Operative Techniques in Orthopaedic Surgery (4 Volume Set) 1st Edition

143. Guided Growth to Correct Limb Deformity

Peter M. Stevens

DEFINITION

images Physiologic genu varum (before age 2) and genu valgum (before age 6) are ubiquitous in children. These deformities are self-correcting and need no intervention.

images At maturity, limb lengths should be symmetric, or at least within 2 cm of each other.

images However, various pathologic processes may cause progressive and harmful angular deformities of the knee or knees, with or without limb-length discrepancy.

images With the insidious deviation of the mechanical axis, secondary ligamentous laxity, patellofemoral instability, and joint subluxation may ensue, resulting in gait disturbance and functional limitations.

images These findings may be unilateral or bilateral, involving the femur, tibia, or both. The deformities may or may not be symmetric.

images Concomitant torsional deformities and length discrepancy of greater than 2 cm may complicate matters.

ANATOMY

images During standing, the normal knee joint line and physes remain horizontal. The mechanical axis, represented by a line joining the center of the hip and center of the ankle, should bisect the knee at an angle of 87 degrees with respect to the joint line (FIG 1A). Allowing for normal variation, the mechanical axis should at least fall within the inner two quadrants (+1 or –1) of the knee (FIG 1B).

images The distal femur normally has about 6 degrees of anatomic valgus relative to its shaft, expressed as a lateral distal femoral angle (LDFA) of 84 degrees.

images The proximal tibia has 3 degrees of varus relative to its shaft; consequently, the medial proximal tibial angle (MPTA) is 87 degrees.

images Weight-bearing forces are relatively evenly divided between the medial and lateral compartments. This results in physiologic loading of the articular surfaces and physes.

images The patella remains centered in the femoral sulcus, guided by the retinacula.

PATHOGENESIS

images Intrinsic weakness within the femoral or tibial epiphyses or physes may inhibit growth, resulting in deviation of the mechanical axis.

images Progressive deviation invokes the Hueter-Volkmann principle, where excessive and chronic compression further inhibits articular and physeal cartilage growth. Thus, a vicious cycle is established, perpetuating the problem (FIG 2A).

images An arthrogram may help to demonstrate the phenomenon of delayed ossification due to malalignment (FIG 2B).

images Direct or indirect trauma may result in physeal damage, with either restricted growth or occasionally overstimulation of growth.

images Secondary effects on the extensor mechanism and patellofemoral joint may compound issues related to genu valgum, and patellar instability may ensue.

images Length discrepancy that is predicted to exceed 2 cm at maturity may warrant surgical intervention; epiphysiodesis is a good option for the 2- to 5-cm range.

NATURAL HISTORY

images The natural history of physiologic knee deformities is spontaneous resolution, without the need for braces, therapy, or surgery.3

images The natural history of pathologic deformities is progressive valgus or varus resulting in knee instability and joint deterioration. As the ground reaction forces are displaced medially or laterally, eccentric compression of the distal femur and proximal tibia exceeds their loading tolerance and inhibits normal growth, not only of the physis but of the epiphysis as well (Hueter-Volkmann effect).

images Gait disturbance and functional limitations will ensue, often accompanied by pain.6

images

FIG 1  A. The mechanical axis is a line drawn on a full-length standing AP radiograph of the legs, preferably with the pelvis leveled and the patellae facing forward. Connecting the center of the head and ankle, it should bisect a horizontal knee. B. Dividing the knee into quadrants, the axis should pass within medial or lateral zone one, allowing for physiologic variations. Mechanical axis deviation into zone 2 or 3 is an indication for surgical intervention.

images

FIG 2  A. This young child has windswept legs owing to skeletal dysplasia, with varus on the right and valgus on the left. B. Bilateral knee arthrography demonstrates the true size and shape of the articular surfaces and the inhibition of epiphyseal ossification (Hueter-Volkmann principle).

