ACL-Reconstruction using patellar tendon

Patellar-Tendon ACL: Operative Technique

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Steps of the Operation:

Graft-Harvest
Graft-Preparation
Arthroscopy
Notch-Plasty
Femoral Socket
Tibial Tunnel
Graft-Passage
Graft-Fixation
Postoperative Procedure



Graft-Harvest

A tourniquet is not used. The joint and the subcutaneous tissues in the region of the planed incisions is infiltrated using 40 ml of 0,25% Bupivacain / Epinephrine solution.

The first 20 mm long horizontal incision is made just proximal to the inferior pole of the patella, the second just medial to the tibial tubercle (Fig. Skin incisions). The skin and the subcutaneous and peritendinous tissue are incised down to the tendon. The space between tendon and paratendon is opened bluntly in all directions. The "seahorse," a specially designed malleable retractor, is inserted underneath the skin bridge from the proximal to the distal incision (Fig. Exposure of the tendon with the "Seahorse"). This retractor protects the retinaculum and the skin bridge during the insertion of the helical tube saw. The plug stamp is used to mark the outline of the patellar bone plug on the periost just proximal to the inferior patellar pole (Fig. Marking of the patellar bone plug).

The periost is incised medially and laterally to the previously placed lines using electrocautery. With the electrocautery turned off the tendon is incised along its fibers for a few millimeters inline with the periosteal cuts. In very dense bone the oscillating saw is used to incise just the superior two or three millimeters of the hard cortical bone. This facilitates harvesting of the plugs later with the hand held helical tube saw.

The retrograde patellar tendon knife is inserted subcutaneously starting at the distal skin incision and directed to the proximal skin incision. The blade is hooked into the previously made cuts of the proximal patellar tendon (Fig. Tendon cuts, frontal view and lateral view.). The knife is pulled distally along the direction of the fibers until the knife touches the proximal tibia. The second cut of the patellar tendon is made in a similar fashion. Since the tendon fibers converge distally, the graft is narrower at the distal end. Because the cross-section of the patellar tendon is slightly convex, the knife blade should always be tilted inwards. The tendon rasp is used to separate the tendon strip from the underlying retro-patellar fat-body ( Fig. Detachment of fat pad, frontal view and lateral view).

A short silicone tube is used to guide the 10 mm helical tube saw (HTS) underneath the skin bridge starting at the distal skin incision and directed toward the proximal incision. The blade is inserted around the patellar tendon. One can use a special holder to fix the HTS against the inferior border of the patella (Fig. Insertion of patellar bone plug cutter, frontal view. and lateral view and crossection ). The corners of the HTS blade must always be seen on both sides of the tendon, i. e. the depth of the bone cuts should not be more than 8 millimeters. Initially the bone is cut using gentle oscillating motions with only little pressure. Once the teeth have cut into the bone, the HTS-holder should be removed. The bone plug is cut according the previously outlined length.

A "pig-tail"tendon hook can be used in order to verify that both bone plugs are resected in line with each other. The tendon hook is inserted subcutaneously from the distal toward the proximal incision. The tendon hook is rotated around the tendon strip and then pulled distally towards the tibia.

The 9 mm HTS blade is guided with a silicon tube subcutaneously from the proximal to the distal incision and rotated around the tendon strip. Here the use of a 9 mm holder to stabilize the osteotom is obligatory. Care is taken to avoid slipping forward on the oblique surface of the proximal tibia which would amputate the patellar tendon from the bone (Fig. Insertion of tibial bone plug cutter, frontal view, and lateral view and crossection ). Once again in dense bone it may be preferable to cut the cortical bone with an oscillating straight saw or straight osteotom.

The proximal end of the patellar bone plug is perforated several times with a 1.5 mm drill bit. Approximately 5 mm from the end a 1.5 mm hole is drilled tangentially to the side of the bone plug through the subcortical bone (Fig. Drilling of the hole for the cerclage wire ). A cerclage wire will be inserted later into this hole in order to pretension the graft after its proximal fixation. At the tibial end there is no risk of fatigue fracture and therefore the end of the bone plug does not have to predrilled.

