JBJS | Evaluation and Treatment of Recurrent Instability After Anterior Cruciate Ligament Reconstruction*†

The Journal of Bone & Joint Surgery, Volume 82, Issue 11

Instructional Course Lecture | November 01, 2000

Evaluation and Treatment of Recurrent Instability After Anterior Cruciate Ligament Reconstruction*†

Christopher D. Harner, M.D.‡; J. Robert Giffin, M.D.F.R.C.S.(C)‡; Roger C. Dunteman, M.D.§; Christopher C. Annunziata, M.D.‡; Marc J. Friedman, M.D.§

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An Instructional Course Lecture, American Academy of Orthopaedic Surgeons
*Printed with permission of the American Academy of Orthopaedic Surgeons. This article, as well as other lectures presented at the Academy's Annual Meeting, will be available in March 2001 in Instructional Course Lectures, Volume 50. The complete volume can be ordered online at www.aaos.org, or by calling 800-626-6726 (8 a.m.-5 p.m., Central time).
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
‡Center for Sports Medicine, 3200 South Water Street, Pittsburgh, Pennsylvania 15203.
Â§Southern California Orthopaedic Institute, 6815 Noble Avenue, Van Nuys, California 91405.

The Journal of Bone & Joint Surgery. 2000; 82:1652-1652

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Introduction

The annual incidence of anterior cruciate ligament injuries in the United States has been estimated to be one in 3000 Americans¹. Reconstruction is now widely accepted as the treatment of choice for the patient with a functionally unstable anterior cruciate ligament-deficient knee. By current estimates, more than 100,000 anterior cruciate ligament reconstructions are performed annually in the United States². The long-term rates of good and excellent results, in terms of functional stability, relief of symptoms, and return to preinjury level of activity, have been reported to be between 75 and 90 percent^3-9. This, however, leaves a substantial group of patients who have an unsatisfactory result from the procedure because of a number of different causes. We will discuss the potential mechanisms of failure of primary intra-articular anterior cruciate ligament reconstruction and will provide the treating orthopaedist with a systematic approach for the evaluation of these difficult cases.

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Fig. 1:: Illustration showing that failure of anterior cruciate ligament reconstruction is due to a broad spectrum of potential causes ranging from subjective patient complaints to objective clinical findings. Intra-articular graft failure (shaded area) commonly results in both recurrent functional instability and increased laxity. (Reproduced, with modification, from: Harner, C. D.: Editorial comment. Clin. Orthop., 325: 3, 1996. Reprinted with permission.)

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Fig. 2:: Illustration showing that the causes of graft failure include surgical error, failure of graft incorporation, and trauma, either alone or in conjunction with one another. (Reproduced, with modification, from: Maday, M. G.; Harner, C. D.; and Fu, F. H.: Revision ACL surgery: evaluation and treatment. In The Crucial Ligaments: Diagnosis and Treatment of Ligamentous Injuries About the Knee, edited by J. A. Feagin, Jr. Ed. 2, p. 712. New York, Churchill Livingstone, 1994. Reprinted with permission.)

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Fig. 3:: Lateral radiograph showing anterior placement of the femoral tunnel resulting in graft-lengthening and subsequent failure.

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Fig. 4:: Lateral radiograph, made with the knee in full extension, demonstrating ideal placement of the tibial tunnel inclined posterior to Blumensaat's line (the line indicating the roof of the intercondylar notch) to avoid graft impingement. The double-headed arrow indicates the width of the tunnel.

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Fig. 5:: Anteroposterior radiograph of a tibial tunnel enlargement (arrows) six months after anterior cruciate ligament reconstruction with use of a ten-millimeter-wide bone-patellar tendon-bone autograft.

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Fig. 6:: Photograph showing coring reamers, clear plastic sheaths, and a revision screwdriver set. These instruments are extremely useful during revision surgery.

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Fig. 7:: Drawing showing the tunnel from a two-incision technique entering the femur at a more acute angle than the tunnel from a one-incision technique. This is very useful during revision surgery, especially when posterior cortical-wall blowout is encountered.

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Fig. 8-A:: Anteroposterior and lateral radiographs of an anterior cruciate ligament reconstruction with use of patellar tendon autograft, demonstrating substantial expansion (more than fifteen millimeters) of both the tibial and the femoral tunnel. A staged procedure consisting of bone-grafting followed by anterior cruciate ligament reconstruction with a hamstring tendon graft was used for revision.

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Fig. 8-B:: Anteroposterior and lateral radiographs of an anterior cruciate ligament reconstruction with use of patellar tendon autograft, demonstrating substantial expansion (more than fifteen millimeters) of both the tibial and the femoral tunnel. A staged procedure consisting of bone-grafting followed by anterior cruciate ligament reconstruction with a hamstring tendon graft was used for revision.

