Comprehensive Orthopedic Deformity, LLD & Hip Biomechanics Board Review | Part 13

Correct Answer: A

Rationale: The superior migration of the collapsed femoral head directly shortens the effective length of the limb from the hip to the ankle. This creates a functional leg length discrepancy (LLD), which alters gait and can cause secondary problems in the spine and contralateral limb. Superior migration *reduces* the ATD (C).

Correct Answer: C

Rationale: The text warns that in the face of severe collapse, a VDRO can be detrimental. It may drive the flattened, incongruent head into the lateral edge of the acetabulum, creating a fulcrum effect (hinge abduction). This concentrates pressure on the acetabular rim and accelerates degenerative changes, rather than achieving true containment.

Correct Answer: C

Rationale: The text explains that during the vulnerable phase of creeping substitution, the weakened segment collapses under physiological load, which is exacerbated by the forces of walking and muscle contraction. This is the fundamental principle behind offloading treatments like femoropelvic distraction.

Correct Answer: D

Rationale: As the femoral head displaces superiorly and laterally, it moves away from the medial wall of the pelvis (the teardrop). This creates an apparent widening of the medial joint space, which is objectively measured as an increased teardrop distance. It is a classic sign of lateralization of the femoral head.

Correct Answer: B

Rationale: The text defines the Articulo-Trochanteric Distance (ATD) as the distance from the tip of the greater trochanter to the superior articular surface of the femoral head. This measurement is a critical indicator of the mechanical lever arm for the hip abductor muscles.

Correct Answer: B

Rationale: When both angulation and translation are present, the intersection of the proximal and distal anatomical axes is defined as the angulation-translation CORA (a-t CORA). The standard CORA applies only to pure angular deformities where the axes intersect at the apex of the deformity.

Correct Answer: C

Rationale: According to Rule 1 of a-t deformity correction, an osteotomy and hinge placed exactly at the a-t CORA will simultaneously correct both the angular and translational components of the deformity through a single rotational movement. This strategy does not, however, eliminate the original cosmetic bump or create a straight canal for nailing.

Correct Answer: C

Rationale: Performing the osteotomy at the point of maximum translation allows the surgeon to physically shave down the sclerotic edges and translate the bone to a flush position, completely eliminating the medial bump. The main disadvantage is that it requires sequential correction (translation and angulation) and involves operating in the zone of injury.

Correct Answer: C

Rationale: By re-canalizing the bone at the malunion site, an intramedullary nail can be inserted. IMN offers excellent load-sharing properties, which promotes healing and allows for earlier weight-bearing compared to plates or external fixators. An IMN cannot be used with an osteotomy at the a-t CORA due to the resulting "zig-zag" deformity of the canal.

Correct Answer: A

Rationale: Strategy 1, the "Accept and Ignore" approach, is used when one component of a multi-planar deformity is clinically and functionally insignificant. A small sagittal translation (e.g., 4 mm) rarely affects the mechanical axis deviation and can be safely ignored to simplify the surgery and reduce morbidity.

Correct Answer: C

Rationale: The most significant advantage of the a-t CORA strategy is biological safety. The a-t CORA is often located away from the original fracture site, allowing the surgeon to operate through pristine, uninjured soft tissues. This drastically reduces the risk of wound breakdown and deep infection, which is a major concern in patients with compromised soft tissues.

Correct Answer: B

Rationale: For acute corrections performed at the malunion site, it is highly preferable to perform translation first, then angulation. Translating the bone ends acutely lines up the medullary canal, which then facilitates the angular correction and subsequent insertion of the intramedullary nail. Reversing the order can make canal alignment difficult.

Correct Answer: A

Rationale: For gradual corrections with an external fixator, the reverse of acute correction is true. It is biomechanically safer to perform angulation first, then translation. Angulating first creates a wedge of regenerate bone, which provides a larger surface area and reduces the risk of the bone ends slipping off one another during the subsequent translation.

