Our initial approach to the acutely injured knee involves a careful history, physical examination involving assessment of all ligaments, and well-done x-rays. An MRI in this setting can be very helpful as physical examination due to the swelling and pain is often unreliable. After obtaining the above studies, the specific diagnosis can be made, and operative versus nonoperative treatment can be decided upon. It is our preference for the acutely swollen knee with poor motion and poor quad control that doesn’t have any collateral ligament injury to enter into rehabilitation until normal motion and gait are restored.

There are certain circumstances in which early surgery may be preferable to delayed ACL reconstruction. If the ACL tear occurs in conjunction with a tibial or femoral fracture requiring reduction and fixation, the fracture care will supersede in importance and should be performed when the soft tissue envelope allows. In a multiligamentous knee injury with an unstable posterolateral corner, early repair or reconstruction of the posterolateral corner, regardless of ACL reconstruction timing, yields good results and potentially better outcomes than delayed surgery [18, 35]. There are two scenarios where an early ACL reconstruction may be of benefit. In the setting of a locked and irreducible meniscal tear, early surgery to reduce and treat the meniscus in conjunction with ACL reconstruction offers earlier motion without chondral damage and likely a better chance to repair the meniscus. Though there is limited evidence to support this, the final scenario is that of the high-level, typically professional, athlete whereby delaying surgery and return to play by a few weeks could potentially have a significant impact, financial and otherwise, upon their lives.

In the majority of the cases, a patient presents with an acutely swollen knee (Fig. 4.1), limited range of motion, and poor control of the quadriceps. In these cases and in the case of the multiligament-injured knee, in the absence of an operative posterolateral corner injury, early surgery is likely to lead to an increased risk of arthrofibrosis [31]. These patients are referred for rehabilitation until they enter the delayed phase with good quadriceps control and a complete active range of motion.

Multiple studies have reported the correlation between timing of ACL surgery and the risk of postoperative stiffness. Harner et al. initially described surgery within a month of injury as a risk factor for postoperative stiffness [13]. In a classic study, Shelbourne found that ACL reconstruction with bone-tendon-bone autograft delayed by more than 3 weeks post-injury resulted in a decreased incidence of arthrofibrosis and lack of full extension [34]. In a later review, Shelbourne listed the advantages of delayed reconstruction as obtaining a full range of motion without knee stiffness and a faster and safer return to full activities, noting that a functional yet lax knee is preferable to a stiff, stable knee [31, 32]. Passler et al. evaluated the complications following bone-tendon-bone ACL reconstruction in a group of 283 patients performed via a mini-arthrotomy. They reported that 18 % of patients who had surgery within a week after injury suffered arthrofibrosis as compared with only 6 % who had reconstruction delayed by more than 4 weeks [26]. Finally, Mauro et al. identified preoperative failure to gain full extension and a shorter interval between injury and surgery as risk factors for postoperative loss of extension [22].

On the other hand, good results have been shown with early reconstruction with bone-tendon-bone autografts [21]. In a prospective study, Hunter et al. reported results of 185 ACL reconstructions done in four different time intervals after injury [14]. In this study, authors divided patients into four groups according to reconstruction times: the first group had immediate surgery within the 48 h, the second group in 1 week, the third group in 3 weeks, and the fourth group after 3 weeks. One hundred forty-eight ACL reconstructions were done within 3 weeks, and only 11 had postoperative complications, which did not reach statistical significance. In these studies, reconstructions were done with bone-tendon-bone autografts, which is reported as an independent risk factor for knee stiffness in adolescents [25].

There is also conflicting data regarding the outcomes of ACL reconstructions performed with hamstring autografts with regard to surgical timing. In the 1990s, Wasilewski et al. reported arthrofibrosis in 22 % of acute reconstructions in a group of 87 ACL reconstructions with hamstring autografts [36]. In the 2000s, Meighan et al. reported an increased rate of complications such as stiffness and deep vein thromboses in the early group (within 2 weeks of injury) as compared with the delayed group (8–12 weeks) in a prospective randomized trial of 31 hamstring autograft ACL reconstructions [24]. However, in another prospective randomized study in 2008, Bottoni et al. performed 34 hamstring autograft ACL reconstructions in the early group at a mean time of 9 days after injury (the earliest surgery was done on the second day), and there was no significant difference between early versus delayed reconstruction group [4]. In 2010, Raviraj et al. randomized 105 patients with an isolated (no concomitant meniscal repair or other ligamentous injury) ACL tear to early (<2 weeks) or delayed (4–6 weeks) ACL reconstruction, and they found no difference in Lysholm or Tegner scores and no difference in range of motion [28].

There is now recent evidence across graft types to suggest that the timing of surgery may not increase the risk of postoperative stiffness for the isolated ACL tear. A recent meta-analysis of eight studies, including three randomized controlled trials, found no difference in adverse outcomes with ACL reconstruction performed at 1, 2, 10, 12, or 20 weeks after injury when performed with a modern reconstruction technique and accelerated rehab protocol [16].

In the experience of the senior authors, the clinical status of the injured knee at time of surgery, not the timing of the injury, is the most important factor. Mayr et al. did not assess the timing of ACL reconstruction, but they assessed preoperative symptoms such as swelling, effusion, and extension or flexion deficits at the time of surgery. They found that failure to regain a full range of motion preoperatively was a risk factor for postoperative stiffness regardless of timing of surgery [23].

ACL reconstruction is an elective procedure, and because of the risk of postoperative stiffness and loss of extension, we routinely wait until a patient has entered the delayed phase. As we previously noted, the delayed phase is patient dependent and may last anywhere from a few days to occasionally a few months. During the time, it is imperative that the patient be actively involved in rehabilitation to assist them in their transition from the early to the delayed phase. Further, the extra time allows the patient to schedule their surgery around their other obligations (social, work, school, family, etc.).

Arthrofibrosis is a known and frustrating complication of ACL tears and reconstructions for both patient and surgeon. Development of postoperative arthrofibrosis and stiffness following elective or urgent ACL reconstruction is a time-consuming and debilitating problem, especially in athletes. It can be seen on MRI as disorganized scar tissue anterior to the ACL (Fig. 4.2). Though arthrofibrosis has been classified into four subtypes with the most mild form being less than a 10° extension loss and normal flexion, a loss of motion of 3–5° in an athlete can lead to significant disability including quadriceps inhibition and a permanent decrease in performance. Further, the treatment of arthrofibrosis, even when successful, can delay return to play, potentially negating any benefits from an early ACL reconstruction [33].

Unfortunately, arthrofibrosis remains a common problem today after ACL reconstructions. A 2015 epidemiologic study on arthrofibrosis after ACL reconstruction found that 1.7 % of patients that underwent ACL reconstruction had postoperative stiffness requiring procedural intervention, and a separate study in 902 pediatric and adolescent patients that had undergone ACL reconstruction required procedural intervention for arthrofibrosis in 8.3 % of patients [25, 30].