Introduction
Anterior cruciate ligament (ACL) injuries are one of the most common injuries seen by orthopedic surgeons and sports medicine specialists. Annually in the United States, there are 68.6 isolated ACL tears per 100,000 person-years. Worldwide there are roughly 1.4 million noncontact ACL tears annually. The ACL is subject to injury most commonly in sports that require movements such as cutting, pivoting, and jumping. These are significant injuries for both recreational and elite athletes alike, and these are associated with delayed recovery and/or inability to return to sport. In addition to the initial acute loss of function, even when the ACL is reconstructed the player then has a predisposition to early-onset osteoarthritis.
The highest incidence of ACL tears overall occurs in teenage female athletes. Age-specific patterns differ between males and females, with a peak incidence in males between 19 and 25 years of age (241.0 per 100,000) and the peak incidence in females between 14 and 18 years of age (227.6 per 100,000).
In the past 30 years, there has been a 10-fold increase in high-school and a 5-fold increase in collegiate sports participation by females. , As the number of females participating in high-level sports continues to increase since the passage of Title IX in 1972, the prevalence of ACL injuries is expected to increase as well. Prior to Title IX, fewer than 10,000 female athletes competed in collegiate sports. More recently, in the 2016–17 academic year, it was reported that there were a record-setting 494,992 collegiate athletes. In 2018, there were 10,586 women’s teams and 9159 men’s teams competing in the NCAA (National Collegiate Athletic Association) championship sports.
Although there is an overall higher number of ACL tears among male athletes than females, female athletes have a higher incidence rate of ACL injury. Multiple studies have shown that the relative risk of ACL injury in female athletes, compared to male athletes, is roughly 1.40–9.74. , Females in the military have been reported to have a relative risk of ACL injury of 2.44 when compared to males.
The increased incidence of ACL injuries in female athletes is most likely multivariate, stemming from mechanical, endocrinologic, and psychologic factors.
Mechanical Factors
Anatomically, the ACL is made up of two bands, the anteromedial and posterolateral, and extends from the region anterior to the tibial intercondylar eminence to the medial portion of the lateral femoral condyle. It works in conjunction with the surrounding muscles to stabilize the knee. With the knee in extension the posterolateral band is the tightest, and during knee flexion the anteromedial band is the tightest. During weight bearing, the ACL prevents the tibia from translating anteriorly. During flexion and extension moments, it works with the posterior cruciate ligament to control movement of the femur on the tibia. It also provides stabilization during internal rotation moments of the tibia and during varus and valgus stresses of the knee joint.
The miserable malalignment syndrome, consisting of a high quadriceps angle (Q-angle), increased pelvic width, anteverted femur, valgus knee, tibial external rotation, and pronated foot, is related to ACL injury. ( Fig. 2.1 ) Together, these individual factors create an environment that encourages extensor mechanism malalignment. This places strain on the patellofemoral joint and ultimately leads to pain. In 2003, Uhorchak et al. showed that other significant risk factors for ACL injury, aside from the miserable malalignment syndrome, include a small femoral notch width, generalized joint laxity, higher than normal body mass index, and anterior to posterior knee laxity values that were one standard deviation or more above the mean. This was further characterized in 2018 in a retrospective study that used magnetic resonance imaging (MRI) to look at anatomic risk factors associated with ACL injury. The group of ACL-injured patients was found to have a more narrow femoral intercondylar notch width index (<0.252), a larger β-angle (>38.5 degrees), and a larger lateral tibial slope (>7.5 degrees).
Femoral notch width and shape is related to the risk of ACL injury. van Eck et al. suggested that ACL injury is associated with the shape of the notch. Using arthroscopy, the authors defined three different notch shapes, which included A-shape, U-shape, and W-shape. Notches with an A-shape were found to be narrower in all width dimensions than the U-shaped variety. Patient height was correlated with notch shape, and there was a positive association with tall height and U-shaped and W-shaped notches. Females were found to have smaller notch widths at the base and in the middle.
