The anterior (frontal) cruciate (crossed) ligament, or "ACL" is an integral part of the knee's hinge mechanism. Working side by side with its immediate neighbor in the knee joint, the posterior cruciate ligament, the ACL holds the two main knee bones (femur & tibia) together and helps keep your knee bending on its proper axis, somewhat similar to a door hinge (see FIGURES 1a - 1c).
Specifically, the ACL prevents the upper tibia, or "shin-bone", from slipping forward, out from under the lower end of the femur (thigh-bone) during knee twisting movements and contraction of the quadriceps (frontal thigh) muscles (see FIGURE 2).
In a knee with a torn or stretched-out ACL, a sudden, unexpected shifting forward of the tibia relative to the femur (i.e., a partial dislocation, or "subluxation") may occur during the weight-bearing phase of a physical activity such as pivoting or changing direction, causing the knee to feel as if it has buckled or given way. Patients often say that their knee suddenly just "went out" on them. Such unanticipated joint subluxation episodes gave rise to the term "trick knee" syndrome, long before orthopedic surgeons recognized that a torn or loose anterior cruciate ligament was usually responsible for this rather common problem. As recently as just three decades ago, the ACL was considered by many surgeons to be a vestigial structure in the human knee that served no useful purpose! People who suffered from a "trick knee" syndrome usually had their problem blamed on cartilage troubles or other knee maladies. Over the course of the past three decades, the ACL has metamorphosed from the most ignored structure in the knee to the most frequently repaired or rebuilt structure! While its importance is now widely recognized amongst physicians, to some extent the prevailing surgical opinion "pendulum" has swung so far back from where it was 30 years ago that perhaps too many torn anterior cruciate ligaments are now being reconstructed. Many knee injury patients today somehow develop the notion that without a functioning anterior cruciate ligament, they have no hope of leading an active life, which is clearly not the case.
Deciding Whether or Not to Undergo Surgery
Whether or not a torn anterior cruciate ligament should be reconstructed depends upon many factors that are evaluated by both patient and surgeon. Each patient must realistically assess the future physical demand that will likely be placed upon their knee. High demand physical activity that involves running, jumping, pivoting, and "cutting" (see FIGURE 3) presents the greatest risk for repeated knee joint subluxations (and thus additional injuries such as bone bruises and cartilage tears) in a knee without a functioning ACL
In general, approximately one-third of individuals who tear their ACL will do rather well without any form of surgery to repair or rebuild it; another third will experience difficulties that may involve limited re-injury and/or an unwanted decrease in activity level, and the remaining third will do poorly if surgery is not performed, re-injuring their knee time after time and often causing irreparable cartilage loss. While many individuals (usually those in the first 1/3 referenced above) possess excellent natural compensatory mechanisms which reduce or eliminate recurrent subluxation injuries, individuals at the opposite end of the spectrum often cannot even perform their routine activities of daily living safely without a functioning ACL in their knee! As of yet, no method exists to accurately differentiate and identify with certainty the "good compensators" vs. the "bad compensators", in advance. Only "trial by fire" (i.e., a return to physical activity without surgical reconstruction of the ligament) allows this determination to be made. However, the medical decision-making process with regard to the choice of treatment is by no means totally blind.
Perhaps the most important predictive factor that assists in this decision-making process is an assessment of the specific physical demands that are likely to be placed upon the patient's knee in the future. If high-performance athletic activity that involves running, jumping, cutting and pivoting is realistically on your future activity list, the odds of your knee suffering recurrent injury (even with appropriate knee brace treatment) are reasonably high and thus, surgical reconstruction of the ACL should seriously be considered. On the other hand, if activities such as cycling, rowing, straight-ahead jogging on level surfaces, or aerobic fitness work on exercise machines (see FIGURE 4) are going to be the most strenuous way in which your knee will be used, conservative (non-operative) treatment by way of a comprehensive program of rehabilitation and knee bracing may work very well and thus save you considerable time, effort, and expense.
Another factor that enters into the decision-making process is exactly how unstable your injured knee joint is, both functionally (how frequently and easily it "gives out" on you) and structurally (how much measurable joint looseness it has). All knees do not depend equally upon the anterior cruciate ligament for maintenance of proper mechanical joint function. Some knees are more "cruciate dependent" than others. For example, a person with a relatively non-cruciate dependent knee might never even appreciate or feel the difference between the knee's condition before vs. after his or her anterior cruciate ligament was torn, once the initial pain from the tear itself has subsided. On the other hand, someone who possesses a very cruciate-dependent knee may have difficulty performing even routine daily activities without having their knee give out on them, after tearing their ACL. The physical examination provided by an experienced knee surgeon can rate or grade the degree of structural joint laxity or instability that you have, thus providing another piece of data to be entered into the overall decision-making equation. In general, a low-grade instability combined with a low-demand physical activity requirement represents a situation that is often best handled by non-operative means, whereas the opposite would be the case for a high-grade instability in the face of a high-demand physical activity requirement.
