Anterior Cruciate Ligament Surgery
In Brief: The anterior cruciate ligament (ACL) is an important stabilizing structure in the knee, which when torn, may result in a "trick knee" syndrome. The more physically or athletically active an individual with a non-functioning ACL is, the more likely their unstable knee will repeatedly buckle or "go out", causing additional knee joint injury. Torn ACLs rarely if ever heal on their own and cannot simply be stitched back together. While non-operative treatment is an option, effective surgical treatment requires that a ruptured or severely stretched out ACL be rebuilt (reconstructed). Multiple methods for surgically rebuilding a torn ACL exist, some of which are better suited for a particular patient than others. Each patient's individual circumstances and knee injury pattern must be taken into account when deciding whether or not to undergo surgery and which surgical method to employ.
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).
FIGURE 1a
Diagrammatic view of a flexed (bent) knee viewed from the front, with the patella removed. The anterior and posterior cruciate ligaments are seen to cross each other within the open, center region of the joint (inter-condylar notch), creating an internal hinge mechanism that controls the knee's axis of rotation as it bends and straightens.
FIGURE 1b
Anatomy laboratory dissection of a knee joint by the author (cut-away, side view), demonstrating that when the knee is extended (straight leg position), the ACL is a relatively flat, ribbon-like ligament composed of many parallel fibers. It connects the tibia (very bottom of picture) to the femur (above). The front of the knee is to the left in this picture.
FIGURE 1c
Diagrammatic illustration by the author, of the ACL's internal fiber anatomy. While the ACL is not naturally divided into physically separate sections as drawn here, some "fiber-regions" of the ACL are more important as "first line" stabilizers of the knee than others. In general, most of the ACL's fibers are relatively tight when the knee is either fully extended (straight, as in FIGURE 1-b and in this diagram) or fully flexed (as in FIGURE 1a). The ACL as a whole is most relaxed when the knee is partially flexed to a mid-range angle of 30-60 degrees. Since it is not possible for surgeons to precisely reconstruct all of the ACL's natural fiber-architecture with currently available tendon grafts, they normally rebuild the most functionally important of the ACL's fiber-regions, these being the anterior (frontal) and central regions. (Reference: Sapega, A., et al: Isometry Testing During Reconstruction of the Anterior Cruciate Ligament. American Journal of Bone and Joint Surgery, Volume 72A:259-267, 1990).
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).
FIGURE 2
This photo shows a rugby player with a combination of weight-bearing and twisting stress, plus quadriceps (frontal thigh) muscle contraction stress, being placed on his left knee (see arrow). While such forces can easily cause a knee with a loose or torn ACL to "go out" or sublux (shift out of place), they can also occasionally cause a healthy ACL to tear suddenly. That is exactly what happened to this athlete at the very instant this photo was taken! He went on to have his ACL reconstructed with a hamstring tendon graft and had an excellent result.
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
FIGURE 3
Activities that involve full-speed running, jumping, cutting and pivoting are "high risk" for someone with a torn or loose ACL. Treating such high-demand athletes by rehabilitation and knee bracing alone has a fairly high failure rate.
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.
FIGURE 4
There are many physical activities that pose little or no risk to an individual with a torn or loose ACL, such as using fitness exercise machines, cycling and rowing.
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.
FIGURE 5
Skiing, skating and roller-blading represent "in between" risk activities for someone with a torn or loose ACL. Treatment with bracing alone may or may not suffice, depending on a host of factors including how strong your leg muscles are and how extreme your participation level is. Remember, even a totally healthy ACL will not necessarily prevent a knee injury if you take a fall.
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.
FIGURE 6
A patient's age may be of little importance in deciding whether or not to have a torn ACL rebuilt. A physically active, 55-year-old may benefit more from ACL reconstruction than a sedentary 20-year-old!
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.
FIGURE 7a
This photo demonstrates the patellar tendon autograft method of ACL reconstruction, whereby the middle 1/3 of this frontal knee tendon, with a bone plug at either end, is first excised and then re-implanted inside the knee where the ACL originally was. The defects in the patellar tendon, patella and tibia left from the graft "harvesting" procedure gradually fill in with scar and repair tissue.
FIGURE 7b
Diagrammatic illustration of how a patellar tendon graft is surgically implanted into the knee where the original ACL was located. Two screws hold the (bone plug) ends of the new ACL in place.
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).
FIGURE 8
This photo demonstrates how two accessory (thus relatively expendable) hamstring tendons can be retrieved from the thigh through a 1½ inch long incision, made just below the knee. These tendons are then doubled or tripled-over, and fashioned into an ACL graft that is arthroscopically implanted into the knee at the site where the original ACL was located.
FIGURE 9
Photo demonstrating an "allograft" bone/patellar-tendon/bone specimen that has been obtained from a certified tissue bank. The photo shows the specimen after it has been cut down to size and fashioned into a new ACL. The white, middle section becomes the new ligament and the bone plugs at either end serve as anchors that become imbedded in the femur and tibia.
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:
a.
performing a manual ligament stress examination while the patient is under anesthesia, carefully comparing the injured knee to its normal mate, and;
b.
while viewing the ACL with the arthroscope, palpating and probing it with a blunt instrument as it is tightened (stretched) by external knee stress - if it becomes taut and rigid rather than remaining lax and soft, it has retained some significant portion of its mechanical integrity.
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.
FIGURE 10
Diagrammatic illustration of how one or more collateral ligaments can be torn in combination with a cruciate ligament injury.
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.
If you have a question concerning your own or a family member's knee condition, you are invited to have those questions answered by way of a consultation here at The Knee and Shoulder Centers. We have anatomic charts, models, and educational videotapes available to help you participate actively in the medical assessment and decision - making process.