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Combined ACL and ALL Reconstruction

Page 3.11.8 · Anterolateral Complex Biomechanics · biomechanics page

Two constructs restraining two coupled motions. They interact, so the second one changes what the first has to do.

Pipeline status. Editorial draft. Evidence verification did not run. Not consultant reviewed. Not for clinical use.

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Combined ACL and ALL Reconstruction

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For Medical Students

The Principle

Two restraints acting on the same coupled motion share the load. Adding the second reduces what the first carries.

That sharing is the point of the addition. A graft carrying less load is a graft less likely to fail.

It is also the risk. Two restraints can between them allow less motion than normal, which is over-constraint.

At the Knee

The cruciate graft restrains anterior translation and some rotation. The lateral construct restrains rotation. 3.7.2 covers the cruciate's primary role.

Internal rotation and anterior translation are coupled, so the two constructs are working on the same event. 3.2.9 covers coupling.

Conventional teaching reports reduced graft failure rates when a lateral procedure is added in defined groups, which is load sharing showing itself. 3.11.7 covers the tenodesis.

Over-constraint is the opposite error, and it is managed by tensioning modestly and fixing with the tibia neutral. 3.11.5 covers internal rotation control.

What Changes It

Whether a lateral procedure is added at all.

Both constructs' positions and tensions.

The order in which they are tensioned and fixed.

Bony morphology, which sets the demand. 3.13 covers alignment.

Clinical Relevance

The addition is for defined groups rather than for everyone, because the benefit is largest where rotational demand is highest. Section 6 covers management.

Two constructs mean two sets of positions to get right, which is more to go wrong.

Tensioning order matters, because each affects the other's tension. 3.7.20 covers the cruciate construct.

A residual pivot shift after both suggests a bony or a meniscal factor rather than a soft tissue one. 3.11.4 covers pivot shift control.

Key Learning Points

  • Two restraints on one coupled motion share the load.
  • A graft carrying less load is less likely to fail.
  • Over-constraint is the risk of the same sharing.
  • Conventional teaching reports reduced graft failure in defined groups.
  • Tensioning order matters because each construct affects the other.

MRCS Level

The Principle

The interaction is mechanical rather than additive. Fixing the lateral construct changes the tibia's rotational position, which changes the cruciate graft's length and therefore its tension.

So the order of fixation is a variable in its own right, and a construct tensioned before the other is fixed is not at the tension intended. 3.7.20 covers the cruciate construct.

Conventional teaching fixes the cruciate graft first and then the lateral construct, with the tibia in neutral rotation.

At the Knee

Robotic testing shows the combined construct restoring rotational control closer to the intact knee than the cruciate graft alone, with over-constraint at higher lateral tensions. 3.11.5 covers over-constraint.

Randomised trial data reports lower graft failure rates with the addition in young pivoting athletes, which is the clinical form of the load sharing argument.

The lateral construct reduces the strain in the cruciate graft in cadaveric measurement, which is the direct mechanical evidence. 3.7.10 covers strain.

Femoral fixation of the two constructs competes for the distal lateral femur, which is a geometric constraint. 3.11.2 covers the region.

What Changes It

Order of fixation and the rotational position at each.

Both constructs' tensions.

Femoral fixation positions and convergence.

Bony morphology and the rotational demand.

How It Is Measured

Robotic testing measures the combined construct against the intact knee in all six degrees of freedom.

Cadaveric graft strain measurement shows the load sharing directly.

Randomised trials report graft failure and reinjury rates.

No clinical measurement shows the load sharing in a patient.

Clinical Relevance

Fix the cruciate graft first and the lateral construct second, with the tibia neutral.

Tension the lateral construct modestly, since over-constraint appears at higher tensions.

Plan both femoral fixations together to avoid convergence.

Expect the load sharing to be demonstrable in cadavers and not in a patient.

