From a clinical standpoint, the long-term outcome of anterior cruciate ligament reconstruction is dependent on surgical and rehabilitation variables and although a substantial amount of clinical and biomechanical investigations have focused on the former, much less research has been directed at the latter. This is not surprising because successful anterior cruciate ligament reconstruction is dependent on many surgical variables that only recently have become well understood (selection of an appropriate graft material, proper positioning of the graft, adequate tensioning of the graft, reliant fixation); however, this presents a concern because optimal healing of an anterior cruciate ligament graft and knee also is dependent on rehabilitation. Although most would agree that the strains applied to an anterior cruciate ligament graft by body weight, muscle activity, and joint motion affect its healing response, there is little consensus regarding how these factors influence the biomechanical behavior of the healing graft and, in turn, how this modulates its healing response.
The objective of the current study was to review the current knowledge regarding the effect of rehabilitation activities on the normal anterior cruciate ligament (data that are useful for establishing the basis of rehabilitation programs), the basic science of the healing response of anterior cruciate ligament grafts, and clinical investigations of the healing anterior cruciate ligament graft and knee.
Biomechanics of the Normal Anterior Cruciate Ligament
Recognizing that it is important to understand the biomechanical behavior of the normal anterior cruciate ligament before developing criteria for reconstruction and rehabilitation of a healing anterior cruciate ligament graft, a technique to measure the strain behavior of the normal anterior cruciate ligament in vivo was developed. 10 The primary objective of this work was to develop clinical criteria for reconstruction and rehabilitation of this important structure that are based on normal muscle function and include the loads produced by body weight. Study participants were patient volunteers with normal anterior cruciate ligaments and no history of ligament trauma who were candidates for diagnostic arthroscopic surgery done under local anesthesia, allowing them full control of their leg muscles. After completion of the surgical procedure that typically involved treatment of a meniscus tear, a Differential Variable Reluctance Transducer (DVRT, MicroStrain Inc, Burlington, VT) was attached to the anterior cruciate ligament to measure its strain behavior. 10 The strain behavior of the anterior cruciate ligament during common rehabilitation activities such as isometric contraction of the quadriceps, 11 isotonic contraction of the quadriceps, 11,13 squatting, 13 bicycling, 25 stair climbing, 26 and while various loads were applied to the knee fitted with a functional brace 12,16,27 have been studied. Rehabilitation exercises that involve isometric contraction of the hamstring muscles, do not strain the anterior cruciate ligament at any knee position or magnitude of muscle contraction. In contrast, exercises that engage the powerful extensor mechanism produce anterior cruciate ligament strain values that depend on knee flexion angle and the magnitude of muscle contraction. Specifically, isometric exercises that strain the anterior cruciate ligament involve contraction of the dominant quadriceps muscle group with the knee between extension and 60° flexion, or involve isotonic contraction of the quadriceps between extension and 50° flexion. The largest anterior cruciate ligament strain magnitudes that have been measured are produced by isometric and isotonic contraction of the quadriceps muscles with the knee near extension. Increasing resistance during active flexion and extension motion of the leg, and open kinetic chain exercise that does not incorporate body weight loading and does not involve appreciable cocontraction of the muscles spanning the knee, generates a significant increase in anterior cruciate ligament strain values. In contrast, increasing resistance during squatting, a closed kinetic chain exercise that involves body weight loading and substantial cocontraction of the muscles spanning the knee, does not create an appreciable change in anterior cruciate ligament strain values. A similar finding was shown for stationary bicycling, another closed kinetic chain exercise; during this activity, different levels of resistance (power settings of 75, 125, and 175 W) and pedal speeds (cadences of 60 and 90 rpms) produced similar anterior cruciate ligament strain values. 25 These findings indicate that rehabilitation after anterior cruciate ligament reconstruction with closed kinetic chain exercises such as squatting and bicycling permits increased muscle activity without subjecting the anterior cruciate ligament to increased strain values.
