Orthopedic Surgery Deformity Correction & Osteotomy Review: ABOS Part I & OITE MCQs | Part 22025

Correct Answer: C

The primary goal of a realignment osteotomy for a varus knee, such as a high tibial osteotomy (HTO), is to shift the mechanical axis laterally. In a varus knee, the mechanical axis passes medial to the center of the knee, overloading the medial compartment. By performing an HTO, the tibia is realigned to shift the weight-bearing axis laterally, typically aiming for the mechanical axis to pass through the central or slightly lateral compartment of the knee. This offloads the diseased medial compartment and transfers load to the healthier lateral compartment, thereby reducing pain and potentially slowing the progression of osteoarthritis.

Option A is incorrect because increasing the mLDFA (normal 85-90 degrees) would correct a valgus deformity originating from the femur, not a varus deformity primarily addressed by HTO. Option B is incorrect because decreasing the MPTA (normal 85-90 degrees) would worsen a varus deformity or create a varus deformity if the MPTA is already normal. An HTO typically increases the MPTA to correct varus. Option D is incorrect because while the anatomical axis is affected, the primary goal of realignment osteotomy is to correct the mechanical axis deviation, which directly relates to load distribution across the joint. Option E is incorrect because while joint line obliquity can be affected, it is a secondary consideration; the primary goal is mechanical axis realignment. Maintaining a relatively neutral joint line is often desired, but it's not the overarching primary goal of the procedure itself.

Correct Answer: B

The Center of Rotation of Angulation (CORA) is a fundamental concept in deformity correction. It is defined as the intersection point of the proximal and distal anatomical axes of the deformed bone. When an osteotomy is performed precisely at the CORA, and the bone segments are rotated around this point, the angular deformity is corrected without introducing any translational deformity (i.e., shift of the bone segments relative to each other). This results in a 'pure' angular correction, which is often desirable for maintaining limb alignment and joint congruity.

Option A is incorrect; the CORA is the intersection of the proximal and distal anatomical axes, not necessarily the joint line. Option C is incorrect; the CORA is identified in the plane of the deformity (e.g., frontal plane for varus/valgus), not necessarily the sagittal plane, and it is the apex of the angular deformity, not just 'at the apex'. Option D is incorrect; while the CORA helps determine the location of the osteotomy, the amount of bone to be resected (wedge size) is determined by the desired angular correction, not directly by the CORA itself. Option E is incorrect; the CORA is used to plan the osteotomy location for angular correction, which in turn affects the mechanical axis, but it does not directly determine the final mechanical axis deviation; rather, the desired final mechanical axis guides the amount of correction needed at the CORA.

Correct Answer: B

The image depicts a wedge osteotomy, illustrating the principles of angular correction. To correct a varus deformity and simultaneously lengthen the limb, an opening wedge osteotomy is the most appropriate choice. In an opening wedge osteotomy, a cut is made through the bone, and a wedge-shaped gap is created on the concave side of the deformity. This gap is then filled with bone graft (autograft or allograft) or a bone substitute, which corrects the angular deformity and increases the overall length of the bone. This is particularly useful when there is an associated limb length discrepancy that needs to be addressed.

Option A, a closing wedge osteotomy, involves removing a wedge of bone from the convex side of the deformity. While it corrects the angular deformity, it results in limb shortening, which is contrary to the goal of lengthening. Option C, a dome osteotomy, involves creating a curved cut, allowing rotation and translation, but it does not inherently lengthen the limb. Option D, a transverse osteotomy with translation, primarily corrects translation and can be used for angular correction with complex maneuvers, but it's not the primary method for lengthening in this context. Option E, a biplanar osteotomy, refers to cuts in two planes, often used for stability or specific corrections, but 'without fixation' is generally not a viable surgical approach for osteotomies requiring stability for healing.