Correct Answer: C

Rationale: A major drawback of the a-t CORA strategy is that the original malunion site is left untouched. This leaves the physical "step-off" or bump of the malunited bone, which can be symptomatic or aesthetically displeasing, especially in subcutaneous locations like the medial tibia.

Correct Answer: D

Rationale: In Strategy 2, an oblique plane angular correction at the frontal a-t CORA simultaneously corrects both the frontal (varus) and sagittal (recurvatum) components of angulation. Because the cut is at the frontal a-t CORA, the frontal plane translation is also eliminated. The sagittal plane translation is what remains to be corrected.

Correct Answer: C

Rationale: The limiting factor for any translational correction is maintaining adequate bone-to-bone contact. If the required translation is too large (typically >30-40% of the bone diameter), sliding the fragments will result in a loss of cortical contact, leading to instability and a high risk of non-union.

Correct Answer: D

Rationale: Strategy 4 recognizes that a multi-planar deformity (e.g., varus and recurvatum) exists as a single, pure angular deformity in a specific oblique plane. By calculating this true oblique plane axis, the surgeon can perform a single oblique-plane angular correction followed by multi-planar translation, which is ideal for restoring the anatomical canal for IM nailing.

Correct Answer: D

Rationale: Strategy 5, the double osteotomy approach, is reserved for massive, complex deformities where a single osteotomy would be biomechanically untenable. By creating two separate osteotomies (e.g., one at the frontal a-t level and one at the sagittal a-t level), the correction is divided into two manageable zones, preserving bone contact and protecting soft tissues. This is almost exclusively managed with a hexapod external fixator.

Correct Answer: C

Rationale: The Mechanical Axis Deviation (MAD) is the perpendicular distance from the mechanical axis of the limb (a line from the center of the femoral head to the center of the ankle) to the center of the knee. This can only be accurately assessed on a full-length standing radiograph that visualizes the hip, knee, and ankle joints simultaneously.

Correct Answer: D

Rationale: The "zig-zag" deformity created by an osteotomy at the a-t CORA involves two opposing kinks in the bone. Passing a straight, rigid intramedullary nail through this S-shaped canal is impossible without iatrogenic fracture. Therefore, this strategy is reserved for plate or external fixation.

Correct Answer: B

Rationale: The a-t CORA strategy is biologically safest because the osteotomy is typically performed in a region of healthy bone and soft tissue, away from the compromised "zone of injury" of the original malunion. This is particularly advantageous in patients with risk factors for poor wound healing, such as diabetes or poor skin quality.

Correct Answer: C

Rationale: The text states that a mechanical axis deviation (MAD) of more than 15 mm into the medial compartment of the knee increases the load on the medial meniscus and articular cartilage exponentially. This is a key threshold used in deformity planning to determine the necessity of correction for joint preservation.

Correct Answer: B

Rationale: Varus angulation shifts the mechanical axis medially. Medial translation also shifts the mechanical axis medially. When both occur together, their effects are additive, compounding the deformity and creating a large medial mechanical axis deviation (MAD).

Correct Answer: C

Rationale: Strategy 3 is the inverse of Strategy 2. The osteotomy is performed at the sagittal a-t CORA, which corrects all angulation and the sagittal translation. This leaves a residual translation in the frontal plane (AP radiograph) that must be corrected by physically sliding the bone.

Correct Answer: C

Rationale: Even if the mechanical axis is restored (correcting compressive forces), an abnormal joint orientation angle (like the MPTA) will lead to pathological shear forces across the joint cartilage during the gait cycle. Restoring both the mechanical axis and the joint orientation angles is the only way to fully normalize joint biomechanics and prevent premature osteoarthritis.

Correct Answer: B

Rationale: While locking plates provide excellent rigid fixation, they are load-bearing devices that typically require a larger surgical incision compared to percutaneous nailing techniques. Additionally, the plate itself can be prominent under the skin, especially over a translated segment, which can be a source of irritation for the patient.

