* Natalie L. Leong, MD, Baltimore VA Medical Center, 10 N Greene St, Baltimore, MD 21201 (email: vog.av@gnoel.eilatan) (Twitter: @NatalieLeongMD).
M.Z. and N.L.L. contributed equally to this work. Copyright © 2021 The Author(s)sj-docx-1-sph-10.1177_19417381211032949 – Supplemental material for Rehabilitation Principles to Consider for Anterior Cruciate Ligament Repair
GUID: 495998CA-F7D9-4AA3-890A-3B865D143A30Supplemental material, sj-docx-1-sph-10.1177_19417381211032949 for Rehabilitation Principles to Consider for Anterior Cruciate Ligament Repair by Jocelyn Wu, Jamie L. Kator, Michael Zarro and Natalie L. Leong in Sports Health: A Multidisciplinary Approach
Injury to the anterior cruciate ligament (ACL) is among the most common orthopaedic injuries, and reconstruction of a ruptured ACL is a common orthopaedic procedure. In general, surgical intervention is necessary to restore stability to the injured knee, and to prevent meniscal damage. Along with surgery, intense postoperative physical therapy is needed to restore function to the injured extremity. ACL reconstruction (ACLR) has been the standard of care in recent decades, and advances in surgical technology have reintroduced the prospect of augmented primary repair of the native ACL via a variety of methods.
A search of PubMed database of articles and reviews available in English was performed through 2020. The search terms ACLR, anterior cruciate ligament repair, bridge enhanced acl repair, suture anchor repair, dynamic intraligamentary stabilization, internal bracing, suture ligament augmentation, and internal brace ligament augmentation were used.
No exact consensus exists on effective rehabilitation protocols after ACL repair techniques, as the variation in published protocols seem even greater than the variation in those for ACLR. For some techniques such as internal bracing and dynamic interligamentary stabilization, it is likely permissible for the patients to progress to full weightbearing and discontinue bracing sooner. However, caution should be applied with regard to earlier return to sport than after ACLR as to minimize risk for retear.
More research is needed to address how physical therapies must adapt to these innovative repair techniques. Until that is accomplished, we recommend that physical therapists understand the differences among the various ACL surgery techniques discussed here and work with the surgeons to develop a rehabilitation protocol for their mutual patients.
Keywords: anterior cruciate ligament repair, bridge-enhanced ACL repair, suture anchor repair, dynamic intraligamentary stabilization, internal bracing, postoperative rehabilitation, physical therapy
The ACL is the most commonly injured ligament in the knee, with approximately 100,000 to 200,000 injuries per year in the United States alone, an incidence rate that has steadily increased since the past century. 30,75 Because of the ACL’s poor innate healing capacity, surgical intervention for ACL ruptures is indicated to restore knee stability and allow for return to near preinjury levels of activity. 49,58,76 ACL reconstruction (ACLR), with autologous or allogenic graft to replace the deficient ACL is currently the standard of care. Despite the success of ACLR, there remains a high rate of reinjury, surgical site pain, suboptimal performance on return to sport, and shortened athletic careers. 13,18,20,31,90
Bone-patellar tendon-bone (BTB) and hamstring autografts are common graft choices for athletes but are associated with donor site morbidities such as pain or weakness. 96 BTB can result in pain while kneeling and associated anterior knee pain while hamstring autograft can result in hamstring muscle weakness. 96 Conversely, allografts circumvent the additional donor site risks, but they have been associated with higher rates of failure and carry a risk of disease transmission posed by allogenic tissue. 90 Because of the limitations associated with obtaining grafts for reconstruction, there is renewed interest in preserving and repairing the native ACL to minimize adjacent tissue damage and outcomes. 44,53
