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< Back Dr. Cemil AKTAN Stability Principles Spinal stability refers to the spine’s ability to maintain proper alignment and load transmission under physiological conditions without producing pain, deformity, or neurological injury. It is governed by the integrated function of three interdependent subsystems — passive (osseoligamentous structures), active (musculotendinous support), and neural control (proprioceptive regulation). Loss of stability — due to trauma, degeneration, iatrogenic injury, or systemic disease — leads to abnormal motion, pain, and potential neural compromise. Therefore, preservation or restoration of spinal stability is a core principle in spine surgery, achieved through fusion, instrumentation, decompression with stabilization, or corrective osteotomies. Spinal Stability Principles Definition: Stability maintenance of vertebral alignment under physiological loads, ensuring load transmission, motion, and neural protection without neurological injury, deformity, or pain. Spine Core Functions: Transmits and distributes spinal loads Permits multidirectional motion Protects the spinal cord and neural structures Important components of stability 1- Spinal Stability Subsystems · Defined by Panjabi · In a healthy spine, stability is maintained through the integrated function of three subsystems: passive, active, and neural control. Passive subsystem: Includes the intervertebral discs, ligaments, facet joints, vertebrae, and passive muscle support. Active subsystem: Comprises spinal muscles, tendons, and thoracolumbar fascia. Neural control subsystem: The nervous system regulates muscle activation based on proprioceptive feedback. 2- Functional Spinal Unit (FSU) · Smallest motion segment; 70% load via vertebral body/discs, 30% via facets; ensures motion and neural protection (Figure 1). 3- Three-column Model · Spinal trauma and stability have been classified using the “Three-column model” proposed by Denis in 1983 (Figure 2). · This system divides the spine into three anatomical columns, with the anterior column comprising the anterior longitudinal ligament and the anterior two-thirds of the vertebral body. · The middle column comprises of the posterior one-third of the vertebral body and posterior longitudinal ligament. · The posterior column consists of the vertebral facets and posterior ligaments. 4- Posterior ligamentous complex (PLC) · Includes facet capsules, interspinous ligaments, ligamentum flavum, and supraspinous ligaments (Figure 2). · Major stabilizer (supraspinous, interspinous, flavum, facet capsule); · Interspinous ligament; A Thin membrane between spinous processes; resists hyperflexion; easily torn in trauma. · Supraspinous ligament; Continuation of ligamentum nuchae below C7, runs along the spinous processes, first to fail in flexion · Ligamentum flavum: Connects adjacent laminae; posterior to thecal sac; hypertrophy/infolding → canal stenosis. · Facet joint capsules are major passive stabilizers; their failure increases motion and decreases stiffness · Disruption = mechanical instability. · Central in Denis’ 3-column model (posterior column) and TLICS PLC integrity decisive for surgery vs. conservative. 5- Spinal ligaments; · C2–sacrum, Predominantly collagenous; ligamentum flavum is elastin-rich, supporting spinal stability (Figure 3) · ALL: Extends occiput–sacrum, broader over bodies, narrower at discs; deep fibers span 1 level, superficial 3–5; resists hyperextension. · PLL: Runs posterior to vertebral bodies; widest at discs, narrow over bodies; thins laterally → cervical disc herniation risk · Intertransverse ligaments: Span between transverse processes; usually preserved in posterolateral fusion. · Ligamentum nuchae: Continuation of supraspinous (C7–occiput); Dorsal raphe (muscle attachment), ventral septum (C2– C6 to interspinous + AA/AO), some fibers to dura → tension in flexion (Figure 4). (AA: Atlanto Axial, AO: Atlanto Oksipital) · Atlantoaxial (AA) Joint Ligament stability: Transverse ligament = principal stabilizer; alar ligaments + tectorial membrane = secondary, but become primary if transverse ruptures (Figure 5). · Regional variation: Lumbar ligaments are strongest → stability; upper cervical is weakest → flexibility (Figure 6). 