The previously mentioned anterior cruciate ligament strain data are a portion of a comprehensive database that includes a ranking of exercises based on the peak strain values produced during the respective activities, which can be used as the basis for rehabilitation of healing anterior cruciate ligament grafts (Table 1). It is important to emphasize that the limits of strain that are safe for an injured ligament or healing graft currently are unknown. Although the current authors cannot identify which exercises are either safe or harmful, these data have been used to design anterior cruciate ligament rehabilitation programs that are being compared in a prospective, randomized, double blinded trial. With adequate followup, this should help identify those exercise programs that are safe for a healing anterior cruciate ligament graft.
Biomechanical Studies of Healing Anterior Cruciate Ligament Grafts
Studies of healing anterior cruciate ligament grafts that have been done using animal models provide insight into the biologic remodeling and biomechanical behavior of the graft during healing 14; however, application of the findings from these studies to the clinical environment and rehabilitation of a healing graft must be done with caution because knees in animals are different than those in humans, and they have an uncontrolled rehabilitation regimen.
Butler et al 20 used the primate model to show that an anterior cruciate ligament graft undergoes a large decrease of its ultimate failure strength and linear stiffness during the first 6 weeks of healing, and with time the structural behavior of the graft improves, although it never returns to that of the normal anterior cruciate ligament. Studies of anterior cruciate ligament reconstruction using the patellar tendon autograft in canine, goat, rabbit and primate models have reported ultimate failure loads that range between 11% and 50% of the control anterior cruciate ligament, and stiffness values that range between 13% and 57% of normal after 1 year or more of healing. 6,43 Likewise, investigations of anterior cruciate ligament reconstruction with an iliotibial tract autograft have revealed ultimate failure load values that range between 23% and 40% of the normal anterior cruciate ligament although stiffness was reported to be 45% of normal. 43
Recognizing that an anterior cruciate ligament graft must have adequate structural properties and control anterior displacement of the tibia relative to the femur, several investigators have used animal models to measure the anteroposterior (AP) load-displacement response of the knee (AP laxity) during graft healing. 6,33,43 Hulse et al 33 revealed that anterior cruciate ligament graft healing is not only associated with a decrease in the structural properties of the graft, but also is accompanied by substantial increases of anterior displacement of tibia relative to the femur. Investigations of the healing patella tendon autograft done in animals have shown that AP joint laxity ranges between 156% and 269% of the contralateral normal side after 1 year of healing. 6,14,33,43 Therefore, investigations of anterior cruciate ligament grafts that have been done in animals indicate that they lose their ultimate failure strength and undergo a decrease of stiffness, and the knees have an increase in anterior laxity develop during healing. The exact cause of these changes and the application of these data to humans are unclear. For example, Rougraff and Shelbourne 49 reported that between 3 and 8 weeks after transplantation, a substantial portion of the graft remained histologically similar to patellar tendon tissue. This led the investigators to suggest that a large proportion of the original tendon survives and that anterior cruciate ligament graft healing in humans may not undergo the same complete necrotic stage that has been reported to occur in animals. 3,44 Additional evidence of dissimilarity of the healing response of anterior cruciate ligament grafts between human and animals can be seen in a case study of a 37-year-old man who had anterior cruciate ligament reconstruction with a bone-patella tendon-bone autograft and 8 months of healing. 15 The ultimate failure load and linear stiffness properties of the graft approached that of the contralateral normal anterior cruciate ligament, and AP laxity of the reconstructed knee was somewhat larger than the normal knee. Compared with the aforementioned animal studies of the biomechanical behavior of healing anterior cruciate ligament grafts, the biomechanical behavior of the reconstructed knee and bone-patellar tendon-bone graft that were measured in the human seem to be superior.
Increased anterior knee laxity is a concern because it is associated with altered contact loading of the tibiofemoral articulation, and this was the motivation for a study of the relationship between AP knee laxity and the structural properties of healing patellar tendon autografts used to reconstruct the anterior cruciate ligament in a canine model. 14 An inverse correlation was established between the structural properties of the anterior cruciate ligament graft (characterized by the ultimate failure strength, and linear stiffness values) and increased anterior knee laxity. Increased anterior knee laxity was correlated with a decrease in the structural properties of the anterior cruciate ligament graft. This finding indicates that clinical studies that show increased anterior displacement of the tibia relative to the femur during graft remodeling may reflect a graft that has inferior structural properties. Unfortunately, the mechanism that created the inverse relationship between increased anterior knee laxity and the structural properties of the graft was not described. It may be that this was produced by surgical variables that were not controlled. Alternatively, it may be that the increase of anterior knee laxity was produced by excessive graft strain during healing that led to permanent elongation of the graft.