A valgus knee is often implicated in knee injuries. Three-dimensional kinematic analyses have shown that while jumping, female athletes have a higher amount of knee valgus. A prospective study assessed 291 female high-school athletes newly enrolled in basketball and handball. They analyzed dynamic knee valgus during single-leg drop jumps. The participants were then followed up for 3 years specifically looking for ACL injury. In the injured group, there was a significantly greater amount of dynamic knee valgus. They concluded that dynamic knee valgus is a risk factor for noncontact ACL injuries in female high-school athletes.
A person’s Q-angle is the angle that is formed from the combined vectors for the pull of the quadriceps muscle and the patellar tendon. The average Q-angle in uninjured males is 12.1 degrees, and 16.7 degrees in uninjured females. This higher Q-angle in females increases the lateral pull of the quadriceps on the patella and potentiates disorders of the knee. Q-angles exceeding 15 degrees in males and 20 degrees in females are considered to be abnormal. An increased Q-angle may contribute to an increased risk for ACL injury by increasing the obliquity of the femur, increasing the knee valgus, and thus increasing the contact pressure applied to the patellofemoral joint. The ligament is under varying degrees of tension throughout all movements. There have been multiple studies that sought to establish an association between knee injury and Q-angle. Two of them showed that there was not a significant association. , However, there have been a couple of other studies that did note an association between Q-angle and increased risk for knee injury. , The opposing outcomes of these studies raise the question of how much a Q-angle measured in a static position correlates to dynamic motion such as in sports. When looking at collegiate basketball players, there was a significant difference in Q-angles between males and females, especially when measuring with the knee in 30 degrees in flexion. This is clinically relevant, because Xerogeanes et al. have shown that the greatest magnitudes of force on the ACL are incurred with the knee in 30 degrees of flexion. Thus having a larger Q-angle in this position is not favorable. This is likely multifactorial considering that Emami et al. also found that 16% of the males and 20% of the females who had an abnormally high Q-angle did not present with a knee injury.
Q-angle has also been associated with a larger moment of tibial internal rotation. Internal rotation of the tibia affects tibiofemoral contact forces and the force seen by the ACL during impact. In model simulations, it has been shown that ACL forces were highly correlated with contact forces on the anterior component of the tibiofemoral joint during impacts with larger knee abduction moments, internal tibial rotation, and larger contact forces.
In animal models, hamstring (HS) contraction helps resist anterior tibial shear force at 30 degrees in flexion, which reduces the amount of force on the ACL. This has also been shown in human subjects. , Activation of the quadriceps had the most significant effect on ACL strain. The HSs are activated independently from the quadriceps, and they act as a protagonist force to the ACL. When the HSs contract, they decrease the amount of anterior tibial translation and internal tibial rotation. They also reduce tension on the ACL, with the knee between 15 and 45 degrees of flexion.
When the pelvis is examined, females have a relatively wider and/or different shaped pelvis compared with males. Several authors have found a significant association between pelvic width and the risk of knee injuries in females. The structural differences of the wider pelvis in females are thought to increase the risk of knee injury by creating a larger coxa vara/genu valgum alignment, with a simultaneous increase in tibiofemoral rotation forces in the transverse plane, which ultimately places a greater force onto the ACL. , With the hip being the most proximal link in the lower extremity, excessive hip adduction and internal rotation while weight bearing affects the kinematics of the entire extremity below it. Hip adduction and internal rotation can cause the mechanical axis of the knee to move medially and results in dynamic knee valgus.
In addition to laxity of the knee, females also demonstrate increased joint laxity of the foot. Excessive pronation in the subtalar joint has been found to be common in the American population. This increase in ligamentous laxity of the foot has been brought up as a potential cause for increased navicular drop in females. Patients with an increased amount of pronation have been found to have an increased amount of knee rotation when the knee is flexed to 5 degrees. In the stance phase of the gait cycle, subtalar pronation and internal rotation of the tibia occur simultaneously and the ACL becomes taut as the tibia rotates. Navicular drop has been reported as a significant predictor of tibial translation by Trimble et al. They also suggested there was a relationship between increased subtalar joint pronation and increased anterior translation of the tibia. When increased navicular drop causes the tibia to move forward, this would ultimately place an increased amount of strain on the ACL. A couple groups have in fact shown that there was an association between increased subtalar joint pronation and ACL injury. They measured the navicular drop height from seated to standing in 22 athletes with an injured ACL and 22 control subjects with an uninjured ACL. What they found was that the subjects with an uninjured ACL dropped an average of 5.9 mm and the ACL-injured subjects dropped an average of 8.4 mm, which was statistically significant.
