- Epiphysiodesis is the surgical ablation of a physis to stop its future growth, generally used to correct a leg length discrepancy
- Prediction of leg length discrepancy at skeletal maturity can be difficult and multiple methods have been developed to provide an estimate
- The most commonly used permanent epiphysiodesis technique is percutaneous drill/burr ablation
Description:The indications for epiphysiodesis include treatment or prevention of leg length discrepancy in a growing child. An epiphysiodesis surgery generally has low morbidity and low complication rates and is an excellent option for surgical correction of projected LLD of 2-6 cm at maturity. It generally does not require postoperative immobilization and only disables a child for a short duration.
An epiphysiodesis essentially slows the growth rate of the longer leg in order to allow the shorter leg to catch up. When this technique is performed in a permanent fashion, it relies on the ability to predict leg length discrepancy at maturity rather than at presentation.
PredictionAlthough temporary epiphysiodesis is an option, permanent epiphysiodesis is more commonly performed and is an all-or-nothing procedure that completely stops growth at a given physis. It is generally assumed that most lower extremity growth occurs in the physes near the knee. After epiphysiodesis surgery, the leg will essentially grow at a slower rate, approximately 27% for the proximal tibia, 38% for the distal femur and 65% for combined epiphysiodesis of both plates. (Green, 1947) Because there is an advantage to being tall and because shorter limbs are more often pathologic and may benefit from room for foot clearance or bracing, it is generally better to err on the side of undercorrection than overcorrection. Several methods can be used to predict the growth remaining in the lower extremities. Three commonly used methods include the arithmetic or “rule of thumb” method of Menelaus, the multiplier method described by Paley et al. and Mosley’s straight-line graph.
The arithmetic or “rule of thumb” method depends on the following statements, which are approximations of the true growth pattern described by Green and Anderson: 1. Girls stop growing at the age of 14 years; 2. Boys stop growing at the age of 16 years; 3. The distal femoral plate grows 3/8 in. (10mm) per year; 4. The proximal tibial plate grows 1/4 in. (6mm) per year; and 5. The discrepancy increases by 1/8 in. (3mm) per year. (Westh, 1981) These approximations are reasonably accurate during the last years of growth but are inaccurate in younger children. This method is convenient because it uses no special tools or graphs; however, it uses chronologic age rather than skeletal age and is therefore subject to error in children who grow very early or very late. It is most commonly used to give families a quick rough estimate of future surgical timing in clinic and to double check the predictions obtained through other methods.
Moseley described a straight-line graph method in 1978 that is based on two principles: the growth of the leg can be charted graphically by straight lines and a nomogram can be used to determine growth percentile from the skeletal age and leg length (Moseley, 1978). Moseley’s graph is also based on the Green and Anderson charts but his purpose was to simplify and improve accuracy by incorporating into the calculations skeletal maturation based on hand-wrist bone films, growth inhibition, and relative size. A straight-line graph can be drawn through a manipulation of the x-axis of the Green and Anderson graphs. Therefore, the growth of the short and “normal” leg is represented by 2 straight lines and the leg length inequality is represented as the vertical distance between the lines. The line corresponding to growth of the shorter leg has a less steep slope and the effect of epiphysiodesis can be predicted by altering the slope of the “normal” leg by the expected amount. Detailed instructions are presented in Dr. Moseley’s website (www.pedipod.com).
