By Caitlin J. Miller, PT, DPT, and Jesse C. Christensen, PT, DPT, SCS
Traditionally, anterior cruciate ligament reconstruction outcomes have been assessed preoperatively and several months postoperatively, but new research suggests the early postoperative stages of recovery may also significantly affect self-reported outcomes.
More than 200,000 anterior cruciate ligament (ACL) injuries are estimated to occur in the US annually, and ACL reconstruction (ACLR) is a commonly performed surgical procedure in active individuals who have expectations of returning to their prior level of function.1-3 Outcomes following ACLR are typically evaluated objectively by such methods as clinical examination, assessment of ligamentous laxity, and radiography. Patients, however, are typically more concerned with more subjective outcomes, such as symptom reduction and functional ability.4 Therefore, both objective and subjective outcomes should be paramount in determining the response to recovery after ACLR.
Traditionally, these outcome measures have been assessed preoperatively and several months postoperatively to determine the effects of ACLR.5-13 However, little is known about the influence the early postoperative stages of recovery have on self-reported outcomes following surgery.
Patient education throughout postoperative rehabilitation is critical to a successful outcome following ACLR. However, the process of a successful recovery can begin well before surgical intervention. One of the most critical first steps in obtaining a successful postoperative outcome is preparing the involved limb appropriately prior to surgery. Following an ACL injury, the patient should be educated on the importance of addressing post-traumatic effusion, loss of range of motion (ROM), limited quadriceps activation, and altered gait mechanics.
Other preoperative steps that can help avoid postoperative complications and improve rehabilitation include achieving symmetrical knee ROM, increasing lower extremity strength, and restoring daily functional mobility. These milestones should be met prior to moving forward with surgical intervention.14,15 Meeting with a rehabilitation clinician (eg, physical therapist or athletic trainer) will provide the necessary interventions to improve in these areas, while providing an opportunity to educate patients on the nature of their injury and to begin to set expectations for their road to recovery.
It has been shown that patients lacking knee ROM prior to surgical intervention have greater difficulty restoring joint mobility postoperatively than those with greater knee ROM.15 Clinicians should emphasize not only obtaining neutral extension of the involved knee joint, but also restoring full symmetric knee hyperextension in the involved limb and flexion ROM (Figure 1). Achievement of full knee motion should serve as a critical milestone prior to patients moving forward with surgical intervention.
Additionally, preoperative rehabilitation should focus on quadriceps strengthening, which not only improves short-term functional mobility, but has also been shown to be predictive of postoperative outcomes.16-18 Logerstedt et al10 found that preoperative quadriceps strength was a significant predictor of International Knee Documentation Committee Subjective Knee Evaluation Form (IKDC) scores six months after surgery. Additionally, de Jong et al16 reported that patients with quadriceps strength deficits greater than 20% preoperatively relative to the contralateral limb demonstrated a significantly lower limb symmetry index at six and nine months postoperatively than those with lesser preoperative strength deficits. Based on the current evidence, there should be a strong emphasis on strengthening prior to surgery without causing increased inflammation that may lead to subsequent loss of ROM.
Recent studies have also highlighted the role of psychosocial components with respect to influencing the ability to successfully recover from an ACL injury.19-23 Several subjective outcome tools—including the ACL Return to Sport after Injury (ACL-RSI), Knee Self-Efficacy Scale (K-SES), and the Tampa Scale for Kinesiophobia (TSK-11)—are available to help clinicians identify patients with an increased risk of not returning to their previous level of function due to psychosocial ramifications. Although minimal research has been conducted in this area preoperatively, Thomee et al24 demonstrated that preoperative K-SES scores can be predictive of patients returning to the same intensity and frequency of physical activity 12 months after ACLR. Patients who perceived their function as successful at 12 months postoperatively had scored themselves significantly higher on the K-SES preoperatively.24
In a recent systematic review, Te Wierike et al25 described how psychosocial factors may affect ACLR recovery. According to Wiese-Bjornstal, the psychosocial responses of injured athletes consist of cognitive, affective, and behavioral factors.26 It is the interaction of these domains that contribute to full recovery following ACL injury. Clinicians may consider incorporating treatment strategies such as relaxation, imagery, training of self-efﬁcacy, and modeling to address cognitive and affective deficits.27-29
Additionally, with regard to behavioral factors, the systematic review25 found a positive association between goal setting and rehabilitation adherence. Patients with higher adherence scores experienced fewer knee symptoms, indicating that adherence to a rehabilitation program had a positive effect on recovery after ACLR.30
Further research is needed in this area to identify the potential influence psychosocial factors have on returning patients to prior levels of function or to identify patients who may require some of the aforementioned treatment strategies.
