3D Printing in Orthopaedic Surgery — MCQs
Identify the marked structure in the given image.
A patient with metastatic breast cancer presents with pathological fracture of femur. What is the best fixation method?
The ideal synthetic material used for femoropopliteal bypass when autologous vein is unavailable is:
All of the following factors affect osseointegration EXCEPT:
In immediate denture, why is clear acrylic stent or surgical template given soon after extraction?
What is the most effective management strategy for hemarthrosis?
What does the given image show?
A surgeon experiences pin-site fracture during reference array fixation in computer-navigated TKA in an osteoporotic patient. Subsequently, three more cases develop similar complications. What systematic approach should be implemented to prevent this complication?
A tertiary care center is planning to implement computer-assisted surgery program for joint replacement. They have limited budget and expertise. Which factor should be prioritized when selecting a navigation system?
A study compares outcomes of computer-navigated versus conventional total knee arthroplasty. Navigation group shows 95% implants within 3 degrees of neutral mechanical axis versus 80% in conventional group (p<0.05). However, 5-year functional outcomes and survival rates are similar. What is the most appropriate interpretation?
3D Printing in Orthopaedic Surgery Indian Medical PG Practice Questions and MCQs
Question 1: Identify the marked structure in the given image.
- A. Electrode
- B. Coil (Correct Answer)
- C. Magnet
- D. Processor
Explanation: ***Coil*** - The marked structure appears to be a **cochlear implant's internal coil**, which is common in X-ray imaging of these devices. - The **cochlear implant internal coil** is crucial for transmitting processed sound signals via electromagnetic induction to the electrode array within the cochlea. *Electrode* - An **electrode array** is typically a thin, flexible wire with multiple contacts inserted into the cochlea, which is not what the arrow is pointing to directly. - While electrodes are part of a cochlear implant, the marked structure's shape and position are more consistent with the **internal coil** that connects to the electrode array. *Magnet* - A **magnet** is present in a cochlear implant system, typically in both the external processor and internal receiver, to hold these two components together through the skin. - Magnets usually appear as dense, circular structures in X-rays, often seen more anteriorly or superiorly to the coil for external component alignment. *Processor* - The **processor** for a cochlear implant is an external device worn behind the ear, not an implanted component visible on an X-ray. It processes sound and sends it to the internal coil. - The structures seen in the X-ray are **implanted components** of the cochlear implant, not the external sound processor.
Question 2: A patient with metastatic breast cancer presents with pathological fracture of femur. What is the best fixation method?
- A. Long Intramedullary Nail (Correct Answer)
- B. External Fixator
- C. Dynamic Hip Screw
- D. Plate and Screws
Explanation: ***Long Intramedullary Nail*** - Provides **strong internal fixation** that can bear weight immediately, crucial for patients with a limited life expectancy due to metastatic disease. - Stabilizes the entire bone, preventing further **pathological fractures** in the diaphysis and allowing earlier mobilization and pain relief. *External Fixator* - Primarily used for **temporary stabilization** in severe open fractures or polytrauma, and not for definitive fixation of pathological fractures. - High risk of **pin tract infections** and patient discomfort, making it unsuitable for long-term management in cancer patients. *Dynamic Hip Screw* - Primarily used for **intertrochanteric hip fractures**, which are typically proximal femur fractures. - Less effective for **diaphyseal fractures** or for stabilizing bone weakened by metastatic disease along its entire length. *Plate and Screws* - While effective for some fractures, plates may not provide sufficient **load-bearing capacity** for extensively lytic or weakened bone in metastatic disease without extensive bone grafting. - Risk of **stress shielding** and subsequent re-fracture proximal or distal to the plate, especially when the intramedullary canal is compromised by tumor.
