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Strength-Duration (SD) Curve in Orthopedics

What is the Strength-Duration Curve?

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Physiological Basis

Law of Excitation (Imax Law / Weiss's Law)

• A brief, high-intensity stimulus is equivalent in effect to a long, low-intensity stimulus.
• Below a critical duration (the utilization time), no contraction is possible regardless of intensity (vertical asymptote).
• Below a critical intensity (the rheobase), no contraction occurs regardless of duration (horizontal asymptote).

Lapicque's Equation (1907)

I = b (1 + c/d)

• I = threshold current
• b = rheobase
• c = chronaxie
• d = stimulus duration

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Key Parameters

1. Rheobase

• Pulse duration used to measure rheobase: 100-300 ms
• Greater rheobase = lower excitability = more denervation

2. Chronaxie

3. Utilization Time

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Types of SD Curves - Diagnostic Patterns

Type 1: Normal Innervation ("Nerve Curve")

• Shape: Smooth, continuous rectangular hyperbola
• Curve begins to rise sharply at approximately 1 ms - the critical point where nerve can no longer be stimulated efficiently
• At longer durations (>1 ms): Intensity plateaus (rheobase reached)
• Rheobase: 2-18 mA / 5-35 V
• Chronaxie: < 1 ms
• A brisk, snap-like (vermicular) contraction is produced

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Type 2: Complete Denervation ("Muscle Curve")

• Curve is shifted far to the right
• Steep rise continuing even below 100 ms - no plateau at short durations
• No response at short pulse durations (< 1 ms)
• Very high rheobase (may need 50-100+ mA)
• Chronaxie: > 10 ms (often 20-100 ms)
• Contraction is slow, worm-like (peristaltic), not brisk
• Requires galvanic (DC) current, not faradic (AC)

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Type 3: Partial Denervation ("Kink Curve")

• A characteristic kink (inflection point) is visible in the curve
• Left side of the curve (short durations): represents intact innervated fibers - curves like a normal SD curve
• Right side of the curve (longer durations): represents denervated muscle fibers - shifted right with high intensity needed
• The kink appears where the two populations of fibers have different thresholds

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Summary Comparison Table

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Clinical Applications in Orthopedics

1. Diagnosis of Nerve Injury / Denervation

• Peripheral nerve injuries (trauma, stretch, laceration)
• Brachial plexus injuries
• Radiculopathies (disc prolapse, spinal stenosis, spondylosis)
• Compartment syndrome with nerve compromise
• Thoracic outlet syndrome

2. Monitoring Re-innervation / Recovery

• Kink appearing in a previously flat denervated curve = early re-innervation (nerve fibers are returning to the muscle)
• Kink shifting left over time = progressive re-innervation
• Return of normal curve pattern = complete re-innervation
• This is often detectable weeks before clinical strength recovery or EMG changes become apparent

3. Lower Motor Neuron vs. Upper Motor Neuron Lesions

• SD curve shows abnormality ONLY in lower motor neuron (LMN) lesions (anterior horn cell, nerve root, peripheral nerve)
• It is normal in upper motor neuron (UMN) lesions (stroke, spinal cord injury above level) because peripheral motor nerves remain intact
• This makes it a useful differentiating tool

4. Guiding Therapeutic Electrical Stimulation

• Use pulse durations around chronaxie for maximum efficiency and patient comfort
• Denervated muscles require much longer pulse widths (10-1000 ms galvanic) vs. innervated muscles (0.1-1 ms faradic)
• Prevents unnecessary fatigue and patient discomfort by avoiding ineffective short pulses

5. Prognosis and Medico-legal Assessment

• A right-shifted curve or high chronaxie = poor prognosis for spontaneous recovery
• Return of the kink = favorable sign of re-innervation
• Serial testing provides objective documentation of nerve recovery progress, useful in medico-legal contexts for compensation assessment

6. Radiculopathy Assessment

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How the Test is Performed

1. Equipment: Galvanic stimulator capable of delivering rectangular pulses from 0.01 ms to 1000 ms
2. Electrodes: Active electrode (cathode, negative) placed over the motor point of the muscle; indifferent electrode (anode) placed proximally
3. Procedure:
   • Start with long-duration pulses (300-1000 ms) to find rheobase
   • Progressively reduce pulse duration while increasing intensity to find minimum threshold at each duration
   • Plot threshold intensity vs. duration on log-log or semi-log paper
4. Timing: Performed 3 weeks post-injury; repeated every 4-6 weeks to monitor progress

