Orthopaedics & MSK — MCQs
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A 38-year-old woman presents to the Emergency Department with sudden onset severe lower back pain and inability to pass urine for 12 hours. She has bilateral leg weakness and numbness in the perineal region. On examination, anal tone is reduced and there is saddle anaesthesia. What is the most appropriate immediate management?
A 66-year-old woman presents with a 3-month history of lower back pain and bilateral leg pain worse on walking. She reports that the pain improves when she leans forward on a shopping trolley. She has no night pain, no bladder or bowel disturbance, and no weight loss. Neurological examination reveals normal power, sensation, and reflexes. What is the most likely diagnosis?
Which of the following Garden classification stages for intracapsular neck of femur fractures has the highest risk of developing avascular necrosis of the femoral head?
A 41-year-old man presents with a 2-week history of severe lower back pain and fevers. He has a past medical history of type 2 diabetes mellitus with poor glycaemic control. On examination, he has tenderness over the L3-L4 vertebrae and his temperature is 38.4°C. Blood tests show: WCC 16.2 × 10⁹/L, CRP 145 mg/L, ESR 78 mm/hr. What is the most appropriate initial imaging investigation?
A 79-year-old woman sustains a displaced intracapsular neck of femur fracture. During preoperative assessment, she is found to have a serum creatinine of 180 μmol/L and an estimated glomerular filtration rate (eGFR) of 28 mL/min/1.73m². She is otherwise medically stable. Which surgical intervention should be performed?
A 78-year-old man with Parkinson's disease sustains a minimally displaced basicervical neck of femur fracture after falling in his care home. His pre-injury mobility was limited to indoor walking with a frame, and he requires assistance with most activities of daily living. The orthopaedic team is considering the optimal surgical management. Which of the following factors makes a basicervical fracture biomechanically distinct from a typical intracapsular neck of femur fracture and influences surgical choice?
A 64-year-old woman presents to the Emergency Department with a 36-hour history of severe lower back pain and urinary retention. She reports numbness in the perineal area and has noticed loss of sensation when wiping after using the toilet. On examination, there is reduced sensation in the S2-S4 dermatomes bilaterally, reduced anal tone, and a palpable bladder. Lower limb power and reflexes are normal. Post-void residual volume is 800 ml. What is the maximum acceptable time from presentation to definitive surgical decompression to optimize neurological outcome?
A 67-year-old man sustains a subtrochanteric femur fracture following a fall from a ladder. He has a 10-year history of bisphosphonate therapy for osteoporosis following a previous vertebral compression fracture. Radiographs show a transverse fracture pattern at the subtrochanteric level with cortical thickening of the lateral femoral cortex. Which feature of this fracture pattern is most characteristic of an atypical femur fracture associated with long-term bisphosphonate use?
A 61-year-old woman with rheumatoid arthritis presents to her GP with a 6-week history of lower back pain and progressive bilateral leg weakness. She has been on long-term methotrexate and prednisolone for 15 years. On examination, there is global weakness in both lower limbs (power 3/5 throughout), with preserved reflexes and normal plantar responses. Sensation is intact. She is apyrexial. Blood tests show CRP 45 mg/L, ESR 68 mm/hr, normal white cell count. Which of the following is the most likely underlying cause of her presentation?
A 72-year-old woman undergoes a dynamic hip screw (DHS) fixation for a stable two-part intertrochanteric neck of femur fracture. Post-operatively, what is the most important radiographic measurement to assess optimal placement of the lag screw within the femoral head?
Orthopaedics & MSK UK Medical PG Practice Questions and MCQs
Question 111: A 38-year-old woman presents to the Emergency Department with sudden onset severe lower back pain and inability to pass urine for 12 hours. She has bilateral leg weakness and numbness in the perineal region. On examination, anal tone is reduced and there is saddle anaesthesia. What is the most appropriate immediate management?
