Pathology of Orthopedic Implants — MCQs
Which microorganism is the most common cause of pyogenic osteomyelitis?
In which of the following conditions is joint erosion NOT a primary feature?
Primary osteoarthritis affects all except:
Which of the following is the commonest material used to make an orthopedic implant?
Most reliable method to identify putrefied bodies with metallic implants?
Arthritis mutilans is seen in?
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 45-year-old was given steroids after renal transplant. After 2 years he had difficulty in walking and pain in both hips. Which one of the following is most likely cause?
All the following are true about nosocomial infections except -
Which statement is incorrect about the pathology of the bone tumor?
Pathology of Orthopedic Implants Indian Medical PG Practice Questions and MCQs
Question 1: Which microorganism is the most common cause of pyogenic osteomyelitis?
- A. S. aureus (Correct Answer)
- B. Streptococcus spp.
- C. Corynebacterium spp.
- D. Neisseria gonorrhoeae (gonococcus)
Explanation: ***Staph aureus*** - **_Staphylococcus aureus_** is the most frequent cause of **pyogenic osteomyelitis** across all age groups and routes of infection. - Its ability to adhere to bone, form biofilms, and produce toxins contributes to its prevalence in bone infections. *Streptococcus spp.* - While various **_Streptococcus_** species can cause infections, they are less common causes of pyogenic osteomyelitis compared to **_Staphylococcus aureus_**. - **Group A _Streptococcus_** can cause severe invasive infections but rarely involves primary bone infection. *Corynebacterium spp.* - **_Corynebacterium_** species, particularly **_Corynebacterium striatum_**, are increasingly recognized as opportunistic pathogens, especially in immunocompromised individuals or those with foreign bodies. - However, they are not the most common cause of osteomyelitis in the general population. *Neisseria gonorrhoeae (gonococcus)* - **_Neisseria gonorrhoeae_** can cause **disseminated gonococcal infection (DGI)**, which may include joint involvement (**septic arthritis**). - While it can lead to bone pain and swelling, it primarily affects joints and is a less common cause of direct **pyogenic osteomyelitis** than **_S. aureus_**.
Question 2: In which of the following conditions is joint erosion NOT a primary feature?
- A. Psoriatic arthropathy
- B. Rheumatoid arthritis
- C. Osteoarthritis
- D. SLE (Correct Answer)
Explanation: ***SLE*** - While arthritis is common in **Systemic Lupus Erythematosus (SLE)**, it is typically **non-erosive**, meaning it does not cause damage to the **cartilage** or **bone** [1]. - Joint involvement in SLE is often characterized by **arthralgias** or a **reversible inflammatory arthritis**. *Osteoarthritis* - **Osteoarthritis** is definitively characterized by the **progressive erosion of articular cartilage**, leading to **bone-on-bone friction** and structural changes. - This condition involves **wear-and-tear** that directly causes damage to the joint surfaces. *Psoriatic arthropathy* - **Psoriatic arthropathy** (Psoriatic Arthritis) is an inflammatory condition that can lead to significant **joint erosion** and **destruction**, particularly in the small joints of the hands and feet [1]. - It often features characteristic radiographic changes such as **"pencil-in-cup" deformities** due to bone resorption and erosion [1]. *Rheumatoid arthritis* - **Rheumatoid arthritis** is a classic example of an inflammatory arthritis where **joint erosion** is a primary and hallmark feature, driven by **synovial inflammation** and pannus formation. - Persistent inflammation in RA leads to **cartilage destruction** and **subchondral bone erosion**.