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Factors Affecting the SD Curve

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Advantages of the SD Curve

• Quick, inexpensive, non-invasive (relatively)
• Requires minimal training
• Can detect denervation before EMG changes become manifest in some cases
• Serial testing objectively tracks re-innervation
• Distinguishes complete from partial denervation
• Differentiates LMN from UMN lesions

Limitations

• Provides qualitative rather than quantitative grading of degree of denervation
• Cannot localize the site of the nerve lesion
• In large muscles, only a small area of fibers is sampled
• Patient cooperation and pain tolerance affect results
• Not reliable in < 3 weeks post-injury
• Largely superseded by EMG/nerve conduction studies for precise lesion characterization, though still used as a complementary tool and in resource-limited settings
• Intrarater reliability is moderate (r = 0.541) while interrater reliability is better (r = 0.945)

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Comparison with Other Electrodiagnostic Tests

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Summary

1. Diagnose peripheral nerve injury and denervation (from 3 weeks post-injury)
2. Monitor recovery and re-innervation serially over time
3. Differentiate complete from partial denervation (the "kink" pattern)
4. Guide therapeutic electrical stimulation parameters
5. Prognosticate nerve recovery in peripheral nerve and root injuries

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• Campbell's Operative Orthopaedics, 15th ed. (2026), Electrical Stimulation section
• Medical Physiology (Boron & Boulpaep), p. 276, Figure 7-3
• Physiopedia: Strength-Duration Curve
• Akulwar-Tajane et al., "Exploring the Role of Strength-Duration Curve in Radiculopathy," EC Orthopaedics 14.9 (2023)

Biopsy Techniques in Orthopedics

Introduction and Importance

• Led to major diagnostic errors in 13.5% of cases
• Caused complications in 15.9%
• Resulted in unnecessary amputations in 3% of patients
• Were 2-12x more likely to cause problems when done at a non-specialist center

Campbell's Operative Orthopaedics (15th ed., 2026): "Errors in diagnosis, nonrepresentative or technically poor biopsy specimens, and wound complications have been found to occur more frequently when the biopsy was done by a surgeon at a referring institution rather than by an orthopaedic oncologist."

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Golden Rule - Pre-Biopsy Planning

1. Full clinical examination
2. Laboratory investigations (CBC, LFT, calcium, phosphate, LDH, PSA, protein electrophoresis)
3. Complete radiological staging:
   • Plain X-rays (AP + lateral)
   • MRI of the entire compartment
   • CT scan of chest, abdomen, pelvis
   • Bone scan (technetium-99)
   • PET-CT where indicated

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Fundamental Principles of Orthopedic Biopsy (Mankin's Principles)

1. The biopsy track must be considered contaminated with tumor cells - both needle and incisional tracks
2. The biopsy track must be excised en bloc with the tumor at the time of definitive resection
3. Placement of the incision/needle must be within the planned definitive surgical incision
4. Refer before you biopsy - if primary malignancy is suspected, refer to a musculoskeletal oncologist first
5. Longitudinal incisions only - never transverse incisions on limbs
6. Work through a single muscle compartment - never violate intermuscular planes
7. Avoid major neurovascular structures
8. Meticulous hemostasis - hematoma spreads tumor cells
9. The surgeon who biopsies should perform the definitive surgery (or work in close coordination)

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Classification of Biopsy Types

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Type 1: Fine-Needle Aspiration Cytology (FNAC)

Principle

Indications

• High suspicion of metastatic disease (most accurate use - 95% accuracy)
• Suspected infection / osteomyelitis (for culture and sensitivity)
• Lymph node assessment
• Recurrent known tumors for rapid confirmation
• Lesions near neurovascular bundles (thin needle = less contamination risk)

Technique

1. 22-25 gauge needle attached to a 20 mL syringe
2. Local anesthesia
3. Needle directed into tumor under imaging guidance (ultrasound/CT) or palpation
4. Suction applied while rotating the needle to collect cells
5. Material expressed onto glass slides for Giemsa/Papanicolaou staining

Accuracy

• 90% accurate for determining malignancy vs. benign
• Much lower accuracy (~60-70%) for specific tumor type (subtype differentiation)
• Accuracy for metastatic disease: ~95%
• Benign primary tumors: ~60-70% (least accurate)

