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C H A P T E R
OBJECTIVES Upon completion of this chapter, you will be able to:
➤ Understand basic functional anatomy for the
knee complex.
➤Understand the mechanisms for common
knee injuries.
➤Determine common risk factors that can lead
to knee injuries.
➤Incorporate a systematic assessment and cor-
rective exercise strategy for knee impairments.
Corrective Strategies
for Knee Impairments
INTRODUCTION
LOWER-EXTREMITY injuries account for more than 50% of injuries in college (1)
and high school athletes (2), and among lower-extremity injuries, the knee is
one of the most commonly injured regions of the body. Researchers have esti-
mated health-care costs to be approximately $2.5 billion annually for anterior
cruciate ligament (ACL) injuries (3). To prevent these injuries from occurring
and allow for individuals to maintain healthy and physically active lifestyles,
it is important to understand the anatomy, causes, and most appropriate cor-
rective exercise strategies for prevention and management. This chapter will
review each of these components as they relate to the knee.
REVIEW OF KNEE FUNCTIONAL ANATOMY
The knee is a part of a kinetic chain that is greatly affected by the linked
segments from the proximal and distal joints. The foot and ankle and the lum-
bo-pelvic-hip complex (LPHC) play a major role in knee impairment, as the
structures that help to form the ankle and hip joints make up the knee joint.
This region is a prime example of how alterations in other joints within the
human movement system can dramatically affect the movement and increase
the stress and injury capacity of another joint, which leads to knee impair-
ments.
268 CHAPTER 13
Bones and Joints
Looking at the knee region specifically (Figure 13-1), the tibia and femur make
up the tibiofemoral joint, and the patella and femur make up the patellofemo-
ral joint. The fibula is also noted as it is the attachment site of the biceps femo-
ris, which crosses and affects the knee.
Proximally, the femur and the pelvis make up the iliofemoral joint, and
the sacrum and pelvis make up the sacroiliac joint (Figure 13-2). Collectively,
these structures anchor the proximal myofascial tissues. These bones and
joints are of importance in corrective exercise because they will also have a
functional impact on the arthrokinematics of the knee.
Distally, the tibia and fibula help form the talocrural (ankle) joint
(Figure 13-3). Collectively, these structures anchor the distal myofascial tissues of
the knee. These bones and joints are of importance in corrective exercise because
they will also have a functional impact on the arthrokinematics of the knee.
C
B
D A
Figure 13.1 Bones of the knee. (A) Tibia. (B) Femur. (C) Patella. (D) Fibula.
C
B
A
Figure 13.2 Proximal bones affecting the knee. (A) Femur. (B) Pelvis. (C) Sacrum.
A B
Figure 13.3 Distal bones affecting the knee. (A) Distal fibula. (B) Distal tibia.
Muscles
There are a number of muscles in the lower leg and lumbo-pelvic-hip com-
plex whose function may be related to the knee (Table 13-1). It is important to
restore and maintain normal range of motion and strength, and eliminate any
muscle inhibition, to ensure joints are operating optimally. See chapter two for
a detailed review of the location and function of these muscles.
Table 13.1 KEY MUSCLES ASSOCIATED WITH THE KNEE
- Gastrocnemius/soleus
- Adductor complex
- Medial and lateral hamstring complex
- Tensor fascia latae/IT-band
- Quadriceps
- Gluteus medius and maximus
270 CHAPTER 13
Patellofemoral Syndrome
One of the most commonly accepted causes of patellofemoral syndrome
(PFS) is abnormal tracking of the patella within the femoral trochlea
(Figure 13-6). When the patella is not properly aligned within the femoral
trochlea, the stress per unit area on the patellar cartilage increases owing
to a smaller contact area between the patella and the trochlea (4). Abnor-
mal tracking of the patella may be attributable to static (i.e., increased
Q-angle) or dynamic lower-extremity malalignment (i.e., increased femoral
rotation, adduction, and knee valgus), altered muscle activation of sur-
rounding knee musculature, decreased strength of the hip musculature, or
various combinations (5–8).
Anterior Cruciate Ligament (ACL) Injury
Beyond the common injuries indicated that are more chronic in onset,
recent studies also indicate that altered lower-extremity neuromusculo-
skeletal control imbalances can increase the risk of acute injures such as
ACL ruptures (Figure 13-7) (9–12). Specifically, peak landing forces were
significantly predicted by valgus torques at the knee, women demon-
strated decreased relative knee flexor torque during landing compared
with men, and women had greater side-to-side differences in normalized
hamstring complex peak torque (13). Insufficient neuromusculoskeletal
control of lower limb biomechanics, particularly frontal plane control of
the knee joint, leads to high-risk patterns in female athletes during execution
of common, albeit potentially hazardous, movements (12). These sex differ-
ences are evident during landing and cutting in soccer and basketball ath-
letes (14,15). Female athletes also have significant differences between their
dominant and nondominant sides in maximum valgus knee angle (14,15).