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TABLE I: Nonanatomical Position of Bone Tunnels Causing Increased Graft Tension and Subsequent Failure

Tunnel Position	Cause of Graft Failure
Femoral
Anterior	Excessive strain (lengthening) in flexion/laxity in extension
Posterior	Excessive strain in extension/laxity in flexion
Tibial
Anterior	Excessive strain in flexion/roof impingement in extension
Posterior	Excessive strain in extension/ posterior cruciate ligament impingement
Medial/lateral	Impingement on ipsilateral femoral condyle

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TABLE I: Nonanatomical Position of Bone Tunnels Causing Increased Graft Tension and Subsequent Failure

Tunnel Position	Cause of Graft Failure
Femoral
Anterior	Excessive strain (lengthening) in flexion/laxity in extension
Posterior	Excessive strain in extension/laxity in flexion
Tibial
Anterior	Excessive strain in flexion/roof impingement in extension
Posterior	Excessive strain in extension/ posterior cruciate ligament impingement
Medial/lateral	Impingement on ipsilateral femoral condyle

Etiology of Failed Anterior Cruciate Ligament Reconstruction

Many factors influence the overall success or failure of anterior cruciate ligament reconstruction, including the integrity of the secondary restraints, the preoperative laxity of the knee, the status of the articular and meniscal cartilage, the selection of the graft material, the surgical technique, the postoperative rehabilitation, and the motivation and expectations of the patient¹⁰. Failure may be due to one or more factors, and it may be associated with both graft and non-graft-related conditions. However, there is no universally accepted definition of what qualifies as an unsatisfactory outcome following anterior cruciate ligament surgery^11,12. In addition, there is often a low correlation between the physician's evaluation and the patient's perception of knee stability and function⁴.

Classification of Failure

Failure of an anterior cruciate ligament reconstruction can be due to a broad spectrum of potential etiologies ranging from general sources to intra-articular graft failure (Fig. 1). Physicians at the University of Pittsburgh developed a classification system for intra-articular graft failure. Even though failure is based on multiple factors and it is difficult to assign a single causal mechanism, the classification represents an attempt to better identify the cause of failure and to improve the outcomes of revision surgery. It also represents an attempt to be more specific in guiding the surgical management of these complex problems. In all cases, a primary cause is assigned and, when possible, a secondary cause is assigned as well (Fig. 2). The cause can usually be classified into one of the following categories: loss of motion or arthrofibrosis^13-16, arthritis or recurrent pain^17,18, extensor mechanism dysfunction^19-22, or recurrent instability^4-7. It has been estimated that 0.7 to 8.0 percent of recurrent instability following primary anterior cruciate ligament reconstruction is caused by graft failure^4-6. In these patients, revision anterior cruciate ligament surgery should be considered, as it may be helpful in alleviating symptoms of instability and may improve the functional result.

Often, the cause of failure can be determined by excluding certain factors as well as by noting the time to failure after surgery. Early failure occurs within the first six months and is often the result of poor surgical technique, failure of graft incorporation, or possibly excessively aggressive rehabilitation. For example, if the patient complains of persistent functional instability in the early postoperative period and an inappropriate position of the femoral tunnel is seen on radiographs, surgical technique would be assigned as the primary cause of failure. Poor graft incorporation, if found, would be the secondary cause. If review of the operative records and the radiographs verify that the procedure was technically successful, then the most likely primary cause of failure would be inadequate graft incorporation.

Failure occurring late (more than one year after surgery) is most commonly due to trauma. In these cases, technical failure and failure of graft incorporation are ruled out if the knee was functionally stable (with intact secondary restraints) on prior examination and if there is no radiographic evidence of surgical error. The cause of failure could be a major single reinjury (a contact or noncontact mechanism), or it could be repetitive traumatic events (for example, aggressive rehabilitation).

Successful revision surgery requires a methodical and organized approach to identify the potential source (or sources) of failure. A thorough preoperative evaluation, including a detailed history, physical examination, and radiographic evaluation, is of paramount importance before surgery is planned, in order to avoid a repetition of errors.

Failure Caused by Surgical Technique

Technical Errors

Errors in surgical technique are the most common cause of graft failure in patients presenting with recurrent instability after anterior cruciate ligament reconstruction^11,22-27,87. Technical shortcomings resulting in graft failure after primary reconstruction include nonanatomical tunnel placement, graft impingement, improper tensioning of the graft, and inadequate fixation of the graft in the osseous tunnels.

Tunnel Placement

The consequences of nonanatomical tunnel placement have been described in the literature^28-35. Inappropriate positioning of either the tibial or the femoral tunnel results in excessive changes in graft length as the knee moves through a range of motion (Table I). Because biological anterior cruciate ligament grafts can accommodate only small changes in length before undergoing plastic deformation, a malpositioned graft results in either capturing of the knee with subsequent loss of motion or lengthening of the graft over time with subsequent recurrent instability.

