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Biomechanics & Biomaterials MCQs

Practice Set 44 of 88

This practice set contains high-yield board review questions covering key concepts in Biomechanics & Biomaterials. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 861

Topic: Biomechanics & Biomaterials

A 45-year-old active female reports feeling a 'pop' in the back of her knee while squatting to pick up a box, followed by posterior knee pain and mild effusion. MRI demonstrates a complete radial tear of the posterior root of the medial meniscus with 4 mm of medial meniscal extrusion. Biomechanical studies have shown that if this injury is left untreated, it alters knee joint contact mechanics to most closely resemble which of the following conditions?

. Intact knee biomechanics due to capsular healing
. Total medial meniscectomy
. Isolated ACL deficiency
. Patellofemoral osteoarthritis
. Total lateral meniscectomy

Correct Answer & Explanation

. Total medial meniscectomy

Explanation

A complete medial meniscus posterior root tear severely disrupts the hoop stresses of the meniscus, rendering it biomechanically incompetent. In cadaveric studies, a complete root tear has been shown to lead to peak contact pressures and decreased contact area in the medial compartment that are equivalent to those seen in a total medial meniscectomy. This results in rapid progression of medial compartment osteoarthritis if not surgically repaired in suitable candidates.

Question 862

Topic: Biomechanics & Biomaterials

A 45-year-old female presents with acute onset of medial joint line pain after a deep squat. MRI reveals a medial meniscus posterior root tear. Which of the following best describes the biomechanical consequence if this tear is left untreated?

. Decreased contact pressure in the medial compartment
. Biomechanics equivalent to a total meniscectomy
. Increased anterior tibial translation during the Lachman test
. Decreased peak contact pressure in the lateral compartment
. Shift of peak contact stresses to the patellofemoral joint

Correct Answer & Explanation

. Biomechanics equivalent to a total meniscectomy

Explanation

A meniscal root tear completely disrupts the hoop stresses of the meniscus, rendering it functionally incompetent. Biomechanical studies have demonstrated that a posterior root tear leads to peak contact pressures and joint kinematics that are essentially equivalent to a total meniscectomy. This drastically accelerates the progression of medial compartment osteoarthritis if left untreated.

Question 863

Topic: Biomechanics & Biomaterials

A 52-year-old female presents with sudden onset medial-sided knee pain and a feeling of a 'pop' while ascending stairs. Physical examination reveals a mild effusion and joint line tenderness. MRI demonstrates an extruded medial meniscus and a high signal defect at the posterior horn attachment of the medial meniscus on the coronal sequences. What is the most likely biomechanical consequence if this injury is treated nonoperatively?

. Decreased contact pressures in the medial compartment
. Anterior translation of the tibia during active quadriceps contraction
. Alteration of knee kinematics equivalent to a total meniscectomy
. Increased varus laxity in full extension
. Healing of the meniscus with progressive scar tissue formation

Correct Answer & Explanation

. Alteration of knee kinematics equivalent to a total meniscectomy

Explanation

The clinical scenario and MRI findings are consistent with a medial meniscus posterior root tear. The posterior root attachments are critical for converting axial loads into hoop stresses within the meniscus. A complete root tear leads to loss of these hoop stresses, resulting in meniscal extrusion and altered peak contact pressures that are biomechanically equivalent to a total meniscectomy. This significantly accelerates the progression of medial compartment osteoarthritis. Nonoperative treatment typically results in rapid joint degeneration rather than healing.

Question 864

Topic: Biomechanics & Biomaterials

A 55-year-old man receives a THA using a highly cross-linked polyethylene liner. What is the primary biochemical purpose of subjecting the polyethylene to a heating process (melting or annealing) immediately following gamma irradiation?

. To increase the ultimate tensile strength of the material
. To eliminate residual free radicals and reduce long-term oxidation
. To decrease the cross-link density for better elasticity
. To improve the elastic modulus of the bearing surface
. To increase the fatigue crack propagation resistance

Correct Answer & Explanation

. To eliminate residual free radicals and reduce long-term oxidation

Explanation

Heating highly cross-linked polyethylene after gamma irradiation eliminates residual free radicals trapped in the polymer chains. This critical step prevents long-term in vivo oxidation, which is a primary cause of polyethylene degradation and late wear.

Question 865

Topic: Biomechanics & Biomaterials
Compared to conventional ultra-high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE) used in total hip arthroplasty has which of the following mechanical characteristics?
. Decreased wear resistance
. Increased yield strength
. Decreased ultimate tensile strength
. Increased fatigue crack propagation resistance
. Increased elongation at break

Correct Answer & Explanation

. Decreased ultimate tensile strength

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured by exposing UHMWPE to radiation (gamma or electron beam), which creates free radicals that form cross-links. While this significantly improves wear resistance (reducing volumetric wear and osteolysis), it alters the bulk mechanical properties of the material. Specifically, cross-linking decreases ultimate tensile strength, yield strength, elongation at break (ductility), and fatigue crack propagation resistance. To mitigate free radical oxidation, it is subsequently remelted, annealed, or doped with Vitamin E.