6- Spinal motion unit: · Each vertebral junction has 3 joints — intervertebral disc–endplate complex + bilateral facet (zygapophyseal) joints. · Facet joint orientation varies regionally, directing motion and limiting instability. · Cervical (45° transverse–frontal): Allows flexion–extension, lateral bending, rotation (high mobility, less stability) · Thoracic (60° transverse, 20° frontal): Allows lateral flexion + rotation; limits flexion–extension · Lumbar (sagittal): Promotes flexion–extension; resists rotation + shear Clinical instability · Dysfunction in one of the three subsystems (passive, active, neural) may be compensated by the others; however, when compensatory capacity is exceeded, mechanical instability ensues, leading to clinical symptoms. Clinical manifestations of spinal instability Pain: Predominantly mechanical back or neck pain, exacerbated by motion and alleviated by rest, often localized to the unstable segment. Mechanical symptoms: Sensations of “catching,” “locking,” or “giving way” during movement, reflecting abnormal intersegmental motion. Neurological signs: Radiculopathy or, in advanced cases, myelopathy due to dynamic neural compression. Postural abnormalities: Progressive deformity, altered sagittal or coronal alignment, and impaired global spinal balance. Muscle-related findings: Paraspinal overactivation → fatigue, spasms, reflexive guarding as compensatory stabilization. Functional limitations: Reduced endurance for standing, sitting, or walking, with activity-related symptom aggravation. · Abnormal motion signs: Instability catch (sudden block/release), painful arc (transient pain range), crepitus (click/grating), shake phenomenon (uncontrolled trembling in flex–ext). Surgical Importance of Stability Preservation or restoration of spinal stability is a primary surgical goal. Adequate stabilization is critical to: o Protect neural elements (prevent compression or further injury) o Prevent deformity progression (kyphosis, listhesis, collapse) o Maintain functional mobility and quality of life Failure to achieve stability may lead to neurological deficits, pain, and structural collapse. Surgical Options for Stabilization Instrumentation and Fusion Pedicle screw–rod constructs (open or percutaneous) Anterior or posterior interbody fusion (ALIF, PLIF, TLIF, LLIF) Posterolateral fusion techniques Cement Augmentation Vertebroplasty, kyphoplasty for osteoporotic or tumoral instability Decompression with Stabilization Laminectomy or corpectomy combined with fixation to avoid iatrogenic instability Corrective Procedures Osteotomies (Smith-Petersen, pedicle subtraction, vertebral column resection) for deformity correction while restoring alignment and stability References 1- Ramachandran M, editor. Basic orthopaedic sciences. CRC Press; 2018 Sep 3. (Figure 1) 2-https://www.anatomystandard.com/ (Figure 4,5) 3- https://www.coloradospineinstitute.com/ (Figure 3) 4- White AA, Panjabi MM. Clinical Biomechanics of the Spine. 2nd ed. Philadelphia: JB Lippincott; 1990(Figure 6) 5-Benzel EC. Spine Surgery: Techniques, Complication Avoidance, and Management. 5th ed. Elsevier; 2021. 6-Rothman RH, Simeone FA. The Spine. 7th ed. Philadelphia: Elsevier; 2018. Previous Next

< Back Alper DUNKI Articular Cartilage: Structure, Components, and Clinical Relevance Overview Spot Knowledge – Articular Cartilage Composition: 95% ECM (water, collagen, proteoglycans), 5% chondrocytes Water: 65–80%, enables load-bearing, nutrient transport Collagen: >50% dry weight, mainly type II (90–95%); tensile strength Proteoglycans: 10–15% dry weight; aggrecan + GAGs provide compressive resilience Zones: Superficial (parallel collagen, friction reduction) Transitional (irregular, load distribution) Deep (vertical, compressive strength) Calcified (anchors to bone) Functions: Low-friction motion, load distribution, joint stability, resistance to forces Clinical relevance: Limited healing (avascular) Water/collagen/PG imbalance → osteoarthritis Collagen II & X defects → chondrodysplasias PG loss → elasticity ↓, cartilage breakdown Articular Cartilage: Structure, Components, and Clinical Relevance Overview Articular cartilage is composed predominantly of extracellular matrix (ECM, ~95%) and