Welcome to the 4th edition of the Learn.Physio Research Review!

Thanks for joining me once again for my fortnightly research reviews! I sincerely hope you enjoy the research reviews I have previously written up, and that you’re learning something valuable to help your clinical practice. If you’re new to the Learn.Physio Journal Club Research Reviews, you can catch up on all the past editions by clicking here.

In this edition, I’m going to turn back the clock to the early 2000’s and share with you 2 papers – which are completely relevant today - that will help you with your chronic knee pain patients and your ACLR patients. Given that there is a translation lag of up to 17yrs between when a paper is published to when it is implemented widely in clinical practice (Morris et al 2011), I would not be surprised if many of you haven’t seen or heard of these papers before!

First up is Thorstensson et al (2004) who showed single leg sit to stand performance (both good and poor) was predictive of those who would show radiographic osteoarthritic changes 5 years after baseline assessment in those with chronic knee pain.

Secondly I look at one of the first studies of its kind, by Mikkelsen et al (2000), looking at the benefits (and no harm) of adding open-chain knee extensions exercises into a comprehensive rehab plan of closed-chain exercises.

I know I have only just started, but this will be the last review for 2020 as I look to switch off for the festive season and be present with my family and loved ones. I will be back on deck in January though, and you’ll have issue number 5 in your inbox first thing Monday morning January 11, 2021.
Until then, have a safe and festive holiday season, and I look forward to sharing plenty more clinical gems with you in 2021!
Our final live webinar for the year introduces Cam Dyer from the Waratahs and Mel Habberfield from North Melbourne AFLW. Listen as Mick joins the duo to talk all things sports physio. 
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Back in the early 2000’s it was estimated that approximately 5% of the population with chronic knee pain aged between 35 and 55 years of age had radiological findings of knee osteoarthritis (OA) (Petersson et al, 1997). Interestingly, it was discovered recently that OA features on MRI in asymptomatic uninjured knees in adults aged <40yrs ranged between 4-14%; and OA features on MRI in asymptomatic uninjured knees in adults aged >40yrs ranged from 19-40% (Culvenor et al, 2019).

Even back in the late 1990s and early 2000s, it was well established that reduced quadriceps strength was a consistent finding in those with symptomatic knee OA. This has since been supported by many, including Muraki et al 2015, Hall et al 2018, Zacharias et al 2014 and Takagi et al 2018. Despite this association, the underlying mechanisms are still not quite fully understood. Could it be age, disuse atrophy due to pain and decreased physical activity leading to quads weakness? Or is quads weakness a cause, and not a consequence, of knee OA?

Whatever the driver to quads weakness is, the authors set out to try and identify the predictive value of 3 separate tests of lower limb functional performance (controlled for age, sex, BMI and baseline knee pain) for the development of radiological knee OA 5 years later in a population of middle-aged subjects with chronic knee pain.

A questionnaire was sent out to 2000 randomly selected people aged between 35-54yrs of age. “Chronic knee pain” was defined as “pain in either of your knees practically daily for the past three months”.
1853 people responded to the questionnaire and 279 reported chronic knee pain. These 279 people were offered a clinical exam and X-ray, and 204 agreed to participate in the study. However only 148 people made themselves available for the 5-year follow-up assessment.
The functional tests were:
  1. Maximum number of one-leg rises from sitting on a stool (48cm height stool)
    1. Patient places one foot on the floor in a self-selected position
    2. The other leg was held out straight with knee extended and arms held by their side
    3. Test should be performed in a controlled manner without losing control on the descent or using arm/trunk movement on the uprising phase
    4. Count the number of repetitions until the patient cannot perform any more
    5. Rest 5mins between legs
  2. Time spent walking 300m indoors
    1. An Indoor corridor of at least 150m was used for this test
    2. A line at the start of the test indicated the start and the end positions
    3. A line at the end of the 150m distance indicated that the person was to turn around towards the start/end line.
    4. Subjects instructed to walk as fast as they could (without running)
    5. Time was taken to complete the 300m distance with a stop watch
    6. Patients answered the question “how much pain do you have in your knees right now?” using a visual analogue scale (0-10) immediately prior to the test and straight after the test.
  3. Time standing on one leg with rapid and repeated neck rotations
    1. Eyes open and arms hanging by their side
    2. Time spent on one leg, without any support was measured with a stopwatch
    3. When the lifted foot touched the floor, or when support was needed, or after 30sec (which was considered normal), the test was stopped
    4. One attempt was allowed each leg
For the clinical exam, a rheumatologist obtained the medical history and recorded the subject’s height, weight and BMI. They also identified any disorders, other than OA, known to cause knee pain and excluded them from further analysis. In regards to the radiological examination, P-A X-rays were taken of the tibiofemoral joints in both knees with straight knees in a weightbearing position.
At 5 years after the baseline assessments were taken, x-rays were performed again using the same protocol with OA changes being assessed via the Kellgren and Lawrence classification system.

