Mark D. Miller
DEFINITION
Anterior cruciate ligament (ACL) injuries result in a disruption of the fibers of this ligament and an ACL-deficient knee.
Although most injuries are complete, partial injuries have been described. In our practice, partial injuries—defined as an asymmetrical Lachman test (or 3 to 4 mm of asymmetry on KT-1000 testing)1 with a negative pivot shift test during examination under anesthesia, or a one-bundle ACL disruption seen arthroscopically—are rare.
The key point in determining how to treat partial injuries is to determine whether functional stability of the ACL has been maintained.
ANATOMY
The ACL is about 33 mm long and 11 mm in diameter.8
The tibial insertion has a broad, irregular diamond shape and is immediately anterior and adjacent to the medial tibial eminence.
The femoral attachment of the ligament is a semicircular area on the posteromedial aspect of the lateral femoral condyle.
It extends from the 9 o'clock position to the 11 o'clock position (right knee).
The ACL is composed of two “bundles”—a more important posterolateral portion, which is tight in extension, and a less critical anteromedial portion, which is tight in flexion.
It is composed of 90% type I collagen; the remaining collagen is predominantly type III.
The main blood supply for the ACL is the middle geniculate artery.
Mechanoreceptor nerve endings have been identified within the ACL and are thought to have a proprioceptive role.
PATHOGENESIS
ACL injuries usually result from a noncontact pivoting injury, typically involving a change of direction or deceleration maneuver.
Patients often describe hearing or feeling a “pop” and will develop an acute or subacute effusion (ie, “swells up like a balloon”).
In most cases, the athlete will not be able to return to play and may need assistance to leave the field or slope (we have termed the latter a “positive ski patrol sign”).
Combined ACL, medial collateral ligament (MCL), and meniscal injuries have been referred to as the “unhappy triad.”11
Lateral meniscal tears are more common in acute ACL injuries.
NATURAL HISTORY
Researchers from Kaiser Permanente in Southern California, including Donald Fithian7 and the late Dale Daniel,6 have done much to contribute to our knowledge of the natural history of the ACL-injured knee.
From their work, we recognize that patients with a high level of participation in jumping or cutting sports and significant side-to-side differences (>5 mm) on KT-1000 arthrometer measurements are at high risk for recurrent injury without ACL reconstruction.
Unfortunately, these same researchers have shown an increased incidence of arthritis in the surgically reconstructed ACL group.6,7
The difficulty with these and other studies is that multiple variables are involved, making comparisons difficult and possibly inaccurate.10
It is clear from the literature that the incidence of meniscal tears and chondral injury can be reduced with ACL reconstruction.
Advocates of double-bundle ACL reconstruction propose that the incidence of arthritis may be reduced with this technique, but that theory has yet to be proved clinically.
PHYSICAL FINDINGS
Physical examination methods include the following.
Effusion: about 70% of acute hemarthrosis cases represent ACL.6
Range of motion (ROM): loss of extension may be a result of a displaced bucket handle meniscal tear or arthrofibrosis (stiff knee). Loss of flexion may be related to a knee effusion.
The Lachman test13 is highly sensitive for ACL deficiency. The patient must relax for this examination, and effusion or a displaced meniscal tear may give a false endpoint.
The anterior drawer test is poorly sensitive and outdated, but is helpful to rule out a posterior cruciate ligament (PCL) injury.
The pivot shift test3 is difficult to perform in the clinic setting, but is an especially helpful and sensitive test during examination under anesthesia.
A complete examination of the knee also should include evaluation of associated injuries and ruling out differential diagnoses, including (but not limited to) the following:
Meniscal tears: joint line tenderness, pain or popping with provocative maneuvers (eg, McMurray, Apley compression, duck walk), and loss of full extension may be present.
PCL injury: a “pseudo-Lachman” may be appreciated if the PCL is present, and the unwary examiner may falsely attribute this to an ACL injury. The key is the starting point on the drawer examination. The tibial stepoff in PCL-injured knees will be absent, or the tibia may actually be displaced (or be displaceable) posteriorly, signifying a PCL injury.
Posterolateral corner (PLC) injury: Injury to the popliteus, popliteofibular ligament, biceps, iliotibial band, or posterior capsule will result in external rotation asymmetry (dial test), a positive posterolateral drawer test, and external rotation recurvatum.
