Preoperative Consideration

The goal of anterior cruciate ligament reconstruction (ACLR) is to stabilize a loose knee so the patient can return to desired activities, often involving pivoting and cutting. Additionally, many patients desire to return to competitive sports. ACLR is performed on a loose knee that either demonstrates or is at risk for instability. A knee that buckles or gives way does not allow the athlete to comfortably or safely return to athletic activities. However, a stiff knee is equally, and often more significantly, disabling than a loose knee. Postoperative stiffness after ACLR is an uncommon but difficult problem. Currently, arthrofibrosis and the best treatment options are poorly defined. Given the lack of consensus regarding the definition of arthrofibrosis, it is difficult to estimate the true incidence. One recent study noted an incidence of 1.7% of patients receiving intervention after ACLR. Female patients were 2.5 times more likely to have arthrofibrosis than males. Arthrofibrosis has both primary and secondary causes. Primary arthrofibrosis, which accounts for less than 5% of arthrofibrosis cases, is caused simply by an exaggerated inflammatory response to injury or surgical insult. Treatment for these cases is clearly nonsurgical. Paulos et al. described infrapatellar contracture syndrome after knee surgery as a combination of loss of flexion and extension and patellar entrapment. They proposed a primary mechanism of an exaggerated pathologic hyperplasia of the anterior soft tissues or secondary to immobilization postoperatively. Secondary causes of arthrofibrosis are directly under the surgeon’s or patient’s control. Many of these cases may be improved by surgical intervention. Stiff knees are frequently persistently painful and do not allow for a functional range of motion (ROM) acceptable to an athlete. With a more significant loss of motion, not only will a patient’s athletic performance suffer, but the patient may have difficulty with activities of daily living. With a significant flexion contracture, a patient will have gait abnormalities and persistent limp. Thus it is important to make certain that a successful ACLR adequately stabilizes the knee, but does not convert it to a knee that is overly stiff. This requires meticulous attention to detail. It is important to consider factors that lead to postoperative stiffness preoperatively, intraoperatively, and postoperatively.

To minimize the risk of postoperative stiffness, it is important to minimize preoperative risk factors. Patients often present to the training room or the office with an acute anterior cruciate ligament (ACL) tear with an inflamed knee, hemarthrosis, and loss of ROM. During the preoperative visit, the timing of surgery must be discussed, and will be dependent on several factors including swelling, ROM, and associated injuries. Historically, it was felt that ACLR surgery should be delayed several weeks from the injury to avoid arthrofibrosis and a suboptimal outcome. Additional studies have substantiated this claim. More recently several studies have supported the safety of early reconstruction. In a prospective randomized clinical trial, Bottani et al. compared early (within 21 days) versus delayed (>6 weeks) ACLRs using hamstring tendon autografts. They concluded that early ACLRs do not result in loss of motion or suboptimal clinical results as long as the postoperative protocol includes early ROM, especially extension. Also, looking at autogenous hamstring reconstructions, Eriksson et al. proposed that acute ACLR within 8 days of injury is safe and does not adversely affect ROM relative to delayed surgery. Furthermore, the patients with acute reconstruction had significantly less hypotrophy in the early phase of rehabilitation, and no difference was found in the other clinical assessments. In an even more aggressive approach, Herbst et al. advocated for acute ACLR within 48 hours in highly active patients or competitive athletes. They compared ACLR within 48 hours after injury versus waiting for the inflammatory-free interval and concluded that the inflammatory state of knee is critical in determining an appropriate time for surgery, as opposed to an absolute temporal cutoff.

With an increasing number of concomitant injuries, it is critical to be diligent in selecting an optimal time for surgery. Identifying an ideal time of surgery is more straightforward with an isolated ACL tear, but with associated meniscal, articular cartilage, or other ligament tears a heightened awareness is critical.

