Technical details of ACL Repair
in the Adult

Deciding on the suitability for Repair

Not every type of ACL tear is suitable  for consideration for a repair procedure. An experienced repair surgeon might consider repair in Type 1 and Type 2 injuries:

Type 1

Type 3

Type 2

Type 4

ACL injuries are usefully classified using the Sherman system:

  • Type I is where it literally comes right off the bone from where it takes its origin
  • Type II is close to, but not quite at the attachment point
  • Type III is about a third of the way along the ligament
  • Type IV is mid-substance

Type I's are the type of tears that do best with a repair. The ideal patient has a femoral detachment with a good quality ACL remnant, and it is a fairly acute injury (less than 6 weeks or a healthy stump if stuck to the PCL).

So, generally speaking the best outcomes are from fresh injuries, although as long as the tissue is satisfactory a repair can be carried out at any stage. The best outcomes seem to be when the repair is performed within the first three months of the original injury - but in the right patient a satisfactory outcome may be achieved in patients who have had an injury maybe six months before. Such early intervention has helped significantly in the management of paediatric cases, where repair offers significant advantages to avoid significant violation of the child's growth plate.

Best outcomes for ACL Repair: Sherman Type 1 tear and surgery within three months of injury.

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The Technical Steps in pictures

The procedure below is primarily referring to Type 1 tears, where the ligament has torn away from the wall of the femur. This is the type of tear that is particularly amenable to ACL Repair. A repair may also be possible in Type 2 tears.

These notes are in considerable detail and are for reference because when you are watching a video recording of the procedure it is really quite confusing with all the different 'strings' being pulled this way and that through the very small tunnels. This diagrammatic walkthrough should make each step a bit clearer.

Creating the portals (keyholes)

Figure 1: Arthroscopic portals into the knee

Standard arthroscopic portals (keyholes) are made through the skin to allow the surgeon to light up the inside of the knee and also pass instruments and sutures (stitches). To make this easy, a soft plastic tube called a PassPort cannula can be put into the main working keyholes and left there, allowing the surgeon to move instruments in and out as necessary without any struggle or trauma to the tissues.

With scissors passed into the knee via the portal and PassPort cannula, the surgeon frees the ACL from any attachment to the PCL ligament behind it. This creates access right around the ACL, so that it can be wrapped around with a suture cinch and pulled back to its original position against the wall of the femur. The instrument that facilitates this cinching is called a Mini Scorpion.

Loading the repair suture into the Mini Scorpion device

Figure 2: Mini Scorpion device

The Mini Scorpion is a very clever device that allows the surgeon, with one hand and through one portal, to both pass a suture through the ligament stump and also cinch a lasso around its 'waist'. By tensioning the free end of the suture, the surgeon can get control of the stump and pull it back onto the wall of the femur where it can heal back in its original place.

The working end of the Mini Scorpion device has two 'jaws', the lower of which houses a disposable retractable curved needle which is pre-loaded into the gun. The device has two triggers on it - and by manipulating one trigger the surgeon can control the internal workings of the needle while the other allows the surgeon to open and close the jaws of the device to grip or release the tissue.

Figure 3: Loading the FiberLink suture

The loop of the strong FiberLink suture is passed loosely over the stem of the Mini Scorpion, and it will later be used to cinch around the ligament like a lasso.

The other end of the FiberLink suture is fed into a slit in the bottom jaw of the Mini Scorpion. Once the suture is engaged in the slot, the handle of the device is squeezed and  suture auto-threads itself into the needle, ready for deployment. The jaws are closed and the 'loaded' device is then passed into the joint via the portal.

Lassoing the ligament

Figure 4: Deploying the needle

Within the knee the surgeon opens the jaws of the Mini Scorpion, and clamps them closed around the ACL stump near its torn end. The surgeon then fires the needle which emerges in a slightly curved manner, deploying about 15-18 mm of needle that passes right through the ACL tissue from the back to the front.

As the trigger is released on the needle the suture remains attached to the gun - rather than the risk of the suture being dragged back through the tissue it actually catches on the Mini Scorpion, so it is really clever.

Figure 4a: Showing the cinch mechanism

Figure 4b: The lassoed ligament

As the Mini Scorpion instrument is removed, the suture remains through the ACL but is now lassoed by the loop, and this part can now be used as a 'cinch' to gain control of the ligament. Usually one 'pass' is not enough and a second or even third suture is passed the same way until the stump is firmly secured.

The free end/s are brought out through the keyhole and secured with some forceps, ready to be retrieved later, when they will be referred to as the repair suture/s and later used to tension the ACL against the wall of the femur (after a tunnel has been made for it). 

So the next step is to make the tunnels, one at the femur end to pull up and tension the ACL stump, and later a second one in the tibia end to pass the material for the 'InternalBrace' which will mechanically support the repair until it has healed. For the drilling of both of these tunnels guide jigs are employed to ensure accuracy.

