Anthony A. Stans
DEFINITION
A physeal bar, or partial premature physeal arrest, is an osseous connection that forms across a physis and has the potential to affect physeal growth.4
Partial physeal arrest may result in three clinically significant consequences:
Angular deformity
Limb-length discrepancy
Bone-length discrepancy in a two-bone limb segment such as the forearm or leg
When evaluating a patient with a physeal bar, one must critically consider whether there is sufficient growth remaining to cause a clinically significant length discrepancy or angular deformity.
One should consider the linear magnitude of anticipated growth remaining, as well as the years of remaining growth.
ANATOMY
The normal physis acts as a physical cartilage barrier separating the trabecular bone of the epiphysis from the metaphysis (FIG 1).
Blood vessels typically do not traverse the physis, necessitating an independent blood supply for the epiphysis and metaphysis.1
FIG 1 • The physis acts as a physical barrier separating the trabecular bone of the epiphysis from the trabecular bone of the metaphysis. The physis also acts as a barrier to blood flow, separating the epiphyseal blood supply (a) from the metaphyseal blood supply (b). Magnification of the physis illustrates the four physeal cell layers: the resting cell zone (c), the proliferating cell zone (d), the hypertrophying cell zone (e), and the endochondral ossification zone (f). Insults that breach the physical separation between metaphyseal and epiphyseal trabecular bone, that significantly compromise epiphyseal blood flow, or that critically injure the resting or proliferating cell layers may result in physeal bar formation.
The physis consists of four cell layers: resting zone, proliferative zone, hypertrophic zone, and enchondral ossification zone.
PATHOGENESIS
Physeal bars form when the cartilage barrier is breached as the result of trauma, infection, or cell death and trabecular bone heals in continuity between the epiphysis and the metaphysis across the physis.6
Variation in physeal anatomy may predispose certain physes to physeal bar formation. For example, the distal radius physis is relatively two-dimensional and uniplanar, while the distal femoral physis has a more complex three dimensional biconcave configuration.
Distal radius physeal fractures are quite common, yet subsequent premature physeal bar formation is relatively rare. In contrast, distal femoral physeal fractures are uncommon but distal femoral physeal bar formation is much more prone to occur after injury.
The three-dimensional configuration of the distal femoral physis contributes to the considerable energy required to fracture through the distal femoral physis, and the complex geometry increases the likelihood for violation of the physeal cartilage barrier between epiphyseal and metaphyseal bone, thereby increasing the risk of partial physeal bar formation after injury.
Breach of the physeal cartilage barrier is most frequently caused by fracture, followed by infection.
Less common pathogenesis for partial physeal bar formation may occur when the germinal or proliferating cells on the epiphyseal side of the physeal plate are injured by ischemia, infection, heat, laser, electricity, or other insult. As the germinal cells die and cell division in this region of the physis stops, partial physeal bar formation may occur.3
NATURAL HISTORY
In almost all situations, once a physeal bar has formed, length discrepancy, angular deformity, or both will continue to increase so long as the patient is skeletally immature and the affected physis (or its contralateral counterpart) continues to grow.
PATIENT HISTORY AND PHYSICAL FINDINGS
Questioning the patient quickly reveals the cause for physeal bar formation in most cases. The most common causes of physeal bar formation, fracture and infection, are typically memorable events that the patient can quickly recall.
The examiner should ask the patient and family if they have noticed a progressive limb-length discrepancy, limp, angular deformity, or bony prominence; this may confirm the presence of a physeal bar.
Ideally the orthopaedist is aware of the physeal injury, is anticipating possible physeal bar formation after injury, and is monitoring the patient at 6-month intervals with clinical examination and radiographs.
The patient is examined for lower extremity limb-length discrepancy using blocks of known height under the shorter limb until the pelvis is level.
The patient is also examined for lower extremity angular deformity. The alignment at knee and ankle is assessed and compared to the contralateral limb.
The patient is also examined for upper extremity limb-length deformity. Length of the affected limb is compared to that of the contralateral limb.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Appropriate imaging is critical for the evaluation of a potential physeal bar. Initial imaging is performed to determine whether the patient has sustained a clinically significant physeal injury and therefore should demonstrate limb-length discrepancy and angular deformity.
True scanograms use a slit beam that is perpendicular to the patient that scans the length of the limb and therefore has no magnification. The scanogram provides limb length and angular information with a single image (FIG 2A).
A teleoroentgenogram, or full-length, standing, hip-to-ankle radiograph taken at a distance, does result in some magnification of the limb.
By placing blocks of known height beneath the shorter limb, a teleoroentgenogram can also provide information about length and angular deformity with a single radiograph.
