Marshall A. Kuremsky, M.D.
Department of Orthopaedic Surgery
Carolinas Medical Center
Charlotte, North Carolina
Nikhil N. Verma, M.D.
Assistant Professor
Department of Orthopaedic Surgery
Section of Sports Medicine
Rush-Presbyterian St. Luke's Medical Center
Chicago, Illinois
Bernard R. Bach Jr., M.D
Director, Division of Sports Medicine
Midwest Orthopaedics at RUSH
Chicago, Illinois
Dana P. Piasecki, M.D.
OrthoCarolina Research Institute
Charlotte, North Carolina
The anterior cruciate ligament (ACL) has garnered a lot of attention in orthopedic literature. As the primary restraint to anterior tibial translation, this ligament plays a role in stabilizing the knee during cutting and pivoting activities and protecting the chondral surfaces and menisci.1 There is attention directed towards defining the ideal way to reconstruct the ACL. A number of recent biomechanical studies have suggested that reconstructive efforts that reproduce the normal ligament's anatomy will restore normal knee kinematics.2,3 Recent clinical emphasis has been placed on reconstructive techniques that accomplish this.1 A specific transtibial technique that closely reproduces the normal tibial and femoral insertions is presented.
The ACL is an intraarticular structure approximated by a 10 mm to 11 mm cylinder, which follows an oblique trajectory from tibia to femur. When viewed during surgery in the coronal plane, the obliquity of the ligament is much greater in the sagittal plane.4 A recent cadaveric study has helped to define the anatomy of the ACL's insertions.4 (Table 1, Table 2) The tibial insertion is ovoid and slightly angled from anteromedial to posterolateral with a mean 10 mm width (coronal plane) and 15 mm length (sagittal plane). The posterior edge of the tibial insertion occurs 7 mm from the retro-eminence ridge and 5 mm to 6 mm from the anterior fibers of the posterior cruciate ligament (PCL). The center of the tibial insertion occurs midway between the tibial spines and 1 mm to 2 mm anterior to the posterior edge of the lateral meniscus' anterior horn (Slide 1). Using the radiographic method of Staubli and collegues,5 the position of the center of the tibial insertion as a percentage of the anterior posterior tibial width occurs between 40% to 45% from the anterior tibia.
Table 1: ACL tibial insertion anatomic data.
Posterior extent to anterior PCL (mm)
Posterior extent to RER (mm)
Anterior extent from anterior PCL (mm)
Anterior extent from posterior border lateral meniscus' AH
Med and Lat edges from base of tibial spines (mm)
Center of Tibial Insertion
Distance from medial spine
Distance from lateral spine
Distance from medial edge of medial tibial plateau
Distance from lateral edge of lateral tibial plateau
Distance from anterior PCL
Distance (ant-post) from posterior border lat meniscus
Position on lateral point clouds as a % of tibial condyle width (%)
Table 2: ACL femoral insertion anatomic data.
10:54+/-21 to 8:26+/-20.8
Top of insertion to roof of notch
Bottom of insertion to cartilage edge of LFC
Posterior extent to posterior wall
Anterior extent to anterior edge of LFC
Center of Femoral Insertion
Distance from roof of notch
Distance from posterior wall
Distance from cartilage edge of LFC
Distance from anterior edge of LFC
Position on lateral point clouds as a % of ant-post notch length
Position on lateral point clouds as a % of prox-distal notch height
Slide 1: Tibial insertion. Image courtesy of Dana Piasecki, MD.
The femoral insertion is also an ovoid footprint and the long axis is angled from proximal posterior to distal anterior (Slide 2). This insertion measures 9 mm in width and 14 mm in length. The top, back, and bottom edges of the insertion maintain a 2 mm space from the roof, posterior wall, and articular cartilage of the lateral femoral condyle. It is important that the top edge of the insertion does not have any fibers on the roof of the notch. When viewed in the coronal plane, the upper border of the femoral insertion is a mean 5 mm to 6 mm from the lateral most fibers of the PCL. When the knee is in 90º of flexion, the center of the femoral insertion occurs 7 mm from the back wall and midway between the roof of the intercondylar notch and the articular cartilage of the lateral femoral condyle. Using the radiographic method described by Bernard and Hertel6 the center of the femoral insertion occurs a mean 25% from the back wall and 30% below the roof of the notch.
