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Genu Valgum (knocked knees)

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

  • 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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