After 5 years, and when compared to baseline in those with no OA changes, 44% of the population developed knee OA changes; with the one-legged rise test significantly predicting the development of knee OA changes 5 years later (median 17 reps vs 25 reps). Meaning that those who could do 25 reps (or more) did not have any OA changes at 5 years follow-up, compared to those who could only do 17 (or less) showed OA changes at 5 years follow-up. The impact of doing fewer one leg rises from sitting on the development of incidental knee OA changes, remained significant even when controlling for age, sex, BMI and baseline pain.

In those who already had some degree of OA changes at baseline, 54% of them showed progression in their knee OA over 5 years – however none of the variables analyzed could explain the progression.
Interestingly, 11 patients actually showed regression in their radiographic knee OA features! A comparison of characteristics between them and the remaining subjects showed that they had a lower BMI on average (23 vs 25.5 kg/m2).

The key finding from this study that we as clinicians can easily translate into our clinical practice is that lower limb functional performance can predict the progression of radiographic knee OA over at least 5 years.

The authors were also able to discover that patients who reported knee pain prior to baseline examination that reduced functional performance (via the one-legged rise test) maybe an early sign of knee OA and the reduced functional performance may in fact be causative of knee OA changes in people with chronic knee pain.

This information is quite valuable as allows us to target those patients – particularly those who we know who are young, and who have also sustained significant knee injuries such as ACL and/or meniscus injuries – that puts them at risk of developing OA changes over time. It also allows us to set targets for our patients to achieve (25 or more repetitions), especially those who have at least 3 months of regular daily knee pains, but don’t have X-ray evidence of knee OA changes yet.

From a practical perspective however, we do need to appreciate that, although the single leg rise test is easy to perform in most clinical settings and requires no special equipment, the single leg rise test is not a direct measure of quadriceps strength. It is however a good measure of global lower limb muscle performance.

Given that quadriceps weakness (>10% strength differences between limbs) has been shown to be associated with knee OA changes over time (as well as many other outcome measures such as impaired walking and running mechanics, function, QOL, return to pre-injury level of sport and subsequent knee injury – Lepley et al 2015 and Palmieri-Smith et al 2015), and knowing that patients who have persistent quad weakness (ACLR patients and chronic knee pain patients) are great at compensating to their strength efforts to the hip (Sigward et al 2018 & Kotsifaki et al 2020), it makes sense to get an objective measure of both – with the combined goals of being able to do more than 25 reps on the single leg rise test AND having >90% limb symmetry index on quadriceps strength testing.

But therein lies a common problem in most settings - Access to isokinetic testing (current gold standard to measure quadriceps and hamstrings strength) can be quite expensive and difficult. Hand-held dynamometry does provide a reasonably valid and reliable alternative to isokinetic testing, but once again, not all clinical settings will have a hand-held dynamometry unit available.

Further to this, from my experience, performing the single leg rise test when someone is symptomatic of knee pain can provoke their symptoms – so care needs to be taken, and clinical reasoning needs to be applied for when and why you perform the single leg rise test with your patients.

