Guided Growth and Angular Deformity Correction

Coronal lower-limb alignment changes normally during childhood. Infants often have genu varum, toddlers pass into genu valgum, and older children gradually settle toward adult alignment. Guided growth is for the child whose alignment is not following that expected pathway or whose deformity is symptomatic, asymmetric, progressive or pathological.

The common clinical problem is genu valgum or genu varum around the knee. The important clinical question is not just whether the knees touch or the ankles separate. The important question is where the mechanical axis passes, what bone creates the deformity, whether the physis is open, how much growth remains, and whether the underlying biology is normal.

Typical indications include persistent genu valgum, pathological genu varum, Blount disease in selected stages, post-traumatic physeal disturbance, skeletal dysplasia and metabolic bone disease after medical optimisation. Guided growth is smaller than osteotomy, but it is not casual. It requires reliable follow-up, timely implant removal and continued surveillance for rebound.

Angular deformity develops when growth is asymmetric across a physis or when a bone or joint segment has abnormal orientation. The mechanical axis is the functional consequence: it shows where load passes from the hip to the ankle across the knee. A medial mechanical axis overloads the medial side; a lateral mechanical axis overloads the lateral side.

Guided growth works by temporary hemiepiphysiodesis. A plate, screw construct or other tether slows one side of an open physis. The other side continues to grow, gradually changing the joint orientation and mechanical axis. The correction rate depends on age, remaining growth, which physis is used, the underlying diagnosis and distance from the knee.

Pathological physes behave differently. Blount disease has disordered medial proximal tibial growth and may recur or fail to correct if severe. Rickets and metabolic disease need medical correction before mechanical correction. Post-traumatic physeal bars can create focal angular growth disturbance and may require bar resection, epiphysiodesis or osteotomy rather than a simple plate.

Blount disease (tibia vara) is the key pathological cause of genu varum to separate from physiological bowing, and it has its own staging and a measurement that the topic's vivas demand.

Early-onset (infantile, under about 3 to 4 years) versus late-onset (juvenile/adolescent): early-onset is bilateral in up to half, linked to early walking and obesity; late-onset tracks adolescent obesity and is more often unilateral with less growth remaining.

History

Ask about age at onset, progression, symmetry and function. Pain, lateral thrust, fatigue, patellofemoral symptoms and unilateral progression are more concerning than cosmetic concern alone. Ask about previous physeal injury, infection, fracture, metabolic disease, vitamin D risk, renal disease, skeletal dysplasia features, family history and obesity.

Ask the family whether follow-up is practical. Guided growth is a commitment to serial imaging and planned hardware removal.

Examination

Observe the child standing and walking. Look for varus thrust, patellar tracking, foot progression, limb length difference, pelvic level and rotational profile. Measure intercondylar or intermalleolar distance as a clinical baseline, but do not use it as a substitute for full-length alignment.

Assess:

• Hip, knee and ankle range of motion.
• Coronal alignment and patella direction.
• Ligament laxity and joint line opening.
• Lateral thrust in varus knees.
• Rotational profile so torsion is not mistaken for coronal deformity.
• Signs of rickets, skeletal dysplasia or systemic disease.
• Skin, BMI and soft-tissue envelope for implant planning.

The key investigation is a standing hip-to-ankle radiograph with patellae facing forward where possible. This allows mechanical axis deviation, LDFA, MPTA and joint line convergence to be assessed. A cropped knee film can miss femoral, tibial, limb-length or global alignment contribution.

The angles named above are only useful against their normal values, and the malalignment test (Paley) is the systematic way to turn a standing film into a deformity diagnosis.

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The malalignment test - a stepwise read:

1. Measure MAD on the standing hip-to-ankle film. The mechanical axis normally passes just medial to the knee centre; the tibial plateau can be divided into zones, and a line falling into the medial or lateral outer zones confirms significant deviation.
2. Find the femoral contribution with the mLDFA - if abnormal, the distal femur is a (or the) source.
3. Find the tibial contribution with the MPTA.
4. Account for the joint with the JLCA - a raised value means part of the "deformity" is intra-articular or ligamentous (joint-line opening or cartilage wear), which guided growth will not correct.