Correct Answer: B

For a high tibial osteotomy (HTO) performed to treat medial compartment osteoarthritis and varus deformity, the ideal target for the mechanical axis deviation (MAD) is to achieve slight valgus alignment. This means the mechanical axis should pass through the central or slightly lateral compartment of the knee, typically 0-5 mm lateral to the center of the knee joint. This slight overcorrection (or 'valgus overcorrection') is intended to offload the diseased medial compartment and transfer weight-bearing forces to the healthier lateral compartment, thereby reducing pain and potentially slowing the progression of osteoarthritis. The image shows the mechanical axis passing through the lateral compartment, indicating successful valgus correction.

Option A is incorrect; passing 10-15 mm medial would indicate persistent or worsened varus, which is the opposite of the desired outcome. Option C is incorrect; passing through the medial tibial spine would still significantly load the medial compartment. Option D is incorrect; the MAD is primarily assessed relative to the knee joint, not the ankle joint, for knee osteotomies. Option E is incorrect; the mechanical and anatomical axes are rarely parallel, and their relationship is crucial for understanding deformity, but parallelism is not the goal of realignment.

Correct Answer: B

The normal range for the mechanical lateral distal femoral angle (mLDFA) is typically 85-90 degrees. A value of 95 degrees indicates that the distal femur is in valgus relative to the femoral mechanical axis (i.e., the distal femur is angled more laterally than normal). The normal range for the medial proximal tibial angle (MPTA) is also typically 85-90 degrees. An MPTA of 88 degrees is within the normal range, indicating no significant deformity originating from the proximal tibia. Therefore, the primary apex of the valgus deformity is located in the distal femur.

Option A is incorrect because the MPTA is normal. Options C and D are incorrect because the mLDFA and MPTA specifically assess the angles at the knee joint, indicating deformities in the metaphyseal regions of the femur and tibia, respectively, not typically the mid-diaphysis unless there's a specific diaphyseal bend. Option E is incorrect as the ankle joint angles are not assessed by mLDFA or MPTA.

Correct Answer: C

The patient presents with a varus knee deformity (mechanical axis 20 mm medial) and medial compartment osteoarthritis. The mLDFA is normal (88 degrees), indicating no significant femoral deformity. The MPTA is 80 degrees, which is less than the normal range (85-90 degrees), indicating a varus deformity originating from the proximal tibia. Therefore, a proximal tibial osteotomy is indicated to correct the deformity. To correct a varus deformity, an opening wedge osteotomy on the medial side of the tibia (or a closing wedge on the lateral side) is performed to increase the MPTA and shift the mechanical axis laterally. An opening wedge osteotomy is often preferred as it allows for precise correction and can also address mild limb length discrepancy if present.

Option A, a distal femoral opening wedge osteotomy, would be used to correct a valgus deformity originating from the femur, which is not the case here. Option B, a proximal tibial closing wedge osteotomy, if performed on the lateral side, would correct varus, but if performed on the medial side, it would worsen varus. Typically, a closing wedge for varus is done laterally. An opening wedge medially is more common for HTO. Option D, total knee arthroplasty, is generally reserved for older patients with more advanced osteoarthritis or those who have failed osteotomy, and the patient is described as not yet a candidate. Option E, ankle fusion, is unrelated to knee deformity correction.

Correct Answer: C

The patient has a valgus knee deformity (mechanical axis 15 mm lateral) and lateral compartment pain. The mLDFA is 94 degrees, which is greater than the normal range (85-90 degrees), indicating a valgus deformity originating from the distal femur. The MPTA is 87 degrees, which is within the normal range, ruling out a significant tibial deformity. Therefore, a distal femoral osteotomy (DFO) is indicated to correct the valgus deformity. To correct valgus, a closing wedge osteotomy on the medial side of the distal femur (or an opening wedge on the lateral side) is performed to decrease the mLDFA and shift the mechanical axis medially, offloading the lateral compartment.

