Injury to the anterior cruciate ligament (ACL) is not the most common of knee injuries but certainly the most well known because of the number of ACL related injuries suffered by professional athletes. Further, you will hear a lot about the ACL because of those many athletes with devastated ACLs, few will return, even fewer will return to a level of play remotely close to that prior to the injury following surgery. Those who do return, because of the extensive physical therapy and rehabilitation needed for a full recovery from ACL reconstructive surgery, usually do so 18-24 months down the road. Those with complete ACL tears do have a few options to chose from besides surgery; do nothing or try to compensate for the ACL damage by strengthening the surrounding areas of the knee.
Many orthopedists may not recommend ACL reconstruction because it is not realistic for the patient. These recommendations may be made to patients who have an isolated ACL tear. These are ACL injuries that did not include meniscus damage, other ligament tearing, or cartilage tear. ACL reconstructions may also not be recommended to people who are not sport active or do physically demanding lines of work. These non-operative anterior cruciate ligament treatments may include physical therapy and exercise programs to strengthen the knee and restore function. However without an ACL, there will be instability. As part of the non-operative treatment, the physical therapist may focus on exercise for the patient that will address this instability. Some patients will also have knee braces designed especially if they want to have a somewhat confident knee function in sports.
ACL reconstruction surgical treatment
As I mentioned, the problems of ACL reconstruction surgery are many. So much so that surgeons are now exploring new surgical repair options. In the medical journal Knee doctors discuss the resurgence of interest in primary anterior cruciate ligament (ACL) repair.(1) This is a surgery that will attempt to fix the remnant or remaining ACL with what is left behind as opposed to using a patellar tendon or tendon autograft.
The first benefit of the primary ACL repair is that this procedure is less invasive than ACL reconstruction. An ACL that can be repaired usually does not need tunnels drilled in bone to thread the ACL graft and screws to hold them down. However, one must remember that the reason transplant became popular was because the primary repair really did not work that well.
Orthopedic surgeons working at some of Turkey’s leading sports medical centers released a paper published in December 2017. (2) Here is what they discovered injury treatment:
“Our data suggest that early surgical reconstruction may not be a prerequisite to returning to recreational physical activities after injury in patients with ACL tears.”
How did they get to this conclusion?
“Whether surgical or conservative treatment is more effective in allowing patients to return to physical activity after anterior cruciate ligament (ACL) injury is controversial. We sought to compare mid-term outcome measures between isolated ACL tear patients who underwent reconstruction followed by closed kinetic chain exercises and those who underwent neuromuscular training only.”
“We retrospectively evaluated patients with ACL tears who underwent post-surgery closed kinetic chain strength training after ACL reconstruction (Group A), and patients who only underwent neuromuscular training (Group B) with a minimum follow-up time of 5 years. Surgical techniques, rehabilitation, assessment of subjective knee function, one-leg hop test, assessment of joint position sense, muscle strength, and the health profile of the patient were evaluated.”
- Patients in both groups returned to their regular physical activity level after a similar time frame (Group A: average, 12 months; Group B, average, 13.4 months).
- No statistical difference was observed between the groups for any of the parameters evaluated, including assessment of subjective knee function, one-leg hop test, assessment of joint position sense, muscle strength, and the health profile.
CONCLUSION: “Our data suggest that early surgical reconstruction may not be a prerequisite to returning to recreational physical activities after injury in patients with ACL tears.”
In 2019 a study from Oxford University (3) gave arguments for rehabilitation as first-line treatment in ACL rupture. They wrote that the three main treatment options for ACL rupture are
- (1) rehabilitation as first-line treatment (followed by ACL reconstruction in patients, who develop functional instability),
- (2) ACL reconstruction and post-operative rehabilitation as the first-line treatment, and
- (3) pre-operative rehabilitation followed by ACL reconstruction and post-operative rehabilitation.
