Technical Note

How to Rapidly Abolish Knee Extension Deficit After

Injury or Surgery: A Practice-Changing Video Pearl
From the Scientific Anterior Cruciate Ligament
Network International (SANTI) Study Group
Jean-Romain Delaloye, M.D., Jozef Murar, M.D., Mauricio González Sánchez, M.D.,
Adnan Saithna, B.Med.Sci.(Hons), M.B.Ch.B., Dip.S.E.M., M.Sc., F.R.C.S.(Tr&Orth),
Hervé Ouanezar, M.D., Mathieu Thaunat, M.D., Thais Dutra Vieira, M.D., and
Bertrand Sonnery-Cottet, M.D.

Abstract: Knee extension deficit is frequently observed after anterior cruciate ligament reconstruction or rupture and
other acute knee injuries. Loss of terminal extension often occurs because of hamstring contracture and quadriceps
inactivation rather than mechanical intra-articular pathology. Failure to regain full extension in the first few weeks after
anterior cruciate ligament reconstruction is a recognized risk factor for adverse long-term outcomes, and therefore, it is
important to try to address it. In this Technical Note, a simple, rapid, and effective technique to help regain full knee
extension and abolish quadriceps activation failure is described.

A patient who presents with an extension deficit

after an acute knee injury or surgery can be
challenging to manage. The medical provider who first
practice, the pathophysiology of the latter scenario
had remained unclear for decades. In 1986 Allum
and Jones1 observed that spasms of the hamstrings
evaluates the patient must differentiate between 2 were related to an extension deficit after knee injury,
separate situations: In the “locked knee,” a displaced but no explanation was given. More recently, there has
intra-articular structure mechanically prevents full been increased interest in the subject, and multiple
extension, whereas the “pseudo-locked knee” occurs authors have postulated that the extension deficit, also
without the presence of any true mechanical block to observed after knee surgery, may be due to a process
motion.1 Although frequently observed in clinical called “arthrogenic muscle inhibition” (AMI).2,3 AMI is
believed to be responsible for the failure of quadriceps
activation that is associated with hamstring contracture.
From the Department of Orthopaedic Surgery and Sports Medicine, Centre In this Technical Note, we describe a set of exercises
Orthopédique Santy, FIFA Medical Centre of Excellence, Hôpital Privé Jean
Mermoz, Groupe Ramsay Générale de Santé (J-R.D., J.M., M.G.S., H.O.,
that reliably counter the physiological pathways of AMI
M.T., T.D.V., B.S-C.), Lyon, France; and Ormskirk Hospital (A.S.), Ormskirk, and quickly regain full active and passive knee extension
England. (Table 1). No special equipment is necessary. Video 1
The authors report the following potential conflict of interest or source of shows the efficacy of the technique in a patient with
funding: A.S. receives support from Arthrex. Consultant. M.T. receives support AMI after an anterior cruciate ligament (ACL) injury.
from Arthrex. Consultant. B.S-C. receives support from Arthrex. Consultant,
royalties. Full ICMJE author disclosure forms are available for this article
online, as supplementary material.
Received January 2, 2018; accepted February 16, 2018. Technique to Abolish Knee Extension
Address correspondence to Bertrand Sonnery-Cottet, M.D., Centre Deficit and Quadriceps Activation Failure
Orthopédique Santy, FIFA Medical Centre of Excellence, Hôpital Privé Jean
Mermoz, Groupe Ramsay GDS, 69008 Lyon, France. E-mail: sonnerycottet@ Step 1: Identification of Quadriceps Activation
aol.com Failure and Hamstring Contracture
Ó 2018 by the Arthroscopy Association of North America. Published by
After a standard acute knee examination is performed
Elsevier. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/). and the presence of an extension deficit is established,
2212-6287/1812 the patient is positioned on the examination couch in a
https://doi.org/10.1016/j.eats.2018.02.006 semi-recumbent position (Fig 1). Quadriceps activation

Arthroscopy Techniques, Vol 7, No 6 (June), 2018: pp e601-e605 e601

e602 J-R. DELALOYE ET AL.

