The Eight-figure plate or eight plate system or simply eight plate consists of the 2-holes plate and the 2 self-tapping screws and is used for control and correction of angular deformities like genu valgum or varus by a performing epiphysiodesis.
Blount staples are the traditional most common implant used for hemiepiphysiodesis. This aims at stopping physeal growth in one half the bone whereas the other half continues to grow and deformity is corrected. It is also called guided growth method.
But these staples are associated with complications like staples breakage, hardware migration or hypercorrection of the original deformity.
The most serious complication is damage of the physis caused by excessive compression. This leads to the subsequent formation of the physeal bar and the effect on the growth.
Another complication is rebound growth after removal of staples.
However, eight plate system serves as a tension band and restores the physiological axis. The tension band plate, with screws on either side of the physis, creates a non-rigid fulcrum outside of the physis, relatively lengthening the moment arm
Due to screw fixation, the risk of hardware extrusion is minimal.
The 8-plate could be applied in children under 10 years of age permitting earlier intervention.
The extraction of the plates can be performed after reaching full correction of the deformity, which means after reaching physiological joint axis.
The resumption of physeal growth physis occurs after hardware removal and deformity recurrence could be seen.
The plates of the system could be used and applied at the area of the knee, hip or ankle joints or to the area of the elbow and wrist.
Most commonly they are used for guided growth and deformity correction in the knee.
The main disadvantage of using eight plates is their significantly higher price.
Eight Plate Design
The plate is roughly a shape of a figure of eight.
The design of the plate has one or two more holes for K-wire guided insertion of the plate. The screws could be cannulated or locking depending on the particular 8-figure plate system.
Screws can be of two sizes 3.5 and 4.0 mm. The 3.5 size was designed for the children up to 8 years
The 8-figure plate is inserted using a minimally invasive approach under fluoroscopy control to allow accurate targeting and localization of the plate straddling the growth plate of the long bone. The periosteum is preserved strictly.
Contraindications for Eight Plate Use
8-figure plate system shouldn´t be used in children
- Under 6 years of age
- Severe axial deviation > 30 degrees
- Joint contractures > 20-30 degrees
- Severe epi- and meta- epiphyseal dysplasia
- Malignancy
- Severe osteoporosis or osteopenia.
Epiphysiodesis Procedure of Knee Deformity Using Eight Plate
Preoperative Assesment
- Measurement of limb lengths
- Evaluation of deformities
- Radiographic assessment of leg lengths
- Skeletal age
Radiographic templating of plating is done in the preoperative period. Mark the bone – distal femur/distal tibia, where the surgery is to be done.
The standard radiolucent operative table is used to allow C-arm fluoroscopy.
The patient is placed supine and the tourniquet is applied high on thigh.
Mark 3 cm incision over the physis of on the convexity of the deformity, ideally at or near the apex. Thus for valgus deformity, apply plate and screws on the medial side and for varus deformity, apply plate and screws on the lateral side.
Confirm the position of physis with C-arm.
Make the skin incision with a scalpel and deepen it with sharp dissection and divide the fascia. Depending on the site different sites different tissues may be divided. For example fascia of the vastus medialis (medially) or IT band (laterally).
In any case, the periosteum underneath should not be disturbed so as to prevent the risk of growth arrest or physeal bar formation.
Insert a needle or small guide pin into the physis and confirm the position with fluoroscopy in both AP and lateral planes. Pre-fixation with K-wires allows easier and safer centering of the screws for final plate fixation.
Ideally, the needle should be at or slightly posterior to the midsagittal plane. If the pin is anterior to the midsagittal plane it may create recurvatum with growth. Slide the plate over the needle and take care to place plate in line with a midsagittal plane.
Place guidepins and predrill the center to hold the plate in the appropriate position. Insert guidepins first epiphyseal and then metaphyseal guide pin.
Confirm position under C-arm. Neither pin should violate the adjacent joint or the physis. Arthrogram in small children may help to improve the visualization.
Predrill using a cannulated drill (3.2mm in most systems) to about 5mm and fix the holes with 4.5 mm cannulated screw over each guide pin and tighten sequentially.
Before screw fixation, confirm that the plate is placed exactly in the center of the lateral diameter of the bone and always strictly parallel with the long axis of both of the bones.
Check the knee movements after screw insertion.
Close the wound in layers and dress.
Allow weight bearing with crutches in the immediate postoperative period
Rehabilitation is initiated to restore the free movement range.
Sutures are removed after two weeks.
The patient is followed regularly to check for correction. Plate extraction is planned after full correction of the lower limb deformity.
References
- Burghardt RD, Herzenberg JE. Temporary hemiepiphysiodesis with the eight-plate for angular deformities: mid-term results. J Orthop Sci. 2010;15:699–704.
- Schroerlucke S, Bertrand S, Clapp J, Bundy J, Gregg FO. Failure of Orthofix eight-Plate for the treatment of Blount disease. J Pediatr Orthop. 2009;29(1):57-60.
- Stevens PM. Guided growth for angular correction: a preliminary series using a tension band plate. J Pediatr Orthop. 2007;27:253–259.
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