With acute isolated ACL tears, typically the patient is permitted to bear weight as tolerated preoperatively in a hinged knee sleeve. Given that patients typically have hemarthrosis and diminished ROM, they are encouraged to ice their knees and are asked to attend “prehabilitation” or “prehab.” The goal of prehab is for the physical therapist to assist the athlete with edema control and ROM exercises. This uniformly includes a home exercise program component. The patient is ready for surgery when swelling is minimal and nearly full ROM is obtained. An acceptable preoperative ROM includes full extension and approximately 120 degrees of flexion. It is critically important that the patient has normal patellofemoral motion equal to the uninvolved knee before surgery, particularly if a patellar tendon autograft is employed. If the patient fails to regain normal passive patellar motion, including glides and tilts, then patellofemoral pain will likely be a lifelong issue. Typically, if these parameters are achieved, the patient can ambulate with minimal to no limp. The authors do not recommend reconstructing the ACL in the face of a significant ROM deficit, particularly extension. Some patients may require up to 4 to 6 months to regain their normal motion after injury. Clearly this patient may have “primary arthrofibrosis.” Waiting for the entire knee inflammatory process to quiet down is of paramount importance. This is also an ideal time for the patient to develop a relationship with a physical therapist, which will assist with postoperative recovery.

Because associated injuries become additive, the situation becomes more complex. Meniscal injuries can be anticipated based on the preoperative magnetic resonance imaging (MRI). As secondary stabilizers of the knee, it is important to save as much meniscal tissue as possible, especially given injury to one or more of the primary stabilizers. The importance of the meniscus in ACLR has been well documented. ^, A substantial repair of one or both menisci will often necessitate partial weight bearing and will increase the likelihood of postoperative stiffness. If meniscal repair is anticipated, it is important that the surgeon is even more diligent in mandating that prehabilitation goals are met before surgery. A special circumstance relative to meniscal surgery is the bucket handle tear or any tear with a significantly displaced fragment that acts as a mechanical block. The patient will never achieve full preoperative motion, most notably extension, without alleviation of this mechanical block. Furthermore, bucket handle tears frequently involve a large portion of the meniscus, and therefore are frequently repairable. If the patient and therapist can get the acutely inflamed ACL-deficient knee calmed down in a reasonable period of time, the ACLR and meniscal surgeries can be performed acutely in a single stage. If this is not possible, then staged surgery is recommended, with meniscal repair as the first stage, and ACLR performed in a delayed fashion once full motion is obtained. Note that there is risk of significantly delaying surgery. Chhadia et al. have demonstrated a strong association of increased risk of medial meniscal injury and decreased repair rate, as well as increased risk of cartilage injury, with increasing time to surgery.

Whereas a detailed discussion of the multiligamentous knee injury is beyond the scope of this chapter, a combined ACL tear and associated medial collateral ligament (MCL) injury is commonly encountered. It is paramount to have an early discussion with the patient regarding the risk for both persistent instability and postoperative stiffness. Associated ACLR and MCL repair will put the patient at substantial risk for stiffness. This underscores the importance of compliance with both preoperative and postoperative physical therapy.

Intraoperative Considerations

There are several intraoperative considerations to proactively decreasing the risk for postoperative stiffness. Specifically, it is important to make certain that, before leaving the operating room, the patient can achieve full ROM. If the tunnels are properly positioned, this will minimize risk. Improper tunnel location can put the patient at significant risk for postoperative stiffness. The effects of tunnel malposition are discussed in the other section of this chapter. The most common error would be placing the femoral tunnel too far anterior, which will lead to loss of flexion. The patient will either be left with a permanent loss of flexion, or the graft will need to stretch out in order for the patient to regain all of his or her motion. Malposition of the tibial tunnel can lead to loss of motion as well. Positioning the tunnel eccentrically in the anterior portion of the tibial footprint has been associated with loss of both flexion and extension. Also, eccentric medial placement has been associated with loss of flexion. If a significant residual displaced ACL tibial stump is left in the knee and displaces anteriorly, then the knee is at risk for development of a mechanical block. After completion of fixation of the graft on the tibial side, we recommend demonstrating that the knee can achieve full passive extension. It should be noted that a cyclops lesion can also develop even after complete surgical removal of all tissue in the anterior intercondylar notch. Limiting extension, this nodule forms anterolateral to the tibial tunnel placement of the graft and is peripheral fibrous tissue and central granulation tissue. An uncommon but devastating reason for an inability to obtain full passive extension at the conclusion of the case is an impinging interference screw placed too proximally and protruding intraarticularly. A short tibial tunnel should raise suspicion of this potential complication. Nonetheless, in all situations, documentation of full passive extension after completion of the tibial fixation will eliminate the potential for this complication.