Advantages

• Outpatient procedure
• Cheap, minimal equipment
• Very low complication rate
• Near-zero contamination risk (22-25G needle tracks don't seed significantly)

Limitations

• No tissue architecture assessment
• Cannot grade tumors
• Cannot perform immunohistochemistry, cytogenetics, flow cytometry on cell aspirate
• Needs a specialist cytopathologist

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Type 2: Core Needle Biopsy (CNB)

Needles Used

Technique - Soft Tissue (Tru-Cut)

1. Local anesthetic infiltration (minimal - don't over-infiltrate, extends contamination zone)
2. Small stab incision (same axis as planned surgical incision)
3. Spring-loaded Tru-Cut gun introduced until tip enters tumor
4. Trigger fired: inner needle advances, slots into tumor; outer sheath slides forward cutting the core
5. Needle withdrawn with core specimen in the slot
6. 2-3 cores obtained from same skin puncture (different angulations)
7. Each core placed in formalin (one kept fresh for culture/molecular studies)

Technique - Bone (Jamshidi Needle)

1. Stab incision through skin
2. Jamshidi needle (outer cannula + inner trocar) directed to bone surface
3. Rotatory drilling motion used to penetrate outer cortex
4. Trocar withdrawn; cannula advanced into bone marrow/tumor
5. Cannula rotated to core out tissue
6. Withdrawn; specimen pushed out with stylet
7. Hole plugged with bone wax or methylcellulose

Image Guidance Options

• CT-guided (gold standard for deep/inaccessible lesions)
• Ultrasound-guided (soft tissue, superficial lesions, real-time)
• Fluoroscopy-guided (bone lesions in theatre)
• MRI-guided (rarely, when CT/US insufficient)

Accuracy of CNB

• Overall diagnostic accuracy: 84-98% (multiple series)
• Determining malignant vs. benign: 97% accurate (252-patient series)
• Specific histopathologic diagnosis and grade: 81% accurate
• CT-guided CNB (Ghelman et al.): 85% histologic diagnoses from 76 specimens
• Kattapuram et al.: 92% accurate diagnoses

Advantages over Open Biopsy

• Outpatient procedure
• Lower complication rate
• Less contamination
• Cheaper
• Multiple cores can be taken through one skin puncture

Indications for CNB over Open

• Most primary bone and soft tissue tumors (first-line at specialist centers)
• Deep lesions where open biopsy would be highly morbid
• Metastatic disease confirmation
• When pre-operative chemotherapy is being considered

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Type 3: Incisional (Open) Biopsy

Definition

When to Use (Indications)

• Core needle biopsy inconclusive or non-diagnostic
• Lesions requiring large tissue volume for ancillary studies (cytogenetics, flow cytometry, molecular studies)
• Cartilaginous tumors (chondrosarcoma grade differentiation requires architectural assessment)
• Small, surgically accessible tumors in expendable locations
• When pathologist requests additional tissue after CNB
• Primary lymphoma of bone (needs large tissue for immunophenotyping)

Critical Technical Rules

• Always longitudinal (along the axis of the limb) - NEVER transverse
• Placed within the planned definitive surgical incision
• Must allow en-bloc excision of the entire track with the tumor

• Through a single muscle belly (not intermuscular plane)
• Shortest route to tumor
• Avoid major NV structures

• If cortical bone must be opened: make a round or oval window - NOT rectangular or irregular
• Oval/round windows distribute stress uniformly; rectangular windows create stress risers leading to pathological fracture
• Plug the window with methylmethacrylate (PMMA bone cement) to prevent hematoma and fracture

• If used: elevate limb gently (do NOT exsanguinate with Esmarch bandage - this squeezes tumor cells into circulation)
• Release tourniquet and achieve meticulous hemostasis before closing (contaminated hematoma = contaminated field)

• Send specimen intraoperatively to confirm diagnostic tissue has been obtained
• If negative, take more samples before closing

• If used: exit in-line with the incision (not separately) so drain track can be excised with tumor
• A drain exiting separately from the wound contaminates a whole new tissue corridor

• Close tightly in layers
• Do NOT use wide retention sutures (they contaminate a wider area)
• Apply compression dressing

• Soft-tissue extension of a bone lesion: sample the leading edge (most viable tumor)
• Avoid sampling just the pseudocapsule
• Do NOT sample the center of large tumors (often necrotic)

