Percutaneous Distal Femoral or Proximal Tibial Epiphysiodesis for Leg Length Discrepancy
Emily R. Dodwell
Roger F. Widmann
Epiphysiodesis involves manipulation of a physis (growth plate) to cause temporary or permanent, partial or complete growth inhibition to correct length or angular deformity in children with growth remaining.
In the setting of leg length discrepancy, epiphysiodesis must cause growth inhibition symmetrically across the physis such that shortening results without development of angular deformity. Epiphysiodesis can be achieved by obliteration of the growth cells through physical disruption (drill, curettage, radioablation, or similar) or tethering with various devices (screws crossing the physis or staples/small plates at the periphery of the physis) or various forms of bone grafting such as the open Phemister technique.22
Today, the two most common techniques are percutaneous drill and percutaneous screw epiphysiodesis.7
Growth of the longer extremity is inhibited by prematurely arresting or tethering growth at one or more physes so that remaining growth of the shorter extremity may “catch up” thus approximating limb lengths at maturity.
Patients with a predicted leg length discrepancy of less than 2 to 2.5 cm do not typically require surgical intervention and may be treated with observation or a shoe lift/insert.
Epiphysiodesis is usually considered when the final limb length discrepancy of the lower extremity is predicted to be in the range of 2 to 5 cm. Patients with leg length discrepancies greater than 5 cm may be considered for other procedures, including lengthening. Some patients with large discrepancies may undergo lengthening on their short side, as well as epiphysiodesis on their long side, to minimize the number of lengthening procedures required.
Limb equalization surgery is considered successful if residual leg length discrepancy is less than 2 cm.
In order to optimize leg length equalization, the surgeon must understand the etiology of the leg length discrepancy and be able to predict growth based on the underlying cause of growth inequality, the child’s maturity by chronologic and bone age, and the child’s own height percentile and parental and sibling heights.
The physis is made up of cartilage cells that are replicating and growing away from the physis.
The germinal cells are on the epiphyseal side of the physis.
The distal femoral physis and proximal tibial physes are undulating and slightly curved.
The neurovascular bundle is posterior and midline at the level of the distal femoral physis.
The common peroneal nerve at the knee runs obliquely along the lateral side of the popliteal fossa, close to the medial border of the biceps femoris muscle and the lateral head of the gastrocnemius muscle, toward the head of the fibula.
The nerve winds posteriorly around the neck of the proximal fibula and passes deep to the peroneus longus muscle, where it divides into the superficial and deep peroneal nerves.
Approximately 25% of people have a leg length discrepancy of 1 cm or more, and the incidence of leg length discrepancy of 2 cm or greater is estimated at 1 in 1000 cases.
Epiphysiodesis is the most frequently used operative procedure in North America for the equalization of limb lengths.
The etiology of a limb length discrepancy can be congenital/developmental; related to tumor; neuromuscular disease; skeletal dysplasia; or otherwise acquired through trauma, infection radiation, or other causes. A partial list of causes includes the following:
Congenital shortening: proximal focal femoral deficiency, coxa vara, congenital short femur, fibular and tibial hemimelia, hemiatrophy
Congenital lengthening: overgrowth syndromes such as hemihypertrophy, Beckwith-Wiedemann syndrome, Klippel-Trenaunay-Weber syndrome, and Parkes-Weber syndrome
Skeletal dysplasia or tumor: Multiple hereditary exostoses may result in limb shortening on the affected side, as growth cartilage cells are diverted to the cartilage tumor. Radiation for malignancies adjacent to the physis may result in growth suppression or complete destruction of physeal cartilage cells, resulting in limb length discrepancy or angular deformity.
Infection: Physeal destruction may result from physeal invasion from adjacent metaphyseal or epiphyseal bacterial osteomyelitis or direct physeal involvement in the case of intracapsular joint physes such as at the hip and shoulder.
Paralysis: Poliomyelitis and cerebral palsy as well as other nervous system afflictions in children typically result in shortening on the more affected side.
Trauma: direct injury to growth plate, posttraumatic bone loss or shortening, and overgrowth following femoral fracture
Miscellaneous: slipped capital femoral epiphysis, Legg-Calvé-Perthes disease
Depending on the underlying cause of the leg length discrepancy, a discrepancy may be static or increase or decrease with remaining growth.
Congenital limb length discrepancies typically maintain proportional growth over time. For instance, a tibia that is 10% shorter than the normal side at birth will be approximately 10% shorter than the normal side at maturity.
Leg length discrepancies under 2 cm are typically well tolerated.
Untreated leg length discrepancy of more than 3 cm may result in pelvic obliquity, visual gait disturbance, short-legged gait, or structural/nonstructural scoliosis.
Leg length discrepancy greater than 5.5% of the long leg has been shown to decrease the efficiency of gait, as determined from kinetic data.23
No causative relationship has been proved between leg length discrepancy and knee or hip pain or arthritis. A large population study has shown an association between leg length discrepancy and knee arthritis, but there was no evidence of causation.9
Although scoliosis has been associated with leg length discrepancy, there is no evidence that leg length discrepancy causes structural curvature of the spine. Assessing the spine with a block under the short leg, with the pelvis level, permits assessment of true scoliosis.
Following drill epiphysiodesis, bony bridges form between the epiphysis and the metaphysis, preventing further physeal growth. Growth arrest has been documented within 3 months of the procedure using radiostereotactic (RSA) three-dimensional imaging.11
Following screw epiphysiodesis, there is compression or tethering across the physis. Physeal closure may be slightly delayed compared to ablative techniques. Growth inhibition has been documented within 6 months of screw epiphysiodesis but has not been measured using RSA or other highly accurate techniques.