This idea of primary repair failure was shown again in a 2023 paper (4) comparing transplant versus primary repair. The doctors of this study compared joint laxity, patient-reported outcome measures (PROMs), and rate of failure following primary repair versus reconstruction for ACL ruptures. They found “ACL reconstruction may yield greater joint stability and lower rate of failure compared with surgical repair.”
You may not need ACL reconstruction – There are treatment options
So non-surgical treatment can be an option if functional stability can be maintained. I will discuss this further later in this article.
When Surgical Treatment Is Not Recommended for Student Athletes
How many times do I say to a patient, “You may not need ACL reconstruction.” How many times do I hear back, “I have a complete rupture, how can I play sports again with this type of ACL injury?” Perhaps nothing is as sacrilegious to these athletes as the notion that they do not need surgery. One of the arguments opponents have to regenerative medicine is the “complete rupture,” argument preventing return to sports.
A November 2021 study (5) examined student athletes with anterior cruciate ligament (ACL) injuries who returned to sports without reconstruction surgery. What the doctors wanted to see was if the student athletes could continue their sporting activities until the end of their season and whether there was an increase in secondary damage associated with knee instability.
What the study found was
- 288 skeletally mature patients aged under the age of 25 years old with new-onset isolated primary ACL injuries were included.
- Of these, 20 student athletes continued playing sports without ACL reconstruction to try to finish the season and were classified as the early return to sports group; the remaining 268 patients, who immediately quit sports and underwent surgery, were classified as the non- early return to sports group.
- Knee symptoms and sporting performance for the rest of the season were assessed for the early return to sports group. The presence of secondary damage, e.g., meniscus injuries and chondral lesions, associated with instability were compared between the two groups.
Results:
- Of 20 student athletes who continued playing sports without ACL reconstruction and tried to finish the season, fourteen of them (70%) indicated that their knees had given way during sporting activities, and seven athletes (35%) were unable to complete the season.
- Medial meniscus tears significantly increased in the athletes who competed without the ACL surgery with three patients experienced locking of the medial meniscus that required immediate surgery.
Conclusions:
- Although return to sports without reconstruction to complete the season may be a reasonable strategy for ACL injury, patients’ self-estimated performance level was low and meniscal and cartilage injury rates significantly increased.
When does a partial tear of the ACL eventually become a full rupture?
A July 2019 study (6) noted:
- Partial anterior cruciate ligament (ACL) tears are observed in 10% to 27% of isolated ACL tears.
- There is currently no consensus on diagnosis and treatment protocols, and the outcomes of nonoperative treatment remain undefined.
In this study a total of 41 patients, all younger than 30 years and active in sports, were diagnosed with a partial ACL tear, with no associated meniscal or chondral lesions on magnetic resonance imaging (MRI). All were assigned to a nonoperative treatment program.
Results:
- At an average of 43 months (range, 24-96 months), the partial ACL injury progressed to a complete ACL tear in 16 (39%) patients.
- Next, 18 (44%) patients returned to their preinjury level of sports activities.
More ACL partial tear patients returned to sports following conservative care, than ACL patients who’s partial tear progressed to a full rupture.
The type of graft recommended for female patients under the age of 25
In March 2022 doctors reported on graft choice recommendations for women 25 years old and younger.(7) They found that bone-patellar tendon-bone autografts showed significantly less graft failure compared with hamstring tendon autografts. However, bone-patellar tendon-bone autografts had comparable patient-reported outcomes compared with hamstring tendon autografts with the available data. The overall state of evidence for graft choice in female patients aged 25 years and younger is low. Future studies should report statistics by age and sex to allow for further analysis of graft choice for this specific population that is known to be more vulnerable to ACL injury.
You already had the ACL reconstruction surgery and your knee is not as strong as you thought? Now what types of injury treatment or options do you have?
You are not alone in asking, doctors are asking the same thing. Now what?
Doctors at the University of Pittsburgh (8) say that despite abundant biological, biomechanical, and clinical research, return to sport after anterior cruciate ligament (ACL) injury treatment remains a significant challenge.