The bone plugs are detached with a small osteotom (Fig. Graft ) A cancellous bone plug is obtained using a 10 mm tube saw through the harvest site at the proximal tibia. (Fig. Harvest of a bone plug from the proximal tibia ). This bone graft will be inserted into the patellar defect (Fig. Bonegrafting the patellar defect ). The proximal incision is closed and the distal bony harvest sites are filled with "Spongostan".

Graft-Preparation

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The patellar plug should fit easily through the 10 mm hole of the working station. An 0.8 mm cerclage wire is inserted into the previously drilled 1.5 mm transverse drill hole. A small indentation at the patellar bone plug helps to identify the location where the tibial interference screw will be introduced. This area should be marked with a pen so that the rotation of the plug inside the tibial tunnel can be easily seen later.

The tibial plug is checked for its 9 mm outer diameter and the entire length of the graft is measured (Fig. Measuring of the graft length ). It is important that the bony and tendinous edges of the leading end are smooth and will not catch during the intra-articular passage of the graft. After having used the HTS instruments it will not be necessary to perform a lot of trimming of the bone plugs. But for further preparation and minor trimming of the graft the 9 mm diameter plug can be inserted into the conical hole of the work-station.

To facilitate trimming, the graft is held tightly with the cerclage-wire. A small indentation is made into the cortical bone of the smaller 9 mm plug using a rongeur and the tendon-bone junction is marked with a pen.

A threaded K-wire is drilled into the bone plug as parallel to its axis as possible (Fig. Graft preparation ). This is facilitated by the use of the drill guide clamp and first drilling of a 1.5 mm hole. The tendon is tubed using several interrupted 3-0 Maxon or PDS sutures. The graft is wrapped into a moist sponge and stored in the trench of the working station for later use.

Arthroscopy

The arthroscope is inserted directly lateral to the patellar tendon at the level of the inferior patellar pole (Fig. Arthroscopy portals). The working portal should be medial to the patellar tendon and as distal as possible. One way to ensure a good position is to insert a spinal needle under direct arthroscopic vision. With this needle one should be able to easily reach the posterior cortical border of the notch.

If indicated one performs at this time additional arthroscopic procedures such as meniscectomies, synovectomies, shavings and so on.

Notch-Plasty

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Remnants of the old ACL are to be removed using a suction punch or motorized full radius resector leaving a small stump at the tibial attachment site (Fig. Debridement of the old ACL). In order to maintain good visibility without the activation of the tourniquet one has always to avoid lowering the fluid pressure below the arterial pressure. In other words the outflow should never be larger than the inflow.

To improve the view of the posterior notch and to avoid lateral impingement of the ACL-graft one has to occasionally remove about 3 mm of bone from the lateral femoral condyle (Fig. Wall-plasty).

In patients with soft bone the "wall" and "notch-plasty" can often be performed using a 4,5 mm "full radius shaver". With the hook of a probe one should verify the posterior cortical border to ensure that one has not mistakenly worked on the so-called "resident's ridge" which is a prominent ridge at the posterior roof of the notch approximately one centimeter in front of the posterior border (Fig. Notch-Plasty, Residents Ridge).

The lateral wall and the roof of the notch has to be smoothed with a sweeping motion using a 4.5 mm. burr from anteriorly to posteriorly. However because the tibial insertion of the ACL-graft will be placed in the postero-medial aspect of the "footprint" one has not to perform an extensive "roof-plasty.

