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Updated: Sep 16 2022

Genu Valgum (knocked knees)

3.6

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Images
https://upload.orthobullets.com/topic/4052/images/knock knee deformity.jpg
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  • summary
    • Genu Valgum is a normal physiologic process in children which may also be pathologic if associated with skeletal dysplasia, physeal injury, tumors or rickets. 
    • Diagnosis is made clinically with presence of progressive genu valgum after the age of 7. 
    • Treatment is observation for genu valgum <15 degrees in a child <7 years of age. Surgical management is indicated for severe and progressive genu valum in a child > 7 years of age. 
  • Epidemiology
    • Incidence
      • common but true incidence unknown 
    • Demographics
      • most common age of presentation 3-5 years
        • range 2-8 yrs
    • Anatomic location
      • distal femur is the more common location of pathological deformity 
    • Risk factors
      • prior infection or trauma 
      • vitamin D deficiency/rickets
      • obesity 
      • skeletal dysplasia
      • lysosomal storage diseases 
  • Etiology
    • Pathophysiology
      • physiologic progression of coronal alignment 
        • genu varum <2 years of age  
        • neutral alignment around 2 years
        • genu valgum will peak at 3-4 years to a tibiofemoral angle of 15-20 degrees 
        • genu valgum rarely worsens after age 7
          • after age 7 valgus should not be worse than 12 degrees of genu valgum
          • after age 7 the intermalleolar distance should be <8 cm
      • lateral deviation of mechanical axis
        • decreased growth from lateral physis relative to medial physis
      • patellar instability
        • increased Q-angle
        • shallow lateral femoral sulcus
          • lateral femoral condyle growth suppressed predisposing to lateral subluxation 
    • Associated conditions
      • bilateral genu valgum
        • physiologic
        • renal osteodystrophy (renal rickets)
        • skeletal dysplasia
          • Morquio syndrome
          • spondyloepiphyseal dysplasia
          • chondroctodermal dysplasia
      • unilateral genu valgum
        • physeal injury from trauma, infection, or vascular insult
        • proximal metaphyseal tibia fracture
          • Cozen Phenomenon 
        • benign tumors
          • fibrous dysplasia
          • osteochondromas
          • enchondromas 
        • fibular hemimelia 
  • Anatomy
    • Osteology 
      • knee
        • normal lateral distal femoral angle (LDFA) = 85-90 degrees 
        • normal medial proximal tibia angle (MPTA) = 85-90 degrees
        • hypoplastic lateral femoral condyle with shallow lateral femoral sulcus 
    • Ligament
      • medial collateral ligament 
        • 2 components 
          • superficial 
            • femoral attachment medial epicondyle 
            • tibial attachment proximal tibia deep and posterior to pes anserinus
          • deep MCL 
            • composed of meniscofemoral and meniscotibial ligaments
        • may be attenuated in genu valgum
    • Tendon 
      • increased combined lateral vector of quadricep and patellar tendon (increased q-angle)
        • predispose to patellar instability 
    • Nerves 
      • common peroneal nerve
        • branch off sciatic nerve that winds laterally around fibular neck 
        • bifurcates into two branches
          • superficial peroneal nerve
            •  innervates lateral compartment of leg which controls eversion of foot
          • deep peroneal 
            • innervates anterior compartment of leg which controls dorsiflexion 
    • Biomechanics
      • mechanical axis 
        • center of femoral head to center of ankle should pass through center of knee
        • lateral deviation of mechanical axis in genu valgum
          • lateral femoral condyle and lateral tibia plateau subjected to increased loads
      • mechanical loading on physis modulates growth
        • Hueter–Volkmann law
          • compression inhibits growth 
          • distraction stimulates growth
        • greater proportion of change in growth rate from hypertrophic zone (75%) than proliferative (25%)
          • greater effect on growth seen from change in size of chondrocytes than number 
  • classification
    • No uniform classification
      • unilateral vs bilateral
      • based on underlying etiology 
  • DIFFERENTIAL DIAGNOSIS
    • Physiologic genu valgum must be differentiated from pathologic causes