a small number of chondrocytes (~5%). Chondrocytes maintain ECM homeostasis throughout life. The main components of ECM are water, collagen, and proteoglycans. Water Water accounts for 65–80% of cartilage. It is 80% in the superficial zone and 65% in the deep zone. Water plays a critical role in load-bearing by deforming in response to compression. Its movement through ECM pores, along with frictional resistance and pressurization, provides high load-bearing capacity. Facilitates the transport of nutrients and metabolites. Alterations in water content affect permeability, stiffness, and elastic modulus. Collagen Collagen constitutes more than 50% of the dry weight and 10–20% of the wet weight. Provides tensile and shear strength. Type II collagen accounts for 90–95% of the total. Minor collagens include types V, VI, IX, X, and XI. Type VI: increases in early osteoarthritis. Type X: produced by hypertrophic chondrocytes during endochondral ossification; associated with calcification. The unique amino acid composition (glycine, proline, hydroxyproline, hydroxylysine) forms a triple-helix structure. Covalent cross-links between fibrils enhance durability. Defects in collagen type II and X can lead to achondroplasia, spondyloepiphyseal dysplasia, Kniest dysplasia, and metaphyseal chondrodysplasia. Proteoglycans Proteoglycans constitute 10–15% of dry weight and provide compressive strength. Synthesized by chondrocytes and secreted into the ECM. Contain glycosaminoglycans (GAGs) composed of repeating disaccharides: chondroitin sulfate and keratan sulfate. Chondroitin sulfate decreases with age, keratan sulfate increases. The most important proteoglycan is aggrecan, which consists of a long protein core with GAG side chains. Aggrecan molecules aggregate with hyaluronic acid and link proteins, imparting resilience to the matrix. Interact with collagen fibrils to form a robust network. Zones Histologically, articular cartilage is organized into four zones: Superficial zone: Collagen fibers are aligned parallel; reduces friction. Transitional zone: Fibers are irregular; distributes load. Deep zone: Fibers are vertically aligned; provides high compressive strength. Calcified zone: Anchors cartilage to bone. Functions Provides low-friction joint motion. Distributes loads and contributes to joint stability. Resists compressive and tensile forces. Maintains nutrient transport and metabolic homeostasis. Clinical Relevance Cartilage is avascular, with limited intrinsic healing capacity. Alterations in water, collagen, and proteoglycan content are associated with degenerative disorders such as osteoarthritis. Defects in type II and X collagen result in genetic chondrodysplasias. Loss of proteoglycans leads to reduced elasticity and cartilage breakdown. Reference 1. Guo L, Li P, Rong X, Wei X. Key roles of the superficial zone in articular cartilage physiology, pathology, and regeneration. Inflamm Regen . 2024;44:21. doi:10.1186/s41232-022-00202-0 2. Alcaide-Ruggiero L, Cugat R, Domínguez JM. Proteoglycans in Articular Cartilage and Their Contribution to Chondral Injury and Repair Mechanisms. Int J Mol Sci . 2023;24(14):11472. doi:10.3390/ijms241411472 3. Karpiński R, Szczodry M, Zawadzki G. Articular Cartilage: Structure, Biomechanics, and the Potential of Regenerative Medicine. Appl Sci . 2025;15(12):6896. doi:10.3390/app15126896 Previous Next

< Back Preoperative Planning Preoperative templating is a cornerstone of modern arthroplasty planning. It helps anticipate anatomical variation, guides implant selection and positioning, and prevents intraoperative surprises such as limb length discrepancy, instability, or cortical perforation. Traditional acetate templating with preset magnification (commonly 120%) often leads to magnification errors (actual 109–128%), while digital templating has improved precision and reproducibility. However, digital 2D methods still rely on accurate radiographic calibration and cannot fully account for 3D bone geometry—especially in complex or dysplastic anatomy. 