PATIENT HISTORY AND PHYSICAL FINDINGS

images Family history may yield important clues regarding the cause and natural history of deformities. The parents and siblings have often been subjected to corrective osteotomies.

images The patient presents with knock knees or bowlegs; the deformity may be unilateral or bilateral. There may be concomitant limb-length discrepancy with both true and apparent foreshortening of the involved limb.

images Knock knees may be accompanied by outward femoral or tibial torsion (or both). Medial collateral laxity may permit medial knee thrust.

images Patellar instability is not uncommon as the deformity progresses. Circumduction gait is inevitable and problematic for walking and running.

images Knock knees are documented by measuring the intermalleolar distance while the patient is standing with the knees touching (patellae neutral) (FIG 3A).

images Bowlegs may be accompanied by inward tibial torsion and intoeing. Lateral ligament laxity may permit lateral knee thrust during walking.

images Bowlegs are readily documented by measuring the intercondylar distance while the patient is standing with the feet together (patellae neutral) (FIG 3B). This should corroborate the mechanical axis deviation from the center of the knee that is measured on the standing radiograph (FIG 3C).

images The spine and feet should be evaluated as well.

images Orthotics may provide knee support but will have no corrective effect upon growth. Whether this is due to suboptimal design or compliance issues is a matter of debate.

images Physical examination should include observation of stance, knee alignment, torsional profile, limb lengths, and gait.

IMAGING AND OTHER DIAGNOSTIC STUDIES

images Weight-bearing anteroposterior (AP) and lateral views of the lower extremities are obtained with the patellae facing forward. For limb-length discrepancy, the pelvis is leveled with blocks.

images A patellar view may document patellar tilt or subluxation.

images Estimation of skeletal maturity (hand or elbow film) may be useful. Guided growth requires at least 6 months to produce demonstrable improvement in alignment.

images Computed tomography (CT) scan or magnetic resonance imaging (MRI) is obtained if a physeal bar is suspected. A “gunsight” CT is obtained for “miserable malalignment” (femoral plus tibial torsion) (FIG 4).

images The landmarks for femoral measurement are a line that bisects the femoral neck versus a line crossing the back of the femoral condyles (normal, 11 to 15 degrees).

images

images

FIG 3  A. Obesity and idiopathic genu valgum afflict this 13-year-old boy with an increased intramalleolar distance (red arrow) and patellar instability. Without limb realignment (not patellar), the natural history is all too obvious. B. This 2-year-old boy with metaphyseal dysplasia manifests an increased intercondylar gap and lateral thrust with walking. C. Progressive mechanical axis deviation is inevitable and nonoperative management is futile.

images For the tibia, it is a line across the back of the condyles versus the bimalleolar axis (normal, 15 to 20 degrees).

DIFFERENTIAL DIAGNOSIS

images Genu valgu.

images Idiopathic genu valgum (see Fig 3A)

images Hereditary multiple exostoses

images Cozen fracture (proximal tibial metaphysis)

images Congenital limb anomalies

images Postaxial hypoplasia

images Neuromuscular disorders: cerebral palsy, spina bifida

images Down syndrome

images Genu varu.

images Blount disease

images Rickets

images Osteochondral dysplasia (see Fig 3B,C)

images Ollier disease

images While the underlying diagnosis (see above) has often been established, the cause has little relevance to the treatment. The degree of deformity and the evolution of symptoms dictate the timing and need for intervention.

NONOPERATIVE MANAGEMENT

images Activity restriction and nonsteroidal anti-inflammatories are not definitive treatments. Valuable time may be wasted, and there is no logical endpoint to this form of management.

images Physical therapy remedial exercises are of no lasting benefit with respect to the established growth pattern.

images

FIG 4  A rotational “gunsight” CT scan documenting femoral anteversion of 35 degrees (normal, 11 ± 3 degrees). The norm for the tibia–fibula is 10 to 20 degrees outward.

images While knee bracing may compensate for muscle weakness or secondary ligamentous laxity, it may not predictably effect growth modulation or improvement in skeletal alignment.

images Furthermore, adequate braces are cumbersome and expensive, so noncompliance may be an issue.

