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The 'Why" Behind Meniscus Rehab

Surgical techniques to repair torn menisci have come a long way in the past 20 years. The meniscus was once thought to be no more than a shock-absorber for the knee and irreparable, as shown by many documented cases of their surgical removal.

Flash forward 20 years, we now know that the meniscus serves several purposes:

- shock absorption

- increasing contact area between bony surfaces (and thus reducing compression)

- mechanical guide for coordinated knee flexion & extension

- proprioceptive input for kinesthesia

For these reasons, today's surgical techniques aim to preserve as much of the meniscus as possible.

Fig 1 (photo courtesy of McDermott, Amis. JBJS Dec 2006)

McDermott et al found that as more of the meniscus is lost, the overall function of the knee decreases. Furthermore, loss of the medial meniscus led to a decrease in contact areas of approximately 75% (meaning instead of distributing weight over a broad area, the pressure between the femur and tibia is taken through a smaller surface area) and an increase in the peak contact pressures of approximately 235% (Fig. 1). Think of this as the difference between stepping on a bed of nails versus 1 tack. Ouch. Therefore, I pose this question:

1: Should we be encouraging our patients with a partial meniscectomy to use their crutches/canes longer?

My patient's instructions generally sounds like this: "you can get rid of your crutches when you can walk without a limp". I find this more useful than identifying a specific time frame for crutches.

Differences also exist in the medial and lateral menisci as well. The lateral aspect of the knee (lateral meniscus included) take greater amounts of load than the medial compartment. This difference is partially due to the shape of the tibia- the lateral compartment are two convex surfaces, whereas the medial compartment is a convex on concave surface. Food for thought:

2: Know which meniscus is pathologic. You may want to delay or modify exercise in order to decrease compressive forces based on their condition.

Escamilla et al published their findings on tibiofemoral compressive forces during common therapy exercises. They found the greatest compressive forces in an open chain activity between 15-29 degrees knee flexion (during both concentric and eccentric phases). This suggests a short-arc quad (SAQ) applies more compressive force than a modified long-arc quad.

Initial rehabilitation goals following knee surgery often include gradually restoring range of motion. We all know there are many methods in how to achieve this, but you may want to choose your methods with this fact in mind: the popliteus muscle attaches to the lateral meniscus, and the hamstring (semimembranosus) attaches on the medial meniscus.

3: In the presence of a repaired meniscus, you should avoid active or resisted knee flexion during the first phase of rehab to protect the surgical repair.

So instead of performing an active heel slide, try gravity (or therapist) assisted knee flexion instead...

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