In order to achieve stability and to retain a full range of motion, near-anatomical placement of the tunnels is important. Anterior placement of the femoral tunnel is the most common surgical error when a one-incision endoscopic technique is used (Fig. 3)^10-12,26. Improper femoral tunnel placement is most often caused by a failure to visualize the most posterior aspect of the notch adequately. Because the femoral attachment of the anterior cruciate ligament is closer to the center of rotation of the knee, small errors in femoral tunnel placement can have deleterious effects on knee kinematics. Ideal femoral tunnel placement is as posterior in the notch as possible without violation of the posterior cortical wall.

Tibial tunnel placement, originally thought to be a less important factor in the outcome of anterior cruciate ligament reconstruction, is now known to have a profound effect on the postoperative result^30-33. Early techniques stressed a relatively anteromedial position, whereas current techniques emphasize a posterior placement of the tibial tunnel, with the ideal position being in the posteromedial portion of the anterior cruciate ligament footprint. The tunnel is parallel and posterior to Blumensaat's line when the knee is in full extension (Fig. 4)^30-33. The more posterior position of the tibial tunnel eliminates graft impingement. In patients with major recurvatum or a vertical intercondylar roof, either the tibial tunnel must be placed in a more posterior position or some bone must be removed from the roof of the notch in order to avoid graft impingement with the knee in extension^2,30.

Graft Impingement

Graft impingement may be avoided by properly positioning the tunnels and ensuring that an adequate notchplasty has been created^36-38. Failure to assess the notch architecture for stenosis or intercondylar osteophytes can lead to impingement and secondary graft failure from repetitive trauma and ligament attrition³². Notch impingement can also compromise the biological incorporation of the graft³⁹. In addition to a loss of extension, a "cyclops" lesion⁴⁰ may form if there is substantial graft impingement. Plain radiographs, computed tomography, or magnetic resonance imaging can be helpful in the preoperative assessment of the notch architecture and the subsequent need for a notchplasty. Notchplasty is not without risk, and there has been a recent trend toward decreasing the amount of bone removed during this procedure in order to avoid distorting the anatomical position of the femoral tunnel, which can produce incongruence at the patellofemoral and tibiofemoral articulations⁴¹.

Graft Tensioning

Improper tensioning of the graft is a potential cause of graft failure. The optimal intraoperative tension remains unknown^42,43. Factors that affect graft tension include the graft material and length, the tunnel placement, the physiological joint laxity, the method of graft fixation, and the knee flexion angle at the time of fixation. Of these variables, the knee flexion angle at the time of fixation and graft placement appear to be the most critical⁴³. Overzealous tensioning has been associated with decreased motion, delayed vascularization, myxoid degeneration, and resultant graft failure^44,45. Furthermore, overconstraining the joint may lead to increased joint contact pressures and osteoarthritis⁴⁶. Inadequate tensioning, on the other hand, may lead to persistent instability and a nonfunctioning graft.

Graft Fixation

The stability of the initial graft fixation is critical to the success of anterior cruciate ligament reconstruction. The fixation must be secure enough to prevent changes in graft position before healing occurs in the tunnels^47,48. Advanced rehabilitation protocols require stable fixation that permits immediate knee motion without compromising graft position or tension. Fixation strength depends on the type of graft, the type of fixation device, and the bone quality at the fixation sites⁴⁷. Regardless of the type of graft and the method of fixation, proper surgical technique is critical to avoid pitfalls during insertion of the fixation device.

Graft Material

The structural and material properties of the graft that is selected play a role in the possible failure of the newly reconstructed anterior cruciate ligament. Carelessness during graft harvest and preparation may damage the graft substance, thereby affecting its structural and material properties. Although a bone-patella tendon-bone autograft remains the graft of choice for many surgeons, the doubled semitendinosus and gracilis tendons have recently gained popularity.

The use of allograft material in primary anterior cruciate ligament reconstruction has increased in recent years. Basic-science and clinical research has provided a greater understanding of the effects of sterilization on the mechanical properties of the graft, its rate of incorporation, and the possibility of an immunological response^49-56. The biological behavior of the different autografts and allografts during incorporation must be understood in order to individualize the rehabilitation program.

The use of synthetic ligaments is not currently recommended for primary or revision anterior cruciate ligament reconstruction because of the high complication and failure rates associated with their use^57,58. The high prevalence of breakage over time, along with reports of effusion, synovitis, and osteolysis, make synthetic grafts undesirable. The value of ligament augmentation devices in improving clinical outcomes has not been proven conclusively, and concerns have been raised regarding the stress-shielding effect of synthetic devices on biological grafts and their role in delaying graft incorporation^50,59,60.

Secondary Stabilizers

A surgeon's failure to recognize and treat a combined instability pattern that involves damaged secondary restraints (that is, the medial collateral ligament, the posterior horn of the medial meniscus, and the posterior aspect of the capsule) to anterior tibial translation may result in the eventual failure of the reconstructed graft. Missed ligamentous and capsular injuries, resulting in combined rotatory instability patterns, place increased loads on the anterior cruciate ligament graft⁶¹. Partial or complete meniscectomy of an irreparable meniscal tear alters the knee-joint kinematics and leads to increased forces on the graft. These forces may have a detrimental effect on graft incorporation and may increase the likelihood of eventual graft failure.