My advice? If you and your patients have affordable access to isokinetic testing – it might be worthwhile testing to see if what you and your patients are dealing with in terms of quads weakness. However, what matters most is; “what will you do to intervene if it is found that your patients have a quads strength difference greater than >10%”?

A progressive strength plan of both isolated knee extensions and closed chain exercises that involve the entire lower limb muscle groups (“functional exercises”), seems to be the best way forward to combat the effects of both acute and chronic knee pain.

In summary, this landmark study from the early 2000s showed that being able to perform at least 25 single leg rises from a 48cm high chair significantly lowered the risk of knee OA changes over a 5 year period in a population of middle aged participants who had at least 3 months of daily knee pain.
The single leg rise test is inexpensive, does not require expensive equipment and is easy to perform in most clinical situations. Its limitation however is that it is not a direct measure of quadriceps weakness and a direct measure of quadriceps strength is a recommended outcome measure in people with chronic knee pain.

One must be mindful that routine imaging of people with knee pain is not recommended – please use sound clinical reasoning here when weighing up if someone should be referred for imaging – and that we should always “treat the person, not the scan”.
  1. Morris, Z. S., Wooding, S., & Grant, J. (2011). The answer is 17 years, what is the question: understanding time lags in translational research. Journal of the Royal Society of Medicine104(12), 510–520. https://doi.org/10.1258/jrsm.2011.110180
  1. Thorstensson CA, Petersson IF, Jacobsson LT, Boegård TL, Roos EM. Reduced functional performance in the lower extremity predicted radiographic knee osteoarthritis five years later. Ann Rheum Dis. 2004 Apr;63(4):402-7. doi: 10.1136/ard.2003.007583. PMID: 15020334; PMCID: PMC1754965.
  1. Petersson IF, Boegård T, Saxne T, Silman AJ, Svensson B. Radiographic osteoarthritis of the knee classified by the Ahlbäck and Kellgren & Lawrence systems for the tibiofemoral joint in people aged 35-54 years with chronic knee pain. Ann Rheum Dis. 1997 Aug;56(8):493-6. doi: 10.1136/ard.56.8.493. PMID: 9306873; PMCID: PMC1752423.
  1. Culvenor, A. G., Øiestad, B. E., Hart, H. F., Stefanik, J. J., Guermazi, A., & Crossley, K. M. (2019). Prevalence of knee osteoarthritis features on magnetic resonance imaging in asymptomatic uninjured adults: a systematic review and meta-analysis. British journal of sports medicine53(20), 1268–1278. https://doi.org/10.1136/bjsports-2018-099257
  1. Muraki, S., Akune, T., Teraguchi, M., Kagotani, R., Asai, Y., Yoshida, M., Tokimura, F., Tanaka, S., Oka, H., Kawaguchi, H., Nakamura, K., & Yoshimura, N. (2015). Quadriceps muscle strength, radiographic knee osteoarthritis and knee pain: the ROAD study. BMC musculoskeletal disorders16, 305. https://doi.org/10.1186/s12891-015-0737-5
  1. Hall M, Hinman RS, Wrigley TV, Kasza J, Lim BW, Bennell KL. Knee extensor strength gains mediate symptom improvement in knee osteoarthritis: secondary analysis of a randomised controlled trial. Osteoarthritis Cartilage. 2018 Apr;26(4):495-500. doi: 10.1016/j.joca.2018.01.018. Epub 2018 Feb 7. PMID: 29427725.
  1. Zacharias A, Green RA, Semciw AI, Kingsley MI, Pizzari T. Efficacy of rehabilitation programs for improving muscle strength in people with hip or knee osteoarthritis: a systematic review with meta-analysis. Osteoarthritis Cartilage. 2014 Nov;22(11):1752-73. doi: 10.1016/j.joca.2014.07.005. Epub 2014 Jul 24. PMID: 25065642.
  1. Takagi S, Omori G, Koga H, Endo K, Koga Y, Nawata A, Endo N. Quadriceps muscle weakness is related to increased risk of radiographic knee OA but not its progression in both women and men: the Matsudai Knee Osteoarthritis Survey. Knee Surg Sports Traumatol Arthrosc. 2018 Sep;26(9):2607-2614. doi: 10.1007/s00167-017-4551-5. Epub 2017 Apr 26. PMID: 28447140.
  1. Antony, Joseph & McGuinness, Kevin & Moran, Kieran & O’Connor, Noel. (2019). Feature Learning to Automatically Assess Radiographic Knee Osteoarthritis Severity.
  2. Lepley LK. Deficits in Quadriceps Strength and Patient-Oriented Outcomes at Return to Activity After ACL Reconstruction: A Review of the Current Literature. Sports Health. 2015 May;7(3):231-8. doi: 10.1177/1941738115578112. PMID: 26131300; PMCID: PMC4482305.
  1. Lepley LK, Palmieri-Smith RM. Quadriceps Strength, Muscle Activation Failure, and Patient-Reported Function at the Time of Return to Activity in Patients Following Anterior Cruciate Ligament Reconstruction: A Cross-sectional Study. J Orthop Sports Phys Ther. 2015 Dec;45(12):1017-25. doi: 10.2519/jospt.2015.5753. Epub 2015 Oct 15. PMID: 26471854; PMCID: PMC4768729.
  1. Palmieri-Smith RM, Lepley LK. Quadriceps Strength Asymmetry After Anterior Cruciate Ligament Reconstruction Alters Knee Joint Biomechanics and Functional Performance at Time of Return to Activity. Am J Sports Med. 2015 Jul;43(7):1662-9. doi: 10.1177/0363546515578252. Epub 2015 Apr 16. PMID: 25883169; PMCID: PMC4758854.
  1. Sigward SM, Chan MM, Lin PE, Almansouri SY, Pratt KA. Compensatory Strategies That Reduce Knee Extensor Demand During a Bilateral Squat Change From 3 to 5 Months Following Anterior Cruciate Ligament Reconstruction. J Orthop Sports Phys Ther. 2018 Sep;48(9):713-718. doi: 10.2519/jospt.2018.7977. Epub 2018 Jun 12. PMID: 29895231.
Kotsifaki A, Korakakis V, Whiteley R, Van Rossom S, Jonkers I. Measuring only hop distance during single leg hop testing is insufficient to detect deficits in knee function after ACL reconstruction: a systematic review and meta-analysis. Br J Sports Med. 2020 Feb;54(3):139-153. doi: 10.1136/bjsports-2018-099918. Epub 2019 May 29. PMID: 31142471.