The goal of primary repair is to reapproximate the torn ends of the ACL resulting in a healed ligament that appears histologically alike that of a spontaneously healing ligament. 66,67,70 However, the native ACL has poor healing potential because of its postinjury instability, lack of vascularity, and harsh synovial intraarticular environment. 49 The first stage of ligament healing, inflammation, is dependent on initial clot formation in damaged tissue. The clot catalyzes local inflammation and serves as a scaffold for further healing via recruited extrinsic inflammatory cells. Clot formation is essential for initiation of the healing cascade and is dependent on local vascularity. 11,49,59,63,92,93 Thus, poorly vascularized tissue, such as the mid portion of the ACL, has poor innate healing ability. 93 Multiple studies, both basic science and clinical, have suggested that the ACL has some degree of healing potential for acute tears that occur in the proximal ACL. 21,33,67,78 Thus, most ACL repair techniques are indicated for Sherman type I ACL tears where there is sufficient tissue length and quality to allow for reapproximation to the femoral footprint. 42 Repair techniques have sought to stabilize the tissue and address these issues in various ways, either by introducing bio-scaffolding to facilitate cellular migration, or by directing repair efforts toward more vascularized portions of the tissue. When clinically appropriate, primary repair has demonstrated improvement in subjective and objective outcomes in restoring function in select patients over ACLR. 54,74,80,84,88 This may be beneficial both functionally and structurally as it allows for vascular and proprioceptive structures to be retained. 10 In the past decade, advances in surgical technology have allowed for the pioneering of several repair techniques. 80
Regardless of surgical approach, postoperative rehabilitation is critical for a full, successful recovery. 4,35,57,85,95 These goals should be determined within the context of surgical technique and be designed to regulate strain on the healing ACL graft or repair. 15,65 Repair techniques aim to minimize tissue damage and may allow an accelerated rehabilitation. However, there is no consensus of what these postoperative protocols should entail. 10,89 The purpose of this review article is to compare and contrast the current surgical techniques for ACLR and ACL repair and the available literature on their respective rehabilitation protocols (Appendix Table A1 available in the online version of this article). We also highlight the rehabilitation considerations as it pertains to the surgical techniques.
From open arthrotomies to arthroscopies, and the introduction of allografts, primary ACL repair and ACLR ( Figure 1 ) has seen many paradigm shifts since its rise to popularity in the 1970s. 16,72 By the early 1990s, clinicians began to note poor long-term outcomes associated with primary ACL repair, ultimately leading to the development of the Sherman classification for ACL tears. 27,45,78 Although proximal avulsions of the ACL from the femoral insertion, classified as Type 1 tears, had better outcomes after primary repair than more distal ruptures, 33,78 repair techniques were nearly abandoned in favor of reconstruction. In the past decade though, innovative surgical technologies and skills have allowed for a resurgence in the use and study of repair techniques.
Depiction of anterior cruciate ligament reconstruction with graft pictured inserting in femoral and tibial tunnels.
Suture anchor repair (SAR) relies heavily on the native ACL’s innate healing ability. In this procedure, the native ACL is repaired and anchored in the femur, without additional construct reinforcement ( Figure 2 ). The methodology is based on the observation that the proximal ACL heals similarly to the medial collateral ligament, a ligament with known excellent healing capacity. 67 As such, SAR is only indicated for Sherman type I proximal tears with otherwise excellent tissue quality. 40 This procedure is unique because it does not require the drilling of a tibial tunnel. However, the pattern of tear amenable to SAR is rare, accounting for only 5.7% to 9.8% of overall ACL injuries. 1,23
Depiction of suture anchor repair with femoral anchors securing the repaired anterior cruciate ligament.
Internal bracing utilizes innovated synthetics to provide additional strength to the healing tissue. These techniques are in the literature under internal brace ligament augmentation (IBLA), suture ligament augmentation, or suture tape augmentation. 19,32,80,91 All rely on similar construct and methodology of using polyethylene tape as an internal brace within the repaired ACL ( Figure 3 ). Biomechanical models have shown its stabilization potential at loads occurring during normal daily activity. 6 In general, IBLA and suture ligament augmentation techniques involve primary repair of the ruptured ACL, with addition of the internal brace for added strength. Mackay and colleagues have been performing IBLA for nearly the past decade and have reported long-term follow-up data on dozens of patients. 38,52,91 The stability and strength provided by internal bracing is not limited to primary repair and variations in the technique have been described as well. 50,79,84,87 Internal bracing is reserved for Sherman type I proximal ruptures with good tissue quality. 52
Depiction of internal brace repair with synthetic tape bracing the repaired anterior cruciate ligament.
