n Feature Article
Fifty Most-Cited Articles in Anterior
Cruciate Ligament Research
Pramod B. Voleti, MD; Fotios P. Tjoumakaris, MD; Gayle Rotmil, BS; Kevin B. Freedman, MD, MSCE
abstract
The number of times an article has been cited in the peer-reviewed literature is indicative
of its impact on its respective medical specialty. No study has used citation analysis to determine the most influential studies pertaining to the anterior cruciate ligament (ACL). The
primary aims of this study were to identify the classic works in ACL research using citation
analysis and to characterize these articles to determine which types of studies have had the
most influence on the field. A systematic query of ISI Web of Science (Thomson Reuters, Philadelphia, Pennsylvania) was performed for articles pertaining to the ACL, and the 50 mostcited articles were selected for evaluation. The following characteristics were determined for
each article: number of citations, citation density, journal, publication year, country of origin,
language, article type, article subtype, and level of evidence. The number of citations ranged
from 219 to 1073 (mean, 326), and the citation densities ranged from 4.9 to 55.6 citations
per year (mean, 18.2). All articles were published in 1 of 11 journals, with the most being
published in The American Journal of Sports Medicine (46%) and The Journal of Bone and
Joint Surgery American (30%). The most common decades of publication were the 1990s
(34%), 1980s (28%), and 2000s (26%). The majority (68%) of articles originated from the
United States, and all were written in English. By article type, 42% were basic science, and
58% were clinical. Of the clinical articles, 3% were Level I, 17% were Level II, 28% were
Level III, and 52% were Level IV. The articles were heterogeneous with regard to article type,
article subtype, and level of evidence and tended to have the following characteristics: highimpact journal of publication, recent publication year, US origin, English language, and low
level of evidence. These works represent some of the most popular scientific contributions
to ACL research. This list may aid residency and fellowship programs in the compilation of
articles for trainee reading curriculums. [Orthopedics. 2015; 38(4):e297-e304.]
The authors are from the Department of Orthopaedic Surgery (PBV), University of Pennsylvania, Philadelphia; Jefferson Medical College (GR), Philadelphia; and The Rothman Institute (KBF), Department of
Orthopaedic Surgery, Thomas Jefferson University, Bryn Mawr, Pennsylvania; and The Rothman Institute
(FPT), Department of Orthopaedic Surgery, Thomas Jefferson University, Egg Harbor Township, New Jersey.
The authors have no relevant financial relationships to disclose.
Correspondence should be addressed to: Kevin B. Freedman, MD, MSCE, The Rothman Institute, Medical Arts Pavilion, 825 Old Lancaster Rd, Ste 200, Bryn Mawr, PA 19010 (kevin.freedman@
rothmaninstitute.com).
Received: March 16, 2014; Accepted: June 13, 2014.
doi: 10.3928/01477447-20150402-58
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n Feature Article
T
he number of times an article has
been cited in the peer-reviewed
literature (citation number) and
the frequency of these citations (citation density) are markers for the article’s
impact on its respective specialty.1 Although citation number and density do
not directly assess the quality of a study,
they do shed light on its readership and
its potential to inspire change in practice. As such, several authors have used
citation analysis to identify classic influential works in a given area of medical
expertise.2-13
With regard to the orthopedic literature, Lefaivre et al9 identified the 100
most-cited articles in orthopedic surgery using citation analysis. The classic
works on this list spanned all orthopedic
subspecialties.9 Other authors have used
similar techniques to identify the most
cited works in orthopedic subspecialties,
including shoulder surgery,14 pediatric orthopedic surgery,15 and fracture surgery.16
However, to the authors’ knowledge, no
authors have published on the most cited
works pertaining to a particular clinical
problem in orthopedics. Specifically, no
study has used citation analysis to determine the most influential studies related to
the anterior cruciate ligament (ACL).
The purposes of this study were to
identify the 50 most-cited articles that
pertain to the ACL and to characterize
these works to determine which types of
articles have had the most influence on the
field.