Range of motion
During the early phase of postoperative rehabilitation, emphasis should be placed on restoring full symmetric knee ROM. A growing body of evidence indicates that postoperative knee ROM deficits are associated with lower subjective outcome scores in the short- and long-term, as well as increased risk of developing knee osteoarthritis (OA).14,31,32
Traditional postoperative restrictions, such as bracing for immobilization and limiting early hyperextension, have been utilized throughout rehabilitation, with the intention of preventing excessive loads on the healing graft.33 Although these are still valid concerns in postoperative management, advancements in surgical technique and fixation have warranted a reevaluation of movement restrictions after ACLR. Postoperative protocols have been influenced largely by theories of graft-tunnel healing and graft selection over time, but gathering evidence suggests that restrictions may not be necessary, and early unrestricted ROM has not been associated with adverse effects on anterior-posterior laxity, ROM deficits, reinjury rate, and/or ability to return to the patient’s previous level of function.31,34
Shelbourne et al35 found that as little as 3° of knee extension loss relative to the contralateral knee can have a negative effect on subjective and objective outcomes. It has further been shown that patients with less than normal knee motion (relative to the contralateral knee) are 2.4 times more likely than those with normal knee motion to have radiographic findings of knee OA 10 years following ACLR.31 More recently, at a mean of 10.5 years following ACLR, normal radiographic findings were identified in 71% of patients with normal symmetrical knee ROM compared with 55% of patients who had knee flexion and/or extension ROM deficits at final study follow-up.12
Further findings have indicated that early ROM deficits may have some influence on patient-reported outcomes following ACLR. In the first month following surgery, deficits in knee flexion ROM have been shown to be related to lower IKDC scores at the equivalent time point.32 This highlights that even subtle ROM deficits may significantly impact patients’ perceived functional ability.
Early progressive ROM exercises should begin within the first 24 to 48 hours following surgery,33 with a specific emphasis on restoring symmetrical extension or hyperextension (if present).35 Postoperative functional bracing may interfere with early motion gains and in recent studies has been shown not to offer any significant advantages over no bracing.33,36,37 Wright et al33 conducted a systematic review, concluding that neither a postoperative knee brace locked in full extension nor an open-hinged brace offered significant advantages over no bracing with regard to self-reported outcomes, knee laxity, ROM, or strength testing. The literature also suggests that emphasis on restoring symmetrical knee ROM relative to the contralateral knee is critical for avoiding possible complications relative to joint mobility limitations, such as graft impingement, development of arthrofibrosis, and inefficient quadriceps activation following isolated ACLR (Figure 2).14,38
Lower extremity strength
In conjunction with restoring symmetrical knee ROM, progressive lower extremity strengthening should also be an area of focus acutely following ACLR. Aggressive strengthening not only improves functional mobility in the early phases of rehabilitation, but may also improve the patient’s capacity to return to his or her previous level of function in the later phases of recovery.
Gerber et al39 found that atrophy of up to 30% in the quadriceps muscle in the surgical limb is evident just three weeks after ACLR, underscoring the importance of early resistive training immediately after surgery in an effort to mitigate atrophy and weakness. It has further been shown that knee extensor weakness of nearly 20% persists one to six years following surgery.40 Quadriceps weakness leads to predominant limitations in functional mobility and has been shown to be the strongest contributor to the strength-function relationship during early recovery after ACLR.41 Initial quadriceps activation and mitigating atrophy can be achieved by allowing full weight bearing with assistive devices (as needed) immediately after surgery. This has been shown to be safe, as well as beneficial, while also decreasing potential future risk of patellofemoral pain and likely improving functional mobility.33
Lower extremity strength may be difficult to measure objectively in the early phase of rehabilitation. However, recent work has shown that examining peak isometric hip and knee extensor strength as early as one month following surgery is safe and appropriate (Figure 3).37 Additionally, the ratio of surgical to nonsurgical limb isometric force measures at one and two months postsurgery has been shown to be significantly associated with one- and two-month IKDC scores.32 This highlights the importance of focused lower extremity strengthening during the early phase of rehabilitation, as this plays a primary role in normalized gait patterns as well as more demanding tasks such as stair climbing.