The knee must be carefully examined preoperatively to assess the integrity of the secondary restraints. These findings are confirmed by reexamining the patient, while he or she is under anesthesia, before proceeding with revision surgery. Close attention must be paid to varus and valgus motion and rotational laxity that are excessive compared with those in the contralateral extremity. Previous operative reports, imaging studies, and arthroscopic examination are helpful in determining the status of the menisci and the articular cartilage and their possible role in graft failure.

Unrecognized or untreated laxity of the medial collateral ligament or the posterior oblique ligament, or both, may play a role in the failure of the primary reconstruction. At the time of the revision surgery, it may be necessary to reef these lax tissues and occasionally to perform an advancement of the medial collateral ligament. If substantial anteromedial rotatory instability is present in the setting of a previous medial meniscectomy, concomitant medial meniscal transplantation should be considered. Meniscal reconstruction with allograft tissue helps to restore the "break-stop" mechanism of the posterior horn of the medial meniscus.

Posterolateral instability is probably the most commonly unrecognized and untreated associated laxity pattern. Surgical options include primary repair, advancement or recession, and augmentation or reconstruction of the popliteus tendon and the popliteofibular and lateral collateral ligaments. If the patient has varus knee alignment and a lateral thrust during the stance phase of gait, a valgus proximal tibial osteotomy should be done to correct the alignment. Persistent lateral thrust after an anterior cruciate ligament reconstruction will lead to failure because of chronic repetitive stretching⁶². A medial opening or lateral closing-wedge osteotomy may be performed as a staged procedure or in combination with the reconstruction.

Failure of Graft Incorporation

Failure of incorporation of the anterior cruciate ligament graft into the host tissue may be a cause of recurrent instability. The causes of graft failure, which have been studied extensively in a variety of animal models, include inadequate vascularity, immunological reaction, and stress-shielding associated with use of an augmentation device^{50,53,60,63-66}.

Biological failure should be suspected in patients presenting with recurrent instability without a history of trauma or an identifiable technical error¹². The process of successful incorporation of both autografts and allografts includes graft necrosis, revascularization, cellular repopulation, collagen deposition, and matrix-remodeling^39,63. This ligamentization process is influenced by the graft source, the host response, and the biomechanical loads affecting the graft during rehabilitation. Furthermore, the rate of incorporation has been shown to depend on both the type of graft material and the method of fixation. This universal biological healing response should be respected in the design of the early rehabilitation program and in the decision as to when the patient can return to normal activities.

Failure Caused by Trauma

Graft failure due to trauma occurs infrequently and takes one of two forms: early failure secondary to trauma before complete graft incorporation and completion of rehabilitation, and late failure occurring after resumption of full activity. Overaggressive rehabilitation or a premature return to athletics before adequate graft incorporation and return of neuromuscular control of the lower extremity may play a role in early failure. During the first year after reconstruction, the graft strength and stiffness are 30 to 50 percent of normal and excessive loads can lead to plastic deformation and elongation^64,65.

As accelerated rehabilitation protocols have gained wider acceptance because of the belief that they improve the functional result and decrease the prevalence of postoperative stiffness associated with anterior cruciate ligament reconstruction, the risk of injury to a partially revascularized graft has increased. Furthermore, it is important that the surgeon understand the limitations and parameters of the initial graft fixation and the time-course of biological incorporation. Poorly fixed grafts that require more than eight to twelve weeks to incorporate do not tolerate early aggressive rehabilitation.

Patients may sustain major trauma to the knee after the graft has matured. Usually these reinjuries occur more than six months (late) after the patient has returned to full activity. The prevalence of traumatic reinjury has been reported to be approximately 5 to 10 percent in the athletic population¹⁰. These patients present with a new hemarthrosis following an injury and have increased laxity compared with that seen on the previous postoperative examination. In the absence of an identifiable cause of graft failure, it is assumed that the graft had incorporated and was functioning at the time of the new injury.

Preoperative Evaluation of Failed Anterior Cruciate Ligament Reconstruction

A comprehensive preoperative evaluation must be performed for all patients being considered for revision anterior cruciate ligament surgery. A detailed history, physical examination, and radiographic assessment are essential to determine the etiology of failure, to classify its primary and secondary causes, and to decide whether the patient is an appropriate candidate for revision surgery.

Patients presenting with pathological anterior laxity on clinical examination that reproduces their symptoms of instability during activities of daily living or athletic activities should be considered candidates for revision surgery. The goals of the operation are to stabilize the knee, to prevent further injury to the articular cartilage and menisci, and to maximize function. The surgeon must take the time to evaluate the patient as an individual and must be alert to the potential "knee abuser," who will undoubtedly have failure of the revision surgery as well.

