The Effect of an Adductor Longus Tenotomy on the Bent Knee Fall Out Test
Conditions: Adductor Tendinitis
Sponsor: Aspetar

 
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Official Title: The effect of an adductor longus tenotomy on the bent knee fall out test 
Document Date: February 11th, 2020. 
 
 
 
 
INTRODUCTION 
Adductor-related groin pain is the most common type of groin pain in athletes,[1,2] and pain at the 
proximal adductor longus insertion is a key finding in the diagnosis of longstanding groin pain.[3] 
“Tightness“ or “shortening” of the adductor longus is considered both a cause and effect of pain,(ref) 
that can lead to increased tension at the proximal insertion, thus playing a role in the persistency of 
longstanding adductor-related pain. For patients who do not respond sufficiently to non-surgical 
procedures, an adductor longus tenotomy is a surgical option that is considered to reduce tension at the 
proximal adductor longus insertion assisting in reduction of pain and return to sport.  
The bent knee fall out test (BKFO) is one of the most commonly used tests to test adductor flexibility.[4–
6] This test involves a combined hip movement with hip flexion, abduction, and external rotation, and a 
high result is generally considered to be related to adductor muscle “tightness”, specifically that of the 
adductor longus.(refs) It is uncertain whether the BKFO test is actually measuring adductor muscle 
flexibility or hip joint range of motion, as the test results may also be affected by a femoral head cam 
morphology.[7] A slightly different test, called the Patrick FABER’s test, involves a similar movement and 
is mainly used as a hip joint pain provocation test.  
By cutting the adductor longus tendon thereby removing the effect of potential adductor longus 
“tightness”, we will be able to show if and how much the flexibility of this muscle effects the test results, 
to assist in future considerations of what this test is actually testing.  

 
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Our aim was to investigate the immediate effect of an adductor longus tenotomy on the results of the 
bent knee fall out test.    
 
METHODS 
Participants 
Athletes with groin pain are consecutively recruited from two clinics of a visceral surgeon specialized in 
groin pain in athletes. The clinics are located in Bordeaux and Paris, France, and patient population 
includes athletes from all over France. Inclusion criteria are: adult (>18 years old) athletes with 
adductor-related groin pain, subcategorized as adductor longus insertion pain, undergoing unilateral or 
bilateral adductor longus tenotomy by one visceral surgeon specialized in groin pain in athletes. 
Adductor-related groin pain is clinically diagnosed as adductor tenderness and pain on resisted 
adduction testing as described in the Doha agreement on terminology and definitions of groin pain in 
athletes.[8] For this study, we further specified both palpation and resistance pain should be present at 
the proximal adductor longus insertion. No specific exclusion criteria were present other than refusal to 
participate in the study. As the vast majority of patients seen in the clinic are male athletes, we based 
our sample size calculation and primary analysis on male athletes only. The results from any female 
athletes included during the same period will be reported separately as a secondary analysis. 
 
Ethics 
Ethics approval was obtained by the ethics committee of Clinique du sport de Bordeaux-Merignac, 
France (#02-2020.2). Athletes will be included in this study after giving their informed consent according 
to the Declaration of Helsinki. 

 
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Patient demographics and injury information. 
Demographic data (age, height, weight, type and level of sport is recorded. Athletes are also asked 
about the duration of their groin pain (weeks), the onset of pain (sudden/gradual), whether the pain is 
unilateral or bilateral, highest pain during their last session of sports on a 0-10 numerical pain rating 
scale (NPRS, 0 being ‘no pain’ and 10 ‘worse pain imaginable’. They will also be asked if they have any 
pain in other locations than the groin. 
 
Bent knee fall out test (BKFO) 
The BKFO test is performed in either general anesthesia or spinal anesthesia, for patients operated in 
Bordeaux and Paris, respectively. This is standard procedure for the surgical procedures and also 
prevents any voluntary activation of the adductor muscles. The patient lies supine on the surgical table 
with app. 90° knee flexion, 45° hip flexion, and the feet together and the hips in external rotation (also 
known as the frog-leg position. Standardization of position is achieved by flexing one leg first, so the 
medial malleolus is placed next to the medial knee joint line of the contralateral leg. The knee is then 
moved laterally, externally rotating the hip with the plantar surface placed towards the contralateral leg. 
The contralateral leg is then flexed, and the plantar surfaces of the feet are aligned. The distance 
between the most distal point on the head of the fibula and the surface of the surgical table is measured 
using a rigid tape measure and distance is recorded in cm to the nearest 0.5 cm (Figure 1) The BKFO test 
has excellent reproducibility with an standard error of the measurement of app 1 cm or less.[4,11,12] 

 
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A 
 B
 
Figure 1   A: Position of the patient’s legs prior to the surgical procedure, B: Measurement from the head 
of the fibula to the surgical table  
 
Surgical procedure 
The proximal adductor longus tendon is identified though palpation, and a longitudinal incision of app 
4cm is made in the line of the tendon.  The fascia of the adductor longus is divided to identify the 
tendon (figure 2), and a transverse incision is made as close to the insertion as possible (app. 0.5cm) 
resulting in a full release of both the adductor longus tendon and muscle, as present on the posterior 
side of the tendon. A minor removal of app 0.5 cm of the released tendon is made, and the adductor 
longus is placed app 5 cm from the pubic bone (figure 2). The wound is closed in layers after careful 
hemostasis. The tenotomy is either performed unilateral or bilateral. 
 