Anterior cruciate ligament (ACL) rupture is a relatively common injury in active adolescents and young adults. Its peak incidence in females occur between the ages of 14-18 years and in the early 40s (Sanders et al 2016 & Nicholls et al 2017), but for males the peak incidence is between the ages of 19-25yrs (Sanders et al 2016). Unfortunately, we are currently seeing a trend over the last 20 years of an increasing number of ACL injuries occurring in pediatrics & adolescents (Shaw & Finch, 2017) and ACL reconstructions (ACLR) being performed (Zbrojkiewicz et al, 2018), especially here in Australia.

Back in the year 2000 when this paper was originally written, there was no consensus regarding the optimal rehabilitation program following ACLR. Fast forward 20 years to this current date, and there are best practice guidelines of what ACLR should entail (van melick et al 2016 and Janssen et al 2018), however in a recent study on ACLR patients here in Australia, it was found that only 5% of this surveyed population completed ACLR rehab that met these guidelines (Ebert et al 2017).

Currently in the year 2020, there is still much debate and uncertainty about the safety and role of open-chain knee exercises within the rehabilitation plan. Much of this debate stems from early work Shellbourne et al (1992), Passler et al (1995) and Bynum et al (1995) who all advocated for the safety of closed chain exercises during ACLR. These early concerns about the structural integrity of the reconstructed ACL tissue were supposed to have eased when Beynnon et al (1995) and Beynnon et al (1997) produced research that showed only minor differences in ACL strain behavior between open-chain exercises and closed chain exercises.

