Introduction

Reconstruction of the anterior cruciate ligament (ACL) has become an increasingly common orthopaedic procedure. In the United Kingdom, approximately 5000 ACL reconstructions are performed per year¹; in the United States, more than 100,000 procedures are currently performed annually.² This trend is likely to continue with the general population’s increasing pursuit of an active lifestyle. Although long-term functional stability and symptom relief after primary ACL reconstruction exceed 90% in some studies,^3,4 overall clinical failure rates of 10% to 25% have been documented.¹ It is currently estimated that between 3000 and 10,000 U.S. patients and approximately 1000 U.K. patients are candidates for revision ACL surgery annually.¹

Revision ACL surgery is recommended for patients who have instability or reduced activity with pathological laxity after a failed primary ACL reconstruction. The important stages in assessing a patient with a failed ACL reconstruction include a detailed history, patient selection, physical examination and appropriate investigations, choice of graft, surgical technique, and rehabilitation.⁵ Eliciting important relevant history from a patient who is usually apprehensive and has some knowledge of the problem (from general practitioners, physiotherapists, and the Internet) can be difficult. One should spend enough time trying to find out the details of the original injury (e.g., high-velocity trauma may suggest multiligament laxity) and also the patient’s experience of previous treatment as well as his or her knowledge of the problem. A full history of occupational and future recreational activities is mandatory. Often the patient’s expectations are not realistic, and therefore despite achieving knee stability, the revision surgery will not result in a contented patient. Instability and/or pain top the list of patient symptoms. It should be clarified with the patient preoperatively that a reduced activity level and/or excellent natural proprioception may result in a reduction or even an abolition in symptoms of instability without the need for surgery. Revision reconstruction should be offered to patients with symptoms of instability or those who wish to increase their activity level to include manoeuvres involving twisting or a sudden change in direction. In such cases symptoms of instability, if left untreated, will contribute to repeated meniscal and chondral damage, leading to an earlier progression of osteoarthritis (OA). At the same time, the patient should be made aware of the risk of a gradual progression of OA, irrespective of the method of treatment but especially if symptoms of instability are ignored. It should be carefully explained that symptoms of pain are likely to be caused by degenerative disease or a torn meniscus and that a revision ACL reconstruction alone is unlikely to be the answer to this problem. One should also alert the patient to the potential need for bone grafting and thus a staged reconstruction.

The most useful investigations are the plain x-ray series of an anteroposterior (AP) standing radiograph and a lateral x-ray in full extension, together with skyline and Rosenberg views (Fig. 58-1).¹ These will show the original tunnel placement and usually the fixation methods used, tunnel widening,^6,7 osteolysis, and the presence and extent of joint space narrowing. If possible, comparison with previous radiographs will help quantify bone loss (tunnel widening). It is our practice to obtain a magnetic resonance imaging (MRI) scan preoperatively, but only rarely has this provided additional information that has changed the course of management. If no reason for the primary failure can be elicited, vigilance for a missed or complex laxity should be exercised. Careful clinical examination and an examination under anesthesia, which may include fluoroscopic stress views, are useful in finding an additional laxity.

Fig. 58-1 Failed anterior cruciate ligament (ACL) reconstruction. Anteroposterior (A) and lateral (B) views.

Causes Of Failure of Primary Procedure

The causes of recurrent patholaxity after primary ACL reconstruction^6–26 can be broadly divided into four groups: technical errors, failure due to biological factors, failure due to significant trauma, and failure owing to laxity in the secondary restraints.¹⁷ By far the most common cause is error in the surgical technique, with 77% to 95% of all cases of ACL failure attributed to technical error.²⁷ This category includes poor graft selection or harvest, improper tensioning or fixation, and especially incorrect tunnel placement.^9,17,18 More than 70% of technical failures, and thus more than 50% of all ACL failures, can be attributed to malpositioned tunnels.^8,17 Inappropriate positioning of either the tibial or the femoral tunnel results in excessive length changes in the graft as the knee moves through a range of motion, resulting in either a limited range of motion or excessive graft laxity.^8,18 Anterior placement of the femoral tunnel, a common mistake, will result in limited flexion and potential graft failure if full flexion is achieved. Tibial tunnel placement may be somewhat more forgiving, but anterior placement leads to impingement in extension and excessive tension in flexion, whereas posterior placement may cause laxity in flexion.¹⁷ Perhaps the most common error in surgical technique involves the anterior placement of femoral and/or tibial tunnels.¹⁶ Carson et al recently published their review of 90 failed ACL reconstructions and quoted 52% of the failures as being due to surgical technical errors.²⁸ Several studies have shown that a posterior and proximal placement of the intraarticular exit of the femoral tunnel is advisable and involves minimal lengthening of the ACL substitute toward extension.

