Congenital Pseudoarthrosis of the Tibia and Dislocation of the Knee


The etiology of CPT is unclear. Approximately 55% of affected children with anterolateral bowing subsequently develop clinical findings of neurofibromatosis, although only 6% of patients with NF1 have anterolateral tibial bowing and CPT. In these patients, the lesion is thought to be the result of a neurofibroma and poor vascular ingrowth at the fracture site. Some describe the pseudarthrosis site as an “invasive fibromatosis” of abnormal collagen, and excision of this fibrous proliferation is generally stressed at the time of treatment.


Treatment. In newborns, anterolateral bowing of the tibia with concurrent dysplastic or cystic changes is an urgent problem that requires immediate treatment, because fracture and pseudarthrosis often develop soon after birth. Treatment of the newborn focuses on preventing a fracture. A custom-made plastic orthosis should be used to protect the limb until the child is ready for a standard orthosis or surgery.


Despite the most intensive conservative management, fractures occur quite frequently and extensive surgery is required to promote healing. Orthotic management is the mainstay of prophylactic treatment. Fracture prophylaxis with bone grafting of the narrowed area or cystic lesion before fracture may be considered, followed by bracing. In many children with CPT, healing does not occur and a significant number of patients ultimately need limb amputation and a prosthesis (see Plate 4-44).


CONGENITAL DISLOCATION OF THE KNEE


Congenital hyperextension and/or dislocation of the knee, although uncommon, is an orthopaedic emergency when it occurs. At birth, the knee may be simply hyperextended (genu recurvatum) or, in the severe form, completely dislocated, with the tibia displaced anterior and lateral to the femur. Dislocations are typically bilateral and associated with “syndromic” patterns, such as Larsen or Ehlers-Danlos syndromes. A mild hereditary or familial tendency has been reported, as well as an association with other “uterine packing” deformities such as torticollis (see Part II in this series, Plates 1-34 and 1-35), dislocation of the elbow (60%), ipsilateral hip dislocation (70%), and clubfoot (50%).


Dislocation of the knee is common in patients with arthrogryposis and myelodysplasia; it is related to muscle imbalance, usually fibrotic contracture of the quadriceps femoris muscle exacerbated by nonfunctional or absent hamstring muscles. In an otherwise normal child, the dislocation is believed to result from an intrauterine position (frank breech presentation), in which the feet of the fetus are locked beneath the mandible or in the axillae.


Clinical Manifestations. The knee appears “backward” and hyperextended, with the examiner typically able to further extend the leg until it nearly touches the chest. The medial hamstring muscles are often displaced forward, anterior to the axis of the knee, thus functioning as knee extensors. The patella may be displaced laterally, and the femoral condyles are prominent posteriorly. Circulation below the knee is usually intact.


Radiographic Findings. Radiographs reveal severe genu recurvatum with malalignment of the tibia and femur, with a spectrum of findings ranging from genu recurvatum to complete anterior dislocation. Deformity of the epiphyses of the distal femur and proximal tibia can be seen in untreated older children.


Treatment. Dislocation and subluxation both require immediate treatment. Within a few hours after birth, the limb should be passively stretched to bring the knee gradually into a flexed position. In most patients, the knee can be manipulated into slight flexion (30 degrees) and splinted in this position. The splint should be changed regularly, with stretching and passive range-of-motion exercises continued until the knee can be flexed to approximately 90 degrees. A removable splint may be then be used for an additional 2 to 3 months to maintain position. Recurrence is uncommon.


If gentle manipulative reduction is not possible immediately after birth, then surgical reduction and lengthening of the extensor muscles should be initiated prior to 1 year of age. Forced manipulation can lead to fracture or growth plate injury and should not be avoided.


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Jul 3, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Congenital Pseudoarthrosis of the Tibia and Dislocation of the Knee
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