As the authors of this paper had previously observed, their ACLR patients were insufficiently able to regain quadriceps torque following ACLR with CKC exercises-alone, so they set out to investigate the following:
  1. Evaluate the effect of closed chain quadriceps exercises versus the same program + open chain exercises on anterior knee laxity and quadriceps torque
  2. Determine whether this leads to differences in knee function and the ability to return to sports

44 ACLR athletes aged between 18-40yrs of age, who had undergone their first ACLR (all bone-patella tendon-bone autografts) were enrolled in this prospective, matched follow-up study.
The 44 subjects were randomized into two groups of 22 patients:

Group 1 consisted of 17 men (average age 25yrs) and 5 women (average age 19yrs) and used only closed kinetic chain (CKC) exercises throughout the first 6 post-op months. See table 1 below for the standardized rehabilitation protocol.
Group 2 also consisted of 17 men (average age 25yrs) and 5 women (average age 19yrs). They too performed the same CKC protocol throughout the first 6 months of rehab, but they added in open kinetic chain (OKC) exercises from 6 weeks post-op through to 6 months post-op. Note: The OKC exercises were performed on an isokinetic machine and were performed in a reduced ROM until week 12 post-op. See table 2 below:
As mentioned, the primary outcomes from this trial were to observe knee laxity and isokinetic muscle torque. Laxity testing was carried out on KT-1000 arthrometer prior to surgery and at 6 months post-op. Isokinetic testing was carried out on a Kin-Com dynamometer pre-operatively and at 6 months post-op; measuring both quadriceps and hamstrings torque at angular velocities of 30deg/sec, 120deg/sec and 240deg/sec.

The secondary outcome was determining knee function and the ability to return to pre-injury level of sports. This was carried out via a questionnaire that was sent out and completed on average 31 months (5yrs) post-op.

In regards to the primary and secondary outcome measures, the results are as follows:

Anterior knee laxity: There were no significant differences between the 2 groups in regards to anterior knee laxity at 6 months post-op. Group 1 had a side to side difference of 1.7mm at 6 months post-op, whereas Group 2 (OKC + CKC) had in fact less knee laxity at 6 months post-op; with 1.2mm side to side difference.

Isokinetic muscle torque: There was a significant difference between groups in favor of group 2 for quadriceps torque at 6 months post-op. There were no significant differences between groups for hamstring torque at 6 months post-op.

Return to pre-injury level of sport: 12 ACLR patients from group 2 (OKC + CKC) returned to pre-injury level of sport after a median of 7.5 months post-op. Whereas only 5 of group 1 returned to pre-injury level of sport at a median of 9.5 months post-op. This difference between groups was a significant.

Ratings of knee function and satisfaction: There were no significant differences between groups.
At a time when OKC exercises had such a bad rap and uncertainty about its effect on ACLR graft loosening and lengthening, the findings from this study clearly show that OKC exercises can be implemented safely in a restricted ROM from as early as 6 weeks post-op. As a result, group 2 (OKC + CKC) participants were able to significantly increase their quadriceps torque by 6 months post-op and were able to return to pre-injury level of sports in significantly greater numbers (and 2 months earlier!).
There were however some details over-looked in the methods section, and some questions that still remain.

Firstly, there was a lack of detail about how many sessions of rehab were completed each week in both groups, especially those in group 2 that conducted the extra sessions of isokinetic strengthening (was it 2x per week, 3x per week, more?).

Secondly, did they open up full ROM knee extensions from 12 weeks post-op? or did they stay restricted to 10-90deg for the entire 6 months of standardized rehab? If so, could this have had an impact on the graft laxity results? Would laxity results at 6 months differ between groups if they opened up full ROM from 12 weeks?

Lastly, the OKC protocol was performed on an isokinetic machine using different rates of muscle contractions and angular velocities. Could the restricted ROM and the rates of muscle contractions be applied safely to a standard knee extension machine in a gymnasium?

Despite some questions being left unanswered, this trial was the first of its kind to show that OKC exercises can be implemented safely into ACLR rehab plans, and importantly help the ACLR patient restore quadriceps strength and torque back quicker than CKC exercises alone.