Postoperative Considerations

If preoperative and intraoperative risk factors for postoperative stiffness are minimized, appropriate postoperative rehabilitation will minimize the risk as well. A significant delay in therapy will put the patient at significant risk for stiffness. In a prospective study of 443 knees undergoing ACLR with patellar tendon autografts, Noyes et al. documented an effective program of immediate knee ROM to prevent arthrofibrosis. It is important to make certain that the patient’s pain is reasonably well controlled in the immediate perioperative period because poorly controlled pain will minimize the patient’s ability to complete the exercises. Allowing the patient to bear weight as tolerated on the acutely reconstructed knee will assist in regaining full knee ROM. It is imperative that the surgeon sees the patient back in the office frequently to confirm that the patient is on schedule. The importance of active communication between the patient, surgeon, and physical therapist cannot be overstated.

The most critical component in treating patients that are behind in rehabilitation and developing stiffness is engaging the patient and identifying the cause. Patients must buy into the rehabilitation process, especially when they are behind. The reason for postoperative stiffness is not always clear. A call from the surgeon to the patient’s therapist, a demonstration of personal engagement, may be all that is necessary. The therapist sees the patient far more frequently than the surgeon and can often provide tremendous insight into the potential barriers to success. If the surgeon, therapist, and patient have similar goals and expectations, and these goals and expectations are communicated appropriately, the likelihood of postoperative success is far greater.

A variety of treatment options exist for patients who are behind in therapy and developing postoperative stiffness. Furthermore, it is much better to be aggressive with treatment to prevent permanent arthrofibrosis. A stepwise approach with early recognition and intervention is best used, rather than prolonged monitoring of a struggling patient. Multiple treatments have been used in treatment of arthrofibrosis following ACLR, including physical therapy, oral corticosteroids, drop casting, manipulation under anesthesia (MUA), arthroscopic lysis of adhesions (LOA), epidural therapy combined with inpatient therapy, and intraarticular interleukin-1 antagonist injection. Assuming the patient is in the hands of a trusted physical therapist, increasing the frequency of therapy and convincing the patient that he or she needs to make substantial progress at home may be all that is necessary initially. A short oral steroid taper is a useful adjunct to slowly progressing rehabilitation if the patient is substantially behind at 1 month postoperatively. The threat of a MUA can motivate a struggling patient as well. At the 4- to 6-week postoperative mark, a substantially stiff patient can benefit from a gentle MUA. At this point, a manipulation can usually obviate the need for an LOA, which may reintroduce an additional inflammatory stimulus. After 8 weeks, typically an arthroscopic LOA and MUA is performed. Specific attention is given to the offending pathology. This may include a cyclops lesion and a tight posterior capsule in a knee with a flexion contracture. Lysis of peripatellar adhesions, as well as addressing pathology in the gutter, will be necessary for addressing a flexion deficit.

If surgical intervention is necessary, the most optimal time is in the first 12 weeks postoperatively. After 3 months postoperatively, if the patient has not regained full ROM, the overall long-term outcome may become guarded. Full active ROM is typically obtained within the first 2 months postoperatively, so a persistent motion deficit into the third month makes it extremely difficult to progress to the more advanced stages of rehab.

Calloway et al. looked at clinical outcomes after arthroscopic release of patellofemoral arthrofibrosis in 32 patients with prior ACLR. They performed an extended lateral release, debridement of the notch and fat pad, and manipulation of the patella. Some 97% of the patients reported the procedure helped, and 78% would have the procedure again. After looking at trends over two decades for procedural intervention for arthrofibrosis after ACLR, Sanders et al. concluded that interventions are effective in preventing permanent arthrofibrosis. Furthermore, they hypothesized that increased awareness, improved surgical techniques, and improved postoperative therapy protocols may diminish the numbers of those needing procedural intervention over time.

In summary, postoperative stiffness and permanent arthrofibrosis after ACLR is a rare but disabling complication. The most optimal solution is prevention through minimizing risks at all phases of care. When stiffness is developing, early intervention is key. Engaging the patient and physical therapist is absolutely critical. A stepwise approach will yield best results. Although nonsurgical treatments are usually successful, patients are often happy with the results of MUA/LOA in refractory cases.