Dynamic intraligamentary stabilization (DIS) seeks to maximize healing of the native ACL by decreasing anterior translation of the tibia, thus bringing the two ends of the ACL stump closer together. 46,47 The DIS construct consists of a tibial preloaded spring that tensions a transosseous suture used to reduce the torn ACL to its femoral footprint ( Figure 4 ). 24,46 However, outcomes have been mixed, with rerupture occurring in 4% to 15% of patients, and an overall re-intervention rate of 40% to 50%. 53 Notably, DIS may be performed on any tear classification, including mid substance ruptures. 5,8,12,37
Depiction of dynamic intraligamentary stabilization with tibial spring-loaded construct traversing the repaired anterior cruciate ligament.
For the DIS technique, the tibial remnants of the torn ACL are reduced to the femoral footprint by transosseous sutures to allow for anatomical repositioning. 24 The femoral footprint undergoes extensive microfracturing, and a strong braided polyethylene cord is passed from behind the tibial footprint to the femoral side, through the anatomical footprint and secured with a button. This approximates the two ends of the ruptured ACL. The cord is brought under tension by a spring-screw implant (Ligamys, Mathys Ltd), which is placed on the anteromedial aspect of the tibia. 24
Bridge enhanced anterior cruciate ligament repair (BEAR) seeks to augment the poor healing response of native ACLs via a collagen bio-scaffold. The torn ACL’s lack of vascularity prohibits the necessary initial clot formation. 11,49,59,63 Modeled after the physiologic scaffold observed in healing medial collateral ligaments, the BEAR scaffold is composed of bovine extracellular matrix proteins. 29,43 When combined with intraoperative autologous blood or platelet-rich plasma, the scaffold optimizes clot formation and cytokine release. 61,70 In its first-in-human trial, the BEAR procedure, performed on mid-substance ACL injuries, produced similar outcomes to ACLR at 2-year follow-up, without significant adverse events. 60
In the BEAR procedure, 70 tibial and femoral tunnels are drilled through part of the ACL footprint. An arthrotomy is made at the medial border of the patellar tendon, and a whipstitch is placed into the tibial stump of the torn ACL. A cortical button with 2 sutures in addition to the suture from the ACL stump are passed through the femoral tunnel and engaged on the lateral femoral cortex. The 4 matched ends of the sutures are passed through the scaffold and through the tibial tunnel. Then, 10 mL of autologous blood is added to the scaffold. The scaffold is then passed up along the sutures into the femoral notch. The sutures are pulled distally and tied over a second cortical button on the anterior tibial cortex with the knee in full extension. The free ends of the suture from the ACL whipstitch coming through the femur are tightened and tied over the femoral cortical button ( Figure 5 ). 61
Depiction of bridge-enhanced anterior cruciate ligament (ACL) reconstruction with bio-scaffold encircling the repaired ACL.
The goal of postoperative rehabilitation is to restore knee function in preparation for activity or sport. Traditionally, postoperative protocols follow a timeline based on the healing and restoration process of the graft. Many of the studies describe the “standard ACLR rehabilitation protocol”; however, there are inconsistencies in what this entails. 30 For the purposes of this review, we will use points made by the Cavanaugh and Powers 2017 review and the Multicenter Orthopaedic Outcomes Network (MOON) guidelines to define the standard protocol for ACLR, summarized in Appendix Table A2 (available online). In the following sections, we describe the main points of consideration in physiotherapy protocols and compare them with the various surgical techniques (summarized in Appendix Table A3 available online).