NB: quadriceps torque had still not returned to pre-op levels in either group at 6 months post-op, and ranged between 65-83% LSI, indicating that at 6 months post-op, ACLR athletes have not restored back to an acceptable level of quadriceps strength (>90% LSI) to participate in pre-injury levels of sport.
This paper also paved the way for others to try and reproduce it, with mixed results, which may add to some of the concern that we’re still seeing about OKC exercises today. Without going into too much detail I’ll give a brief of summary of the 2 follow-up papers and how their protocols differed in design:
Heijne & Werner (2007) – started OKC exercises from week 4 post-op with no resistance between 40-90deg and went full ROM from 6 weeks post-op 3x15 reps with unlimited external resistance (according to symptoms and tolerance of each patient).
They broke down the laxity scores into those who had a hamstring autograft vs those who had a patella-tendon autograft and discovered that the hamstring autograft patients who performed OKC exercises from week 4 had significantly different KT-1000 scores at 7 months post-op (2.3mm) vs patella-tendon OKC from 4 weeks (1.3mm) vs full ROM OKC from 12 weeks (both patella tendon and hamstring grafts were 1.3mm).
Although that this result was significant, and it appears that hamstring autografts are more vulnerable to “stretching” in the first 12 weeks during full ROM OKC exercises – especially when performed with unrestricted loads.
Fukuda et al (2013) – were more conservative and started OKC exercises from week 4 post-op restricted ROM 45-90deg (early group) and full ROM week 12 (late group) in ACLR patients who all underwent hamstring autograft ACLR. The early group performed isometric quads 10x10sec holds at 60deg and 3x10 (70% 1RM) knee extensions between 45-90deg.
In this study there were no differences between early group and late group in regards to knee laxity. Of note however was in this study, the early OKC group were able to restore quads torque symmetry to >90% LSI by 5 and 6 months post-op, whereas the late start group were not quite achieving this by the same timeframe.

