< Back Alper DUNKI Skeletal Muscle Spot Knowledge Structure Motor unit = motor neuron + innervated fibers Sarcomere = contractile unit (actin + myosin) Membranes: Sarcolemma, T-tubule, SR → form “triad” for excitation–contraction coupling Connective layers: Endomysium, perimysium, epimysium Neuromuscular Transmission ACh release at NMJ → depolarization → Ca²⁺ release → contraction Drugs: Non-depolarizing blockers → receptor antagonists Depolarizing (succinylcholine) → persistent depolarization AChE inhibitors → prolong transmission Disorder: Myasthenia gravis → ↓ ACh receptors Contraction Twitch → summation → tetanus Contraction types: isotonic, isokinetic, isometric Eccentric > concentric in force (but ↑ injury risk) Force ∝ cross-sectional area + fiber length + pennation angle Fiber Types Type I: Slow, oxidative, fatigue-resistant Type IIA: Intermediate Type IIB: Fast, glycolytic, fatigue-prone Training shifts capacity (endurance ↑ mitochondria, oxidative enzymes) Energetics Phosphagen system → ATP + creatine phosphate (seconds) Anaerobic glycolysis → lactate (20–120 sec) Aerobic metabolism → Krebs + oxidative phosphorylation (long-term, efficient) Injury & Repair Repair: Macrophages + cytokines → activate satellite cells Limitations: Fibrosis may impair full recovery Clinical: DOMS = 24–72h after eccentric work Strains = at myotendinous junction Lacerations → scar tissue Denervation → fibrillation potentials (2–4 weeks), ↑ ACh sensitivity Immobilization Leads to rapid atrophy, loss of strength Atrophy worse in slack position Muscles in stretch add sarcomeres but still ↓ cross-sectional area Skeletal Muscle: Structure, Function, Energetics, Injury, and Repair General Information Skeletal muscles are innervated by the peripheral nervous system. They provide voluntary movement of the axial and appendicular skeleton. A motor unit consists of a single motor neuron and the muscle fibers it innervates. Hierarchical Structure of Muscle A muscle fiber is a multinucleated, highly specialized cell. The contractile unit is the sarcomere. Sarcomeres are aligned in series to form myofibrils. Mechanical coupling between myofibrils is provided by intermediate filaments. Each fiber is surrounded by endomysium, fascicles by perimysium, and the whole muscle by epimysium. Membrane Systems The T-tubule system originates as invaginations of the sarcolemma and transmits excitation to myofibrils. The sarcoplasmic reticulum stores, releases, and reuptakes calcium. The T-tubule and two adjacent terminal cisternae form the “triad” structure. This arrangement enables rapid and synchronized activation of contraction. Composition and Organization of the Sarcomere The thick filament is myosin; the thin filament is actin. Tropomyosin covers myosin-binding sites on actin in the resting state. Upon calcium binding, the troponin complex induces a conformational shift of tropomyosin, initiating actin–myosin interaction. The A band (actin + myosin), I band (actin), H band (myosin), and Z line create the typical striation pattern. During contraction, the sarcomere shortens; filament lengths remain constant, but overlap increases. Neuromuscular Junction (NMJ) and Transmission Each muscle fiber is activated by a single motor endplate. Acetylcholine (ACh) is released from the presynaptic terminal, activates postsynaptic receptors, and generates an action potential. The impulse propagates via the T-tubule/SR network. ACh is rapidly degraded by acetylcholinesterase. Transmission can be modulated pharmacologically: – Non-depolarizing agents competitively block receptors. – Depolarizing agents (succinylcholine) cause persistent depolarization. – AChE inhibitors prolong transmission by preventing ACh degradation. Myasthenia gravis is characterized by a reduction in postsynaptic ACh receptors. Mechanical Responses of Muscle A single stimulus produces a “twitch” response. Repeated stimuli lead to temporal summation and tetanus. Force is proportional to the physiological cross-sectional area; fiber length and pennation angle are also determinants. Types of contraction: isotonic, isokinetic, isometric; concentric (shortening) and eccentric (lengthening) behaviors occur. According to the force–velocity relationship, eccentric contraction produces the greatest tension and carries higher risk of injury. Fiber Types and Performance Type I fibers are slow, oxidative, and fatigue-resistant. Type IIA fibers display intermediate properties. Type IIB fibers are fast, glycolytic, and fatigue rapidly. Training can modify distribution and oxidative capacity; endurance training increases mitochondrial content and oxidative enzyme activity. Energy Systems Skeletal muscle contraction is fueled by three main pathways: Phosphagen system: Provides very short-term, anaerobic energy via ATP and creatine phosphate. Anaerobic glycolysis: Produces lactate from glucose, supporting 20–120 seconds of high-intensity activity. Aerobic metabolism: Krebs cycle and oxidative phosphorylation yield high ATP output; fat and protein substrates can also be utilized. Endurance training enhances oxidative efficiency and promotes fat utilization. Muscle Injury and Repair Repair is mediated by cytokines released from neutrophils, monocytes/macrophages, fibroblasts, and endothelial cells. Necrotic fibers are cleared by macrophages. The source of regeneration is satellite cells , which are activated upon injury. Concurrent fibrosis can limit full functional recovery. Delayed-onset muscle soreness (DOMS) arises 24–72 hours after eccentric loading; edema and increased intramuscular pressure are implicated. Contusions involve hematoma, inflammation, and variable regeneration; myositis ossificans may develop within 2–4 weeks. Muscle strains typically occur at the myotendinous junction in muscles crossing two joints; incomplete tears show early inflammation and force reduction with recovery within a week (experimental data). Complete ruptures present with contour deformity. Healing after laceration usually results in scar tissue; regeneration and reinnervation are limited. Denervation manifests within 2–4 weeks with fibrillation potentials and increased ACh sensitivity. Immobilization and Disuse Rapid atrophy, loss of strength, and increased fatigability occur. Myofibrillar loss is the main cellular finding. The length at which the muscle is immobilized is important: atrophy is greater in a slack position (e.g., quadriceps in knee extension). Muscles held under stretch add new sarcomeres, partially compensating for atrophy, although cross-sectional area continues to decrease. Clinical Implications Selection of anesthetics and neuromuscular blockers is based on NMJ physiology. Eccentric loading should be appropriately dosed in rehabilitation. Early and adequate loading supports mitochondrial and oxidative adaptations. Timing of inflammation and duration of immobilization are critical in limiting fibrosis and optimizing satellite cell response after injury. Summary This overview presents the cellular and mechanical foundations of skeletal muscle, its energy utilization, adaptive responses, and the dynamics of injury and repair in relation to clinical decision-making. References 1. Jin JB, Zhao D, Wu H, et al. Metabolic and molecular regulation in skeletal muscle function and regeneration. Front Cell Dev Biol . .doi:10.3389/fcell.2025.1651553 2. Yeowell GJ, Dunbar PJ, Carré MJ, Tarsuslugil A, Mason PH, Hennessey P. Molecular mechanisms of muscle wasting in muscle disuse, denervation, and chronic disease. J Cachexia Sarcopenia Muscle . 2023;14(3):799–815. doi:10.1002/jcsm.13098 3. Brorson J, Lin L, Wang J, et al. Complementing muscle regeneration—fibro-adipogenic progenitor and macrophage-mediated repair of elderly human skeletal muscle. Nat Commun . 2025;16:5233. doi:10.1038/s41467-025-60627-2 Previous Next