The patient must be given realistic goals with regard to the expected outcome and must understand that motivation and compliance are critical to success. These cases are technically demanding and complex, so care must be taken when discussing the long-term prognosis. It has proven difficult (if not impossible) to achieve results similar to those of primary anterior cruciate ligament reconstruction; therefore, results should not be compared between the two procedures^24,55. False expectations on the part of the patient will certainly lead to subjective failure despite an otherwise technically successful procedure.

History

A detailed history should include the chief presenting symptom or symptoms and should elicit the sequence of events that transpired from the time of the initial injury. It is important to determine the nature of the original injury, the preoperative symptoms, the timing of the surgery, the postoperative rehabilitation, the ability to return to preinjury activity, any history of major reinjury, and the time at which the patient realized that he or she was no longer improving. Review of the previous records, including the operative note, is helpful in determining the extent of the primary surgery. Information about the type of graft used, the status of the menisci, the condition of the articular surfaces, and associated ligamentous injuries at the time of the original procedure can serve as a guide in planning the revision surgery and in making the prognosis.

Pain must be clearly differentiated from instability. The patient who has pain with activities of daily living is different from the patient who has recurrent instability while participating in vigorous sports activity. Potential causes of increasing pain include instability and possibly early arthrosis from a previous meniscectomy or osteochondral injury. If the revision surgery is to be successful, the pain arising from these causes must be addressed separately or simultaneously⁵.

Infection should be considered as a potential cause of pain. Although this is an uncommon complication of anterior cruciate ligament reconstruction, the patient must be asked whether there has been purulent drainage, cellulitis, fever, or chills at any time since the original operation. This is especially important if the failed primary reconstruction had been performed with a prosthetic graft.

Physical Examination

A comprehensive physical examination of the patient, including the entire lower extremity, must be performed. The examination usually begins with an observation of gait and lower-extremity alignment while the patient is standing. The presence of a lateral thrust during stance phase and/or varus alignment is important to recognize because each can be a source of graft failure due to excessive strain on the reconstructed anterior cruciate ligament. In these cases, a valgus high tibial osteotomy should be performed before or in conjunction with the revision anterior cruciate ligament surgery.

The presence and extent of an effusion (acute or chronic) are important, as effusion may indicate a variety of abnormalities ranging from recurrent trauma to intra-articular pathology. The range of motion of the knee is carefully assessed to determine whether there is any residual loss due to the original injury and the operation or whether acute changes from recurrent trauma have led to reduced motion. Differences in heel height and heel-to-buttock distance are useful in measuring loss of extension and flexion^2,21. Decreased range of motion, extensor mechanism dysfunction, and/or the presence of a bent-knee gait pattern must be addressed before the revision surgery is done. In most cases, a staged surgical procedure should be done; the intent of the initial surgical intervention should be to decrease the loss of motion, and the revision should be performed after an adequate range of motion has been obtained.

The status of the primary anterior cruciate ligament reconstruction is evaluated with use of the Lachman, pivot-shift, and anterior drawer tests. Other provocative tests should also be performed to assess the integrity of the secondary restraints. Particular attention must be paid to excessive varus and valgus motion and rotational laxity. Failure to identify and treat associated ligamentous laxity and combined instability patterns will result in recurrent surgical failure.

Radiographic Evaluation

Radiographic evaluation should include anteroposterior, lateral, 45-degree posteroanterior flexion weight-bearing, and Merchant views. The anteroposterior and lateral radiographs are used to assess the position and size of the femoral and tibial tunnels as well as the type of material used for graft fixation. Assessment of the size of the tunnels is critical in formulating a surgical plan. Expansion of the bone tunnels, seen radiographically, has been well described following anterior cruciate ligament reconstruction with use of both autografts (Fig. 5) and allografts^67-70. Despite appropriate positioning of the tunnels, bone-grafting may be required.

A standing lateral radiograph with the knee in full extension should be made to look for graft impingement. The 45-degree posteroanterior flexion radiograph provides a view of the femoral condylar notch, allowing assessment of its architecture and the degree of articular cartilage narrowing and other associated degenerative changes. A standing long-cassette radiograph should be made to determine the mechanical axis of the lower extremity.

Other imaging modalities that may be used include bone scintigraphy⁷¹, for the evaluation of potential early degenerative changes; computed tomography, for the definition of bone defects; and magnetic resonance imaging. In selected cases, magnetic resonance imaging can be helpful in evaluating graft integrity as well as in determining the presence of any associated meniscal, ligamentous, or chondral pathology.

Treatment of Failed Anterior Cruciate Ligament Reconstruction

Preoperative Planning

Preoperative discussions should alert the patient to the possible need for a staged procedure if there is major bone-tunnel expansion or arthrofibrosis. If osteolysis or cystic expansion has occurred at the tunnel sites, consideration must be given to removal of hardware and to bone-grafting of lesions, with later revision surgery to occur at six to twelve weeks after incorporation of the graft. In selected cases of cystic widening, nonanatomical femoral tunnel placement, or difficult hardware removal, it has been our preference to use the over-the-top position for the reconstructed anterior cruciate ligament. An extension loss of more than 5 degrees or a flexion loss of more than 20 degrees should be addressed separately in a staged fashion in an attempt to regain motion before anterior cruciate ligament revision is considered.

