Physeal Bar Resection: A Masterclass in Growth Plate Salvage and Deformity Correction

Introduction and Epidemiology

A physeal bar, or partial premature physeal arrest, is an osseous connection that forms across a physis and has the potential to profoundly affect longitudinal and angular physeal growth. The physis is highly susceptible to injury, and partial physeal arrest may result in three clinically significant consequences. First, eccentric tethering of the growth plate leads to progressive angular deformity. Second, global or significant partial arrest causes limb length discrepancy. Third, in a two-bone limb segment such as the forearm or leg, partial arrest can cause severe bone length discrepancy leading to joint subluxation, radiocapitellar dislocation, or distal radioulnar joint incongruity.

When evaluating a pediatric patient with a suspected physeal bar, the orthopedic surgeon must critically consider whether there is sufficient growth remaining to cause a clinically significant length discrepancy or angular deformity. The linear magnitude of anticipated growth remaining, as well as the chronological years of remaining growth, dictate the treatment algorithm.

Epidemiologically, physeal bars most commonly occur following trauma, specifically Salter-Harris type III and IV fractures, which inherently violate the germinal layers of the physis. However, high-energy Salter-Harris type I and II fractures, particularly in the distal femur or distal tibia, can also result in crush injuries to the proliferative zone, leading to bar formation. Non-traumatic etiologies include osteomyelitis, septic arthritis, meningococcemia, thermal injuries, frostbite, and iatrogenic causes such as hardware placement across the open physis.

Surgical Anatomy and Biomechanics

Structural Anatomy of the Physis

The normal physis acts as a physical cartilage barrier separating the trabecular bone of the epiphysis from the metaphysis. Blood vessels typically do not traverse the physis, necessitating an independent blood supply for the epiphysis and metaphysis. The epiphyseal vessels supply the resting and proliferative zones, while the metaphyseal vessels supply the zone of provisional calcification. Disruption of the epiphyseal blood supply leads to ischemic necrosis of the germinal cells, whereas disruption of the metaphyseal supply only temporarily halts ossification.

The physis consists of four distinct histological cell layers:
1. Resting Zone: Located adjacent to the epiphysis, containing germinal cells and a high matrix-to-cell ratio.
2. Proliferative Zone: Chondrocytes undergo active mitosis and stack in longitudinal columns.
3. Hypertrophic Zone: Subdivided into maturation, degeneration, and provisional calcification zones. This is the mechanically weakest layer of the physis and the most common site of failure in Salter-Harris type I and II fractures.
4. Endochondral Ossification Zone: The metaphyseal junction where osteoblasts lay down bone on the calcified cartilage matrix.

Pathogenesis of Partial Physeal Arrest

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. Variation in physeal anatomy may predispose certain physes to physeal bar formation. For example, the distal radius physis is relatively two-dimensional and uniplanar, whereas 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.

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 insults. As the germinal cells die and cell division in this region of the physis stops, partial physeal bar formation occurs.

Indications and Contraindications

The decision to resect a physeal bar depends heavily on the size of the bar, the location of the bar, and the amount of growth remaining in the affected limb. The general consensus in pediatric orthopedics dictates that a physeal bar may be successfully resected if it occupies less than 50 percent of the cross-sectional area of the physis and the patient has at least two years of growth remaining.

If the bar occupies greater than 50 percent of the physis, resection is generally contraindicated due to a high rate of recurrence and insufficient remaining healthy physis to drive meaningful longitudinal growth. In these cases, completion epiphysiodesis of the affected growth plate, combined with contralateral epiphysiodesis or future limb lengthening, is the preferred management strategy.

Operative vs Non Operative Management

Pre Operative Planning and Patient Positioning

Advanced Imaging and Bar Mapping

Precise preoperative mapping of the physeal bar is the most critical step in surgical planning. While plain radiographs (including anteroposterior, lateral, and oblique views) can identify the presence of a bar and associated angular deformity, they are insufficient for determining the exact size and anatomical morphology of the osseous bridge.