Studies of tendon repairs have revealed that controlled loading can enhance the quality and rate of healing. For example, matrix collagen and repair cells become aligned with the axis of load applied to a healing tendon repair, whereas in the absence of load the matrix and repair cells become disorganized. 1,5 In addition, controlled loading after medial collateral ligament injury also enhances the healing repair site by increasing the wet and dry weight of the injured ligament, and inducing the rapid return of normal tissue deoxyribonucleic acid content, collagen synthesis, and strength. 4,28,40,54 In contrast, excessive loading has the potential to disrupt a healing ligament and may inhibit repair, particularly in a knee with combined injuries. For example, a study of healing medial collateral ligaments in rats with otherwise stable knees revealed that forced exercise increased the strength and stiffness of the ligament repair and those animals with unstable joints did not suffer a change in structural properties of the ligament, but instead had increased joint instability develop. 19 Tendon repair combined with 3 weeks of mobilization results in a construct with a twofold increase in failure strength compared with the same repair with 3 weeks of immobilization when evaluated 12 weeks after the index injury. 29 Most of what is known about the biology of healing connective tissue has come from studies done on injured medial collateral ligaments and tendons, both of which are extraarticular structures, and it is unclear how the findings from these studies relate to healing intraarticular tissues such as an anterior cruciate ligament graft.
Retrospective and Observational Studies of Anterior Cruciate Ligament Rehabilitation
Basic science and clinical investigations of subjects after anterior cruciate reconstruction have revealed that immobilization of the knee, or limited motion without muscle activity, results in an unwanted outcome (inferior structural and material properties) for the structures that surround the knee (ligaments, cartilage, bone, and musculature). 2,5,31,35–37,39,45,55 Early joint motion after anterior cruciate ligament reconstruction certainly is beneficial, it leads to a reduction in pain, lessens adverse changes in articular cartilage, and helps prevent the formation of scar and capsular contractions that have the potential to limit joint motion. 18,38
A retrospective investigation of rehabilitation after anterior cruciate ligament reconstruction was done by Shelbourne and Nitz. 52 They showed that aggressive rehabilitation that included immediate walking with full weightbearing, and return to sports by 8 weeks was more effective than a conservative rehabilitation program. One quarter of the individuals in the aggressive and conservative treatment groups had a 3-mm increase in anterior knee laxity of the reconstructed side in comparison with the normal side. An increase of this magnitude is a concern from a biomechanical perspective because it is greater then 2.7 mm, or the side-to-side difference in AP knee laxity measured from subjects with normal knees. 22 However, it is unclear whether this increase is a concern from a biologic perspective; it may be that increases of knee laxity that are within certain limits of normal do not result in altered metabolism of the articular cartilage and meniscus, or produce additional intraarticular injury. There currently are no data that describe this relationship.
A retrospective study of early (2–6 months) versus late (7–14 months) return to activities that involve cutting was done by Glasgow et al. 30 Early return to activity did not produce an increased prevalence of reinjury. The subjects’ report of knee function and KT-1000 measurements of anterior knee laxity were similar between the two treatments.
