Mechanisms of overuse injury
In the skeletally immature athlete, the tissues most vulnerable
to injury are the cartilaginous growth centers, the physes and apophyses,
which account for 15% of all youth sports injuries.[2 ] Physes are
primary ossification centers, located at the ends of the long bones. Physes are
responsible for longitudinal bone growth. Apophyses are secondary centers of
ossification, found where major tendons attach to bone. Apophyses provide
contour and shape to growing bones without adding length. Since cartilage is
less resistant to tensile forces than bones, ligaments, and muscle-tendon units,
these growth centers are the weakest links in the musculoskeletal chain. The
same injury mechanisms that cause muscle strains and tendonitis in adults result
in growth center injuries in children and teens. During a growth spurt, bones
grow faster than muscle-tendon units. The resulting tight muscle-tendon units
put increased traction stress on the growth centers where they insert. When the
growth spurt coincides with a period of increased physical activity, the
repetitive stress on the growth centers can cause inflammation and
micro-avulsions at the bone-cartilage junction. When adequate healing time is
not allowed to occur between exercise sessions, tissue repair is incomplete and
overuse injury results.
Risk factors
Training errors are the leading cause of overuse injury, and
include any increase in workout intensity, duration, or frequency. Both novice
and elite athletes are susceptible to training errors. Sports camps that require
increased levels of exertion from unfit or inadequately conditioned young
athletes are a common source of overuse injury, as is specialization in a single
sport at an early age.[3 ]Training at a high intensity and/or year-round for only
1 sport, not only puts a large degree of stress on the growth centers, but also
denies these young athletes the beneficial effects that varied physical activity
has on neuromuscular development. As a result, strength and flexibility may
become overdeveloped in certain groups of muscles at the expense of others,
increasing the risk for injury, and setting a pattern of neuromuscular
imbalances that can persist into adulthood. The risk for overuse injury also
increases with use of improper technique, equipment that fits poorly or is worn
out, a change in playing surface, and certain variants of normal skeletal
alignment, such as external tibial torsion, patella alta (high patella), pes
planus (flatfoot) and subtalar joint overpronation.
Diagnosis
Overuse injuries are diagnosed by history and physical
examination. Radiographs are not necessary to make the diagnosis, but can be
useful to rule out other pathology, such as fractures or bone lesions, when the
presentation is less clear. Athletes with overuse injuries present with
insidious onset of pain that worsens with activity and improves with rest. A
comprehensive history will reveal the cause, and should focus on recent growth
spurts, and changes in training volume, technique, equipment, and playing
surface. For instance, runners usually develop symptoms after increasing their
mileage, adding hills, or changing running surface. Pitchers often develop
symptoms shortly after learning a new pitch, or pitching in more innings. Injury
risk increases when shoes are worn out or do not fit properly, or when the grip
on a tennis racket is too large or string tension too low. On physical
examination, athletes will have tenderness at the affected growth center,
sometimes with minor swelling. An assessment of skeletal alignment, muscle
strength, and flexibility will identify additional risk factors.
Treatment
General treatment principles apply to all overuse injuries,
regardless of the anatomic location. The most important aspect of treatment is
rest until the pain and tenderness resolve. Ice is usually effective in reducing
pain. If pain is not controlled with ice, nonsteroidal anti-inflammatory
medications (NSAIDs) can be tried. However, because ice and NSAIDs can mask
symptoms of overuse, they should never be used before activity in an attempt to
decrease pain to allow participation. Treatment should also include daily
stretching of tight muscle groups. Athletes with lower extremity overuse
injuries who have excessive subtalar pronation or pes planus may benefit from
custom-fitted shoe orthoses. A short course of physical therapy may be required
to address significant strength and flexibility deficits, and should focus on
stretching and progressive strengthening exercises within a pain-free range. It
is important to reassure the athlete that "rest" is relative. He/she may
continue to participate in activities that do not cause discomfort. This is an
important aspect of treatment because lower impact activities (ie, swimming or
cycling) that put less stress on the injured growth center will help prevent
muscle atrophy from disuse and maintain cardiovascular fitness. When symptoms
are not alleviated by adequate rest, a short period of immobilization and/or
non-weight-bearing may be necessary. Return to sport is allowed when
sport-specific activities can be performed without pain. Almost all overuse
injuries will heal uneventfully with conservative treatment. If symptoms persist
despite several weeks of conservative management, referral to a sports medicine
specialist is recommended.
Common overuse injuries
Osgood-Schlatter disease (OSD),
or apophysitis of the
tibial tubercle (Figure 1), is the most common pediatric overuse injury,
occurring in 20% of young athletes, affecting girls between ages 8 and 13 years,
and boys between ages 10 and 15 years.
Figure 1: Osgood-Schlatter disease. Lateral radiograph of the knee
demonstrating fragmentation of the tibial tubercle with overlying soft tissue
swelling.