Table 1. Steps, Pearls, and Pitfalls of Conservative Method to Regain Full Extension of Knee and Recover Activation of
Quadriceps
Step Pearls Pitfalls
1 and 3 The patient should be examined in a semi-recumbent If the patient is lying completely flat, it is more difficult to
position. evaluate quadriceps function because the rectus femoris is
already under tension.
1 It is important to differentiate between rectus femoris and Rectus femoris function is typically preserved in AMI and can
vastus medialis contractions. mislead the practitioner into thinking that quadriceps
activation failure is not present.
2 The foot should be supported in the relaxation phase of Without support, the patient will be in pain, and therefore, it
hamstring fatigue exercises. will be more difficult for him or her to relax.
Eccentric exercises should not be performed; rather, the foot Forcing the hamstring into eccentric contraction will cause
should be held to cause an isometric contraction. pain.
3 When the patient is performing quadriceps activation Recurrent hamstring contracture can occur. Using a pillow
exercises, a pillow under the knee should be used initially under the knee helps to relax the hamstrings.
to facilitate hamstring relaxation.
If quadriceps activation failure persists, it is important to If hamstring contracture is present, it is counterproductive to
reassess the hamstrings for recurrent contracture. continue with quadriceps activation exercises. Instead, a
return to step 2 is necessary.
The practitioner should teach the patient hamstring If patient compliance is low, then AMI may not improve
relaxation and quadriceps activation exercises and instruct rapidly.
the patient to perform the exercises frequently. This
repetition targets cortical neuroplasticity.
AMI, arthrogenic muscle inhibition.

failure is identified by asking the patient to contract the

quadriceps muscles. The practitioner should observe
specifically for contraction of the vastus medialis. Pa-
tients with AMI typically maintain the ability to con-
tract the rectus femoris (hip flexor) but have a more
profound inability to contract the vastus medialis (knee
extensor) (Fig 2).
After identification of quadriceps activation failure,
the patient is placed prone on the examination couch.
In this position, side-to-side palpation of the hamstrings
allows determination of the presence of muscle
contracture. If a hamstring contracture is not present,
this should raise the suspicion that the extension deficit
does not result from AMI and the differential diagnosis
of a locked knee should be considered further.

Fig 2. Right quadriceps inactivation with lack of vastus

medialis contraction (section sign) and active knee extension
Fig 1. Knee extension deficit evaluation of right knee deficit. The rectus femoris contraction (pound sign) is main-
(asterisk) with patient in supine position. tained with active hip flexion.
 KNEE EXTENSION DEFICIT e603

Fig 3. Hamstring fatigue. The

patient is asked to repetitively
contract against resistance (A)
and relax the hamstrings (B).
To help fully relax the ham-
strings, the practitioner should
gently support the foot on its
way down to the examination
table. A right knee is shown
with the patient in the prone
position.

Step 2: Hamstring Fatiguing quadriceps, a recurrent extension deficit is likely to

In the prone position, the patient is asked to repeti- occur when the hamstrings recover from the fatiguing
tively contract and relax the hamstrings. The practitioner exercises. Therefore, it is important that the patient
places his or her hand against the patient’s leg to provide regain the ability to strongly contract the quadriceps,
resistance against the contraction (Fig 3A). This limits the primarily the vastus medialis.
range of motion required to perform the exercise, thus In the semi-recumbent position, a small pillow is
making it more comfortable, but also helps to fatigue the placed under the knee to obtain approximately 30 of
hamstrings more rapidly. The contraction should be held flexion. This helps to allow relaxation of the
for 2 to 3 seconds. Between each contraction, the patient
is asked to relax the hamstrings completely to the best of
his or her ability. To help fully relax the hamstrings,
without causing pain, the practitioner should also gently
support the foot on its way down to the examination
table (Fig 3B). Once the hamstrings are fully fatigued, the
muscle contracture resolves, leading to full extension of
the knee (Fig 4). Usually, this can be achieved within
10 minutes, but on some occasions, it can take longer. It
is important to note that the practitioner should never
push against the leg to gain passive extension of the knee
because it is painful.

Step 3: Reactivation of Quadriceps Muscle

Contraction
Once full passive extension of the knee is recovered, it Fig 4. Full knee extension (asterisk) recovery after hamstring
is important to regain active extension. If the patient fatigue. A right knee is shown with the patient in the prone
remains unable to perform effective contraction of the position.
e604 J-R. DELALOYE ET AL.