Figure 13.6 Patellofemoral syndrome.
Figure 13.7A Anterior force. Figure 13.7B Lateral force. Figure 13.7C Rotational force.
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These differences in valgus measures (ligament dominance) and limb-to-limb
asymmetries (leg dominance) reflect neuromusculoskeletal control deficits
that may be indicative of decreased dynamic knee joint control in female
athletes (14).
Subsequent studies systematically evaluated more proximal neuromusculosk-
eletal control deficits at the hip and trunk to help determine potential contributing
mechanisms to high-risk knee mechanics during landing (16,17). When performing
single-leg landing tasks, female athletes demonstrated increased trunk flexion and
lateral tilt range of motion. In addition to greater knee abduction angles, female
athletes had increased hip frontal plane excursion compared with men during
both types of landings (18). The increased hip adduction motion seen in the frontal
plane during athletic activities likely contributes to the dynamic valgus knee posi-
tion that may place the athlete at increased risk of knee injury (17–20).
ASSESSMENT AND CORRECTIVE EXERCISE STRATEGIES FOR KNEE
IMPAIRMENTS
➤ SYSTEMATIC PROCESS TO DETERMINE KNEE IMPAIRMENTS
The first step in developing a corrective exercise strategy for knee impairments is an inte- grated assessment process. On the basis of the information obtained from these assess- ments collectively, the neuromusculoskeletal control deficits can be identified for targeted treatments. A summary of the assessment process for knee impairments and common findings indicating potential dysfunction are listed below.
SAMPLE KNEE ASSESSMENT PROCESS AND OBSERVATIONS
Assessment Observation
Static Posture Pronation distortion syndrome (tibial and femoral adduction and internal rotation)
Overhead Squat Knees move inward (adduct and internally rotate) Knees move outward (abduct and externally rotate) Single-leg Squat Knee moves inward (adduct and internally rotate)
Tuck Jump Assessment
Knee and thigh deficits (i.e., excessive knee valgus on landing) Foot placement deficits and poor landing technique
Goniometric Measurement
Decreased dorsiflexion (less than 15°) Decreased knee extension in 90/90 position (hamstring complex–biceps femoris) Decreased hip extension (TFL) Decreased hip internal rotation (biceps femoris, piriformis, and/or adductor magnus)
Manual Muscle Testing
One or more of the following muscles tested “weak”: Anterior/posterior tibialis, gluteus medius and/or maximus, medial hamstring complex, adductors (knees move outward during overhead squat)
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The single-leg squat is also an important transitional assessment to perform to assess potential injury risks at the knee joint. Having to squat on one leg may show dysfunction not evident when squatting on two feet. Like the overhead squat, the key compensation to look for when performing the single-leg squat is whether the knee moves inward.
Compensation During Single-Leg Squat, Knee Moves Inward
DYNAMIC MOVEMENT ASSESSMENTS
The tuck jump exercise may be useful to the health and fitness professional for the identifi- cation of lower-extremity technical flaws during a plyometric activity (19,21). The tuck jump requires a high level of effort from the individual, which may allow a health and fitness pro- fessional to readily identify potential deficits, especially during the first few repetitions when the individual places most of his or her cognitive efforts solely on the performance of this difficult jump (19,21). In addition, the tuck jump exercise may be used to assess improve- ment in lower-extremity biomechanics as the individual progresses through training (19,21).
Start Movement Finish
Tuck Jump Assessment
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The below figure provides the “health and fitness professional friendly” landing as- sessment tool that the health and fitness professional may use to monitor an individual’s technical performance of the tuck jump before, during, and after training. As reviewed in chapter six, the individual is instructed to perform repeated tuck jumps for 10 seconds, while the health and fitness professional visually grades the outlined criteria (19). To im- prove the ease of the assessment, a standard two-dimensional camera in the frontal and sagittal planes may be used to assist the health and fitness professional. The individual’s technique should be subjectively graded as either having an apparent deficit (checked) or not. Indicators of flawed techniques should be noted for each individual and should be the focus of feedback during subsequent training sessions (19). The individual’s baseline performance can be compared with repeated assessments performed at the midpoint and conclusion of training protocols to objectively track improvement with jumping and land- ing technique. Empiric laboratory evidence suggests that individuals who do not improve their scores, or who demonstrate six or more flawed techniques, should be targeted for further technique training (19).