FIG 1 • A. Segond (lateral capsular) sign. A small avulsion fracture in this area is highly associated with an ACL injury. B. MRI of ACL-injured knee with associated bone bruises. These impaction injuries are in the classic locations—the most lateral aspect of the middle third of the lateral femoral condyle and the posterior aspect of the tibia.
Collateral ligament injury: MCL injuries are recognized as opening with valgus force, and lateral collateral ligament (LCL) injuries open with varus stress. These examinations are tested in both 30 and 0 degrees of knee flexion. Opening to valgus or varus stress in 0 degrees (ie, full extension) signifies a more severe injury, usually involving one or both cruciate ligaments.
Patellar instability: localized tenderness or instability with apprehension testing is essential to rule out a patellar dislocation that reduced spontaneously. This type of injury also can cause an acute knee effusion and can be easily confused with an acute ACL injury.
IMAGING AND DIAGNOSTIC STUDIES
Plain radiographs, including anteroposterior, lateral, and patellar views, should be obtained to rule out bony avulsion fractures or associated injuries.
A small avulsion fracture off the lateral tibial plateau (FIG 1A) represents a lateral capsular avulsion (Segond sign) and is highly associated with an ACL injury. It is very specific, but not sensitive.
Flexion weight-bearing radiographs are important in older or posttraumatic patients to rule out associated osteoarthritis.
Long-leg hip-to-ankle radiographs must be obtained in patients with varus or valgus malalignment.
An osteotomy should be performed before ACL reconstruction in select cases.
MRI is highly sensitive and specific in diagnosing ACL tears as well as associated injuries.
Bone contusions, or bruises, also may be detected in the mid-lateral potion of the lateral femoral condyle (near the sulcus terminalis) and the posterior tibial plateau (FIG 1B).
DIFFERENTIAL DIAGNOSIS
Meniscal tear
Osteochondral injury
Contusion
Patellar dislocation
Other ligament/capsular injury (eg, MCL, LCL, PLC, multiple ligament injury)
NONOPERATIVE MANAGEMENT
Although nonoperative management is controversial, patients with less laxity and those who are less involved with high-level pivoting sports may be treated nonoperatively.
Nonoperative treatment is done in three phases over a period of about 3 months.
In the initial phase, emphasis is placed on regaining full motion, controlling effusion, and maintaining quadriceps tone. (This is appropriate for patients who are surgical candidates as well.)
In the second phase, quadriceps and hamstring strengthening is emphasized.
In the third and final phase, sport-specific rehabilitation is accomplished.
Patients may attempt to return to sports after their effusion has completely resolved, they have full ROM, their quadriceps tone and strength have been restored (isokinetic testing is helpful), and they have no residual symptoms of instability (functional testing is helpful).
FIG 2 • Positioning for ACL reconstruction. A. The foot of the bed is dropped, a leg holder is used for the operative side, and the contralateral leg is cushioned in another holder. B. Appropriate draping. The nonoperative leg is not included in the operative field. C. The table is dropped to flex the knee. This positioning allows free movement of the operative knee and easy access by the surgeon.
SURGICAL MANAGEMENT
Preoperative Planning
All imaging studies are reviewed.
Plain radiographs should be reviewed for fractures, loose bodies, patellar height and alignment, and the presence of any hardware (from previous procedures) or foreign bodies.
Associated fractures, meniscal tears, articular cartilage lesions, and multiple ligament injuries should be addressed concurrently.
Examination under anesthesia should be accomplished prior to positioning.
Lachman, pivot shift, varus/valgus, and dial testing should be included in the examination under anesthesia.
POSITIONING
Although some surgeons prefer to perform ACL reconstruction with the patient supine and the foot of the table up, we prefer to drop the foot of the bed and use a commercially available knee holder for the operative knee. We place the contralateral leg in a well-padded holder that is not included in the operative field (FIG 2).
This allows us to freely flex the knee and have global access.
Approach
The approach depends on graft choice.
There are two gold standards for ACL grafts—bone–patellar tendon–bone autograft and four-strand semitendinosus gracilis (hamstring) autograft. We use both patellar tendon and hamstring grafts and have found that certain parameters are helpful in determining graft choice (Table 1).
Other graft choices include quadriceps tendon autograft and a variety of allografts. Although these grafts may be useful in certain cases, they are not popular choices for most surgeons.
After the graft is selected, the procedure involves arthroscopic diagnosis and repair of pathology, tibial and femoral tunnel placement, graft passage and fixation, and wound closure.
