Generalized joint hypermobility (GJH) affects the knee joint is two ways: 

• Hyperextension of the knee which affects standing posture and LE weight-bearing function.
• Increased range of knee rotation. 

Knee hyperextension

Hypermobility of the knee commonly recognised. 

The knee can be extended beyond 0⁰  sometimes as much as 10-15⁰. 

Hyperextension of the knee is usually associated with anterior pelvic tilt and extension of the lumbar spine. 

Knee rotation

A typically developing child has 8-10⁰ of medial and lateral rotation. 

The resting position for the foot is 0⁰.

The child sits and stands with the feet parallel or in a few degrees of lateral rotation. 

Knee rotation is best tested in prone with the knee flexed to 90⁰

x    

In GJH lateral rotation is often increased, with very limited range of medial rotation. 

The child stands and sits with the feet turned out at the knee. 

Medial rotation of the knee is often restricted to 0⁰. 

The combination of restricted adduction/medial rotation of the hip in extension along with lateral tibial torsion results in the child standing with the feet wide apart and turned out. 

This position is comfortable for the child. 

A quick test for the impact of hip and knee restricted movement on standing posture. 

Ask a child who habitually stands with the legs wide apart and the feet turned out to stand with the feet parallel and about 10 cm apart for 20s.

Enquire whether this position is comfortable - or if it gets "boring". Ask the child to identify where he/she feels the discomfort. 

Now let the child stand with the feet about 20 cm apart and and then in the habitual wide stance. Enquire each time about comfort.

Children are usually quite clear about the difference in comfort between the different positions. 

Tibial torsion and walking 

Lateral tibial torsion affects walking

During the stance phase the foot is rotated laterally with respect to the line of progression. 

In a child with good LE alignment the foot is positioned with a few degrees of lateral rotation with respect to the line of progression when walking. 
This allows the lower leg to pivot forwards over the foot during mid to late stance, and then allows for effective push-off. 

If the foot is positioned with lateral rotation relative to the line of progression, the tendency is for the child to roll sideways over the foot.  

Why do children develop lateral tibial torsion?

The altered pattern of ROM of the knee is probably associated with the tightness in the fascia lata and associated deep fascia. 

Sitting with the hips in medial rotation (W-sitting or side sitting) also imposes a lateral torsion force on the knee joint. 

Cross leg sitting is uncomfortable

The restricted range of medial rotation of the knee makes sitting cross legged on the floor uncomfortable

In cross leg sitting the knee is typically medially rotated. If medial rotation is limited to 00, cross leg sitting imposes a strong medial rotation stretch on the knee.

If you ask a child who does not like sitting cross legged where they experience discomfort they wil usually indicate the lateral aspect of the lower leg. 

Clinical application

Clinically I have found that active stretching of the tight fascia lata a related structures followed by standing activities with the feet parallel does improve the range of medial rotation of the knee and improve foot placement in walking and running. 

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Active mobilization of hip adduction and medial rotation of the knee