Barber-Westin and Noyes 7 did a retrospective study of rehabilitation after anterior cruciate ligament reconstruction. Rehabilitation consisted of four separate phases, the first of which was an assisted ambulatory phase involving immediate continuous passive knee motion and partial weightbearing with crutch support until postoperative Weeks 7 to 9. The second phase was from postoperative Week 9 through Week 16 and consisted of early strength training. The third phase was from postoperative Week 16 through Week 52 and was comprised of intensive strength training. The fourth phase was the return to sport-specific activity. Fifty-four percent of the subjects who had anterior cruciate ligament reconstruction with a bone-patellar tendon-bone autograft experienced an increase in anterior knee laxity of 3 mm or greater as evaluated with the KT-1000 arthrometer. Half of these subjects had increased anterior knee laxity greater than normal within 1 year of the operation, whereas the remaining ½ experienced increases 1 year or later after reconstruction. Twenty-eight percent of subjects who had anterior cruciate ligament reconstruction with a bone-patellar tendon-bone autograft combined with an iliotibial band extraarticular procedure had an increase in anterior knee laxity that was greater than 3 mm. Again, ½ of these subjects sustained abnormal increases of laxity within the first year of surgical reconstruction, whereas the other ½ had abnormal increases in laxity after the first year of healing was complete. This investigation emphasizes the importance of following up subjects for a minimum of 2 to 4 years after reconstruction before establishing the merits of a particular reconstruction and rehabilitation protocol. Barber-Westin et al 8 did a subsequent observational study of rehabilitation after anterior cruciate ligament reconstruction with the bone-patella tendon-bone autograft using the same four phases of rehabilitation previously described. This was comprised of the assisted ambulatory phase that lasted until postoperative Weeks 4 to 8 and included partial weightbearing with the use of a cane or a crutch and closed kinetic chain exercises such as minisquats and toe raises, isometric quadriceps contraction, range of motion (ROM) exercises, and straight leg raises. The second phase (early strength training) occurred from Weeks 4 to 8 through Weeks 12 to 16, and added proprioceptive, balance, and gait training. The third phase varied depending on the subjects’ needs and took place between Weeks 12 to 16 and Weeks 24 to 52. This included running, stair climbing, and bicycling programs combined with progressive resistive exercises. Successful completion of the aforementioned phase qualified the patient for the fourth and final phase, return to sports. At 2-year followup, 85% of the subjects had KT-1000 arthrometer measurements of knee laxity that were less than 3 mm (injured minus normal differences), 10% had differences between 3 and 5.5 mm, and 5% had differences greater than 5.5 mm. This finding led the authors 8 to conclude that anterior cruciate ligament reconstruction with a bone-patella tendon-bone graft and the four-phase rehabilitation described results in an acceptable failure rate of 5%.
Howell and Taylor 32 did an observational study of anterior cruciate ligament reconstruction with the double-looped semitendinosus and gracilis graft. Rehabilitation included continuous passive motion for the first 1 to 2 days after surgery, followed by toe touch weightbearing for 3 weeks, unrestricted exercises after 4 weeks, running in a straight line after 8 to 10 weeks, and then return to sports after 4 months of healing. Evaluation of AP knee laxity with the KT-1000 manual maximum examination at the 4-month and 2-year followup resulted in differences in laxity that were 3 mm or greater in 18% and 11% of the subjects, respectively. At these same intervals, the incidence of a positive pivot test was 11% and 10%, respectively. Thigh girth and range of joint motion were similar at 4 month and at 2 years. From these findings, the authors concluded that unlimited return to sport and work activities 4 months after anterior cruciate ligament reconstruction with a double-looped semitendinosus-gracilis graft is safe and effective. 32
The findings from the retrospective and observational studies of anterior cruciate ligament rehabilitation should be considered with appreciation for the design characteristics associated with these approaches. For example, because inclusion and exclusion admission criteria were not established a priori, there is a potential for a susceptibility bias to be introduced. This bias could arise from comparing the outcomes of rehabilitation between groups of subjects that differ prognostically. Comparing patients with multiple ligament injuries (anterior cruciate ligament and medial collateral ligament injury, or anterior cruciate ligament and posterior lateral ligament complex injury), or combined articular injuries (meniscus or chondral lesions) with those who have an isolated