Repetitive activity and tight quadriceps cause chronic traction
stress at the tibial tubercle apophysis, leading to 1 or more of the following:
cartilage swelling, cortical bone fragmentation, patellar tendon thickening,
and/or infrapatellar bursitis. Athletes present with pain and swelling
at the tibial tubercle. The pain worsens with activity and is alleviated
with rest. Symptoms are bilateral in 20% of cases. Usually the onset is
insidious, but occasionally is triggered by direct trauma. A soccer player may
report onset of OSD symptoms shortly after a blow to the knee. Athletes will be
tender at the tibial tubercle, and will often have tight quadriceps and hip flexors,
which can be demonstrated by performing a Thomas test. While supine with
the affected limb at the edge of the examining table, the athlete brings both
knees to the chest, then while holding the unaffected knee in place lowers the
affected leg to hang off the side of the table. If the affected thigh fails to
rest on the table, the test is positive for tight hip flexors. If the knee fails
to flex at least 50 degrees, the test is positive for tight quadriceps. Other
risk factors for OSD include external tibial torsion and patella alta. Treatment
includes rest, quadriceps and hip flexor stretching, and use of ice and
NSAIDs until pain and tenderness resolve. A patellar tendon strap may provide
some pain relief, as it decreases the traction stress on the tibial tubercle.
Avulsion or complete fracture of the tibial tubercle is rare, and does not
warrant restriction from sports for those with OSD. OSD usually resolves with
conservative treatment. In some cases symptoms will persist into adulthood. In
a survey of adults with a history of OSD, 24% reported some limitation in activities,
and 60% reported painful kneeling. There was a low incidence of patellar
instability or anterior knee pain, and no cases of premature proximal tibial
epiphyseal arrest.[4 ] For painful ossicles that persist into adulthood,
surgical excision is usually curative.
Sinding-Larsen-Johansson syndrome
, or apophysitis of
the inferior pole of the patella, affects athletes between ages 10 and 12 years,
and is most common in running and jumping sports, such as basketball and
volleyball. Athletes present with anterior knee pain that worsens with running,
jumping, climbing stairs, and kneeling. There will be tenderness at the inferior
pole of the patella and often tight quadriceps. While not necessary for the
diagnosis, radiographs may reveal fragmentation of the inferior patella (Figure
2) and/or calcifications in the proximal patellar tendon. Treatment includes
rest, quadriceps stretching, and use of ice and NSAIDs until pain and tenderness
resolve.
Figure 2: Sinding-Larsen-Johansson syndrome. Lateral radiograph of the knee
demonstrating fragmentation of the apophysis at the inferior pole of the
patella.
Sever's disease
, or apophysitis of the calcaneus,
affects boys and girls between ages 8 and 13 years, and is most common in
soccer, basketball, and gymnastics. Repetitive heel impact and traction stress
from the Achilles tendon and plantar fascia lead to inflammation at the
calcaneal apophysis. Athletes present with heel pain that is worse with activity
and with wearing cleats. Pain is bilateral in 60% of cases. Athletes will have
tenderness with mediolateral compression of the heel. Many also will have tight
heel cords (passive ankle dorsiflexion is less then 10 degrees with the knee at
full extension), weak ankle dorsiflexors, and subtalar overpronation. While not
necessary for diagnosis, radiographs will frequently demonstrate enlargement,
fragmentation, sclerosis, or thickening of the apophysis, all of which are
consistent with normal apophyseal development. Treatment includes rest,
heel-cord stretching, and use of ice and NSAIDs until pain and tenderness
resolve. Gel heel cups may help to relieve pain and speed return to play.
Little League elbow
, or medial epicondylitis, affects
skeletally immature pitchers who throw with great frequency. More than half of
all high school pitchers will report a history of significant elbow pain by the
end of their high school career.[5] The pitching motion generates significant
valgus stress at the elbow, resulting in tension on the medial structures, and
compression of the lateral structures. In the growing athletes, the medial elbow
structure most vulnerable to tension stress is the growth center at the medial
epicondyle. Repetitive throwing causes chronic traction stress on the medial
epicondyle, producing 1 or more of the following: cartilage swelling, irregular
ossification, and/or avulsion. Athletes report insidious onset of pain while
throwing. Some also may note a loss of pitch velocity or control. There will be
tenderness and occasionally swelling at the medial epicondyle, pain when valgus
stress is applied to the elbow at 20 degrees of flexion, and often an inability
to fully extend the elbow. Radiographs are usually normal, but may show
fragmentation or widening at the medial epicondylar apophysis. Rest from
pitching is required until pain and tenderness resolve – usually 3 to 6 weeks.
Ice and NSAIDs are used to reduce pain and swelling. Return to throwing should
be gradual, and should include a supervised interval throwing program over 6 to
8 weeks, beginning with short tosses, then incrementally progressing to long
tosses, then to higher velocity throws over a longer and longer distance, until
the athlete can throw an adequate number of pitches without recurrence of pain.
