Biomechanics of Sports Injuries

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Biomechanics Basics - Force & Failure Fun

  • Stress ($\.sigma\.): Force/Area ($F/A$). Types: tension, compression, shear.
  • Strain ($\.epsilon\.): Deformation/Original Length ($\.Delta L/L_0\.$).
  • Stress-Strain Curve:
    • Elastic Region: Reversible. Slope = Young's Modulus (E) (stiffness).
    • Yield Point: Elastic limit.
    • Plastic Region: Permanent deformation.
    • Ultimate Strength: Max stress.
    • Failure Point: Fracture.
  • Material Properties: Ductile (deforms), Brittle (fractures easily), Toughness (energy absorption).
  • Viscoelasticity: Time-dependent.
    • Creep: ↑ strain @ constant stress.
    • Stress Relaxation: ↓ stress @ constant strain.
    • Rate-dependent: Stiffer at ↑ loading rates.
  • Wolff's Law: Bone adapts to loads.

    ⭐ Bone remodels along lines of maximal stress.

  • Failure Modes:
    • Load Types: Tension, compression, shear, bending, torsion.
    • Fatigue: Repetitive sub-maximal loads.
    • Acute: Single traumatic overload. Stress-Strain Curves for Bone and Ligament

Injury Mechanisms - Snap, Crackle, Pop!

  • Primary Forces Causing Injury:
    • Tensile: Stretching/pulling (e.g., muscle/tendon strain, ligament sprain).
    • Compressive: Direct impact/crushing (e.g., contusion, cartilage damage).
    • Shear: Parallel forces in opposite directions (e.g., ACL tear, blister).
    • Torsional: Twisting/rotational (e.g., spiral fracture, meniscal tear).
  • Injury Classification by Onset:
    • Acute (Traumatic): Single, identifiable high-energy event. Results in macrotrauma.
    • Chronic (Overuse): Repetitive submaximal stress. Leads to microtrauma accumulation.
  • Tissue Biomechanical Response: Load → Stress → Strain. Exceeding elastic limit → Plastic deformation → Tissue failure.
  • Characteristic Sounds (Audible Clues):
    • Snap: Often indicates acute ligament or tendon rupture.
    • Crackle/Crepitus: Suggests fracture fragments rubbing or chondromalacia.
    • Pop: Common with ACL tears, meniscal injuries, or joint subluxation.

Forces on a Joint

⭐ The stress-strain curve illustrates tissue behavior: elastic region (reversible deformation), yield point, plastic region (irreversible), and ultimate failure point.

Joint Hotspots - High-Stress Zones

  • Knee Joint: High valgus & rotational loads (cutting/pivoting).
    • ACL Injury: Non-contact deceleration, hyperextension, valgus + tibial rotation. Audible "pop".
      • 📌 Unhappy Triad (O'Donoghue's): ACL, MCL, Medial Meniscus tear (ATM).
    • Meniscal Tears: Twisting on flexed, weight-bearing knee. Locking/catching. Bucket-handle type.
  • Shoulder Joint (Glenohumeral): ↑ROM compromises stability; overuse risk.
    • Rotator Cuff Tears: Overuse (overhead sports), impingement. Supraspinatus most common; pain on abduction.
    • Dislocations (Anterior > Posterior): Abduction, external rotation, extension (FOOSH). Bankart & Hill-Sachs lesions.
  • Ankle Joint: Most frequently injured in sports.
    • Lateral Ankle Sprains: Inversion & plantarflexion (ATFL most common, then CFL).
    • High Ankle Sprain (Syndesmotic): Forced dorsiflexion/external rotation (AITFL/PITFL). Squeeze test positive.

⭐ The anterior talofibular ligament (ATFL) is the weakest and most commonly injured ligament in lateral ankle sprains.

Prevention & Performance - Biomechanical Shield

  • Injury Prevention Strategies:
    • Technique analysis & correction: Optimizes load distribution, minimizes joint stress.
    • Equipment modification: Custom footwear, appropriate protective gear (helmets, pads), taping/bracing.
    • Targeted conditioning: Enhances strength, flexibility, endurance, and proprioception.
    • Load management & recovery: Prevents overuse injuries, allows tissue adaptation.
  • Performance Enhancement:
    • Movement efficiency: Reduces energy cost, delays fatigue.
    • Force optimization: Maximizes power output and skill execution. Injury Prevention Program Steps

⭐ Eccentric strengthening programs are highly effective in preventing muscle strains, particularly hamstring injuries in athletes (e.g., Nordic hamstring exercise).

High‑Yield Points - ⚡ Biggest Takeaways

  • Tensile loading causes ligament sprains (e.g., ACL) and muscle-tendon strains.
  • Compressive forces lead to cartilage damage, meniscal tears, and impaction fractures.
  • Shear forces are critical in rotational injuries, causing chondral defects or avulsions.
  • Repetitive microtrauma underlies overuse syndromes like tendinopathies and stress fractures.
  • Eccentric muscle actions frequently cause muscle fiber damage and DOMS.
  • Valgus stress is key for MCL tears, often with ACL/meniscus (e.g., O'Donoghue's triad).
  • Altered kinematics and excessive loads are primary sports injury risk factors.

Practice Questions: Biomechanics of Sports Injuries

Test your understanding with these related questions

Which among the following results in a combination of elastic and viscous behavior, where only the elastic component is recovered when the stress is removed?

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Flashcards: Biomechanics of Sports Injuries

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When the knee is extended, the _____ bundle of ACL is tight, and the AM bundle is moderately lax.

TAP TO REVEAL ANSWER

When the knee is extended, the _____ bundle of ACL is tight, and the AM bundle is moderately lax.

PL

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