TECHNIQUES
PATELLAR TENDON GRAFT HARVESTING
Patellar tendon grafts (TECH FIG 1) are harvested through a 5- to 7-cm paramedian incision.
Saphenous nerve branches are protected if identified.
The paratenon is incised vertically and reflected off the underlying tendon.
The central third of the tendon (typically 10 mm) is harvested, with care taken not to cut across the longitudinal fibers of the tendon.
Bone blocks (approximately 25 mm long) are obtained using a micro oscillating saw.
Care is taken to saw no deeper than 10 mm, particularly on the patellar side, to avoid an iatrogenic fracture.
The tibial bone block can be either more rectangular or more trapezoidal in cross section.
The patellar bone block should be more triangular in cross section, to avoid injury to the patella.
The bone blocks are removed using a curved osteotome (again, being careful on the tibial side) and taken to the back table for preparation.
A rongeur or burr is used to fashion the bone blocks so that they will fit through an appropriately sized tunnel.
With retraction, the lower portion of the incision can be used to prepare the tibial tunnel.
If the tendon is harvested at the beginning of the procedure, arthroscopic portals can be made through the incision.
TECH FIG 1 • Patellar tendon graft harvesting. A. Exposure of the patellar tendon and paratenon. B. The middle third (~10 mm) of the patellar tendon is measured. C. Vertical incisions are made, with care taken not to transect any of the longitudinal fibers of the tendon. D. After the tendon is excised, bone blocks are made on either end.
HAMSTRING TENDON GRAFT HARVESTING
Hamstring grafts (TECH FIG 2) are harvested through a 2- to 3-cm paramedian incision centered at the level of the tibial tubercle, approximately 6 cm below the medial joint line.
The sartorial fascia is exposed, and the tendons are palpated.
The tendons insert in an oblique fashion and are more horizontal than vertical.
The gracilis tendon insertion is superior to the semitendinosus tendon insertion, but both tendons converge at the pes anserine.
It is necessary to reflect the overlying sartorial fascia that covers both tendons.
Alternatively, the tendons can be exposed from their deep side if their insertions are sharply reflected off the tibia.
Once the tendons are identified, a whipstitch is placed in them near their insertions so that they can be reflected off their insertions and mobilized.
Blunt dissection and palpation are essential in mobilizing the tendons.
Both tendons must be mobilized and all tendinous slips freed.
The semitendinosus will have one or more large bands that attach to the medial head of the gastrocnemius. These must be incised before a tendon stripper is used, or the tendon will be inadvertently cut at this location.
After harvesting, the tendons are prepared on the back table.
Muscle fibers are removed from the tendons using a curette or elevator, a whipstitch is placed in the free end, and the tendons are tensioned using a commercially available graft board.
The grafts are folded in half and the diameter of the four-strand graft measured before tensioning.
The harvest incision can easily be used for tibial tunnel placement.
Standard arthroscopic portals are made through the skin at the level of the joint.
TECH FIG 2 • Hamstring graft harvesting. A. The gracilis (top) and semitendinosus (bottom) tendons are isolated by dissecting under the sartorial fascia. B. Whipstitches are placed in the tendons prior to detaching them. C.The tendons are freed from any attachments using blunt dissection and scissors. D. A tendon stripper is used to harvest the tendons. The tendinous slip that was cut would have prevented the stripper from passing unless it was first released.
ARTHROSCOPY
Diagnostic arthroscopy is completed, and all pathology is identified.
Meniscal tears are repaired if possible.
Articular cartilage lesions are addressed.
Loose bodies that are identified are removed.
The ACL is visualized and, if torn, it is débrided with baskets and a shaver.
The tibial footprint of the ACL and the “over-the-top” position in the back of the notch are cleared of all soft tissue (TECH FIG 3).
Although most surgeons no longer perform an aggressive notchplasty, it is important to clear enough soft tissue and bone to identify all landmarks and to ensure that the graft will not be impinged upon.
It also is important to ensure that the roof of the notch will not impinge on the graft. (This is more important in hamstring reconstructions because the anterior portion of the graft may be more easily impinged.)
TECH FIG 3 • A. Remnant ACL tissue is débrided with a combination of arthroscopic shaver, scissors, osteotome, and electrocautery. B. Notchplasty is performed with a combination of a ¼-inch curved osteotome, mallet, and grasper, or with a spherical motorized burr. Some patients may require minimal or even no notchplasty. The goal is to have enough space for graft placement and visualization purposes. Notchplasty should not extend cephalad to the intercondylar apex. A 3- to 5-mm notchplasty usually is performed, depending on the width of the intercondylar notch. C. The torn ACL. D. Notchplasty is performed. E. Careful débridement of the notch is done before drilling tunnels. F. Notchplasty/débridement of the ACL stump.