Tuck Jump Assessment Pre Knee and Thigh Motion 1 Lower extremity valgus at landing 2 Thighs do not reach parallel (peak of jump) 3 Thighs do not equal side-to-side (during flight)
Foot Position During Landing 4 Foot placement not shoulder width apart 5 Foot placement not parallel (front to back) 6 Foot contact timing not equal Excessive landing contact noise
Plyometric Technique Pause between jumps Technique declines prior to 10 seconds Does not land in same footprint (excessive in-flight motion)
Mid Post Comments
Total _____ Total _____ Total _____
7
8 9 10
Tuck Jump Assessment Chart
One specific area that the health and fitness professional should focus on when train- ing to prevent ACL injury risk is the correction of lower-extremity valgus at landing and improvement of side-to-side differences in lower-extremity movements, which are both target deficits to be assessed with the tuck jump assessment tool (12,19). The tuck jump assessment tool can be used to improve these high-risk techniques during an exercise that requires a high effort level from the individual (19). If individuals can improve their neuromusculoskeletal control and biomechanics during this difficult jump and landing sequence, they may gain dynamic neuromusculoskeletal control of the lower extremity and create a learned skill that can be transferred to competitive play (if performing with an athlete) and ultimately reduces their injury risk (12,19).
276 CHAPTER 13
Before teaching the dynamic movement exercises, individuals should be shown the proper athletic position. The athletic position is a functionally stable position with the knees comfortably flexed, shoulders back, eyes up, feet approximately shoulder-width apart, and the body mass balanced over the balls of the feet. The knees should be over the balls of the feet, and the chest should be over the knees (13,21). This is the individual’s ready position and should be the starting and fi nishing position for most of the training exercises.
Athletic Position
Wall jumps are an example of an integrated dynamic movement exercise that could be used to target ligament dominance deficits. This low-to-moderate intensity jump move- ment allows the health and fitness professional to begin analysis of the athlete’s degree of valgus or varus motion in the knee (21). During wall jumps, the individual does not go through deep knee flexion angles, with most of the vertical movement provided by active ankle plantar flexion (21). The relatively straight knee makes even slight amounts of medial knee motion easy to identify visually. When medial knee motion is observed, the health and fitness professional should begin to give verbal feedback cues to the individual during this low-to-moderate intensity exercise (21). This feedback allows the athlete to cognitively process the proper knee motion required to perform the exercise. Neuromusculoskeletal control of medial knee motion is critical when landing with knee angles close to full exten- sion, as this is a commonly reported mechanism of injury (22).
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Start Movement Finish
Wall Jumps
Another useful exercise to target the ligament-dominant individual is the tuck jump (as shown earlier in the chapter). Although used as an assessment, the tuck jump can also be used as an exercise that is on the opposite end of the intensity spectrum from the wall jump and requires a high level of effort from the individual. During the tuck jump exercise, the health and fitness professional can quickly identify an individual who may demonstrate abnormal levels of frontal plane knee displacement during jumping and landing because the individual usually devotes minimal attention to technique on the first few repetitions (21). As mentioned earlier, tuck jumps can also be used to assess improvements in lower- extremity biomechanics (19). The long jump and hold exercise allows the health and fi tness professional to as- sess the individual’s knee motion while he or she progresses through movements in the sagittal plane (21). The achievement of dynamic knee control during tasks performed in all planes of movement is critical to address defi cits that may transfer into competitive sports participation or everyday activities. During competition, athletes may display “ac- tive valgus,” a position of hip adduction and knee abduction that is the result of muscular contraction rather than ground reaction forces (21). The long jump is a moderate-intensity integrated dynamic movement exercise that can provide another opportunity for the health and fitness professional to assess active valgus and provide feedback on more desir- able techniques, which can assist the individual’s cognitive recognition during each jump to perfect technique. When performing the long jump exercise, individuals may dem- onstrate active valgus when taking off from a jump rather than landing. This movement deficit should be identified and corrected during training. In addition, individuals should
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continue to maintain deep knee flexion when landing and control unwanted frontal plane motion at the knee (21). Proper progression into the single-leg hop and hold is critical to ensure individual safety during training (21). This point is salient for the health and fitness professional, as ACL injury prevention tech- niques should not introduce inappropriate risk of injury during training. The end stages of training targeted to- ward ligament-dominance deficits is achieved through the use of unanticipated cutting move- ments. Before teaching unanticipated cutting, individuals should first be able to attain proper athletic position proficiently (21). This ready po- sition is the goal position to achieve before ini- tiating a directional cut. Adding the directional cues to the unanticipated part of training can be as simple as pointing or as sports-specific as using partner mimic or ball retrieval drills (21).