Advantages

• Maximum tissue for diagnosis
• Allows grading, molecular studies, cytogenetics, flow cytometry
• Best for heterogeneous tumors

Disadvantages

• Higher complication rate (bleeding, infection, wound dehiscence, pathological fracture, hematoma)
• Greater contamination of tissue planes
• Longer recovery
• Should be done only in a specialist center

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Type 4: Excisional Biopsy

Definition

Indications

• Small lesions (< 3 cm) in expendable bones (fibula, rib, clavicle, iliac wing)
• Lesions strongly suspected to be benign (e.g., small enchondroma, fibrous cortical defect)
• Soft tissue lipomas that are clearly benign radiologically
• Superficial, small soft-tissue nodules unlikely to be malignant

Contraindications

• Any lesion where malignancy cannot be excluded prior to excision
• Large tumors (cannot achieve adequate margins)
• Tumors where pre-operative staging is incomplete

Risks

• If malignancy is confirmed on final pathology, the contaminated pseudocapsule margins mean the patient will need re-excision with wider margins, radiation, or in the worst case - amputation
• The "whoops" lesion: excision of what was thought to be benign, found to be malignant

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Type 5: Image-Guided Percutaneous Biopsy

CT-Guided Biopsy

1. Patient positioned in CT gantry
2. Scout images obtained; target lesion identified
3. Needle trajectory planned: avoids NV structures, crosses minimum number of compartments, stays in planned surgical corridor
4. Needle advanced under intermittent CT guidance
5. Position confirmed within lesion before firing/coring
6. Multiple cores obtained (2-3 minimum)

• Precise needle placement
• Avoids neurovascular structures
• Real-time confirmation of needle position within lesion
• Can target soft-tissue component, viable edges, or specific zones

Ultrasound-Guided Biopsy

• Used for superficial soft-tissue masses and vascular lesions
• Real-time needle visualization
• No ionizing radiation
• Cannot penetrate intact cortical bone

Fluoroscopy-Guided Biopsy

• Used for bone lesions accessible under C-arm
• Quick, good for lytic lesions
• Less precise than CT for small or deep lesions

MRI-Guided Biopsy

• Rarely used; MRI-compatible needles required
• Best tissue contrast, but expensive and time-consuming

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Type 6: Trephine Biopsy (Bone Marrow Biopsy)

Specific Use

Technique (Jamshidi - PSIS)

1. Patient prone or lateral decubitus
2. Posterior superior iliac spine identified and marked
3. Local anesthetic to periosteum (most painful step)
4. Small skin incision
5. Jamshidi needle with stylet locked - advanced through skin and subcutaneous tissue to bone
6. Rotatory clockwise-counterclockwise motion used to penetrate cortex
7. Stylet removed; cannula advanced 1.5-2 cm into marrow
8. Rotate 360° CW and then CCW to free the core
9. Withdraw while rotating counterclockwise
10. Extractor used to push out the bone core specimen
11. Placed in formalin; specimen should be 1.5-2 cm long for adequate assessment

Combination with Aspirate

• Aspirate first (before biopsy needle traumatizes marrow): 0.5-2 mL aspirated for cytology, cytogenetics, flow cytometry
• Then trephine core for histology

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Special Situations in Orthopedic Biopsy

Spine Tumors

• Usually CT-guided transpedicular approach
• Coaxial bone needle (Cook's needle) used
• Must plan approach to stay within planned surgical corridor
• Weinstein-Boriani-Biagini classification used to plan which zone to sample

Pelvic Tumors

• High risk area: close proximity to iliac vessels, bowel, bladder
• CT guidance essential
• Consider pre-operative embolization for hypervascular lesions (renal cell carcinoma metastases, thyroid metastases)
• Approach: lateral, not medial (to avoid bowel/bladder contamination)

Suspected Renal / Thyroid Metastases

• Pre-biopsy embolization reduces bleeding risk significantly
• CT-guided core needle is preferred
• Do NOT perform open biopsy without embolization

Infection vs. Tumor (Cannot Differentiate Clinically)

• Rule: Culture what you biopsy and biopsy what you culture
• Always send tissue for both microbiology AND histology
• Acid-fast bacilli (AFB) culture and sensitivity for suspected tuberculosis (6-8 week incubation period required)

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Complications of Biopsy

• Local recurrence rate after open biopsy increases 5-fold (from 7% to 38%) if the scar is not removed at definitive resection
• 5-year survival after local recurrence of osteosarcoma: 29%; Ewing sarcoma: only 14%

