Tribology in Orthopaedics — MCQs
Among the following dental files made of the same steel and size 55, which one is more prone to fracture?
In a functional implant, bone loss seen annually after 1 year is:
Most reliable method to identify putrefied bodies with metallic implants?
Which prosthesis is shown below in the X-ray?
A 65-year-old lady presented with a swollen and painful knee. On examination, she was found to have grade III osteoarthritic changes. What is the best course of action?
During performing a total hip replacement, the surgeon found destruction of the articular cartilage and multiple wedge-shaped subchondral depressions. What is this called?
What is the primary use of stainless steel in orthodontics?
What is the latent period in distraction osteogenesis?
Bone resorption is enhanced by which of the following?
Which anatomical structure is considered a dynamic stabilizer of the shoulder joint?
Tribology in Orthopaedics Indian Medical PG Practice Questions and MCQs
Question 1: Among the following dental files made of the same steel and size 55, which one is more prone to fracture?
- A. Square cross-section file
- B. Triangular reamer
- C. Headstrom file (Correct Answer)
- D. Rhomboid cross-section file
Explanation: ***Headstrom file*** - Headstrom files are manufactured by grinding a spiral groove into a tapered round wire, creating sharp cutting edges and a **deep flute**. - This design results in a **reduced core mass** compared to other file types, making it inherently weaker and more susceptible to fracture, especially under torsional stress or when used improperly. *Triangular reamer* - A triangular reamer has a **triangular cross-section** which generally provides good flexibility and fracture resistance due to its symmetrical design. - While it has cutting efficiency, its broader core mass compared to the Headstrom file makes it less prone to fracture. *Square cross-section file* - Files with a **square cross-section** possess the largest core mass among conventional designs, offering excellent resistance to fracture. - This design provides high strength but may have reduced flexibility compared to other shapes. *Rhomboid cross-section file* - A rhomboid cross-section file offers a balance between flexibility and cutting efficiency, similar to a K-file but with slightly different angles. - Its cross-sectional area is still significantly larger and more robust than the deeply fluted Headstrom file, providing greater fracture resistance.
Question 2: In a functional implant, bone loss seen annually after 1 year is:
- A. 1 to 1.5 mm
- B. Less than 0.1 mm (Correct Answer)
- C. 1 to 2 mm
- D. 1.5 to 2 mm
Explanation: ***Less than 0.1 mm*** - In a functional implant, **crestal bone loss** after the first year of initial healing is expected to be minimal. - This minimal bone loss indicates successful **osseointegration** and long-term stability of the implant. *1 to 1.5 mm* - This amount of annual bone loss is generally considered **excessive** and may indicate issues such as peri-implantitis or improper loading. - Such bone loss could compromise the **long-term prognosis** and stability of the dental implant. *1 to 2 mm* - An annual bone loss in this range would be deemed **unacceptable** for a healthy, functional implant. - This level of bone loss suggests significant **peri-implant inflammation** or biomechanical overload, requiring intervention. *1.5 to 2 mm* - This degree of bone loss is a clear sign of significant **implant pathology** and would likely lead to implant failure if not addressed. - It is far beyond the clinically acceptable limits for bone remodeling around a **stable implant**.
Question 3: Most reliable method to identify putrefied bodies with metallic implants?
- A. Serial number matching (Correct Answer)
- B. X-ray superimposition
- C. Dental comparison
- D. DNA profiling
Explanation: ***Serial number matching*** - Metallic implants, such as orthopedic prostheses or pacemakers, often carry **unique serial numbers** that can be traced back to the manufacturer and patient records. - This method is highly reliable even in cases of severe **putrefaction** or fragmentation, as the implant itself is resistant to decomposition. *X-ray superimposition* - This method involves superimposing antemortem (before death) and postmortem (after death) X-rays to look for matching anatomical features. - While useful for bone and tooth identification, it is less reliable for specific identification with metallic implants compared to direct serial number matching, especially if the antemortem X-rays predate the implant. *Dental comparison* - **Dental comparison** involves comparing antemortem dental records (X-rays, charts) with postmortem dental findings. - This method is very effective for identification in general, but it does not directly utilize the metallic implant for identification and thus is not the *most reliable* method when an implant is present. *DNA profiling* - **DNA profiling** is highly effective for identification using biological samples, but it relies on obtaining viable DNA. - In cases of severe putrefaction, obtaining **high-quality, uncontaminated DNA** suitable for profiling can be very challenging or impossible from the remains themselves.