As early as 1982, differences in the transverse plane, in the form of femoral anteversion, have been discussed as a factor in ACL injuries. Greater femoral anteversion (as seen in females compared to males) as well as a smaller pelvic angle have been found to be a predictor of greater hip internal rotation and knee excursion. It is these motions, as described in this chapter, that play a significant role in the higher incidence of ACL injuries in female athletes.
There are likely multiple mechanical variables that factor into the increased ACL injury risk for females, as discussed earlier. One of the functions of the ACL is to prevent internal rotation of the tibia. When the knee is at 30 degrees of flexion, there is an increase in tibial internal rotation. At this position, there is also a decrease in the HSs-to-eccentric quadriceps strength ratio. This means that during deceleration with the knee at 30 degrees of flexion the joint is taking on two simultaneous forces that compromise the ACL.
Many of the forces on the knee and the ACL are easiest to describe in a static state. However, it is more realistic to think about forces during a dynamic movement. Motion perturbations (contact with another player) also likely have a role in altering the biomechanics associated with ACL injuries. During videographic and biomechanical analysis, it has been shown that motion perturbation changes an athlete’s coordination and movement. When looking at a group of injured basketball players, they all sustained their injuries while handling the ball and within the first 0–3 steps. During side-cutting in the presence of a nearby opponent, females were found to have greater amount of knee valgus, greater variability in knee valgus, an increase in foot pronation angles, and increased tibial internal rotation. Looking at hip biomechanics, females also had a decreased amount of hip and knee flexion as well as hip abduction during cutting. These results combined suggest that the dynamic lower extremity biomechanical changes at the hips, knees, and ankles play a significant role in the higher rate of ACL injuries seen in female athletes.
Biomechanical differences between genders, as described earlier, are further exacerbated by muscular fatigue. This increases the alterations in the trunk, pelvis, and lower extremity kinematics involved in injuries to the ACL. As shown in a study, when landing from a single-leg drop after being fatigued, males had a greater amount of trunk flexion than females. Males also had a decrease in peak knee flexion and a higher amount of gluteus maximus and biceps femoris activation than their female counterparts.
Neuromuscular Factors
There are many systems within the human body that operate automatically and subconsciously to maintain the body in its homeostatic state. One of these systems is the sensorimotor system, which incorporates all the afferent, efferent, and central integrating and processing components that are involved in providing functional joint stability during motion. A prior study showed that mechanoreceptor density in the ACL is highest at its most proximal and distal osseous attachments. About 1% of the ligament’s dry weight is made up of neural tissue.
A neurologic link between the cerebral cortex and the ACL has been documented using electroencephalographic signals by stimulating the ACL during arthroscopy. Following an injury to the ACL, multiple sensorimotor impairments may occur. These include proprioceptive deficits, decreased strength of the stabilizing muscles of the knee, and alterations in muscle activation onset patterns.
One proposed method to reduce ACL injuries is to implement a neuromuscular training regimen into adolescent female athlete training programs. In a large study looking at 23,554 female athletes, four variables were found to reduce ACL injury risk. The variables included a younger participant age, neuromuscular training performed for at least 20 min and at least twice per week, a greater number of exercise variations, and more usage of verbal feedback.
Endocrinologic Factors
A higher magnitude of knee joint laxity has been seen in females and has also been associated with a higher risk of ACL injury. There is a known correlation between estrogen and ACL laxity, as well as progesterone levels and ACL laxity. As the concentration of the hormones in the serum increases, so does ACL laxity (measured using a knee arthrometer). Estrogen concentrations in the blood fluctuate substantially during the menstrual cycle. Musculoskeletal function is closely related to estrogen concentrations. Estrogen works to improve muscle protein homeostasis and increases collagen content. These physiologic effects of estrogen have been shown to contribute to decrease in power and performance, which makes females more prone for injury.