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Specimen Handling

1. Never crush the specimen with forceps - use gentle technique
2. Fresh tissue for: cytogenetics, molecular studies, flow cytometry (kept on ice, not formalin)
3. Formalin-fixed (10% buffered formalin): for routine histology and immunohistochemistry
4. Additional aliquot in glutaraldehyde for electron microscopy if needed
5. Label with: patient name, site, surgeon, date, orientation markers if relevant
6. Send with clinical/imaging summary for the pathologist
7. Frozen section intraoperatively: confirms representative tumor tissue obtained before closing

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Choosing the Right Biopsy Method

Suspected Lesion
    |
    ├── Clearly benign, small (< 3 cm), expendable bone?
    |       → EXCISIONAL BIOPSY
    |
    ├── Metastatic disease highly suspected?
    |       → FNAC (fast, cheap) ± CNB
    |
    ├── Primary bone tumor (any size)?
    |       → CORE NEEDLE BIOPSY (CT-guided preferred)
    |       → Open INCISIONAL biopsy if CNB non-diagnostic
    |
    ├── Soft tissue mass, intermediate/large?
    |       → CORE NEEDLE BIOPSY (US or CT-guided)
    |       → Open INCISIONAL biopsy if CNB inconclusive
    |
    ├── Diffuse marrow disease (myeloma, lymphoma)?
    |       → TREPHINE BIOPSY (PSIS) + aspirate
    |
    └── Deep/inaccessible lesion?
            → CT-GUIDED core needle biopsy

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Summary Comparison

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Key Teaching Points (Mnemonics)

• Longitudinal only (never transverse)
• One compartment (single muscle belly)
• Not near neurovascular bundles
• En-bloc excision planned for track

• Round or Oval defect only
• Avoid rectangular/irregular shapes
• Defect plugged (with methylmethacrylate)

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• Campbell's Operative Orthopaedics, 15th ed. (2026), Chapter 26, pp. 1091-1092 - Biopsy section
• Mankin HJ et al., "The hazards of biopsy, revisited." J Bone Joint Surg (1996)
• Agarwal M et al., "Biopsy for Musculoskeletal Tumors - An Orthopaedic Surgeon's Guide." J Clin Orthop (2016)
• Anatomically Based Guidelines for Core Needle Biopsy of Bone Tumors (Radiographics, 2007)
• Biopsy of bone tumors: a literature review, PMC 11164262 (2024)Here is the complete, detailed guide on biopsy techniques in orthopedics:

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Biopsy Techniques in Orthopedics

Introduction and Why It Matters

• Major diagnostic errors in 13.5% of patients
• Complication rate of 15.9%
• Unnecessary amputations in 3%
• Problems 2-12x more frequent when biopsy was performed at non-specialist centers

"Errors in diagnosis, nonrepresentative or technically poor biopsy specimens, and wound complications have been found to occur more frequently when the biopsy was done by a surgeon at a referring institution rather than by an orthopaedic oncologist." - Campbell's Operative Orthopaedics, 15th ed. (2026)

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Pre-Biopsy Planning (Mandatory Steps)

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The 10 Golden Rules of Orthopedic Biopsy (Mankin's Principles)

1. Refer before you biopsy - if primary malignancy is suspected, send to a musculoskeletal oncologist first
2. The biopsy track is contaminated - treat both needle and open incision tracks as permanently seeded with tumor cells
3. The track must be excised en bloc with the tumor at definitive surgery
4. Incision placement is critical - must lie within the planned limb salvage incision
5. Longitudinal incisions only - transverse incisions on limbs are absolutely forbidden
6. Single compartment approach - never violate intermuscular planes
7. Avoid major neurovascular structures at all costs
8. Meticulous hemostasis - hematoma dissects tumor cells through tissue planes
9. Plugging of bone windows with methylmethacrylate cement to prevent fracture and hematoma
10. The biopsy surgeon = the definitive surgeon (or must communicate in intimate detail)

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Classification of Biopsy Techniques

BIOPSY TECHNIQUES
│
├── PERCUTANEOUS (Minimally Invasive)
│   ├── Fine-Needle Aspiration Cytology (FNAC)
│   ├── Core Needle Biopsy (Tru-Cut / Jamshidi)
│   └── Image-Guided (CT / Ultrasound / Fluoroscopy)
│
└── OPEN (Surgical)
    ├── Incisional Biopsy (Gold standard tissue yield)
    └── Excisional Biopsy (Diagnosis + treatment together)

