Marc Darrow MD,JD

The problems of ACL reconstruction surgery are many. So much so that surgeons are now exploring new surgical 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. This of course as opposed to using transplanted material to reconstruct the ligament. 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.

So to take this idea one step further, how do you make the surgery more successful? in December 2019, a study from the Mayo Clinic (2) 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.

You may not need ACL reconstruction

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?” 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.

Orthopedic surgeons working at some of Turkey’s leading sports medical centers released a paper published in December 2017. (3) Here is what they discovered:

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 (4) 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.

So non-surgical treatment can be an option if functional stability can be maintained. I will discuss this further later in this article.

When does a partial tear of the ACL eventually become a full rupture?

A July 2019 study (5) 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.


  • 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.

You already had the ACL reconstruction surgery and your knee is not as strong as you thought? Now what?

You are not alone in asking, doctors are asking the same thing. Now what?

Doctors at the University of Pittsburgh (6) say that despite abundant biological, biomechanical, and clinical research, return to sport after anterior cruciate ligament (ACL) injury 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.​

ACL reconstruction re-rupture – blame it on the tunnels

A May 2021 paper (7) 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 (8) 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.

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 (9) 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.

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 (10) 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

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 research above, none of the studies mentions stem cells or blood platelets as remedy for knee instability. 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.”(9)

Soccer players were not ready to return from ACL reconstruction

A May 2021 paper (11) 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 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 (12) 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 out of pooled blood and use this blood as the foundation to regenerate a ligament – even a complete ruptured ACL.

Doctors shared a case history (13) 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. 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.

So what are your options?

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 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.

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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 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.
3 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.
4 Filbay SR, Grindem H. Evidence-based recommendations for the management of anterior cruciate ligament (ACL) rupture. Best Practice & Research Clinical Rheumatology. 2019 Feb 21.
5 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.
6 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.
7 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.
8 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.
9 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.
10 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.
11 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.
12 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.
13 Reported by Deren Bagsby, MD, George Gantsoudes, MD, and Robert Klitzman, MD Am J Orthop. 2015;44(8):E294-E297. —2452


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