- A. Arrange urgent MRI spine within 24 hours and refer to physiotherapy
- B. Prescribe oral prednisolone and arrange outpatient MRI
- C. Insert urinary catheter, arrange emergency MRI, and contact neurosurgery/spinal team immediately (Correct Answer)
- D. Arrange CT lumbar spine and admit for bed rest
- E. Commence high-dose NSAIDs and arrange urgent orthopaedic outpatient review
Explanation: ***Insert urinary catheter, arrange emergency MRI, and contact neurosurgery/spinal team immediately*** - This patient presents with hallmark signs of **Cauda Equina Syndrome (CES)**, including **urinary retention**, **saddle anesthesia**, and **reduced anal tone**, which constitutes a surgical emergency. - Immediate management requires **emergency MRI** to confirm compression and urgent **neurosurgical/spinal consultation** for decompression to prevent permanent neurological deficits. *Arrange urgent MRI spine within 24 hours and refer to physiotherapy* - A "within 24 hours" timeframe is insufficient for suspected CES, which requires **emergency imaging** and intervention ideally as soon as possible to optimize recovery. - **Physiotherapy** is an inappropriate primary referral for an acute cord/cauda equina compression where surgical intervention is the priority. *Prescribe oral prednisolone and arrange outpatient MRI* - **Outpatient MRI** is dangerously slow for CES, as neurological damage can become **irreversible** within hours. - While steroids are used for **Malignant Spinal Cord Compression (MSCC)**, they are not the definitive treatment for mechanical causes of CES like a massive disc prolapse. *Arrange CT lumbar spine and admit for bed rest* - **MRI** is the gold standard imaging modality because **CT** provides poor visualization of soft tissues, nerve roots, and the extent of canal compromise. - **Bed rest** alone is a passive management strategy that fails to address the underlying physical compression of the **cauda equina**. *Commence high-dose NSAIDs and arrange urgent orthopaedic outpatient review* - **NSAIDs** are for symptomatic relief of simple back pain and are entirely inadequate for the profound **neurological compromise** seen in this patient. - **Outpatient review** is an inappropriate delay for a condition that requires **emergency decompression surgery** to save bladder and bowel function.
Question 112: A 66-year-old woman presents with a 3-month history of lower back pain and bilateral leg pain worse on walking. She reports that the pain improves when she leans forward on a shopping trolley. She has no night pain, no bladder or bowel disturbance, and no weight loss. Neurological examination reveals normal power, sensation, and reflexes. What is the most likely diagnosis?
- A. Lumbar disc herniation
- B. Cauda equina syndrome
- C. Spinal stenosis (Correct Answer)
- D. Ankylosing spondylitis
- E. Malignant spinal cord compression
Explanation: ***Spinal stenosis*** - This patient presents with classic **neurogenic claudication**, where bilateral leg pain is triggered by walking and relieved by spine flexion, often called the **'shopping trolley sign'**. - Forward flexion increases the **spinal canal diameter**, reducing pressure on nerve roots caused by degenerative changes like **ligamentum flavum hypertrophy** or facet joint arthropathy. *Lumbar disc herniation* - Typically presents with **acute onset** unilateral radicular pain (sciatica) that is often worsened by sitting or forward flexion, rather than relieved by it. - Physical examination usually reveals a positive **straight leg raise test** and specific dermatomal or myotomal deficits, which are absent here. *Cauda equina syndrome* - A surgical emergency characterized by **saddle anesthesia**, new-onset **urinary retention** or fecal incontinence, and significant bilateral neurological deficits. - The absence of **bladder/bowel disturbance** and a normal neurological exam effectively rule out this diagnosis. *Ankylosing spondylitis* - Usually presents in **younger patients** (under 45) with chronic inflammatory back pain and **morning stiffness** that improves with exercise. - It is associated with the **HLA-B27** gene and involves progressive spinal fusion rather than mechanical claudication symptoms. *Malignant spinal cord compression* - Characterized by **'red flag' symptoms** such as persistent night pain, unexplained weight loss, and a history of primary malignancy. - This patient lacks constitutional symptoms, and her pain is specifically related to **posture and walking** rather than being constant or nocturnal.
Question 113: Which of the following Garden classification stages for intracapsular neck of femur fractures has the highest risk of developing avascular necrosis of the femoral head?
- A. Garden I - incomplete fracture, undisplaced
- B. Garden II - complete fracture, undisplaced
- C. Garden III - complete fracture, partially displaced
- D. Garden IV - complete fracture, completely displaced (Correct Answer)
- E. All Garden stages have equal risk
Explanation: ***Garden IV - complete fracture, completely displaced*** - This stage represents a total loss of contact between the fragments, leading to the highest degree of disruption to the **medial circumflex femoral artery** and retinacular vessels. - The significant displacement correlates with an **avascular necrosis (AVN)** risk of approximately 30-35%, the highest among all Garden categories. *Garden I - incomplete fracture, undisplaced* - These are **impacted or incomplete** fractures where the blood supply remains largely intact, resulting in a low AVN risk of about 5-10%. - The **trabeculae** are angulated but not completely disrupted, maintaining better physiological stability than higher stages. *Garden II - complete fracture, undisplaced* - While the fracture is complete, the lack of displacement means the **vascular supply** to the femoral head is generally preserved. - The risk of developing **avascular necrosis** is relatively low (10-15%) compared to displaced fracture patterns. *Garden III - complete fracture, partially displaced* - This stage involves partial displacement where the distal fragment is **externally rotated**, causing significant but incomplete vascular compromise. - Although the risk of **AVN** is high (20-30%), it is statistically lower than the total disruption seen in Stage IV. *All Garden stages have equal risk* - This statement is incorrect because the classification is specifically designed to predict the likelihood of **vascular impairment** based on displacement. - Clinical management differs significantly between stages because the risk of **non-union** and AVN increases progressively from Stage I to Stage IV.