Materials and Methods
The authors performed a systematic
query of the ISI Web of Science (v5.11;
Thomson Reuters, Philadelphia, Pennsylvania) using the Advanced Search tool
on April 12, 2013. They searched for all
published articles with a topic listed as
anterior cruciate ligament, ACL, or knee
ligament. The retrieved articles were then
sorted in order of the number of citations,
and the 50 most-cited articles were selected for analysis. The full texts of each
e298
of these articles were individually scrutinized by 2 authors to ensure that they contained material related to the ACL. After
meticulous evaluation, all 50 articles were
deemed to appropriately pertain to the
ACL. The authors’ query technique was
identical to that used in previous analyses of orthopedic literature,9,14-16 with the
exception that the authors expanded their
search to include all journals, not just those
listed under the Web of Science Subject
Category of “Orthopedics.” The following characteristics were then recorded for
each of the 50 most-cited articles: citation
number, citation density, journal, publication year, country of origin, and language.
In addition, 2 independent evaluators
characterized each article by type (basic
science vs clinical), subtype (basic science subtypes: animal studies, anatomic
studies, biomechanical studies; clinical
subtypes: review articles, technique articles, case series, case-control studies,
prospective cohort studies, randomized
controlled trials, and meta-analyses),
and level of evidence for clinical articles.
Level of evidence was determined using
the classification system jointly developed
by The Journal of Bone and Joint Surgery
and the American Academy of Orthopaedic Surgeons.17 Interobserver agreement
for all subjective variables was excellent:
100% for article type, 100% for article
subtype, and 98% for level of evidence.
All discrepancies between authors were
resolved by consensus. The results were
then analyzed to determine which characteristics were most common among the 50
most-cited articles.
Results
The 50 most-cited articles pertaining
to the ACL had citation numbers ranging from 219 to 1073 citations (mean,
326) and citation densities ranging from
4.9 to 55.6 citations per year (mean, 18.2)
(Table 1). The 2 articles with the greatest number of citations were “Rating systems in the evaluation of knee ligament
injuries” by Tegner et al18 (1073 citations)
and “Evaluation of knee ligament surgery
results with special emphasis on use of
a scoring scale” by Lysholm et al19 (943
citations). Interestingly, these were the
only 2 articles that introduced instruments
for outcome evaluation. The article with
the greatest citation density was “Biomechanical measures of neuromuscular control and valgus loading of the knee predict
ACL injury risk in female athletes” by
Hewett et al20 (55.6 citations per year).
All of the top 50 articles were published in 1 of 11 journals (Table 2), with
the most being published in The American Journal of Sports Medicine (AJSM)
(46%) and The Journal of Bone and Joint
Surgery American (JBJS-A) (30%). The
publication years of the 50 most-cited
articles spanned from 1963 to 2007. The
most common decades of publication
were the 1990s (34%), 1980s (28%), and
2000s (26%) (Figure 1). Of the 50 mostcited articles, those published in the 1980s
had the greatest mean number of citations
(421) by decade (Figure 2). On the other
hand, mean citation density increased
with each successive decade (Figure 3),
with the top 50 articles published in the
2000s having the greatest mean citation
density (30.7).
The 50 most-cited articles originated
from 10 countries (Table 3). The majority
(68%) originated from the United States,
and all of the top 50 articles were written
in the English language. The only individual with lead authorship for 3 different
articles on the top 50 list was FR Noyes,
whereas DM Daniel, JC Hughston, LS
Lohmander, KL Markolf, and KD Shelbourne each had lead authorship on 2 of
the articles on the list.
By article type, 42% were basic science and 58% were clinical. There was a
wide variety of article subtypes (Table 4),
but the most common was basic science
biomechanical studies (32%). Of the 29
clinical articles, more than half (52%) had
Level IV evidence, while the remaining
had Level I (3%), Level II (17%), or Level
III (28%) evidence (Table 5).
Copyright © SLACK Incorporated
n Feature Article
Table 1
Top 50 Most Cited Articles in Anterior Cruciate Ligament Research
Rank
Article
Citation
Number
Citation
Density
1
Tegner Y, Lysholm J. Rating systems in the evaluation of knee ligament injuries. Clin Orthop Relat Res. 1985;
(198):43-49.
1073
38.3
2
Lysholm J, Gillquist J. Evaluation of knee ligament surgery results with special emphasis on use of a scoring
scale. Am J Sports Med. 1982; 10(3):150-154.
943
30.4
3
Noyes FR, Butler DL, Grood ES, Zernicke RF, Hefzy MS. Biomechanical analysis of human ligament grafts
used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am. 1984; 66(3):344-352.