- Residual rotatory knee laxity (loose knee) has been identified as one of the factors responsible for poor functional outcome. In this study the doctors simply sort to come up with a scoring system to determine how loose was loose.
We see many patients in our office following ACL reconstruction because of knee weakness and instability. This is not limited to recent surgeries, some of our patients had ACL reconstruction decades ago and have had knee problems since.
Knee laxity post-surgery
A March 2022 review study (9) suggests that a loose knee after ACL surgery is a high risk indicator of revision surgery. In this study, 17,114 Dutch patients who had ACL reconstruction were placed into three groups on the basis of objective side-to-side differences in sagittal (right or left side) laxity one year after surgery: Group A (laxity less than 2 mm), Group B (3-5 mm) and Group C (laxity more 5 mm).
- The main outcome measure was revision rate within 2 years of primary surgery.
Results: The study found the risk for revision surgery was more than five times higher for Group C (high level laxity) than for Group A (low level laxity). These results indicate that increased post-operative sagittal laxity is correlated with an increased risk for revision surgery and might correlate with poorer knee-related quality of life, as well as a decreased function in sports. The clinical relevance of the present study is that high knee laxity at 1-year follow-up is a predictor of the risk of revision surgery.
ACL reconstruction re-rupture – blame it on the tunnels
A May 2021 paper (10) examined the problems of rupturing the ACL graft.
“Re-injury rates following reconstruction of the anterior cruciate ligament (ACL) are significant; in more than 20% of patients a rupture of the graft occurs.
One of the main reasons for graft failure is malposition of the femoral tunnel. The femoral origin of the torn ACL can be hard to visualize during arthroscopy, plus many individual variation in femoral origin anatomy exists, which may lead to this malpositioning.”
To possible solve this problem it is suggested that MRIs be taken before the ACL reconstruction with the purpose of try to pinpoint the footmark of where the drilling should take place in the bones. The study writes: “a preoperative MRI is needed to identify the patient specific femoral origin of the ACL. The issue here is that there may be a difference in the reliability of identification of the femoral footprint of the ACL on MRI between different observers with different backgrounds and level of experience.”
A May 2021 (11) continued this line of suggestion. In this retrospective study of 58 patients with successful primary ACL reconstruction compared with 59 patients with failed ACL reconstruction, anterior and proximal (high) femoral tunnels for ACL reconstruction were shown to be independent risk factors for ACL revision surgery. As revision ACL reconstruction is associated with patient- and economic burden, particular attention should be given to achieving an individualized, anatomic primary ACL reconstruction. Surgeons may reduce the risk of revision ACL reconstruction by placing the center of the femoral tunnel within the anatomic ACL footprint.
ACL reconstruction re-rupture – blame it on a missing meniscus and ligament instability injury treatment
In a December 2021 paper (12) orthopedic surgeons created a comprehensive list of degenerative knee problems that doctors should look for which could cause or did cause ACL re-tear and re-rupture. The study authors found that medial and lateral meniscectomies, peripheral meniscus tears, medial meniscus ramp tears, lateral meniscus root tears, posterolateral corner injuries, medial collateral ligament tears, increased tibial slope and valgus and varus alignment had a significant impact on ACL forces and related knee kinematics and should be looked for if the patient wanted to have a revision surgery to prevent another graft failure surgical treatment.
Doctors in Australia asked: How do people with knee symptoms describe their quality of life and experiences 5 to 20 years after anterior cruciate ligament reconstruction? What factors impact upon the quality of life of these people?
Here is what the patients told them as recorded in the Archives of orthopaedic and trauma surgery (13) Four consistent themes emerged from the interviews as common determinants of quality of life following ACL reconstruction: physical activity preferences; lifestyle modifications; adaptation and acceptance; and fear of re-injury.
- All participants described the importance of maintaining a physically active lifestyle and the relationship between physical activity and quality of life.
- Participants who suppressed or overcame re-injury fears to continue sport participation described experiencing a satisfactory quality of life while taking part in sport despite knee symptoms.