In the short term, bracing is used to reduce pain, 94 immobilize the joint, and/or limit range of motion (ROM) after surgery. It may also protect the graft site by limiting varus and valgus stresses and restricting ROM. 10,94 Functional bracing on return to sport may help to protect from future injury 94 ; however, it should be noted that the American Academy of Orthopedic Surgery does not recommend routine functional bracing given the lack of evidence supporting its benefits. 14,94
After ACLR, there are mixed beliefs about the benefits of bracing. 2,74,94 A 2008 survey of orthopaedic surgeons showed that globally most recommended bracing for 1 to 3 weeks. 17 After the BEAR procedure, use of a locking hinged brace was recommended for 6 weeks as the repaired ligament and scaffold is initially fragile. 60 -62 Similarly, after SAR, bracing was done for the first 4 weeks to protect the early repair. 3,34 Alternately, the DIS and IBLA constructs are inherently stable and a short period of bracing until quadricep control is restored or even no bracing has been described. 5,12,24,48
ROM guidelines exist to minimize excess stress on the healing graft or repair, but with the ultimate goal of restoring symmetrical motion as compared with the uninjured knee. 10,83
After ACLR, early full extension is advocated along with progressively increasing flexion. 15 This principle holds true for repair approaches as well. After BEAR, the authors suggest limiting knee flexion to 50° for 2 weeks then to 90° for the next 4 weeks. 60 -62 These restrictions minimize stress across the repair, which is held together by only sutures. DIS and IBLA protect the repair to allow for immediate ROM without formal restriction. 5,12,24,41,48,53,59 On the other hand, there are inconsistencies in reported ROM guidelines after SAR, with Achtnich et al 1 limiting flexion to 90° until week 6, but DiFelice et al 21 -23 allowing progression of ROM immediately after surgery.
Weightbearing (WB) progression allows the joint to accommodate to increased loads in a safe manner. Assistive devices, such as crutches, are used to promote normal gait, and abandoned once the patient builds adequate quadricep strength. 15 Immediate partial WB is known to be safe after isolated ACLR 81 and is associated with decreased patellofemoral pain. 95 However, there is variability in practice, with only 50.3% North American orthopaedic surgeons recommending immediate WB after surgery. 17 After repair techniques, WB recommendations vary to account for the initial strength of repair. For example, after BEAR, partial WB was prescribed for 2 weeks followed by weightbearing as tolerated (WBAT) until week 4. 60 -62 After DIS, WBAT or a quick transition to full WB may be allowed immediately as the stabilizer applies continuous tension on the tibia. 12,37,48 Similarly, full WBAT may be allowed immediately after IBLA, as the repair is inherently stable. 19,32,56,82 Instructions after SAR are variable, with Achtnich et al 1 recommending conservative partial WB with crutches for 6 weeks and DiFelice et al 21 -23 allowing immediate WBAT.
Neuromuscular and proprioceptive training is extremely important to protect the graft from stress and enhance dynamic stability of the knee. 10,73 Techniques may include balance boards, unstable surfaces, perturbation training, and Theraband exercises. 15,95
Neuromuscular and proprioceptive training generally begins 2 to 4 weeks post-ACLR, or whenever walking is possible without crutches to promote limb control. 28 MOON guidelines recommend incorporating neuromuscular and proprioceptive training into all phases of rehabilitation. 95 After BEAR, neuromuscular and proprioceptive training recommendations followed the MOON. 60 After IBLA, DIS, and SAR, there was no specific mention of proprioceptive and neuromuscular training included in their postoperative protocols; however, it is logical that this type of training is critical to maximize recovery. 32,42,82
Exercise programs aim to reestablish muscle strength, power, and endurance. This is particularly important as leg strength is a key factor used to determine return to play (RTP) and is related to quality of motion. 10 After ACLR, closed kinetic chain exercises are generally considered safe, as they promote strengthening while minimizing stress on the ACL. 15 Open kinetic chain (OKC) exercises are controversial, as they may stress the graft. 69 Initial restriction of OKC knee extension exercises may begin with ROM to 90° to 45° to prevent graft elongation and progress to full ROM as the graft matures. 69 At 12 weeks, plyometric and return-to-sport exercises are incorporated, after a stepwise progression. 15
