Physeal Bar (Bony Bridge): Definition, Pathology, and Management

Definition

Pathophysiology

• Normal physeal cartilage, when damaged, is replaced by bone rather than regenerating
• The bony bridge acts as a tether, preventing that segment of the physis from contributing to longitudinal growth
• The uninjured portion of the physis continues to grow, creating a differential that produces angular deformity or limb-length discrepancy (LLD), or both
• Spontaneous resolution is exceedingly rare

Causes

Classification by Location

1. Peripheral Bar

• Located at the edge of the physis
• More accessible surgically
• Produces predominantly angular deformity
• Better prognosis after resection (especially if small and in young patients)

2. Central Bar

• Located in the central area of the physis
• Surrounded on all sides by normal physeal cartilage
• Produces predominantly limb-length discrepancy / shortening
• More challenging to access; approached via a metaphyseal cortical window or osteotomy
• Arthroscopically assisted resection has been described

3. Combined (Mixed) Bar

• Most cases have components of both shortening and angular deformity

MRI of Physeal Bar at the Knee

Diagnosis / Imaging

• Location (peripheral vs. central)
• Percentage of physis involved
• Remaining normal physeal area

Decision-Making Algorithm

1. Percentage of physis involved by the bar
2. Age of the child / growth remaining
3. Location of the bar (peripheral vs. central)
4. Expected deformity at skeletal maturity

Bar identified on CT/MRI
        |
        ├── Near skeletal maturity / minimal growth remaining
        |         └── Observation / shoe lift / epiphysiodesis
        |
        ├── Bar < 50% physis + young child + significant morbidity expected
        |         └── BAR RESECTION (with fat/Silastic interposition)
        |              ± concurrent osteotomy for established angular deformity
        |
        └── Bar > 50% physis OR large / central / inaccessible
                  └── Completion epiphysiodesis (ipsilateral)
                      + Contralateral epiphysiodesis (for LLD)
                      OR Limb lengthening (if LLD >5 cm expected)

Indications for Bar Resection

• Child young enough to have significant growth remaining (>2 cm)
• Bar involves <50% of the physis (ideally <30%)
• Bar is peripheral and accessible
• Progressive angular deformity or LLD is expected
• Results are unpredictable; unsuccessful outcomes occur in 10% to 40% of patients
• Young patients with small peripheral bars have the highest success rates

Surgical Techniques

Technique 1: Peripheral Bar Resection - Langenskiold Technique (38.35)

1. Preoperative exact localization and sizing by MRI, CT, and tomography in two planes
2. Expose periphery of physis near the bony bridge with a bloodless field (tourniquet); use microscope or binocular loupe
3. Remove overlying periosteum and resect the bony bridge until normal periphery of the physis is reached on both sides, with physeal cartilage visible all around the cavity - no bridge remnant left, no unnecessary normal cartilage removal
4. Release tourniquet; obtain hemostasis
5. Fill cavity with autogenous fat from subcutaneous tissue (gluteal fold or groin), dividing into pieces if irregular
6. Suture ligament/muscle/subcutaneous tissue over defect to retain the fat graft
7. Close in layers; plaster splint; limit weight-bearing until healed

Technique 2: Bony Bridge Resection + Angulation Osteotomy - Ingram Technique (38.36)

1. Perform an osteotomy at the level of the bony bridge, adjacent and parallel to the physis (opening-wedge, same side as the bar)
2. Place a guide pin parallel to the physis under fluoroscopy, adjacent to the bar
3. Open the osteotomy widely with a laminar spreader
4. Using a dental burr and operating microscope/loupe, resect the white sclerotic bony bridge until normal physeal cartilage appears on all sides (dental mirror aids visualization)
5. Fill defect with free fat graft or silicone
6. Secure the osteotomy after inserting a wedge of autogenous bone to correct deformity; smooth pins hold osteotomy

Technique 3: Peripheral Bar Resection - Birch Technique (38.37)