Question 866

Topic: Biomechanics & Biomaterials

During the cementation of the femoral component in an 82-year-old patient undergoing a cemented hemiarthroplasty for a femoral neck fracture, the patient's end-tidal CO2 abruptly drops, followed by severe hypotension and hypoxia. Which of the following is the most likely pathophysiological mechanism of this intraoperative event?

. Anaphylactic reaction to polymethylmethacrylate (PMMA) monomer
. Embolization of fat, marrow, and air into the pulmonary circulation
. Acute myocardial infarction from coronary vasospasm
. Rapid absorption of toxic unreacted cement monomer causing direct vasodilation
. Exothermic reaction causing thermal necrosis of the endosteum leading to cytokine release

Correct Answer & Explanation

. Embolization of fat, marrow, and air into the pulmonary circulation

Explanation

Bone Cement Implantation Syndrome (BCIS) is characterized by hypoxia, hypotension, cardiac arrhythmias, increased pulmonary vascular resistance, and potentially cardiac arrest occurring around the time of cementation and prosthesis insertion. The most widely accepted pathophysiological mechanism is the embolization of marrow contents (fat, marrow, air, and bone particles) into the pulmonary circulation. The high intramedullary pressure generated during cement pressurization and prosthesis insertion forces these contents into the venous system. Although monomer toxicity was historically theorized, embolic showers are now known to be the primary cause.

Question 867

Topic: Biomechanics & Biomaterials

A 70-year-old patient reports a feeling of instability and giving way when rising from a chair or using stairs 1 year after a TKA. Clinical examination demonstrates stability at 0 degrees and 90 degrees of flexion, but excessive varus-valgus laxity at 30 to 45 degrees of flexion. What is the primary cause of this presentation?

. Excessive femoral component internal rotation
. Undersized tibial component
. Elevation of the joint line
. Use of a highly cross-linked polyethylene
. Anterior placement of the femoral component

Correct Answer & Explanation

. Elevation of the joint line

Explanation

Mid-flexion instability typically occurs when the joint line is elevated, often due to excessive distal femoral resection compensated by a thicker polyethylene insert. This leaves the collateral ligaments lax in mid-flexion despite being tight in extension and 90 degrees of flexion.

Question 868

Topic: Biomechanics & Biomaterials

A 62-year-old woman requires a TKA for severe osteoarthritis. She has a documented severe nickel hypersensitivity with previous blistering from inexpensive jewelry. What is the most appropriate implant choice to minimize the risk of a hypersensitivity reaction?

. Standard cobalt-chromium alloy femur and tibia
. Oxidized zirconium femur with a titanium alloy tibial tray
. Stainless steel femoral and tibial components
. Cobalt-chromium femur with an all-polyethylene tibia
. Porous tantalum femur and tibia

Correct Answer & Explanation

. Oxidized zirconium femur with a titanium alloy tibial tray

Explanation

Standard cobalt-chromium implants contain small amounts of nickel, which can elicit reactions in highly sensitized patients. Oxidized zirconium (Oxinium) femurs paired with titanium tibial trays contain virtually zero nickel and are preferred in confirmed metal allergy.

Question 869

Topic: Biomechanics & Biomaterials
Which of the following sterilization methods for ultra-high molecular weight polyethylene (UHMWPE) is most strongly associated with late oxidative degradation and accelerated wear in total joint arthroplasty?
. Gamma irradiation in a vacuum
. Gamma irradiation in an inert gas (Argon)
. Ethylene oxide
. Gas plasma
. Gamma irradiation in air

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Historically, sterilizing UHMWPE by gamma irradiation in the presence of oxygen (air) generated free radicals that combined with oxygen, causing oxidative degradation over time. This led to embrittlement, delamination, and accelerated wear. Modern highly cross-linked polyethylenes are irradiated to induce cross-linking, melted or annealed to extinguish free radicals, and sterilized in a vacuum or inert gas to prevent oxidation.

Question 870

Topic: Biomechanics & Biomaterials

A 55-year-old male presents with groin pain and a progressive limp 6 years after an uncomplicated metal-on-polyethylene THA using a large-diameter cobalt-chromium head on a titanium stem. Radiographs show a well-fixed prosthesis. Aspiration yields fluid with a normal cell count and negative cultures. Serum cobalt levels are markedly elevated, while serum chromium levels are mildly elevated. What is the most likely source of the elevated metal ions?

