Classification principles
Modern clinical assessment of rickets is based on three fundamental criteria:
- Severity grade: mild (I), moderate (II), and severe (III). The division is based on the predominant type of bone lesion.
- Disease period: acute (height of illness), convalescence (recovery), and residual effects.
- Course character: acute or subacute.
The morphological basis of all changes is a failure of epiphyseal growth: cartilage tissue changes in the epiphyses, while defective osteoid tissue proliferates in the metaphyses, forming a specific "rachitic metaphysis".
Severity grades and bone deformities
The progression of symptoms ranges from soft, pliable bones to systemic curvatures and marked delay in the child's motor development.
- Grade I (Mild): The process of bone softening—osteomalacia—dominates. Palpation of the skull reveals pliability, and the occiput is flattened. Thickening appears at the junction of the bone and cartilage of the ribs, known as "rachitic rosary". Muscle tone (hypotonia) is moderately decreased.
- Grade II (Moderate): Active proliferation of defective tissue—osteoid hyperplasia—joins the process. Pronounced frontal and parietal tuberosities form on the skull. The chest becomes deformed: a transverse depression appears along the line of diaphragmatic attachment ("Harrison's sulcus"). Legs curve into an O-shape (varus deformity). Due to marked muscle weakness, the abdomen spreads out, acquiring a "frog-belly" appearance.
- Grade III (Severe): Skeletal deformities become severe. The skull acquires an "olympian brow" shape, and the spine curves into an arc ("rachitic kyphosis"). X-shaped (valgus) or severe varus curvatures appear on the limbs, along with increasing thickening on the forearms ("richet's bracelets") and phalanges («string of pearls»). The risk of pathological fractures increases. Profound muscle weakness prevents the child from standing or sitting.
Muscular and electrolyte disorders
Decreased muscle tone in rickets is not of neurological, but of electrolyte origin. Calcium deficiency (less commonly, magnesium) disrupts the normal contraction of muscle fibers.
The systemic nature of the lesion is manifested by the involvement of not only skeletal muscles, but also the myocardium and diaphragm. Ion imbalance frequently triggers pathological muscle spasms:
- Laryngospasm: sharp difficulty in inspiration during crying or fright, up to brief respiratory arrest (apnea).
- Carpopedal spasm: painful tonic contractions of the foot and hand muscles.
- Brief limb convulsions.
Period dynamics and laboratory diagnostics
Acute period Most commonly manifests in the first six months of life. Osteomalacia absolutely predominates in the bones. Blood tests reveal the primary marker—an increase in alkaline phosphatase levels (a signal of osteoblast hyperactivity). Less frequently, a decrease in phosphorus (hypophosphatemia) is detected, and transient calcium deficiency (hypocalcemia) is possible. Urinalysis determines excessive calcium excretion (calciuria).
Convalescence period Characterized by the reverse development of the disease. Osteomalacia is arrested: skull bone softening (craniotabes) and occipital flattening disappear, and limb deformities diminish. Muscle hypotonia subsides, and the child rapidly masters motor skills that were previously delayed. Meanwhile, alkaline phosphatase may remain moderately high—this is a normal reflection of ongoing recovery processes.
Residual effects period This diagnosis is valid only for children under the age of 3 years. In this phase, metabolism and laboratory tests completely return to normal, yet visual consequences of the past disease (prominent frontal tuberosities, minor leg curvature) persist.
Remembering the pathogenesis progression is aided by the O-O-D rule: Osteomalacia (softening, Grade I) → Osteoid hyperplasia (proliferation, Grade II) → Severe deformities (Grade III).
Class and exam questions
Why does a "frog belly" occur in rickets?
This is a direct consequence of systemic muscle hypotonia due to electrolyte deficiency. Weakness of the anterior abdominal wall muscles causes the abdomen to spread out when the child lies on their back.
Can a diagnosis of active rickets be made in a school-aged child due to leg curvature?
No. If mineral metabolism is normal, these are residual effects of a disease suffered in infancy. Furthermore, the diagnosis of "residual effects period" is valid only up to 3 years of age.
What does high alkaline phosphatase indicate during the recovery period?
Moderately elevated alkaline phosphatase during convalescence is normal. It reflects the ongoing activity of osteoblasts in bone tissue repair.
What else to study on this topic
- Prenatal risk factors: FGR (fetal growth restriction), multiple pregnancy, and placental pathology.
- Postnatal nutritional and growth factors in the development of mineral deficiency.
- The impact of vitamin D, copper, iron, and vitamin C deficiency on bone collagen strength.
- Biomechanic risk factors: the impact of tight swaddling and immobilization on bone.
- Differential diagnosis of electrolyte muscle spasms.
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Other topics in "Chapter 3. Adaptation, Early Childhood Nutrition, Rickets"
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