Correct Answer: B

Rationale: The mechanical axis of the lower extremity is the weight-bearing line connecting the center of the femoral head to the center of the ankle. The anatomic axis (A) follows the medullary canal of the femur. Restoring the mechanical axis is a primary goal of deformity correction.

Correct Answer: C

Rationale: The Mechanical Lateral Proximal Femoral Angle (mLPFA) is the cornerstone measurement for proximal femoral deformity analysis, as it defines the relationship of the proximal femur to the weight-bearing axis. The Neck-Shaft Angle (A) is related but is measured against the anatomic, not mechanical, axis.

Correct Answer: B

Rationale: The normal range for the mLPFA is 85° to 95°. Values below this range indicate coxa valga, while values above this range indicate coxa vara. The range of 120° to 135° (D) is typical for the neck-shaft angle, not the mLPFA.

Correct Answer: D

Rationale: Coxa vara is characterized by an increased mLPFA, typically greater than 95°. An mLPFA of 110° is a classic finding in coxa vara. A value of 80° (A) would be indicative of coxa valga.

Correct Answer: A

Rationale: Coxa valga, which is common in cerebral palsy and characterized by an increased neck-shaft angle, results in a decreased mLPFA (<85°). An increased mLPFA (C) is seen in coxa vara.

Correct Answer: B

Rationale: In the class one lever system of the hip, the center of the femoral head acts as the fulcrum. The body weight acts as the load, and the abductor muscle force acts as the effort applied at the greater trochanter (A).

Correct Answer: C

Rationale: The total Joint Reaction Force (JRF) across the hip articular cartilage is the sum of the body weight and the force generated by the abductor muscles to keep the pelvis level. Because the abductors have a short moment arm, their force is typically 2-3 times body weight, making the JRF immense.

Correct Answer: B

Rationale: Coxa valga lateralizes the femoral shaft relative to the head, which critically shortens the horizontal distance from the femoral head (fulcrum) to the greater trochanter (abductor insertion). This shortens the abductor moment arm, forcing the muscles to work much harder and increasing the JRF.

Correct Answer: B

Rationale: The varus alignment of the proximal femur in coxa vara medializes the entire mechanical axis of the lower limb, resulting in a medial Mechanical Axis Deviation (MAD). This places the weight-bearing line medial to the center of the knee.

Correct Answer: B

Rationale: The combination of an increased neck-shaft angle (>140°) and a decreased mLPFA (<85°) is the classic definition of coxa valga. Coxa vara (A) would present with a decreased neck-shaft angle and an increased mLPFA.

Correct Answer: B

Rationale: The valgus deformity shortens the abductor moment arm, which severely weakens the abductor muscles' ability to stabilize the pelvis and compress the femoral head into the acetabulum. This abductor insufficiency is a primary driver of the superolateral subluxation seen in the image.

Correct Answer: C

Rationale: As shown in the transition from the center to the right image, the varus osteotomy lateralizes the greater trochanter. This increases the horizontal distance from the fulcrum (femoral head) to the abductor insertion, thereby lengthening the abductor moment arm. This gives the muscles a mechanical advantage, requiring less force to stabilize the pelvis and thus reducing the overall JRF.

Correct Answer: C

Rationale: The text specifically describes the Nishio helical dome osteotomy as a powerful solution for coxa valga and anteversion, as seen in the clinical example. The postoperative image shows correction on the femoral side of the joint, making a pelvic osteotomy like a PAO (A) or Salter (B) incorrect. A valgus osteotomy (D) would worsen the deformity.

Correct Answer: D

Rationale: The Nishio osteotomy is specifically defined by its sophisticated helical or dome-shaped cut made at the base of the femoral neck. This unique geometry allows for simultaneous varus and derotational correction without creating a large bone gap or causing significant shortening.