Tunnel Malposition

Multiple technical errors can occur in ACLR. A common error is tunnel malposition. This can occur on the femoral or tibial side. In a study from 2018, Achtnich et al. noted a high incidence of partially anatomic tunnels in failed single-bundle ACLR. Despite the relative lack of agreement between surgeons regarding the cause of failure, malposition of the femoral tunnel is felt to be the most common cause of failure of ACLR. ^, In a study of 10 French orthopedic centers, Trojani et al. found that femoral tunnel malposition was the main cause of failure in 36% of patients and, overall, the most common cause for failure in ACLR. Furthermore, they considered femoral tunnel malposition in the index operation to be a positive predictor for a good result in revision. Historically, transtibial drilling of the femoral tunnel was common. Recently, surgeons have explored the value of independent drilling of the femoral tunnel either through an accessory medial portal or an outside-in technique to allow for anatomic positioning of the femoral tunnel. ^, Transtibial drilling often leads to a vertical graft inserting on the roof of the notch. This can lead to a feeling of persistent instability and inability to perform at the preinjury level. This underscores the point that an intact graft does not necessarily mean a functioning graft.

Independent anteromedial or outside-in femoral tunnel drilling can still lead to malposition. One common reason for this is failing to evaluate the proposed tunnel position with the 30-degree arthroscope in the medial portal before drilling the tunnel. ^, Viewing exclusively through the lateral portal, even with a notchplasty, will minimize depth perception and can lead to an anteriorized tunnel. ^, Alternatively, a 70-degree arthroscope can be used through a more lateral portal. With an anterior femoral tunnel, the graft is short. The patient can have difficulty obtaining flexion in the early postoperative period. As the patient regains full flexion, the graft stretches out, leading to increased tibial translation and increased risk of failure.

The tibial tunnel can be malpositioned as well. Malposition of the tibial tunnel can lead to loss of motion. The bony and soft tissue landmarks of the tibial insertion site have been described to assist in tunnel placement for anatomic ACLR. Tibial tunnel malposition has been cited as the technical reason for failure only a third as frequently as malposition of the femoral tunnel. ^{, , ,} The appropriately positioned lateral portal is optimal for viewing the tibial footprint. ^{, ,} If the anterolateral viewing portal is too distal, it becomes very difficult to appropriately position the tibial tunnel. An anterolateral viewing portal positioned proximally can allow the surgeon to look down on the tibial footprint and appropriately position the tibial tunnel in both the anterior and posterior, as well as the medial, lateral plane. ^,

Associated Pathology

It is important to determine the status of the meniscus when evaluating the failed ACLR. The meniscus is a critically important knee stabilizer. ^, Trojani et al. validated this concept in a recent study that evaluted failed ACLR and looked critically at the role of the meniscus. The cumulative incidence of menisectomies were evaluated in this retrospective study at several time periods from a primary ACLR, through the revision ACLR, and throughout the follow-up period. Some 23% of patients had menisectomies before or during the index ACLR. The incidence increased to 33% between the index surgery and the revision, and climbed to 67% during the revision ACLR. Ultimately, 70% of the patients had a menisectomy. Patients with a conserved meniscus had a higher objective International Knee Documentation Committee score. At last follow-up, the patients with conserved menisci had better knee stability and a better functional results than those with a total menisectomy.

Increased posterior tibial slope will increase risk of failure after ACLR. Christensen et al. performed an MRI study of patients with early failure of ACLR and found the mean lateral posterior tibial slope in the failed group to be 8.4 degrees, which was significantly greater than that of the control group at 6.5 degrees. The odds ratio for graft failure was 1.6, 2.4, or 3.8, considering an increase in the lateral tibial posterior slope of 2 degrees, 4 degrees, or 6 degrees, respectively. In another study in which the slope was calculated on a lateral plain radiograph, Webb et al. found the risk of further ACL injury after ACLR to be most pronounced with a posterior tibial slope of 12 degrees or more. Recently a study documented that increased medial and lateral tibial slopes are independent risk factors for graft failure following ACLR, with the most notable risk in patients with a lateral tibial slope of 10 degrees or more.

