The term genu valgum or valgus knee is used to describe knock-knee deformity. Knock-knee deformity is commonly seen as as a passing trait in otherwise healthy children but some individuals retain or develop this deformity due to hereditary, metabolic or other causes.
As genu valgum is a normal physiologic process in children, therefore it is critical to differentiate between a physiologic and pathologic process
Both deformities in upper tibia and distal femur can give rise to genu valgum. The distal femur is the most common location of primary pathologic genu valgum.
Adolescent idiopathic genu valgum may be familial or it may occur sporadically. The true incidence is unknown.
Anatomy and Relevant Measurements
Normal physiologic process of genu valgum starts between 3-4 years of age children and have up to 20 degrees of genu valgum can be seen. Genu valgum rarely worsens after age 7 and after age 7 valgus should not be worse than 12 degrees of genu valgum.
Intermalleolar distance is the distance between two malleoli measured when knee touch each other with patella facing forward. After age of 7 years, the intermalleolar distance should be <8 cm.
[read about anatomy of knee]
Measurements are based on full length standing AP xray of lower limbs including hip, knee and ankle
The lateral distal femoral angle is the angle between the femoral shaft and its condyles. The the normal angle is 84°.
Proximal medial tibial angle; this is the angle between the tibial shaft and its plateau. The normal angle is 87°.
The mechanical axis (center of gravity) is a straight line drawn from the center of the femoral head to the center of the ankle; this should bisect the knee. An axis within the two central quadrants (zones +1 or -1) of the knee is deemed acceptable.
Pathophysiology of Genu Valgum
With normal alignment, the lower-extremity lengths are equal, and the mechanical axis bisects the knee when the patient is standing erect with the patellae facing forward.
With normal alignment, the physes and epiphyses are subjected to physiologic and intermittent compression and tension. Balanced growth is important for preserving straight legs, symmetrical limb lengths, and normal function.
When genu valgum is present, there is a shift of the mechanical axis laterally which causes pathologic stress on the lateral femur and tibia.
Moreover the normal expansion of entire hemiphysis is prevented [Hueter-Volkmann effect–continuous or excessive compressive forces on the epiphysis have an inhibitory effect on growth. ]
A vicious cycle ensues.
The growth suppression of the lateral condyle of the femur leads to shallow femoral sulcus and increased propensity for the patella to tilt and subluxate laterally. In extreme cases, patellar dislocation with or without osteochondral fractures may ensue.
Shallow, incongruous, or unstable patellofemoral joint may cause activity related anterior pain, causing activity-related anterior knee pain.
During walking thrust of the tibia relative to the femur may cause strain of medial collateral ligaments, resulting in localized pain and progressive joint laxity.
The patients may develop a circumduction gait because outward swinging of the legs is required to avoid knocking their knees together leading to an awkward and laborious.
Depending on the severity, the patient may find it difficult to run, ride a bicycle, play sports.
Left untreated, the condition may progress and deteriorate.
Meniscal tears, articular cartilage attrition, and arthrosis of the anterior and lateral compartments during may occur during adult years.
Causes of Genu Valgum
Bilateral Genu Valgum
- Physiologic
- Metabolic [Nutritional rickets]
- Renal osteodystrophy (renal rickets)
- Genetic Disorders
- Skeletal dysplasia
Unilateral Genu Valgum
- physeal injury from trauma, infection, or vascular insult
- Fracture malunion
- Poliomyelitis
- Benign tumors
- fibrous dysplasia
- osteochondromas
- Ollier’s disease
Phyiologic Genu Valgum or Not?
Physiologic genu valgum is seen in aged 2-6 years may have physiologic genu valgum.
The typical features include symmetrical deformity, ligamentous laxity, and lack of pain or functional limitations. It is important to differentiate physiologic genu valgum from the rest as it does not require any treatment.
And it is also important not to miss pathological causes of genu valgum.
Postaxial limb deficiencies, genetic disorders such [ Down syndrome, hereditary multiple exostoses, neurofibromatosis] and vitamin D–resistant rickets may cause persistent and symptomatic genu valgum and present early.
In contrast, adolescent idiopathic genu valgum is not benign or self-limiting. Teenagers may present with a circumduction gait, anterior knee pain, and, occasionally, patellofemoral instability.
Clinical Presentation of Genu Valgum
Usually, the genu valgum apparentonly when the child reaches the walking age.
The physiologic genu valgum generally resolves spontaneously by age of six years.
The deformity could be seen early in life when there is some kind of localized or generalized skeletal malformation or dysplasia.
Family history is to consider or rule out hereditary multiple exostoses, Marfan syndrome, osteogenesis imperfecta, or vitamin D–resistant rickets.
Nutritonal deficiency vitamin D and calcium is prevalent in certain countries and nutritional rickets should be considered as differential diagnosis.
A unilateral valgus is always pathological and investigated accordingly.
The physical examination should assess gait and evaluation of lower extremities.
