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Structural and functional consequences of meniscectomy

varus thrust
varus thrust
© KNEEguru

Modern knee surgeons understand the importance of preserving the meniscus wherever possible, and techniques have been developed to repair tears in the hope of restoring normal anatomy and function. However, certain tears cannot be repaired and it may be necessary for the surgeon to remove meniscal tissue. In this case the modern surgeon has been taught to preserve as much viable tissue as possible, and especially the all important outer rim.

This focus on meniscal preservation was not always the case, and only two decades ago it was commonplace for surgeons to remove the whole meniscus with little regard for the long term consequences, as the importance of the menisci in load bearing, shock absorption and knee stability had not at that stage been fully appreciated.

After a meniscus has been removed the patient may initially notice little alteration in these parameters. Indeed, initially the patient may be delighted at the improvement in their symptoms, but with time negative changes are likely to become apparent.

These may include -

Changes to the joint cartilage in the absence of symptoms

Although the patient who has had a meniscectomy may have none or few symptoms, cartilage-sensitive MRI scans may reveal subtle changes to the joint cartilage1. This may identify the patient at future risk of joint cartilage breakdown and subsequent arthritis.

Deterioration in functional knee scores

If taken through a scoring system such as the Knee injury and Osteoarthritis Outcome Score (KOOS), the patient will answer questions that include changes in their activities of daily living and quality of life. Comparison with pre-injury answers and with answers over a period of time after surgery may reveal a gradual deterioration even though the patient may not complain particularly of pain 2.

Decreased gap between long bones on stress testing

Decreased joint space on one side of knee

Between the long bones of femur and tibia on X-ray, there is a gap which is the space occupied by the normal meniscus. It shows as a gap because the meniscus is not easily visible on X-ray.

This X-ray actually already shows signs of joint damage, but ignore that for now and just observe the differences in the gap. The red circle shows the gap completely closed - compare the other side which is normal.

Early non-weight-bearing X-rays after a meniscectomy may look completely normal, but taking the X-rays while the joint is being stressed to the side (varus or valgus stress), or while the patient is standing, may demonstrate that the gap is less on the affected side, even though the patient may not be symptomatic.

Abnormal sideways thrust during walking

As the stability of the knee becomes stressed by the lack of the meniscus, there may be the development of a sideways thrust of the knee during walking. This happens as the patient shifts their weight onto the meniscectomised knee. The thrust occurs because of the lack of the meniscus which usually is there as a spacer and shock absorber. Depending on the direction of the thrust this is called varus thrust or valgus thrust.

This video, embedded from YouTube courtesy of 'ACPM74' demonstrates the nature of a lateral thrust, although this patient may have other problems such as ligament instability -

 

 

In someone with a thrust like this, the knee might look completely normal to the observer when the patient simply stands still.

Abnormal standing leg alignment

In investigations of structural and functional changes like these, it is important to take X-rays with the patient standing and weight bearing. This may reveal alignment problems not evident otherwise, such as a varus deformity (bow leg) rather than the sort of functional thrust seen in the video above.

Unicompartmental osteoarthritis

Long term studies of patients after meniscectomy highlight the issue of the development of osteoarthritis2. On X-ray, this may be demonstrated by flattening of femoral condyle (as in the above X-ray), lipping of joint edges and later frank bony outgrowths called osteophytes.

References

  1. MRI Evaluation of Isolated Arthroscopic Partial Meniscectomy Patients at a Minimum Five-Year Follow-up
  2. Total meniscectomy in adolescents: a 40-year follow-up.

 

Further reading

 

 

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Updated: 23 Sep, 2013
ABOUT THE AUTHOR

Dr Sheila Strover

Clinical Editor
Degrees: 
BSc (Hons)
MB BCh
MBA

Dr Sheila Strover is the founder of the KNEEguru website. Although not a knee surgeon, she has a sound understanding of knee surgery and...

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