anterior cruciate ligament injury all would yield a susceptibility bias. The findings from retrospective studies of rehabilitation also may be influenced by a performance bias that results from changes in the level of skill in doing a particular surgical procedure, or executing a rehabilitation program. A transfer bias also may exist when comparisons are made to a historic rehabilitation group that had a substantially longer followup. For example, it may be that as time progresses, anterior knee laxity increases for reasons other than the rehabilitation program or the subject’s activity level; other factors intrinsic to the biology of the healing graft that currently are unknown may influence the graft during an extended time. Control of the treatment being studied also is important if the eventual goal is to understand its effect on outcome. This is evidenced by the findings from a recent prospective, randomized, double blinded investigation of rehabilitation after anterior cruciate ligament reconstruction that revealed compliance with a clinic-based program varies between subjects and declines substantially with time (Fig 1). (Uh BS, Beynnon BD, Johnson RJ, et al: A prospective, randomized study of patient compliance with two rehabilitation programs following anterior cruciate ligament reconstruction. Presented at the Eighth Congress of the European Society of Sports Traumatology, Knee Surgery and Arthroscopy, Nice, France, 1998.) Subjects with acute, isolated anterior cruciate ligament disruptions had reconstruction with a bone-patellar-tendon graft and then were randomized to either an accelerated or conservative rehabilitation program. After 16 weeks of rehabilitation, there was no difference between the programs regarding the subject’s total compliance with the exercises that were prescribed (Fig 1). After this period, there was a significant decrease in compliance for both programs, and subjects attributed this to the length of the program. This finding is important because compliance with rehabilitation is a measure of the cumulative strains imparted to a healing graft, and in view of the fact that this biomechanical dose is directly linked to the healing response of the graft and knee, it is important for establishing the type of rehabilitation the subject had. For example, a subject could be considered to be in an accelerated rehabilitation program, and after participating for a week, have patellofemoral pain develop that limits his or her participation with aggressive exercises such as isolated contraction of the quadriceps with the knee near extension. Subsequently, he or she may self-select out of the program by altering the frequency and magnitude of the extension exercises, or even immobilize the limb. In effect, this would result in a program that was conservative. Conversely, disregarding the limitations of a conservative program could make it equivalent to a more accelerated program. Unless compliance is monitored during a clinical study of rehabilitation, it is very difficult to assess what a subject actually completes throughout the program, it is even more complex to evaluate how the graft is loaded during healing, and therefore, it may become unclear what effect the rehabilitation treatment being studied has on outcome. This is very difficult to recreate with a retrospective study design.
Prospective, Randomized Studies of Anterior Cruciate Ligament Rehabilitation
Noyes et al 46 did a prospective, randomized investigation of immediate versus delayed motion rehabilitation after anterior cruciate ligament reconstruction and revealed that continuous passive knee motion immediately after anterior cruciate ligament reconstruction did not lead to an increase in anterior knee laxity during healing. Subjects in the immediate motion program had continuous passive motion of the knee on the second postoperative day, whereas those in the delayed motion group had their knees placed in a brace at 10° flexion, and began continuous passive motion on the seventh postoperative day. Subjects in both rehabilitation programs reported similar incidences of joint effusion, hemarthrosis, soft tissue swelling, flexion and extension limits of the knee, use of pain medications, and time of stay in the hospital.
Rosen et al 48 did a prospective, randomized study of rehabilitation after arthroscopically-assisted anterior cruciate ligament reconstruction with a bone-patellar tendon-bone autograft. They extended the work of Noyes et al, 46 by showing that continuous passive motion during the first month after anterior cruciate ligament reconstruction compared with early active motion produced similar range of joint motion, and KT-1000 measurements of AP knee laxity.
Richmond et al 47 did a prospective, randomized study that compared the effects of continuous passive knee motion for 4 days versus 14 days after arthroscopically-assisted anterior cruciate ligament reconstruction with a bone-patellar tendon-bone autograft. They reported similar values of knee ROM and lower limb girth between treatment groups.