 
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Figure 2   Adductor longus tendon before and after the tenotomy. 
 
Statistical analysis 
Data are presented as means with standard deviation (SD), unless indicated otherwise, and non-
normally distributed data are expressed as medians with the 25th–75th interquartile range (IQR25, 
IQR75). A paired T-test is used to compare the BKFO results pre- and post- tenotomy. Additionally, 
correlation between baseline values and change in BKFO will be analyzed to investigate whether 
patients with higher baseline test results also have a larger change. Analyses are carried out in Statistical 
Package for Social Sciences (SPSS; version 21, IBM). Effect sizes were calculated using Cohen’s d and 
assessed as; small (d = 0.2), moderate (d = 0.5), and large (d = 0.8).[13] 
 
Sample size 
We calculated our sample size using G*power software (v. 3.1, Heinrich-Heine-Universität, Düsseldorf, 
Germany). We used BKFO values from non-injured football players; mean 13.1 cm, standard deviation 
(SD) 4.4cm.[4] We performed pilot measurements pre- and post-tenotomy on five patients. These had a 

 
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mean of 2.1 cm reduction, which we used for the sample size calculation. We set the required power at 
95%, used an α-error probability of 5%, and a correlation between measurements of 0.5. This resulted in 
a total sample size requirement of 60 participants.  
 
 
 
 

 
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REFERENCES 
1  Holmich P, Thorborg K, Dehlendorff C, et al. Incidence and clinical presentation of groin injuries in 
sub-elite male soccer. British Journal of Sports Medicine Published Online First: 16 August 2013. 
doi:10.1136/bjsports-2013-092627 
2  Serner A, Tol JL, Jomaah N, et al. Diagnosis of acute groin injuries: a prospective study of 110 athletes. 
Am J Sports Med 2015;43:1857–64. doi:10.1177/0363546515585123 
3  Hölmich P. Long-standing groin pain in sportspeople falls into three primary patterns, a “clinical 
entity” approach: a prospective study of 207 patients. Br J Sports Med 2007;41:247–52. 
doi:10.1136/bjsm.2006.033373 
4  Mosler A, Crossley K, Thorborg K, et al. Normative profiles for hip strength and flexibility in elite 
footballers. Journal of Science and Medicine in Sport 2014;18, Supplement 1:e32–3. 
doi:10.1016/j.jsams.2014.11.216 
5  Mosler AB, Weir A, Serner A, et al. Musculoskeletal Screening Tests and Bony Hip Morphology Cannot 
Identify Male Professional Soccer Players at Risk of Groin Injuries: A 2-Year Prospective Cohort Study. 
Am J Sports Med 2018;46:1294–305. doi:10.1177/0363546518763373 
6  Nevin F, Delahunt E. Adductor squeeze test values and hip joint range of motion in Gaelic football 
athletes with longstanding groin pain. Journal of Science and Medicine in Sport 2014;17:155–9. 
doi:10.1016/j.jsams.2013.04.008 
7  Tak I, Glasgow P, Langhout R, et al. Hip Range of Motion Is Lower in Professional Soccer Players With 
Hip and Groin Symptoms or Previous Injuries, Independent of Cam Deformities. Am J Sports Med 
2016;44:682–8. doi:10.1177/0363546515617747 
8  Weir A, Brukner P, Delahunt E, et al. Doha agreement meeting on terminology and definitions in 
groin pain in athletes. British Journal of Sports Medicine 2015;49:768–74. doi:10.1136/bjsports-2015-
094869 
9  Thorborg K, Hölmich P, Christensen R, et al. The Copenhagen Hip and Groin Outcome Score (HAGOS): 
development and validation according to the COSMIN checklist. Br J Sports Med 2011;45:478–91. 
doi:10.1136/bjsm.2010.080937 
10  
Clarsen B, Myklebust G, Bahr R. Development and validation of a new method for the 
registration of overuse injuries in sports injury epidemiology: the Oslo Sports Trauma Research 
Centre (OSTRC) Overuse Injury Questionnaire. British Journal of Sports Medicine 2013;47:495–502. 
doi:10.1136/bjsports-2012-091524 
11  
O’Brien J, Santner E, Finch CF. The inter-tester reliability of the squeeze and bent-knee-fall-out 
tests in elite academy football players. Phys Ther Sport 2018;34:8–13. doi:10.1016/j.ptsp.2018.08.004 
12  
Malliaras P, Hogan A, Nawrocki A, et al. Hip flexibility and strength measures: reliability and 
association with athletic groin pain. British Journal of Sports Medicine 2009;43:739–44. 
doi:10.1136/bjsm.2008.055749 

 
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13  
Cohen J. A power primer. Psychol Bull 1992;112:155–9.