The multiplier method described by Paley et al. uses a table of multipliers that can be used to predict the discrepancy at maturity given present discrepancy and age of the child (Paley, 2000). They derived these multipliers from the Green and Anderson charts (Green, 1960) that show leg lengths achieved at a given age. From this data, the proportion of adult leg length achieved at any given age can also be determined by simple division. If one were to assume that congenital deficiencies increased in proportion to leg length, then it would follow that proportion of final discrepancy is the same as proportion of final adult length achieved. Paley et al. then calculated these proportions, inverted them, and provided a table of multipliers that can be used to predict discrepancy at maturity. The disadvantage of this method is that it becomes more complex in cases of developmental discrepancies where the discrepancy does not actually increase in proportion to leg length. These cases require more complicated calculations that Paley et al. have formulated. This approach has the advantage of requiring only one radiograph and is thus particularly helpful in counseling the families of children initially presenting with congenital deformities and establishing expectations for future surgeries. The multiplier method has been shown to be as accurate as the Mosley method when using chronological age (Aguilar, 2005; Aguilar, 2005). Two popular apps have been developed to facilitate the clinical use of this approach: “Paley Growth” by Paley Institute and “Multiplier” by International Center (Townsend, 2007, Lifebridge Health, 2014).
TechniqueThe goal of permanent epiphysiodesis is to produce a symmetrical bony bridge that tethers the physis and prevents future growth. Ablation of the peripheral margins of the medial and lateral physis can cause a bony bridge to form between the physis and metaphysis. In theory, the central part of the physis does not require treatment because it will close spontaneously, although it is often drilled in practice. This procedure is indicated in predicted leg length discrepancies of 2-6 cm.
Phemister is credited with the first description of the open epiphysiodesis technique in 1933 and many variations of his technique have since followed (Phemister, 1933). Phemister’s surgical technique involved removal of a rectangular block of bone from the medial and lateral physes that spanned two-thirds of the metaphyseal and one-third of the epiphyseal side of the plate. He would then replace the rectangular block of bone in reverse position that would ultimately produce a bar across the growth plate.
A percutaneous epiphysiodesis has also been described to avoid unsightly scarring and has gained wide acceptance. It is considered the technique of choice. (Bowen, 1984; Canale, 1986; Olgivie, 1986) This is done with either a drill or burr through 3-10 mm incisions medially and laterally or just laterally at the level of the physis, located using fluoroscopy. With fluoroscopy guidance, the drill or burr is inserted into the physis and used to ablate the peripheral one-third of the plate, therefore leaving the middle one-third of the plate intact. Specific attention should be directed toward adequate ablation of the most peripheral aspect of the plate as well. If necessary, a fibular epiphysiodesis can also be performed through the same skin incision for the lateral proximal tibia but is approached anteriorly instead of laterally to avoid the peroneal nerve.
Because the growth plates are not perfectly flat, it is a technical challenge to make sure the tip of the drill or burr is in the plate. In the distal femur the intercondylar notch enters the posterior aspect of the distal femoral growth plate and particular attention should be paid to not to enter the notch inadvertently. Complications of drill epiphysiodesis include hematoma, effusion, wound infection, and joint penetration (Edmonds, 2007).
Ultimately, this process of physeal destruction is routinely adequate enough to assure arrest of physeal growth and also maintains enough bone strength through the residual plate and surrounding periosteum to make postoperative immobilization unnecessary.
Internal fixation crossing the physis has also been used to slow the growth of a physis. Blount staples were used but were complicated by backing out of the staples, breakage of the implants and deformities in the coronal plane (Blount 1949). A technique of percutanteous epiphysiodesis with transphyseal screws (PETS) was developed by Métaizeau and has shown to slow the growth of the knee physes by 89-95% (Metaizeau 1998). The guided growth technique using tension band plates and screws has been shown to also slow the growth comparable to staples and PETS (Lykissas 2013). Since these techniques slow the growth as opposed to an abrupt growth arrest, it is recommended that surgery be performed up to one year earlier since hardware can be removed after leg length equality is achieved (Pendleton 2013).
One minor disadvantage to epiphysiodesis is that it is a compensatory and not a corrective procedure because it essentially makes the “normal” leg “abnormal”. A large amount of shortening can theoretically decrease the expected length of the major muscles and weaken them, which is one reason it is not recommended for large discrepancies. Epiphysiodesis also results in a decrease in patient’s stature which can be undesirable
Epiphysiodesis of the long leg is a reasonable and a commonly instituted technique for mild limb length inequality of 2-6 cm and is primarily limited by the accuracy of prediction.
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