1. General Principles & Basic Science MCQs

A 55-year-old patient presents with a clinical Fixed Flexion Deformity (FFD) of 30°. A true lateral radiograph is obtained for detailed analysis. The measured Posterior Proximal Tibial Angle (PPTA) is 65°. Using the standard normal reference values from the case (PDFA 84°, PPTA 80°), what is the calculated contribution of tibial procurvatum to the overall FFD?

A 70-year-old patient presents with a severe crouched gait and a clinical Fixed Flexion Deformity (FFD) of 35°. Radiographic analysis using Paley's principles reveals a Posterior Distal Femoral Angle (PDFA) of 70° and a Posterior Proximal Tibial Angle (PPTA) of 72°. Using the standard normal reference values from the case (PDFA 84°, PPTA 80°), what is the calculated true soft tissue flexion contracture component?

A 40-year-old patient presents with a 40° clinical Fixed Flexion Deformity (FFD). Radiographic analysis, as depicted in the case example, reveals a 10° femoral procurvatum, a 20° tibial procurvatum, and a 10° soft tissue flexion contracture. According to the Paley Doctrine of Anatomic Correction, what is the ideal surgical strategy for this patient?

An inexperienced orthopedic surgeon attempts to correct a 30° Fixed Flexion Deformity (FFD) by performing a 30° proximal tibial extension osteotomy, without addressing the underlying 10° femoral procurvatum and 10° soft tissue contracture. Based on the principles discussed, what is the MOST likely long-term consequence of this flawed surgical approach?

When planning an anterior opening wedge high tibial osteotomy (HTO) to correct a severe sagittal plane recurvatum deformity, what associated modification must be considered to prevent iatrogenic patella infera (baja)?

According to Paley's principles of deformity correction, if an osteotomy is performed at a level outside the Center of Rotation of Angulation (CORA), but the mechanical hinge is placed exactly at the CORA, what is the geometric result of the correction?

A 45-year-old patient exhibits a unilateral fixed equinus contracture of the ankle. What is the classic compensatory sagittal plane deformity observed at the ipsilateral knee during the stance phase of gait?

A 35-year-old patient presents with 20 degrees of clinical knee recurvatum. Radiographic evaluation shows a Mechanical Posterior Distal Femoral Angle (mPDFA) of 83° and an mPPTA of 81°. What is the most appropriate primary intervention for this patient?

A surgeon applies Paley's Rule 3 to correct a severe distal femoral procurvatum deformity. The osteotomy is performed proximal to the CORA, and the mechanical hinge is also placed proximal to the CORA. What is the expected postoperative alignment?

A surgeon is considering a focal dome osteotomy to correct a 25-degree recurvatum deformity of the proximal tibia. What is the primary geometric advantage of utilizing a dome osteotomy centered perfectly on the CORA?

Which radiographic study is considered the gold standard for accurately measuring a bony sagittal plane deformity of the lower extremity prior to deformity correction surgery?

A patient has a tibial procurvatum (apex anterior) deformity resulting in a lack of full extension. An anterior closing wedge high tibial osteotomy is performed to restore the mechanical axis. What is a known consequence of this specific technique?

A patient requires an osteotomy for a combined angulation and translation deformity in the sagittal plane of the tibia. Which of the following describes the correct identification of the CORA in this specific combined deformity?

When evaluating a patient for sagittal plane knee deformity, accurate measurement of the mechanical axes is critical. What are the generally accepted normal values for the Mechanical Posterior Distal Femoral Angle (mPDFA) and the Mechanical Posterior Proximal Tibial Angle (mPPTA)?

According to Paley's principles of deformity correction, if a surgeon plans an osteotomy to correct a severe sagittal plane distal femoral deformity, what is the geometric outcome if the osteotomy is made exactly at the Center of Rotation of Angulation (CORA) and the hinge is also placed exactly at the CORA?

A patient requires a distal femoral osteotomy for a severe recurvatum deformity. Due to poor metaphyseal bone stock, the surgeon places the osteotomy in the diaphysis, significantly proximal to the CORA. However, the hinge (axis of rotation) is placed exactly at the CORA. What is the expected outcome based on Paley's Rule 2?

When performing a standard medial opening-wedge High Tibial Osteotomy (HTO) for a coronal varus deformity, what is the most common unintended iatrogenic change in the sagittal plane if the gap is opened equally at the anterior and posterior cortices?

A patient with a distal femoral recurvatum deformity (mPDFA = 95°) is planned for a corrective anterior opening wedge osteotomy using an external circular fixator. To adhere to Paley's Rule 1 and avoid translation, where must the hinge be strategically placed?

A surgeon plans to correct a distal femoral procurvatum deformity using Paley's Osteotomy Rule 1. If the osteotomy is performed exactly at the Center of Rotation of Angulation (CORA) and the hinge is placed at the CORA, what is the expected geometric outcome?

A patient with a distal femoral recurvatum deformity (mPDFA = 98 degrees) undergoes a compensatory flexion osteotomy of the proximal tibia instead of the femur. What is the most significant long-term biomechanical consequence of this mismatch correction?