Preparing the femoral tunnel

Figure 5 a&b: The guide jig ensures that the femoral tunnel is drilled in the correct place

The jig (figure 5a) is positioned with the aiming target against the wall of the femur at the site where the ligament has torn away and the drill sleeve is secured on the outer side of the femur. Through the drill sleeve a 2.4mm drill is passed and the surgeon can drill down and be sure to accurately hit the target. 

Then the jig can be removed, leaving the patient with a 2.4 mm tunnel in the femur. Such a 2.4 mm  tunnel is very small, and won't compromise the knee if a revision procedure later becomes necessary. The innocuous nature of these narrow tunnels also contributes to a quick recovery. 

So figure 5b shows the knee after the femoral tunnel has been drilled. The repair suture is waiting to be pulled up through the femoral tunnel. 

Figure 6:  Suture passer

The tiny 2.4 mm tunnels are a challenge when it comes to passing and securing the sutures. The surgeon needs to focus on the task at hand.

He/she passes down the tunnel a fine suture-passer, threaded with a long 'passing-wire', retrieving its looped end through the knee via the keyhole.

Professor Wilson uses FiberWire for this purpose - it is made of metal and is rigid and this helps it pass smoothly through the tunnel to be retrieved through the portal at the other end of the joint.

Figure 7: Long thin FiberWire passing-wire threaded through the suture-passer

Figure 8: Passing-wire pulled out through the portal as a loop

The loop is then cut, leaving the surgeon effectively with two passing-wires. One of these is tied to the repair suture, and used to pull it up through the femoral tunnel, snugging the ACL back against the wall of the femur. That passing-wire is then discarded. The other one remains sitting in readiness for the next step.

Figure 9: The loop of the passing-wire is cut, so there are now two

Figure 10: One passing-wire is tied to the repair suture

Figure 11: That passing-wire is pulled out of the tunnel, dragging the repair suture out with it. The passing-wire is then discarded

So that is the first half of the procedure almost completed - the ACL stump is ready to be pulled up and tensioned against the femur into its pre-injury position. The second half of the procedure is to introduce the FiberTape InternalBrace through or alongside the ACL, and secure it at both ends in the femur and in the tibia.

Figure 12: Positioning a guide jig to make the tibial tunnel

A guide jig is now positioned on the tibia to make the second of the two tunnels - this time in the tibia. This tunnel will be used to introduce the FiberTape InternalBrace and the button that will secure it at the femur end. 

This tibial tunnel is again only 2.4 mm in diameter. It is drilled up from a point on the upper tibia to emerge at the footprint of the ACL. Often a small show of blood appears as the drill penetrates the vascular ACL tissue.

So now there are two tunnels - a femoral tunnel holding the repair suture and the remaining passing-wire, and a tibial tunnel, still empty. The other end of the passing-wire is still sitting waiting via the portal.

Figure 13: The second of the two tunnels is drilled

Figure 14: The rigid passing-wire is re-routed through the ligament stump and into the tibial tunnel

Figure 15: The passing-wire is pulled straight ready to tie onto the TightRope

Figure 16: TightRope construct, before adding the FiberTape

A TightRope is now used to pull a loop of braided polyethylene via the tibial tunnel up through the ligament stump to serve as an InternalBrace which will be secured at the femoral end by its button. Its two white sutures are pre-looped twice through the button and will allow a cinching mechanism to pull the InternalBrace into position.

Figure 17: The braided FiberTape InternalBrace is looped through the TightRope

Figure 18: The FiberWire passing-wire is tied directly to the free ends of the TightRope and pulled up the tibial tunnel, through the ligament and up the femoral tunnel

FiberTape is a flat ribbon of braided polyethylene which is very strong. A long FiberTape is looped through the loop of the TightRope, so on one side there are the white tensioning sutures and the blue lead suture, and on the other end is the loop of FiberTape.

Professor Wilson prefers to discard the lead suture, and simply knots the passing-wire directly to the white TightRope sutures.

The button itself is a long oval, and can be passed via its narrow end through the two tunnels and then flipped to its wider end to lock the construct against the bone.

The two white sutures of the TightRope have a self-tightening mechanism, or cinch, so that cycling between the two white sutures externally shortens the distance between the button and the loop. So as you are pulling on the free ends of the white sutures the loop is shortening, until there is enough of the InternalBrace FiberTape inside the femoral tunnel. When the surgeon is happy he stops cycling and ties down to those sutures the two ends of the repair suture/s from the ACL repair.

The FiberTape is fixed into the bone about 1.5 cm below the tibial tunnel exit with a little screw. 

Additional Resources

One Size Does Not Fit All- Innovative Approach to Repair Torn ACLs (Dr Greg DiFelice)