Question 4: Which prosthesis is shown below in the X-ray?
- A. Articular resurfacing
- B. Thompson prosthesis
- C. Austin Moore's prosthesis (Correct Answer)
- D. Birmingham hip replacement
Explanation: ***Austin Moore's prosthesis*** - The image clearly shows a **femoral stem with a long intramedullary component** and an **integrated prosthetic head** that articulates directly with the native acetabulum. This is characteristic of a hemiarthroplasty design, specifically resembling an Austin Moore prosthesis. - This type of prosthesis is commonly used for **femoral neck fractures** in older patients, replacing only the femoral head and neck rather than the entire hip joint. *Articular resurfacing* - **Articular resurfacing** involves capping the femoral head and lining the acetabulum with metallic implants, preserving more bone than a traditional total hip replacement. - The X-ray image does not show a cap on the femoral head or a separate acetabular component, which are features of resurfacing. *Thompson prosthesis* - The **Thompson prosthesis** is another type of hemiarthroplasty, but it typically has a **shorter, bulkier femoral stem** and a **relatively smaller head** compared to the Austin Moore prosthesis shown. - While both Thompson and Austin Moore prostheses are hemiarthroplasties, the specific shape and length of the stem in the X-ray are more consistent with an Austin Moore design. *Birmingham hip replacement* - The **Birmingham hip replacement** is a type of **hip resurfacing arthroplasty**, which, as explained earlier, involves capping the femoral head and is not depicted in this image. - It maintains more of the patient's original bone structure compared to conventional total hip replacement but still requires both femoral and acetabular components.
Question 5: A 65-year-old lady presented with a swollen and painful knee. On examination, she was found to have grade III osteoarthritic changes. What is the best course of action?
- A. Conservative management
- B. Total knee replacement (Correct Answer)
- C. Arthroscopic washing
- D. Partial knee replacement
Explanation: ***Total knee replacement*** - For **grade III osteoarthritis** in a 65-year-old, a total knee replacement is the most definitive and effective treatment to relieve pain and restore function in a severely damaged joint. - This procedure addresses widespread cartilage loss and structural changes typical of advanced osteoarthritis. *Conservative management* - This approach is typically favored for **mild to moderate osteoarthritis**, involving physical therapy, NSAIDs, and lifestyle modifications. - For **grade III changes** with significant pain and swelling, conservative measures are unlikely to provide sufficient relief or halt disease progression effectively. *Arthroscopic washing* - **Arthroscopic lavage** and debridement are rarely recommended for osteoarthritis as they have not shown sustained benefits for pain or function. - It is sometimes used for specific mechanical symptoms, but it does not address the underlying cartilage loss and structural damage in severe osteoarthritis. *Partial knee replacement* - A **partial knee replacement** is suitable when osteoarthritis is confined to a single compartment of the knee, and the other compartments are healthy. - Given the indication of "grade III osteoarthritic changes" without specifying a single compartment, a total knee replacement is generally more appropriate for widespread disease.
Question 6: During performing a total hip replacement, the surgeon found destruction of the articular cartilage and multiple wedge-shaped subchondral depressions. What is this called?
