1. General Principles & Basic Science MCQs

A surgeon plans to correct a diaphyseal tibial deformity. The CORA is identified, but due to poor anterior skin quality at the site, the osteotomy is made proximal to the CORA. If the external fixator hinge (axis of rotation) is maintained at the CORA, what will occur at the osteotomy site during correction?

During preoperative planning for a distal femoral osteotomy to correct a symptomatic valgus deformity, the surgeon measures the mechanical lateral distal femoral angle (mLDFA). What is the normal average value for the mLDFA?

A patient presents with a complex post-traumatic lower limb deformity. When drawing the mechanical axes of the proximal and distal bone segments, the surgeon notes they do not intersect at a single point, but rather run parallel to each other. What does this pattern define?

A 16-year-old male undergoes a corticotomy for tibial lengthening using a circular external fixator. According to the principles of distraction osteogenesis, what is the optimal latency period before beginning distraction?

According to Paley's principles for precise preoperative deformity planning, what is the standard method for calibrating magnification on full-length standing lower extremity digital radiographs?

A patient requires correction of a symptomatic genu recurvatum deformity via an opening wedge proximal tibial osteotomy. To avoid secondary translation and purely angulate the bone, where must the hinge of the external fixator be placed?

What does the Bone Healing Index (BHI) commonly used in distraction osteogenesis represent?

The Taylor Spatial Frame (TSF) utilizes a hexapod system allowing for simultaneous multi-planar correction. Which of the following parameters is NOT explicitly required by the software to compute the daily strut adjustment schedule?

When applying a circular external fixator to the proximal tibia, half-pins or tensioned wires must be placed carefully. Which nerve is most at risk during transverse wire placement from lateral to medial in the proximal third of the tibia?

A 15-year-old male presents with a distal femoral valgus deformity. Radiographic analysis identifies the Center of Rotation of Angulation (CORA) at the distal femoral metaphysis. The surgeon plans a corrective osteotomy at the diaphyseal level, proximal to the CORA, but aligns the angulation correction axis (ACA) exactly through the CORA. According to Paley's osteotomy rules, what is the expected outcome of this configuration?

A 50-year-old female presents with severe bilateral genu varum. On a standing full-length AP radiograph, the mechanical axis deviation (MAD) is 45 mm medial, and the Joint Line Congruency Angle (JLCA) is measured at 7 degrees (normal 0-2 degrees). Under valgus stress, the JLCA corrects to 1 degree. If the surgeon plans a high tibial osteotomy based solely on the standing AP radiograph without accounting for the stress view, what is the most likely postoperative outcome?

During the correction of a distal tibial valgus deformity, the surgeon performs the osteotomy in the tibial diaphysis, significantly proximal to the juxta-articular CORA. Furthermore, the angulation correction axis (ACA) is placed at the level of the osteotomy rather than at the CORA. According to Paley's osteotomy rules, what is the resulting alignment effect?

A 38-year-old male presents with progressive genu varum. As per Paley's principles, the most critical initial step in preoperative planning for lower limb deformity correction, upon which all subsequent surgical skill and fixation depend, is:

An experienced orthopedic surgeon is teaching a new fellow about the fundamental objectives of deformity correction using Paley's principles, emphasizing the shift from subjective assessment to a rigorous, standardized approach.

What is the ultimate primary goal of applying Paley's systematic methodology to lower extremity deformity correction?

Before the widespread adoption of Paley's principles, a surgeon performed an osteotomy based on a subjective visual assessment of a patient's genu varum, without precise angular measurements or mechanical axis analysis.

According to the case, what was a common outcome of osteotomies planned based on intuition and subjective visual assessment in the pre-Paley era?

According to Paley's Osteotomy Rule 1, if an osteotomy and the axis of rotation (hinge) are both placed exactly at the Center of Rotation of Angulation (CORA), which of the following describes the radiographic outcome after correction?

A 30-year-old male presents with a diaphyseal tibial deformity. The apex of the deformity is identified at the mid-diaphysis. According to Paley's Rule 1 of osteotomy, if the osteotomy and the hinge are both placed exactly at the Center of Rotation of Angulation (CORA), what is the expected radiographic outcome after correction?

A 45-year-old female presents with a distal femoral valgus deformity where the CORA is located at the level of the joint line. To avoid an intra-articular osteotomy, the osteotomy is performed in the metaphysis, but the hinge of the fixation device is placed at the CORA. Based on Paley's Rule 2,

what is the expected result?

A 15-year-old male has severe tibial varus. The surgeon performs the osteotomy proximal to the CORA and places the hinge at the osteotomy site. According to Paley's Rule 3,

what is the alignment outcome?

When evaluating coronal plane alignment using Paley's principles on a full-length standing AP radiograph, which of the following accurately represents the normal population range for the mechanical lateral distal femoral angle (mLDFA)?