• Trephine Biopsy (bone marrow)

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Type 1: Fine-Needle Aspiration Cytology (FNAC)

Principle

Indications

• Strongly suspected metastatic bone disease (95% accuracy)
• Suspected osteomyelitis / infection (for culture + sensitivity)
• Lymph node assessment
• Known primary tumor: rapid confirmation of recurrence
• Lesions very close to neurovascular bundles (thin needle = minimal contamination)

Technique

1. Clean skin with antiseptic
2. Local anesthetic to skin and subcutaneous tissue (do not over-inject - extends contamination zone)
3. 22-25G needle on a 20 mL syringe introduced directly into tumor
4. Strong suction applied while making 3-4 passes through tumor in different directions
5. Release suction before withdrawing needle (prevents aspirate going back into syringe)
6. Material expressed onto glass slides, smeared, and fixed immediately
7. Staining: Giemsa, Papanicolaou (Pap), or Diff-Quik

Accuracy

• Distinguishing malignant vs. benign: ~90%
• Specific tumor type identification: 60-70% (limited without architecture)
• Metastatic disease: ~95% (most accurate application)

Advantages

• Outpatient, no incision
• Essentially zero track-seeding risk (< 1 mm needle)
• Rapid results (same day)
• Very low complication rate
• Cheap

Disadvantages

• No tissue architecture (cannot grade primary tumors)
• Cannot perform immunohistochemistry, cytogenetics, or flow cytometry reliably
• Requires a specialist cytopathologist
• Not adequate for primary bone sarcomas as the sole biopsy

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Type 2: Core Needle Biopsy (CNB)

Needles Used

• A spring-loaded gun mechanism reduces crushing artifact and patient discomfort
• Disposable guns available commercially
• Needle size: typically 14-18 gauge

Technique - Soft Tissue (Tru-Cut Gun)

1. Plan needle trajectory to be within planned surgical incision corridor
2. Minimal local anesthetic (over-infiltration widens contamination zone)
3. Small stab skin incision with No.11 blade
4. Spring-loaded biopsy gun introduced until tip at tumor margin
5. Safety released, gun fired: inner needle advances into tumor, sheath cuts core
6. Entire assembly withdrawn; core removed from slot and placed in formalin
7. Repeat 2-3 times through the same skin puncture at slightly different angles
8. One core kept fresh (unfixed) for cytogenetics/molecular studies

Technique - Bone (Jamshidi)

1. Stab incision in line with planned surgical incision
2. Jamshidi needle (with inner trocar locked) directed to bone cortex
3. Rotatory drilling motion (clockwise + counterclockwise alternating) to penetrate outer cortex
4. Feel for loss of resistance when marrow cavity entered
5. Inner trocar removed; cannula advanced further into tumor
6. Rotate cannula to core out tissue
7. Withdraw while rotating; use stylet/extractor to push specimen out from tip end
8. Plug cortical hole with bone wax or PMMA cement
9. Take 2-3 cores

Image Guidance

Accuracy of CNB

• Overall diagnostic accuracy: 84-98% across multiple studies
• Malignant vs. benign determination: 97% (series of 252 patients)
• Specific diagnosis and grade: 81%
• CT-guided series (Ghelman): 85% histologic diagnoses
• CT-guided series (Kattapuram et al.): 92% accurate diagnoses
• Metastatic disease: 95% (most accurate)
• Benign primary tumors: ~82% (least accurate - may need open biopsy)

Advantages over Open Biopsy

• Outpatient procedure (no general anesthesia needed)
• Lower complication rate
• Preserves tissue architecture (unlike FNAC)
• Multiple cores from single skin puncture
• Smaller contamination zone
• Faster recovery

When CNB Should Be Escalated to Open Biopsy

• Non-diagnostic CNB (repeat CNB first; if still non-diagnostic - open biopsy)
• Cartilaginous lesions (grading chondrosarcoma requires architecture and cellularity assessment over large area)
• Primary lymphoma of bone (needs ample tissue for immunophenotyping)
• When ancillary studies require more tissue than cores provide

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Type 3: Incisional (Open) Biopsy