- A. Osteolysis
- B. Osteomyelitis
- C. Osteonecrosis (Correct Answer)
- D. Osteogenesis
Explanation: ***Osteonecrosis*** - **Osteonecrosis**, also known as **avascular necrosis**, is characterized by the death of bone tissue due to a lack of blood supply, which leads to the collapse of the subchondral bone and articular cartilage destruction. - The description of **wedge-shaped subchondral depressions** and **articular cartilage destruction** is highly indicative of osteonecrosis, especially in the context of advanced hip joint pathology requiring total hip replacement. *Osteolysis* - **Osteolysis** refers to the active resorption of bone, often seen around implants in prosthetic joints due to wear particles, leading to bone loss. - While it involves bone destruction, it typically presents as diffuse bone loss rather than specific wedge-shaped subchondral depressions. *Osteomyelitis* - **Osteomyelitis** is an infection of the bone or bone marrow, often leading to bone destruction, but it is primarily characterized by inflammation and pus formation. - The presented scenario does not mention signs of infection (e.g., fever, pus, inflammation) but focuses purely on structural destruction consistent with vascular compromise. *Osteogenesis* - **Osteogenesis** is the process of bone formation or development. - This term describes the creation of bone tissue and is the opposite of bone destruction, making it an incorrect answer for a condition involving cartilage and bone deterioration.
Question 7: What is the primary use of stainless steel in orthodontics?
- A. To enhance the strength of dental materials
- B. For making clasps in partial dentures
- C. To replace gold restorations in teeth
- D. In the fabrication of orthodontic wires (Correct Answer)
Explanation: ***In the fabrication of orthodontic wires*** - Stainless steel is widely used in orthodontics for **wires** due to its excellent **strength**, **formability**, and corrosion resistance. - Its **elasticity** allows for controlled force application to move teeth effectively and predictably. *To enhance the strength of dental materials* - While stainless steel is strong, its primary orthodontic use is not as an additive to **enhance** other bulk dental materials like composites or ceramics. - Other materials or processing methods are typically used for strengthening restorative or prosthetic dental materials. *For making clasps in partial dentures* - Stainless steel can be used for clasps, but **cobalt-chromium alloys** or **wrought wire clasps** made from other alloys are more common in partial dentures for their specific mechanical properties and biocompatibility. - The context of the question points to a primary orthodontic application beyond general prosthodontics. *To replace gold restorations in teeth* - Stainless steel is not typically used as a direct replacement for **gold restorations** (inlays, onlays, crowns) in permanent dentition due to aesthetic and long-term wear considerations. - While stainless steel crowns are used in pediatric dentistry, they serve a different purpose than replacing gold in adults.
Question 8: What is the latent period in distraction osteogenesis?
- A. 4-6 weeks
- B. 5-7 days (Correct Answer)
- C. 6-8 months
- D. 4 months
Explanation: **Explanation:** **Distraction Osteogenesis** (Ilizarov technique) is a process of growing new bone by mechanically stretching a vascularized callus. The procedure follows a specific chronological sequence: 1. **Latent Period (The Correct Answer):** This is the duration between the corticotomy (surgical bone cut) and the commencement of distraction. It typically lasts **5–7 days**. This period allows for the inflammatory phase of bone healing to occur and for the initial soft tissue/callus bridge to form. Starting distraction too early (before 5 days) can lead to poor callus formation, while starting too late (after 10–14 days) may result in premature consolidation (early fusion). 2. **Distraction Phase:** The bone is stretched at a rate of **1 mm per day**, usually divided into four increments (0.25 mm every 6 hours). 3. **Consolidation Phase:** The period where the newly formed "regenerate" bone mineralizes and hardens. **Analysis of Incorrect Options:** * **A (4-6 weeks):** This is the typical time for clinical union in simple fractures, not the latent period for distraction. * **C & D (6-8 months / 4 months):** These timeframes are more representative of the total duration an Ilizarov fixator might remain on a limb for complex lengthening or non-union treatments. **High-Yield Clinical Pearls for NEET-PG:** * **The Law of Tension-Stress:** Proposed by Ilizarov, stating that gradual traction on living tissues stimulates and maintains the regeneration and growth of those tissues. * **Rate of Distraction:** 1 mm/day is the gold standard. <0.5 mm/day leads to premature fusion; >2 mm/day leads to non-union and nerve damage. * **Most common complication:** Pin tract infection. * **Best site for corticotomy:** Metaphysis (due to superior vascularity and osteogenic potential).