- For some participants, resuming competitive sport resulted in subsequent knee trauma, anterior cruciate ligament re-rupture or progressive deterioration of knee function, with negative impacts on quality of life following sport cessation.
- Participants who enjoyed recreational exercise often adapted their lifestyle early after ACLR, while others described adapting their lifestyle at a later stage to accommodate knee impairments; this was associated with feelings of acceptance and satisfaction, irrespective of knee symptoms.
Here is the reality of it all – knee problems continued well after the ACL Reconstruction.
Study 12.7% of patient – post-surgical saw declining function after ACL reconstruction
A March 2022 study (14) looked at 245 patients who had ACL reconstructive surgery and divided the patients into three post-surgical recovery groups
- Group 1 had improvement from preoperative to 1-year follow-up, with sustained improvement from 1-to2-years postoperatively, consisted of 77.1% of the study population. This group represent 189 of the 245 patients.
- Group 2, demonstrated functional improvement between 1-and 2-year follow-up. This group represented 10.2% of the study population (25 of the 245 patients), and,
- Group 3, demonstrated slight improvement at 1-year follow-up with a subsequent decline in knee function scores between 1-and 2-year follow-up. This groups represented 12.7% of the study population (31 of the 245 patients).
- Revision surgery, psychiatric history, preoperative chronic knee pain, subsequent knee injury within follow-up were the predictors of group 2 and group 3 rate of recovery patterns.
How about the professional athletes? They come back all the time from ACL reconstruction – don’t they?
Some do yes. Doctors at New York University (15) examined National Basketball Association players (NBA) to see what type of impact ACL reconstruction had on their careers. At the forefront non-professional athletes need to understand that these players have huge medical and training resources behind them. Even with these resources – here is what the NYU doctors found:
- The players: Seventy-nine players (80 knees) with acute ACL tears in the NBA between the 1984-2014 seasons.
- The study: Pre- and post-injury performance outcomes including seasons played, games played, games started, minutes per game, points per game, field goals, 3-point shots, rebounds, assists, steals, blocks, turnovers, personal fouls, usage percentage and player efficiency ratings were compared .
The findings:
- Sixty-eight of seventy-nine players (86.1 %) returned to play in the NBA following ACL reconstruction.
- Many did not last – “There was a significantly higher rate of attrition from professional basketball for players with a history of ACL reconstruction”
- Over the length of their careers, players competed in 22.2 fewer games per season
CONCLUSIONS:
There is a high rate of return to sport in the NBA following ACL reconstruction, although playing time, games played, player efficiency ratings and career lengths are significantly impacted in the post-operative period.
Interestingly, the unstable surgically repaired ACL has the potential to heal upon intensive non-surgical rehabilitation procedures.
In the acl tear treatment research above, from the Archives of orthopaedic and trauma surgery, none of the studies mentions stem cells or blood platelets as remedy for knee instability or anterior knee pain or ACL injury. Researchers have noted that these biological factors influence the healing process as local intraligamentous cytokines (healing growth factors within the ligament) and by mainly cell repair mechanisms controlled by stem cells or progenitor cells (a cell that can morph itself into something else that aids in repair). The researchers conclude: “Understanding the mechanisms of this regeneration process and the cells involved may pave the way for novel, less invasive and biology-based strategies for ACL repair.”
Soccer players were not ready to return from ACL reconstruction
A May 2021 paper (16) suggested that while the effects of exercise on anterior knee laxity and anterior knee stiffness have been documented in healthy participants, only limited evidence has been provided for surgically treated patients (athletes) cleared to return to sports after anterior cruciate ligament (ACL) reconstruction (ACLR). The purpose of this study then was to to determine if 45 minutes of a soccer match simulation lead to acute (beneficial) changes in anterior knee laxity and anterior knee stiffness in soccer players returning to sport within 12 months after ACLR. The researchers thought that the reconstructed knee of the ACLR group would exhibit an “altered” response to sport-specific exercise. Altered meaning less successful.
