Hypermobile infants and toddlers have joints that bend further than usual, often have some muscle weakness which leads to a diagnosis of low muscle tone, in most cases have a cautious nature.
Infants and toddlers with joint hypermobility may:
What is joint hypermobility?
Babies with joint hypermobility have joints that are able to bend further than usual and a trunk and limbs that appear to be floppy and weak.
The increased range of movement at the joints (sometimes called joint laxity or being double jointed) is due to differences in the connective tissue that forms the joint capsule and ligaments.
The joint capsule and ligaments hold together the bones that form the joint. The joint capsule and ligaments are formed by a strong but pliable material called connective tissue. Connective tissue can be stretched a little way, just enough to allow the joint to move through the typical full range of movement.
In joint hypermobility the connective tissue has more give and can be stretched further than usual. This means that the joints are less firmly held together and can be moved further than usual.
The increased pliability in the connective tissue also affects the muscles, which may appear to be floppy and are often weak. This in turn affects how the infant moves and develops and may mean that the infant is late achieving the major developmental milestones.
Jessie locks her hypermobile elbow joints and bends her back more than usual. Her hips are also abducted more than usual ie her thighs are wide apart.
Together these ways of moving make it difficult for her to push up onto all fours.
Toesies sits with his back very rounded and his legs flat on the floor.
The widely abducted position of the hips makes it difficult for him to sit erect and may also lead to tightness in the hip muscles.
Low muscle tone and joint hypermobility
Infants who appear to be floppy and have hypermobile joints are often given a diagnosis of low muscle tone. The term muscle tone refers to the muscles' readiness for action. This readiness for action depends on the sensitivity of the stretch receptors in the muscles. If the sensitivity to stretch is very low the muscles are slow to respond and they appear to be weak and floppy.
In infants with joint hypermobility the connective tissue that holds the muscles together and connects the muscles to the bones via the tendons is very pliable. This affects the sensitivity of the stretch receptors and the muscle's readiness for action.
In most instances the low muscle tone is linked to joint hypermobility. However, if a baby is floppy and appears to be weak a full assessment by a pediatrician is important to rule out other causes.
Read more Low muscle tone
Different developmental pathways for hypermobile and "low tone" infants
Posture at birth
At birth typically developing full term infants lie with their arms and legs flexed. In fact the the muscles of the hips and knees are tight and cannot be completely stretched out.
The slight tightness (stiffness) in the muscles of the hips and knees helps the newborn infant to lift the arms and legs up when kicking and reaching.
Newborn hypermobile (and pre-term) babies lie with their legs and arms more extended and flat on the cot mattress. The usual tightness of the hip and knee muscles is absent and the the hips and knees can be fully extended.
The laxity in the muscles means that it requires more effort to lift up the arms to reach for toys and kick the legs.
Typically developing babies are very active
Within weeks active infants have learned to keep their trunks steady when they kick, lift their legs up and reach for toys. They also start to push down on their feet and lift up their buttocks. All this movement strengthens the muscles and gets them ready for sitting.
Hypermobile, low tone and premature babies may be less active and fail to develop good muscle strength
If the infant is hypermobile and also cautious she may not kick vigorously and fail to develop the muscle strength needed to support the hypermobile joints and get them ready for rolling and sitting up.
Hip stiffness affects the baby's ability to get up onto the knees
The stiffness in the hip muscles affects the infants ability to get up into kneeling or onto all fours. The legs are held wide apart when they are on their tummies and this makes it difficult to get up onto the hands and knees in readiness for crawling.
Hypermobile infants lock their elbows
Hypermobile infants lock their elbows into hyperextension when they push up on their arms. As a result they do not develop the arm strength needed for getting up onto all fours and crawling.
Hypermobile (low tone) infants often bottom shuffle, and skip the crawling stage
Hypermobile and low tone infants sometimes do not crawl. Instead they may scoot on their bottoms to get around.
This little fellow manages to hop along on his bottom with great speed.
Standing, cruising and walking may be delayed
Hypermobile infants stand with their knees locked back in hyperextension. They may also start standing with their feet wide apart and turned out. This makes it difficult to shift the weight onto one foot to take a step.
If their hip and knee muscles are weak, they have difficulty bending down to retrieve objects from the floor, and take longer to sit down with good control.
They often fall back with their knees straight when they want to sit down again.
Walking is usually delayed
Hypermobile and low tone infants tend to walk a few months later than usual, sometimes as late as 18-20 months.
Hypermobility, developmental delay and brain development
Most infants and toddlers are curious and adventurous. They spend a lot of time exploring different ways of doing things and will persist and work hard at achieving their goals. They also enjoy being social and seek out opportunities for social engagement. By the end of the first year they are also becoming more able to manage their negative emotions as they become more goal focused.
Hypermobile infants with a cautious nature tend to avoid new or challenging activities. They are less curious and adventurous and spend less time exploring different ways to to things. They have slow to learn to manage negative emotions and use avoidance as their only strategy for moderating negative emotions.
The cautious/fearful infant's avoidant behavioral style has long term consequences: the mind-body foundations needed for later developing motor, communication, language, emotion and cognitive tasks are not well established.