Question 3: Primary osteoarthritis affects all except:
- A. Metacarpophalangeal joint (Correct Answer)
- B. Hip Joint
- C. Distal interphalangeal joint
- D. Knee joint
Explanation: ***Metacarpophalangeal joint*** - The **metacarpophalangeal (MCP) joints** are typically spared in primary osteoarthritis, making their involvement a less common presentation. - Involvement of the MCP joints, particularly with significant inflammation, might suggest other conditions like **rheumatoid arthritis**. *Hip Joint* - The hip joint is a common site for primary osteoarthritis due to its **weight-bearing function** and susceptibility to mechanical stress. - Patients often experience **groin pain** and reduced range of motion, particularly internal rotation. *Distal interphalangeal joint* - The **distal interphalangeal (DIP) joints** are very commonly affected in primary osteoarthritis, leading to the formation of **Heberden's nodes**. - These nodes are bony enlargements that indicate osteophyte formation and cartilage loss. *Knee joint* - The knee joint is another frequently affected large joint in primary osteoarthritis, often presenting with **pain**, **stiffness**, and **crepitus**. - Its **weight-bearing role** contributes significantly to its vulnerability to degenerative changes.
Question 4: Which of the following is the commonest material used to make an orthopedic implant?
- A. Methyl-methacrylate
- B. Polyethylene (UHMWPE)
- C. Titanium (Correct Answer)
- D. Stainless steel
Explanation: ***Titanium*** - **Titanium** and its alloys (e.g., Ti-6Al-4V) are widely favored for orthopedic implants due to their **excellent biocompatibility**, high strength-to-weight ratio, and corrosion resistance. - Its **osseointegrative properties** allow bone to grow directly onto the implant surface, providing stable fixation without an intervening fibrous layer. *Methyl-methacrylate* - **Methyl-methacrylate** is primarily used as a **bone cement** (PMMA) to fix implants to bone, rather than as the primary material for the implant itself. - It provides immediate mechanical stability but does not integrate with bone. *Polyethylene (UHMWPE)* - **Ultra-high molecular weight polyethylene (UHMWPE)** is commonly used as a bearing surface in joint replacements (e.g., acetabular liner in hip replacements) for its **low friction** and good wear resistance. - It is not typically used for the structural components of the implant that bear the primary load. *Stainless steel* - **Stainless steel** (e.g., 316L) was historically a common implant material, particularly for temporary fixation devices like plates and screws. - While it has good strength and corrosion resistance, it generally has a **lower biocompatibility** and more elastic modulus mismatch with bone compared to titanium, making it less preferred for permanent, load-bearing implants.
Question 5: 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 6: Arthritis mutilans is seen in?
- A. Rheumatoid arthritis
- B. Spondyloarthropathy
- C. Reactive arthritis
- D. Psoriatic arthropathy (Correct Answer)
Explanation: ***Psoriatic arthropathy*** - **Arthritis mutilans** is a severe, destructive form of psoriatic arthritis characterized by marked **osteolysis** and telescoping deformities of the digits [1]. - This condition is almost exclusively associated with **psoriatic arthritis**, representing its most aggressive subtype [1]. *Rheumatoid arthritis* - While rheumatoid arthritis can cause severe joint destruction, it typically manifests as **erosive arthritis** with joint deformities like **swan-neck** and **boutonnière deformities**, but not true arthritis mutilans [3]. - The pattern of bone destruction (osteolysis) seen in arthritis mutilans is distinct from the erosions in rheumatoid arthritis. *Spondyloarthropathy* - This is a broad category that includes diseases like ankylosing spondylitis and reactive arthritis, which primarily affect the **axial skeleton** and entheses. - While some spondyloarthropathies can cause peripheral joint involvement, they generally do not lead to the extreme osteolysis and telescoping digits characteristic of arthritis mutilans. *Reactive arthritis* - Reactive arthritis is an aseptic inflammatory arthritis that often follows infection, characterized by **oligoarthritis**, dactylitis, and enthesitis [2]. - This condition does not typically cause the severe, mutilating joint destruction seen in arthritis mutilans.
Question 7: 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 8: A 45-year-old was given steroids after renal transplant. After 2 years he had difficulty in walking and pain in both hips. Which one of the following is most likely cause?