Regaining full symmetrical extension is a primary

goal of early-phase rehabilitation after ACL recon-
struction. Failure to regain full extension by 3 weeks
after ACL reconstruction is an important predictive
factor for subsequent cyclops syndrome.2 We believe
that this technique has transformed our practice. We
have previously reported a posteACL reconstruction
cyclops rate of 2.1%, which was noted to reduce to
0.1% after we introduced this technique.2
After knee injury, it is important not to confuse AMI
with a locked knee. It should be noted that a magnetic
resonance imagingeproven displaced bucket-handle
tear does not definitively show that the extension
Fig 5. Passive muscle contraction of quadriceps. The patient is deficit is due to a mechanical block to extension.
requested to do a heel lift (arrow) and straighten the knee. Shakespeare and Rigby4 observed that 10% of patients
The practitioner can facilitate the movement by holding the with a displaced bucket-handle tear of the meniscus did
great toe. A right knee is shown with the patient in the supine not present with any locking of the knee. In addition,
position. Allum and Jones1 reported that among patients pre-
senting with a knee extension deficit after injury, 92%
had intra-articular pathology but only 16% of the knees
hamstrings; it also allows the patient visual feedback of remained locked after induction of anesthesia. They
quadriceps contraction. Next, the patient is asked to concluded that the knee extension deficit present in
perform heel lifts and straighten the knee. The practi- most patients was due to hamstring muscle spasms.
tioner can facilitate the movement by holding the great Since the 1990s, studies have shown that hamstring
toe (passive muscle contraction) (Fig 5). This phase contracture was associated with quadriceps inactivation
focuses on isometric quadriceps contractions. The pa- and that this occurred because of a process known as
tient is asked to contract the muscle without lifting the AMI.3 Orthopaedic surgeons deal with these types of
heel. An easy way to check the correct contraction of clinical presentations on a daily basis. However, AMI is
the muscle is to palpate the patella (Fig 6). During not a well-established orthopaedic concept because
each contraction, the patella has to migrate proximally. most articles on this subject have been published in
If the patient only contracts the rectus femoris, the non-orthopaedic journals.
practitioner will observe a muscular contraction of The underlying mechanism of AMI is not fully un-
the thigh without any movement of the patella. Once derstood but is believed to be initiated by acute
the patient is able to reliably contract the vastus swelling, inflammation, pain, and joint laxity.3
medialis, the thickness of the pillow placed under the These pathologies lead to changes in the discharges of
knee is progressively reduced until it can be removed
completely and the patient can still show good
contraction.
During these exercises, it is important to check that
the patient does not have co-contraction of the quad-
riceps and hamstrings. If this is the case, then the
thickness of the pillow should be increased and quad-
riceps contractions repeated. It is also important to
make sure the hamstrings remain relaxed and are not
again in contracture. If a recurrent contracture is
observed, then hamstring fatigue exercises (step 2)
should be repeated.

Discussion
This Technical Note and accompanying video describe Fig 6. Active isometric muscle contraction of quadriceps. The
a simple set of exercises that typically result in full patient is asked to contract the muscle without lifting the heel.
restoration of extension and good quadriceps activation To check the correct contraction of the muscle, the practi-
within a few minutes. These exercises are therefore a tioner should palpate the patella to feel its proximal migration
quick and easy solution to what has traditionally been (arrow). A right knee is shown with the patient in the supine
considered a difficult problem in some patients. position.
 KNEE EXTENSION DEFICIT e605

Table 2. Advantages and Disadvantages of Proposed Method been described to combat AMI, but these all require
to Combat AMI additional equipment, are time-consuming, and have
Advantages varied results.3 The exercises described in this technical
Easy to perform article are a simple and effective method for restoration
Rapid restoration of full extension and quadriceps activation
of full knee extension and quadriceps activation within
Reduced rate of cyclops lesions
No special equipment necessary minutes (Table 2). It is our opinion that everyone
Pain alleviation dealing with acute knee injuries should be familiar with
Easier postoperative recovery if patient is aware of how to contract these exercises because they are easy to perform and
quadriceps immediately highly effective.
Speeds up time taken for patient to achieve full extension and, if
necessary, can proceed with surgery sooner without increased
risk of arthrofibrosis
No recognized reliable alternative References
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Takes extra time in office
256-258.
Can be painful to patient if performed incorrectly (Table 1)
2. Pinto FG, Thaunat M, Daggett M, et al. Hamstring
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increased risk of cyclops syndrome. Orthop J Sports Med
intra-articular receptors, which subsequently result in 2017;5. 2325967116684121.
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bition: Neural mechanisms and treatment perspectives.
such as the flexion reflex.3 This reflex results in over-
Semin Arthritis Rheum 2010;40:250-266.
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the quadriceps. The described exercises specifically meniscus. A clinical and arthrographic study. J Bone Joint
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Henriksson M. Functional and muscle morphometric ef-
been shown to result in muscle atrophy, poor function,
fects of ACL reconstruction. A prospective CT study with 1
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