It has been shown that females have about 25% overall decreased stiffness of the knee, 30% greater frontal plane (varus-valgus) knee laxity, and about 35% greater transverse plane (internal and external rotation) knee laxity compared with males. The previously described joint laxities that are greater in the frontal and transverse planes occur in females during low, externally applied loads and are most pronounced during initial loading of the knee joint.
Shultz et al. showed that females experience larger cyclic variations in anterior knee laxity, genu recurvatum, and generalized joint laxity compared with frontal and transverse plane laxity and stiffness. In addition, females have significantly greater overall transverse and frontal plane laxity and lower stiffness when than males. One study used the KT-1000 arthrometer to measure anterior-posterior knee laxity throughout the menstrual cycle and found that the fluctuations in cyclic estrogen and progesterone levels during menstruation do not have a defined relationship with anterior-posterior laxity of the knee joint. In another study by the same author, a case-control study of recreational alpine skiers was performed and it was found that the likelihood of sustaining an injury to the ACL fluctuates during the menstrual cycle. The risk of sustaining a disruption of the ACL is significantly greater during the preovulatory phase than the postovulatory phase.
Estrogen receptors are present in all musculoskeletal tissues, including ligament. Immunohistochemical localization was performed in 17 human specimens and showed that both estrogen and progesterone receptors were localized to fibroblasts in the ACL stroma and cells in the blood vessel walls of the ligament. These estrogen receptors have a relationship with the ACL and most likely have a periodic effect on ligament laxity. Acute cyclic variations in the menstruating female athlete have been shown to cause physiologic changes in fibroblast proliferation and procollagen synthesis, which are markers of collagen synthesis. During days of high estradiol concentration (days 1 and 3 of the menstrual cycle), subjects have been found to have a decreased amount of fibroblast proliferation. During days 7, 10, and 14 of the menstrual cycle, this effect was attenuated.
Multiple studies have shown a statistically significant association between noncontact ACL injury and the phases of the menstrual cycle. There is a significant increase in injuries in teenage female athletes during the ovulatory phase when compared to the other phases ( Fig. 2.2 ). It has even been shown that there is more laxity in the ankle joint during ovulation.
There is limited evidence that suggests oral contraceptive use in females may reduce the risk of injury to the ACL. However, there has yet to be any conclusion drawn regarding differences in ACL injury risk among oral contraceptive users and nonusers throughout different points of the menstrual cycle.
Genetic Factors
If one could predict an individuals’ risk for injury based on genomic testing, this would allow for identified predisposed athletes to undergo more specific prevention programs and perhaps guide future treatment technologies. It is known that type V collagen plays a crucial role in the regulation of size and structure of other fibrillar collagens that support many tissues in the body, which include ligaments such as the ACL. This collagen is coded by the COL5A1 gene, which is located on chromosome 9q34.3. Mutations of this gene result in a 50% reduction in the quantity of type V collagen, which leads to poorly organized fibrils, decreased tensile strength, and reduced stiffness of connective tissue. Prior studies have shown variants of multiple DNA genes that have been associated with an increased propensity for ACL injury. These include COL1A1, COL3A1, COL5A1, COL12A1, ELN, FBN2, matrix metalloproteinase, and genes encoding multiple proteoglycans.
While the aforementioned genes have been associated with ligamentous injury risk, there has not been translational work performed to figure out how to modify them. However, with the information we do have at this time, athletes and trainers theoretically are able to figure out those athletes who are most at risk for ACL injury and to work toward prevention.
Psychologic Factors
Elite athlete training requires special consideration. Performance efforts in high-intensity sports are defined by explosive strength and speed. Athletes use their mental fortitude to push past physical limits and commit to difficult goals and exceptional performance. Injury in these athletes is a stressful and adverse event. To improve the efforts of prevention and management of sports injuries among athletes, it is important to focus on athlete health and performance outcomes as well as psychologic factors. Career longevity and performance depend on both physical and mental health. Psychology and socioculture are both involved in sports injury risk, response, and recovery.