1. Carefully expose the peripheral junction of the bar and healthy perichondral ring at one or both edges - use fluoroscopy throughout to stay at the physeal level and not drift into metaphysis/epiphysis
2. Continue resection until physis is visible from each edge of healthy perichondrium throughout the depth; alternatively, use periosteal stripping + fluoroscopic guidance to develop a cavity directed toward the physis
3. Fill defect with autogenous fat from local subcutaneous tissue or a separate groin/buttock incision

Technique 4: Central Physeal Bar Resection (38 approach)

• Approached from the metaphyseal marrow cavity through a metaphyseal cortical window or an osteotomy
• Arthroscopically assisted central bar resection: scope identifies normal cartilage after dental burr resection in the defect
• More technically demanding; results are less predictable than for peripheral bars

Interposition Materials (After Resection)

Management of Residual / Predicted Deformity

Clinical Case Example: Physeal Bar Resection

Prognosis and Key Points Summary (Miller's Review)

• Physeal bar resection with fat/Silastic interposition is reserved for patients with >2 cm of growth remaining and <50% physeal involvement
• Smaller peripheral bars in young patients have the highest success rate
• MRI and CT define location and amount of physeal closure
• Arrest involving >50% of the physis should be treated with ipsilateral completion of arrest + contralateral epiphysiodesis or lengthening

• Campbell's Operative Orthopaedics, 15th Ed (2026), Techniques 38.35, 38.36, 38.37 and Growth Arrest section
• Miller's Review of Orthopaedics, 9th Edition - Partial Growth Arrest summary

Macro and Microscopic Structure of Adult Cortical Bone

Part 1 — Macroscopic (Gross) Structure

Overview of a Typical Long Bone

The THIEME Atlas Diagram - Structure of a Typical Tubular Bone (Femur)

Layers from Outside to Inside in the Diaphysis

PERIOSTEUM
    ↓
OUTER CIRCUMFERENTIAL LAMELLAE (subperiosteal)
    ↓
HAVERSIAN SYSTEMS (osteons) — the bulk of compact bone
    ↓
INNER CIRCUMFERENTIAL LAMELLAE (perimedullary)
    ↓
ENDOSTEUM
    ↓
MEDULLARY CAVITY (yellow marrow / fat in adults)

1. Periosteum

• Stratum fibrosum (outer layer) - dense collagenous fibrous tissue; the stratum of mechanical attachment
• Stratum germinativum / cambium layer (inner layer) - contains osteoprogenitor cells and active osteoblasts; responsible for appositional (periosteal) bone growth and fracture repair

2. Cortical (Compact) Bone

• Forms the outer wall of the diaphysis; appears dense and ivory-white on gross examination
• Porosity is only ~5-10% (vs. ~75-95% for cancellous bone)
• The structural units are osteons (Haversian systems), cylinders approximately 1 cm long and 250-350 µm in diameter, oriented parallel to the long axis of the bone
• Haversian canals run longitudinally and are interconnected by Volkmann canals (transverse/oblique) and also communicate with periosteal and medullary vessels via the nutrient foramen

3. Medullary Cavity

• Central hollow space within the diaphysis
• In adults, contains yellow bone marrow (primarily adipose tissue)
• Lined internally by endosteum (described below)
• Metaphyseal/epiphyseal regions contain red bone marrow (haematopoietic)

4. Endosteum

• A thin single cell layer lining all internal bone surfaces: medullary cavity, trabecular surfaces, Haversian canal walls, and Volkmann canal walls
• Contains osteoprogenitor cells (endosteal cells), osteoblasts, and osteoclasts
• The endosteal surface is the main site of bone remodeling and marrow-bone cell exchange

Part 2 — Microscopic Structure

Four Components of Compact Lamellar Bone

The Osteon (Haversian System) - In Detail

Histology: Ground bone cross-section (Junqueira's)