629
21.7
4
Daniel DM, Stone ML, Dobson BE, Fithian DC, Rossman DJ, Kaufman KR. Fate of the ACL-injured patient: a
prospective outcome study. Am J Sports Med. 1994; 22(5):632-644.
558
29.4
5
Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. Am J Sports
Med. 1990; 18(3):292-299.
535
23.3
6
Hewett TE, Myer GD, Ford KR, et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. Am J Sports Med. 2005;
33(4):492-501.
445
55.6
7
Solomonow M, Baratta R, Zhou BH, et al. The synergistic action of the anterior cruciate ligament and thigh
muscles in maintaining joint stability. Am J Sports Med. 1987; 15(3):207-213.
418
16.1
8
Woo SLY, Hollis JM, Adams DJ, Lyon RM, Takai S. Tensile properties of the human femur-anterior cruciate
ligament-tibia complex: the effects of specimen age and orientation. Am J Sports Med. 1991; 19(3):217-225.
395
18.0
9
Noyes FR, Grood ES. Strength of anterior cruciate ligament in humans and rhesus-monkeys. J Bone Joint Surg
Am. 1976; 58(8):1074-1082.
381
10.3
10a
Kurosaka M, Yoshiya S, Andrish JT. A biomechanical comparison of different surgical techniques of graft fixation in anterior cruciate ligament reconstruction. Am J Sports Med. 1987; 15(3):225-229.
362
13.9
11
Yagi M, Wong EK, Kanamori A, Debski RE, Fu FH, Woo SLY. Biomechanical analysis of an anatomic anterior
cruciate ligament reconstruction. Am J Sports Med. 2002; 30(5):660-666.
362
32.9
12
Sachs RA, Daniel DM, Stone ML, Garfein RF. Patellofemoral problems after anterior cruciate ligament reconstruction. Am J Sports Med. 1989; 17(6):760-765.
357
14.9
13
Noyes FR, Delucas JL, Torvik PJ. Biomechanics of anterior cruciate ligament failure: analysis of strain-rate
sensitivity and mechanisms of failure in primates. J Bone Joint Surg Am. 1974; 56(2):236-253.
345
8.8
14
Boden BP, Dean GS, Feagin JA, Garrett WE. Mechanisms of anterior cruciate ligament injury. Orthopedics.
2000; 23(6):573-578.
341
26.2
15
Hughston JC, Andrews JR, Cross MJ, Moschi A. Classification of knee ligament instabilities: 1. Medial compartment and cruciate ligaments. J Bone Joint Surg Am. 1976; 58(2):159-172.
333
9.0
16
Aglietti P, Buzzi R, Zaccherotti G, Debiase P. Patellar tendon versus doubled semitendinosus and gracilis
tendons for anterior cruciate ligament reconstruction. Am J Sports Med. 1994; 22(2):211-218.
320
16.8
17
Marder RA, Raskind JR, Carroll M. Prospective evaluation of arthroscopically assisted anterior cruciate ligament reconstruction: patellar tendon versus semitendinosus and gracilis tendons. Am J Sports Med. 1991;
19(5):478-484.
304
13.8
18
Mink JH, Levy T, Crues JV. Tears of the anterior cruciate ligament and menisci of the knee: MR imaging
evaluation. Radiology. 1988; 167(3):769-774.
294
11.8
19
Daniel DM, Stone ML, Sachs R, Malcom L. Instrumented measurement of anterior knee laxity in patients
with acute anterior cruciate ligament disruption. Am J Sports Med. 1985; 13(6):401-407.
290
10.4
20
Clancy WG, Nelson DA, Reider B, Narechania RG. Anterior cruciate ligament reconstruction using 1/3 of
the patellar ligament, augmented by extra-articular tendon transfers. J Bone Joint Surg Am. 1982; 64(3):352359.
289
9.3
21
Markolf KL, Burchfield DI, Shapiro MM, Shepard ME, Finerman GAM, Slauterbeck JL. Combined knee loading states that generate high anterior cruciate ligament forces. J Orthop Res. 1995; 13(6):930-935.
279
15.5
22
Obrien SJ, Warren RF, Pavlov H, Panariello R, Wickiewicz TL. Reconstruction of the chronically insufficient anterior cruciate ligament with the central 3rd of the patellar ligament. J Bone Joint Surg Am. 1991;
73(2):278-286.
272
12.4
23
Renstrom P, Arms SW, Stanwyck TS, Johnson RJ, Pope MH. Strain within the anterior cruciate ligament during hamstring and quadriceps activity. Am J Sports Med. 1986; 14(1):83-87.