Correct Answer: C

Rationale: A key advantage of the Nishio osteotomy is its ability to correct the deformity while minimizing proximal migration of the greater trochanter. This preserves the physiological length-tension relationship (Blix curve) of the abductor muscles, preventing the iatrogenic weakness often seen with traditional closing-wedge osteotomies.

Correct Answer: B

Rationale: Traditional closing-wedge osteotomies often cause the greater trochanter to migrate proximally relative to the center of the femoral head. This slackens the abductor muscles, placing them on an unfavorable portion of the Blix curve and causing persistent weakness, even with corrected bony alignment. The Nishio osteotomy is designed to avoid this specific complication.

Correct Answer: C

Rationale: By medially translating the femoral shaft, the greater trochanter is effectively lateralized relative to the center of the femoral head. This dramatically increases the horizontal distance between the fulcrum and the abductor insertion, thus lengthening the abductor moment arm and improving mechanical efficiency.

Correct Answer: C

Rationale: By increasing the abductor moment arm, the abductor muscles need to generate substantially less force to balance the pelvis. Since the Joint Reaction Force (JRF) is the sum of body weight and abductor force, a significant reduction in the required abductor force directly and drastically reduces the overall JRF, protecting the articular cartilage.

Correct Answer: B

Rationale: The text explicitly states that LLD is a "complex, multi-dimensional deformity defined fundamentally by two distinct parameters: magnitude and direction." Magnitude is the quantitative difference, and direction refers to whether it is shortening or overgrowth and its interaction with other deformities.

Correct Answer: C

Rationale: The text identifies the Paley Multiplier Method as the "modern gold standard" for predicting LLD at skeletal maturity, noting its speed and accuracy compared to older methods like the Anderson, Green, and Messner charts or the Moseley graph.

Correct Answer: B

Rationale: The text emphasizes that the block test is paramount because it "reveals the tolerable correction, which may differ significantly from the radiographic correction," especially in adults with long-standing discrepancies and compensatory mechanisms.

Correct Answer: B

Rationale: The measurement from the ASIS to the MM represents the "True LLD." A difference in this measurement (88 cm vs. 85 cm) indicates a structural difference in bone length. The difference in the umbilicus-to-MM measurement is consistent with this true shortening, not an apparent discrepancy.

Correct Answer: C

Rationale: The text defines an "Apparent LLD" as a condition where true bone lengths are equal (equal ASIS-to-MM measurements) but a discrepancy exists from a midline landmark (umbilicus). This is caused by factors like fixed pelvic obliquity, which can result from a hip adduction contracture.

Correct Answer: C

Rationale: The text describes the Galeazzi test and states, "If one knee is lower, the tibia is short." Since the left knee is lower, this indicates a short left tibia. If the femur were short, the knee would project less anteriorly.

Correct Answer: C

Rationale: The text explicitly states that the primary advantage of orthoroentgenograms is "Minimal Magnification" because the central X-ray beam is positioned directly over each joint, eliminating the parallax effect of a divergent beam.

Correct Answer: C

Rationale: The text explains that teleoroentgenograms are used to overcome the "alignment blindness" of scanograms. A standing teleoroentgenogram exposes the entire limb on a single plate, allowing for a "comprehensive Paley alignment analysis" including mechanical axis deviation (MAD).

Correct Answer: C

Rationale: The text describes the "Lift Protocol," stating it is "absolutely critical to position a patient with LLD standing on a lift" with a height "approximately equal to their clinically determined LLD" to level the pelvis for an accurate assessment.

Correct Answer: C

Rationale: The text clearly states that while CT scout films are excellent for absolute length, they "are obtained supine. Therefore, they do not demonstrate the dynamic effects of weight-bearing, such as joint space narrowing, ligamentous laxity, or compensatory pelvic tilt."