Slide 2: Femoral insertion. Image courtesy of Dana Piasecki, MD.
When considering a transtibial technique for reconstructing the ACL, the challenge is accessing the femur via the tibial tunnel. The transtibial femoral access is provided by a tibial tunnel superimposed on a line connecting the center of the femoral and tibial insertions. The exit point for this line (Slide 3) occurs a mean 11 mm to 14 mm distal to the medial plateau edge, 27 mm proximal to the superior border of the pes anserinus, 8.5 mm posterior to the medial margin of the tibial tubercle, and 31 mm from the anterior edge of the medial collateral ligament.4,7 While this point is too close to the joint line to be a tibial starting position, a 10 mm or 11 mm tunnel started at a point 6 mm to 7 mm below this (18mm to 20 mm below the medial plateau edge) will provide a mean 12 mm proximal bone bridge and a degree of bone-patellar tendon-bone (BTB) autograft mismatch.4 Once reamed, this tibial tunnel will provide the maneuverability to place a transtibial femoral guide-wire within 2 mm of the center of the femoral insertion4. When both the tibial and femoral tunnels are reamed from these positions overlap of the native insertions is 98% on the tibia and 88% on the femur.4
Slide 3: Anatomic exit point relative to medial tibial plateau, medial border of the tibial tubercle, superior border of pes tendons, and anterior border of MCL. The yellow dot represents the anatomic exit point. Image courtesy of Dana Piasecki, MD.
Diagnostic arthroscopy
An initial diagnostic arthroscopy is always performed using a superomedial outflow portal and standard inferolateral (IL) viewing and inferomedial (IM) instrumentation portals.8 If hamstring or allograft BTB grafts are used, then these portals are created through individual portal incisions. In cases where autograft patellar tendon grafts are harvested first, the IL and IM portals may be created within the graft harvest incision site. During the arthroscopy, attention should be paid to the articular surfaces, meniscal status, and the presence or absence of loose bodies.
Exposure of ligament insertions
The innermost position of the fat pad can be debrided to maximize visualization and subsequent instrumentation of the intercondylar notch.8 Once visualization of the notch is maximized, the ACL stump and status of the PCL can be easily assessed. Intercondylar notch preparation begins with the removal of the ACL stump and remnant soft tissue attachments from the lateral intercondylar notch wall and the tibial insertion. The posterior wall of the notch and lateral border of the PCL, in addition to the osseous tibial insertion of the ACL, can then be visualized (Slide 4, Slide 5, Slide 6).
Slide 4: Exposed insertions. Exposure of the tibial insertional center (right knee). Note that the center of the insertion (yellow dot) occurs at or slightly anterior to the posterior edge of the lateral meniscus' anterior horn (dotted line). Image courtesy of Dana Piasecki, MD.
Slide 5. Exposure of the femoral insertion (viewed from IM portal). Note that the margins of the insertion maintain a 2 mm boundary from the roof, back wall and bottom of the LFC. The center of the femoral insertion (yellow dot) occurs 7 mm from the posterior wall. Image courtesy of Dana Piasecki, MD.
Slide 6. Exposure of the femoral insertion (viewed from IL portal after notchplasty). The center of the femoral insertion occurs midway from the roof to the bottom of the lateral femoral condyle. Image courtesy of Dana Piasecki, MD.
A bony notchplasty is then created with a curved ¼ inch osteotome introduced through the IM portal and used to remove a width of bone from the anteromedial portion of the lateral femoral condyle so that 1 cm of space is created between the PCL and the lateral wall following resection (Slide 7).8 The lateral wall is further resected from anterior to posterior using a spherical burr, contouring the roof and superolateral corner of the notch from a “Gothic arch” to a “Roman arch” configuration, with a more squared corner.9 A notchplasty improves the visualization from the IL portal, which contributes to the anatomic positioning of the femoral tunnel via a transtibial technique.
Slide 7. Notchplasty. Use of a curved osteotome to initiate the notchplasty. Image courtesy of Dana Piasecki, MD.