It has been shown that an individual’s expectations, motivation, and satisfaction before, during, and after rehabilitation after ACL reconstruction are associated with return to preinjury sport activity at 1-year follow-up. Prior to ACL reconstruction, most patients expect to return to their preinjury activity level. One study included 65 individuals (male and female) who underwent ACL reconstruction. Those who returned to their preinjury sport level were found to have been more motivated during rehabilitation. They were also more satisfied with their activity level and knee function at 1-syear follow-up. The authors concluded that facilitating motivation may be important to support individuals in achieving their goals after ACL reconstruction.
When looking at female football players with ACL injuries who underwent reconstruction, there were three core themes of psychosocial factors that characterized their resilience during rehabilitation. Those three cores were constructive communication and rich interaction with significant others, strong belief in the important and efficacy of one’s own actions, and the ability to set reasonable goals. These findings are the start of a conversation regarding how coaches and athletic trainers can facilitate and optimize their athletes’ return to sport.
Continuing efforts in researching and protecting athletes’ physical and mental health are necessary in preventing and rehabbing injuries such as ACL tears.
Other proposed mechanisms of increased ACL injury risk include the weather conditions and type of ground surface, both of which equate to the quality of interactions between the player and the ground. A study out of Australia found that low water evaporation and high rainfall significantly lowered the risk of ACL injuries in the sport of football. The proposed mechanism is that the ground softens and the shoe-surface traction is decreased as a result. They suggested that consistent extra watering and covering of grounds during periods of high water evaporation may lower ACL injury rates.
Prevention
A recent emphasis on preventing ACL injuries has been highlighted. With the identification of specific risk factors for ACL injury, rather than intervene on an entire population, athletes who are predisposed could undergo targeted intervention.
The idea of prophylactic knee bracing and its effect is controversial. Looking retrospectively at a group of athletes, 2% of their acquired ACL injuries occurred while the affected leg was braced. When assessing six different brace designs for patients with ACL deficiency and chronic instability, anterior tibial translation and neuromuscular function have been questioned. Bracing in these ACL-injured subjects was shown to decrease anterior tibial translation by 29–39% without accounting for the activation and stabilization provided by the surrounding muscles. When bracing and muscle activation were combined, anterior tibial translation was found to decrease between 70% and 85%. Notably, the study also did find that the braces caused a decrease in the HS muscle reaction times.
Sports-related injuries can be minimized with comprehensive injury prevention training, which includes plyometrics, agility, and balance. Trunk control is a significant pillar of this concept. To examine the isolated effects of core muscle training on lower body neuromuscular control and biomechanics, female collegiate basketball players in Japan were split into two groups. One group underwent core muscle training, while the other group underwent standard training for 8 weeks. When three-dimensional hip, knee, and trunk mechanics were measured at the posttraining phase, there were significant differences between the two groups. During the drop-jump test and the single-leg squat, the maximum trunk-flexion angle increased and the peak knee valgus moment decreased in the core training group. These alterations in neuromuscular control and biomechanics would be favorable in the prevention of sports-related knee injuries.
Reconstruction
ACL reconstruction is the typical management of ACL injuries. It has been estimated that in the United States, 90% of patients who sustain an ACL injury eventually undergo reconstruction. The rate at which ACL reconstruction is successful in restoring knee stability and patient satisfaction is 90%. In both adults and the pediatric population, it is common for ACL injuries to be further complicated by meniscus or cartilage damage. When left untreated, ACL deficiency can lead to recurrent instability and medial meniscal damage. This subsequently predisposes a patient to radiographic signs of osteoarthritis. The likelihood that they will be symptomatic enough to eventually require a total knee replacement is quoted to be as high as five times as much when compared to non-ACL-injured patients. The appropriate treatment in a timely manner is crucial to patient outcome. Depending on the patient, the treatment options are conservative or surgical in nature. Conservative treatment entails focusing on the prevention of further episodes of instability, which likely involves lifestyle changes and activity modifications.
A study out of Canada looked to assess the association between the time from ACL injury to ACL reconstruction. Consistent with prior studies, the study found that increases in time to reconstruction were associated with medial meniscal tears, irreparable medial meniscal tears, medial femoral condyle damage, and early medial compartment degenerative changes at the time of reconstruction. However, increases in the time to surgery were not found to be associated with degenerative changes of the lateral or patellofemoral compartments of the knee. Some studies report that patients have a higher incidence of subsequent intra-articular pathology when they are 12 months or more out from injury.