Option A, medial opening wedge high tibial osteotomy, is used for varus correction originating from the tibia. Option B, lateral closing wedge high tibial osteotomy, is also used for varus correction originating from the tibia. Option D, lateral opening wedge distal femoral osteotomy, would worsen a valgus deformity by increasing the mLDFA further. Option E, proximal fibular osteotomy, is a newer technique primarily for medial compartment osteoarthritis and varus knee, not for valgus deformity.

Correct Answer: C

Smoking is a well-established risk factor for delayed union and nonunion in various orthopedic procedures, including osteotomies. Nicotine and other toxins in tobacco smoke impair blood flow, reduce osteoblast activity, and interfere with the inflammatory and reparative phases of bone healing, significantly increasing the risk of complications.

Option A, aggressive early weight-bearing, can contribute to fixation failure or loss of correction, but delayed union is more directly related to biological healing factors. Controlled, protected weight-bearing is typically part of the rehabilitation protocol. Option B, use of a locking plate, generally provides stable fixation, which is beneficial for healing, making it less likely to cause delayed union compared to less stable fixation methods. Option D, while opening wedge osteotomies require bone graft and have a larger gap to heal, both opening and closing wedge osteotomies have good union rates with proper technique and patient selection. The choice between them is often based on limb length and specific deformity characteristics, not a significantly higher nonunion rate for one over the other in general. Option E, correction of less than 5 degrees of deformity, is unlikely to cause delayed union; in fact, larger corrections might theoretically pose more healing challenges due to larger gaps or more stress on fixation, though this is not a primary cause of nonunion.

Correct Answer: D

Realignment osteotomy is generally preferred for younger, active patients with unicompartmental osteoarthritis, good bone stock, and no inflammatory arthritis. These patients often desire to maintain a high activity level, including sports, which may be limited or contraindicated after TKA. Osteotomy preserves the native joint and allows for future TKA if needed. The image illustrates the concept of correcting deformity to restore alignment, which is the goal of osteotomy in such patients.

Option A, a sedentary lifestyle with multiple comorbidities, would typically favor TKA, especially if the patient's activity demands are low and the risks of osteotomy (longer recovery, potential for nonunion) outweigh the benefits. Option B, advanced tricompartmental osteoarthritis, is a strong contraindication for osteotomy, as osteotomy is designed for unicompartmental disease. TKA would be the treatment of choice. Option C, age greater than 70 years, generally favors TKA due to the higher likelihood of advanced osteoarthritis, lower activity demands, and faster recovery compared to osteotomy. Option E, significant knee instability and ligamentous laxity, is often a contraindication for osteotomy, as osteotomy primarily corrects angular deformity and does not address ligamentous instability. TKA, especially with constrained components, might be more appropriate in such cases.

Correct Answer: C

The image ch_53_fig_13ca8f.webp illustrates a varus deformity, which often presents with some degree of joint line obliquity. When performing a medial opening wedge high tibial osteotomy, the medial side of the tibia is opened, and a wedge is inserted. This effectively lengthens the medial side of the tibia relative to the lateral side. If the osteotomy is not perfectly parallel to the joint line or if the correction is significant, this can lead to an elevation of the medial joint line, potentially increasing the overall joint line obliquity (making the joint line more sloped). This is a known consideration with opening wedge HTOs, especially if the hinge is not precisely controlled or if the correction is large.

Option A is incorrect; an opening wedge can increase or decrease obliquity depending on the hinge and amount of correction, but it does not always decrease it. Option B is incorrect; a lateral closing wedge osteotomy removes bone from the lateral side, which can lower the lateral joint line. This can also affect joint line obliquity, but it doesn't always increase it; it often aims to make it more horizontal. Option D is incorrect; while a lateral closing wedge lowers the lateral joint line, it doesn't always result in a more horizontal joint line; the final obliquity depends on the initial deformity and the precise execution of the osteotomy. Option E is incorrect; while identifying the CORA helps with angular correction without translation, both opening and closing wedge osteotomies, especially if performed away from the joint line or with specific hinge points, can influence joint line obliquity. The effect on joint line obliquity is a critical consideration in osteotomy planning.