266
9.9
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n Feature Article
Table 1 (cont’d)
Top 50 Most Cited Articles in Anterior Cruciate Ligament Research
Rank
Article
Citation
Number
Citation
Density
24
Arnoczky SP, Tarvin GB, Marshall JL. Anterior cruciate ligament replacement using patellar tendon: an evaluation of graft revascularization in the dog. J Bone Joint Surg Am. 1982; 64(2):217-224.
261
8.4
25a
Lohmander LS, Ostenberg A, Englund M, Roos H. High prevalence of knee osteoarthritis, pain, and functional limitations in female soccer players twelve years after anterior cruciate ligament injury. Arthritis Rheum.
2004; 50(10):3145-3152.
260
28.9
26
Markolf KL, Gorek JF, Kabo JM, Shapiro MS. Direct measurement of resultant forces in the anterior cruciate ligament: an in vitro study performed with a new experimental-technique. J Bone Joint Surg Am. 1990;
72(4):557-567.
260
11.3
27
Berchuck M, Andriacchi TP, Bach BR, Reider B. Gait adaptations by patients who have a deficient anterior
cruciate ligament. J Bone Joint Surg Am. 1990; 72(6):871-877.
258
11.2
28
Kennedy JC, Weinberg HW, Wilson AS. Anatomy and function of anterior cruciate ligament—as determined
by clinical and morphological studies. J Bone Joint Surg Am. 1974; 56(2):223-235.
257
6.6
29
Loh JC, Fukuda Y, Tsuda E, Steadman RJ, Fu FH, Woo SLY. Knee stability and graft function following anterior
cruciate ligament reconstruction: comparison between 11 o’clock and 10 o’clock femoral tunnel placement.
Arthroscopy. 2003; 19(3):297-304.
256
25.6
30
Lohmander LS, Englund PM, Dahl LL, Roos EM. The long-term consequence of anterior cruciate ligament
and meniscus injuries: osteoarthritis. Am J Sports Med. 2007; 35(10):1756-1769.
255
42.5
31
Frank CB, Jackson DW. Current concepts review: the science of reconstruction of the anterior cruciate ligament. J Bone Joint Surg Am. 1997; 79(10):1556-1576.
254
15.9
32
Olsen OE, Myklebust G, Engebretsen L, Bahr R. Injury mechanisms for anterior cruciate ligament injuries in
team handball a systematic video analysis. Am J Sports Med. 2004; 32(4):1002-1012.
253
28.1
33
Freedman KB, D’Amato MJ, Nedeff DD, Kaz A, Bach BR. Arthroscopic anterior cruciate ligament reconstruction: a metaanalysis comparing patellar tendon and hamstring tendon autografts. Am J Sports Med. 2003;
31(1):2-11.
247
24.7
34a
Mandelbaum BR, Silvers HJ, Watanabe DS, et al. Effectiveness of a neuromuscular and proprioceptive
training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up. Am J
Sports Med. 2005; 33(7):1003-1010.
246
30.8
35
Jones KG. Reconstruction of the anterior cruciate ligament: a technique using the central 1/3 of the patellar
ligament. J Bone Joint Surg Am. 1963; 45(5):925-932.
246
4.9
36
Arms SW, Pope MH, Johnson RJ, Fischer RA, Arvidsson I, Eriksson E. The biomechanics of anterior cruciate
ligament rehabilitation and reconstruction. Am J Sports Med. 1984; 12(1):8-18.
244
8.4
37a
Myklebust G, Engebretsen L, Braekken IH, Skjolberg A, Olsen OE, Bahr R. Prevention of anterior cruciate
ligament injuries in female team handball players: a prospective intervention study over three seasons. Clin J
Sport Med. 2003; 13(2):71-78.
241
24.1
38
Odensten M, Gillquist J. Functional-anatomy of the anterior cruciate ligament and a rationale for reconstruction. J Bone Joint Surg Am. 1985; 67(2):257-262.
241
8.6
39a
Corry IS, Webb JM, Clingeleffer AJ, Pinczewski LA. Arthroscopic reconstruction of the anterior cruciate
ligament: a comparison of patellar tendon autograft and four-strand hamstring tendon autograft. Am J Sports
Med. 1999; 27(4):444-454.