SURGICAL MANAGEMENT

images Any child or skeletally immature adolescent being considered for corrective osteotomy may be a candidate for guided growth.

images As long as the physes are open, hemiepiphysiodesis or guided growth offers advantages and has few associated complications compared to more invasive osteotomies.

images The indications for surgery include progressive deformity resulting in gait disturbance, functional limitations, and pain. Many patients have already exhausted other options, including nonsteroidal anti-inflammatories, bracing, activity restriction, and physical therapy or even osteotomy.

images Options for growth modulation include.

images Phemister bone block: permanent; requires precise timing and close follow-up5

images Percutaneous drilling: permanent; same drawbacks as Phemister technique2

images Epiphyseal stapling (Blount): rigid implant compresses dynamic physis1

images Percutaneous screw (Metaizeau): reversibility unknown; rigid implant violates or compresses the physis; limited applications (adolescence, frontal plane deformities)4

images Guided growth with eight-plate (Stevens): reversible; tension band principle; versatile (any age, diagnosis, or plane)

Preoperative Planning

images Both the clinical examination and appropriate radiographs should reveal and document varus or valgus deformities of the knee as well as limb lengths. The torsional profile should be documented.

images When indicated, bilateral or multilevel surgery may be accomplished at one sitting (outpatient).

images Length discrepancies and rotational malalignment may not be directly addressed by guided growth. However, relative length is gained and there may be subsequent rotational improvement when the mechanical axis is restored to neutral.

images Occasionally an intraoperative arthrogram will demonstrate the true shape of the articular surfaces (see Fig 2B).

images A modular approach may permit angular correction to neutral mechanical axis, followed by length adjustment.

Positioning

images The patient is positioned supine on the operating table.

images Fluoroscopy is recommended.

images Thigh tourniquets are employed for speed and accuracy of hardware placement.

Approach

images The surgical approach is minimally invasive, directly over the physis, at the apex of the deformity.

images Hardware should be midsagittal unless correcting an oblique or sagittal-plane deformity. Placement is confirmed with fluoroscopy and the implant position is adjusted as needed.

TECHNIQUES

GUIDED GROWTH: EIGHT-PLATE

images With the patient in the supine position and (preferably) under tourniquet control, the medial or lateral aspect (or both) of the distal femoral or proximal tibia (or both) are identified fluoroscopically and 2- to 3-cm skin incisions are marked.6,7

images It is helpful to inject them with 0.25% Marcaine for postoperative comfort.

images When approaching the medial femur, the fascia of the vastus medialis is incised parallel to its inferior border, and the muscle is retracted. On the lateral femoral approach, the iliotibial band is split longitudinally. Over the medial tibia, the medial collateral ligament is split longitudinally; over the lateral tibia, the anterior compartment muscles are left intact and the fibula is undisturbed.

images The dissection is deepened sharply, dividing fascia and retracting muscles as necessary but preserving the periosteum.

images A Keith needle is inserted into the physis (this characteristically feels like pushing a needle into a bar of soap), and the position and direction are confirmed with the image intensifier.

images The 12- or 16-mm plate (surgeon preference) is centered on the Keith needle using the middle hole; it is inserted deep to the soft tissues to rest in an extraperiosteal position.

images The 1.6-mm smooth guide pins are inserted, placing the epiphyseal one first, followed by the metaphyseal pin.

images The cortex is drilled to a depth of 5 mm to permit insertion of the 24- or 36-mm (surgeon preference) fully threaded, cannulated, self-tapping screws (TECH FIG 1).

images The screws do not have to be parallel or to match in length.

images If the position looks good, the guide pins are removed and the screws are further tightened so that the heads are countersunk in the plate.

images After routine wound closure, a soft compression dressing is applied.

images

TECH FIG 1  A. The eight-plate instrumentation includes a soft tissue guide with 1.6-mm cannulation for the guide pin and 3.2 mm for the “stubby” drill that permits a 5-mm depth of penetration. B. The 4.5-mm screws are cannulated and self-tapping and come in three lengths: 16 mm (shown here), 24 mm, and 32 mm. C,D. The plate application is extraphyseal, over a localizing guide pin, while preserving the periosteum. Any open and approachable physis may be instrumented for correction in the frontal, sagittal, or oblique planes as well as for length correction.

STAPLING (BLOUNT)

images The surgical approach is the same, preserving the periosteum.

images A guide needle is inserted.

images One to three rigid Blount staples (Zimmaloy) are inserted per physis.

images Simple closure is done with a elastic bandage.