Clinical Evaluation

As mentioned, a detailed history is critical in evaluating the failed ACLR. The history of the event which ultimately caused the graft failure is important. As mentioned, a new significant trauma can rupture the graft. However, it is also important to review the history regarding the initial injury and the index operation. A typical noncontact ACL injury can be quite different than a high-energy contact injury with a potential associated lateral- or medial-sided injury that may have been missed. It is also critical to review the perioperative and postoperative courses. A discussion of any ROM struggles, as well as well as how long it took the patient to regain full motion, may assist the surgeon in determining the reason for failure. Note how much postoperative physical therapy the patient attended, as well as when the patient was permitted to return to sport. Failure after achieving objective return-to-play criteria can be quite different than simply returning to sport before the athlete was ready. If the patient made it back to the preinjury level of sport and at some time “trusted” his or her knee, that often indicates that, at least for a period of time, the patient’s ACLR was working.

The physical examination will also guide the surgeon in determining the reason for failure. Initially, the patient is asked to stand to evaluate the alignment of the limbs, as well as the presence of an effusion. Significant malalignment can lead to failure even if the graft is properly positioned. Evaluation of the surgical scars will give insight into the surgical technique used in the index operation in terms of both performing the ACLR and addressing the meniscus. With the patient lying supine, the surgeon can examine both knees. A ligamentous examination is compared with the normal side. The collateral ligaments are evaluated, and the Lachmann and pivot shift tests are performed. The menisci are evaluated. On examination, substantial instability can often be appreciated in an ACL-deficient knee with absent portions of the meniscus, either from injury or from previous partial menisectomy. A marked pivot shift in the presence of intact menisci should clue the surgeon to a potentially missed associated injury, such as the posterolateral corner or posterior oblique ligament, or other abnormality such as increased posterior tibial slope.

If the treating physician did not perform the index operation, consulting the operative report and the previous arthroscopic pictures, when possible, can be valuable. This gives the surgeon insight into the perceived state of the meniscus and articular cartilage at the time of the index operation. For example, a missed lateral meniscal root avulsion will result in a marked pivot shift and increased stress on the graft, potentially leading to failure. Understanding the rationale for medical decision making, as well as associated procedures, can be critical for moving forward. Simply stated, every detail about the first ACL occurrence and surgery is important. Also, if a revision is planned, the appropriate instrumentation and surgical equipment can be available to remove the fixation devices or any potential foreign bodies from a failed meniscal repair.

It is critical to obtain and interpret the appropriate radiological studies in evaluating a failed ACL graft. Plain films will allow the surgeon to evaluate the index surgery tunnel placement, as well as evaluate for tunnel lysis. In older patients, joint space narrowing can sometimes be observed, as well as other findings consistent with degenerative change. Large osteochondral lesions can be seen. Occasionally a misplaced fixation device, such as an endobutton in the soft tissues or in the center of the lateral femoral condyle, can give insight into the reason for failure. If there is any question of alignment, alignment films should be obtained. Stress radiographs can be helpful if there is concern about the collateral ligaments.

Advanced imaging can give the surgeon additional information not obtained with the plain radiographs. MRI images are extremely valuable, and every patient with a failed graft should undergo MRI if possible because this will give the treating physician tremendous insight into the reason for failure. The tunnels and integrity of the graft are evaluated. Malpositioned tunnels will give insight into the reason for failure, independent of graft continuity. It is imperative to understand that an intact graft does not necessarily indicate a functioning graft or a stable knee. Meniscal integrity and evaluation of both primary and secondary stabilizers of the knee are important. The presence or absence of bone bruises can provide information not only regarding injury pattern, but also the chronicity of the instability. Focal chondral or osteochondral defects can be appreciated, as well as subchondral stress reactions from more advanced articular cartilage degenerative changes. Posterior tibial slope can be calculated on MRI in cases of failed ACLR.

The computed tomography (CT) scan can be a useful test if the plain films and MRI do not give the surgeon all the information he or she needs to evaluate the tunnels. Tunnel position and lysis can be predictably determined with the CT scan. This will give the surgeon information not only regarding the reason for the failure, but also about the revision, specifically whether the revision may have to be staged. Completely nonanatomic tunnels can typically be ignored in revision ACLR. However, partially anatomic bone tunnels often require a staged procedure with bone grafting and subsequent revision ACLR.

The failed ACLR is a complex problem. However, mastering the evaluation and management of the failed graft can assist the surgeon in helping an increasingly active patient population. The key to a successful revision surgery is determining why the index operation failed. A detailed history, physical examination, and evaluation of appropriate radiology will give the surgeon an outstanding opportunity to plan to move forward. Understanding the most common reasons for failure outlined in this chapter will assist the skilled sports medicine surgeon in individualizing patient care.