Treatment Options

Revision ACL surgery is often considered a salvage procedure with very limited goals, distinctly different from those of primary ACL reconstruction.^5,29 Many reports in the literature quote inferior results for revision cases compared with primary reconstruction. However, with many categories of failure, the population of failed ACLs is a diverse group and a difficult subset to study.³⁰

We ask the following questions before deciding on a definitive treatment plan:

Unless the answers to all these questions are positive, we tend to favor a cautious two-stage approach. If revision ACL surgery is staged, then the first stage gives the surgeon an added opportunity to assess the chondral and meniscal pathology and then give the patient a more realistic prognosis.

It is also important to ascertain whether the tibial tunnel of primary surgery will interfere with the correctly placed revision tibial tunnel and the extent of loss of bone stock due to tunnel widening. In addition, one needs to determine whether the hardware needs to be removed and, if so, whether that will further contribute to the loss of bone stock. For the revision graft to function optimally, one needs to ensure that the tunnels are placed in an optimal position in a good-quality bone so that the fixation achieved will be as robust as the primary surgery.

Management of previous tunnel malposition is technically demanding, and different surgeons have used various approaches for dealing with bony defects resulting from incorrectly positioned prior tunnels. In some cases of gross tunnel malposition, a new tunnel may simply be drilled without violating the original tunnel or removing any tunnel hardware. Alternatively, tunnels can be oriented in a divergent pathway that maintains the appropriate articular surface attachment. In many cases, however, new tunnels cannot be drilled without overlapping or breaking into a previous tunnel. Two or more screws can be used to supplement fixation and fill the cavity of an enlarged tunnel. Although this might be useful in limited cases, the fixation achieved tends to be inferior and postoperative rehabilitation may be compromised. Graduated tunnel dilators may allow controlled expansion of a previous tunnel, compacting rather than removing additional bone.¹⁷ In such instances, options include the use of an allograft tendon with an enlarged bony portion, an oversized interference screw, or stacked interference screws.³¹ If the original tunnel is correctly positioned and only slightly larger (3–5 mm) than the new graft, stacking two interference screws may be sufficient to fill the tunnel and secure the graft.^32,33 Battaglia and Miller³⁴ have described use of freeze-dried allograft bone dowels to address bony defects during revision ACL reconstruction. These allografts are readily available and can be easily used to fill deficiencies resulting from previous tunnels or osteolysis. The grafts provide sufficient structural support to allow redrilling of new tunnels through or next to the bone plug. Unfortunately this option implies slower graft incorporation³⁵ and has implications for the rehabilitation regimen.

Some authors have tried to stratify the treatment options by the extent of bony defect. For defects larger than 10 mm, they advocate the use of bone graft and a staged procedure. Although this stratification is useful, it has certain limitations. Accurate preoperative assessment of the tunnel size is difficult and unreliable with plain x-rays. CT is the most accurate method.

After clearing the debris from the earlier drilled tunnel, the resultant defect is almost always larger than 10 mm. Therefore we usually favor a staged reconstruction as a default technique. The first stage involves an EUA, an assessment of chondral and meniscal pathology, the removal of old graft, tunnel curettage, drilling, and bone grafting. The second stage is revision ACL reconstruction after incorporation of bone graft, 3 to 6 months after the first stage, when a CT scan has shown adequate incorporation of the bone graft.

Definition of knee instability

The IKDC classifies knees that are within 2 mm of the normal contralateral knee by means of KT-1000 or similar testing as “normal.”³⁶ Knees that have greater than 5 mm of difference are classified as “abnormal.” The KT-1000 applies a force of 134N to assess knee laxity.

For the past 15 years, we have used the Westminster cruciometer (University College, London) for laxity measurements. It is a validated tool that applies an 89N force during the laxity measurement. Similar to the KT-1000, this cruciometer has been shown to give a reproducible quantitative evaluation of the Lachman test, and a previous study has shown average displacement of normal knee to be 3.2 mm as compared with 8.4 mm in the ACL deficient knee.³⁷ A further validation of the Westminster cruciometer was done recently by comparing the laxity measurements in normal, ACL deficient, and ACL reconstructed knees. The correlation between the Westminster cruciometer and KT-2000 was found to be excellent (Pearson’s coefficient: 97%). The KT-2000 reading can be obtained using the following equation:

Since the original recommendations by the IKDC, various published results have used slightly different criteria in defining knee stability. In addition to instrumented laxity measurements, the clinically relevant pivot-shift test is widely used. The pivot-shift test has various grades, and one needs to be clear in reporting the grade (1+, glide; 2+, clunk; 3+, subluxation) that is being considered as abnormal. In our practice using the Westminster cruciometer (applying a force of 89N rather than 134N) to assess the knees, we use the following criteria to define normal laxity: The side-to-side difference (SSD) in anterior tibial translation is considered normal if within 2 mm and nearly normal if between 3 and 4 mm. Values of 5 mm and greater are considered unsatisfactory. Overall anterior laxity is considered satisfactory if the SSD is less than 5 mm and the pivot shift is absent or 1+ (glide). In the presence of an SSD greater than 4 mm and/or a pivot shift of 2+ (clunk) or 3+ (subluxation), the anterior laxity is considered unsatisfactory.

Surgical procedure