Start Movement Finish
Cutting Maneuvers
Single-faceted sagittal plane training and conditioning protocols that do not incorporate cutting maneuvers will not provide similar levels of external varus or valgus or rotational loads that are seen during sport-specific cutting maneuvers (21,25). Train- ing programs that incorporate safe levels of varus or valgus stress may induce more muscle-dominant neuromusculoskeletal adaptations (26). Such adaptations may pre- pare the individual for the multidirectional movement demands that occur during sport competition, which can improve performance and reduce risk of lower-extremity injury (12,13,21,23,27,28). Research has shown that female athletes perform cutting techniques with decreased knee flexion and increased valgus angles (15,21,29). Knee valgus loads can double when performing unanticipated cutting maneuvers similar to those used in sport (21,30). Thus the end point of training designed to reduce ACL loading via valgus torques can be gained through training the athlete to use movement techniques that produce low frontal plane knee loads (26). Recent evidence demonstrates that training which
Start Finish
Single-Leg Hop and Hold
280 CHAPTER 13
incorporates unanticipated movements can reduce knee joint loads and lower-extremity injury risk (12,23,31). Additionally, training individuals to preactivate their musculature before ground contact may facilitate kinematic adjustments, reducing the potential for increased knee loads (21,30,32,33). Training the individual to use safe cutting techniques in unanticipated sport situations or everyday activities may also help impart technique adap- tations that will integrate into the athlete’s competitive movements during sport competi- tion or during activities of daily living. If naturally ligament-dominant individuals achieve muscular (sagittal) -dominant movement strategies, their future risk of ACL and other knee injuries will likely be reduced (13,21,28). It is important to note that not all individuals will have the physical capabilities to per- form many of the aforementioned jump task progressions. In this situation, a basic func- tional movement progression that incorporates total body integration in multiple planes can be used as integrated dynamic movements. This progression could begin with ball squats, then to step-ups, then to lunges, then to single-leg squats (from more stable/less dynamic to more unstable/more dynamic). For each exercise, it will be important to cue the individual to keep the knee(s) in line with the toes and to not allow the knee to move inside or outside of the foot to ensure proper arthrokinematics and neuromuscular control.
Squatting Step-up Lunging Single-leg Squatting
Functional Movement Progressions
The following table provides a sample programming strategy using the Corrective Exercise Continuum for knee impairments. The photos illustrate the exercises that can be done for each component of the continuum to help address the issue of knee impairments (knees move inward and knees move outward). Which exercises are used will be depen- dent on the findings of the assessments and the individual’s physical capabilities (integra- tion exercises).
282 CHAPTER 13
TFL/IT-band Biceps femoris
Self-Myofascial Release
Key lengthening exercises via static and/or neuromuscular stretches would include the gastrocnemius/soleus, adductors, TFL, and biceps femoris (short head).
Gastrocnemius/soleus Adductors TFL
Static Stretches
Biceps femoris (short head)
Step 2: Lengthen
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Gastrocnemius/soleus Adductors Biceps femoris
Neuromuscular Stretches
Key activation exercises via isolated strengthening exercises and/or positional isometrics include the anterior tibialis, posterior tibialis, gluteus medius, and gluteus maximus.
Anterior tibialis Posterior tibialis Gluteus medius Gluteus maximus
Isolated Strengthening Exercises
Step 3: Activate
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KNEE IMPAIRMENT: KNEES MOVE OUTWARD
Key regions to inhibit via foam rolling include the gastrocnemius/soleus, piriformis, and biceps femoris (long head).
Biceps femoris
Gastrocnemius/soleus Piriformis
Self-Myofascial Release
Key lengthening exercises via static and/or neuromuscular stretches would include the gastrocnemius/soleus, piriformis, and biceps femoris (long head).
Step 1: Inhibit
Step 2: Lengthen
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Static Stretches
Biceps femoris (long head)
Piriformis
Gastrocnemius/soleus
Gastrocnemius/soleus Piriformis Biceps femoris
Neuromuscular Stretches
Key activation exercises via isolated strengthening exercises and/or positional isometrics include the adductors, medial hamstring complex, and gluteus maximus.
Step 3: Activate