      • physiologic 
      • apparent 
        • obesity resulting in large thighs
        • excessive femoral anteversion 
        • excessive external tibial torsion  
      • idiopathic
      • post-traumatic 
        • Cozen phenomenon
        • malunion 
        • physeal arrest 
      • metabolic
        • renal osteodystrophy 
        • hypophosphatemic rickets 
      • infection 
        • osteomyelitis 
      • neuromuscular
        •  poliomyelitis 
      • neoplastic
        • multiple hereditary exostoses
        • fibrous dysplasia 
        • osteochondromas
      • lysosomal storage disease
        • mucopolysaccharidosis type IV (Morquio)
      • skeletal dysplasia
        • Chondroectodermal dysplasia (Ellis-van Creveld)
        • Spondyloepiphyseal dysplasia tarda
        • Pseudoachondroplasia 
        • Focal Fibrocartilaginous dysplasia 
  • PRESENTATION
    • History 
      • medical and family history can help differentiate between physiological and pathological etiology
    • Symptoms 
      • cosmetic deformity most common complaint
      • often asymptomatic 
      • medial sided knee pain
    • Physical exam
      • abnormal circumduction gait
      • inspection
        • hip adduction
        • medial aspect of knees touching
        • wide intermalleolar distance (>8 cm) 
        • leg lengths 
      • range of motion
        • assess patellar tracking 
      • rotational profile
        • apparent genu valgum with excessive femoral anteversion or external tibial torsion  
      • general exam to assess stigmata of associated conditions 
        • rickets 
        • syndromic features
        • skeletal dysplasias 
        • Maffucci syndrome 
  • IMAGING
    • Radiographs 
      • indication
        • asymmetrical findings
        • excessive genu valgum clinically age group beyond which is expected of physiologic changes
        • short stature
        • history of trauma or infection
        • limb length discrepancy 
      • views
        • AP standing long-length film 
          • patella should be facing forward to ensure proper positioning 
      • findings
        • lateral deviation of mechanical axis through knee
        • physeal narrowing or premature closing
        • Park-Harris lines
    • CT or MRI
      • rarely indicated
        • evaluate underlying malignancy
        • evaluate for physeal bar  
  • STUDIES 
    • lab studies 
      • depends on suspected underlying medical conditions
        • rickets
          • serum calcium and phosphate
          • 25-OH Vit D3 levels
          • PTH 
        • mucopolysaccharidoses
          • urinalysis for excess muscopolysaccharides (ie keratan sulfate - Morquio)
        • syndromic
          • genetic testing
  • TREATMENT
    • Nonoperative
      • indications
        • first line treatment 
        • tibiofemoral angle <15 degrees
        • children <7 years of age
      • modalities
        • observation and medical management 
        • bracing
          • rarely used
      • outcomes
        • vast majority of physiological genu valgum will resolve spontaneously 
        • medical management of underlying etiology may slow progression 
        • bracing may provide temporary relief but is an ineffective long-term solution
    • Operative
      • indications
        • tibiofemoral angle > 15 degrees
        • intramalleolar distance of 10 cm after age 10 years 
        • rapidly progressive deformity after age of 7  
      • modalities
        • medial hemiepiphysiodesis
          • temporary (more common) 
          • permanent
        • osteotomy 
          • distal femoral osteotomy 
          • high tibial osteotomy 
      • outcomes
        • eight-plate hemiepiphysiodesis
          • >95% complete correction for idiopathic 
          • 80% complete correction for pathological 
        • rate of correction with hemiepiphysiodesis is variable
          • angular correction of 7 degrees per year at the distal femur
          • angular correction of 5 degrees per year at the proximal tibia
  • TECHNIQUE
    • Observation
      • techniques
        • observation and reassurance 
    • Medial hemiepiphysiodesis  
      • indications
        • > 15-20° of valgus in a patient between ages 7-10
        • if line drawn from center of femoral head to center of ankle falls in lateral quadrant of tibial plateau in patient > 10 yrs of age
      • options
        • temporary hemiepiphysiodesis
          • rigid stapling
          • percutaneous screw (Metaizeau)