Notably, one study has found that intra-articular pathology can be associated as early as 3 months following injury.
While there are many differences in the implications of an ACL injury in males versus females, significant differences in surgical techniques have not been established. The optimal choice of graft tissue for ACL reconstruction remains a topic of ongoing debate. There is even less consensus regarding graft choice in young, female athletes. Salem et al. reviewed the outcomes of two different age groups undergoing ACL reconstruction. In females aged 15–20 years undergoing ACL reconstruction, the bone-patellar tendon-bone (BPTB) autograft may lead to fewer graft ruptures than HS autograft. This difference was not observed in females aged 21–25 years. Important to note, however, is that BPTB autograft significantly increased the risk of kneeling pain as compared with HS, regardless of age. Similarly, in a smaller patient cohort, Shakked et al. found that there were significantly fewer subsequent procedures and a lower rate of graft failures in the BPTB group than the HS group. On the contrary, Kautzner et al. concluded that graft choice for reconstruction in female patients should be surgeon specific and individualized, as both grafts studied achieved comparable results.
Outcomes After Reconstruction
Overall, ACL reconstruction is a reliable surgery with successful clinical outcomes. However, it has been shown that it does not restore normal knee kinematics during gait. In the transverse plane, it has been shown that there are differences in tibial rotation during the gait cycle in ACL-reconstructed knees when compared to a patient’s contralateral knee. When comparing graft type, there is a reduced amount of knee varus in the HS group after reconstruction, which may relate to the graft harvest. The HS group also had a reduction in the amount of internal tibial rotation postoperatively. These alterations in the joint kinematics could be an important factor in the increased incidence of osteoarthritis of the knee after reconstruction. The identification of modifiable risk factors that affect outcomes would provide future interventions to improve ACL reconstruction. Some of those that have been identified are body mass index, smoking status, allograft, and lateral meniscus pathology. Lower socioeconomic status has been associated with worse patient reported outcomes after many orthopedic procedures. ACL reconstruction is one of those procedures. Given that a large proportion of the ACL reconstructions performed in the United States are of children, different factors have to be taken into account. It has been demonstrated that lower neighborhood socioeconomic status is associated with worse patient reported outcomes after ACL reconstruction and that the patient’s age and education have a significant interaction in a younger population.
When evaluating the success of ACL reconstruction surgery, return to sport is an important outcome. One important end-stage outcome for athletes is being able to play their sport specifically at preinjury levels of performance. This decision is made on a regular basis by surgeons, athletes, and coaches. Defining return to sport is a continuum and includes return to participation, return to sport, and return to performance. Progressions in postoperative management have been made possible because of the advances in techniques and protocols. When the ACL is reconstructed without other pathologic conditions, it is currently standard to let the patient weight-bear immediately. About 67% of surgeons stated they allow patients to return to sport between 6 and 9 months, and 94% stated they allowed patients to return to sport between 6 and 12 months. About 84% of surgeons used braces postoperatively, and 48% used braces after return to sport.
Overall, females are less likely to return to their preinjury sport level, or even return to any sport, after an ACL injury and reconstruction. In a meta-analysis of 69 published articles that reported return-to-sport outcomes postoperatively, there were two primary factors that favored return to sport: younger age and male gender. On average, 75% of females compared to 80% of males returned to any sport. About 52% of females returned to preinjury levels of sport, compared with 61% of males. About 68% of females returned to competitive level sport, compared with 78% of males.
In a cohort of 222 patients in Australia who had ACL reconstruction and completed a 12-month postoperative assessment, along with follow-up of at least 2 years, 61% of patients reported that they had returned to their preinjury level of performance. There was not a significant difference between males and females, with 59% of males and 63% of females reporting preinjury level of performance. The investigators did find a significant association with return to sport and higher psychologic readiness, greater limb symmetry, higher subjective knee scores, and a higher activity level. However, when they looked at the multivariate model, psychologic readiness was the only variable that remained a significant predictor.