If you are in an in-between or "middle of the road" situation (see FIGURE 5), another factor worth considering relates to the timing of surgical treatment. Anterior cruciate ligament tears that are reconstructed fairly early on following injury (within the first six to twelve weeks or so) tend to achieve a slightly more stable and successful result with surgery than those knees that have been loose a long time and whose secondary ligamentous constraints (remaining knee ligaments) have been stretched out by recurrent giving-way episodes. Several surgical researchers have observed that an anterior cruciate ligament injury that is treated sooner rather than later has perhaps a 5% to 10% better prognosis for a successful surgical restoration of ligament stability than an anterior cruciate ligament injury that is treated in a delayed fashion, after the instability condition has been allowed to become chronic. For someone who is in a situation where both non-operative treatment and operative treatment would appear to be reasonable, this slightly different prognosis for the results of acute (early) versus chronic (late) surgical treatment may become the "tie breaker" that leads the patient to opt for surgical management at the outset.
An additional factor that must be weighed in the decision-making process is the status of the various other knee joint structures. When other knee ligaments are torn along with the ACL it may be more desirable to rebuild the ACL than otherwise. The presence of surgically repairable knee cartilage (meniscus) tears also favors ACL reconstruction because repaired menisci generally heal better and last longer when the ACL is fixed at the same time.
Interestingly enough, age by itself is of little importance
in deciding whether or not to have a torn anterior cruciate ligament
reconstructed. All other things being equal (i.e., similar activity
level and grade of knee instability), a patient between 40 and 60
may be just as good a candidate for surgery as someone in their twenties.
A patient's age, however, may affect the particular surgical technique
that is best suited for them.
Methods of ACL Reconstruction
Completely torn ACLs almost never heal on their own, and unlike tears in some other knee ligaments, cannot be stitched back together very effectively. The injured ACL must almost always be surgically rebuilt, or "reconstructed", using a replacement ligament (tendon autograft or allograft). Autograft tissue is harvested from the patient's own body whereas allograft tissue is obtained from a tissue bank. Many orthopedic surgeons who perform ACL reconstruction have one preferred surgical method or technique, which they learned during their surgical training, and thus feel most comfortable with. They therefore use this method in the great majority of their cases, regardless of the patient's age, sex, activity level or occupation. This is not the approach that we take at The Knee and Shoulder Centers. We feel comfortable performing all of the commonly used methods of anterior cruciate ligament reconstruction and use a variety of different tendon grafts as an ACL replacement. Each person with a torn ACL represents a unique situation that calls for surgical decision-making customized to the particular context of that patient's case.
For example, a time-tested and very commonly performed method of ACL reconstruction that utilizes an implanted ligament graft composed of the middle third of the patient's own patellar tendon (see FIGURES 7a, 7b) typically provides excellent restoration of knee stability 90 or more percent of the time, but is sometimes a difficult procedure to recover from.
In our experience, this surgical method poses a higher risk for unwanted side-effects such as patellar tendinitis, patellar pain, joint stiffness, internal scarring, and an inability to kneel on firm surfaces (any or all of which could be permanent). For this reason, we view this particular procedure as being more ideally suited to younger (under 25), high-demand athletes who are not likely to be called upon to kneel on hard surfaces in an occupational setting. Patellar tendon autograft ACL reconstruction, done in the wrong patient, has a significant chance of leading to an unhappy result. We are of the opinion that an individual over 25 with an acute (recent) anterior cruciate ligament injury that has not yet resulted in a highly unstable joint, and who later may be required to do more kneeling activity in an occupational setting than cutting or pivoting in an athletic environment, is better suited for other methods of anterior cruciate ligament reconstruction. These alternate methods utilize either two of the patient's own accessory hamstring tendons (semitendinosus and gracilis) as an ACL graft (see FIGURE 8), a part of the patient's own quadriceps tendon from the front of the lower thigh, or an allograft tendon specimen obtained from a tissue bank (see FIGURE 9).
These alternate techniques leave the patient's own patellar tendon untouched and rarely produce sensitive areas in the front of the knee to be bothered later on by floor contact when kneeling. While there is no surgical knee procedure that poses zero risk of an unhappy or frankly failed outcome, these alternate methods are often better tolerated by many patients as compared with ACL reconstruction using their own patellar tendon.
There are also various specific technical advantages and disadvantages
to each particular surgical method and/or ACL graft when considered
in the context of a patient's exact clinical circumstances. Taking
into account these various details, educating the patient about them
and then jointly arriving at a decision as to how to proceed, is our
preferred approach to the problem of the ruptured anterior cruciate
ligament. Our goal is to subject a patient's knee to no more
surgical stress than is necessary to achieve the desired result.