Magnetic Resonance Imaging (MRI) is the gold standard for evaluating physeal bars. Specific sequences, such as 3D spoiled gradient-recalled echo (SPGR) or fast imaging employing steady-state acquisition (FIESTA), provide high-resolution, thin-slice visualization of the physeal cartilage. On these sequences, the normal physeal cartilage appears hyperintense (bright), while the osseous bar appears hypointense (dark).

Computed Tomography (CT) can also be utilized, particularly with multiplanar reconstruction. CT is highly effective at delineating the bony architecture of the bar, though it exposes the pediatric patient to ionizing radiation and does not visualize the healthy cartilage as effectively as MRI.

Calculating Cross Sectional Area

Once advanced imaging is obtained, the surgeon must calculate the cross-sectional area of the bar relative to the entire physis. This is typically performed using axial MRI or CT cuts parallel to the physis. The area of the bar is mapped onto a grid or calculated using digital templating software. Bars are anatomically classified into three types:
1. Peripheral: Located at the periphery of the physis, often causing severe angular deformity.
2. Central: Surrounded completely by normal physis, often causing tenting of the physis and limb length discrepancy without significant angular deformity.
3. Linear: Extending across the physis from one periphery to another, often following the path of a previous fracture line.

Patient Positioning and Setup

The patient is positioned supine on a radiolucent operating table to allow for unencumbered intraoperative fluoroscopy. A tourniquet is applied to the proximal limb to ensure a bloodless surgical field, which is critical for visualizing the subtle transition between the osseous bar and normal physeal cartilage. Prophylactic intravenous antibiotics are administered prior to tourniquet inflation.

Detailed Surgical Approach and Technique

The surgical approach is dictated by the location of the bar (peripheral vs. central). The fundamental goal of the procedure is complete excision of the tethering bone, visualization of normal healthy physeal cartilage around the entire periphery of the resection cavity, and placement of an interpositional material to prevent reformation of the bone bridge.

Peripheral Bar Resection Technique

Peripheral bars are approached directly through the overlying soft tissues.
1. Incision and Exposure: A longitudinal incision is made directly over the site of the peripheral bar. The periosteum is carefully incised and elevated. It is critical to excise the periosteum overlying the bar, as retained osteogenic periosteum can lead to rapid bar recurrence.
2. Bone Resection: A high-speed burr or fine curette is used to meticulously remove the osseous bridge. The surgeon must differentiate between the hard, gritty texture of metaphyseal and epiphyseal bone and the soft, white, glistening appearance of normal physeal cartilage.
3. Visualizing Healthy Physis: Resection continues until normal, healthy physeal cartilage is visualized circumferentially around the defect. A dental mirror or a 30-degree arthroscope can be inserted into the cavity to inspect the margins and ensure no residual bony tethers remain.
4. Hemostasis: Punctate bleeding from the metaphyseal and epiphyseal cancellous bone must be controlled to prevent hematoma formation, which can ossify and recreate the bar. Bone wax is meticulously applied to the exposed cancellous bone surfaces, taking care not to place wax on the healthy physeal cartilage.

Central Bar Resection Technique

Central bars require a more complex approach to avoid damaging the surrounding healthy peripheral physis.
1. Metaphyseal Window: A cortical window is created in the metaphysis, proximal to the physis. The window must be large enough to allow the introduction of instruments and visualization equipment.
2. Tunneling to the Bar: Using curettes and a burr, a tunnel is created through the metaphyseal cancellous bone directed toward the central bar, guided by intraoperative fluoroscopy.
3. Bar Excision: Once the bar is reached, it is removed from the inside out. The surgeon works radially until the normal physis is encountered on all sides. The use of an endoscope is highly recommended for central bar resections to ensure complete removal.
4. Preparation of the Cavity: Similar to the peripheral approach, bone wax is applied to the raw bony surfaces to achieve hemostasis.