Skin incisions around the knee should be carefully planned to avoid skin compromise and infection. Surgical technique and handling of the soft tissues must be meticulous to avoid complications in the revision setting. Previous skin incisions should be used or extended if they allow for hardware removal, graft-harvesting, and proper placement and fixation of the new graft. Skin bridges of less than seven centimeters in width should be avoided.

Graft Selection

The surgeon has numerous options when selecting a graft for revision anterior cruciate ligament surgery. Currently, autograft and allograft are the tissues of choice. In the past, synthetic grafts have been used; however, unacceptably high complication and failure rates led to their abandonment in both primary and revision anterior cruciate ligament reconstruction^57,58,72. Many factors must be taken into consideration when a graft is chosen for revision surgery. These include the graft source used in the primary surgery, the incisions used for harvesting the previous graft, the bone-tunnel size (enlargement), and associated ligamentous laxity².

If the surgeon elects to use autogenous tissue, many sources are available, including patellar tendon (contralateral or ipsilateral), hamstring tendon, and quadriceps tendon. Use of autogenous grafts eliminates the potential of disease transmission or immunological reaction associated with allografts while allowing faster incorporation. However, they pose potential problems. Donor-site morbidity and lack of availability are major concerns.

Ipsilateral patellar tendon is often the preferred graft when it is available^73,74; however, due to its popularity as a graft source during primary anterior cruciate ligament reconstruction, it is often not available. This preference for patellar tendon autograft leads to reharvesting of the ipsilateral patellar tendon⁷⁵. A magnetic resonance imaging study supported reharvesting of this tendon by demonstrating high signal intensity consistent with edema and scar in the early postoperative period with a subsequent decrease in signal intensity at progressive follow-up intervals⁷⁶. At eighteen months, the donor site appeared normal. The authors of that study believed that these findings showed the ability of the patellar tendon to remodel and regenerate⁷⁶. More recently, however, two animal studies demonstrated inferior biomechanical properties of these tendons after harvest. Using a canine model, LaPrade et al. found a substantially lower load to failure in the reharvested patellar tendon compared with that in the contralateral tendon at one year postoperatively⁷⁷. Proctor et al., in a goat model, demonstrated histological characteristics consistent with reparative scar rather than ligament⁷⁸. Biomechanical testing at twenty-one months revealed that the tensile strength was inferior to that of the contralateral tendon⁷⁸. These results led the authors of both studies to recommend the use of other graft sources. A recent clinical study by Kartus et al. also argues against the use of reharvested patellar tendon⁷⁹. In that study, twenty patients who had revision anterior cruciate ligament surgery were divided into two groups of ten each. One group had revision surgery with use of reharvested patellar tendon as the graft, and the other group had revision with use of graft harvested from the contralateral patellar tendon. The Lysholm score, International Knee Documentation Committee (IKDC) rating, and Tegner activity score all were lower in the group treated with reharvested patellar tendon. There were also two major complications in that group: a patellar tendon rupture and a patellar fracture. Consequently, Kartus et al. did not recommend use of the ipsilateral patellar tendon for revision anterior cruciate ligament reconstruction.

The role of harvest of the contralateral patellar tendon has also been examined. Rubenstein et al. found no major complications in twenty-six patients in whom a graft from the contralateral patellar tendon was used for primary anterior cruciate ligament reconstruction⁸⁰. All patients regained a full range of motion at three weeks, and quadriceps strength returned to 93 percent at one year. Even though no patient complained of patellofemoral pain, half experienced patellar tendinitis; most of these cases resolved during the first year. The authors of this study recommended the contralateral patellar tendon as an acceptable graft choice, believing that patellar tendinitis at the donor site resolves quickly, with no long-term effects. However, the possibility of extensor mechanism disruption and patellar fracture in overzealous patients during the postoperative period has been noted as a potential complication⁸¹. Consideration should be given to use of a graft source other than patellar tendon autograft in the presence of substantial degenerative changes at the patellofemoral joint.

The remaining sources of autogenous tissue are the hamstring and quadriceps tendons. Quadrupled hamstring tendons offer the advantage of being readily available, with decreased donor-site morbidity; however, their size can be a disadvantage in the revision setting⁸². Because hamstring grafts are generally several millimeters smaller in diameter than patellar tendon grafts, which typically have a diameter of ten millimeters, their use in revision of a primary reconstruction that had been performed with patellar tendon is limited. In the presence of femoral tunnel enlargement, bone defects, or prior reconstruction with patellar tendon, the hamstring tendons' small size and the lack of a bone block often provide an inadequate fill of the tunnel². Bone graft can be used in the enlarged tunnel, and a two-stage procedure can be performed. On the other hand, if new tunnels or an over-the-top position can be used, hamstring tendons make excellent grafts. Another source of autogenous tissue is the quadriceps tendon, which provides both a large cross-sectional area and a single bone block. This graft is helpful when dealing with enlarged tunnels.

