Effects of Radial Tears

For Medical Students

The Principle

Cutting across a rope weakens it in proportion to how many fibres are cut. Cutting halfway through leaves half the strength.

Cutting along a rope does far less. The fibres are still continuous from end to end.

So the direction of a cut matters more than its length, and the depth of a cut across matters more than anything else.

At the Knee

A radial tear runs from the free edge towards the periphery, across the circumferential fibres. 3.6.3 covers the fibres.

It interrupts the hoop tension path in proportion to its depth. A tear reaching the rim interrupts it completely. 3.6.2 covers hoop stress.

A longitudinal tear runs along the fibres and leaves both parts able to carry tension, which is why it is mechanically less costly.

That is the mechanical reason tear patterns are classified rather than tear sizes. 6.31 covers radial tears.

What Changes It

The depth of the tear towards the periphery, which is the mechanical variable.

Whether the peripheral rim is reached, since the rim carries most of the tension.

Tissue quality, which affects what the remaining fibres can carry.

Which compartment, with the lateral more dependent on its meniscus.

Clinical Relevance

A short radial tear reaching the rim costs more than a long longitudinal one, which is counterintuitive and mechanically straightforward.

Repairing a radial tear restores the tension path, and the construct carries that tension until it heals. 3.6.13 covers repair.

Resecting a radial tear removes the part that would have been repaired, so the decision matters. Section 6 covers management.

The depth of the tear is the question to ask about, rather than its length.

MRCS Level

The Principle

Depth towards the periphery is the mechanical variable, and it is a continuous one, so radial tears are a dose response like resection. 3.5.9 covers the dose response.

The dose is steeper than for resection, because the peripheral third carries most of the tension. A tear reaching the outer third costs disproportionately.

A complete radial tear is mechanically equivalent to a root tear: the ring is interrupted and tension cannot be generated. 3.6.11 covers root tears.

At the Knee

Conventional teaching holds that contact pressure rises progressively with the depth of a radial tear and approaches the meniscectomised state when the tear reaches the capsular margin.

The lateral meniscus tolerates it less well, which combines with lateral radial tears being associated with anterior cruciate injury. 2.6.1 covers the anatomy.

Radial tears in degenerate tissue behave differently, because the fibres being cut were already carrying less. 6.38 covers degenerative disease.

Repair of a radial tear requires the construct to carry hoop tension across the tear until healing, which is a larger demand than a longitudinal repair. 3.6.4 covers the fibre systems.

What Changes It

Depth towards the capsular margin, as the dominant variable.

Tissue quality, which decides what the intact remainder carries.

Compartment, with the lateral less tolerant.

Load and alignment, which set what the reduced tension path has to manage.

How It Is Measured

Cadaveric studies creating radial tears of graded depth in the same specimen measure the dose response directly.

Contact pressure and area are the outcomes measured, under an applied load without muscle.

Clinical imaging describes the tear and estimates its depth, with limited precision. 5.6 covers imaging.

Construct testing measures whether a repair holds the tension, separately from whether the tear heals.

Clinical Relevance

Assess the depth towards the rim rather than the length of a radial tear.

Treat a complete radial tear as mechanically equivalent to a root tear.

Expect a radial repair to make larger demands of the construct than a longitudinal one.

Distinguish a radial tear in degenerate tissue from one in healthy tissue.

FRCS Level

At the Knee

Treat the radial tear as the pattern where the repair decision has the most mechanical consequence and the least reliable healing. The two facts pull in opposite directions and both are real.

Conventional teaching reports lower healing rates for radial repairs than for longitudinal ones, which follows from the construct carrying the hoop tension rather than approximating a split.

That is the mechanical argument for the configurations developed specifically for radial tears, and for protecting load afterwards. 3.6.13 covers constructs.

What Changes It

Construct configuration and the number of fixation points across the tear.

Tissue quality and vascularity at the tear, which decide healing. 2.5.3 covers blood supply.

Postoperative load protection, since the construct is the tension path meanwhile.

Alignment, which sets the tension the construct must hold.

How It Is Measured

Cadaveric construct testing by configuration under cyclic load measures gap formation, which is the relevant failure for this pattern.

Pull to failure measures ultimate strength, which matters less than cyclic behaviour here.

Clinical healing rates by pattern are reported and are consistently lower for radial tears.

No measurement confirms the hoop tension path was restored in a patient.

Clinical Relevance

Choose a construct developed for radial tears rather than a default configuration.

Protect load after a radial repair, since the construct carries the tension.

Counsel on lower healing rates for this pattern, with the mechanical reason.

Correct alignment where the construct would otherwise carry an excessive tension.