Correct Answer: C

Rationale: The text defines the Mechanical Axis of the lower extremity as "a line drawn from the center of the femoral head to the center of the ankle plafond." This is a fundamental concept in Paley's principles.

Correct Answer: B

Rationale: The Medial Proximal Tibial Angle (MPTA) is the angle that determines proximal tibia varus/valgus. The text lists its normal value as 87.2°. The mLDFA relates to the distal femur.

Correct Answer: B

Rationale: This question directly tests Paley's Osteotomy Rule 1, which states: "If the osteotomy and the hinge (axis of correction) are placed exactly at the CORA, the bone will achieve pure angular correction without translation."

Correct Answer: B

Rationale: The text indicates that acute shortening is a viable option for skeletally mature patients with LLDs between 2 to 3 cm. It is a single-stage procedure. Acute lengthening beyond 2-3 cm is contraindicated due to neurovascular risk, and gradual lengthening is a prolonged process.

Correct Answer: C

Rationale: The text is unequivocal on this point: "Acute lengthening is highly restricted by the soft tissue envelope. Stretching nerves... and blood vessels acutely beyond 2 to 3 cm carries a severe, unacceptable risk of neuropraxia, compartment syndrome, and vascular compromise."

Correct Answer: C

Rationale: The text outlines the parameters of distraction osteogenesis, stating that the "Latency Phase" occurs first. "After the osteotomy, the bone is left to rest for 5 to 7 days" to allow the initial hematoma to form before distraction begins.

Correct Answer: D

Rationale: The text specifies the optimal parameters: "The optimal rate is 1 mm per day... this rate is divided into a specific rhythm: typically four 0.25 mm increments spread throughout the 24-hour period."

Correct Answer: C

Rationale: The text defines the "Consolidation Phase" as the period when the regenerate bone mineralizes. It explicitly states, "This phase takes roughly twice as long as the distraction phase."

Correct Answer: B

Rationale: The text highlights several benefits of internal lengthening nails, but the first and most prominent is that they "Eliminate pin-site infections entirely," which is a major source of morbidity with external fixators.

Correct Answer: C

Rationale: The "Surgical Pearls" table advises to "Perform a multiple drill-hole and osteotome technique (low-energy corticotomy)." It specifically warns, "Never use a high-speed saw, as thermal necrosis will destroy the osteogenic potential of the regenerate."

Correct Answer: C

Rationale: The "Surgical Pearls" table suggests that "intramuscular lengthening of the gastrocnemius may be required to prevent joint contractures during massive lengthenings." An equinus contracture is caused by tightness of the gastrocnemius-soleus complex.

Correct Answer: B

Rationale: The symptoms described (sensory changes on the dorsum of the foot and weak dorsiflexion) are classic for common peroneal nerve palsy (foot drop). The text advises, "For tibial lengthenings >3 cm, consider a prophylactic common peroneal nerve decompression at the fibular neck to prevent foot drop."

Correct Answer: D

Rationale: The text defines "Premature Consolidation" as the complication where "the bone may heal prematurely before the target length is reached." This requires a return to the OR to re-osteotomize the bone.

Correct Answer: C

Rationale: The text describes "Poor Regenerate / Non-Union" as a complication that can occur if the rate is too fast or the biology is compromised (e.g., smoking). The management involves "slowing or reversing the distraction ('accordion technique') to compress the gap and stimulate osteogenesis."

Correct Answer: C

Rationale: The text explicitly states that in a chronically dislocated hip, the fulcrum is lost, and the abductors become insufficient. The core rationale of the PSO is to create a new, stable fulcrum by creating a bony abutment against the ischium, thereby restoring abductor function.

Correct Answer: B

Rationale: The text clearly states that early single-level PSO techniques were "fraught with complications—most notably, creating severe knee valgus and limb shortening." The modern double-level osteotomy was developed specifically to solve this problem of catastrophic knee malalignment.