The allograft tissue most commonly used in primary and revision anterior cruciate ligament reconstruction is the Achilles tendon or the patellar tendon. When an allograft is used, there is no donor-site morbidity, the incisions are smaller, the operative time is shorter, and there are no size limitations. Disadvantages include longer incorporation time, the possibility of an immunological reaction, the risk of disease transmission, and higher cost. Jackson et al. demonstrated, in a goat model, slower biological incorporation of patellar tendon allograft compared with patellar tendon autograft⁵². Even though there have been no reported cases of viral transmission from frozen allogeneic connective tissues when current American Association of Tissue Banks guidelines have been used, infection is still a concern⁴⁹. Attempts to eradicate viruses from tissue with use of radiation have been made, but the dose required to kill a virus (more than three megarad [30,000 gray]) weakens the strength of the allograft tissue by altering its collagen structure⁸³. In an attempt to avoid many of these complications, the current techniques used to sterilize grafts include aseptic harvest, multiple antibiotic soaks, multiple cultures, and low-dose irradiation (less than three megarad)⁸⁴. Despite these problems, allograft tissue is commonly used in both primary and revision anterior cruciate ligament reconstruction. In the revision setting, where larger tunnel diameters are often encountered, the larger size of the allograft bone blocks is extremely useful.

Several studies comparing allograft with autograft for revision anterior cruciate ligament reconstruction demonstrated no significant difference between the two groups from either a functional or an objective standpoint^25,85,86. Uribe et al. reported greater objective stability with autograft than with allograft tissue, with average KT-1000 arthrometer scores of 2.2 and 3.3 points, respectively, but these results, as well as the Tegner and Lysholm scores, were not significantly different²⁵. Noyes and Barber-Westin found less than three millimeters of displacement on KT-2000 arthrometer testing in thirty of fifty-seven patients in the allograft group and in twelve of eighteen in the autograft group⁸⁵. When failures during the first postoperative year were included, thirty-two of seventy-five patients in the allograft group and thirteen of twenty-two in the autograft group had a functional reconstruction at an average of twenty-seven months. However, the difference between the groups with regard to the objective and functional results was not significant.

Because each revision anterior cruciate ligament reconstruction presents a unique problem, graft selection must be individualized. When the appropriate graft is selected, the surgeon should be able to restore stability to the knee. Because autografts and allografts yield similar results, the potential advantages and disadvantages of each must be considered. The final decision is between the patient and the physician.

Femoral Tunnel

Instruments designed specifically for anterior cruciate ligament revision are helpful and should be obtained preoperatively. These instruments include coring reamers and ten-millimeter plastic sheaths for screw removal (Fig. 6).

As mentioned previously, the surgical error encountered most commonly during anterior cruciate ligament reconstruction is anterior positioning of the femoral tunnel² (Fig. 3). The surgeon has many options when revising the femoral tunnel. The simplest scenario is when the tunnel has been properly placed. In this case, simply redrilling the previous tunnel is adequate, and hardware can be retained if it does not interfere with proper tunnel placement. The surgeon must be aware of the difficulty with extraction of the screw as well as the large osseous defect created next to the revised tunnel if hardware (the interference screw) is removed. In order to avoid any compromise of the fixation, the screw can be retained and a portion of it can actually be drilled without any adverse effects⁸⁸. The threads can be smoothed with the drill to eliminate graft abrasion, and a soft-tissue graft can be passed into the tunnel and secured on the posterior cortex. If the previous tunnel is more than one tunnel diameter anterior to the anatomical site, a new tunnel can simply be drilled posterior to it. However, if the tunnel is only slightly anterior, possible overlap of the two tunnels can be a problem because of the enlarged tunnel diameter. One choice is to use a smaller graft such as a hamstring tendon graft, as its typical diameter of seven to nine millimeters may allow posterior placement of the graft without tunnel overlap. The hamstring tendon graft can be fixed on the lateral femoral condyle with either an Endobutton (Smith and Nephew, Mansfield, Massachusetts) or a two-incision technique, thereby allowing the surgeon to drill the tunnel posteriorly and to effectively eliminate the difficulties encountered with posterior cortical-wall blowout⁵⁸ (Fig. 7). Another option is to enlarge the slightly anterior tunnel and to use an allograft with a large bone block. Conversely, when the femoral tunnel is too posterior and there is posterior cortical-wall blowout, a two-incision, over-the-top, or Endobutton technique permits stable fixation on the lateral femoral condyle.