A ruler or magnification markers can also be placed next to the limb to allow more accurate measurement of limb length.
Orthoroentgenograms (separate exposures of the hip, knee, and ankle on a single film with a ruler) or CT scout images can be used to determine limb length.
These must be supplemented by a full-length image of the limb to assess angular deformity.
If the distal tibial physis is the injured physis in question, standing anteroposterior (AP) and lateral ankle radiographs are indicated to assess angular deformity.
If limb-length discrepancy or angular deformity is confirmed, additional imaging is indicated to determine the size and location of the physeal bar.
Either fine-cut CT or MRI may be used, and axial, coronal, and sagittal plane images are obtained.
The CT or MRI images are used to create a map that illustrates the location and approximate cross-sectional area of the physeal bar (FIG 2B,C).
The relative cross-sectional area of the bar is important because physeal bars occupying greater than 50% of the cross-sectional area of the physis have a less favorable result after resection. Excision of bars greater than 50% of the physeal cross-sectional area may still be indicated in young patients, such as a 5-year-old patient with a 65% bar of the distal femoral physis.
A skeletal age radiograph of the hand and wrist may be helpful in older patients if one is trying to determine if there is sufficient growth remaining for physeal bar resection to be indicated.
DIFFERENTIAL DIAGNOSIS
Physeal injury without growth abnormality
Idiopathic limb-length discrepancy
Developmental cause for limb-length discrepancy or angular deformity
Blount disease
Madelung deformity of the distal radius
NONOPERATIVE MANAGEMENT
Anticipated lower extremity limb-length discrepancy of less than 1 cm requires no treatment.
The simplest means of correcting a lower extremity limblength discrepancy is to place a lift either inside or on the bottom of the shoe on the shorter limb.
FIG 2 • A. A true scanogram uses a slit beam of radiation that moves or “scans” down the length of the extremity. Because the radiation beam always remains perpendicular to the film, there is no magnification of the radiographic image, and distances can accurately be measured directly on the radiograph. The entire limb is included on the image so angular deformity can be measured as well as length. Using multiple CT or MRI images (B), a map of the physeal bar is created (C) and the relative cross-sectional area of the bar is estimated.
Anticipated lower extremity discrepancy of 1 or 2 cm is most easily treated with a shoe lift inside the shoe.
Discrepancy greater than 2 cm treated nonoperatively is typically managed by a lift placed on the shoe sole.
There is no effective nonoperative treatment to correct clinically significant angular deformity caused by a physeal bar.
SURGICAL MANAGEMENT
Lower extremity physeal arrest resection should be considered in patients with an anticipated growth remaining from the affected physis of about 2 years or 2 cm.
Pure length discrepancy in the upper extremity caused by a physeal bar in the proximal humerus causes little functional problem, and anticipated discrepancy of up to 5 cm may be observed.
Bone-length discrepancy in a two-bone limb segment such as the forearm or leg is less well tolerated. Anticipated bone-length discrepancy of greater than 1 cm at the wrist may warrant surgical treatment either by physeal bar resection or complete epiphysiodesis of both bones to prevent bone-length discrepancy.
Surgical treatment for a physeal bar may consist of physeal bar resection, complete epiphysiodesis of the involved physis, epiphysiodesis of the adjacent bone in leg or forearm, epiphysiodesis of the contralateral physis, or an approach combining more than one of these.5 The surgical technique for physeal bar resection alone will be discussed below.
If the decision has been made to perform physeal bar excision and an angular deformity is present, one is faced with the question as to whether an osteotomy should be performed at the time of physeal arrest resection to correct angular deformity.
Our philosophy is to first perform physeal bar resection alone.
Physeal bar resection is a relatively minor procedure with rapid recovery and the potential to correct (at least partially) the angular deformity. Accurate prediction of angular correction after physeal bar resection is not possible, making it very difficult to know with certainty the degree of osteotomy angular correction to perform.
We would prefer to perform physeal bar resection alone first, then correct any residual angular deformity when physeal growth is complete.
At skeletal maturity, the target is no longer moving and any additional adjustment in limb length can be addressed as well.
Preoperative Planning
Imaging studies are reviewed and a map of the size and location of the physeal bar is created.
A strategy is determined to provide the safest and most direct surgical approach to the physeal bar.
Positioning
The patient is positioned to facilitate a direct approach to the physeal bar. For example, if a lateral approach is determined to be the most direct and safe route to a distal femoral bar, the patient is positioned with a generous bump elevating the hemipelvis and affected limb, with a tourniquet placed on the proximal thigh.
Fluoroscopy is used to guide physeal bar resection, so the patient must be placed on a radiolucent table in a position to facilitate AP and lateral fluoroscopic images.