TIBIAL TUNNEL PLACEMENT
A commercially available guide is used to place a guidewire for the tibial tunnel.
The intra-articular landmarks for the tibial tunnel are as follows (TECH FIG 4):
Posteromedial aspect of the ACL footprint
Adjacent to the slope of the medial eminence
Along a line extended from the posterior border of the anterior horn of the lateral meniscus
7 mm in front of the PCL
The extra-articular portion of the guide should be positioned midway between the tibial tubercle and the posteromedial aspect of the tibia.5
For patellar tendon reconstructions, the angle of the guide should be set based on the “N + 7 rule”9 and checked based on the “N + 2 rule.”12 That is, the guide is provisionally set at an angle that is 7 degrees more that the tendon length (in mm) between the bone blocks, and the distance is checked on the plunger for the guide—it should be 2 mm longer than the tendon length. The guide is set between 45 and 50 degrees for hamstring grafts.
Once the guidewire is placed and checked, a cannulated drill is used to complete the tibial tunnel.
We use a fully threaded drill bit and save the bone graft that collects in the flutes of the drill to fill the patellar defect (it usually is discarded for hamstring graft reconstructions).
The PCL is protected with a curette during final tunnel drilling.
The back edge of the tibial tunnel is rasped to keep the graft from being abraded.
TECH FIG 4 • A. Tibial targeting guide set at N + 7. B. Arthroscopic view of ACL tibial tunnel guide pin placement. C. Fluted reamer showing collected bone graft following tibial tunnel drilling. D. Tibial pin placement usually is performed at an angle 10 degrees greater than the graft–soft tissue construct. For example, a 45-mm soft tissue construct usually is drilled at 55 degrees. This illustration demonstrates that if a steeper angle is selected, it may be more difficult to place the femoral tunnel anatomically.
FEMORAL TUNNEL PLACEMENT
An endoscopic offset guide is placed through the tibial tunnel and off the back of the posterolateral notch (TECH FIG 5). Some surgeons prefer to place this guide through the medial portal with the knee hyperflexed.
The guide pin should be placed in the 10:30 (right knee) or 1:30 (left knee) position. (While looking arthroscopically, the top of the notch is the 12:00 position.)
The offset guide should be chosen to retain a 1-mm posterior wall following drilling. A 10-mm tunnel should be made with a 6-mm offset guide, because the guide is used to place a guidewire for the center of the tunnel and the radius of a 10-mm drill is 5 mm.
TECH FIG 5 • A. Retrograde placement of a 7-mm femoral offset aimer through the tibial tunnel. The knee should be flexed 75 to 90 degrees. B. Alternatively, an accessory inferomedial portal can be used to position the aimer. The knee should be flexed at least 110 degrees. C. Femoral “over the top” guide in correct position. D. Acorn drill bit positioned prior to drilling femoral tunnel. E. The femoral tunnel is drilled to a depth of approximately 30 mm for a patellar tendon graft. F. View after drilling of tunnel, showing intact posterior wall.
The femoral tunnel is drilled to a depth of approximately 30 mm for a patellar tendon graft and to within 5 to 8 mm of the far cortex for a hamstring graft.
Depending on the surgeon's choice for femoral graft fixation, additional tunnel preparation may be necessary.
For Endobutton (Smith & Nephew Arthroscopy, Andover, MA) fixation, a 4.5-mm tunnel is drilled through the far cortex.
For TransFix (Arthrex, Naples, FL), Bone Mulch (Arthrotek, Warsaw, IN), Rigid Fix (DePuy Mitek, Norwood, MA), and other similar fixation systems, transverse pilot holes are created from lateral to medial.
GRAFT PASSAGE AND FIXATION
A Beath needle is placed through both tunnels and pierces the quadriceps muscles and skin.
Sutures from the graft or fixation device are pulled through the tunnels and outside the thigh.
The graft is pulled into both tunnels and fixed with an interference screw or a fixation device of the surgeon's choice.
Once the femoral side is fixed, the knee is cycled through the complete ROM, and the graft is tensioned.
The tibial side is then fixed with an interference screw or secured to the tibia with a screw and washer or staple (TECH FIG 6).
The graft is probed and inspected before wound closure is performed.