Concise orthopaedic education for residents and specialists, including surgical guides, core topics, and case-based learning." Where Orthopedic Minds Meet & Share OrthoRico is a modern orthopedic education platform designed for residents and specialists, offering evidence-based content, case-based learning, and step-by-step illustrated surgical guides. Why OrthoRico ? Learning and growing in orthopedics should be collaborative, visual, and accessible. OrthoRico is a non-commercial, academic platform created by and for orthopedic professionals. Whether you're a resident preparing for exams or a surgeon looking for clear visual guidance, OrthoRico offers: Evidence-based summaries of core orthopedic topics Step-by-step illustrated surgical procedures Real clinical cases and exam-style questions A growing community of orthopedic minds sharing knowledge Everything is peer-driven. Free. And focused on practical learning. Explore Our Sections Core Orthopedic Topics Each topic aims to provide concise information and key points about the subject, serving as a guide for orthopedic assistants and specialists. Read More Surgical Guides This section offers step-by-step surgical techniques, providing detailed instructions and insights for orthopedic procedures. Read More Literature Updates This section provides the latest research, studies, and reviews in the field of orthopaedics. Stay informed with the most recent advancements and evidence-based practices. Read More Contributors & Acknowledgements This section highlights the valuable contributions of authors, researchers, and professionals who have shared their expertise to enhance the content. Read More This Week’s Highlights Optimal Tightrope Positioning for Adequate Syndesmotic Stabilization in Simulated Syndesmotic Injuries Alignment Techniques in Total Knee Arthroplasty Short-term contemporary outcomes for staged versus primary lower limb amputation in diabetic foot disease Mirels' Score for Upper Limb Metastatic Lesions: Do We Need a Different Cutoff for Recommending Prophylactic Fixation? Working With the Best Associates & Partners