Question 114: A 41-year-old man presents with a 2-week history of severe lower back pain and fevers. He has a past medical history of type 2 diabetes mellitus with poor glycaemic control. On examination, he has tenderness over the L3-L4 vertebrae and his temperature is 38.4°C. Blood tests show: WCC 16.2 × 10⁹/L, CRP 145 mg/L, ESR 78 mm/hr. What is the most appropriate initial imaging investigation?
- A. Plain radiograph of lumbar spine
- B. CT scan of lumbar spine
- C. MRI scan of whole spine (Correct Answer)
- D. Bone scintigraphy
- E. Ultrasound-guided biopsy
Explanation: ***MRI scan of whole spine*** - **MRI** is the gold standard and most appropriate initial imaging because it has the highest sensitivity (96%) and specificity (93%) for detecting early **spinal infection** (discitis/osteomyelitis). - A **whole spine** scan is mandatory as it can identify **skip lesions**, localized **epidural abscesses**, and paraspinal collections that are not clinically apparent. *Plain radiograph of lumbar spine* - **Plain X-rays** have very low sensitivity in the acute phase, as bone destruction or **disc space narrowing** may not be visible for 2 to 4 weeks after symptoms start. - They often appear normal in the early presentation of **vertebral osteomyelitis**, delaying critical diagnosis. *CT scan of lumbar spine* - **CT scanning** provides excellent detail of **cortical bone destruction**, but it is significantly less sensitive than MRI for detecting early **marrow edema** and soft tissue involvement. - It is generally reserved for patients who have a **contraindication to MRI**, such as certain metallic implants or severe claustrophobia. *Bone scintigraphy* - **Technetium-99m bone scans** are sensitive to increased bone turnover but lack **anatomical specificity**, making it difficult to distinguish infection from degenerative changes or tumors. - This modality is rarely used as a first-line test when MRI is available due to the high rate of **false positives** in elderly populations. *Ultrasound-guided biopsy* - While a **biopsy** is essential for microbiological diagnosis and antibiotic sensitivity, it should be performed **after imaging** has localized the pathology. - Imaging must be obtained first to determine the **extent of the infection** and provide a safe anatomical window for the needle insertion.
Question 115: A 79-year-old woman sustains a displaced intracapsular neck of femur fracture. During preoperative assessment, she is found to have a serum creatinine of 180 μmol/L and an estimated glomerular filtration rate (eGFR) of 28 mL/min/1.73m². She is otherwise medically stable. Which surgical intervention should be performed?
- A. Total hip replacement with uncemented components
- B. Cemented hemiarthroplasty
- C. Uncemented hemiarthroplasty (Correct Answer)
- D. Cannulated screw fixation
- E. Dynamic hip screw fixation
Explanation: ***Uncemented hemiarthroplasty***- For patients with significant **renal impairment** (eGFR of 28 mL/min/1.73m²), **uncemented** components are preferred to avoid the risk of **Bone Cement Implantation Syndrome (BCIS)**, which can cause severe cardiovascular instability.- **Hemiarthroplasty** is the standard treatment for a **displaced intracapsular neck of femur fracture** in a 79-year-old to ensure early mobilization and reduce the risk of **avascular necrosis** and non-union.*Total hip replacement with uncemented components*- **Total hip replacement (THR)** is typically reserved for **fitter, more active** elderly patients with good cognitive function and minimal comorbidities.- While uncemented avoids BCIS, a **hemiarthroplasty** is generally more appropriate for a 79-year-old with significant comorbidities like **chronic kidney disease** due to less operative time and surgical stress.*Cemented hemiarthroplasty*- **Cemented components** are often preferred in the elderly for immediate stability and reduced periprosthetic fracture risk, but the use of bone cement carries a risk of **BCIS**.- Given the patient's severe **renal impairment** (eGFR 28), the systemic effects of cement polymerization could lead to dangerous **cardiovascular compromise**, making cemented arthroplasty contraindicated.*Cannulated screw fixation*- **Cannulated screw fixation** is primarily indicated for **undisplaced** intracapsular femoral neck fractures or in younger, physiologically active patients.- In a 79-year-old with a **displaced fracture**, this method has a very **high failure rate** due to **non-union** and increased risk of **avascular necrosis** of the femoral head.*Dynamic hip screw fixation*- A **dynamic hip screw (DHS)** is the treatment of choice for **extracapsular** (intertrochanteric and subtrochanteric) fractures of the femur.- It is **not indicated** for **intracapsular fractures** because it does not protect the vascular supply to the femoral head, leaving a high risk of **avascular necrosis**.
