Peter M. Stevens
DEFINITION
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.
At maturity, limb lengths should be symmetric, or at least within 2 cm of each other.
However, various pathologic processes may cause progressive and harmful angular deformities of the knee or knees, with or without limb-length discrepancy.
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.
These findings may be unilateral or bilateral, involving the femur, tibia, or both. The deformities may or may not be symmetric.
Concomitant torsional deformities and length discrepancy of greater than 2 cm may complicate matters.
ANATOMY
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).
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.
The proximal tibia has 3 degrees of varus relative to its shaft; consequently, the medial proximal tibial angle (MPTA) is 87 degrees.
Weight-bearing forces are relatively evenly divided between the medial and lateral compartments. This results in physiologic loading of the articular surfaces and physes.
The patella remains centered in the femoral sulcus, guided by the retinacula.
PATHOGENESIS
Intrinsic weakness within the femoral or tibial epiphyses or physes may inhibit growth, resulting in deviation of the mechanical axis.
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).
An arthrogram may help to demonstrate the phenomenon of delayed ossification due to malalignment (FIG 2B).
Direct or indirect trauma may result in physeal damage, with either restricted growth or occasionally overstimulation of growth.
Secondary effects on the extensor mechanism and patellofemoral joint may compound issues related to genu valgum, and patellar instability may ensue.
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
The natural history of physiologic knee deformities is spontaneous resolution, without the need for braces, therapy, or surgery.3
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).
Gait disturbance and functional limitations will ensue, often accompanied by pain.6
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.
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
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.
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.
Knock knees may be accompanied by outward femoral or tibial torsion (or both). Medial collateral laxity may permit medial knee thrust.
Patellar instability is not uncommon as the deformity progresses. Circumduction gait is inevitable and problematic for walking and running.
Knock knees are documented by measuring the intermalleolar distance while the patient is standing with the knees touching (patellae neutral) (FIG 3A).
Bowlegs may be accompanied by inward tibial torsion and intoeing. Lateral ligament laxity may permit lateral knee thrust during walking.
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).
The spine and feet should be evaluated as well.
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.
Physical examination should include observation of stance, knee alignment, torsional profile, limb lengths, and gait.
IMAGING AND OTHER DIAGNOSTIC STUDIES
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.
A patellar view may document patellar tilt or subluxation.
Estimation of skeletal maturity (hand or elbow film) may be useful. Guided growth requires at least 6 months to produce demonstrable improvement in alignment.
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).
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).
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.
For the tibia, it is a line across the back of the condyles versus the bimalleolar axis (normal, 15 to 20 degrees).
DIFFERENTIAL DIAGNOSIS
Genu valgu.
Idiopathic genu valgum (see Fig 3A)
Hereditary multiple exostoses
Cozen fracture (proximal tibial metaphysis)
Congenital limb anomalies
Postaxial hypoplasia
Neuromuscular disorders: cerebral palsy, spina bifida
Down syndrome
Genu varu.
Blount disease
Rickets
Osteochondral dysplasia (see Fig 3B,C)
Ollier disease
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
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.
Physical therapy remedial exercises are of no lasting benefit with respect to the established growth pattern.
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.
While knee bracing may compensate for muscle weakness or secondary ligamentous laxity, it may not predictably effect growth modulation or improvement in skeletal alignment.
Furthermore, adequate braces are cumbersome and expensive, so noncompliance may be an issue.
SURGICAL MANAGEMENT
Any child or skeletally immature adolescent being considered for corrective osteotomy may be a candidate for guided growth.
As long as the physes are open, hemiepiphysiodesis or guided growth offers advantages and has few associated complications compared to more invasive osteotomies.
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.
Options for growth modulation include.
Phemister bone block: permanent; requires precise timing and close follow-up5
Percutaneous drilling: permanent; same drawbacks as Phemister technique2
Epiphyseal stapling (Blount): rigid implant compresses dynamic physis1
Percutaneous screw (Metaizeau): reversibility unknown; rigid implant violates or compresses the physis; limited applications (adolescence, frontal plane deformities)4
Guided growth with eight-plate (Stevens): reversible; tension band principle; versatile (any age, diagnosis, or plane)
Preoperative Planning
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.
When indicated, bilateral or multilevel surgery may be accomplished at one sitting (outpatient).
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.
Occasionally an intraoperative arthrogram will demonstrate the true shape of the articular surfaces (see Fig 2B).
A modular approach may permit angular correction to neutral mechanical axis, followed by length adjustment.
Positioning
The patient is positioned supine on the operating table.
Fluoroscopy is recommended.
Thigh tourniquets are employed for speed and accuracy of hardware placement.
Approach
The surgical approach is minimally invasive, directly over the physis, at the apex of the deformity.
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
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
It is helpful to inject them with 0.25% Marcaine for postoperative comfort.
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.
The dissection is deepened sharply, dividing fascia and retracting muscles as necessary but preserving the periosteum.
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.
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.
The 1.6-mm smooth guide pins are inserted, placing the epiphyseal one first, followed by the metaphyseal pin.
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).
The screws do not have to be parallel or to match in length.
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.
After routine wound closure, a soft compression dressing is applied.
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)
The surgical approach is the same, preserving the periosteum.
A guide needle is inserted.
One to three rigid Blount staples (Zimmaloy) are inserted per physis.
Simple closure is done with a elastic bandage.
PERCUTANEOUS SCREW (METAIZEAU)
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.
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.
Upon correction to neutral, the screw is removed.
PHEMISTER
This approach is mainly of historic interest.
The same approach is used as for stapling or eight-plate.
Periosteal flaps are raised to visualize the physis.
A bone rectangle is removed and inverted to establish a bony bridge.
This technique is permanent and thus most suitable for teenagers. It requires precise timing and calculations.
PERCUTANEOUS EPIPHYSIODESIS (MODIFIED FROM PHEMISTER)
Under fluoroscopic guidance the physis is drilled or curetted (or both) to produce a bony physeal bar.
The requisite depth of penetration has yet to be specified.
There may be a delay in effect until a bone bridge is established.
This technique is permanent and thus suitable only for teenagers. It requires precise timing and calculations.
POSTOPERATIVE CARE
No immobilization is required.
Immediate weight bearing is permitted.
No activity restriction is imposed.
Follow-up is done at 3-month intervals with weight-bearing AP radiographs of the legs when clinically straight.
Hardware is removed, avoiding periosteal damage, when the mechanical axis is neutral or limb lengths are equal.
Continued follow-up is important. Guided growth can be repeated if rebound growth causes recurrence.
Osteotomy may be reserved for rotational correction or further length equalization.
OUTCOMES
Initially after hemiepiphysiodesis there is no visible difference, and the family needs to be forewarned of this.
The correction is gradual and subtle, and therefore routine follow-up is imperative.
Correction to neutral (eight-plates) will take 12 months on average; staples take somewhat longer.
The hardware is removed upon correction of the valgus or varus deformity. (The surgeon must preserve the periosteum!)
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.
Premature physeal closure is unlikely, provided the hardware is inserted and removed uneventfully, leaving the periosteum intact.
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.
Modular adjustment of limb lengths is convenient and simple to accomplish.
If secured with cannulated screws, eight-plate survivorship is rarely problematic.
COMPLICATIONS
There is a race between deformity correction and hardware failure. Failure is more likely with a rigid implant.
The rigid staples are at a disadvantage owing to occasional migration or breakage, necessitating unplanned revision surgery (FIG 6).
A bent staple may permit excellent correction but is more difficult to monitor and remove.
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.