239
17.1
40
Tashman S, Collon D, Anderson K, Kolowich P, Anderst W. Abnormal rotational knee motion during running
after anterior cruciate ligament reconstruction. Am J Sports Med. 2004; 32(4):975-983.
239
26.6
41
Amis AA, Dawkins GPC. Functional-anatomy of the anterior cruciate ligament: fiber bundle actions related
to ligament replacements and injuries. J Bone Joint Surg Br. 1991; 73(2):260-267.
237
10.8
42
Matsusue Y, Yamamuro T, Hama H. Arthroscopic multiple osteochondral transplantation to the chondral
defect in the knee associated with anterior cruciate ligament disruption. Arthroscopy. 1993; 9(3):318-321.
236
11.8
43
Noyes FR, Barber SD, Mangine RE. Abnormal lower-limb symmetry determined by function hop tests after
anterior cruciate ligament rupture. Am J Sports Med. 1991; 19(5):513-518.
234
10.6
44
McDaniel WJ, Dameron TB. Untreated ruptures of the anterior cruciate ligament: a follow-up-study. J Bone
Joint Surg Am. 1980; 62(5):696-705.
227
6.9
45a
Jackson DW, Grood ES, Goldstein JD, et al. A comparison of patellar tendon autograft and allograft used for
anterior cruciate ligament reconstruction in the goat model. Am J Sports Med. 1993; 21(2):176-185.
225
11.3
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n Feature Article
Table 1 (cont’d)
Top 50 Most Cited Articles in Anterior Cruciate Ligament Research
Rank
Article
Citation
Number
Citation
Density
46
Sakane M, Fox RJ, Woo SLY, Livesay GA, Li G, Fu FH. In situ forces in the anterior cruciate ligament and its
bundles in response to anterior tibial loads. J Orthop Res. 1997; 15(2):285-293.
225
14.1
47
Lee CH, Shin HJ, Cho IH, et al. Nanofiber alignment and direction of mechanical strain affect the ECM production of human ACL fibroblast. Biomaterials. 2005;26(11):1261-1270.
224
28.0
48
Gabriel MT, Wong EK, Woo SLY, Yagi M, Debski RE. Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads. J Orthop Res. 2004; 22(1):85-89.
221
24.6
49
Shelbourne KD, Gray T. Anterior cruciate ligament reconstruction with autogenous patellar tendon graft followed by accelerated rehabilitation: a two- to nine-year followup. Am J Sports Med. 1997; 25(6):786-795.
220
13.8
50
Hughston JC, Andrews JR, Cross MJ, Moschi A. Classification of knee ligament instabilities: 2. Lateral compartment. J Bone Joint Surg Am. 1976; 58(2):173-179.
219
5.9
a
Two or more citations tied for the same rank.
Table 2
Number of Top 50 Anterior Cruciate Ligament Articles by
Source Journal
Source Journal
No. of Articles
The American Journal of Sports Medicine
23
The Journal of Bone and Joint Surgery–American
15
Journal of Orthopaedic Research
3
Arthroscopy
2
Arthritis and Rheumatism
1
Biomaterials
1
Clinical Journal of Sport Medicine
1
Clinical Orthopaedics and Related Research
1
The Journal of Bone and Joint Surgery–British
1
Orthopedics
1
Radiology
1
Discussion
The number of times an article has
been cited in the peer-reviewed literature
is indicative of its impact on its respective specialty. The current study identifies
the 50 most-cited articles pertaining to
the ACL. This list represents some of the
most popular works published on the subject. Although citation number and density are important markers for an article’s
impact on a medical specialty, they are not
APRIL 2015 | Volume 38 • Number 4
the only such measures. As such, the authors’ list of the 50 most-cited articles pertaining to the ACL is not exclusive—there
are certainly several articles not on the list
that have had a significant impact on the
field. Nevertheless, the list does successfully identify many of the classic studies
that have advanced the understanding
of the anatomy and biomechanics of the
ACL, as well as the diagnosis, management, and prognosis of ACL injuries.
Figure 1: Number of top 50 anterior cruciate ligament articles by decade of publication.
Figure 2: Mean number of citations of top 50 anterior cruciate ligament articles by decade of publication.
