MCQs – Basic 1

Modern Study Review (AI-Generated)

High-Yield Summary

Bone porosity thresholds distinguish cortical (<30%) from cancellous (?30%) bone, a fundamental concept in orthopaedics and biomaterials. Antibiotic-loaded cement elutes maximal drug in the first days, with efficacy waning by 6-8 weeks; dosing above 2g antibiotic per 4g cement compromises mechanical integrity. Muscle strength gains initially rely on neural adaptations before hypertrophy, with failure commonly at the myotendinous junction during eccentric loading. Tourniquet use demands strict timing: irreversible nerve injury can occur beneath the cuff within 2 hours, while distal ischemic tissues tolerate up to 3 hours. Allograft processing balances immunogenicity and osteoinductivity, with freeze drying (-30°C) abolishing osteoinductivity and deep freezing (-80°C) preserving some. This topic is a staple of the Royal College exam, focusing heavily on thresholds for bone porosity, antibiotic dosing in cement, and tourniquet safety. The examiner often forces a choice between maximizing antibiotic dose and preserving cement strength or between tourniquet time and nerve injury risk. While classic answers emphasize fixed thresholds, modern practice increasingly individualizes tourniquet protocols and graft selection based on patient factors.

High-Yield Decision Matrix

Active Recall Q&A

Bone Porosity

Q: What is the maximum porosity allowed in cortical bone by definition?
A: Cortical bone should have a porosity less than 30%, typically around 10%.
Related Pearl: Cortical bone’s low porosity underpins its high mechanical strength and fracture resistance.

Q: What is the minimum porosity defining cancellous bone?
A: Cancellous bone has a porosity greater than or equal to 30%.
Related Pearl: High porosity facilitates marrow space and metabolic activity but reduces mechanical strength.

Antibiotics in Cement

Q: How does antibiotic elution from bone cement behave over time?
A: Maximal antibiotic elution occurs in the first few days, then drops exponentially, with significant levels ceasing by 6-8 weeks.
Related Pearl: This elution profile guides timing for infection prophylaxis and treatment in cemented arthroplasty.

Q: What is the optimal antibiotic concentration in bone cement?
A: 2 grams of antibiotic per 4 grams of cement is sufficient; higher doses weaken the cement.
Related Pearl: Excess antibiotic compromises cement integrity, increasing risk of implant loosening.

Muscle Physiology and Injury

Q: What causes the increase in muscle strength due to training?
A: Mainly hypertrophy and increased motor unit recruitment; early gains are mostly due to improved neural firing patterns.
Related Pearl: Neural adaptations precede hypertrophy in early rehab, critical for training design.

Q: How does muscle hypertrophy occur at the cellular level?
A: By increasing the number of myofibrils per muscle fiber.
Related Pearl: This structural change enhances force generation capacity.

Q: What is the function of muscle spindles?
A: They monitor tension within the muscle.
Related Pearl: Muscle spindles provide proprioceptive feedback essential for coordinated movement.

Q: Where is ATP concentrated within the muscle fiber?
A: ATP is concentrated in the myosin molecules.
Related Pearl: Myosin ATPase activity drives cross-bridge cycling and contraction.

Q: Where does muscle failure typically occur during eccentric loading?
A: At or near the myotendinous junction.
Related Pearl: This junction is a biomechanical weak point due to stress concentration during lengthening contractions.

Q: What happens if muscle is strained to failure without vascular channel disruption?
A: Cell death and degeneration occur, followed by regeneration; the regenerated fiber type depends on the motor nerve type.
Related Pearl: Preserved vascular channels are critical for muscle regeneration and functional recovery.

Q: What is the healing response if muscle strain disrupts vascular channels?
A: Healing occurs with inflammation and scar formation, which can block regeneration; early motion improves scar mechanical quality.
Related Pearl: Scar tissue is less elastic and can impair function if not managed properly.

Q: What factors determine muscle recovery after laceration?
A: Amount of scar, regeneration across the injury site, and degree of distal muscle denervation or reinnervation ability.
Related Pearl: Effective reinnervation is essential to restore strength and prevent atrophy.

Tourniquet Physiology and Safety

Q: What metabolic change occurs locally after applying a tourniquet?
A: Local acidosis with a drop in pH occurs beneath the cuff.
Related Pearl: Acidosis contributes to tissue injury and nerve dysfunction during prolonged use.

Q: What defines the compression zone in tourniquet application?
A: Tissue directly beneath the cuff subjected to compression forces.
Related Pearl: Compression zone is more vulnerable to shear injury and ischemia than distal tissues.

Q: What defines the ischemic zone in tourniquet application?
A: Tissue distal to the cuff experiencing ischemia.
Related Pearl: Ischemic zone tolerates up to 3 hours of ischemia with minimal sequelae.

Q: How long can tissues in the ischemic zone tolerate ischemia with little damage?
A: Up to 3 hours.
Related Pearl: This tolerance guides safe tourniquet time limits.

Q: How quickly can irreversible nerve damage occur beneath the tourniquet cuff?
A: Within 2 hours.
Related Pearl: Nerve injury risk mandates strict monitoring and time limits.

Q: How does cuff width affect tourniquet safety?
A: Wider cuffs distribute pressure better and reduce tissue damage.
Related Pearl: Wider cuffs reduce peak pressure and nerve injury risk.

Q: What is the recommended reperfusion protocol after 90 minutes of tourniquet time?
A: Deflate the cuff for 5 minutes to allow reperfusion.
Related Pearl: Intermittent reperfusion reduces ischemic injury during prolonged procedures.

Q: What is the recommended reperfusion protocol after 3 hours of tourniquet time?
A: Deflate the cuff for 15 minutes to allow reperfusion.
Related Pearl: Longer reperfusion intervals prevent tissue damage after extended ischemia.