In summary, OKC exercise have been shown to be safe and effective to the recovering ACL reconstruction. Based on these findings, and err-ing on the side of caution, it appears that hamstring and patella tendon autograft ACL reconstruction tissue can and should be able to be loaded from week 4 post-op in a reduced ROM of 45-90deg with 70% 1RM loads. Patella tendon reconstructions in fact can actually handle the loads better, so feel free to change the way you prescribe OKC exercises if dealing with patella-tendon autografts.
From week 12 post-op it appears that the ACLR patient can safely perform full ROM knee extensions with at least 70% 1RM loads without any detrimental effect on their graft and their long-term knee health.
Like always, use sound clinical reasoning with the patient sitting in front of you, when determining the contraction type, the ROM performed, the loads being lifted, sets and reps and frequency of training that is being performed each week. And don’t forget to progressively overload over time!
  1. Mikkelsen C, Werner S, Eriksson E. Closed kinetic chain alone compared to combined open and closed kinetic chain exercises for quadriceps strengthening after anterior cruciate ligament reconstruction with respect to return to sports: a prospective matched follow-up study. Knee Surg Sports Traumatol Arthrosc. 2000;8(6):337-42. doi: 10.1007/s001670000143. PMID: 11147151.
  1. Shaw L, Finch CF. Trends in Pediatric and Adolescent Anterior Cruciate Ligament Injuries in Victoria, Australia 2005-2015. Int J Environ Res Public Health. 2017 Jun 5;14(6):599. doi: 10.3390/ijerph14060599. PMID: 28587262; PMCID: PMC5486285.
  1. Zbrojkiewicz D, Vertullo C, Grayson JE. Increasing rates of anterior cruciate ligament reconstruction in young Australians, 2000-2015. Med J Aust. 2018 May 7;208(8):354-358. Epub 2018 Apr 23. PMID: 29669497.
  1. Sanders TL, Maradit Kremers H, Bryan AJ, Larson DR, Dahm DL, Levy BA, Stuart MJ, Krych AJ. Incidence of Anterior Cruciate Ligament Tears and Reconstruction: A 21-Year Population-Based Study. Am J Sports Med. 2016 Jun;44(6):1502-7. doi: 10.1177/0363546516629944. Epub 2016 Feb 26. PMID: 26920430.
  1. Nicholls M, Aspelund T, Ingvarsson T, Briem K. Nationwide study highlights a second peak in ACL tears for women in their early forties. Knee Surg Sports Traumatol Arthrosc. 2018 Feb;26(2):648-654. doi: 10.1007/s00167-017-4807-0. Epub 2017 Nov 21. PMID: 29164266.
  1. van Melick N, van Cingel RE, Brooijmans F, Neeter C, van Tienen T, Hullegie W, Nijhuis-van der Sanden MW. Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus. Br J Sports Med. 2016 Dec;50(24):1506-1515. doi: 10.1136/bjsports-2015-095898. Epub 2016 Aug 18. PMID: 27539507.
  1. Janssen RPA, van Melick N, van Mourik JBA, Reijman M, van Rhijn LW. ACL reconstruction with hamstring tendon autograft and accelerated brace-free rehabilitation: a systematic review of clinical outcomes. BMJ Open Sport Exerc Med. 2018 Apr 9;4(1):e000301. doi: 10.1136/bmjsem-2017-000301. PMID: 29682311; PMCID: PMC5905729.
  1. Ebert JR, Edwards P, Yi L, Joss B, Ackland T, Carey-Smith R, Buelow JU, Hewitt B. Strength and functional symmetry is associated with post-operative rehabilitation in patients following anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2018 Aug;26(8):2353-2361. doi: 10.1007/s00167-017-4712-6. Epub 2017 Sep 15. PMID: 28916871.
  1. Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther. 1992;15(6):256-64. doi: 10.2519/jospt.1992.15.6.256. PMID: 18780999.
  1. Shelbourne KD, Klootwyk TE, Decarlo MS. Update on accelerated rehabilitation after anterior cruciate ligament reconstruction. J Orthop Sports Phys Ther. 1992;15(6):303-8. doi: 10.2519/jospt.1992.15.6.303. PMID: 18781000.
  1. Pässler HH, Shelbourne KD (1995) Biological, biomechanical and clinical approaches to the follow-up treatment of ligament surgery in the knee. Sports Exerc Injury 1:83–95
  1. Bynum EB, Barrack RL, Alexander AH. Open versus closed chain kinetic exercises after anterior cruciate ligament reconstruction. A prospective randomized study. Am J Sports Med. 1995 Jul-Aug;23(4):401-6. doi: 10.1177/036354659502300405. PMID: 7573647.
  1. Beynnon BD, Fleming BC, Johnson RJ, Nichols CE, Renström PA, Pope MH. Anterior cruciate ligament strain behavior during rehabilitation exercises in vivo. Am J Sports Med. 1995 Jan-Feb;23(1):24-34. doi: 10.1177/036354659502300105. PMID: 7726347.
  1. Beynnon BD, Johnson RJ, Fleming BC, Stankewich CJ, Renström PA, Nichols CE. The strain behavior of the anterior cruciate ligament during squatting and active flexion-extension. A comparison of an open and a closed kinetic chain exercise. Am J Sports Med. 1997 Nov-Dec;25(6):823-9. doi: 10.1177/036354659702500616. PMID: 9397272.
  1. Fukuda, Thiago & Fingerhut, Deborah & Moreira, Viviane & Camarini, Paula & Scodeller, Nathalia & Duarte, Aires & Martinelli, Mauro & Bryk, Flavio. (2013). Open Kinetic Chain Exercises in a Restricted Range of Motion After Anterior Cruciate Ligament Reconstruction A Randomized Controlled Clinical Trial. The American journal of sports medicine. 41. 10.1177/0363546513476482.
  1. Heijne, Annette & Werner, Suzanne. (2007). Early versus late start of open kinetic chain quadriceps exercises after ACL reconstruction with patellar tendon or hamstring grafts: A prospective randomized outcome study. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 15. 402-14. 10.1007/s00167-006-0246-z.

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