Tibial tunnel
The starting point on the tibial metaphysis is identified. The coronal plane orientation of the native ligament is used as a reference, and can be determined by passing a spinal needle into the joint just above the medial tibial plateau (Slide 8). The entrance point will be 5 mm to 10 mm medial to the medial margin of the tibial tubercle, but should be adjusted so that the entrance point of the needle passes directly over the center of the tibial insertion to the center of the femoral insertion. It may be helpful during this step to reposition the scope to the inferomedial portal with the light source directed to the floor, as this aligns the scope view with the axis of the needle (Slide 9). The center of the tibial insertion will occur at or slightly anterior to the posterior edge of the lateral meniscus' anterior horn. The center of the femoral insertion occurs halfway from the roof to the bottom of the lateral wall (when viewed from the IL portal) and should be 7 mm anterior to the posterior wall (when visualized from the IM portal) (Slide 10). Once the spinal needle is positioned, a point is marked on the proximal tibia below the needle's entrance point, which is 18 mm to 20 mm below the medial plateau edge. Reference the proximity of the starting point to the medial plateau edge and the medial margin of the tibial tubercle. A starting point which is too proximal and medial may risk compromise of the medial plateau. The starting point should be no more than 10 mm medial to the medial margin of the tibial tubercle and no closer to the medial plateau edge than 16 mm. When in doubt, the author finds that it is safer to err on a starting point which is closer to the tibial tubercle.
Slide 8. Completion of the “Roman arch” configuration. Image courtesy of Dana Piasecki, MD.
Slide 9: Determine native ACL coronal plane alignment. A spinal needle is inserted into the joint just above the medial plateau such that a straight line trajectory can be referenced connecting the center of the femoral and tibial insertions. IL portal view: the needle passes over the tibial insertion to a point on the femoral notch wall midway from the roof to the bottom of the lateral femoral condyle. Image courtesy of Dana Piasecki, MD.
Slide 10. IM portal view: the needle is seen to pass directly over the center of the tibial insertion to the center of the femoral insertion. Image courtesy of Dana Piasecki, MD.
In the location of the spinal needle an accessory IM portal is created and used for later interference screw insertion. Depending on surgeon preference and exposure, the tip of the tibial drill guide is then introduced through either this accessory IM portal or the standard IM portal (Slide 11). The tibial tunnel parameters have already been established by the center of the tibial insertion and the ideal tibial tunnel starting point so it is not necessary to use a given drill guide angle. If using a tip guide, first position the tip of the guide at the center of the tibial insertion, then place the trocar of the guide on the tibial starting point and fix the angle of the guide. With a more proximal tibial starting point the angle of the guide will be around 45º. Prior to drilling, a final external check of the alignment of the guide is performed.8 The angle of the guide with respect to the vertical should be 1:30 on the clock face for a left knee or 10:30 on a right knee, using the center of the patella as the 12:00 reference. If the position is accepted, a 3/32 inch Steinmann pin is drilled through the guide into the joint. Ideal placement will position the tip of the pin midway between the 2 spines and along the posterior horn of the lateral meniscus. For a left knee, the pin should be at the 1:30 position along the lateral wall of the notch. The guide is then removed and the knee extended to check for impingement of the pin on the roof of the notch (eg, too anterior on the femur). The knee is then flexed and the pin tapped into the femur securing the trajectory. Then the tibial tunnel is reamed with a chosen cannulated reamer size. If appropriately oriented, then use of the previously defined starting point should create an oblong tunnel entrance within the joint that closely reproduces the normal tibial insertion's boundaries (Slide 12). Avoid excessive posteriorization of the tunnel, whose back edge should be 5 mm to 6 mm anterior to the PCL.
Slide 11: Tibial tunnel preparation. Tibial aimer with tip at the center of the tibial insertion. Image courtesy of Dana Piasecki, MD.
Slide 12. Position of tibial guide pin. Image courtesy of Dana Piasecki, MD.