Approach
The particular approach for each patient is determined by the location of the physis affected by the physeal bar and the location of the bar within the physis.
A direct approach to the bone surface at the level of the physis is used for peripheral bars.
Central physeal bar resection is typically performed by approaching the physis through the metaphysis adjacent to the physeal bar.
The general strategy for central physeal bar excision in a long bone is to access the bar through a metaphyseal bone tunnel, resect the bar, and place an interposition material that will prevent recurrent bar formation (FIG 3).
FIG 3 • The general strategy for central physeal bar resection (A) is to create a cortical window (B) through which the surgeon can excise the bar (C) and then place interposition material (D) to prevent bar recurrence. (Adapted from Peterson HA. Partial growth plate arrest and its treatment. J Pediatr Orthop 1984;4:246–258.)
TECHNIQUES
PHYSEAL BAR LOCALIZATION
With the patient prepared and draped, fluoroscopy is brought into the field and the location of the physis is marked on the skin surface.
Next, using a blunt pin or straight instrument, mark on the skin the desired approach trajectory to the physeal bar.
Draw the skin incision line on the approach trajectory (TECH FIG1A).
Exsanguinate the limb and incise the skin longitudinally where an internervous plane can be used.
With metaphyseal bone exposed, using AP and lateral fluoroscopic imaging, consider advancing a Kirschner wire or Steinmann pin along the approach trajectory from the metaphysis into the center of the physeal bar.
This Kirschner wire will act as a guide to the location and depth of the physeal bar (TECH FIG1B).
Using multiple drill holes and an osteotome, create an oval cortical window in metaphyseal bone (TECH FIG1C).
Remove and save the cortical window and superficial metaphyseal bone to be used for later closure.
As the tip of the reference Kirschner wire is approached, use a motorized burr to carefully remove bone until the center of the physeal bar is reached, as confirmed fluoroscopically.
Within the center of the physeal bar, no physis will be seen. Under fluoroscopic guidance, use the motorized burr to carefully expand the area of resection until normal physis is encountered (TECH FIG1D).
TECH FIG 1 • A. Before making a skin incision, fluoroscopy is brought into the surgical field and the surgeon draws on the skin the physis location, the physeal bar location, the surgical approach trajectory, and the skin incision location that will permit the desired approach. B. Under fluoroscopic guidance a Kirschner wire is advanced to the level of the physeal bar along the desired surgical approach trajectory. Multiple drill holes are then made that incorporate the Kirschner wire into the periphery of an elliptical cortical window. The Kirschner wire will act as a guide to the location and depth of the physeal bar. C.Multiple drill holes are connected with a narrow osteotome to create a cortical window. The window is saved and replaced during closure. (Kirschner wire guide is not shown in this photograph.) D. After removing metaphyseal bone with a curette, a burr is guided by fluoroscopy to expand the bar resection cavity until normal physis is visualized within the cavity. (C,D: From Peterson HA. Epiphyseal Growth Plate Fractures. Heidelberg: Springer, 2007. With kind permission of Spring Science and Business Media.)
BAR RESECTION
Once the physis is identified within the resection cavity, the motorized burr is used to remove bone along the leading edge of the exposed physis until normal-appearing physis is exposed throughout the entire circumference of the resection cavity.
The exposed normal physis should appear flat and smooth (TECH FIG2A).
A surgical headlight is helpful to visualize the physis within the resection cavity.
If a region of the resection area cannot be seen by direct vision, use a dental mirror or small joint arthroscope to visualize the physis and confirm complete physeal bar excision (TECH FIG2B).
Topical liquid thrombin may be applied to the resection cavity bone surface to reduce hematoma formation, which in theory might promote recurrent bar formation.
TECH FIG2 • A. Within the resection cavity the physis should appear smooth, flat, and healthy after bar resection. B. A dental mirror is used to look back at the physis in regions within the cavity where the physis cannot be directly visualized. At the conclusion of bar resection, normal physis should be visualized as a continuous cartilage line around the full circumference of the resection cavity.
MARKER PLACEMENT
Place titanium markers in the epiphysis and metaphysis to facilitate later measurement of physeal growth (TECH FIG3A).
Marker position in the center of the bone prevents the metaphyseal marker from becoming extraosseous with future remodeling.
Our preference is a titanium 0.062 Kirschner wire notched 10 mm from the tip, which can be broken off within bone (TECH FIG3B).
Titanium markers avoid artifact on subsequent MRI or CT scans.
