Paediatric Musculoskeletal Development

Intro

As an infant grows, movement patterns develop that affect their bony alignment. As movement patterns are practiced thousands of times a day any abnormal muscle pull can create atypical alignment. Abnormal muscle pulls can be caused by genetic conditions and impairments with abnormal tone. Atypical alignment can directly affect form and functional activities and participation.

The following sections will highlight typical musculoskeletal development for an infant as well as changes that progress over time.

Rib Cage

Rib Cage	Shape	Location of Ribs	Other
Infant	Barrel-Shaped	Elevated; Perpendicular to Spine	Rigid
2 years old	Oblong-Shaped	Depressed due to diagragm pull and sitting/standing/walking	Lateral Expansion
Abnormal	Persistence of Barrel-Shape

Trunk

• begin with rounded spine (kyphotic)
• prone push-up and sitting activates posterior chain musculature
• crawling: co-contraction of anterior and posterior muscles
• begin in kyphotic posture moving into a more neutral spine

** Abnormal: abnormal muscle pull can change spine position

Pelvis

• over time increased lumbar and hip extension
• begin with rounded pelvis and posterior tilt
• sit and stand: activate posterior chain and core muscles and anterior pelvic tilt
• 12 months: 12 degrees of anterior pelvic tilt
• 30 months: 15 degrees of anterior tilt
• increased gluteal activity, anterior tilt decreases slightly until age 8
• adult: 10 degrees of anterior pelvic tilt

lower extremity:

• infants 34 degrees of hip extension limitation
• more time in prone - stretch anterior capsule
• 6 weeks-19 degrees of hip extension limitation
• toddlerhood-7 degrees limited
• birth- hip adduction limitation
• birth- high external rotation which decreases over time
• birth- slight limitation in knee flexion
• five years- knee straight when hip flexed to 90

LE norm: hip: flexion, abduction and lateral rotation, knee: flexion, genu varum, medial rotation of tibia; ankle: dorsiflexion, slight pronation

hip

• newborn: increased coxa valga 140-160
• decreases over time to adult 126
• anterversion of the femur newborn: 40 moving to 16 in adult

** children who are more ambulatory, more independent will have a mean femoral neck angle that is lower than those who are more involved and less ambulatory.

** abnormal: femoral neck angle remains quite high, so they remain with this femoral anteversion. And this is a really big deal because what this can do is it can actually increase risk of hip dislocation.(posterior)

too much pelvic tilt:

• abs are too long
• hip extensors are too long
• hip flexors and lumbar extensors are too short
• unable to have appropriate muscle pull of both your core muscles and your glute muscles when you're performing functional activities.

too little of a pelvic tilt

• ilipsoas is stretched out
• anterior hip capsule is stretched out
• glute max is short
• hip laxity in the front and hip instability.

pelvic obliquity.

• common in patients with hemiplegia and diplegia
• lower side, the side where the hip is dropped down, this is typically a shorter, lower extremity, or there is increased pronation of the foot on that extremity.
• reduced stance time on the short side
• reduced loading on the short side
• functional ankle plantarflexion on the short side so that they are able to reach the ground.
• On the long side we'll often see foot pronation as a compensatory mechanism to allow that leg to be slightly shorter as that foot collapses in.
• medial rotation of the lower extremity and knee flexion to compensate.
• gait asymmetry and we will see that the pelvis rotates as they walk towards that short side.

Knee

• baby: genu varum
• toddler: knock-knee to genu valgus (max out around 2 1/2) that decreases over time
• adult: neutral
• birth- 30 degree knee flexion contracture
• resolves first few months of life
• infant: medial rotation of the tibia
• 12 months- medial rotation of tibia is resolved

** too much lateral tibial torsion, crouched posture.

** too much medial tibial torsion. And so this is when we don't have a resolution of the torsion and it stays in that internal twist. This is really not as common to see. A lot of times when we think about our kids that toe inward most of the time that medial rotation is happening a little higher up and not so much at the tibia.

Too much genu valgus:

• calf, thigh and knee pain
• fatique more quickly with activities
• less efficient with gait
• increase Q-angle makes quad less efficient secondary to abnormal muscle pull
• lateral subluxation of the patella,
• medial arch of the foot collapse in
• protective in-toeing
• decreased gait velocity
• decreased balance.

feet

• baby-straight forward or slight toeing out
• adulthood-toeing out increase
• birth- nice arch
• adult- moving to flat foot
• hindfoot varus: birth (bowing in of heel)
• standing moves it into valgus

important because depending on what disease process a patient has. Depending on if it's a genetic condition that is causing different activation of their muscles, that's causing abnormal bony alignment then their form and their function can both be directly impacted. This is also really important because whenever these babies have atypical alignment, they're going to practise an atypical alignment thousands of times a day. So if we don't have good alignment, you're going to get potentially an exacerbation of this malformation. It's also really important because again, as they start to stand and weight shift and have these ground reaction forces, if they're placed in the incorrect locations, then again you can get bony deposition in the wrong areas. And it's also really important because it can directly affect how our brain is wired and how much our body is actually mapped in our brain. And we'll go into that a little bit more.