After ACL injury, female athletes have a poorer functional recovery than males. Studies have shown that they also have lower activity levels than males at both 2 and 6 years after reconstruction. When females do return to sport, statistics show that they are more likely than males to sustain a second ACL injury. Patients of both genders who underwent reconstruction are roughly six times more likely to sustain an ACL injury within the first 2 years after returning to sport. After reconstruction, female athletes were almost five times more likely to sustain another ACL injury than females without any history of ACL injury. About 30% of athletes who underwent reconstruction and then returned to cutting and pivoting sports sustained a second ACL injury within 2 years after reconstruction and returning to sport. Of those patients who did sustain a second ACL injury, there was no significant difference between the times to return to sport.
In a randomized controlled trial out of the University of Delaware, 40 females 3–9 months after primary ACL reconstruction were randomized to 10 strength, agility, plyometrics, and secondary prevention (SAPP) exercises with or without perturbation training. They found that the perturbation training provided no added benefit. However, among young, high-level female athletes who have undergone ACL reconstruction, 10 sessions of return-to-sport training, compared with criterion-based postoperative rehab alone, yielded statistically significant and clinically meaningful higher 2-year functional outcomes.
Following ACL reconstruction, it has been suggested that knee proprioception returns to normal. The amount of time it takes to get back to a normal baseline has been a recent question. Past studies had reported that it took 12 months to regain normal sensorimotor function. One of those studies compared males and females postoperatively and found that by the 12-month mark after surgery, patients had recovered their sagittal plane alignment (knee flexion angle and extension moment) equally in both genders.
Overall, the literature has been somewhat conflicting when looking at return of proprioception and the type of ACL reconstruction performed. When comparing ACL reconstruction using HSs or BPTB autograft, one study found that there is no statistically significant difference in postoperative knee proprioception at any time point up to 12 months. Yet, others have suggested that the type of reconstruction may be an important factor in the impairment of sensorimotor control. It has been reported that the semitendinosus and the gracilis tendons regenerate after being harvested for ACL reconstruction. Using postoperative MRI, one group found that the semitendinosus tendon is regenerated at or below the joint line, and no gracilis tendon was observed below the joint line. Yet, the ACL-reconstructed knees, when compared to the healthy knees, had no significant difference in HS muscle activation during and after knee flexion. Their results indicated that both the semitendinosus and the gracilis muscles were highly recruited during flexion of the knee regardless of the amount of tendon regeneration. A group out of Italy looked at postoperative sensorimotor control after ACL reconstruction. When they compared results between HS tendon and the BPTB groups, they found that between 6 and 12 months after surgery there was no significant difference in steadiness and onset of muscle activation. There was also no significant difference between those who underwent reconstruction and the uninjured control group. When combining all these studies and data, it appears as though the selected surgical approach for ACL reconstruction does not affect the knee joint sensorimotor function to a significant degree. Further research would be necessary to further characterize this by gender.
Compared to healthy individuals, patients who have undergone ACL reconstruction have also been found to have diminished quadriceps submaximal force control, which is reflective of their medial quadriceps and HS altered muscular activity patterns and deficits in coordination. In addition, the knee adduction moment has been shown to be increased following ACL reconstruction surgery. One study found that the knee adduction moment was 23% greater in females than in males, where both had undergone reconstructions. This higher knee adduction moment seen in females may suggest an increased risk of developing osteoarthritis in ACL-reconstructed females down the road.
As discussed earlier in this chapter, the use of preinjury braces in athletes is controversial.
Functional bracing after ACL reconstruction surgery and its effect on graft reinjury rates is also a topic of debate. In one prospective, randomized, multicenter study, athletes were randomized into two groups postoperatively: braced and nonbraced. After reconstruction the braced group wore a functional knee brace on the affected limb for 1 year during all activities that involved jumping, pivoting, and/or cutting. The nonbraced group did not use any brace for these activities. The investigators found that there were no significant differences between the two groups in regard to stability or function of the knee, range of motion, strength of the knee, or subjective knee scores, which suggests that bracing postoperatively does not change outcomes and is not recommended.
References
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