Femoral Socket

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For this part of the procedure the knee joint should be bent to at least 90. The center of the femoral socket entrance should be about 5 mm in front of the cortical border. That way one will leave only approximately 2 mm of bony bridge posteriorly

The entrance of the socket in the right knee will be between 10 and 11 O'clock and in the left knee between 1 and 2 O'clock (Fig. Entrance of the femoral socket ). At this location one performs a small bony excavation according to the diameter of the bone plug. (Fig. Excavation at the entrance of the femoral socket ). In order to avoid difficulties during insertion and fixation of the graft, this area should be fairly clean and have no soft-tissue debris.

A pilot hole is made using the special screwdriver, turning it counterclockwise (Fig. Creation of pilothole using the screwdriver ). The femoral dilator is pushed into the bone using a mallet (Fig. Insertion of the femoral dilator, frontal and lateral view ). The blade of the dilator should be kept vertically in order to allow the blade to be deviated anteriorly and not to exit through the hard posterior wall. Once the dilator is fully inserted, an oscillating motion of the dilator will create a cylindrical hole (Fig. Crossection of the femoral socket). The correct shape and depth of the socket can be verified using a 9 mm sizer.

Tibial Tunnel

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The tibial drill guide is introduced via the antero-medial portal. The tunnel will exit at the postero-medial aspect of the old ACL were it intercepts a line drawn between the posterior border of the anterior horn of the lateral meniscus and the medial tibial spine (Fig. Tunnel exit on the tibial joint surface). The guide wire will exit on the tibial plateau just behind the hook of the tibial drill guide. The hook of the drill guide has therefore to be inserted 2 mm anterior to the desired position of the center of the tibial tunnel (Craig Morgan).

The medial / lateral orientation should have about the same direction as the femoral socket. The tunnel entrance should be approximately 1 cm medial to the tibial tubercle and distally enough so that the tibial tunnel will accommodate the entire graft (Fig. Tibial tunnel entrance, frontal view).

The required tunnel length is about 5 cm. This is slightly longer than the graft length (average 9.5 cm) minus the femoral socket depth (2,5 cm) minus the intra-articular distance (2.5 cm). Because of the obliquity of the tibial surface one will obtain a 0.5 cm shorter tibial tunnel than the length marked on the drill guide. The marked length on the tibial drill guide should therefore always be 0.5 cm longer than the calculated required tunnel length. The angle between tibial tunnel and the knee joint should be approximately 55 (Fig. Position of the tibial drill guide).

A 2.4 mm guide wire with drill tip is drilled through the drill guide. The tip will enter the joint just behind the hook. It can be easily advanced into the joint which allows good visual control of the future tunnel. The drill guide is removed and the periosteum at the wire entrance is incised and freed with a small rasp. Often there will be some bleeding which should be stopped using electrocautery

Using the cannulated 10 mm tibial dilator like a drill bit one perforates the cortical bone. In hard bone this part of the procedure can be performed with a conventional motorized 10 mm drill bit. The tibial dilator is advanced just underneath the tibial joint surface using oscillating motions and if necessary a mallet. (Fig. Tibial tunnel Frontal view , lateral view, crossection). The transtibial saw is used for the penetration of the dense subchondral bone and to remove remaining rests of the old ACL. Using the manual transtibial saw one is able to correct the exact tunnel exit by a few millimeters in all directions. After penetration of the joint the saw has to be advanced and oscillated further until all soft-tissue fibers are disconnected so that the bone plug can be removed by withdrawal of the saw. (Fig. Manual correction of tunnel exit Fine tunning of the tibial tunnel exit). The tibial tunnel is plugged with the impingement-rod. This rod measures 9 mm diameter at the tip and 10 mm at the lower end.

Free floating parts of the ACL are removed and the edge of the tunnel is cleaned using a suction-punch, shaver or bonerasp.

Free movement of the impingement-rod in extension ensures that there will be no anterior impingement of the graft in full extension (Fig. No impingement in extension). The impingement-rod should in flexion not touch the lateral femoral condyle. Otherwise one has to complete at this point the roof- respectively the notchplasty (Fig. No impingement in flexion).