Key Learning Points

  • The interaction is mechanical rather than additive.
  • Fixing the lateral construct changes the cruciate graft's tension.
  • Order of fixation is a variable in its own right.
  • Conventional teaching fixes the cruciate first, then the lateral, with the tibia neutral.
  • Cadaveric strain measurement shows the load sharing directly.

FRCS Level

At the Knee

Treat the combination as the current answer for the high risk knee and the indications as the part still being refined. 3.11.9 covers the controversies.

The mechanical case is load sharing and the clinical case is reduced graft failure, and the two agree, which is less common than it should be. 3.11.7 covers the tenodesis.

The remaining question is whether the addition should be routine in young pivoting athletes or reserved by laxity grade and morphology, and conventional teaching has not settled it.

What Changes It

Which indication group the patient falls in.

Slope and plateau morphology, which may be corrected instead. 3.13 covers alignment.

Graft availability and femoral fixation space.

Whether the knee is a revision.

How It Is Measured

Randomised trials and registry data report graft failure by whether the addition was made.

Robotic testing gives the mechanical effect.

Instrumented pivot shift measures the rotational result in cohorts.

Subgroup data on who benefits most is limited by sample size.

Clinical Relevance

Add a lateral procedure in the high risk groups the trials cover.

Consider slope correction as an alternative in the right knee.

Plan graft and fixation space for both constructs before theatre.

State that routine against selective use is unsettled.

Key Learning Points

  • The combination is the current answer for the high risk knee.
  • The mechanical case and the clinical case agree, which is less common than it should be.
  • Whether to add routinely or by laxity and morphology is unsettled.
  • Subgroup data on who benefits most is limited by sample size.
  • Slope correction is an alternative in the right knee.

Fellowship Level

At the Knee

The fellowship problem is the revision knee with a failed graft, a wide tunnel, an increased slope and a high grade pivot shift, where the cruciate graft, the lateral construct and a slope correction are all indicated. 3.7.20 covers the revision framing.

Sequencing and tunnel geometry decide what is possible in one sitting. A slope correcting osteotomy changes the tibial anatomy a cruciate tunnel will use, which is an argument for doing it first or simultaneously. 3.13 covers alignment.

A tenodesis is the lateral construct of choice here on geometric grounds, because it adds no tibial tunnel. 3.11.7 covers it.

What Changes It

Tunnel condition from the previous surgery.

Slope and whether it is being corrected.

Graft availability after previous harvests.

Femoral fixation space on the lateral side.

How It Is Measured

Computed tomography plans the tunnels and the convergence.

Lateral radiography measures the slope and plans the correction.

Revision registry data reports outcomes, which are worse than primary.

No measurement establishes the optimal sequence for a given combination.

Clinical Relevance

Plan tunnel geometry and slope correction together in a revision.

Prefer a tenodesis, which adds no tibial tunnel.

Stage where tunnels, graft or soft tissues will not allow one sitting.

Counsel that revision outcomes are worse than primary.

Key Learning Points

  • The revision knee may need graft, lateral construct and slope correction together.
  • A slope correcting osteotomy changes the anatomy a cruciate tunnel will use.
  • A tenodesis adds no tibial tunnel, which is a geometric advantage in revision.
  • Sequencing and tunnel geometry decide what is possible in one sitting.
  • No measurement establishes the optimal sequence.

Explore Further

Where this topic came from and where it goes next in the spiral.

References

No reference list is attached to this draft. Evidence verification has not run, because source retrieval was unavailable at generation time. Under the Operations Handbook a missing reference is acceptable and an invented one is a critical failure, so nothing has been cited and no citation marker appears in the text. Every measurement on this page is written from standard teaching rather than from a retrieved paper, and none has been checked against a source. Under decision 006 each one is registered in pipeline/config/figures with the sentence it supports and a verification state of UNVERIFIED_FROM_MEMORY, so the whole list can be checked and corrected rather than hunted for.

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