Question 3: The ideal synthetic material used for femoropopliteal bypass when autologous vein is unavailable is:
- A. Dacron
- B. Xenograft
- C. Saphenous vein
- D. PTFE (non-expanded)
- E. Cryopreserved vein graft
- F. ePTFE (Correct Answer)
- . Polyethylene terephthalate (PET)
- . Allograft
Explanation: ***ePTFE (Expanded Polytetrafluoroethylene)*** - **ePTFE** is the preferred synthetic graft for femoropopliteal bypass when autologous vein is unavailable - Offers good **biocompatibility** and relative resistance to **thrombosis** - Provides superior patency rates in above-knee femoropopliteal bypasses compared to other synthetic materials (5-year patency ~50-60%) - The expanded structure allows tissue ingrowth and better integration *Dacron (Polyethylene terephthalate)* - Generally used for **larger diameter vessels** (e.g., aortoiliac grafts) - Has **inferior patency rates** in smaller diameter femoropopliteal position compared to ePTFE - More prone to kinking and associated with higher rates of intimal hyperplasia in peripheral circulation *Saphenous vein* - The autologous saphenous vein is the **gold standard** for femoropopliteal bypass with superior long-term patency (5-year patency ~70-80%) - However, this question specifically asks for synthetic material when vein is unavailable or unsuitable - Not always available or of adequate quality in all patients *PTFE (non-expanded)* - **Non-expanded PTFE** lacks the porous structure of ePTFE - Not used for vascular grafts due to absence of tissue ingrowth capability - The **expanded** form is specifically engineered for vascular applications
Question 4: All of the following factors affect osseointegration EXCEPT:
- A. Biocompatibility of implant material.
- B. Implant design.
- C. Patient's blood type (Correct Answer)
- D. Status of the host bed.
Explanation: ***Patient's blood type*** - A patient's **blood type** (e.g., A, B, AB, O) is determined by antigens present on red blood cells and plays no direct role in the biological processes of bone healing or the integration of a dental implant with bone. - While systemic factors can influence osseointegration, blood type itself does not affect the cellular and molecular mechanisms required for direct bone-to-implant contact. *Biocompatibility of implant material* - The **biocompatibility** of the implant material (e.g., **titanium**) is crucial for osseointegration, as it must not elicit adverse reactions and must permit host bone growth on its surface. - Materials that are cytotoxic or inflammatory will prevent bone apposition and lead to fibrous encapsulation rather than direct bone contact. *Implant design* - **Implant design**, including features like **surface roughness**, thread pitch, and macro-geometry, significantly influences the initial stability and long-term success of osseointegration. - A greater surface area and appropriate surface treatments can enhance bone cell attachment and differentiation, promoting faster and stronger bone integration. *Status of the host bed* - The **status of the host bone bed** refers to its quality and quantity (e.g., bone density, vascularity), which are critical for the biological processes of osseointegration. - Adequate bone volume and good bone quality provide a stable foundation and sufficient blood supply for bone regeneration around the implant.
Question 5: In immediate denture, why is clear acrylic stent or surgical template given soon after extraction?
- A. For trimming jagged bone margins (Correct Answer)
- B. Condition tissues
- C. For impression taking
- D. Contain socket healing substances
Explanation: ***For trimming jagged bone margins*** - A clear acrylic stent aids in visualizing the underlying bone during surgery, allowing the clinician to **trim any sharp or jagged bone margins** post-extraction. - This process is crucial for creating a smooth, even ridge that will properly support the immediate denture and prevent **pressure sores** or discomfort. *Condition tissues* - Tissue conditioning is typically performed with a soft reline material placed inside an existing denture or a temporary base to improve the health of abused oral tissues. - A clear acrylic stent is a rigid device used during surgery and does not possess properties to condition tissues. *For impression taking* - Impressions for immediate dentures are taken *before* extractions to capture the existing dentition and soft tissue contours, which are then used to fabricate the denture. - A clear acrylic stent is used *during* the surgical phase, after extractions, to guide bone reshaping, not for taking an impression. *Contain socket healing substances* - While some materials can be placed in extraction sockets to aid healing, the primary purpose of a clear acrylic surgical template is mechanical guidance for bone reduction. - It itself does not typically contain or deliver healing substances to the socket.