Jorgensen et al 34 did a prospective, randomized investigation of the effect of weightbearing after anterior cruciate ligament reconstruction with the iliotibial band. After surgery, subjects were randomized to rehabilitation with either immediate weightbearing or rehabilitation with nonweightbearing for 5 weeks followed by a gradual return to full weightbearing during the first 9 weeks of healing. At the 2-year followup, there was no difference between the groups regarding AP knee laxity, and patient activity level (evaluated with the Tegner and International Knee Documentation Committee scores). Similar findings were reported by Tyler et al, 53 who did a prospective, randomized investigation of anterior cruciate ligament reconstruction with a central third bone-patellar tendon-bone autograft followed by rehabilitation with either immediate weightbearing, or the same program but with a 2-week delay of weightbearing. Immediate weightbearing did not effect AP knee laxity (evaluated by clinical examination and KT-1000), and resulted in a decreased incidence of patellofemoral pain compared with rehabilitation with a 2-week delay of weightbearing. The findings from these investigations indicate that weightbearing immediately after anterior cruciate ligament reconstruction does not seem to produce excessive loads across a healing graft that permanently deform the graft or its fixation and is beneficial because it lowers the incidence of patellofemoral pain.
Bynum et al 21 did a prospective, randomized study that compared open kinetic chain versus closed kinetic chain rehabilitation after anterior cruciate ligament reconstruction with a bone-patella tendon-bone autograft. Immediately after surgery, the subject’s knees were placed in a rehabilitation brace that was adjusted to allow 0° through 90° motion, and started continuous passive motion from 0° to 60° flexion. Rehabilitation started on the first postoperative day and included passive and active motion of the knee without external resistance for all subjects. Partial weightbearing with the use of crutches was permitted, and subjects progressed to full weightbearing as tolerated. Subjects randomized to the open kinetic chain treatment group had rehabilitation with introduction of exercises in the following sequence: Weeks 0 through 3 (cocontraction isometrics, hamstring concentric and eccentric isotonics); Week 3 (straight leg raises with the knee at 30° flexion); Week 6 (isotonic quadriceps contraction with low resistance, biking, and proprioception training); Week 8 (isokinetic hamstrings); Week 12 (unrestricted isotonic contraction of the quadriceps); Week 16 (jogging, forward and backward running, and single-leg deep knee bends); Week 24 (unrestricted progressive resistance training, and isokinetic quadriceps contractions); Weeks 24 through 28 (progressive running and sport-specific activity); Week 32 (noncutting, pivoting, and jumping); and Week 52 (return to unrestricted sports). Those subjects randomized to the closed kinetic chain rehabilitation treatment had the following sequence: Weeks 0 through 8 (⅓ knee bends during double-leg stance, seated leg presses, and hamstring curls); Week 6 (stationary bicycling and proprioception training); Week 8 (⅓ knee bends during single-leg stance, forward and backward walking against resistance produced by the Sport Cord (Sport Cord Inc, Sandy, UT) with progression to slow jogging); Week 12 (continuation of previous exercises with the progressive use of a stiffer Sport Cord with the addition of side–to-side jumping against the resistance of the Sport Cord); Week 16 (sport-specific exercises against the elastic resistance produced by the Sport Cord, with addition of free weight leg presses and squats); Week 24 (progressive running and sport-specific activity); Week 32 (noncutting, pivoting, and jumping sports); and Week 52 (return to unrestricted sports). At a followup of 1 year or greater, the closed kinetic chain rehabilitation program produced KT-1000 arthrometer measurements of AP knee laxity that were closer to normal, and earlier return to normal daily activities, compared with the open kinetic chain rehabilitation program. The AP laxity values of the closed kinetic chain group that were closer to normal, compared with the open kinetic chain group, were attributed to lower strains on the healing graft. Subsequent study of the anterior cruciate ligament in vivo 13,25 confirmed this observation by showing that increasing resistance during closed kinetic chain activities such as squatting or bicycling does not significantly increase anterior cruciate ligament strain values compared with the baseline performance of the activity, whereas increasing resistance during open kinetic chain exercises such as isotonic contraction of the quadriceps produces significant increases of anterior cruciate ligament strain values. 10
Mikkelsen et al 41 did a prospective, randomized study that compared closed kinetic chain versus combined closed and open kinetic chain rehabilitation initiated 6 weeks after anterior cruciate ligament surgery. Six-month followup revealed that the addition of open kinetic chain exercises produced a significant improvement in quadriceps strength (evidenced by moderate improvements in extension torque), an earlier return to sport at the preinjury level, and did not effect KT-1000 arthrometer measurements of AP knee laxity.