Further evidence suggests that neuromuscular electrical stimulation (NMES) may play a role in enhancing quadriceps strength during the early phase of rehabilitation. Kim et al42 performed a systematic review evaluating the efficacy of NMES for improving quadriceps strength measures, functional performance measures, and self-reported outcomes. A moderate effect was shown for improved subjective outcome scores on the Knee Outcome Survey using NMES in conjunction with postoperative rehabilitation exercises relative to exercise alone or electromyography biofeedback during the first month following ACLR.43 There is inconclusive evidence to support a significant difference in functional outcomes, including the anterior reach, lateral step up, and unilateral squat tests44 when using NMES; however, it appears to be most beneficial when used at a high intensity in the first few weeks following surgery.45 Future studies with improved methodological quality and consistent treatment parameters are needed to assess the potential benefit of NMES in this population.42
Criteria for returning patients to their previous level of sports function following ACLR generally focuses on ligamentous stability, normalization of knee ROM, restoration of lower extremity strength, improved biomechanics, and limb symmetry on functional tests.46,47 Although the physical factors that contribute to a successful recovery are critical, clinicians must also consider the influence of psychological factors in returning patients to their prior level of function. Ardern et al21 reported that only 44% of competitive athletes who were classified as having normal or near-normal physical function after ACLR were able to return to their previous level of competitive sport activity at a mean follow-up of 41.5 months. A growing body of literature suggests patients may not be achieving their desired level of function postoperatively due to psychological factors, including fear avoidance behaviors, kinesiophobia (fear of movement/re-injury), or both.21,23,48 It has been reported that nearly 20% of patients cited fear of reinjury at 12 months following ACLR as their reason for not returning to their previous level of sport function.21 This highlights a potential area of rehabilitation that may be overlooked.
Currently, we know that these fear avoidance behaviors are present, but further research is needed to determine the most clinically effective ways to use kinesiophobia measures and implement psychological interventions during relevant timeframes following ACLR. The development of novel interventions that address the psychological aspect of injury and provide a platform for patients to improve in these areas is warranted. These interventions could be implemented in the early phase of recovery, while providing the necessary guidance to minimize fear avoidance behaviors throughout rehabilitation and likely increasing patients’ ability to return to their prior level of function.
Identifying the patients at highest risk for fear avoidance and implementing interventions specifically in those patients could also be beneficial; however, this can be a challenging process due to the scarcity of subjective outcome tools and currently limited research in this area. The TSK-11 has been adapted for patients following ACLR.49 The TSK-11 is a valid measure of fear of movement/re-injury with response items related to somatic sensations (eg, “Pain always means I have injured my body”) and activity avoidance (eg, “I’m afraid that I may injure myself if I exercise”). Although this tool showed a strong association with knee function as assessed by IKDC scores at six to 12 months postoperatively, no association has been found in the six months following surgery.50 The ACL-RSI scale has also been used to examine psychological readiness to return to sport and recreational activity.19,49,51 Müller et al52 prospectively followed ACLR patients and at six months found that the ACL-RSI was a strong predictor of patients’ return to sport. Ardern et al also reported that, when assessed in a long-term follow up (mean = 35 months), for every one-point increase on the ACL-RSI outcome tool, patients had approximately twice the odds of returning to activities.19
The medical literature has focused largely on long-term postoperative outcomes following ACLR, with less attention drawn to how deficits in the early phase of recovery influence overall outcomes. Normal gait mechanics, reduced swelling, and restoration of symmetrical knee ROM should be achieved prior to surgical intervention. Immediate unrestricted knee ROM should be implemented postoperatively to improve subjective outcomes and minimize long-term risk of knee OA. Full weight bearing to tolerance and quadriceps strengthening should begin immediately following surgery to minimize lower extremity atrophy. Patients should be screened for psychosocial deficits and fear avoidance behaviors preoperatively and during early phases of recovery to help identify those with risk of factors that may interfere with returning to their prior level of function.
There are many factors to consider when developing a rehabilitation protocol for ACLR. These guidelines serve to highlight key areas that should be addressed preoperatively and in the early postoperative period to further improve subjective and objective outcomes. Future research is needed to examine how addressing these early deficits will affect long-term outcomes following ACLR.
Caitlin J. Miller, PT, DPT, is a practicing physical therapist at The Orthopedic Specialty Hospital, a division of Intermountain Healthcare, and a graduate student in the MS Clinical Investigation program at the University of Utah in Salt Lake City. Jesse C. Christensen, PT, DPT, SCS, is a practicing physical therapist at The Orthopedic Specialty Hospital and a PhD student within the Department of Physical Therapy/Orthopaedics at the University of Utah.
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