Question 6: What is the most effective management strategy for hemarthrosis?
- A. Immobilization with a P.O.P. cast
- B. Application of a compression bandage
- C. Needle aspiration to remove excess blood (Correct Answer)
- D. All of the options
Explanation: ***Needle aspiration to remove excess blood*** - **Aspirating the blood** from the joint effectively reduces intra-articular pressure, pain, and inflammation. - This procedure also helps prevent **synovial hypertrophy** and **cartilage damage** caused by the presence of blood in the joint. *Application of a compression bandage* - While helpful for reducing swelling and providing support, a **compression bandage alone** does not remove the accumulated blood. - It may alleviate some discomfort but does not address the underlying issue of **intra-articular blood accumulation**. *Immobilization with a P.O.P. cast* - **Immobilization** can help rest the joint and reduce pain, but it does not remove the blood from the joint space. - Prolonged immobilization can lead to **joint stiffness** and **muscle atrophy**, which are undesirable outcomes. *All of the options* - While compression and immobilization can be supportive measures, they are not the **most effective primary strategy** for managing hemarthrosis. - The direct removal of blood via **aspiration** is crucial for alleviating pressure and preventing long-term joint damage.
Question 7: What does the given image show?
- A. Doyen's periosteal elevator (Correct Answer)
- B. Cobb's spinal elevator
- C. Leksell's rongeur
- D. Key periosteal elevator
Explanation: ***Doyen's periosteal elevator*** - This instrument is characterized by its **curved, spoon-like working end** and solid handle, designed for **elevating the periosteum** from bone. - Doyen's elevator comes in various sizes and angles, but the distinct hook-like curve is a key identifying feature, distinguishing it from other elevators. *Cobb's spinal elevator* - Cobb's elevator typically has a **flat, broad, and slightly curved blade** with a rounded or tapered tip, suitable for dissecting along bony surfaces, particularly in spinal surgery. - Its design prioritizes broad, even separation of tissue layers, contrasting with the more acute curve of the Doyen's. *Leksell's rongeur* - A rongeur is a biting instrument used for **gnawing away bone or tough tissue**, characterized by hinged jaws with sharp, cup-shaped ends. - The image clearly shows a single-piece instrument without hinged jaws, ruling out a rongeur. *Key periosteal elevator* - The Key elevator typically features a **broader, more rounded or slightly angled tip** and a flat, somewhat spatula-like working end, used for general periosteal elevation. - While also a periosteal elevator, its working end does not exhibit the characteristic deep, hook-like curve seen in the Doyen's elevator.
Question 8: A surgeon experiences pin-site fracture during reference array fixation in computer-navigated TKA in an osteoporotic patient. Subsequently, three more cases develop similar complications. What systematic approach should be implemented to prevent this complication?
- A. Switch to electromagnetic navigation system
- B. Use unicortical pins instead of bicortical pins with reduced insertion torque protocol (Correct Answer)
- C. Abandon navigation in all osteoporotic patients
- D. Increase pin diameter for better fixation
Explanation: ***Use unicortical pins instead of bicortical pins with reduced insertion torque protocol*** - **Pin-site fractures** are a known complication in navigated TKA, especially in **osteoporotic bone**, and can be mitigated by reducing the **stress risers** created by drilling. - Using **unicortical pins** and avoiding power drivers to limit **insertion torque** provides sufficient stability for reference arrays while minimizing the risk of cortical failure. *Switch to electromagnetic navigation system* - **Electromagnetic navigation** aims to resolve line-of-sight issues but does not inherently eliminate the need for stable skeletal fixation of reference sensors. - Switching systems is a costly equipment change that does not directly address the underlying **biomechanical failure** of the bone-pin interface in osteoporosis. *Abandon navigation in all osteoporotic patients* - Abandoning navigation denies the patient population the benefits of **precise alignment** and component positioning where it is often most needed due to poor bone quality. - Systematic technical modifications are preferred over total abandonment of a beneficial **surgical technology**. *Increase pin diameter for better fixation* - Increasing the **pin diameter** is counterproductive as larger holes create larger **stress concentrators**, significantly increasing the risk of **periprosthetic fracture** in brittle bone. - A thicker pin displaces more cortical volume, which reduces the **structural integrity** of the femur or tibia in osteoporotic patients.