3D CT-based templating offers superior accuracy and spatial understanding but remains limited by cost, radiation exposure, and logistics. Thus, digital 2D templating remains the gold standard in daily arthroplasty practice, complemented by emerging AI-assisted tools. Total Hip Arthroplasty (THA) Preoperative templating in THA is essential for anticipating anatomic and technical challenges such as center of rotation, limb length discrepancy, offset, and acetabular or femoral geometry . Accurate templating guides neck resection level , predicts implant size , and minimizes complications like dislocation, limb inequality, and periprosthetic fracture . Spot Knowledge AspectKey PointsTraditional (Acetate) Templating Performed with 120% preset magnification; error-prone (true magnification 109–128%). Digital 2D Templating More precise, faster, permanent record; depends on proper calibration. 3D CT-Based Templating Offers superior anatomical visualization and 86–94% implant prediction accuracy but limited by cost, radiation, and logistics. Calibration Marker (ECM) Must be placed at hip center level; misplacement (too anterior/lateral) distorts scaling.Institutional Protocols Standardized ECM use improves accuracy and reproducibility in templating results. 💡 Common error: placing the calibration ball on the table or thigh — leads to magnification mismatch and oversizing. Clinical Implications Standardized radiographic protocols (scaling ball at hip center) enhance reproducibility. Digital 2D templating remains the current gold standard in daily practice. 3D methods may become routine as low-dose CT and AI-based segmentation evolve. Total Knee Arthroplasty (TKA) Overview Digital templating for TKA assists in predicting implant sizes and alignment , aiming to optimize motion and minimize stiffness or loosening. However, its impact on postoperative function and alignment remains limited . Spot Knowledge AspectKey Findings Accuracy : Predicts component size within one size of the final implant in most cases. Alignment & Function: No consistent effect on postoperative alignment, ROM, or PROMs. Efficiency: Adds cost and time (software, licensing, training). Alternatives: Demographic-based models (height, sex, BMI) predict size equally well. Clinical Use: Best suited for inventory and surgical planning , not for outcome prediction. 💡 Tip: Use templating as a preoperative checklist tool, not as a strict sizing determinant. Clinical Implications Digital templating is a useful planning adjunct but not an outcome determinant. Demographic prediction models may replace templating in routine TKA workflows. Integration with AI-based morphometrics could improve predictive precision. Clinical Relevance Standardized imaging protocols (AP pelvis with centered scaling ball) are essential for reproducible THA planning. Digital templating reduces operative time, implant mismatch, and intraoperative guesswork. TKA templating , while less predictive of functional outcome, assists in logistics and implant preparation . In both THA and TKA, templating accuracy improves with experience, consistent magnification calibration , and software familiarity . Emerging AI-assisted 3D templating is likely to redefine precision planning and patient-specific arthroplasty. 💡 Clinical Pearl: Calibration marker placed at hip joint level (not on the table) prevents oversizing — a small detail that avoids major intraoperative complications. Common Pitfalls ⚠️ Oversized components due to miscalibrated images → higher fracture risk. ⚠️ Ignoring 3D bone morphology in dysplastic or post-traumatic hips → malposition risk. ⚠️ Excessive reliance on digital software without radiographic standardization → poor reproducibility. References Kothari M, et al. Digital Templating for Total Hip Arthroplasty: Accuracy and Clinical Relevance. J Arthroplasty. 2023. O’Neill S, et al. Evaluation of Calibration Marker Position in THA Templating. Bone Joint J. 2022;104-B(6):742–749. Sunil T, et al. Digital Templating Accuracy in Total Knee Arthroplasty. Cureus. 2024;16:e48720. MacDessi SJ, et al. 2D vs 3D Preoperative Planning in Arthroplasty. Bone Joint J. 2024. Guyen O, et al. Calibration and Digital Planning in Modern Hip Surgery. J Arthroplasty. 2023. Previous Next

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< Back Dr. Ahmet Müçteba YILDIRIM Istanbul Medeniyet University, Orthopedics and Traumatology Department Oncologic Orthopaedics ahmetmuctebaitf@gmail.com Previous Next