Definition

Indications

• CNB non-diagnostic or inconclusive
• Large primary bone tumors needing grading
• Cartilaginous tumors (chondrosarcoma grading)
• Lymphoma of bone
• Complex tumors requiring cytogenetics, flow cytometry, molecular studies
• Surgeons performing definitive surgery at the same center

Technique - Step by Step

• Always longitudinal along the limb axis
• Centered over the most accessible/prominent part of the tumor
• Shortest path to tumor
• Must be placeable within the definitive surgical incision

• Through a single muscle belly (e.g., through vastus lateralis, not between vastus and rectus)
• Never through intermuscular planes (these connect to multiple compartments - wide contamination)
• Avoid neurovascular bundles

• Sample the leading edge (soft-tissue extension) - most viable, most representative
• Avoid the center of large tumors (necrotic, non-diagnostic)
• Avoid sampling just the pseudocapsule
• Take 2-3 pieces of representative tissue

• Create a round or oval defect - NOT rectangular, not irregular
• Round/oval windows distribute mechanical stress uniformly, preventing pathologic fracture
• Rectangular windows create stress risers at corners
• Plug with methylmethacrylate (PMMA) after sampling to prevent hematoma and reduce fracture risk

• Send tissue to pathologist intraoperatively
• Confirms: "Is this diagnostic tumor tissue?"
• If negative: take more tissue before closing

• Release tourniquet and achieve perfect hemostasis before closing (contaminated hematoma dissects tumor cells everywhere)
• Close tightly in layers
• No wide retention/tension sutures
• If drain needed: exit in line with the wound (NOT through a separate stab far from the incision)

What NOT to Do

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Type 4: Excisional Biopsy

Definition

Indications

• Small lesions (< 3 cm) in expendable bones: fibula head, rib, small bones of hand/foot, clavicle, iliac crest
• Lesions where imaging very strongly suggests benign (osteoid osteoma, fibrous cortical defect, small enchondroma)
• Small superficial soft-tissue masses radiologically consistent with lipoma

Risks and "Whoops" Lesion

• No pre-operative staging (compromised)
• A contaminated pseudocapsule (margins likely inadequate)
• Need for re-excision with much wider margins, possible radiation, or amputation

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Type 5: Trephine Biopsy (Bone Marrow Biopsy)

Specific Application

Site: Posterior Superior Iliac Spine (PSIS)

Technique - Jamshidi at PSIS

1. Patient prone or lateral decubitus
2. PSIS identified and marked (most accessible, greatest marrow volume)
3. Local anesthetic - skin, subcutaneous, and periosteum (most painful; wait 2-3 minutes)
4. Small skin incision with No. 11 blade
5. Jamshidi needle with stylet locked - advanced to bone, then rotated through cortex
6. Once cortex penetrated (sudden loss of resistance): advance 1-2 cm into marrow
7. Rotate 360° CW then CCW to sever specimen from surrounding marrow
8. Withdraw slowly while rotating counterclockwise
9. Extractor rod inserted through the top to push specimen out distally (not proximally - avoids crushing)
10. Specimen should be 1.5-2.5 cm long for adequate assessment

Aspirate + Trephine Together

• Aspirate first (before trephine traumatizes marrow architecture): 0.5-2 mL into EDTA tubes
  • Aspirate for: morphology, flow cytometry, cytogenetics (karyotype/FISH), molecular studies
• Trephine after: for histology, IHC, gene rearrangement studies on fixed tissue

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Specimen Handling - Universal Rules

• Always send with clinical and imaging summary for the pathologist
• Label clearly: patient ID, site, orientation if relevant
• Do not crush with forceps - use atraumatic handling

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Complications

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Summary Table

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Key Mnemonics

• Longitudinal only
• One compartment (single muscle)
• Not near neurovascular structures
• En-bloc excision planned for entire track

• Round or Oval defect only (never rectangular)
• Avoid stress risers
• Defect plugged with PMMA immediately

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• Campbell's Operative Orthopaedics, 15th ed. (2026), Chapter 26, pp. 1091-1092
• Mankin HJ et al. "The hazards of the biopsy, revisited." J Bone Joint Surg Am. 1996;78(5):656-663
• Agarwal M et al. "Biopsy for Musculoskeletal Tumors." J Clin Orthop. 2016
• Anatomically Based Guidelines for Core Needle Biopsy of Bone Tumors. Radiographics 2007;27(1)
• Biopsy of bone tumors: a literature review. PMC 11164262 (2024)