Question 116: A 78-year-old man with Parkinson's disease sustains a minimally displaced basicervical neck of femur fracture after falling in his care home. His pre-injury mobility was limited to indoor walking with a frame, and he requires assistance with most activities of daily living. The orthopaedic team is considering the optimal surgical management. Which of the following factors makes a basicervical fracture biomechanically distinct from a typical intracapsular neck of femur fracture and influences surgical choice?
- A. Higher risk of avascular necrosis due to disruption of retinacular blood supply
- B. Greater tendency to displace into varus due to orientation outside the capsular attachment (Correct Answer)
- C. Lower risk of non-union due to better blood supply than intracapsular fractures
- D. Higher incidence of associated femoral shaft fracture requiring longer implants
- E. Reduced risk of fixation failure due to increased bone density at the basicervical region
Explanation: ***Greater tendency to displace into varus due to orientation outside the capsular attachment*** - **Basicervical fractures** occur at the junction of the femoral neck and the **intertrochanteric region**, making them biomechanically unstable with a significant tendency toward **varus collapse**. - Because they are located at or just outside the **capsular attachment**, they lack the stabilizing effect of the joint capsule and often feature a **vertical fracture line**, necessitating robust fixation like a **Dynamic Hip Screw (DHS)**. *Higher risk of avascular necrosis due to disruption of retinacular blood supply* - Basicervical fractures actually have a **lower risk** of **avascular necrosis** compared to intracapsular fractures because they are distal to the main **retinacular vessels**. - The blood supply to the femoral head is more likely to be preserved as the fracture sparing the **medial circumflex femoral artery** branches. *Lower risk of non-union due to better blood supply than intracapsular fractures* - While the blood supply is better, these fractures have a **higher risk of mechanical failure** and non-union if treated with simple screws due to **high shear forces**. - Clinical outcomes for **non-union** in basicervical fractures are often related to **fixation stability** rather than just biological blood supply. *Higher incidence of associated femoral shaft fracture requiring longer implants* - There is no specific clinical association between **basicervical neck fractures** and concomitant **femoral shaft fractures**. - While **cephalomedullary nails** are an option, the choice is driven by fracture stability at the neck, not by a distal shaft injury risk. *Reduced risk of fixation failure due to increased bone density at the basicervical region* - The basicervical region does not possess **increased bone density**; in elderly patients with **Parkinson's disease**, the bone is typically **osteoporotic**. - These fractures actually have a **higher risk of fixation failure** (up to 30%) if managed with standard cannulated screws instead of more stable extracapsular-style constructs.
Question 117: A 64-year-old woman presents to the Emergency Department with a 36-hour history of severe lower back pain and urinary retention. She reports numbness in the perineal area and has noticed loss of sensation when wiping after using the toilet. On examination, there is reduced sensation in the S2-S4 dermatomes bilaterally, reduced anal tone, and a palpable bladder. Lower limb power and reflexes are normal. Post-void residual volume is 800 ml. What is the maximum acceptable time from presentation to definitive surgical decompression to optimize neurological outcome?