Correct Answer: B

The case describes a mechanical axis passing 15 mm medial to the center of the knee joint. According to the teaching case, a varus deformity is characterized by the mechanical axis passing significantly medial to the knee center, resulting in a positive MAD. This pathologically overloads the medial compartment of the knee, which aligns with the patient's symptoms of medial compartment tenderness and osteoarthritis. The fundamental goal of a frontal plane osteotomy is to shift the mechanical axis back to its neutral position, reducing the MAD to zero.

Option A is incorrect because a valgus deformity would have the mechanical axis passing lateral to the knee center, resulting in a negative MAD and lateral compartment overload. Option C incorrectly associates a valgus deformity with a positive MAD. Option D incorrectly associates a varus deformity with a negative MAD and lateral compartment overload. Option E is incorrect as a 15 mm deviation indicates significant malalignment, not neutral alignment, and MAD is a measure of alignment, not primarily ligamentous laxity (though laxity can influence joint line convergence).

Correct Answer: B

The teaching case states that the mLDFA defines the orientation of the knee joint relative to the femur, and an abnormal mLDFA indicates a femoral deformity, requiring a Distal Femoral Osteotomy (DFO). The patient's mLDFA is 95°, which is significantly higher than the normal average of 88°. This indicates a valgus deformity originating from the distal femur, which can contribute to a varus knee if the femur is in relative valgus. Conversely, the MPTA is 87°, which is within the normal range (87°), indicating no significant deformity originating from the proximal tibia. The JLCA of 1° is also within the normal range (0-2°), suggesting no significant ligamentous laxity or asymmetric cartilage loss.

Therefore, the primary anatomical location of the deformity is the distal femur, necessitating a Distal Femoral Osteotomy (DFO) to correct the abnormal mLDFA. Options A, C, D, and E are incorrect as they misidentify the primary location of the deformity based on the given angle measurements.

Correct Answer: C

The teaching case explicitly defines how to locate the CORA: 'Draw the proximal axis line (either the anatomic mid-diaphyseal line or the mechanical axis line) of the deformed bone and extend it distally past the deformity. Draw the distal axis line of the deformed bone and extend it proximally past the deformity. The exact point where these two lines intersect is the CORA.' This geometric construction identifies the apex of the deformity.

Option A describes drawing the mechanical axis, which is used to determine MAD, not CORA. Option B describes measuring the MAD. Option D describes measuring the Joint Line Convergence Angle (JLCA). Option E describes the placement of the osteotomy and Angulation Correction Axis (ACA), which is related to surgical execution, not the initial identification of the CORA.

Correct Answer: A

Paley's Rule One states: 'When the osteotomy is performed at the level of the CORA, and the Angulation Correction Axis (ACA) also passes exactly through the CORA, the result is pure angular correction with zero translation.' The teaching case describes this as the 'anatomic ideal' where proximal and distal mechanical axes are perfectly restored to a single, collinear line. Diagram set (b) illustrates an opening wedge osteotomy. Within this set, Roman numeral (i) depicts the osteotomy line passing through the ACA-CORA, resulting in 37° angular correction, no MAD, perfect anatomic axis alignment, and normal ankle and knee joint orientation. This perfectly matches the description of Rule One and the desired outcome.

Options B, C, and D refer to other outcomes within diagram set (b) that involve translation or residual deformity, which are not consistent with Rule One. Option E refers to a closing wedge osteotomy (diagram set c), which is not the technique described in the question.

Correct Answer: D

Paley's Rule Two states: 'When the ACA passes through the CORA, but the osteotomy is performed at a different level (either proximal or distal to the CORA), the mechanical axes will align perfectly, but the bone segments will translate.' The teaching case describes this as a common pragmatic approach when the CORA is in a difficult location. The image's 'Deformity Planning and Osteotomy Considerations' section for 'Opening Wedge Sequence' describes Rule 2 Variation (iv) as: 'Osteotomy line is distal to CORA, ACA is through the CORA. Result: 37° angular correction, no MAD, normal anatomic axis alignment of the distal tibia (though a cortical bump is present because of the level of osteotomy and obligatory translation), and normal ankle and knee joint orientation.' This perfectly matches the scenario described in the question, where the osteotomy is performed away from the CORA but the ACA is at the CORA, leading to correction with translation.