Femoral tunnel
The femoral tunnel is then created using a transtibial approach.8 With the knee maintained in 90º of flexion at all times, a 7 mm offset aimer is introduced retrograde through the tibial tunnel, the lip of the guide placed along the posterior wall of the notch and its handle externally rotated to bring the inserted pin to an even lower position along the lateral wall (Slide 13). If the tibial tunnel has been positioned correctly, then this maneuver should allow positioning of the guide pin within 2 mm of the center of the femoral insertion.4 The center of the femoral insertion is halfway from the roof to the bottom of the condyle. If the pin cannot be positioned in this location, then remove the guide and introduce the ball burr into the tibial tunnel to bevel 1 mm to 2 mm of bone from the posterolateral rim of the tunnel's entrance within the joint. This allows the aimer to be repositioned and further lowered on the notch wall. If pin position is still not correct after this maneuver, then the surgeon may elect to position the femoral guidewire via the accessory AM portal with the knee in 110º of flexion.10Once positioned, a slotted Beath pin is drilled into the femur through the guide and out the distal thigh. Care should be taken during this step to keep the knee at 90º of flexion. There is a tendency to extend the knee during femoral pin positioning in order to accomplish a lower intersection with the notch wall, but this will result in a more posteriorly directed guidewire that can cause posterior tunnel compromise. Additionally, in the authors' experience, if the pin exits the thigh in the anterior half of the distal femur, then posterior wall compromise is highly unlikely. Once the wire is positioned, a cannulated reamer (10 mm for BTB, 8 mm to 9 mm for hamstring grafts) is then inserted by hand over the wire and maneuvered until up against the lateral wall of the notch. Avoid power reaming until this is accomplished because doing so will remove substantial bone from the posterior aspect of the tibial tunnel.4 Once the reamer is up against the notch wall, it is reattached to the drill and reamed to a provisional depth of 5 mm to 8 mm (Slide 14). If the guide pin has been positioned 7 mm from the roof, back wall, and bottom of the femoral condyle a 10 mm reamer (eg, 5 mm radius) should leave a 2 mm margin of bone at the margins of the tunnel, just as it occurs with the native femoral insertion. A probe should be used through the IM portal to ensure integrity of the posterior wall after the reamer is removed. If the posterior wall is compromised, then the pin should be repositioned before the definitive reaming performed. Once the trajectory is correct, the cannulated reamer is advanced. In BTB grafts up to 10 mm of graft tunnel mismatch can occur on the tibial side, which can be managed by recessing the graft further on the femoral side. The femoral tunnel must be reamed to a depth of at least 35 mm and the distance from the lateral wall to the lateral cortex is 35 mm to 40 mm. Once reamed, a final inspection is performed by passing the arthroscope through both the IL and IM portals to view the femoral tunnel retrograde verifying integrity of the posterior aspect of the tunnel (Slide 15, Slide 16).
Slide 13: Femoral guidepin positioning. A 7 mm over-the-top guide is passed through the tibial tunnel, hooked around the posterior wall and externally rotated to position the femoral guidepin. Image courtesy of Dana Piasecki, MD.
Slide 14. Tibial tunnel. Note the close overlap of the tunnel's entrance with the boundaries of the native insertion. Image courtesy of Dana Piasecki, MD.
Slide 15: Femoral tunnel. View from the IL portal. Image courtesy of Dana Piasecki, MD.
Slide 16. View from the IM portal. Image courtesy of Dana Piasecki, MD.
Graft passage and fixation
Using BTB as a representative graft, the femoral bone plug is either pulled through the tunnel via the slotted Beath pin, or pushed through the tibial tunnel with a graft pusher. Care should be taken to orient the cancellous surface of the plug anteriorly (eg, cortex posteriorly). With the arthroscope in the IL portal and a curved hemostat in the IM portal, the latter is used to receive and direct the bone plug into the entrance of the femoral tunnel. The plug is inserted 66% of the way in and a straight hemostat is used to dilate the plug-femoral tunnel interface at the 11 o'clock position.8 Once the graft is seated on the femoral side, tibial sided mismatch should be evaluated. With 5 mm to 10 mm of excess graft length on the tibial side, the femoral plug can be recessed in the femoral tunnel. The knee is then brought into extension to demonstrate the absence of roof impingement. Anatomic positioning of a single bundle graft rarely results in any abnormal roof impingement. If this does occur, then a roof plasty should be performed until the graft obtains adequate clearance in full extension. Graft fixation on the femoral side is then undertaken with the knee in 90º of flexion. A flexible nitinol wire is inserted through the accessory IM portal into the dilated portion of the plug tunnel interface. The knee is flexed 100º to 110º during screw insertion to facilitate subsequent screw insertion colinear with the femoral tunnel. The graft is cycled to remove creep and a pretibial fixation Lachman exam performed.