So idiopathic scoliosis, muscular dystrophies, trisomy 21, CP (cerebral palsy) if they have decreased tone. All of these things can cause abnormal muscle pull and abnormal alignment of your joints, which directly affects their functional participation.

Now, there are some things that we can do as physical therapists that will have an impact on their alignment to improve both their form and their function as they continue to grow and develop. As we talked about already, you have from birth through those first couple years, and then a little bit of influence all the way up until 25. We can have some interventions that we apply to these children to allow them to have more appropriate biomechanical alignment, and the earlier we can have appropriate biomechanical alignment, the better their function is going to be.

So if we can find ways to influence the alignment of that child then what we can do is they will then practise movement patterns because we know they weight shift thousands of times a day in appropriate alignment. And the more they can do that, the better off their form is going to be going forward.

So one, we know that movement is essential. So we've got to get them in appropriate alignment and then we have to get them to move because this is going to be what changes how that skeletal system is modeled.

• static positioning device
• splinting/bracing
• weight shifts
• loading
• surgery
• So we want them to do this in the right alignment. If we have them in inappropriate alignment, they're going to reinforce aberrant muscle pull, reinforce atypical movement patterns, which doesn't help them in the long run.

.children who cannot walk more than 10 steps by the age of 30 months we really need to watch their hips. We really need to watch their spine. So if you have a child that you are treating who has cerebral palsy and they are non ambulatory, or walking very, very little by the age of 30 months. Know that we need to get them in for hip X-rays because we know that if they don't have this appropriate loading force, if they don't have appropriate weightbearing, they're going to have that coxa valga that persists or increases. We know that they are going to have hip anteversion. And both of these things together really put them at a very high risk of dislocating their hip posteriorly, which is painful and bad for alignment. So we want hip X-rays to measure the migration of their hip. So how much that hip is moving in the socket every six to 12 months until the age of seven.

So for children that are unable to stand by the age of five, we want to have imaging of their spine. Do they have scoliosis that's developing? What is their ribcage doing? Are they able to maintain appropriate alignment? Because if you have too much curvature in your spine, it affects your breathing. It can affect your lung position, it can affect where your heart is at. So it can affect visceral function if they have too much compression on those organs due to a curved spine.it's really important to make sure that you know what that child is doing and what they look like functionally because it can have significant impact on pain, on mobility, and even on things like breathing and cardiac function as they continue to grow and develop.

cortical plasticity: So it's really important that we provide opportunities for our patients to be able to use these body parts that they might have deficits in so that they continue to have good neural mapping to those areas.

Muscle pull over time

already, you have this greater trochanter as weight shifts happen, there is increased pull on the greater trochanter because there's so many muscle attachment points in that region. And as those muscles pull and attach, what we get is both compression and a laydown of bone on the uppermost border of the femoral neck. And this can actually change the angle of inclination over time. So you have these muscles like the piriformis which does a lot of external rotation and abduction. The gluteus medius that's going to do abduction, external rotation and internal rotation depending on its angle. And then the gluteus minimus it's going to be doing abduction and internal rotation. So as these muscles are all firing, as they're activating, as infants are starting to stand, as they're starting to do weight shifts, we get this compression on. So you think about all these muscles pulling in on the greater trochanter so that's going to cause laydown of more bony tissue. And as that does that we're going to see changes in the angle of inclination.

Next, let's look at those torsional forces on the femur. So we know that originally there's this medial twist on the femoral shaft. In newborns it's around 40 degrees. This decreases over time into adulthood to around 10 to 16 degrees. And what we're really looking at when we measure this is drawing a line that goes through the femoral head. And then another line that is going to go along the condyles of the femur distally. And we're looking at the angle between those two. So if you look at this change here, so what we're really looking at is we have that femoral head, that femoral neck, how much that is rotated on the shaft is really what is causing that change between the positioning of the femoral head and then that twist downwards to where the condyles are at. This changes over time due to, again, function. So this form is directly related to function and vice versa. So all of these activities that require stabilisation by the glute med will help to resolve not only the coxa valga, but also this antetorsion, this anteverion. This also helps to resolve the hip flexion contracture. So as babies are starting to crawl, as they're extending their hips, as they're using their glute max all of these things will cause different muscle pulls on the femur, on the femoral head. And then also we'll start to see some activation of the adductors along the thigh. And all of these loading forces will actually help to extend and laterally rotate the hip.

As that is done, what we will see is that twist decreases over time. Now, what happens if this doesn't go right? This is really looking at femoral anteversion. So they're looking at this femoral neck angle, axis of the femoral neck in relation to that trans condylar line. And so typically we would expect to see that this anteversion is changing and decreasing over time. But what we see is that for infants who have cerebral palsy so this is looking at the GMFCS (Gross Motor Function Classification System) which is a scale that we use to be able to classify level of involvement of individuals who have cerebral palsy. So a GMFCS level of one is the most independent, and a GMFCS level of five is the least independent when we're talking about our children with cerebral palsy. So you can see that those children who are more ambulatory, more independent will have a mean femoral neck angle that is lower than those who are more involved and less ambulatory. So their femoral neck angle remains quite high, so they remain with this femoral anteversion. And this is a really big deal because what this can do is it can actually increase risk of hip dislocation.