TECH FIG 3 • A. The first titanium marker has been placed centrally within the metaphysis proximal to the physis. A second marker is going to be placed within the epiphysis distal to the physis. B. A 0.062 titanium Kirschner wire notched 10 mm from the end makes an ideal radiographic marker that will not interfere with future MRI imaging. (From Peterson HA. Epiphyseal Growth Plate Fractures. Heidelberg: Springer, 2007. With kind permission of Spring Science and Business Media.)
CRANIOPLAST INTERPOSITION
An interposition material is then placed in the physeal bar defect. Some authors have recommended fat as an interposition material, but we prefer cranioplast polymethylmethacrylate for several reasons:
Cranioplast has a slow polymerization rate and does not generate heat, which might be harmful to the physis.
Cranioplast confers immediate structural strength to the resection area, allowing full weight-bearing after surgery.
No loosening has ever been reported after physeal bar resection.
Cranioplast stays securely within the resection bed and cannot “float” out of the resection bed on hematoma.
An additional incision to harvest fat interposition material is avoided.
Cranioplast can be injected into the resection defect in its liquid state, or it can be allowed to polymerize to the consistency of putty, then gently digitally pressurized into the cancellous bone of the resection bed, preventing displacement.
FAT INTERPOSITION
If fat is chosen as the interposition material, a donor site must be chosen.
Rarely, in a patient with a small physeal bar, local fat may be harvested.
Most patients require harvesting fat from a distant site, and the gluteal region is typically used.
Our current indications for fat interposition material include:
Physeal bars caused by infection, where this is a concern for recurrent infection
Peripheral physeal bar resection, where cranioplast may become prominent during future growth and remodeling (TECH FIG4)
TECH FIG 4 • Peripheral physeal bar resection (A) is performed by approaching the bar directly (no bone tunnel) and excising the bar with a burr (B). Fat works well as an interposition material for peripheral bars (C) because bone remodeling and growth may result in cranioplast becoming prominent with time. (Adapted from Peterson HA. Partial growth plate arrest and its treatment. J Pediatr Orthop 1984;4:246–258.)
CLOSURE
After placement of the interposition material, cancellous bone saved during exposure is gently packed into the remaining bone cavity.
The cortical window of bone is replaced and may be sutured in place if desired.
Periosteum is closed over the cortical bone window.
POSTOPERATIVE CARE
At the conclusion of the operation, local anesthetic is injected into the incision site, ketorolac (Toradol) is administered unless there is a medical contraindication, and the patient is placed in a gentle compressive dressing, which is removed on the first postoperative day.
Patients are allowed to bear weight as tolerated with crutches as needed for comfort, and early active joint range of motion is encouraged.
Noncontact sports are typically permitted 3 months after surgery and full-contact sports are allowed 6 months postoperatively in most patients.
OUTCOMES
One hundred patients treated at the Mayo Clinic with physeal bar resection in the femur or tibia were followed to skeletal maturity.7
13% of the patients required no additional treatment; the physeal bar was definitively treated by a single physeal bar resection procedure.
94% of the patients did experience some growth after physeal arrest resection.
Restored physeal growth was, on average, 86% of the contralateral physeal growth rate.
118 additional procedures were performed, for an average of 1.2 additional procedures per patient.
In all patients (except the six in whom there was no growth), any subsequent surgery was of lesser magnitude than would have been necessary had physeal bar resection not been performed.
COMPLICATIONS
In 100 patients treated at the Mayo Clinic with physeal bar resection and cranioplast interposition followed to skeletal maturity, 2 patients had a surgical wound infection and 2 patients had a late fracture at the cranioplast site, for a total complication rate of 4%.7
Fracture through the resection cavity after using fat as an interposition material has also been reported.2
REFERENCES
1. Dietz FR, Morcuende JA. Embryology and development of the musculoskeletal system. In Morrissy RT, Weinstein SL, eds. Lovell and Winter's Pediatric Orthopaedics, 6th ed. Philadelphia: Lippincott Williams & Williams, 2005:1–33.
2. Langenskiold A. Surgical treatment of partial closure of the growth plate. J Pediatr Orthop 1981;1:3–11.
3. Ogden JA. Injury to the growth mechanisms of the immature skeleton. Skeletal Radiol 1981;6:237–253.
4. Peterson HA. Epiphyseal Growth Plate Fractures. Heidelberg: Springer, 2007.
5. Peterson HA. Partial growth plate arrest and its treatment. J Pediatr Orthop 1984;4:246–258.
6. Salter RB, Harris WR. Injuries involving the epiphyseal plate. J Bone Joint Surg Am 1963;45A:587–622.
7. Stans AA, Klassen RA, Shaughnessy WJ, et al. Excision of partial physeal arrest followed to skeletal maturity. Presented at AAOS annual meeting, 2006.