Collagen Biology

Q: Describe the intracellular steps of collagen formation.
A: Translation, hydroxylation, and glycosylation form soluble procollagen (a triple helix) inside the cell.
Related Pearl: Proper post-translational modification is essential for collagen stability.

Q: What happens to procollagen extracellularly?
A: Procollagen propeptidase cleaves terminal peptides forming insoluble tropocollagen, which crosslinks to form collagen.
Related Pearl: Extracellular crosslinking provides tensile strength to collagen fibers.

Q: How is collagen breakdown assessed clinically?
A: By measuring urinary hydroxyproline levels.
Related Pearl: Elevated hydroxyproline indicates increased collagen turnover, useful in metabolic bone diseases.

Allograft Biology and Remodeling

Q: How does freeze drying affect allograft osteoinductivity?
A: Freeze drying at -30°C eliminates osteoinductivity.
Related Pearl: Loss of osteoinductive factors reduces graft incorporation potential.

Q: How does deep freezing affect allograft immunogenicity and osteoinductivity?
A: Deep freezing at -80°C reduces immunogenicity and may preserve some osteoinductivity.
Related Pearl: Deep frozen grafts balance immune tolerance with biological activity.

Q: Compare fresh and frozen allografts in terms of incorporation and immune response.
A: Fresh allografts incorporate more but provoke stronger immune responses; freezing reduces immunogenicity but may impair incorporation.
Related Pearl: Immunosuppression and graft processing influence clinical outcomes.

Q: How do cancellous grafts remodel after implantation?
A: They undergo bone formation before resorption via creeping substitution.
Related Pearl: Early osteocyte invasion promotes faster graft incorporation.

Q: How do cortical grafts remodel after implantation?
A: They undergo resorption before new bone formation.
Related Pearl: Cortical grafts provide initial mechanical strength but remodel more slowly.

Q: What is the strength retention of cortical grafts at 6 months?
A: Approximately 50% of initial strength remains.
Related Pearl: Mechanical weakening during remodeling necessitates protected weight-bearing protocols.

Classic Clinical Notes

• Cortical bone by definition should have a porosity LESS THAN 30% – in fact, most cortical bone has a porosity about 10%.

• Cancellous bone by definition should have a porosity GREATER THAN 30%. Ie. it is AT LEAST 30% porous.

• Antibiotics in cement – maximal elution in first few days, then exponential drop off; “cease to be present in significant levels at 6-8 weeks.”

• 2 grams of antibiotics in 4 grams of cement is enough – higher concentrations tend to weaken the cement.

• Increase in muscle strength due to training is due to hypertrophy, and increased recruitment; there MAY be an element of hyperplasia, but most agree that the majority is from hypertrophy. A number of sources state that, particularly early, muscle strength increases by improved neuronal firing and recruitment.

• “Recovery of muscle strength in the initial stages of rehab are often due to improved neural firing patterns more than anything else.”

• Muscle hypertrophy occurs by increased numbers of myofibrils/fiber.

• Muscle spindles monitor tension in the muscle.

• ATP in the muscle fiber is concentrated in the MYOSIN.

• Muscle failure occurs with eccentric loading, with failure most often occurring at or near the myotendinous junction.

• If muscle is strained to failure but does not disrupt the vascular channels – cell death and degeneration ensues, then regeneration proceeds – the muscle fiber type formed depends on the motor nerve type.

• If muscle is strained and vessels are torn – heals with inflammation and scar (which can block regeneration). The scar is mechanically better if the muscle undergoes early motion.

• The amount of recovery seen after muscle laceration depends on the amount of scar, the regeneration across the site, and the degree of denervation of distal muscle (or its ability to be re-innervated).

• After applying a tourniquet, expect local acidosis with a drop in pH.

• Tissues beneath the cuff – the compression zone.

• Tissues distal to the cuff – the ischemic zone.

• Tissues in the ischemic zone seem to tolerate up to 3 hours with little sequela.

• Tissues in the compression zone, however, are subject to shear forces and ischemia, particularly at the cuff-limb interface. Irreversible nerve damage directly beneath the cuff can occur within 2 hours.

• Hence, the tissue beneath the cuff is much more vulnerable than the tissue distal to it.

• Wider cuffs are better.

• After 90 minutes of tourniquet time – need to let it down for 5 minutes to reperfuse; 15 minutes if time is 3 hours.

• Sequence of collagen formation: translation, hydroxylation, and glycosylation all occur within the cell to form the soluble procollagen (a triple helix). This is then exuded OUT of the cell where the terminal peptidase is cleaved off by procollagen propeptidase and it forms the insoluble tropocollagen. The tropocollagen then crosslinks to form collagen.

• Hence, the procollagen is intracellular, the tropocollagen is extracellular.

• Collagen breakdown is well assessed with urinary hydroxyproline (Paget’s).

• Comparing fresh and deep frozen allografts: the freezing process makes it less immunogenic; freeze dried are kept at minus 30, deep frozen at minus 80; deep freezing may actually maintain some osteoinductivity, but freeze drying definitely eliminates any of the osteoinductivity; fresh allografts would probably incorporate more, but are subject to the immune response.

• The key concept is that FREEZING diminishes the immunogenicity.

• Interestingly, both cortical and cancellous grafts undergo creeping substitution, but in the opposite order – cancellous grafts are weak, but they are invaded by osteocytes, which lay down bone, which later is resorbed and replaced (ie. they undergo bone formation before bone resorption). Cortical grafts are strong at first, but are broken down first before new bone is laid down.

• Cortical grafts are 50% of their initial strength at 6 months.

Last Updated on January 25, 2026 by Christian Veillette