- A. Within 6 hours of symptom onset
- B. Within 24 hours of symptom onset
- C. Within 48 hours of symptom onset (Correct Answer)
- D. Within 72 hours of symptom onset
- E. Within 1 week of symptom onset
Explanation: ***Within 48 hours of symptom onset***- Clinical evidence suggests that **surgical decompression** performed within **48 hours** of symptom onset is the critical window to optimize recovery of bladder, bowel, and sexual function.- This patient presents with **Cauda Equina Syndrome (CES)**, characterized by **saddle anesthesia**, urinary retention, and reduced **anal tone**, necessitating urgent intervention to prevent permanent neurological damage.*Within 6 hours of symptom onset*- While very early intervention is ideal, clinical studies do not show a statistically significant difference in outcomes for surgery under **6 hours** compared to the **48-hour** threshold.- This timeframe is often logistically impossible due to the time required for **MRI diagnosis** and surgical preparation.*Within 24 hours of symptom onset*- Decompression within **24 hours** is excellent and often targeted, but failing to meet this does not necessarily preclude a good outcome as long as it occurs within **48 hours**.- The literature reinforces the **48-hour window** as the primary prognostic divider for long-term neurological recovery.*Within 72 hours of symptom onset*- Waiting until **72 hours** is associated with significantly worse outcomes and a higher risk of **permanent bladder dysfunction**.- Surgical delay beyond the 48-hour mark is considered inadequate for a **surgical emergency** like CES.*Within 1 week of symptom onset*- Delaying surgery for a week would likely result in **permanent nerve root damage** and chronic disability.- CES is an **acute neurosurgical emergency**, and intervention after a week would only be for stabilization rather than functional recovery.
Question 118: A 67-year-old man sustains a subtrochanteric femur fracture following a fall from a ladder. He has a 10-year history of bisphosphonate therapy for osteoporosis following a previous vertebral compression fracture. Radiographs show a transverse fracture pattern at the subtrochanteric level with cortical thickening of the lateral femoral cortex. Which feature of this fracture pattern is most characteristic of an atypical femur fracture associated with long-term bisphosphonate use?
- A. Fracture location in the subtrochanteric or diaphyseal region
- B. Transverse or short oblique fracture orientation
- C. Presence of medial cortical spike or beak (Correct Answer)
- D. Cortical thickening (periosteal or endosteal) at the fracture site
- E. Association with prodromal pain in the affected limb
Explanation: ***Presence of medial cortical spike or beak*** - A **medial cortical spike** (or beak) is a **pathognomonic major diagnostic criterion** for **atypical femur fractures (AFFs)** associated with bisphosphonate use. - It signifies a complete fracture with a distinct **medial flare** that helps differentiate AFFs from typical osteoporotic fractures. *Fracture location in the subtrochanteric or diaphyseal region* - This location is a **major diagnostic criterion** for AFFs but is less specific than a medial cortical spike. - It defines the general area (below the lesser trochanter to just above the supracondylar flare) but doesn't describe a unique morphological feature. *Transverse or short oblique fracture orientation* - This describes the **fracture morphology**, with an angle of **≤ 30 degrees**, often mimicking a stress fracture. - While a major criterion, it is not as unique to AFFs as the medial spike, as similar patterns can be seen in other trauma types. *Cortical thickening (periosteal or endosteal) at the fracture site* - **Cortical thickening**, particularly on the **lateral femoral cortex**, is often a **minor criterion** or a sign of prodromal stress reaction. - It can be seen as a "dreaded black line" indicating attempts at bone remodeling, but it's not the definitive fracture characteristic. *Association with prodromal pain in the affected limb* - **Prodromal pain** in the thigh or groin is a common **minor clinical feature** preceding AFFs in many patients. - However, it is a **subjective symptom** and not a radiographic characteristic of the fracture pattern itself.
Question 119: A 61-year-old woman with rheumatoid arthritis presents to her GP with a 6-week history of lower back pain and progressive bilateral leg weakness. She has been on long-term methotrexate and prednisolone for 15 years. On examination, there is global weakness in both lower limbs (power 3/5 throughout), with preserved reflexes and normal plantar responses. Sensation is intact. She is apyrexial. Blood tests show CRP 45 mg/L, ESR 68 mm/hr, normal white cell count. Which of the following is the most likely underlying cause of her presentation?