Dimensions

• Diameter: 100-250 µm (Junqueira) / 250-350 µm for the full osteon including circumferential zone (THIEME)
• Length: approximately 1 cm along bone axis, sometimes branching (bifurcated)
• Number of concentric lamellae per osteon: 5-20

Components of the osteon from center outward:

1. Haversian canal (central canal)
   • Contains 1-2 small blood vessels (capillaries/postcapillary venules), unmyelinated nerve fibers, and endosteum
   • Diameter: ~20-50 µm
   • All cells of the osteon are nourished via diffusion from these vessels
2. Concentric lamellae
   • Rings of mineralized bone matrix deposited concentrically around the Haversian canal
   • Each lamella is ~3-7 µm thick
   • The collagen fibers in each lamella run parallel to each other but at an angle to adjacent lamellae (alternating orientations)
   • This plywood-like arrangement is responsible for the resistance to torsional, bending, and compressive forces
3. Lacunae
   • Small lens-shaped spaces between lamellae (and within them)
   • Each contains one osteocyte
   • Interconnected by canaliculi
4. Canaliculi
   • Fine tunnels radiating from each lacuna in all directions
   • Contain the dendritic (cytoplasmic) processes of osteocytes
   • Connect adjacent osteocytes via gap junctions
   • Provide the nutrient-waste exchange pathway between the Haversian canal and the furthest osteocytes
5. Cement line (reversal line)
   • Outer boundary of each osteon; marks where osteoclast resorption stopped and osteoblast deposition began
   • Rich in non-collagenous proteins (osteopontin, osteocalcin) and mineralized collagen
   • Acts as a crack-arresting interface - prevents fracture propagation across osteon boundaries

Polarized Light Appearance of Lamellar Bone

• Bright (birefringent) bands = lamellae with collagen fibers oriented perpendicular to the polarizer
• Dark bands = lamellae with collagen fibers parallel to the polarizer
• This alternation indicates that fibers in successive lamellae have different orientations - the structural basis of the bone's strength

Interstitial Lamellae and Generations of Osteons

• Most compact bone in adult humans = secondary bone (remodeled osteons)
• Interstitial lamellae are the remnants of the first-, second-, and third-generation osteons
• Successive generations are visible by their different degrees of mineralization (darker = more mineralized = older)

Canal Systems of Cortical Bone

• Adjacent Haversian canals to each other
• Haversian canals to periosteal vessels
• Haversian canals to the medullary cavity

The Cells of Cortical Bone

Extracellular Matrix (ECM) Composition

• 65-70% inorganic (mineral): Hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ crystals deposited on and between collagen fibers; provides compressive strength and hardness
• 30-35% organic (osteoid): predominantly Type I collagen (~90% of organic matrix); the remaining ~10% = non-collagenous proteins

Cortical Bone Remodeling (The Cutting Cone / BMU)

1. Activation - Osteoclasts are recruited to a site (triggered by mechanical strain, microdamage, hormonal signals)
2. Resorption - Osteoclasts tunnel through cortical bone forming a cylindrical "cutting cone" (~200 µm diameter)
3. Reversal - Transition from resorption to formation; mononuclear cells smooth the surface; cement line is deposited
4. Formation - Osteoblasts follow the advancing tunnel ("closing cone"), deposit concentric lamellae inward, trapping themselves as osteocytes
5. The residual central canal = new Haversian canal with its blood supply

Summary Table

• Junqueira's Basic Histology - Text and Atlas, 17th Ed - Types & Organisation of Bone, Lamellar Bone sections
• Histology: A Text and Atlas with Correlated Cell and Molecular Biology - General Structure of Bone Tissue
• THIEME Atlas of Anatomy: General Anatomy and Musculoskeletal System - Structure of a Typical Tubular Bone (femur)
• Forensic Anthropology: A Comprehensive Introduction, 2nd Ed - Bone Structure
• Rheumatology, 2-Volume Set (2022, Elsevier) - Microscopic level and Effects of Remodeling on Cortical Bone