Graft-Passage

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The knee joint is extended to about 40 and the graft is inserted through the tibial tunnel into the femoral socket (Fig. Graft-Passage). One has to be careful that the tendinous portion of the proximal bone plug is facing posteriorly towards the cortical bone. The distal end is twisted 180 externally, in the right knee, viewed from below counterclockwise and in the left knee clockwise. This way the tendon is moved away from the lateral femoral condyle and more towards the posterior cruciate ligament which simulates the twist of the normal ACL.

The tendinous portion of the distal plug faces anteriorly and should be moving freely within the tunnel. If the distal bone plug gets stuck inside the tunnel one may risk to perforate the proximal bone plug with the threaded guide wire and one will not be able to insert the proximal bone plug all the way into the femoral socket. The proximal bone plug should not be inserted beyond the level of the femur.

Graft-Fixation

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If there is good press fit or very hard bone one has to dilate the gap between plug and socket wall at the planned location of the interference screw. This can be done with a screw driver or a 4 mm dilator. With this instrument in place one unscrews the threaded guide wire. The guide wire is left inside the tibial tunnel. This way it will serve as a guide to ensure parallel insertion of the tibial interference screw.

During dilation and screw insertion the graft should be hold tight distally with the cerclage wire to avoid that the proximal bone plug is further pushed into the femoral socket.

A 8 X 23 mm SYSORB- interference screw is introduced into the joint rotating it through the anteromedial portal. Slowly it is inserted between the cancellous part of the plug and the socket wall (Fig. Femoral graft-fixation, lateral view and crossectional view). Fast inserting motions could increase the temperature of the screw beyond its melting point (about 40 Celsius) and should be therefore avoided.

A pretensioning force of 60 Newton is applied to the graft with a scale hooked to the distal cerclage wire. The joint is brought several times through a full arc of motion. One should notice little motion of the bone plug inside the tibial tunnel. If there is no motion at all one should check that the bone plug can move freely inside the tibial tunnel (Fig. Pretensioning of the graft).

The distal bone plug should be rotated 180 in relation to the proximal bone plug. Thus the previously marked indentation where the site for the interference screw should be lies at the posterior and inferior wall of the tunnel. The exact rotation can be fixed with the cerclage wire and if the plug is entirely within the tibial tunnel one can introduce the arthroscope to verify the correct position.

The tension of the scale is reduced to 20 Newton and after dilating of the gap using a screwdriver or a 4 mm dilator the distal bioresorbable screw is inserted into the gap between cancellous bone plug and the compacted wall of the posterior tunnel (Fig. Distal fixation of the graft inside the tibial tunnel, lateral view, resp. crossectional view). In order to avoid divergence one inserts the screw as parallel as possible to the guide wire left in place inside the tibial tunnel on top of the distal bone plug.

If the bone plug is distally protruding, an interference fit fixation might not be sufficient. In this case one can fix the distal bone plug into a previously made bone trough using a K-wire, metallic cortical screw or a staple.

One closes the peritendinous tissue but the tendon defect will be left open. The skin insision is closed in layers. The medial and lateral arthroscopy portal are left open and no drains are used. The last figure depicts a lateral view of the finished reconstructed anterior cruciate ligament. (Fig. The finished ACL Reconstruction).

Postoperative Procedure

Neither CPM nor splintage is required.

During the first week cold therapy is frequently used (Aircast-Cryocuff) and at least three times a day the knee joint has to be kept fully extended for 20 minutes while the heel rests on a pillow. Full weight bearing is allowed in full extension.

After the second week unrestricted active and passive physical therapy is began. Crutches can be used for comfort as long as the patient desires, but most of them do not use it for more than on week. After full range of motion is obtained (usually after one month) strengthening exercices can be added.

Usually patients are allowed back to sports after the third month, once they have regained their agility, strength and coordination.

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Copyright 1996 Andreas C. Staehelin
Most recent update Februar 12, 1996