Question 9: Bone resorption is enhanced by which of the following?
- A. PGD2
- B. PDF2
- C. PGE2 (Correct Answer)
- D. PGI2
Explanation: **Explanation:** Bone remodeling is a dynamic process regulated by various systemic hormones and local inflammatory mediators. Prostaglandins, which are derivatives of arachidonic acid, play a significant role in this process. **Why PGE2 is the Correct Answer:** **Prostaglandin E2 (PGE2)** is the most potent stimulator of bone resorption among the prostaglandins. It acts by stimulating the **RANKL (Receptor Activator of Nuclear Factor kappa-B Ligand)** expression in osteoblasts. This RANKL then binds to RANK receptors on osteoclast precursors, leading to their maturation and activation. While PGE2 has a dual role (it can also stimulate bone formation in certain concentrations), its primary clinical significance in inflammatory states (like rheumatoid arthritis or periodontal disease) is the induction of osteoclastogenesis and subsequent bone loss. **Analysis of Incorrect Options:** * **PGD2 (Prostaglandin D2):** Primarily involved in smooth muscle relaxation and allergic responses; it does not have a significant stimulatory effect on bone resorption. * **PGF2α (often mislabeled as PDF2):** While it can influence bone metabolism, it is significantly less potent than PGE2 and is more associated with uterine contraction. * **PGI2 (Prostacyclin):** Mainly acts as a potent vasodilator and inhibitor of platelet aggregation; it has minimal to no role in enhancing bone resorption. **High-Yield Clinical Pearls for NEET-PG:** * **NSAIDs and Bone:** Since NSAIDs inhibit prostaglandin synthesis (COX inhibition), they can theoretically delay fracture healing by reducing PGE2-mediated bone remodeling. * **IL-1 and TNF-α:** These cytokines also enhance bone resorption by stimulating PGE2 production. * **Bisphosphonates:** These are the drugs of choice to *inhibit* bone resorption by inducing osteoclast apoptosis.
Question 10: Which anatomical structure is considered a dynamic stabilizer of the shoulder joint?
- A. Rotator cuff (Correct Answer)
- B. Glenoid labrum
- C. Coracohumeral ligament
- D. Glenohumeral ligament
Explanation: **Explanation:** The stability of the shoulder (glenohumeral) joint is maintained by a complex interplay between static and dynamic stabilizers. **1. Why the Rotator Cuff is correct:** The **Rotator Cuff** (comprising the Supraspinatus, Infraspinatus, Teres minor, and Subscapularis—SITS muscles) is the primary **dynamic stabilizer**. These muscles stabilize the joint through "concavity compression." As they contract, they pull the large humeral head into the shallow glenoid fossa, centering it during movement. Because they require active muscular contraction to provide stability, they are classified as dynamic. **2. Why the other options are incorrect:** * **Glenoid Labrum (B):** This is a fibrocartilaginous rim that deepens the glenoid cavity. It is a **static stabilizer** because it provides structural stability without active contraction. * **Coracohumeral Ligament (C) & Glenohumeral Ligaments (D):** These are capsular thickenings that act as **static stabilizers**. They provide stability only at the end-range of motion when they become taut, preventing excessive translation of the humeral head. **High-Yield Clinical Pearls for NEET-PG:** * **Static Stabilizers:** Include the glenoid labrum, joint capsule, glenohumeral ligaments (Superior, Middle, and Inferior), and negative intra-articular pressure. * **The "Safety Belt" of the Shoulder:** The **Inferior Glenohumeral Ligament (IGHL)** is the most important static stabilizer against anterior dislocation when the shoulder is abducted and externally rotated. * **Long Head of Biceps:** Often considered a secondary dynamic stabilizer, as it depresses the humeral head. * **Rotator Interval:** A triangular space between the Supraspinatus and Subscapularis; it is a common site for pathology in shoulder instability.
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