The Partially Torn ACL
Not all ACL injuries represent complete ligament ruptures. In some cases only a portion of the ligament's fibers are torn, or the ligament has merely been permanently stretched out to some degree. When less than 50% of the ACL's fibers are torn and the remaining intact ones have not been severely stretched, the ACL has a reasonable chance of gradually reconstituting itself back to near-normal status. More severe partial tears, on the other hand, usually go on to behave like complete disruptions once the patient returns to physical activity. For that reason, severe partial tears should usually be treated as would a complete rupture. Most minor partial tears are best treated non-operatively, at least initially. The clinical behavior (symptoms) of the knee and the serial physical examination findings of a skilled knee surgeon will provide guidance as to how to proceed as time passes.
If a diagnostic knee arthroscopy is performed to assess the status of the ACL, great care should be taken because the visual appearance of a partially torn ACL can be very misleading. Sometimes an injured but still strong and stable ACL may look ominously lax and/or appear to have irregular, damaged fibers. Conversely, a severely compromised ACL that allows positive "pivot shift" joint instability to occur, will on occasion, be afflicted only with internal fiber disruption and generalized plastic deformation (permanent stretching), thus providing the appearance of merely being slack as opposed to being torn outright. This may cause a surgeon to underestimate the degree of ligament damage present.
Rather than basing a diagnostic opinion and/or recommendation for reconstructive surgery solely on the appearance of a partially torn ACL at arthroscopy, it is advisable for the surgeon to mechanically assess the ligament's functional integrity by:
Thermal (heat-induced) ligament shrinkage/tightening procedures
for loose or stretched out cruciate ligaments have not yet been proven
effective over the long term and have occasionally been reported to
cause ligament necrosis (tissue death) followed by complete dissolution
or rupture. They should, therefore, be approached with caution.
Related Ligament Injuries and Complex Instabilities
In particularly severe knee sprains, there is usually more damage than
just a ruptured anterior cruciate ligament. In some cases additional
ligaments such as the medial collateral (inner-side) ligament, posterior
cruciate ligament, lateral collateral (outer-side) ligament, or portions
of the joint's capsular (surrounding envelope) ligament are traumatically
compromised as well (see FIGURE 10). The
decision whether or not to perform surgical work on these additional
damaged structures at the time of ACL reconstruction requires a good
deal of insight and experience on the part of the surgeon, as this
decision is often a "judgment call". Surgery to correct
collateral ligament and capsular defects or laxities is known as "extra-articular"
(external to the joint cavity) repair and/or augmentation, and is done
in addition to the "intra-articular" anterior cruciate ligament
reconstruction within the joint cavity. While formerly performed with
great frequency (and often to the exclusion of intra-articular ACL reconstruction),
supplemental extra-articular surgery today is not commonly performed.
To some extent it has become a "lost surgical art." Few orthopedic
textbooks describe methods of rebuilding a chronically torn medial collateral
ligament, and very few surgeons have much experience in performing this
type of surgical work. Various supplemental, extra-articular reconstructions
involving "reefing" (capsule over-folding and tightening)
and "tenodesis" (converting a nearby tendon into an
auxiliary ligament) procedures may be needed when attempting to treat
a knee that demonstrates a more severe (complex or multi-directional)
instability as compared to a simple, isolated anterior cruciate ligament
laxity. The older (more chronic) the ACL tear is, the more likely "complex"
instability will be encountered. The experienced reconstructive knee
surgeon will know when such supplemental procedures are likely to contribute
to a successful outcome and which particular method to perform.
Selecting a Surgeon
At The Knee and Shoulder Centers we have the subspecialty training and experience to make such complex decisions and perform these difficult procedures. In addition, with advanced anesthetic and postoperative pain management techniques, almost all reconstructive knee ligament surgery can now be performed arthroscopically, on an outpatient basis, making the entire experience more comfortable and less disruptive. We take prudent precautions for your safety and have an extremely low rate of surgical complications. While we do not take "short-cuts" in treating our patients, the surgical incisions we make are the smallest that are technically possible. We perform all of our surgery personally, from start to finish. We also routinely utilize post-operative cryotherapy for pain control in addition to advanced pharmacological pain management and a portable device that allows continuous passive knee motion ("C.P.M.") treatment to be taken right into your home. These measures combine to reduce the discomforts of reconstructive knee surgery and facilitate early healing, while at the same time reducing complications such as excessive swelling and knee joint stiffness. Most students and individuals who hold an office job can be back attending school / work within five to ten days of surgery, as long as they can elevate their leg while seated. The healing time required to return to driving will usually vary from one to six weeks, depending on which leg was operated upon, the type of vehicle transmission used, and the particular surgical procedure performed. Securely implanted grafts allow most patients to be placed in a sports-type ACL brace for walking without crutches within two weeks postoperatively. A return to full, unrestricted athletic or heavy work activities will typically take 5 to 8 months, depending on the particular surgical procedure performed, how well the patient tolerates it, and how diligently rehabilitation is pursued. Detailed, written physical therapy protocols, customized to your particular surgical situation, are dispensed to your physical therapist. This facilitates a safe, structured progression through your course of rehabilitation.