Stature, craniofacial features, the spine, and the upper extremities should be evaluated.
Compare the relative limb and look for any torsional deformities of the femur, tibia, or both. Look for retropatellar crepitus and tenderness and note patellar tilt, tracking, and stability.
Laboratory Studies
Relevant blood and urine studies are warranted.
This includes routine tests, calcium levels and vitamin D levels. Endocrine studies may be done depending on the codition suspected.
Bone densitometry may be warranted in certain patients.
Imaging Studies
X-rays
Standing anteroposterior radiograph of the lower extremities, taken with the patellae facing forward s the standard exposure. This allows visualization of both the true and the apparent limb lengths and deformities.
The mechanical axis is a line drawn from the center of the head of the femur to the center of the ankle; this line should bisect the knee. Genu valgum is defined by lateral deviation of the axis or deviation toward or beyond the joint margin.
The deformity may be in the femur, the tibia, or both. The normal lateral distal femoral angle is 84° (6° of valgus), and the medial proximal tibial angle is 87° (3° of varus).
When the physeal abnormalities are suspected, AP and lateral radiographs of the hip or knee provide better visualization of the physis. If a skeletal dysplasia is suggested, a skeletal survey is warranted.
A skyline or sunrise or Merchant view of the kned may reveal tilt, subluxation, and, occasionally, osteochondral defects or loose bodies of patella.
An AP radiograph of the wrist for bone age is done to know the remaining growth potential.
Treatment of Genu Valgum
The treatment aims at correction of genu valgum and neutralization of the forces across the knee are the goals of treatment and, if necessary, repeated intervention.
Non-Operative Treatment
The child with vitamin D–resistant rickets should be on appropriate medication to optimize bone formation and mineralization. Likewise, children with osteogenesis imperfecta may benefit from treatment with bisphosphonates to increase bone density and decrease the risk of fractures.
Nutritional deficiency is corrected when required.
Observation is indicated in genu valgum <15 degrees in a child <6 years of age. Bracing is rarely used.
It is not effective in pathologic genu valgum and unnecessary in physiologic genu valgum
Operative Treatment
Hemiepiphysiodesis or Physeal Tethering of Medial Side
This aims at arresting the growth of medial physis. As the lateral condyle continues to grow, the limb straightens. Its indicated in > 15-20° of valgus in a patient <10 years of age
Its also indicated 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.
The arrest of growth could be temporary or permanent. Staples are used for temporay halt. Growth begins within 24 months after removal of the tether
Apart from staples, screws or plate/screws can also be used.
Its important to place them extraperiosteally as to avoid physeal injury.
Hemiphysiodesis works only when sufficient growth potential is remaining.
When the mechanical axis has been restored to neutral, the implants are removed. Growth should be monitored because if the valgus recurs, guided growth may have to be repeated.
Corrective Osteotomy
Distal femoral varus osteotomy and other corrective osteotomies are used when there is insufficient remaining growth for hemiepiphysiodesis or after skeletal maturity.
Peroneal nerve injury is common and it is important to perform a peroneal nerve release prior to surgery
Prognosis
Untreated, this condition may result in premature degenerative changes in the patellofemoral joint and in the lateral compartment of the knee.
The threshold of deformity that leads to future degenerative changes is unknown
Results of guided growth [controlling the growth of physis by hemiphysiodesis] are uniformly gratifying.
References
- Stevens PM, Klatt JB. Guided growth for pathological physes: radiographic improvement during realignment. J Pediatr Orthop. 2008 Sep. 28(6):632-9.
- Stevens PM, Novais EN. Multilevel guided growth for hip and knee varus secondary to chondrodysplasia. J Pediatr Orthop. 2012 Sep. 32(6):626-30.
- Stevens PM, Arms D. Postaxial hypoplasia of the lower extremity. J Pediatr Orthop. 2000 Mar-Apr. 20(2):166-72.
- Koshino T. Osteotomy around young deformed knees: 38-year super-long-term follow-up to detect osteoarthritis. Int Orthop. 2009 Sep 24.
- Kramer A, Stevens PM. Anterior femoral stapling. J Pediatr Orthop. 2001 Nov-Dec. 21(6):804-7.
- Mast, N, Brown N, Stevens, P. Validation of a Genu Valgum Model in a Rabbit Hind Limb. Journal of Pediatric Orthopaedics. April/May 2008. 28:375-380.
- Stevens PM, MacWilliams B, Mohr RA. Gait analysis of stapling for genu valgum. J Pediatr Orthop. 2004 Jan-Feb. 24(1):70-4. .
- Stevens PM, Maguire M, Dales MD, Robins AJ. Physeal stapling for idiopathic genu valgum. J Pediatr Orthop. 1999 Sep-Oct. 19(5):645-9.
- Stevens, P, Klatt, J. Guided Growth for Fixed Knee Flexion Deformity. Journal of Pediatric Orthopaedics. Sept. 2008. 28:632-639.
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