After identifying the 50 most-cited
articles pertaining to the ACL, the authors analyzed the characteristics of
these studies. They found that the 2 most
cited articles18,19 were the only 2 articles
that introduced instruments for outcome
evaluation. Outcome evaluation tools are
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n Feature Article
Table 3
Number of Top 50
Anterior Cruciate
Ligament Articles by
Country of Origin
Country of Origin
Figure 3: Mean citation density of top 50 anterior
cruciate ligament articles by decade of publication.
United States
34
Sweden
5
Canada
2
Japan
2
Table 4
Norway
2
Number of Top 50
Anterior Cruciate
Ligament Articles by
Article Subtype
Australia
1
England
1
Italy
1
South Korea
1
Turkey
1
Article Subtype
No. of
Articles
Basic science—animal
study
2
Basic science—anatomic
study
3
Basic science—biomechanical study
16
Clinical—review article
4
Clinical—technique article
2
Clinical—case series
8
Clinical—case-control
study
8
Clinical—prospective cohort
study
5
Clinical—randomized, controlled trial
1
Clinical—meta-analysis
1
extremely useful in providing objective
measurements to assess the efficacy of
a given intervention. A study that introduces and validates an effective outcome
evaluation instrument is likely to be cited
repeatedly—whenever that particular instrument is used in another study. Lefaivre
et al9 found that the most cited article in
orthopedic surgery introduced Harris Hip
Scores,21 and Namdari et al14 found that
the most cited article in shoulder surgery
introduced Constant scores.22 It is consis-
e302
No. of
Articles
Table 5
Number of Top 50
Anterior Cruciate
Ligament Articles by
Level of Evidence
Level of Evidence
No. of
Articles
I
1
II
5
III
8
IV
15
V
0
Basic science article
21
tent with these findings that the outcome
evaluation tools introduced by Tegner et
al18 and Lysholm et al19 have been cited so
frequently in the ACL literature.
The majority of the top 50 mostcited articles list were published in AJSM
(46%) or JBJS-A (30%). Indeed, articles
published in these 2 journals tend to have
a high impact. The annual Thomson Reuters Journal Citation Reports rank journals according to impact factor, which is a
measure of the frequency with which the
average article in a particular journal has
been cited in a certain period of time.23
According to the 2012 version of this report, of the 65 journals in the subject category of Orthopedics, AJSM was ranked
first (impact factor: 4.439) and JBJS-A
was ranked third (impact factor: 3.234).23
Consistent with these findings, Siebelt et
al24 found that AJSM was the specialized
orthopedic journal with the greatest impact factor, whereas JBJS-A was the general orthopedic journal with the greatest
impact factor.
However, it is important to keep in
mind that citation number and density
for articles, as well as impact factor for
journals, can be affected by self-citation
rates.25 Hakkalamani et al26 found that,
of the 7 general orthopedic journals that
they examined, JBJS-A had the greatest
self-citation rate, with more than 40% of
JBJS-A references being made to other
JBJS-A articles. The most common decades of publication for the 50 mostcited articles were the 1990s (34%), 1980s
(28%), and 2000s (26%). Therefore, although older articles pertaining to the
ACL have had more time to accumulate
citations, it seems that more recent articles
on the subject have generally had a greater
impact. Furthermore, the current authors
found that mean citation density increased
with each successive decade, with the
articles published in the 2000s having
the greatest mean citation density (30.7).
These findings are in stark contrast to the
study by Lefaivre et al,9 which identified
the 100 most-cited articles in orthopedic
surgery. They found that the 1980s had
the greatest number of top 100 articles,
with more than twice as many articles as
any other decade.9 They also found that
mean citation density was greatest in articles published in the 1940s, 1960s, and
1970s.9 These differences reflect the fact
that the community’s understanding of the
anatomy and biomechanics of the ACL
and of the diagnosis, management, and
prognosis of ACL injuries is relatively re-
Copyright © SLACK Incorporated
n Feature Article
cent. Indeed, available knowledge on the
subject has evolved tremendously over the
past few decades with the advent of novel
techniques and technologies.
The 50 most-cited ACL articles originated from 10 different countries, with
68% originating from the United States.