- A total of 13 soccer players cleared to return to sport after ACLR and 13 healthy control soccer players were recruited for the study.
- Results: Soccer players at the time of return to sport after ACLR showed an altered mechanical response to a sport-specific match simulation consisting of bilaterally unchanged anterior knee laxity and anterior knee stiffness.
- Clinical relevance: Soccer players showing altered anterior knee laxity and anterior knee stiffness in response to exercise after ACLR may not be ready to sustain their preinjury levels of sport, thus potentially increasing the risk of second ACL injuries.
NFL wide receivers were not as good after ACLR
A February 2021 study (17) of wide receivers playing in the National Football League who had an recovered from ACLR surgery found that many of these players did not return to pre-injury form. In this study team doctors examined the time to return to play and evaluate the performance level in wide receivers in the National Football League following anterior cruciate ligament (ACL) reconstruction.
A total of 29 wide receivers in the National Football League who underwent ACL reconstruction between 2013 and 2017 were included in the study.
- Of the wide receivers, 9 of 29 (31%) did not return to play in a regular season game following ACL reconstruction.
- For players who did return to play, 20 of 29 (69%), the average time was 10.9 months.
- When the researchers compared the ACL tear group with the matched control cohort, players with ACL tears ended their careers on an average of 1.9 seasons earlier and also played less than half the number of games.
- Those that returned to play also saw decreased performance statistics in targets, receptions, receiving yards, and touchdowns.
How does an ACL heal? Is it all about blood?
Understanding how an ACL heals – even a complete rupture has lead doctors to continuously look at bio-materials – blood platelets and stem cells. One of the things they look at is “Scaffolding.” This is a surgical procedure where a cartilage patch is placed over a cartilage defect and them “pasted in with PRP or stem cell gel.” However in some instances the body may make its own scaffolding following an injury out of pooled blood and use this blood as the foundation to regenerate a ligament – even a complete ruptured ACL.
In one case, (18) doctors shared the history of a 12 year old boy who grievously injured his knee after being hit by a car – the boy was also a high level hockey player. What makes this story so amazing is that the knee damage was so severe in regard to broken bones, that an ACL reconstruction surgery had to be postponed until the other damaged healed. When doctors went in 14 months later to start the processes of ACL reconstruction, they found a completely regenerated ACL. The attending doctors point out that the body of evidence says that this should not have happened. The medical literature states a completely ruptured ACL does not heal because blood and healing cells cannot reach it.
Yet, their patient with traumatic knee injury with multiple ruptured ligaments healed over the course of 20 months.
It is likely that bracing associated with the patient’s second surgery and delayed union of his tibial fracture allowed healing tissue to be protected from excessive stress until it remodeled with sufficient strength. It is possible that intra-articular scar formation contributed to his healing capacity. (Possibly the blood scaffold.) At age 14 the boy returned to playing competitive hockey – and two and a half years later – still playing with no adverse effects to his knee.
In the above scenarios and in the surgical procedure, the common factor in ACL healing is time.
However many active people do not have the time to rehab. This lack of patience creates more patients. In Anterior cruciate ligament reconstruction the overall incidence rate of having to go through it again within 24 months is 6 times greater than incidences of first time ACL tear. That was research presented at the American Orthopaedic Society for Sports Medicine’s (AOSSM) Annual Meeting 2013.
The doctors found that female athletes after Anterior cruciate ligament reconstruction demonstrated more than four times greater rate of injury within 24 months than their healthy counterparts.
Researchers looked at 78 patients (59 female, 19 male) between 10 and 25 years old, who underwent Anterior cruciate ligament reconstruction and were ready to return to a pivoting/cutting sport and 47 healthy, control individuals. Each subject was followed for injury and athletic exposure for a 24-month period after returning to play.
Twenty-three of the Anterior cruciate ligament reconstruction individuals and 4 control subjects suffered an ACL injury. Within the Anterior cruciate ligament reconstruction group, there also appeared to be a trend for female subjects to be two times more likely to suffer an injury on the opposite knee than on the previously injured one.