- A. Tuberculosis
- B. Primary Osteoarthritis
- C. Aluminum toxicity
- D. Avascular necrosis (Correct Answer)
Explanation: ***Avascular necrosis*** - Chronic **steroid use**, especially after organ transplantation, is a major risk factor for avascular necrosis (AVN) due to impaired blood supply to bone, particularly in the femoral head. - **Hip pain** and **difficulty walking** are classic symptoms of AVN, which can lead to collapse of the femoral head if untreated. *Tuberculosis* - While tuberculosis can affect bones and joints (**Pott's disease**), it typically presents with more systemic symptoms like fever, weight loss, and night sweats, which are not mentioned. - Skeletal TB often affects the spine more commonly and usually presents with granulomatous inflammation and bone destruction rather than isolated joint pain in the hips *Primary Osteoarthritis* - Primary osteoarthritis is typically an **age-related degenerative joint disease** occurring in older individuals, and while it causes hip pain, it is not directly linked to steroid use in a 45-year-old. - The onset of pain in this scenario, following long-term steroid use, strongly points away from primary osteoarthritis as the primary driving factor. *Aluminum toxicity* - Aluminum toxicity can occur in patients with **renal failure** and can cause **osteomalacia** or **dialysis encephalopathy**. - Its presentation typically involves bone pain, fractures, and neurological symptoms, but it does not specifically cause avascular necrosis of the femoral head as seen with steroid use.
Question 9: All the following are true about nosocomial infections except -
- A. May develop after discharge of patient from the hospital
- B. May already present at the time of admission (Correct Answer)
- C. Denote a new condition which is unrelated to the patient's primary conditions
- D. May manifest 48 hours or more after admission
Explanation: ***May already present at the time of admission*** - This statement is **incorrect** because a **nosocomial infection** is defined as an infection acquired in a hospital or healthcare setting, meaning it was **not present** or incubating at the time of admission. - If an infection is present upon admission, it is considered a **community-acquired infection**, not nosocomial. *May develop after discharge of patient from the hospital* - Nosocomial infections can indeed **manifest after discharge**, especially for infections with longer incubation periods or those related to procedures or devices. - For example, a surgical site infection might not become apparent until several days or weeks after discharge (within 30 days for most infections, or up to 90 days for certain surgical site infections). *May manifest 48 hours or more after admission* - An infection is considered nosocomial if it appears **48 hours or more** after hospital admission. - This is the standard criterion to differentiate hospital-acquired infections from community-acquired infections that were incubating at the time of admission. *Denote a new condition which is unrelated to the patient's primary conditions* - Nosocomial infections are **new infections** that arise during the hospital stay and are not directly related to the patient's existing primary diagnosis. - While a patient's underlying condition might make them **more susceptible**, the infection itself is distinct and newly acquired from the healthcare environment.
Question 10: Which statement is incorrect about the pathology of the bone tumor?
- A. Tumor has distinct margin
- B. Tumor arises from epiphyseal to metaphyseal region
- C. Eccentric lesion
- D. Chemotherapy is the treatment of choice for all bone tumors. (Correct Answer)
Explanation: ***Tumor has distinct margin*** - A **distinct margin** often indicates a benign tumor, while malignant tumors typically show **infiltrative margins**. - In bone tumors, particularly malignant ones, the lack of clear demarcation is a key pathological feature. *Chemotherapy is the treatment of choice* - While chemotherapy may be used for certain **malignant bone tumors**, it is not the first-line treatment for most bone tumors [1]. - The primary treatment is often **surgical excision**, especially for localized lesions [1]. *Tumor arise from epiphyseal to metaphyseal region* - While some tumors can originate in these areas, many actually arise from the **diaphyseal** region in bone tumors like osteosarcoma. - This option misrepresents the common locations where various tumors develop, as osteochondromas tend to develop near the epiphyses of limb bones [2]. *Eccentric lesion* - Many bone tumors do indeed present as **eccentric lesions**, especially benign ones like **osteochondromas**. - However, this feature does not apply universally, as some malignant tumors can also be **central or infiltrative** in nature. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 673-674. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 672-673.
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