The preponderance of classic articles
from the United States has also been demonstrated in the literature of anesthesia,8
critical care,7 emergency medicine,13 plastic surgery,12 general surgery,6 and orthopedic surgery.9 Potential explanations for
this finding may be that (1) more studies
in general originate from the United States
than from any other nation, (2) studies
from the United States are more likely to
have a greater impact, or (3) authors from
the United States have an advantage in
publishing in high-impact journals. This
advantage may be due to inherent language barriers encountered by foreign authors who are attempting to publish their
work in high-impact journals, which tend
to be published in the English language. In
this regard, English-speaking authors may
possess a substantial advantage over their
counterparts. The current study found that
all of the top 50 articles were written in
the English language. However, it should
be noted that ISI Web of Science only
includes a limited number of journals in
languages other than English. Therefore,
this investigation may have excluded influential articles published in foreign languages, as well as citations from articles
published in foreign languages.
The authors found a fairly even split
between basic science (42%) and clinical
(58%) articles within the 50 most-cited
ACL articles. Lefaivre et al9 demonstrated a less even breakdown of the top 100
articles in orthopedic surgery (24% basic science vs 76% clinical). In addition,
studies analyzing the classic articles in
other fields also found a dominance of
clinical studies over basic science studies.6,8,12,13 Therefore, it seems that basic
science ACL studies are more likely to
be classic articles than basic science stud-
APRIL 2015 | Volume 38 • Number 4
ies in other medical fields. In support of
this notion, the current authors found that
the most common article subtype among
the 50 most-cited ACL articles was not a
clinical subtype, but rather basic science
biomechanical studies (32%).
When looking at just the clinical articles in the top 50 list, 52% had Level
IV evidence, whereas the remaining had
Level I (3%), Level II (17%), or Level III
(28%) evidence. Samuelsson et al27 examined the level of evidence of all therapeutic studies written in English published
from January 1995 to August 2011 that
reported on isolated primary ACL reconstruction with clinical outcome measurements. Consistent with the results of the
current study, Samuelsson et al27 found
that the most common level of evidence
encountered in their search was Level IV
(33.7%). Furthermore, the orthopedic citation analyses by Lefaivre et al,9 Baldwin
et al,15 Baldwin and Namdari,16 and Namdari et al14 also demonstrated a preponderance of Level IV studies among the classic
articles identified within all of orthopedics
and various orthopedic subspecialties.
Because the concept of evidence-based
medicine is relatively new, it is possible
that higher level studies will infiltrate the
top 50 list over time. In support of this
notion, Samuelsson et al27 demonstrated
a significant trend toward higher mean
level of evidence over time. In addition,
the current study found that higher level
studies on the top 50 most-cited list tended to be published more recently. It will
be interesting to study the changes in level
of evidence frequencies that occur as ACL
research matures. Nevertheless, there will
likely always be a role for classic ACL
studies, even those that are based on Level
IV evidence.
This study has several weaknesses.
First, the authors arbitrarily selected to
identify the top 50 most-cited articles
pertaining to the ACL. There are certainly classic and influential articles that
may not fall in the top 50. They selected
50 because this is a reasonable number of
articles to include in a resident or fellow
reading curriculum and because previous analyses of orthopedic subspecialty
literature used the same number.14,15 Second, citation number and density may be
affected by confounding factors, such as
author self-citation, journal self-citation,
exposure time, and journal impact factor.
The authors encourage further study of
these factors and how they affect frequency of citation. Third, they only included
citations from published articles; they did
not include citations from lectures, presentations, textbooks, or other non-peerreviewed literature. As such, the authors
may have missed out on certain classic
articles or teaching references that tend to
be more frequently cited in these venues.
Fourth, as proposed in the article by Lefaivre et al,9 some articles may be subject
to a “snowball effect” of citation, where
they are repeatedly cited because of previous citations rather than for their quality
or content. Others may be cited simply because they include well-known authors or
authors who sit on editorial boards or serve
as peer reviewers. In addition, others may
be cited frequently because they address
timely and popular topics. These biases
may result in inflated citation rates that
do not truly reflect influence on the field.
Fifth, the study does not address conflicts
of interests, which can potentially introduce bias, and the influence of conflicts of
interests on citation rates. Finally, citation
number and density are only 2 measures
of the impact of an article. Therefore, the
authors’ list of the top 50 most-cited ACL
articles is not exclusive.
Conclusion
This study identifies the 50 most-cited
articles pertaining to the ACL: classic
works that have greatly influenced the
community’s understanding of the subject.
This list may aid residency and fellowship
programs in the compilation of articles for
trainee reading curriculums. In addition,
this investigation identifies characteristics
that are common and varied among these
e303
n Feature Article
top 50 most-cited articles, thus providing
insight into what factors make an article
on the ACL influential.
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