< Back Toddler’s Fracture (Tibia) toddlers-fracture Previous Next

< Back Optimal Tightrope Positioning for Adequate Syndesmotic Stabilization in Simulated Syndesmotic Injuries Use of syndesmotic suture button fixation has gained in popularity for treating an injury to the tibiofibular syndesmosis. Biomechanical fixation stability with suture button device (TightRope; Arthrex, Naples, FL) placed at 4 distances from the tibiotalar joint line (0.5, 1.5, 2.5, and 3.5 cm) and 3 trajectories (anterior, medial, and posterior) were studied using cadaveric lower extremities with created syndesmotic injuries. Fixation placed at 0.5 or 1.5 cm from the joint line in medial or posterior trajectories resulted in the lowest increases in fibular rotation. More proximal or anterior placements led to increased fibular motion and decreased rotational stability. 🧠 Key Points Syndesmotic suture button placement 0.5–1.5 cm from the joint line provides the most rotationally stable fixation. Medial and posterior trajectories are more stable than anterior placements. Proximal placements beyond 1.5 cm increase fibular motion and reduce stability. Ankle width changes were minimal but increased slightly with anterior or proximal placement. Biomechanical cadaveric testing simulates in vivo weightbearing and rotational loads. Foot & Ankle Orthopaedics (2025) DOI: 10.1177/24730114251342243 Previous Next