Question 9: A tertiary care center is planning to implement computer-assisted surgery program for joint replacement. They have limited budget and expertise. Which factor should be prioritized when selecting a navigation system?
- A. Image-based system requiring dedicated CT scanner
- B. Imageless navigation with good technical support and training program (Correct Answer)
- C. Most expensive system with all features available
- D. System with steepest learning curve to ensure only expert surgeons use it
Explanation: ***Imageless navigation with good technical support and training program*** - **Imageless navigation** is the most cost-effective choice for limited budgets as it avoids the preoperative costs and infrastructure associated with **CT scans** or dedicated imaging. - Prioritizing **technical support** and **training programs** is essential for overcoming the **learning curve** (typically 15-20 cases) in a center with limited initial expertise. *Image-based system requiring dedicated CT scanner* - These systems increase the **per-case cost** and require significant capital investment in preoperative **CT imaging** infrastructure. - They introduce additional **radiation exposure** to the patient and complex logistics that may not suit a center with limited resources. *Most expensive system with all features available* - Purchasing the most expensive system is counterproductive for a facility with a **limited budget**, as many advanced features may not be utilized during the initial phase. - High-cost systems often have higher **maintenance contracts** and operational costs that can lead to program failure in resource-constrained environments. *System with steepest learning curve to ensure only expert surgeons use it* - A **steep learning curve** is a major barrier to the adoption of new technology and can lead to increased **operation time** and operative complications. - The goal of implementing a new program should be **sustainable integration** and broad clinical utility rather than restricting access through technical difficulty.
Question 10: A study compares outcomes of computer-navigated versus conventional total knee arthroplasty. Navigation group shows 95% implants within 3 degrees of neutral mechanical axis versus 80% in conventional group (p<0.05). However, 5-year functional outcomes and survival rates are similar. What is the most appropriate interpretation?
- A. Navigation is inferior due to longer operative time without functional benefit
- B. Conventional technique should be abandoned
- C. Improved radiographic alignment may not translate to short-term functional improvement but could affect long-term survival (Correct Answer)
- D. The study proves navigation provides no clinical benefit
Explanation: ***Improved radiographic alignment may not translate to short-term functional improvement but could affect long-term survival*** - Navigation significantly improves **radiographic alignment** consistency (p<0.05), but high-quality evidence shows this does not always create immediate **functional differences** within 5 years. - While **short-term functional outcomes** are similar, reducing **outliers** to within 3 degrees of the neutral axis is theoretically linked to better **implant survival** beyond 10-15 years. *Navigation is inferior due to longer operative time without functional benefit* - Increased **operative time** is a known drawback, but it does not make the technique **inferior** if it achieves superior technical precision. - The term "inferior" is clinically inaccurate here as the study demonstrates **statistically significant** improvements in surgical accuracy. *Conventional technique should be abandoned* - **Conventional techniques** are still the gold standard because they provide identical **short-term survival** and clinical scores at a lower cost. - Abandonment is unjustified as long as the **clinical outcome** parity exists and long-term superiority of navigation is not yet definitively proven by this data. *The study proves navigation provides no clinical benefit* - Improved **mechanical axis** alignment is itself a technical clinical benefit that reduces mechanical stress on the polyethene liner. - A lack of difference in **5-year scores** does not prove a lack of benefit; it only indicates that **short-term follow-up** may be insufficient to detect long-term wear advantages.
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