- A. Metastatic spinal cord compression from undiagnosed malignancy
- B. Atlantoaxial subluxation causing cervical myelopathy (Correct Answer)
- C. Spinal infection (discitis/osteomyelitis) secondary to immunosuppression
- D. Guillain-Barré syndrome presenting with ascending paralysis
- E. Cauda equina syndrome from large central disc prolapse
Explanation: ***Atlantoaxial subluxation causing cervical myelopathy***- In patients with long-standing **rheumatoid arthritis**, inflammation and laxity of the **transverse ligament** can lead to **atlantoaxial subluxation**, causing **cervical cord compression**.- The presentation of **progressive bilateral leg weakness** with **preserved reflexes** and intact sensation is characteristic of **cervical myelopathy**, indicating an upper motor neuron lesion in the cervical spine.*Metastatic spinal cord compression from undiagnosed malignancy*- While possible in any elderly patient, spinal cord compression from malignancy usually presents with more **acute onset**, severe localized **bony pain**, and often **rapid neurological deterioration**.- The patient's **preserved reflexes** and lack of specific systemic malignancy symptoms (e.g., weight loss, night sweats) make this less likely than a complication directly related to her long-standing RA.*Spinal infection (discitis/osteomyelitis) secondary to immunosuppression*- Although the patient is **immunosuppressed** with methotrexate and prednisolone, which increases infection risk, she is **apyrexial** and has a normal white cell count.- Spinal infection typically causes severe **localized spinal pain**, often worse at night, and more pronounced systemic signs of infection like fever, although these can be blunted in immunosuppressed patients. The elevated ESR/CRP are non-specific and can be due to active RA.*Guillain-Barré syndrome presenting with ascending paralysis*- **Guillain-Barré syndrome** is an acute demyelinating polyneuropathy characterized by **areflexia** (absent reflexes) and often **ascending paralysis**, which is contrary to the patient's **preserved reflexes**.- The 6-week progressive course and the specific context of long-standing RA make a structural neurological complication of RA more likely than GBS.*Cauda equina syndrome from large central disc prolapse*- **Cauda equina syndrome** presents with **lower motor neuron signs**, including **flaccid paralysis**, **areflexia** (absent reflexes), and often **saddle anesthesia** or **bladder/bowel dysfunction**.- This patient has **preserved reflexes** and intact sensation, and no mention of bladder/bowel issues, making cauda equina syndrome an unlikely diagnosis. The leg weakness is also described as global rather than radicular.
Question 120: A 72-year-old woman undergoes a dynamic hip screw (DHS) fixation for a stable two-part intertrochanteric neck of femur fracture. Post-operatively, what is the most important radiographic measurement to assess optimal placement of the lag screw within the femoral head?
- A. The lag screw should be positioned in the superior and anterior quadrant of the femoral head on AP and lateral views
- B. The lag screw tip should be within 10 mm of the subchondral bone on both AP and lateral radiographs
- C. The lag screw should be positioned in the inferior and posterior quadrant of the femoral head for maximum purchase
- D. The barrel plate should be positioned at least 2 cm distal to the vastus ridge on the lateral femur
- E. The tip-apex distance should be less than 25 mm when measured on AP and lateral radiographs (Correct Answer)
Explanation: ***The tip-apex distance should be less than 25 mm when measured on AP and lateral radiographs*** - The **tip-apex distance (TAD)** is the most critical radiographic measurement used to predict **lag screw cut-out** and fixation failure in intertrochanteric hip fractures. - A **TAD of less than 25 mm** indicates optimal screw placement, significantly reducing the risk of complications and promoting stable fracture healing. *The lag screw should be positioned in the superior and anterior quadrant of the femoral head on AP and lateral views* - Positioning the lag screw in the **superior-anterior quadrant** is associated with a higher risk of **screw cut-out** due to the relatively weaker bone in this region and unfavorable biomechanical forces. - Optimal placement for a dynamic hip screw (DHS) is typically in the **center-center** or **inferior-central** region of the femoral head on both AP and lateral views for maximum stability. *The lag screw tip should be within 10 mm of the subchondral bone on both AP and lateral radiographs* - While proximity to the **subchondral bone** (usually 5-10mm) is important to maximize bone purchase, it does not fully capture the three-dimensional stability of the screw. - This parameter is a component of good technique but is secondary to the **Tip-Apex Distance (TAD)**, which comprehensively assesses the lag screw's position relative to the femoral head apex. *The lag screw should be positioned in the inferior and posterior quadrant of the femoral head for maximum purchase* - While an **inferior position** on the AP view can be acceptable (inferior-center), a **posterior position** on the lateral view is generally suboptimal and can lead to eccentric loading and potential failure. - Optimal placement aims for a **central position** on the lateral view and often an **inferior-central** position on the AP view to achieve the best mechanical purchase and prevent cut-out. *The barrel plate should be positioned at least 2 cm distal to the vastus ridge on the lateral femur* - The position of the **barrel plate** on the femoral shaft primarily relates to the length of the plate and the stability of the fracture in the diaphyseal segment, not the stability of the lag screw within the femoral head. - This measurement is less critical for preventing **lag screw cut-out** compared to the precise placement of the lag screw itself within the femoral head.
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