• Physiological genu varum or genu valgum.
• Infantile or adolescent Blount disease.
• Nutritional rickets or hypophosphataemic rickets.
• Renal osteodystrophy or endocrine bone disease.
• Post-traumatic physeal bar.
• Skeletal dysplasia.
• Ligamentous laxity or joint line convergence.
• Rotational profile creating apparent coronal malalignment.
• Limb-length difference with pelvic compensation.

Early

• Wrong diagnosis: physiological alignment treated surgically.
• Wrong level or wrong side tethering.
• Infection, wound irritation or hardware prominence.
• No correction because growth remaining is inadequate.
• Family lost to follow-up before planned removal.

Late

• Overcorrection.
• Undercorrection.
• Rebound deformity after removal.
• Hardware breakage or migration.
• Physeal tethering or bar formation.
• Need for repeat guided growth or osteotomy.

Guided growth is a timed growth-modulation operation. It is not an acute correction. The child must have enough growth remaining, the deformity source must be correctly identified, and the family must understand that overcorrection, undercorrection and rebound are surveillance problems.

For genu valgum or varum, treatment begins with the full-length standing film, not a knee-only radiograph. The question is whether deformity arises from distal femur, proximal tibia, both, joint-line obliquity, ligament laxity or extra-articular deformity. Guided growth works poorly if the wrong physis is tethered or if the deformity is mainly intra-articular.

Osteotomy is preferred when correction is urgent, growth remaining is insufficient, deformity is severe and rigid, there is joint depression, or the child is near maturity. Guided growth is preferred when gradual correction is safe, there is enough growth remaining, and the joint surface is acceptable.

Structured clinical approach

Use a structured sequence:

• Define physiological versus pathological alignment.
• Describe symptoms, progression and asymmetry.
• Obtain standing hip-to-ankle films.
• State mechanical axis deviation.
• Use LDFA, MPTA and JLCA to localise source.
• Check growth remaining and bone age.
• Look for metabolic disease, Blount disease or physeal bar.
• Choose observation, medical treatment, guided growth or osteotomy.
• Plan follow-up, removal timing and rebound surveillance.

Common pitfalls

• Planning from a knee-only X-ray.
• Operating on physiological alignment.
• Ignoring bone age.
• Forgetting rickets or renal bone disease.
• Confusing rotational deformity with coronal deformity.
• Using guided growth when osteotomy is required.
• Not removing implants on time.
• Discharging after removal without rebound surveillance.

Guided growth is practised worldwide, but the supporting framework is principle-based and society reviews rather than randomised trials or implant registries, because these are paediatric soft-tissue-sparing procedures in growing bone.

Global epidemiology

• Physiological genu varum is usual in infancy and physiological genu valgum peaks around age 3 to 4 years, settling toward adult alignment (mild valgus) by about age 7, across populations.
• Idiopathic genu valgum needing intervention is uncommon; most referrals are physiological and resolve with observation.
• Blount disease prevalence varies by region and body habitus: infantile (early-onset) disease is more frequent where early walking and higher childhood BMI are common, while late-onset (adolescent) disease tracks adolescent obesity.
• Nutritional rickets remains a leading cause of pathological bowing in limited-resource settings, whereas X-linked hypophosphataemic rickets dominates where nutrition is adequate.

Side-by-side guidance

The common thread across societies is that the analysis (full-length alignment, source localisation, growth remaining and underlying diagnosis) governs the decision, not the appearance of the knee.

Registry and evidence notes

• There is no dedicated international guided-growth implant registry comparable to arthroplasty registries (NJR, AJRR, AOANJRR); evidence comes from multicentre series such as the multinational tension band plating cohort of 967 physes.
• Best available data are cohort-level (Level III to IV), so counselling rests on pooled series rather than registry survivorship.

High- versus limited-resource practice

• Where full-length standing radiography and reliable follow-up are available, tension band plating with planned removal is standard.
• Where imaging or follow-up is limited, percutaneous transphyseal screws (lower cost, low profile) or single-stage osteotomy may be preferred, because guided growth fails without serial alignment review.
• In settings with high nutritional rickets burden, medical optimisation precedes any mechanical correction, and untreated metabolic disease is a frequent reason guided growth fails.

Guided growth is established, but several questions remain genuinely contested and are favourite viva territory.