Syme and Boyd Amputations for Fibular Deficiency



Syme and Boyd Amputations for Fibular Deficiency


Anthony Scaduto

Robert M. Bernstein





ANATOMY



  • Fibular deficiency is best considered an abnormality that affects the entire limb, not just the fibula (FIG 1A).


  • The appearance of the leg can vary from nearly normal to severely deformed (FIG 1B).



  • Potential ipsilateral deformities associated with fibular deficiency are as follows:



    • Femur: mild femoral shortening, femoral retroversion, lateral femoral hypoplasia


    • Knee: cruciate ligament deficiency, valgus alignment, patellofemoral instability


    • Tibia: shortening, anteromedial diaphyseal bowing


    • Ankle: ankle valgus, absent lateral malleolus, ball-and-socket ankle


    • Foot: absent tarsal bones, tarsal coalitions, absence of one or more lateral rays


  • The amount of fibula present does not aid treatment planning. For example, some patients with complete fibular absence have minimal leg length inequality and foot deformity.


  • An understanding of the anatomy of the ankle and heel is necessary to perform either the Syme or Boyd amputation procedure.



    • The posterior tibial nerve and artery course posterior to the medial malleolus and split into the medial and lateral plantar nerves. These structures must be protected for the heel pad to maintain its sensation and viability.


PATHOGENESIS



  • Unlike tibial deficiency, fibular deficiency occurs sporadically with no inheritance pattern.


  • No genetic defect has been identified, and no common teratogen is linked to fibular deficiency.


  • Major limb malformations associated with fibular deficiency occur by the seventh week of fetal development.


NATURAL HISTORY



  • Without surgical intervention, the growth of the abnormal limb remains proportional to the normal side. Therefore, a final leg length discrepancy is predictable.



    • For example, if the short leg is 85% the length of the long side at age 2 years, the length of the short side at maturity also will be 85% of the estimated length of the long side at maturity.


  • Tibial bowing is present in most cases of complete absence of the fibula. In some cases, this bowing will improve with age.



    • Unlike anterolateral bowing of the tibia, bowing associated with fibular deficiency does not increase the risk of fracture or pseudarthrosis.


  • Knee valgus commonly worsens through childhood. It may require surgical treatment when prosthetic modifications are inadequate to compensate for the deformity.


PATIENT HISTORY AND PHYSICAL FINDINGS



  • Classically, the limb is short, with an equinovalgus foot and skin dimpling over the midanterior tibia.


  • Because presentation varies widely, an examination to assess length, alignment, and function is critical to treatment.


  • Hip range of motion: A common finding is limited internal rotation (<20 to 60 degrees) indicating femoral retroversion.


  • Leg length assessment: There should be minimal shortening of the thigh. Otherwise, consider proximal femoral focal deficiency. Small leg length discrepancies can be corrected with a shoe lift or lengthening.


  • Lachman test: Severe anterior/posterior laxity increases the risk of subluxation during lengthening.


  • Valgus alignment and stability: Small angulation is accommodated through prosthetic adjustment, but larger angulation requires correction.


  • Tibial bowing requires prosthetic adjustments or correction.


  • Ankle alignment and stability: Amputation is preferred over lengthening when severe subluxation or instability exists.


  • Hindfoot mobility: Suspect tarsal coalition if subtalar motion is reduced.


  • Ray deficiency (number of missing rays): Amputation is indicated when the foot is nonfunctional.


IMAGING AND OTHER DIAGNOSTIC STUDIES



  • Anteroposterior (AP) and lateral radiographs of the leg (including the distal femur) should be obtained.



    • Absence of the anterior cruciate ligament and hypoplasia of the lateral femoral condyle with a valgus joint alignment are common (FIG 2A,B).


    • The amount of anterior bowing (tibial kyphosis) also can be assessed (FIG 2C).


  • Additional radiographs of the affected limb (ie, femur, ankle, and foot) are obtained as necessary (FIG 2D).


  • A full-length standing radiograph from hips to ankles should be obtained to check alignment in those children able to stand (FIG 2E).


  • A scanogram and bone age should be obtained to determine the expected leg length discrepancy at maturity.



    • The desired limb length difference at maturity should be at least 3.5 cm to accommodate the height of the prosthetic foot. Epiphysiodesis may be necessary to achieve this and should be planned appropriately.


  • An ankle and foot series should be obtained when abnormal position or motion is present at the ankle or subtalar joint or when lateral rays are absent. These views may reveal a ball-and-socket ankle (FIG 2F), tarsal coalitions, or absent or hypoplastic tarsal bones (FIG 2G).




NONOPERATIVE MANAGEMENT



  • If the leg length discrepancy is small, the ankle is stable, and the foot is plantigrade, a shoe insert or lift may be all that is required.


  • When amputation or lengthening is needed but must be deferred, an atypical prosthesis that accommodates the foot position can be used.


SURGICAL MANAGEMENT


Syme Amputation

Jul 22, 2016 | Posted by in ORTHOPEDIC | Comments Off on Syme and Boyd Amputations for Fibular Deficiency
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