Overall, 29.5% of athletes suffered a second ACL injury within 24 months of returning to activity with 20.5% sustaining an opposite leg injury and 9.0% incurring graft re-tear injury on the same leg. A higher proportion of females (23.7%) suffered an opposite leg injury compared to males (10.5%).
Recently, doctors addressed the epidemic of anterior cruciate ligament injuries among young athletes, and the large number of patients who have surgery to reconstruct a torn ACL and undergo a second knee operation later on following another injury or rupture. Compiling statistics from a New York State database, researchers found that eight percent of patients with a primary ACL reconstruction had another ACL surgery, and 14 percent had non-ACL knee surgery at a later date. Researchers noted that the study may underestimate the actual number of repeat ACL tears, as the database only included patients who underwent surgery, and did not include those who chose not to have additional surgery following their injury or other injury treatment.
In December 2019, a study from the Mayo Clinic (19) suggested that stem cell therapy may offer a viable enhancement to post-surgical ACL reconstruction repair. They write, “improved outcomes spanning from higher patient-reported outcome scores to magnetic resonance imaging evidence of ligament healing in the setting of anterior cruciate ligament tears.”
The idea of improvement to surgery is expressed in many patients we see for ACL tears and knee problems who are unfortunately on their second or even third ACL reconstruction surgery recommendation. They are weighing their options knowing already what a surgery and rehabilitation will be like. For them the appeal of surgery has lost some luster.
Meniscus injury and tears after ACL reconstructive surgery
A December 2021 editorial in the medical journal Arthroscopy (20) discussed whether or not a meniscus tear should or should not be treated at the time of an ACL surgical treatment. “Meniscus tears seen at the time of anterior cruciate ligament reconstruction are usually asymptomatic, and treatment varies greatly between surgeons, with meniscus repair being used for tears that could be left in situ (as it was). Recent outcome studies of most types of lateral meniscus tears show that leaving the tears in situ can give equal or superior results. Meniscus repair being performed for degenerative medial meniscus tears does not give better results than removing the tears. As an alternative to repair, trephination (a method of poking tissue to draw blood) through the meniscus into the peripheral capsule can create many bloody channels to promote healing. Long-term follow-up of meniscus treatment with anterior cruciate ligament reconstruction can help us understand outcomes and prevent us from overtreating tears.”
The ACL surgery caused meniscus damage
A November 2022 study wrote of the ACL surgery causing meniscus damage: “Iatrogenic posterior meniscal root avulsions after malpositioning of the transtibial tunnels during anterior cruciate ligament (ACL) reconstruction can account for poor long-term outcomes seen in some patients following ACL reconstruction. . . .Clinicians treating patients with a history of cruciate ligament reconstruction presenting with postoperative pain and instability should consider this pathology in their differential diagnosis.” (21)
Researchers did not find any clinical benefit of intraarticular hyaluronic acid injection following ACLR surgery
A March 2022 paper (22) examined the many problems that patients suffer from following ACL reconstruction. These are the problems of pain, swelling and joint stiffness. Part of the problem this paper noted was that the surgery recovery restricted early return to sports and athletic activities. Further, patients often receive prolonged doses of pain medications. To see if a solution could be provided, the researchers evaluated the safety and efficacy of intraarticular hyaluronic acid injections following ACL reconstruction (ACLR). What the researchers found was while studies demonstrated a short-term positive response regarding pain control and swelling reduction, the pooled analysis (of previously published research) did not find any clinical benefit of intraarticular hyaluronic acid injection following ACLR surgery.
What about older patients? PRP injections or ACL Surgery?
PRP treatments involve collecting a small amount of your blood and spinning it in a centrifuge to separate the platelets from the red cells. The collected platelets are then injected back into knee to stimulate healing and regeneration. PRP injections do not grow a new ACL, they strengthen the other support structures within the knee to help offset ACL deficiency.