< Back DISH (Diffuse Idiopathic Skeletal Hyperostosis) Previous Next

< Back Alper DUNKI Bone and Joint Biology Bone Functions: Support, mineral homeostasis, marrow housing Bone Types: Long (endochondral), flat (intramembranous) Macrostructure: Cortical → dense, load-bearing Trabecular → porous, marrow-rich, weak in osteoporosis Cells: Osteoblasts (matrix formation, Runx2, osterix) Osteocytes (mechanosensors, RANKL secretion) Osteoclasts (resorption, RANKL/M-CSF, inhibited by OPG) Matrix: Mineral (HA, TCP) + collagen (type I) + growth factors (BMP, TGF-β, IGF) Bone Homeostasis: Balance of formation/resorption → disrupted in osteoporosis, osteopetrosis Fracture Healing: Primary → direct, stable fixation Secondary → hematoma, callus, endochondral ossification, remodelling Therapies: Bisphosphonates, PTH (intermittent), anti-RANKL, calcitonin Synovial Joint: Cavity, capsule, cartilage, synovium (Type A & B cells), synovial fluid (HA, lubricin); proprioception (A fibers), pain (C fibers). Non-Synovial Joints: Symphysis (fibrocartilage, e.g. pubic symphysis) Synchondrosis (cartilage-only, e.g. costal, cranial base) Syndesmosis (fibrous, e.g. distal tibiofibular) Bone Functions: Provides mechanical support, regulates mineral homeostasis, harbors bone marrow elements. Types: Long bones: Formed via endochondral ossification from a cartilage model. Flat bones: Formed via intramembranous ossification directly from mesenchymal tissue. Anatomy: Diaphysis: Cortical bone tube enclosing the medullary canal with trabecular bone; surfaces consist of periosteum and endosteum. Metaphysis: Transition zone between epiphysis and diaphysis; composed of loose trabecular bone. Epiphysis: Articular end containing subchondral bone and the growth plate. Vascular and neural supply: Neurovascular bundles enter through the periosteum and run within Haversian and Volkmann canals. Inner two-thirds of cortical bone are supplied by the nutrient artery, while the outer one-third is nourished by periosteal vessels. Macrostructure: Cortical bone: Dense, load-bearing; serves as boundary in metaphysis/epiphysis. Trabecular bone: Porous, marrow-containing; architecture compromised in osteoporosis. Microstructure: Woven bone: Primary bone, irregular collagen alignment. Lamellar bone: Secondary bone, organized structure. Lacunar–canalicular system: Provides osteocyte interconnections. Extracellular matrix: Mineral (60–70%): Hydroxyapatite, tricalcium phosphate; provides compressive strength and mineral reservoir. Organic (20–25%): 90% type I collagen, other collagens, adhesive proteins (fibronectin, vitronectin), matrix proteins, proteoglycans, growth factors (BMP, TGF-β, IGF). Cells: Osteoblasts: Synthesize bone matrix, regulate osteoclasts; differentiation via Runx2 and osterix. Osteocytes: Mechanosensors, secrete RANKL, maintain bone homeostasis. Osteoclasts: Multinucleated, perform bone resorption; activated by RANKL and M-CSF, inhibited by OPG. Bone homeostasis: Maintained by the balance of osteoblast and osteoclast activity. Renewal occurs via Howship’s lacunae in trabecular bone and osteons in cortical bone. Disease and treatment: Remodeling impaired in conditions like osteoporosis and osteopetrosis . Therapies: Bisphosphonates, intermittent PTH, anti-RANKL agents, calcitonin. Fracture healing: Primary healing: Direct bone formation under stable fixation. Secondary healing: Hematoma, inflammation, cartilage callus, endochondral ossification, and remodeling. Growth factors (BMP, TGF-β, IGF) and angiogenesis play critical roles. 2. Synovial Joint Structure: Joint cavity, articular cartilage, capsule, ligaments, tendons. Development: Arises from mesenchymal condensation; apoptosis within interzone forms the cavity. Components: Articular cartilage: Provides low-friction motion. Ligaments: Provide stability. Capsule: Encloses the joint. Synovium: Contains type A cells (macrophage-like) and type B cells (fibroblast-like, producing hyaluronan); provides nutrition and synovial fluid. Synovial fluid: Plasma ultrafiltrate rich in hyaluronic acid and lubricin. Innervation: Type A fibers (proprioception). Type C fibers (pain). Function: Enables wide range of motion between bones with minimal friction. 3. Non-Synovial Joints Types: Symphysis: Fibrocartilaginous disc between bones (e.g., intervertebral disc, pubic symphysis); stability, load transfer, limited mobility. Synchondrosis: Cartilage-covered joint surfaces without synovium; limited motion (e.g., sternomanubrial, costal cartilage, cranial base). Syndesmosis: Fibrous connection without cartilage interface; limited movement (e.g., distal tibiofibular joint). 1. Parini P, Canalis E, Schilling T. Bone remodeling: an operational process ensuring survival and function. Bone Res . 2022;10:8. doi:10.1038/s41413-022-00219-8 2. Sims NA, Gooi JH. Current perspectives on the multiple roles of osteoclasts. J Mol Endocrinol . 2024 Previous Next