Interpositional Graft Placement

Once the bar is completely resected, the dead space must be filled with an interpositional material to prevent hematoma accumulation and subsequent re-ossification. Historically, various materials have been used, including polymethylmethacrylate (PMMA / Cranioplast), silastic, and bone wax. However, autologous fat graft is currently the most widely accepted and preferred material.

Autologous fat is typically harvested from the gluteal fold or from the local surgical incision if sufficient subcutaneous fat is present. The fat graft must be handled gently to preserve adipocyte viability. It is packed tightly into the resection cavity, ensuring it is in direct contact with the exposed physeal cartilage and the bone wax covering the cancellous bone. The metaphyseal window (in central resections) or the periosteal defect (in peripheral resections) is then carefully closed over the fat graft to prevent extrusion.

Concomitant Osteotomy

If the patient presents with an established angular deformity greater than 10 to 15 degrees, bar resection alone will not acutely correct the alignment. In these scenarios, a concomitant corrective osteotomy (typically in the metaphysis) is performed during the same surgical setting. The osteotomy is stabilized with internal fixation (e.g., Kirschner wires, plates, or external fixation), ensuring that the hardware does not violate the newly freed physis.

Complications and Management

Physeal bar resection is a technically demanding procedure with a high potential for complications. Meticulous surgical technique and strict adherence to indications are required to minimize adverse outcomes.

Common Complications and Salvage Strategies

If a bar recurs and the patient develops a significant limb length discrepancy, the surgeon must transition to limb reconstruction techniques. This may involve completion of the arrest to prevent further angular deformity, followed by a lengthening procedure (e.g., using a circular external fixator or a motorized intramedullary lengthening nail) once the patient is closer to skeletal maturity.

Post Operative Rehabilitation Protocols

Immediate postoperative management focuses on protecting the surgical site and preventing displacement of the interpositional fat graft.
1. Immobilization: The affected limb is typically immobilized in a well-padded splint or cast for 2 to 4 weeks. This allows the soft tissues to heal and reduces the risk of fat graft extrusion from the resection cavity.
2. Weight-Bearing: Patients are kept strictly non-weight-bearing on the operative extremity during the initial immobilization phase. Weight-bearing forces can compress the physis and potentially displace the interpositional material.
3. Physical Therapy: Following the removal of the cast or splint, a progressive physical therapy program is initiated to restore joint range of motion and muscle strength. Weight-bearing is advanced gradually as tolerated.

Long-term follow-up is mandatory until the patient reaches skeletal maturity. Radiographs (including scanograms or orthoroentgenograms) should be obtained at 3- to 6-month intervals to monitor for resumption of longitudinal growth, assess for recurrence of the physeal bar, and evaluate the mechanical axis for any progressive angular deformity. Harris growth arrest lines, which appear parallel to the physis, can serve as a radiographic marker of resumed symmetrical growth following a successful resection.

Summary of Key Literature and Guidelines

The foundational principles of physeal bar resection were established by Langenskiöld in the 1960s and 1970s. Langenskiöld demonstrated that an established osseous bridge could be resected and replaced with an interpositional material (initially fat) to restore longitudinal growth. His experimental and clinical work remains the cornerstone of modern treatment algorithms.

Peterson further advanced the field by classifying physeal bars into peripheral, central, and linear types, which directly dictates the surgical approach. Peterson's extensive clinical series highlighted the absolute necessity of complete bar excision and the superiority of autologous fat over synthetic materials like silastic.

Current clinical guidelines emphasize the critical role of MRI in preoperative planning. The "50 percent rule"—stating that bars occupying more than 50% of the cross-sectional area should not be resected—is widely accepted and supported by numerous outcome studies demonstrating unacceptably high failure rates in larger bars. Recent literature also supports the use of intraoperative endoscopy, particularly for central bars, to significantly reduce the rate of incomplete resection and subsequent bar recurrence.