1. General Principles & Basic Science MCQs

According to Paley's first rule of osteotomy, if both the osteotomy and the angulation correction axis (ACA) pass through the center of rotation of angulation (CORA), what is the resulting alignment?

A surgeon plans a deformity correction placing the angulation correction axis (ACA) at the CORA, but performs the osteotomy at a different level due to poor local skin. According to Paley's second rule, what is the geometric consequence of this setup?

If a surgeon mistakenly places the angulation correction axis (ACA) at a site other than the center of rotation of angulation (CORA), what is the resultant alignment effect regardless of where the osteotomy is performed?

A patient presents with a severe varus knee. Standing radiographs reveal a mechanical axis deviation (MAD) passing through the medial compartment. The mechanical lateral distal femoral angle (mLDFA) is 87 degrees, and the medial proximal tibial angle (MPTA) is 88 degrees. The joint line convergence angle (JLCA) is 6 degrees (open laterally). What is the primary cause of the varus MAD?

When evaluating the coronal alignment of the lower extremity, what is the generally accepted normal range for the mechanical lateral distal femoral angle (mLDFA)?

In a structurally normal lower extremity, the angle between the anatomical axis of the femur and the mechanical axis of the femur is approximately:

What is the widely accepted optimal rate and rhythm of distraction for achieving high-quality bone regenerate in limb lengthening?

A patient with a multi-apical diaphyseal tibial deformity has two distinct centers of rotation of angulation (CORAs). If a single mid-diaphyseal osteotomy is performed to correct both angulations simultaneously, what is the inevitable geometric result?

In the Taylor Spatial Frame (TSF) software, the "mounting parameters" strictly define the geometric relationship between which two structures?

A standing full-length anteroposterior radiograph of the lower extremities shows a mechanical axis line passing lateral to the center of the knee joint. This finding primarily indicates which type of deformity?

A 14-year-old female undergoes femoral lengthening with a monolateral external fixator. During the consolidation phase, she develops a 30-degree restriction in active and passive knee flexion. What is the most common cause of this complication?

On a normal lateral radiograph of the tibia, what is the normal relationship of the posterior proximal tibial angle (PPTA), which reflects the sagittal tibial slope?

A patient has a supramalleolar deformity. To analyze the deformity, a normal LDTA line is drawn from the center of the tibial plafond proximally, and it intersects the proximal anatomical axis of the tibia. What does this intersection point geometrically represent?

A 12-year-old boy is undergoing distraction osteogenesis of the tibia. At 3 weeks post-corticotomy, radiographs show dense bridging trabeculae across the distraction gap, and the frame is difficult to distract despite turning the struts. What is the most appropriate management?

A patient presents with a severe hyperextension deformity of the proximal tibia (genu recurvatum). If an opening wedge osteotomy is planned to correct the deformity without inducing translation, where must the hinge (ACA) be positioned?

A surgeon plans a deformity correction for a patient with a mid-diaphyseal tibial varus. The Center of Rotation of Angulation (CORA) is determined to be at the mid-diaphysis. Due to poor soft tissue envelope at the CORA, the surgeon performs the osteotomy in the proximal metaphysis while placing the Angulation Correction Axis (ACA) at the mid-diaphyseal CORA. According to Paley's rules of deformity correction, what is the expected geometric outcome?

During distraction osteogenesis utilizing the Ilizarov method, bone regeneration occurs primarily through which of the following biological processes?

A 16-year-old male is undergoing tibial lengthening with a circular external fixator. Radiographs taken during the consolidation phase reveal a procurvatum deformity of the proximal tibia. Measurement of the Posterior Proximal Tibial Angle (PPTA) is most likely to be:

Which of the following is the most frequent major complication associated with extensive diaphyseal lengthening of the femur using a monolateral or circular external fixator?

A 35-year-old male sustains a severe open tibial fracture resulting in bone loss, requiring bone transport via distraction osteogenesis. The surgeon plans a 7-day latency period before initiating distraction. What is the primary rationale for this latency period?