An enlarged femoral tunnel is often encountered during revision of an allograft or synthetic ligament reconstruction^57,89. The extent of tunnel enlargement can be evaluated on a preoperative radiograph (Fig. 8-A and Fig. 8-B) or magnetic resonance image. If the tunnel is more than fifteen millimeters wide, a staged reconstruction with bone-grafting should be considered. An over-the-top technique has also been shown to yield results comparable with those of the standard technique of drilling a femoral tunnel⁹⁰. Other technical options include use of stacked interference screws or a large bone-block allograft to fill the defect. This large bone-block allograft can be rotated either anteriorly or posteriorly, thereby filling the defect and allowing proper positioning of the allograft. Finally, bone-grafting of the enlarged tunnel and an anterior cruciate ligament reconstruction can be performed simultaneously or the reconstruction can be done following incorporation of the bone graft.

Tibial Tunnel

Even though technical error associated with femoral tunnel placement is a more common reason for failure of anterior cruciate ligament reconstruction, correct positioning of the tibial tunnel is also important for a successful outcome. Many of the same techniques used for revising the femoral tunnel apply to the tibial tunnel. However, locating the tibial interference screw can be more difficult. Two techniques are extremely useful for locating the tibial screw: an arthroscope can be inserted up the tibial tunnel to visualize the screw directly, or a radiograph can be used to find the screw and to place a guide-wire into the cannulated screw-hole.

Predictable situations commonly arise when an attempt is made to correct a malpositioned tibial tunnel. If the existing tunnel and hardware are more than one tunnel diameter anterior to the correct position, they can be ignored and a new tunnel can be drilled in a more posterior location. If the tunnel is less than one tunnel diameter anterior to its correct location (slightly anterior), then options similar to those used for the femoral tunnel can be applied. Coring reamers can be used, and the core of bone from the tibia can be placed in the anterior defect, or the tunnel can be expanded and the large bone block from an allograft can be inserted. If the defect is extremely large, bone-grafting of the enlarged tunnel with autogenous iliac crest, followed by either simultaneous or delayed anterior cruciate ligament reconstruction, can be performed. Brown and Carson described another technique, consisting of identification of the optimal intra-articular location for the tibial tunnel and drilling of a new tunnel divergent to the existing one by varying the external starting point².

Posterior positioning of the tibial tunnel is less frequently encountered, and similar techniques can be used. If the tibial tunnel is grossly (more than one tunnel diameter) posterior, a new tunnel can be drilled anterior to the existing one. If it is only slightly posterior, techniques similar to those used for a slightly anterior tunnel are applicable. Coring reamers, large bone-block allografts, and bone-grafting are all acceptable alternatives.

Overview

Revision anterior cruciate ligament surgery has become increasingly common. Successful revision surgery requires a thorough preoperative evaluation, including a detailed history and a physical and radiographic examination. Preoperative planning is imperative for a successful outcome, as it limits the potential for repeating the errors that led to the failure of the primary procedure. This begins with a determination of the mechanism of failure. Often, a primary as well as a secondary cause of failure can be identified. Determination of the etiology of failure is the first step in a carefully constructed treatment plan, which includes the type of revision and skin incision, graft and hardware removal, tunnel placement, graft selection and fixation, and the rehabilitation protocol. The preoperative plan should have enough flexibility to accommodate unanticipated findings in the operating room.

Finally, the importance of counseling the patient preoperatively regarding potential results must be emphasized. Given the complexity of revision anterior cruciate ligament reconstruction, the patient's expectations must be adjusted to realistically match the potential for success. The goal of successful revision surgery may be only to return the patient to activities of daily living or work, especially if there is evidence of degenerative joint disease. With proper planning and attention to detail, revision anterior cruciate ligament surgery can provide a satisfying solution to difficult cases of knee instability.

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Fig. 3:: Lateral radiograph showing anterior placement of the femoral tunnel resulting in graft-lengthening and subsequent failure.

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Fig. 6:: Photograph showing coring reamers, clear plastic sheaths, and a revision screwdriver set. These instruments are extremely useful during revision surgery.

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TABLE I: Nonanatomical Position of Bone Tunnels Causing Increased Graft Tension and Subsequent Failure

Tunnel Position	Cause of Graft Failure
Femoral
Anterior	Excessive strain (lengthening) in flexion/laxity in extension
Posterior	Excessive strain in extension/laxity in flexion
Tibial
Anterior	Excessive strain in flexion/roof impingement in extension
Posterior	Excessive strain in extension/ posterior cruciate ligament impingement
Medial/lateral	Impingement on ipsilateral femoral condyle

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TABLE I: Nonanatomical Position of Bone Tunnels Causing Increased Graft Tension and Subsequent Failure

Tunnel Position	Cause of Graft Failure
Femoral
Anterior	Excessive strain (lengthening) in flexion/laxity in extension
Posterior	Excessive strain in extension/laxity in flexion
Tibial
Anterior	Excessive strain in flexion/roof impingement in extension
Posterior	Excessive strain in extension/ posterior cruciate ligament impingement
Medial/lateral	Impingement on ipsilateral femoral condyle