PERCUTANEOUS SCREW (METAIZEAU)

images Under fluoroscopic guidance, a single 7.3-mm transphyseal screw is placed either from the medial or lateral side of the bone, crossing the physis near its perimeter.

images The goal is to place the tip of the screw just inside the medial or lateral aspect of a given physis to effect angular growth.

images Upon correction to neutral, the screw is removed.

PHEMISTER

images This approach is mainly of historic interest.

images The same approach is used as for stapling or eight-plate.

images Periosteal flaps are raised to visualize the physis.

images A bone rectangle is removed and inverted to establish a bony bridge.

images This technique is permanent and thus most suitable for teenagers. It requires precise timing and calculations.

PERCUTANEOUS EPIPHYSIODESIS (MODIFIED FROM PHEMISTER)

images Under fluoroscopic guidance the physis is drilled or curetted (or both) to produce a bony physeal bar.

images The requisite depth of penetration has yet to be specified.

images There may be a delay in effect until a bone bridge is established.

images This technique is permanent and thus suitable only for teenagers. It requires precise timing and calculations.

images

POSTOPERATIVE CARE

images No immobilization is required.

images Immediate weight bearing is permitted.

images No activity restriction is imposed.

images Follow-up is done at 3-month intervals with weight-bearing AP radiographs of the legs when clinically straight.

images Hardware is removed, avoiding periosteal damage, when the mechanical axis is neutral or limb lengths are equal.

images Continued follow-up is important. Guided growth can be repeated if rebound growth causes recurrence.

images Osteotomy may be reserved for rotational correction or further length equalization.

OUTCOMES

images Initially after hemiepiphysiodesis there is no visible difference, and the family needs to be forewarned of this.

images The correction is gradual and subtle, and therefore routine follow-up is imperative.

images Correction to neutral (eight-plates) will take 12 months on average; staples take somewhat longer.

images The hardware is removed upon correction of the valgus or varus deformity. (The surgeon must preserve the periosteum!)

images Follow-up should continue until maturity to watch for recurrent deformity due to rebound growth. While this is unpredictable, it will be evident within 12 months of hardware removal.

images Premature physeal closure is unlikely, provided the hardware is inserted and removed uneventfully, leaving the periosteum intact.

images Because the plate–screw construct is flexible and serves as a tension band, it is unlikely to break or migrate, making revision surgery less likely.

images Modular adjustment of limb lengths is convenient and simple to accomplish.

images If secured with cannulated screws, eight-plate survivorship is rarely problematic.

COMPLICATIONS

images There is a race between deformity correction and hardware failure. Failure is more likely with a rigid implant.

images The rigid staples are at a disadvantage owing to occasional migration or breakage, necessitating unplanned revision surgery (FIG 6).

images A bent staple may permit excellent correction but is more difficult to monitor and remove.

images

FIG 6  A 14-year-old boy 1 year after tibial stapling for limblength inequality due to congenital clubfoot. The lateral staples have loosened, resulting in mechanical axis deviation into medial zone 2. The lateral eight-plate corrected this iatrogenic varus deformity to neutral.

REFERENCES

· Blount WP, Clark GR. Control of bone growth by epiphyseal stapling. J Bone Joint Surg Am 1949;31A:464–471.

· Canale S, Russell T, Holcomb R. Percutaneous epiphysiodesis: experimental study and preliminary results. J Pediatr Orthop 1986;6:150.

· Heath D, Staheli L. Normal limits of knee angle in children: genu varum and genu valgum. J Pediatr Orthop 1993;13:259–262.

· Metaizeau JP, Wong-Chung J, Bertrand H, et al. Percutaneous epiphysiodesis using transphyseal screws (PETS). J Pediatric Orthop 1998;18: 363–369.

· Phemister DB. Operative arrestment of longitudinal growth of bones in the treatment of deformities. J Bone Joint Surg 1933;15:1–15.

· Stevens P. Guided growth: 1933 to the present. Strat Traum Limb Reconst 2006;1:29–35.

· Stevens P. Guided growth for angular correction. J Pediatr Orthop 2007;27:253–259.

· Stevens P, MacWilliams B, Mohr A. Gait analysis of stapling for genu valgum. J Pediatr Orthop 2004;24:70–74.



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