1. General Principles & Basic Science MCQs

A 14-year-old male is undergoing surgical correction of a post-traumatic tibial deformity.

According to the First Rule of osteotomy defined by Paley, if the osteotomy and the axis of correction of angulation (ACA) both pass through the center of rotation of angulation (CORA), which of the following accurately describes the resulting correction?

A 14-year-old male has a mid-diaphyseal tibial deformity. The Center of Rotation of Angulation (CORA) is determined. The surgeon plans an osteotomy at a level distant from the CORA, but places the hinge axis exactly on the CORA. Which of the following best describes the resulting correction according to Paley's rules?

During normal human gait, maximum ankle dorsiflexion typically occurs during which specific phase of the gait cycle?

A 22-year-old undergoes tibial lengthening utilizing the distraction osteogenesis technique. Histologic analysis of the normal regenerate bone forming in the distraction gap would predominantly demonstrate which type of bone formation?

In planning a deformity correction using a Taylor Spatial Frame (TSF), a six-axis hexapod external fixator relies on the mathematical principles of the Stewart-Gough platform. Which of the following is an essential input parameter required by the software to compute the precise strut length changes?

A 28-year-old male is undergoing corrective osteotomy for a post-traumatic diaphyseal tibial varus deformity. The surgeon plans an osteotomy at a level proximal to the center of rotation of angulation (CORA). To achieve colinear realignment of the proximal and distal anatomical axes, which of the following maneuvers is mechanically required?

During a formal gait analysis, a patient demonstrates excessive knee flexion and delayed heel off during the terminal stance phase of the gait cycle. Weakness in which of the following muscle groups is the most likely biomechanical cause of this abnormal gait pattern?

During the loading response phase of normal human gait, the knee undergoes approximately 15 degrees of flexion. Which of the following best describes the primary muscle activity controlling this specific motion?

When evaluating a standing full-length lower extremity radiograph for coronal plane deformity planning, which of the following pairs correctly defines the normal physiological averages for the mechanical lateral distal femoral angle (mLDFA) and mechanical medial proximal tibial angle (mMPTA)?

In a normal gait cycle, the vertical ground reaction force (GRF) curve demonstrates a distinct bimodal (two-peak) shape. The first peak occurs during early stance and the second during late stance. What biomechanical event is primarily responsible for the measured trough (valley) between these two peaks?

A 16-year-old male with a spinal osteoid osteoma reports dramatic relief of his severe night pain following the administration of nonsteroidal anti-inflammatory drugs (NSAIDs). Which molecular mediator is most directly responsible for this classic pain response?

A surgeon is performing a second MTPJ plantar plate repair via a dorsal approach, as depicted in the image.

After incising the skin and subcutaneous tissue, which of the following structures must be meticulously identified and protected to prevent iatrogenic injury during the initial dissection to expose the extensor mechanism?

A 55-year-old female presents with pain at the plantar aspect of the second metatarsophalangeal (MTP) joint and a progressive medial deviation of the second toe. This crossover toe deformity is primarily driven by the attenuation and failure of which of the following structures?

A 55-year-old female presents with progressive pain and a "crossover" deformity of her second toe.

The pathoanatomy of this condition primarily involves attenuation or rupture of which of the following structures?

A 55-year-old female presents with a progressive crossover toe deformity of her second toe, which rests in a dorsomedial position over the hallux. What is the typical sequence of soft tissue structural failure that leads to this specific deformity?

A 30-year-old patient presents with 20 degrees of knee hyperextension on passive examination. Their full-length lateral radiograph shows a Mechanical Posterior Distal Femoral Angle (mPDFA) of 84° and a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 80°. The clinical presentation is analogous to Panel (i) in the provided diagram.

A surgeon is planning a proximal tibial flexion osteotomy for a patient with tibial recurvatum (Mechanical Posterior Proximal Tibial Angle (mPPTA) = 86°). The patient also has patella alta.

During a distal femoral flexion osteotomy via a lateral sub-vastus approach for femoral recurvatum, the surgeon is performing an anterior opening wedge osteotomy.

A patient with a distal femoral extension deformity (Mechanical Posterior Distal Femoral Angle (mPDFA) = 90°, Mechanical Posterior Proximal Tibial Angle (mPPTA) = 81°) undergoes a proximal tibial flexion osteotomy to correct their clinical hyperextension.

A 62-year-old patient presents with a chronic, progressive crouched gait and significant anterior knee pain, particularly with ambulation. Clinical examination reveals a fixed flexion deformity (FFD) of the knee. The patient reports rapid quadriceps fatigue even with short distances. Based on the biomechanical principles outlined in the case, which of the following is the MOST accurate explanation for the patient's symptoms?