          • tension band plate and screws
        • permanent hemiepiphysiodesis
          • modified Phemister technique
      • technique
        • location of hemiepiphysiodesis dependent on 3 factors
          • amount of remaining growth
          • location of deformity
          • severity of deformity 
        • place extraperiosteally to avoid physeal injury 
        • implant placed midsagittal to avoid sagittal plane deformity 
        • one eight-plate or two staples per physis is generally sufficient
        • postop
          • follow patients often to avoid varus overcorrection 
          • implant removal
            • remove once mechanical axis passes through center or knee or slightly medial 
            • account for rebound medial overgrowth resulting in loss of correction
              • more likely in younger patients
          • growth begins within 24 months after removal of the tether
      • complications (~5-10%)
        • screw loosening or failure
        • rebound deformity after removal
        • infection
        • premature physeal closure
    • Osteotomy
      • indications
        • insufficient remaining growth to correct deformity with hemiepiphysiodesis
        • skeletally mature patients
        • non-functional growth plate (ie presence of bar, infection etc) 
      • options
        • lateral distal femur opening wedge osteotomy
          • pros
            • angular correction can be adjusted to desired correction
          • cons
            • requires grafting
            • less stable construct 
            • prolonged immobilization to allow graft to heal
        • medial distal femur closing wedge osteotomy
          • pros
            • stable osteotomy 
            • shorter period of immobilization
            • avoid distracting lateral common peroneal nerve
          • cons
            • technically demanding to remove precise angular wedge
        • high tibial osteotomy
      •  technique
        • determining site of osteotomy
          •  dependent on site of deformity 
            • assess mLDFA and mPMTA 
            • femur most common site of deformity
      •   complications
        • nonunion
        • neurovascular complication
        • compartment syndrome
        • hardware failure
  • complications
    • Peroneal nerve injury
      • risk factors
        • opening wedge technique
      • prevention
        • perform a peroneal nerve decompression at the time of surgery prior to distraction
          • two potential areas of entrapment
            • fascia of the lateral compartment
            • intermuscular septum separating the anterior and lateral compartments
        • gradual correction of severe deformities can be done with circular external fixator
    • Nonunion
      • risk factors
        • opening wedge osteotomy
        • >20 deg deformity 
    • Limb length discrepancy
      • closing wedge osteotomy shortens limb
      • opening wedge osteotomy lengthens limb
    • Undercorrection
      • insufficient physeal growth or encroaching maturity
    • Overcorrection
      • lost to follow-up (12%) 
    • Rebound phenomenon 
      • incidence
        • 56%
      • defined as a loss of 5 degrees of correction once the plate is removed
      • risk factors
        • femoral deformity
        • younger age at plate application and removal
        • faster correction rate 
        • intentional overcorrection increased risk
      • treatment 
        • consider slight overcorrection prior to implant removal 
          • may not prevent rebound growth but may limit recurrence of deformity
        • consider performing growth modulation closer to skeletal maturity for milder deformities
    • Physeal closure
      • very rare (<1%)
      • prevention
        • place implant extraperiosteally 
        • remove implant with 2-3 years after insertion
  • Prognosis
    • Idiopathic genu valgum has a better prognosis than pathological etiology with hemiepiphysiodesis
      • higher rate of complete correction 
      • faster correction rate
      • fewer complications
    • Physiologic genu valgum resolves spontaneous in vast majority by age of 7
    • Deformity after a proximal metaphyseal tibia fracture (Cozen) should be observed as most remodel
      • maximum magnitude of deformity reached approximately 12-18 mo after injury
      • resolve spontaneously within 2-4 years 
    • Threshold of deformity that leads to future degenerative changes is unknown
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