< Back Osgood Schlatter's Disease Previous Next

< Back Pediatric Bone Healing pediatric-bone-healing Previous Next

< Back Imaging in Orthopaedics Spot Knowledge Radiography Principle: X-ray transmission → high density = white + Cheap, fast, widely available, good for bones/interventions – Poor soft tissue contrast, radiation, magnification, pregnancy risk Computed Tomography (CT) Principle: X-rays, Hounsfield units, cross-sectional, 3D + High resolution, bone detail, biopsy guidance – High dose radiation, metal artifact, not safe in pregnancy Magnetic Resonance Imaging (MRI) Principle: Protons in magnetic field, RF pulses + Best for soft tissues (ligaments, tendons, cartilage, marrow) – Long scan time, motion/metal artifact, not safe with pacemaker, gadolinium risk in renal failure Ultrasonography Principle: High-frequency sound waves ± Doppler + Portable, cheap, safe (pregnancy, children), dynamic, interventional guidance – Operator-dependent, poor for bone & deep joints Nuclear Medicine (Scintigraphy, PET) Principle: Radioisotopes (Tc-99m, FDG) → metabolic activity + Detects osteomyelitis, metastasis, stress & occult fractures – Low resolution, delayed acute detection, contraindicated in breastfeeding Radiography Radiography is based on obtaining images by transmitting x-ray beams through tissues. Structures with high radiodensity (bone, metal) appear white. Today, digital radiography is widely used; with the PACS system, images can be easily stored and transferred. Advantages: Inexpensive, widely available, rapid, and effective in guiding interventional procedures. Disadvantages: Limited soft tissue contrast, involves radiation, images are magnified. Requires caution during pregnancy. Computed Tomography (CT) CT produces cross-sectional images using x-rays. Densities are measured in Hounsfield units. Multidetector CT scanners provide high resolution in a short time. Advantages: High contrast resolution, 3D reconstruction, ease of measurement. Cortical bone and trabecular structures are demonstrated in detail. Provides guidance for biopsy and interventions. Disadvantages: Artifacts with metallic implants, motion sensitivity, limitations related to obesity. Radiation dose is high, contraindicated during pregnancy. Magnetic Resonance Imaging (MRI) MRI generates images using the motion of protons within a strong magnetic field and radiofrequency waves. It does not involve ionizing radiation. The most commonly used sequences are T1 and T2. Advantages: Optimal visualization of soft tissues (ligament, tendon, cartilage, muscle, bone marrow). Tomographic structure, relative safety of gadolinium contrast, and absence of radiation. Disadvantages: Long acquisition time, motion artifacts, image distortion due to metallic implants. Sedation may be required in young children. Risks: The magnetic field may be hazardous for devices such as pacemakers or cochlear implants. Gadolinium is contraindicated in renal failure (risk of NSF). Its safety during pregnancy is uncertain. Ultrasonography Ultrasound operates with high-frequency sound waves. Superficial tissues are imaged with high frequency, deep tissues with low frequency. With Doppler technique, vascular flow can be demonstrated. Advantages: Portable, inexpensive, radiation-free, safe for pregnant women and children. Enables dynamic evaluation (tendon and nerve subluxation). Serves as guidance for needle placement and interventions. Disadvantages: Image quality is operator-dependent. Cortical bone and deep intra-articular structures are imaged with limitations. Nuclear Medicine Biological agents labeled with radioactive isotopes are used. Bone scintigraphy is performed with Tc-99m and demonstrates bone metabolism. PET uses FDG to reveal metabolic activity; it is particularly common in oncology. Advantages: Evaluation of metabolic processes, detection of osteomyelitis, metastases, stress fractures, and occult fractures. Disadvantages: Low spatial resolution, delayed sensitivity in acute lesions, limited efficacy in lytic lesions. Contraindicated in breastfeeding women. Radiation Safety Children and fetuses are sensitive to ionizing radiation. CT exposes patients to the highest dose (5–15 mSv). Low-dose principles and the ALARA (“as low as reasonably achievable”) approach are essential. Risks: DNA damage, cancer development, fetal malformation, and childhood leukemia. Protection: Shielding of gonads and radiosensitive organs, reduction of dose through distance, and the obligatory use of protective equipment. Conclusion Medical imaging modalities are indispensable in diagnostic and therapeutic processes. Radiography and CT demonstrate osseous structures. MRI provides superior visualization of soft tissues. Ultrasonography enables dynamic evaluation and safe use. Nuclear medicine offers insight into metabolic processes. Each modality’s advantages and limitations should be considered, and radiation safety principles must be observed. Appropriately selected imaging methods enhance patient safety and diagnostic accuracy. 1. Islam SKM, Nasim MA, Hossain I, Ullah MA, Gupta KD, Bhuiyan MM. Introduction of medical imaging modalities. arXiv . 2023 Jun 1;2306.01022. doi:10.48550/arXiv.2306.01022 2. Huang Y, Li Y, Li J, Hua T, Liu Y. Advances in medical imaging techniques. BMC Methods . 2024; doi:10.1186/s44330-024-00010-7 Previous Next

< Back Biomechanics CCDCDCDCDCD shoulder-elbow-biomechanics Previous Next

< Back Bone Transport Techniques bone-transport-techniques Previous Next

< Back Gait Analysis gait-analysis Previous Next