. Impingement of the femoral neck on the acetabular cup
. Fretting and crevice corrosion at the head-neck taper junction
. Third-body wear of the polyethylene liner
. Loosening of the titanium stem
. Unrecognized low-grade periprosthetic infection

Correct Answer & Explanation

. Fretting and crevice corrosion at the head-neck taper junction

Explanation

The clinical scenario describes trunnionosis, which involves fretting and crevice corrosion at the modular head-neck taper junction (trunnion). It is increasingly recognized in metal-on-polyethylene implants, particularly when large-diameter cobalt-chromium heads are used on titanium stems. This leads to disproportionately elevated serum cobalt levels compared to chromium and can cause an adverse local tissue reaction (ALTR).

Question 871

Topic: Biomechanics & Biomaterials

A surgeon places a stainless steel screw through a titanium plate. Which of the following best describes the resulting electrochemical interaction between these two implants?

. Fretting corrosion occurs due to micromotion between the screw and plate
. Galvanic corrosion occurs, with the stainless steel acting as the anode and preferentially corroding
. Galvanic corrosion occurs, with the titanium acting as the anode and preferentially corroding
. Crevice corrosion occurs specifically in the threads of the titanium plate
. No corrosion occurs because both metals form completely identical passivation layers

Correct Answer & Explanation

. Galvanic corrosion occurs, with the stainless steel acting as the anode and preferentially corroding

Explanation

When two dissimilar metals are placed in an electrolytic solution (such as body fluid) and are in electrical contact, galvanic corrosion occurs. The less noble metal (stainless steel) acts as the anode and preferentially corrodes, while the more noble metal (titanium) acts as the cathode and is protected. To prevent this, mixing dissimilar metals in direct contact should generally be avoided in orthopedic surgery.

Question 872

Topic: Biomechanics & Biomaterials

Rank the following common orthopedic implant materials in order of decreasing Young's modulus (stiffness):

. Alumina Ceramic > Cobalt-Chrome > Titanium > Cortical Bone
. Cobalt-Chrome > Alumina Ceramic > Titanium > Cortical Bone
. Titanium > Cobalt-Chrome > Cortical Bone > Cancellous Bone
. Cobalt-Chrome > Titanium > Alumina Ceramic > Cortical Bone
. Alumina Ceramic > Titanium > Cobalt-Chrome > Cortical Bone

Correct Answer & Explanation

. Alumina Ceramic > Cobalt-Chrome > Titanium > Cortical Bone

Explanation

Young's modulus is a fundamental biomechanical measure of the stiffness of a solid material. The correct order from stiffest (highest modulus) to most flexible (lowest modulus) is Alumina Ceramic (approx. 380 GPa) > Cobalt-Chrome alloys (approx. 210-240 GPa) > Stainless Steel (approx. 200 GPa) > Titanium alloys (approx. 100-110 GPa) > Cortical Bone (approx. 15-20 GPa) > PMMA bone cement (approx. 3 GPa) > Cancellous bone (approx. 0.1-2 GPa).

Question 873

Topic: Biomechanics & Biomaterials



Ligaments and tendons exhibit viscoelastic properties, making their mechanical behavior dependent on the rate of loading. Which of the following best describes the biomechanical phenomenon of 'creep'?

. Increasing deformation over time when subjected to a constant load
. Decreasing stress over time when held at a constant deformation
. The energy lost as heat during a cyclical loading and unloading process
. The initial non-linear flattening of the collagen crimp pattern
. Permanent plastic deformation that occurs after exceeding the yield point

Correct Answer & Explanation

. Increasing deformation over time when subjected to a constant load

Explanation

Creep is a fundamental viscoelastic property defined as the progressive, time-dependent deformation of a material under a constant load (or stress). This is clinically relevant in casting and soft tissue stretching. 'Stress relaxation' is the decrease in stress over time when a material is held at a constant length or deformation. 'Hysteresis' is the loss of energy (usually as heat) between the loading and unloading curves.

Question 874

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, highly cross-linked polyethylene is typically subjected to a remelting process above its melting temperature (approximately 150°C). What is the primary purpose of this remelting step?
. To increase the ultimate tensile strength of the polymer
. To eliminate free radicals and prevent long-term in vivo oxidation
. To increase the crystallinity of the polyethylene chains
. To enhance the yield strength of the material to prevent creep
. To increase the chain mobility to promote further cross-linking

Correct Answer & Explanation

. To eliminate free radicals and prevent long-term in vivo oxidation

Explanation

Gamma irradiation is used to induce cross-linking in UHMWPE, which vastly improves its wear resistance. However, irradiation cleaves polymer chains and generates free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to chain scission, oxidation, embrittlement, and catastrophic failure of the bearing. Thermal treatment (remelting or annealing) is performed to extinguish these free radicals. Remelting eliminates free radicals effectively but comes at the cost of a slight decrease in crystallinity and certain mechanical properties (like yield strength and fatigue resistance).