PATIENT HISTORY AND PHYSICAL FINDINGS
The underlying cause of a leg length discrepancy can typically be elucidated by careful history and physical examination.
The common symptoms at presentation are limp, compensatory gait mechanics, pelvic obliquity, and nonstructural scoliosis.
Physical findings depend on the etiologic factors.
In hemihypertrophy (both syndromic and nonsyndromic), the affected extremity may be larger in both length and girth. In classic hemihypertrophy, upper extremity hypertrophy as well as hemifacial asymmetry may be present. Vascular overgrowth syndromes may be associated with cutaneous or deep hemangiomas, which may alter surgical approaches to attempted limb equalization.
Clinically, leg length discrepancy is best measured by the block test, in which the shorter leg is placed on increasingly larger measured blocks until the posterior iliac crest is level. Discrepancies as small as 2 cm are accurately detected by this method, and detection of discrepancies is largely unaffected by patient size or body mass.
True leg length is measured from the anterior superior iliac spine to the tip of the medial malleolus. It is important to place the legs in identical positions to measure true leg length, and for this reason, this measurement is less accurate than the block test.
If the patient has a 20-degree abduction deformity of right hip, the left hip is placed in 20 degrees of abduction to measure true length.
Apparent leg length is measured with the patient supine with the legs parallel to each other. The landmarks are the umbilicus to the tip of medial malleolus. Pelvic obliquity and fixed deformities of the hip and knee affect the reading. This method is also significantly less accurate than block measurement.
Range of motion is noted for all joints, primarily the hip, knee, ankle, and subtalar joints. The ankle joint range of motion is measured with the knee in extension and flexion.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain radiographs have traditionally been used to document the objective measurement of leg length discrepancy.
Full-length (hip to ankle) anteroposterior (AP) radiographs are obtained in standing position with both patellae facing directly anteriorly. The appropriate-sized block is placed beneath the shorter leg to level the pelvis. A long x-ray cassette (51-inch) is used with the x-ray beam center focused on the knee from a distance of 10 feet. A radiolucent ruler often is used to assist in calculation of limb discrepancies.
A lateral hip to ankle view can be included to further assess length, as contractures in the sagittal plane may result in inaccuracies on AP measurements. This view can also assess for angular deformities in the coronal plane.
Computed tomography (CT) scanogram has been the gold standard for low-dose accurate imaging of leg length discrepancy.
CT scanogram is as precise in measuring leg length discrepancy as the slit scanogram and it has the added benefit of more easily measuring leg length discrepancy in the setting of joint contractures. Slit scanogram is of historical interest only and is no longer typically used for measuring leg length discrepancy.
EOS8 is a low-dose, high-resolution radiologic imaging system that captures standing simultaneous posteroanterior (PA) and lateral radiographs and full-body radiographs.17
Recently, EOS biplanar imaging systems have been shown to be equally accurate/reliable with the added benefit of imaging the patient in a standing position such that leg length and alignment can be obtained from a single low-dose image. Radiation exposure is also lower with EOS.6
Skeletal age can be determined by a left hand/wrist radiograph in combination with the Greulich and Pyle method.10
Alternatively, the Hospital for Special Surgery (HSS) shorthand method can be used. This method was derived from Greulich and Pyle and uses a single radiographic criteria is used for each age, allowing for rapid bone age determination.12
The leg length discrepancy at maturity can be predicted in a variety of ways:
Applications/programs that incorporate the Paley multiplication factors are readily available on smartphones/computers for clinical use. These allow calculation of length
discrepancy at maturity for both congenital and acquired deformities.
Parental and sibling height may be useful in interpreting predicted height be the above methods.
In leg length discrepancy secondary to physeal growth arrest, graphical or arithmetic methods are helpful in determining appropriate timing of epiphysiodesis.
True shortening (eg, femoral or tibial)
Apparent shortening due to dislocated hip
Apparent shortening from contractures
Angular deformity causing apparent shortening
Overgrowth syndrome with both increased length and limb girth: hemihypertrophy
Congenital limb deficiency
Trauma, radiation, tumor, infection, burns, and other causes.
No treatment is required for a predicted limb length discrepancy of less than to 2.5 cm at maturity.
A shoe lift can be used as treatment for leg length discrepancies at maturity below 2 cm.
Often, a lift is used in children until an appropriate skeletal age is reached to perform an equalization procedure.
Epiphysiodesis is most commonly performed at the distal femoral physis or the proximal tibia with or without fibular physis.
Ablation of the medial and lateral physis causes bony bridges to form between the epiphysis and metaphysis that accomplish growth inhibition in that physis (epiphysiodesis).
This can be accomplished by different instruments, including a curette, a drill, a burr, a reamer, or radioablation.
Some authors recommend ablation only at the periphery, as bony bridge formation at the peripheral margins of the physis both medially and laterally has been shown to cause spontaneous closure of the central physis.
The authors’ preferred method for mechanical ablation involves ablating the majority of the physis, including the central portion.
Due to intact cortex at the physis (with the exception of two small drill holes), stability of the bone is maintained postoperatively and the patient may weight bear as tolerated, although traditionally, the child is protected with a brace and crutches for the first few weeks.
There is no clear evidence to support when a child should return to sports, although given the potential destabilizing effect of disruption the physis and theoretical concern for Salter Harris fracture, it is reasonable to delay return to sports for the first 6 weeks following mechanical ablation of the physis.
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