Correct Answer: A

Rationale: The text states, "The core rationale of the pelvic support osteotomy is elegantly simple: If the hip cannot adduct, the pelvis cannot drop." The valgus osteotomy creates a bony abutment against the ischium that physically prevents adduction beyond a certain point, thus stabilizing the pelvis.

Correct Answer: C

Rationale: The text explains that the extreme valgus correction "drives the greater trochanter distally and laterally. This effectively tensions the slack abductor muscles, restoring their resting length and dramatically improving their mechanical advantage." This tensioning is a key biomechanical benefit of the procedure.

Correct Answer: B

Rationale: The text states, "This medialization shortens the body weight lever arm and lengthens the abductor lever arm, further enhancing the mechanical efficiency of the newly reconstructed hip." This is a fundamental principle of hip biomechanics applied in the PSO.

Correct Answer: D

Rationale: The text provides a table of primary surgical indications. Salvage of a Girdlestone arthroplasty is explicitly listed as an ideal scenario for PSO, especially in cases of chronic infection where implants are undesirable. The other options are typically managed with other procedures.

Correct Answer: C

Rationale: The text states that the historical failure was the creation of massive knee valgus. "Dr. Paley's introduction of a second, distal osteotomy solved this problem." The distal osteotomy's purpose is to create a compensatory varus correction to realign the mechanical axis through the knee center.

Correct Answer: C

Rationale: The text is very specific: "In an unstable hip, the femoral head center is absent. Therefore, a new proximal reference point must be established: the new medialized pivot point of the proximal femur against the pelvis." The entire goal is to align the axis from this new point to the ankle, through the knee.

Correct Answer: A

Rationale: The text explicitly states Paley Osteotomy Rule 2: "If an osteotomy is performed *away from* the CORA, pure angular correction will cause a parallel shift (translation) of the mechanical axis. To prevent this, a corrective translation must be built into the osteotomy plan."

Correct Answer: C

Rationale: The text specifies that a goal of the distal osteotomy is to restore normal joint orientation angles. It states, "The Mechanical Lateral Distal Femoral Angle (mLDFA)...should be 87° (± 3°)." This prevents shear forces across the knee.

Correct Answer: C

Rationale: The caption for diagram (e) in the text states: "This diagram shows the initial deformity planning. A single proximal valgus osteotomy has stabilized the hip, but the mechanical axis (red line) is now severely deviated laterally from the knee center, resulting in an abnormal mLDFA." This highlights the problem that the second osteotomy solves.

Correct Answer: D

Rationale: Diagram (f) shows the limb after lengthening, but with the mechanical axis still deviated. Diagram (g) shows the final corrected state. The text explains this transition: "After lengthening is complete, a varusization at the distal osteotomy site through the lengthening zone has perfectly realigned the limb."

Correct Answer: B

Rationale: The text identifies two "non-negotiable" clinical measurements for planning the proximal osteotomy: maximum passive adduction and maximum pelvic drop angle. The pelvic drop angle directly quantifies the dynamic instability that the osteotomy must overcome.

Correct Answer: C

Rationale: The text lists a specific, mandatory radiographic protocol. A "Full-Length Standing AP Radiograph" is the first item on the list, required to assess overall mechanical alignment and leg length discrepancy, which is essential for planning the double-level correction.

Correct Answer: D

Rationale: The text explicitly states, "The Supine AP Pelvis in Maximum Adduction (Cross-Legged View) is the key radiograph for planning the proximal osteotomy." This view is used to identify the point where the femur crosses the ischial tuberosity line, defining the osteotomy level.

Correct Answer: C

Rationale: The methodology is described precisely in the text: "The exact point where the medial cortex of the adducted femur crosses this line defines the ideal level for the proximal osteotomy." This ensures the proximal fragment will abut the pelvis correctly.

Correct Answer: D

Rationale: The text provides an "unforgiving formula": Total Valgus Correction = (Single Leg Stance Pelvic Drop Angle) + 15° of Overcorrection. Therefore, the calculation is 35° + 15° = 50°.