Question 875

Topic: Biomechanics & Biomaterials

A 65-year-old patient undergoes a revision total hip arthroplasty where a cobalt-chromium (CoCr) femoral head is placed onto a titanium alloy (Ti-6Al-4V) stem. Which of the following best describes the dominant type of corrosion that is uniquely facilitated by combining these two dissimilar metals?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in direct electrical contact within an electrolytic solution (such as body fluids). The less noble metal acts as the anode and preferentially corrodes. While CoCr and Titanium alloys are frequently paired in orthopedics due to their closely matched electrochemical potentials and passive oxide layers, mixing dissimilar metals inherently risks galvanic corrosion. Fretting and crevice corrosion also occur at modular junctions (like the trunnion) but are mechanically and geometrically driven phenomena that occur even in monobloc or mixed metal constructs.

Question 876

Topic: Biomechanics & Biomaterials
The addition of Vitamin E (alpha-tocopherol) to highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) in total joint arthroplasty primarily serves to:
. Increase the crystalline structure of the polymer
. Decrease the need for irradiation
. Scavenge free radicals to prevent oxidative degradation
. Enhance the fatigue strength to levels above conventional UHMWPE
. Promote osteointegration at the cementless interface

Correct Answer & Explanation

. Scavenge free radicals to prevent oxidative degradation

Explanation

Irradiation of UHMWPE creates cross-links that improve wear resistance but also generates free radicals that can lead to oxidative degradation and embrittlement over time. Vitamin E is added as an antioxidant to scavenge these free radicals, preventing oxidation without the need to melt or anneal the plastic, thereby preserving its mechanical properties and fatigue strength.

Question 877

Topic: Biomechanics & Biomaterials
Which of the following orthopedic biomaterials possesses a Young's modulus of elasticity most closely resembling that of human cortical bone?
. Stainless steel (316L)
. Cobalt-chromium alloy
. Titanium alloy (Ti-6Al-4V)
. Ultra-high molecular weight polyethylene (UHMWPE)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

Young's modulus is a measure of material stiffness. Human cortical bone has a Young's modulus of approximately 15-20 GPa. Titanium alloy (approx. 100-110 GPa) is the closest metallic biomaterial to cortical bone compared to Stainless Steel (approx. 200 GPa) and Cobalt-Chromium (approx. 210-240 GPa). This closer modulus match helps reduce stress shielding around implants.

Question 878

Topic: Biomechanics & Biomaterials

An orthopaedic surgeon uses a stainless steel screw to secure a titanium plate during fracture fixation. Postoperatively, rapid degradation of the screw is observed at the interface with the plate. Which of the following best describes the primary mechanism of this implant degradation?

. Galvanic corrosion
. Fretting corrosion
. Crevice corrosion
. Pitting corrosion
. Fatigue failure

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are placed in electrical contact within an electrolytic environment (such as bodily fluids). This establishes an electrochemical potential difference, causing the less noble (more anodic) metal to undergo accelerated corrosion. To prevent this, orthopaedic constructs should typically utilize components composed of the same metal or compatible alloys.

Question 879

Topic: Biomechanics & Biomaterials

Cortical bone exhibits viscoelastic properties, meaning its biomechanical behavior alters depending on the rate of loading. Which of the following statements best describes the response of cortical bone to a high strain rate (e.g., a high-velocity gunshot wound)?

. It becomes more ductile and absorbs less energy before failure.
. It becomes stiffer, sustaining higher loads, and absorbs more energy before failure.
. Its ultimate tensile strength decreases significantly.
. It behaves as a purely elastic material without plastic deformation.
. Its modulus of elasticity decreases, leading to failure at lower loads.

Correct Answer & Explanation

. It becomes stiffer, sustaining higher loads, and absorbs more energy before failure.

Explanation

Bone is a viscoelastic and anisotropic material. At higher strain rates (rapid loading), bone becomes stiffer (has a higher modulus of elasticity) and its ultimate strength increases. Consequently, it can absorb more energy prior to failure compared to low loading rates. However, when the energy capacity is finally exceeded, the energy release often results in highly comminuted fractures with extensive soft tissue damage.

Question 880

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit time-dependent viscoelastic properties that are clinically relevant to orthopedics. Which of the following biomechanical phenomena describes the progressive deformation of a viscoelastic material when it is subjected to a constant load over a prolonged period?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Resilience

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent, progressive deformation of a viscoelastic material under a constant load (e.g., a serial cast applied to correct a clubfoot). Stress relaxation is the decrease in stress over time when a material is held at a constant length/strain. Hysteresis represents the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

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