More recently, two prospective, randomized studies were reported that compared rehabilitation with and without the use of a brace. 17,42 Rehabilitation with the use of a brace during the first 3 weeks after surgery resulted in fewer problems with swelling, a lower prevalence of hemarthrosis and wound leakage, and less pain throughout the early recovery period in comparison with rehabilitation without the use of a brace.
Three randomized controlled trials have been reported that showed that anterior cruciate ligament reconstruction with a bone-patella tendon-bone graft followed by a home-based rehabilitation program produces a similar outcome compared with reconstruction with the same graft material and clinic-based rehabilitation. 9,24,50 The most recent of these studies showed that subjects randomized to home-based rehabilitation had an average of five physical therapy visits (range, 3–7 visits) whereas those treated with clinic-based rehabilitation had 20 visits (range, 10–28 visits). Details were not presented regarding the specific activities and restrictions that were associated with both programs; instead a goal based approach was used with the following temporal sequence of activities: restoration of ROM, beginning strengthening, advanced strengthening, and then improvement of agility and speed. There was no difference between the treatments regarding physical examination (including ROM, thigh atrophy, Lachman test, anterior drawer and pivot shift examinations, and KT-1000 testing), one-leg hop, and the health status questionnaire.
The current review of the literature did not identify a consensus regarding what variables should be used to characterize a rehabilitation program, nor did it reveal how this information should be used to compare different programs, for example, to distinguish between an accelerated and conservative rehabilitation program. Consequently, for the purpose of this review, the authors considered anterior cruciate ligament rehabilitation as a series of activities (or restrictions) that a subject (knee) is directed to do, the time when the activities are recommended and the duration of the activities (the number or sets and repetitions per day, week, month), and the point when a subject is advised to return to sport or at risk activity. Most of the prospective studies that were reviewed clearly described the activities (restrictions) a subject was advised to do and the time that the activities were recommended. There was, however, little information presented regarding the frequency and duration of the activities and how well subjects complied with the program that was specified. Therefore, the authors’ interpretation of the literature is that there is some information available that derives from prospective, randomized clinical trials regarding how much loading and motion a knee with a healing anterior cruciate ligament graft can sustain without permanently stretching the graft (as evidenced by abnormal increases of anterior knee laxity), disrupting the graft, or creating failure of graft fixation, but that additional research is needed. For example, currently, it has become almost universally accepted that rehabilitation of a healing anterior cruciate ligament graft with rapid return to sports that have the potential to generate high stresses in the graft and knee does not lead to any deleterious effects, yet the current review revealed that relatively few studies actually have been published that advocate return to sports between 4 and 6 months after an anterior cruciate ligament reconstruction. 32,51,52 Six months after anterior cruciate ligament reconstruction patients walk with normal kinematics, but do so with dramatic alterations in torque and power about the hip and knee that have the potential to influence the graft and articular cartilage metabolism. 23 From this perspective there is little evidence in the literature that early return to sport is safe or efficacious. In contrast, the well-designed prospective study of closed versus open kinetic chain rehabilitation reported by Bynum et al 21 recommended initiation of noncutting, pivoting, and jumping activities at 8 months, followed by return to unrestricted sports at 1 year. No randomized clinical trial that compares accelerated rehabilitation with the more conservative rehabilitation ever has been published that indicates that there are no significant risks to what currently is termed accelerated rehabilitation. Although a prospective, randomized clinical study with blinding of the patient and the physician to the rehabilitation regimen is difficult to do, it is the only way that the biases that plague many of the studies that are now in the literature can be avoided. Until such a study or group of studies becomes available, there is reason to be concerned about the assumption that accelerated rehabilitation is appropriate. The authors encourage others to use prospective, randomized, blinded clinical trials that can lead to validation of the methods that are appropriate and safe. Only until this is accomplished can individuals speculate as to the effectiveness of any rehabilitation protocol or program.
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Kurt P. Spindler, MD; and Edward M. Wojtys, MD—Guest Editors