Correct Answer: C

Rationale: The text explains that this "15° of overcorrection is a crucial safety factor. It ensures that the hip remains mechanically locked against adduction even under the high dynamic forces of the gait cycle, completely eliminating the Trendelenburg lurch."

Correct Answer: B

Rationale: The caption for diagram (c) in the text explicitly states: "Measurement of the single-leg stance pelvic drop, which is 40°." This value is then used in the final calculation shown in diagram (d).

Correct Answer: C

Rationale: Diagram (d) shows the final calculation. The text explains the formula: pelvic drop angle (40° from diagram c) plus an obligatory overcorrection (15°), resulting in a total planned valgus correction of 55°.

Correct Answer: D

Rationale: The text specifies the sagittal plane correction: "the femur should be extended by the amount of the flexion deformity of the hip **plus an additional 5° of extension**." Therefore, 20° (FFD) + 5° (extra extension) = 25° of total extension.

Correct Answer: B

Rationale: The text highlights this "critical, often-missed biomechanical observation" and states, "the surgeon needs to internally rotate the proximal osteotomy to compensate for this automatic external torsion" to avoid a dysfunctional out-toeing gait.

Correct Answer: C

Rationale: The text defines the CORA as "the geometric point at the intersection of the proximal and distal axes of a deformed bone." In the planning section for the distal osteotomy, it reiterates that the CORA is "The intersection point of the proximal and distal axis lines."

Correct Answer: C

Rationale: The mechanical axis of the lower limb, representing the true line of weight-bearing, is defined as a continuous line from the center of the femoral head to the center of the ankle plafond. The anatomic axis (B) is the mid-diaphyseal line of the bones, which is not a single straight line for the entire limb.

Correct Answer: B

Rationale: The Mechanical Axis Deviation (MAD) is the distance between the mechanical axis line of the lower limb and the center of the knee in the frontal plane. A medial deviation, as described, indicates a varus malalignment. CORA (A) is the intersection point of proximal and distal axis lines used for osteotomy planning.

Correct Answer: B

Rationale: The text explicitly states that Paley et al. found the normal MAD to be 9.7 ± 6.8 mm medial to the center of the knee. A value of 0 mm (A) is a common textbook oversimplification but not the clinical reality.

Correct Answer: D

Rationale: A "knock-kneed" appearance corresponds to a valgus malalignment. In valgus, the mechanical axis of the lower limb falls lateral to the center of the knee. A medial MAD (A) would indicate varus malalignment.

Correct Answer: B

Rationale: The anatomic tibiofemoral angle is formed by the intersection of the mid-diaphyseal lines (anatomic axes) of the femur and tibia. The angle between the mechanical axes (A) defines the mechanical tibiofemoral angle.

Correct Answer: D

Rationale: The text states that the normal anatomic tibiofemoral angle, which is commonly referenced in clinical practice, is approximately 6° valgus. The 1.2° varus value (B) corresponds to the normal mechanical tibiofemoral angle.

Correct Answer: D

Rationale: The provided text specifies that the normal mechanical tibiofemoral angle, formed by the mechanical axes of the femur and tibia, is 1.2° to 1.3° varus. The 6° valgus value (A) is the normal anatomic tibiofemoral angle.

Correct Answer: C

Rationale: The Lateral Proximal Femoral Angle (LPFA), as described by Paley and Tetsworth, is the angle formed between the femoral mechanical axis and a line from the tip of the greater trochanter to the center of the femoral head. The MNSA (A) involves the axis of the femoral neck, not the trochanteric tip line.

Correct Answer: C

Rationale: The text states that based on pooled data, the accepted normal LPFA is 89.9° ± 5.2°, which is often simplified to 90° in practice. The value of 129° (E) is more representative of the anatomic neck-shaft angle.