After BEAR, specific guidance on exercise prescription mirrors protocols after ACLR. 60 -62 The DIS construct supports the healing ACL through ROM and approaches that allow exercise as tolerated have been described. 5,12,37 After IBLA, early strengthening to tolerance is advocated as well. 32,82 However, MacKay et al 52 held OKC exercises until week 6 using an approach similar to what is described after ACLR. There are considerable variations in exercise instructions after SAR. The lack of additional internal construct in SAR suggest that exercise approaches should focus on initial protection of the healing ligament. For example, Bigoni et al 9 recommend early isometric co-contraction of quadriceps and hamstrings, closed kinetic chain exercises, and pool therapy starting at week 4 and delaying OKC exercises and plyometrics until at least month 3. 9
Returning to running is a critical step in rehabilitation. Common criteria to begin running include full or near full ROM, minimal to no effusion, quadriceps strength limb symmetry index >80%, 71 and adequate motor control during step down task. 15 Initiating a running progression of introductory drills or partial body weight running has been described as early as week 7 post-ACLR. 95 Full return to run over ground typically occurs at 3-months postoperation, 95 with progression that gradually increases speed and distance. 15 There is consistency across all surgical techniques of BEAR, 62 IBLA, 32,52,79,82 and SAR, 21 -23,40,42 all reporting similar criteria and return to running timing of 3 months. The DIS literature is slightly more aggressive and generally allows for initiation of running between weeks 6 and 10. 5,12,37
RTP is a controversial topic as the patient must demonstrate adequate physiological healing and functional control of their limb. 95
After ACLR, initiation of the RTP process generally occurs at 6 to 9 months. 95 Sport specific training often begins between weeks 17 and 20 postoperatively and continues until the patients demonstrates the appropriate functional capacity to progress in to unrestricted sport. 32 Official clearance for RTP are based on results of functional tests of strength, power, and stability compared with noninjured knee, 28 and subjective ratings of function. 95 RTP criteria after BEAR, 62 DIS, 5 IBLA, 32,42,82 and SAR 9,21 -23,40,42 are similar to those after ACLR. Some authors reported earlier RTP, such as return to pivoting sports at 20 weeks post-IBLA 38 or 12 weeks post-DIS. 24 Eggli et al 24 permitted return to competitive soccer and skiing 20 weeks post-DIS. 24
Novel ACL primary repair techniques have shown promising results 1,22,53,68,88 in treatment of ACL rupture; however, there is no consensus on rehabilitation protocols. There is a wide variability on recommendations regarding bracing, ROM restrictions, WB status, exercise progression, and return to sport. As these techniques become more popular, there is a need for orthopedic surgeons and physical therapists to collaborate and provide optimal rehabilitation guidelines in a technique specific manner.
Our review findings are similar to those of a recent survey of the members of the European Society for Sports Traumatology, Knee Surgery and Arthroscopy that highlighted the lack of agreement in the preferred rehabilitation protocol after ACL repair. 89
Bousquet et al 10 developed a criterion-based progression of rehabilitation that is based on physiological healing frames for ACL primary repair. Although they identified reference points for recovery, this protocol is not necessarily generalizable to all repair techniques. Each of the repair techniques mentioned in this review article are unique and have implications for the strength of the repair at various stages of recovery. It is important for rehabilitation professionals to familiarize themselves with novel repair techniques and consider how various movements or exercises will strain the ACL and affect the healing tissue.
For example, use of WB restriction or bracing in the immediate postoperative period is helpful to protect the healing repair from excessive forces as the knee may lack dynamic stability because of pain, swelling, or reduced quadriceps control. Benefits of ACL repair include preservation of the native tendon along with its proprioceptive elements and a lack of associated donor site morbidity as there is no need to harvest a graft. 77,80,88 This may result in reduced pain or swelling and improved quadriceps function, allowing for smoother progression through the early stages of rehabilitation and minimize the need for external support from crutches or a brace. 12 Coupled with the external support provided by IBLA and DIS, patients after these procedures may be able to be full WB and discharge use of their brace rather quickly and allow their symptoms guide the progress. However, after BEAR or SARS, the repair site is inherently less stable and despite self-perceived improvement, use of crutches or a brace should be recommended for longer periods.