An August 2022 study (23) compared PRP injections to ACL reconstructive surgery. These are the findings: “In old patients with ACL rupture, surgery is not recommended due to the person’s low level of activity and knee osteoarthritis. Platelet-rich plasma (PRP) is a good treatment option in inflammatory cases in orthopedics.” This study was to assess and comparison of the effect of PRP and arthroscopic surgery on anterior cruciate ligament rupture.
- 100 patients were randomly divided into two groups.
- The first group of patients underwent ACL tendon repair surgery by arthroscopy and tendon graft.
- The second group were treated by PRP injection.
- Patients in both groups had significant improvements in decreased pain severity after 14 months. The surgical treatment group had lower pain and higher range of motion compared to PRP group.
For the older patient PRP presented a non-surgical option that was comparable to ACL reconstruction.
Summary
The ACL’s main function is to keep the thigh and shin bones aligned within the knee. When the ACL is not there, the job of knee stability is then taken up by the tendons and other ligaments of the knee. Because this was not their intended job, osteoarthritis can develop more rapidly. It may be possible however to strengthen these connective tissues in the ACL deficient knee (nonsurgically treated patients) and allow the athlete to return to sport. Please email below your case or questions so we can assess if this may be a realistic options for you.
References
1 van der List JP, DiFelice GS. Range of motion and complications following primary repair versus reconstruction of the anterior cruciate ligament. The Knee. 2017 May 24.
2 Kovalak E, Atay T, Çetin C, Atay IM, Serbest MO. Is ACL reconstruction a prerequisite for the patients having recreational sporting activities?. Acta orthopaedica et traumatologica turcica. 2017 Dec 28.
3 Filbay SR, Grindem H. Evidence-based recommendations for the management of anterior cruciate ligament (ACL) rupture. Best Practice & Research Clinical Rheumatology. 2019 Feb 21.
4 Migliorini F, Vecchio G, Eschweiler J, Schneider SM, Hildebrand F, Maffulli N. Reduced knee laxity and failure rate following anterior cruciate ligament reconstruction compared with repair for acute tears: a meta-analysis. Journal of Orthopaedics and Traumatology. 2023 Feb 20;24(1):8.
5 Iio K, Kimura Y, Sasaki E, Sasaki S, Yamamoto Y, Tsuda E, Ishibashi Y. Early Return to Sports to Continue the Season after Anterior Cruciate Ligament Injury Is Not Recommended for Student Athletes. Progress in Rehabilitation Medicine. 2021;6:20210046.
6 Fayard JM, Sonnery-Cottet B, Vrgoc G, O’Loughlin P, de Mont Marin GD, Freychet B, Vieira TD, Thaunat M. Incidence and risk factors for a partial anterior cruciate ligament tear progressing to a complete tear after nonoperative treatment in patients younger than 30 years. Orthopaedic journal of sports medicine. 2019 Jul 16;7(7):2325967119856624.
7 Etzel CM, Nadeem M, Gao B, Boduch AN, Owens BD. Graft Choice for Anterior Cruciate Ligament Reconstruction in Women Aged 25 Years and Younger: A Systematic Review. Sports Health. 2022 Mar 27:19417381221079632. doi: 10.1177/19417381221079632.
8 Rahnemai-Azar AA, Naendrup JH, Soni A, Olsen A, Zlotnicki J, Musahl V. Knee instability scores for ACL reconstruction. Curr Rev Musculoskelet Med. 2016 Mar 15. [Epub ahead of print] Review.
9 Fiil M, Nielsen TG, Lind M. A high level of knee laxity after anterior cruciate ligament reconstruction results in high revision rates. Knee Surgery, Sports Traumatology, Arthroscopy. 2022 Mar 25:1-8.
10 Zee MJM, Sulaihem RA, Diercks RL, van den Akker-Scheek I. Intra-and interobserver reliability of determining the femoral footprint of the torn anterior cruciate ligament on MRI scans. BMC Musculoskelet Disord. 2021 May 28;22(1):493. doi: 10.1186/s12891-021-04376-5. PMID: 34049511.
