, older people often don’t notice a specific moment when they injure their meniscus as it usually just slowly fails and becomes frayed. Conversely,  younger people do often report a specific incident where they hurt their knee as the force required to tear a young strong meniscus is much higher. In the older knee, meniscal tears are now being considered as part of osteoarthritis instead of a separate injury needing specific treatment.

KEY FACTS:

  • 1 in 3 people over 50 years old have a meniscal tear (expected degenerative change)
  • 20% of people over 50 years old with knee pain have a meniscal tear
  • 25% of people over 50 years old WITHOUT knee pain have a meniscal tear!

KEY DIAGNOSTIC POINT:

SEEING A MENISCAL TEAR ON MRI DOES NOT CONFIRM THE MENISCUS AS THE SOURCE OF PAIN

Does a Meniscus Tear Need Surgery?

Meniscal red zoneThe only meniscal tears that need surgery are those that can be repaired, or tears that give persistent pain despite good quality non-operative care. In general, if you are over 30 years old the meniscus has reduced healing potential and is less likely to be repaired as the blood supply to your meniscus starts to diminish.

Meniscal repair

If you have a tear of the meniscus in or near the blood supply, the meniscus may heal if surgical stitches hold it together whilst it heals (similar to how skin stitches only hold the skin together whist waiting for the skin to heal). The stitches themselves are not very strong so if the meniscus injury is in an area without blood supply (white zone), the stitches will not repair the meniscus by themselves.

A specific type of meniscal tear called a ‘bucket handle tear’ can occur and cause your knee to be locked (cannot fully straighten your knee). In all cases of a locked knee further medical assessment is required urgently as there are several causes of a locked knee. If you have a bucket handle meniscal tear you will need urgent surgical referral for either repair or partial meniscectomy. Non-operative treatment is not an option for bucket handle meniscal tears.

Can Your Meniscal Tear Heal On Its Own?

Small meniscal tears in the ‘red zone’ in younger people may heal without surgery though. If you have a tear of the meniscus away from the blood supply it is unlikely to heal on its own. However, even if your meniscal tear is outside of the ‘red zone’ or you are older than 30, you can still treat your pain successfully in a few ways;

What Is The Best Treatment For Meniscal Tears?

A large number of scientific studies involving thousands of patients have improved our understanding of meniscus treatment options.

Meniscal Surgery

A meniscal tear pre-meniscectomy

For many years the most frequent treatment for meniscal tears was to cut out the part of the meniscus that was torn via keyhole surgery (known as arthroscopic partial meniscectomy) to try and prevent ongoing inflammation within the knee. By and large, this surgery was successful for treating knee pain, but it was recognized that the risk of developing knee problems later in life was increased once you had had a partial meniscectomy. A group of patients were seen to have poor outcomes after partial meniscectomy surgery. These patients already had osteoarthritis in the knee and once the meniscus (suspension) had been removed, their pain increased. Patients with this response have few treatment options available beyond a total knee replacement which is undesirable for most until absolutely necessary. Therefore, partial meniscectomies in people with osteoarthritis is not recommended.

Meniscus post-meniscectomy

An issue with meniscal surgery is the amount of meniscus that needs to be removed. Successful surgery requires the meniscus to be resected back to a stable base. Although the tear in the meniscus may be small, its effect on meniscal function is potentially large. The meniscus is made up of fibres the run all the way through it from the front to the back – like multiple washing lines stacked together to make a strong unit. A small tear in the meniscus is like snipping the washing lines in half – the injury to the fibre is quite localized but the entire fibre is defunctioned. Surgery tries to remove all of the injured fibres working on the theory that this will reduce the number of re-tears that occur. Unfortunately, this means a small tear still results in a significant amount of meniscus being removed and resecting as little as 15-35% of the meniscus can result in forces increasing in the knee by up to 300%. This subsequently stresses the bones and the smooth cartilage that lines them and results in early osteoarthritis in many people.

Subsequent scientific studies have found that having a partial meniscectomy did not improve people’s pain any more than did ‘sham (fake) surgery’. In these studies patients were anaesthetized (put to sleep) and the knee was explored via keyhole surgery. In one group of patients the meniscus was not touched. The other group had the meniscus surgery. None of the patients knew if they had the real or fake operation. At all follow up points after the operation, there was no difference in patients’ pain scores whether they had the fake surgery or the partial meniscectomy.

The results from the sham surgery prompted further research into non-operative treatments such as anti-inflammatories, injections and rehabilitation for meniscal injuries.