Rarely, inadequate rest will result in failure of physeal fusion and chronic
pain due to non-union.
Little League shoulder
, or stress fracture of the
proximal humeral physis, is less common than Little League elbow. Little League
shoulder affects male pitchers between ages 11 and 13 years who throw with great
frequency and improper mechanics. It can also occur in other overhand sports,
such as tennis. Athletes present with shoulder pain and tenderness at the
proximal humerus. There may be weakness with shoulder abduction and external
rotation. An anteroposterior radiograph of the shoulder in external rotation
will typically reveal subtle widening of the physis when compared to the
uninjured arm. Treatment is rest until pain and tenderness resolve, followed by
an interval throwing program and correction of improper mechanics.
Apophysitis of the hip
can involve any of the muscle
insertion sites on the pelvis or proximal femur (Figure 3) and usually affects
runners, sprinters, dancers, soccer players, and ice hockey players.
Figure 3: Location of apophyses in the pelvis and hip.
Apophysitis of the hip is less common than OSD or Sever's
disease, and occurs in adolescents between ages 14 and 18 years.[6] Athletes
present with dull hip pain that worsens with activity. There is tenderness at
the affected apophysis. Radiographs should be performed to rule out avulsion
fracture or other hip pathology. In apophysitis of the hip, radiographs are
usually normal, but can sometimes show irregular ossification at the apophysis.
Treatment is rest until pain and tenderness resolve, followed by progressive
stretching and strengthening of the muscles that insert into the affected
apophysis.
Prevention
Educating the athlete, parents, and coach about injury
prevention is essential to treatment. Athletes should be instructed to perform a
5 to 10 minute warm-up before activity. This will increase circulation to
muscles, making them more pliable and less prone to injury. Fitness and
sports-specific skills should be developed gradually. Any progressions in
intensity, frequency, and duration should be made separately and in small,
incremental amounts. For example, runners are advised to increase distance by no
more than 10% per week. Even with proper progression, there is a limit to the
volume of repetition the growing skeleton can tolerate. The risk of overuse
injury in young pitchers has been shown to increase with the number of pitches
thrown.[7] Consequently, the USA Baseball Medical & Safety Advisory Committee
has published guidelines to limit the maximum number of balls thrown by young
pitchers (50 pitches per game for ages 9 to 10 years; 75 pitches per game for
ages 11 to 14 years).[8] A minimum of 4 days rest is recommended between outings.
Because breaking balls (curve balls, sliders, etc.) tend to produce more valgus
stress on the elbow than fastballs, athletes should not throw breaking pitches
in competition until they are near skeletal maturity, which typically occurs
between ages 13 to 15 years. Prior to returning to sport after an overuse
injury, equipment should be inspected for proper condition and fit, and improper
technique should be corrected. Runners should replace shoes after 300 to 500
miles. When changing playing surfaces, athletes should temporarily reduce
training frequency and duration. The most important injury prevention message
that pediatricians can communicate to patients, parents, and coaches is that
young athletes should not play through pain. Pain is a sign of overuse, and if
unresolved after a few days of rest, should be evaluated by a physician.
Summary
Skeletally immature athletes are susceptible to a unique set
of overuse injuries. An understanding of the injury mechanisms and an ability to
identify individual risk factors enable the pediatrician to successfully
diagnose, treat, and prevent overuse injuries unique to young athletes.
References
1. Watkins J, Peabody P. Sports injuries in children and
adolescents treated at a sports injury clinic. J Sports Med Phys Fitness
1996;36(1):43-48.
2. Pill SG, Flynn JM, Ganley TJ. Managing and preventing
overuse injuries in young athletes. J Musculoskel Med 2003;20:434-442.
3. American Academy of Pediatrics Committee on Sports Medicine
and Fitness. Intensive training and sports specialization in young athletes.
Pediatrics 2000;106:154-157.
4. Krause BL, Williams JP, Catterall A. Natural History of
Osgood-Schlatter disease. J Pediatr Orthop 1990;10(1):65-68.
5. Lyman S, Fleisig GS, Waterbor JW, et al. Longitudinal study
of elbow and shoulder pain in youth baseball pitchers. Med Sci Sports Exerc
2001;33(11):1803-1810.
6. Moeller JL. Pelvic and hip apophyseal avulsion injuries in
young athletes. Curr Sports Med Rep 2003;2:110-115.
7. Lyman S, Fleisig GS, Andrews JR, et al. Effect of pitch
type, pitch count, and pitching mechanics on risk of elbow and shoulder pain in
youth baseball pitchers. Am J Sport Med 2002;30(4):463-468.
8. USA Baseball Medical & Safety Advisory Committee. Young
pitchers at risk for serious injuries. July 2004.
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