Why and how the axis is determined
Assessing the limb axis helps the physician identify the consequences of injuries, as well as congenital or acquired diseases of the musculoskeletal system. Curvatures can affect one side or be bilateral (as, for example, in rickets).
A critical condition for a reliable examination is focusing exclusively on bony prominences. Relying on soft tissue contours easily leads to diagnostic errors: pronounced edema often creates the appearance of deformity where the bone structure is intact.
Normal axes and frontal deformities
Depending on how the line shifts relative to the joints, normal alignment, valgus, and varus deformities are distinguished.
| Limb | Normal | Valgus deformity | Varus deformity |
|---|---|---|---|
| Lower | Line: anterior superior iliac spine → medial edge of the patella → first toe of the foot | The axis passes lateral to the patella | The axis passes medial to the patella |
| Upper | The line passes through the heads of the humerus, radius, and ulna | The axis passes lateral to the elbow joint | The axis passes medial to the elbow joint |
Deformities in the sagittal plane
If the axis curves in the anteroposterior direction (sagittal plane), special terms are used:
- Recurvatum (recurvatum) is a deformity in which an angle pointing anteriorly is formed.
- Antecurvatum (antecurvatum) is a deformity with the formation of an angle pointing posteriorly.
Rules of patient examination
To correctly assess axes and identify deformities, the examination (status localis) must be carried out according to clear rules:
- Complete undressing of the patient is mandatory.
- Symmetrical areas of the healthy and injured sides must be compared.
- The patient's position (standing, sitting, lying) is chosen based on the severity of the injury.
- In severe polytrauma, the patient is examined directly on a stretcher, and clothing is cut away with shears.
Briefly: answers to topical questions
What bony landmarks form Hüter's line and triangle in the area of the elbow joint?
Hüter's line and triangle are formed by three bony landmarks of the elbow joint:
- medial epicondyle of the humerus;
- lateral epicondyle of the humerus;
- tip of the olecranon.
In extension, they form Hüter's straight line; in flexion, Hüter's isosceles triangle; and when flexed to 90°, Hüter's equilateral triangle.
How to correctly measure the relative and absolute length of the lower extremity?
Measurement of the lower limb length is performed with a measuring tape without slack, strictly between identifiable bony prominences, with the limbs extended along the body axis while the anterior superior iliac spines (spina iliaca anterior superior) are symmetrically positioned. The result must be evaluated in comparison with the healthy side. The distal landmark for both types of measurement is the tip of the medial malleolus, while proximal landmarks differ:
- Relative length — measured from the anterior superior iliac spine (spina iliaca anterior superior) to the tip of the medial malleolus.
- Absolute length — measured from the tip of the greater trochanter of the femur to the tip of the medial malleolus.
Class and exam questions
Why should the limb axis not be determined by soft tissue contours?
Due to potentially pronounced soft tissue swelling, visual contours may change, creating a false picture of bone curvature.
How does valgus deformity differ from varus deformity in the legs?
In valgus deformity, the axis passes lateral to the patella (knock-knees), while in varus deformity, it passes medial to it (bowlegs).
What is recurvatum?
This is a curvature of the limb axis in the sagittal plane, forming an angle pointing anteriorly (recurvatum).
What else to study on this topic
- Types of patient positions (active, passive, forced)
- Posture assessment and signs of normal status
- Determination of trunk symmetry using bony points
- Examination of the skin in traumatology
- Gait assessment in joint pathologies
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