11 Byrne KJ, Hughes JD, Gibbs C, Vaswani R, Meredith SJ, Popchak A, Lesniak BP, Karlsson J, Irrgang JJ, Musahl V. Non-anatomic tunnel position increases the risk of revision anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2021 May 13. doi: 10.1007/s00167-021-06607-7. Epub ahead of print. PMID: 33983487.
12 van der Wal WA, Meijer DT, Hoogeslag RA, LaPrade RF. Meniscal Tears, Posterolateral and Posteromedial Corner Injuries, Increased Coronal Plane, and Increased Sagittal Plane Tibial Slope All Influence Anterior Cruciate Ligament–Related Knee Kinematics and Increase Forces on the Native and Reconstructed Anterior Cruciate Ligament: A Systematic Review of Cadaveric Studies. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2022 May 1;38(5):1664-88.
13 Hirzinger C, Tauber M, Korntner S, Quirchmayr M, Bauer HC, Traweger A, Tempfer H. ACL injuries and stem cell therapy. Archives of orthopaedic and trauma surgery. 2014 Nov 1;134(11):1573-8.
14 Gursoy S, Clapp IM, Perry AK, Kerzner B, Singh H, Vadhera AS, Bach Jr BR, Bush-Joseph CA, Forsythe B, Yanke AB, Verma NN. Patients Follow Three Different Rate of Recovery Patterns Following Anterior Cruciate Ligament Reconstruction Based on IKDC Score. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2022 Mar 22.
15 Kester BS, Behery OA, Minhas SV, Hsu WK. Athletic performance and career longevity following anterior cruciate ligament reconstruction in the National Basketball Association. Knee Surg Sports Traumatol Arthrosc. 2016 Mar 12.
16 Nuccio S, Labanca L, Rocchi JE, Mariani PP, Sbriccoli P, Macaluso A. Altered Knee Laxity and Stiffness in Response to a Soccer Match Simulation in Players Returning to Sport Within 12 Months After Anterior Cruciate Ligament Reconstruction. Am J Sports Med. 2021 May 26:3635465211013020. doi: 10.1177/03635465211013020. Epub ahead of print. PMID: 34038185.
17 Burgess CJ, Stapleton E, Choy K, Iturriaga C, Cohn RM. Decreased Performance and Return to Play Following Anterior Cruciate Ligament Reconstruction in National Football League Wide Receivers. Arthroscopy, sports medicine, and rehabilitation. 2021 Apr 1;3(2):e455-61.
18 Reported by Deren Bagsby, MD, George Gantsoudes, MD, and Robert Klitzman, MD Am J Orthop. 2015;44(8):E294-E297. —2452
19 Hevesi M, LaPrade M, Saris DB, Krych AJ. Stem Cell Treatment for Ligament Repair and Reconstruction. Current Reviews in Musculoskeletal Medicine. 2019 Jan 1:1-5.
20 Shelbourne KD. Editorial Commentary: Meniscus Tears Seen at the Time of Anterior Cruciate Ligament Reconstruction Are Overtreated. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2021 Dec 1;37(12):3507-9.
21 Vadhera AS, Lee JS, Singh H, Gursoy S, Kunze KN, Verma NN, Chahla J. Injury to the Posterior Horn of the Lateral Meniscus from a Misplaced Tibial Tunnel for Anterior Cruciate Ligament Reconstruction: A Case Report. The American Journal of Case Reports. 2022;23:e937581-1.
22 Tripathy SK, Varghese P, Behera H, Balagod R, Rao PB, Sahoo AK, Panda A. Intraarticular viscosupplementation following arthroscopic anterior cruciate ligament reconstruction: A systematic review. Journal of Clinical Orthopaedics & Trauma. 2022 May 1;28.
23 Eslami S, Fattah S, Taher SA, Rezasoltani Z. Platelet-rich plasma therapy or arthroscopic surgery on repair of anterior cruciate ligament rupture. Eur J Transl Myol. 2022 Aug 1.