Meniscal Surgery Summary

  • Surgery helps pain but is not more successful than fake surgery, anti-inflammatories or exercise in most people
  • Partial meniscectomy affects function of the knee and will speed up the onset of degenerative osteoarthritis

Non-Operative Treatment For Meniscus Injuries

physioWe now know that the majority of patients have at least as good outcomes (reduction of pain and improved function) if they perform a physiotherapist supervised exercise rehabilitation program  for a few  months instead of having surgery. Not all physiotherapy is the same and it is important that the physiotherapist that guides your rehab performs a thorough examination of your knees, understands your specific needs and tailors your exercise program accordingly.

In some cases, the pain in the knee is too severe to perform the rehab exercises or too swollen to allow the muscles around the knee to work effectively. In these circumstances, treatment with either anti-inflammatory tablets (guided by a doctor) or an injection into the knee (preferably under ultrasound guidance) are recommended. These treatments can settle your pain and swelling sufficiently to allow you to perform rehabilitation work.

Although the majority of patients will not need surgery for their meniscus injury, some people will still have pain after performing rehab. When this is the case, surgery for the meniscus should be considered.

What is a Discoid Meniscus?

Children and adolescents with lateral knee pain will often have an injury to a discoid meniscus. A discoid meniscus is something some people are born with and it is a meniscus that is circular rather than moon-shaped. A discoid meniscus is vulnerable to tearing but resecting the excessively large fragment of a discoid meniscus does not seem to have any adverse effects as the patient is left with a normal looking moon-shaped meniscus.

discoid meniscus

What Is A Meniscal Root Avulsion?

Occasionally people can rip the meniscus off the bone where it attaches. The injury mechanism is no different to other meniscal tears, but the resulting pain and loss of function is severe. There is often significant posterior knee pain and difficulty with weight bearing. Swelling may not be significant. Occasionally these can be repaired through a specific surgical technique. If it cannot be repaired and there is underlying osteoarthritis present, the injury can be devastating. This is then managed as a severely painful osteoarthritic knee and can result in a total knee replacement if non-operative treatments are unsuccessful.

New Technology On The Horizon?

In the United States, there is ongoing research in to the use of meniscal allograft surgery where a meniscus donated from a deceased person is used to replace the injured meniscus. The results for this procedure are promising but it is not available in Australia and is unlikely to be a treatment option in the near future due to a lack of availability of donor menisci.

SUMMARY OF MENISCAL ISSUES

  • Meniscal tears are common in middle-aged people and may not be the cause of knee pain
  • Symptomatic meniscal tears should be treated with non-operative treatments (supervised physiotherapy, anti-inflammatories, injection therapy) for a few months before considering any surgical intervention
  • Surgery is a good option for pain that persists despite good quality non-operative treatment
  • Although surgery may help pain it will affect knee function and speed up osteoarthritis
  • The only tears that can be repaired are those in the outer edge of the meniscus, usually in people less than 30 years old
  • If you have a locked knee (can’t fully straighten) you need to see a doctor for urgent assessment

The Sports Medicine Physicians and Sports Physiotherapists at Newcastle Sports Medicine are experts in assessing and treating all knee issues including meniscal injuries. If you would like your knee assessed or treated please call (02) 4910 0805 to make an appointment.

Click here to listen to Professor Jarvinen discuss his research on meniscal injury

References

  1. Thorlund et al. Patient reported outcomes in patients undergoing arthroscopic partial meniscectomy for traumatic or degenerative meniscal tears: comparative prospective cohort study. BMJ 2017;356:j356
  2. Kise et al. Exercise therapy versus arthroscopic partial meniscectomy for degenerative meniscal tear in middle aged patients: randomised control trial with two year follow-up. BMJ 2016; 354:13740
  3. Sihvonen et al. Arthroscopic partial meniscectomy versus placebo surgery for a degenerative meniscus tear: a 2-year follow-up of the randomised controlled trial. Ann Rheum Dis 2017;0:1-9
  4. Sihvonen et al. Mechanical symptoms as an indication for knee arthroscopy in patients with degenerative meniscus tear: a prospective cohort study. Osteoarthritis and cartilage 2016:24;1367-1375
  5. Sihvonen et al. Mechanical symtpoms and arthroscopic partial meniscectomy in patients with degenerative meniscal tear: A secondary analysis of a randomized trial. Annals of Internal Medicine 2016:164);449-455
  6. Buchbinder et al. Management of degenerative meniscal tears and the role of surgery. BMJ 2015;350:h2212
  7. Khan et al. Arthroscopic surgery for degenerative tears of the meniscus: a systematic review and meta-analysis. CMAJ 2014. DOI:10.1503/cmaj.140433
  8. Herrlin et al. Arthroscopic or conservative treatment of degenerative medial meniscus tears: a prospective randomised trial. Knee Surg Sports Traumatol Arthrosc 2007:15;393-401
  9. Roos et al. Knee Osteoarthritis after meniscectomy. Arthritis and Rheumatism 1998 (41):4;687-693

 

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