In the context of exercise rehabilitation, anterior tibial shear is thought to stress the ACL as peak ACL strain occurs between 10° and 30° of knee flexion during OKC knee extension exercise. 26,51 It is unclear how these stresses impact the healing of an ACL reconstructed with graft tissue or repaired ACL with any of the techniques described earlier. Therefore, use of OKC exercise is controversial and though beneficial for improving quadriceps strength, should be used with caution. 7,36,69 After IBLA and DIS, there is external support applied to the repair, suggesting that OKC may be appropriate in the early stages as the support will prevent excess strain on the graft. 56 It is possible that full ROM OKC knee extension exercises may be appropriate to initiate immediately after surgery. However, after SARS or BEAR, the lack of external support may result in excessive strain or lengthening on the graft if OKC knee extension exercises are used before repair maturation. Therefore, OKC knee extension exercises should be used cautiously or in restricted ROM (90°-30°) to avoid strain to the repair in the early stages of rehabilitation.
Conversely, inducing a posterior tibial shear force has been linked with unloading or protecting the ACL. Exercises that target the soleus and hamstrings should be emphasized as they promote posterior tibial shear and reduce strain on the ACL throughout all stages of rehabilitation in a progressive nature. 55 Examples include seated calf raises, hamstring curl variations, and hip hinge patterns.
The ACL also is subject to strain during common sporting activities of landing from a jump and cutting in positions of knee extension and abduction. Later stages of all ACL repair protocols should include neuromuscular training to increase knee flexion and reduce dynamic valgus during activities of daily living, landing, and change of direction tasks to offload the ACL. 25,39,64 Examples include training landing mechanics to enhance eccentric control of the quadriceps and hip abductors to avoid anterior shear and valgus moments at the knee and change of directions drills to improve trunk control and limb coordination.
In terms of return to sport, current strategies to determine readiness involve assessments of knee laxity testing, strength, hop function, balance, movement quality, patient-reported outcomes, and are similar to concepts used after ACLR. 15,28,86 Current American Academy of Orthopedic Surgery guidelines do not recommend either achievement of milestones or postoperative timepoint as criteria for RTP. 14 It is important to recall that the reduced trauma to the knee during repair may result in reduced swelling and pain in the early postoperative stages; however, this does not mean that a less invasive surgery should result in a faster return to sport. The criterion-based RTP process should assess all relevant components of knee function to determine overall readiness.
Overall, our review found many similarities and differences among primary repair techniques and postoperative protocols. We recognize that many of these techniques are still in their infancy however more thorough reporting of postoperative protocols and their rationales should be advocated for. Currently, we strongly recommend that rehabilitation professionals take the time to understand the surgical approaches to ACL repair detailed here and attempt to devise individualized rehabilitation protocols in collaboration with the referring surgeon. These protocols should include specific instructions for use of bracing, WB restrictions, exercise selection, running, sporting activities, and return-to-sport criteria that are based on surgical technique and the strength of the healing repair construct.
sj-docx-1-sph-10.1177_19417381211032949 – Supplemental material for Rehabilitation Principles to Consider for Anterior Cruciate Ligament Repair:
Supplemental material, sj-docx-1-sph-10.1177_19417381211032949 for Rehabilitation Principles to Consider for Anterior Cruciate Ligament Repair by Jocelyn Wu, Jamie L. Kator, Michael Zarro and Natalie L. Leong in Sports Health: A Multidisciplinary Approach
The authors report no potential conflicts of interest in the development and publication of this article.
This work was supported in part by Career Development Award Number IK2 BX004879 from the United States Department of Veterans Affairs Biomedical Laboratory R&D (BLRD) Service.
Clinical Recommendations: This study highlights the importance of tailoring physical therapy protocols to match the operative technique used to address ACL injury.
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