TECH FIG 6 • A. Graft passage from the tibia to the femur. B. Graft fixation with interference scope. C. Passage of the graft with bone plug. D. Final position of the graft and hardware.
WOUND CLOSURE
The wounds are closed in layers.
Bone graft from the drill bit or bone block preparation is packed into the patellar defect, and the paratenon is closed for patellar tendon graft cases.
The sartorial fascia is closed for hamstring graft cases.
Subcutaneous tissue and skin are closed in standard fashion.
POSTOPERATIVE CARE
Radiographs are evaluated to ensure that graft placement and fixation are appropriate (FIG 3).
Some surgeons place the patient in a knee immobilizer or a hinged brace, but we have found that this may restrict their motion and does not provide any benefit.
Early range of motion (especially extension) is emphasized.
It is important that a pillow be placed under the heel (not under the knee, which is more comfortable), beginning in the recovery room.
Closed-chain rehabilitation (beginning with a stationary cycle) is emphasized in the early postoperative course.
Running typically is delayed until 3 or 4 months postoperatively, and most athletes can return to their sport by 6 months.
OUTCOMES
With appropriate indications and surgical technique, success rates for ACL reconstruction are on the order of 90% to 95%.
In one study, 96% of patients had KT-1000 side-to-side differences of less than 5 mm.2
Comparisons between patellar tendon and hamstring reconstruction have yielded equivalent results.
Some studies suggest that hamstring grafts may have slightly increased laxity (1 to 2 mm) compared with patellar grafts.
Other studies have cited an increased incidence of anterior knee pain following ACL reconstruction with patellar tendon grafts.
COMPLICATIONS
Intraoperative graft mishandling4
Graft failure or rupture
Patellar fracture
Deep venous thrombosis
Infection
Loss of motion
Tunnel enlargement (a later complication)14
REFERENCES
1. Bach BR Jr, Nho SJ. Anterior cruciate ligament: diagnosis and decision making. In: Miller MD, Cole BJ, eds. Textbook of Arthroscopy. Philadelphia: Elsevier, 2004:633–643.
2. Bach BR Jr, Tradonsky S, Bojchuk J, et al. Arthroscopically assisted anterior cruciate ligament reconstruction using patellar tendon autograft: Five to nine year follow-up evaluation. Am J Sports Med 1998;26:20–29.
3. Bach BR Jr, Warren RF, Wickiewicz TL. The pivot shift phenomenon: results and a description of a modified clinical test for anterior cruciate ligament insufficiency. Am J Sports Med 1988;16: 571–576.
4. Cain EL Jr, Gillogly SD, Andrews JR. Management of intraoperative complications associated with autogenous patellar tendon graft anterior cruciate ligament reconstruction. Instr Course Lect 2003; 52:359–367.
5. Chhabra A, Diduch DR, Blessey PB, et al. Recreating an acceptable angle of the tibial tunnel in the coronal plane in ACL reconstruction using external landmarks. Arthroscopy 2004;20:328–330.
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7. Fithian DC, Paxton EW, Stone ML, et al. Prospective trial of a treatment algorithm for the management of the anterior cruciate ligamentinjured knee. Am J Sports Med 2005;33:335–346.
8. Girgis FG, Marshall JL, Al Monajem ARS. The cruciate ligaments of the knee joint: anatomical, functional, and experimental analysis. Clin Orthop 1975;106:216–231.
9. Miller MD, Hinkin DT. The N+7 rule for tibial tunnel placement during endoscopic ACL reconstruction. Arthroscopy 1996;12: 124–126.
10. Nedeff D, Bach BR Jr. Arthroscopy assisted ACL reconstruction using patellar tendon autograft: a comprehensive review of contemporary literature. Am J Knee Surg 2001;14:243–258.
11. O'Donoghue DH. Surgical treatment of fresh injuries to the major ligaments of the knee. J Bone Joint Surg Am 1950;32A:721–738.
12. Olszewski AD, Miller MD, Ritchie JR. Ideal tibial tunnel length for endoscopic anterior cruciate ligament injuries. Arthroscopy 1998;14: 9–14.
13. Torg JS, Conrad W, Kalen V. Clinical diagnosis of anterior cruciate ligament instability in athletes. Am J Sports Med 1976;4:84–93.
14. Wilson TC, Kanatara A, Johnson DL. Tunnel enlargement after anterior cruciate ligament surgery. Am J Sports Med 2004;32:543.