During tibial fixation, the knee is axially loaded in extension, which prevents overconstraining of the joint.8 Prior to tibial fixation, a hemostat is used to externally rotate the tibial bone plug 180º so that the cancellous portion of the graft faces posteriorly. The terminal position of the bone plug may catch on the inner rim of the tunnel preventing tensioning of the graft and should be checked prior to fixation. If there is satisfactory mobility of the plug within the tunnel, then a 9 mm x 20 mm metal interference screw is introduced over a nitinol wire into the interface between the plug and anterior aspect of the tunnel while tension is maintained on the graft's traction sutures. Pullout strength is maximized as the screw interdigitates with the cortical surface of the graft, and the cancellous portion of the bone plug is impacted into the posterior margin of the tunnel.8 With the tibial screw anterior to the graft (rather than posterior), potential ligament abrasion on the tip of the screw during knee flexion can be avoided, in the event there should be some backout of the screw beyond the tendo-osseous interval. The surgeon should be aware of the shorter tibial tunnel length when a proximal tibial starting point is used. The anterior aspect of the tunnel will be 22 mm to 25 mm in length, which accommodates the traditional 20 mm screw length. Routinely inspect the joint after tibial fixation to confirm the absence of any prominent hardware. If there is any question of the adequacy of tibial fixation or if less than 10 mm to 15 mm of interference fit is accomplished with a BTB graft, then additional tibial fixation may be considered in the form of a supplemental staple or screw/post to augment the fixation stability on the tibia. Once the screw is completely inserted, the Lachman exam is repeated and compared to the prefixation exam as a final check of knee stability. The knee should be brought through a range of motion to confirm that symmetric extension and flexion can be accomplished. The arthroscope is used to confirm final graft appearance arthroscopically (Slide 17), and should mirror normal ACL anatomy with respect to the tibial and femoral insertions. On the femoral side, an anatomically placed graft should recreate the normal triangular space between the ACL and PCL and be centered on the lateral intercondylar notch wall. On the tibial side, the center of the graft should be roughly aligned with the back edge of the anterior horn of the lateral meniscus in the sagittal plane (Slide 18, Slide 19).
Slide 17: Final graft inspection.View from the IL portal: note that the entire graft is on the lateral wall of the notch with no fibers on the roof. The central axis of the graft intersects with a point midway from the roof to the bottom of the lateral femoral condyle and a 5mm to 6 mm space exists from the top of the graft to the lateral aspect of the PCL. Image courtesy of Dana Piasecki, MD.
Slide 18. View from the IM portal: the graft occupies an insertion closely reapproximating the native femoral insertion. Image courtesy of Dana Piasecki, MD.
Slide 19. View in full extension: an anatomically oriented graft should not impinge on the roof any more than the native ligament. Image courtesy of Dana Piasecki, MD.
Avoiding Complications
The potential for error during arthroscopic ACL reconstruction occurs during tunnel placement. The described landmarks should enable the surgeon to place the tibial tunnel in a practical and anatomically oriented position, which both anatomically restores the tibial footprint and allows access to the center of the femoral insertion. Close attention needs to be paid to locate the tibial tunnel starting point. Failure to do so can result in a compromise of the medial tibial plateau or the proximal bone bridge. Sometimes the tibial tunnel does not allow adequate access to the femoral insertion. If a proper femoral tunnel position and orientation is not possible using a transtibial technique, then the femoral guide pin should be positioned using alternative methods either by use of the accessory anteromedial portal or by conversion to a 2 incision technique. Once the femoral guide pin is positioned, paying attention to the sagittal plane orientation of the wire can prevent posterior wall blow out. The use of a proximal tibial starting position will leave a smaller proximal bone bridge for interference screw fixation on the tibia. If the quality of fixation is in question, then backup fixation should be used.
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