Option A represents Rule One (no translation). Option B represents Rule 3 (ACA on osteotomy line, away from CORA, leading to residual MAD). Option C represents Rule 3 with overcorrection, but the question asks for the direct application of Rule 2. Option E refers to a closing wedge osteotomy.

Correct Answer: C

The scenario describes a situation where both the osteotomy cut and the Angulation Correction Axis (ACA) are located at the same level, but this level is away from the true CORA. The teaching case explicitly states that this is Paley's Rule Three: 'When both the osteotomy cut and the ACA are located at the same level, but this level is away from the CORA, a new deformity is created.' The consequence is that 'the angular deformity (the "bend" in the bone) may visually appear corrected, but the mechanical axes of the proximal and distal segments will become parallel but not collinear. This introduces a massive, iatrogenic translation, and the Mechanical Axis Deviation (MAD) will persist, meaning the knee joint remains pathologically overloaded.' This perfectly matches the clinical outcome described in the question.

Rule One describes perfect correction at the CORA with no translation. Rule Two describes correction with translation when the osteotomy is away from the CORA but the ACA is at the CORA. Options D and E are not among Paley's three fundamental osteotomy rules.

Correct Answer: C

The teaching case highlights that a crucial biomechanical consequence of an opening wedge osteotomy is that it inherently lengthens the bone. This is a 'massive advantage if the patient has a pre-existing limb length discrepancy (LLD) and the operative leg is shorter,' which is precisely the scenario described for this patient (1.5 cm LLD with the affected limb being shorter). Regarding surgical pearls, the case emphasizes 'Hinge Protection': 'The cortical hinge is the lifeline of the procedure. Meticulously protect it. Use fluoroscopy to ensure the saw blade stops 1cm short of the far cortex. A broken hinge ("hinge fracture") leads to multi-planar instability and potential loss of correction.'

Option A is incorrect; opening wedge lengthens, not shortens, and it involves adding graft, not removing bone. Option B is incorrect; opening wedge is not inherently more stable than closing wedge, and neurovascular structures (common peroneal nerve, popliteal artery) are at risk, especially on the lateral side (peroneal nerve) and posterior (popliteal artery) with opening on the medial side. Option D is incorrect; larger gaps often require structural graft, and compartment syndrome risk is higher with larger corrections, not smaller ones. Option E is incorrect; opening wedge does not inherently reduce infection risk, and the superficial MCL is typically released, not the LCL, to facilitate opening and reduce tension on neurovascular structures.

Correct Answer: D

The teaching case describes the closing wedge osteotomy as 'the conceptual and geometric inverse of the opening wedge. It is an excellent, stable choice when limb shortening is desired, when the deformity is excessively large, or when avoiding the morbidity of bone grafting is a top priority.' This aligns perfectly with the patient's needs: avoiding limb lengthening (implying a desire for shortening or no change), prioritizing stability, and avoiding bone grafting. A closing wedge osteotomy involves removing a wedge of bone, which inherently shortens the limb (or prevents lengthening) and provides inherent stability upon compression, often negating the need for additional graft material.

Options A and B (opening wedge osteotomies) inherently lengthen the limb and require bone grafting, which are contrary to the patient's requirements. Option C (dome osteotomy) is a different technique, not specifically detailed for these advantages in the provided text. Option E (callus distraction osteogenesis) is a lengthening technique, which is not desired here.

Correct Answer: C

The teaching case emphasizes that 'while the MAD tells us if there is a problem and how severe it is, the joint orientation angles tell us exactly where the problem is located.' In this patient, both the mLDFA and MPTA are abnormal. The mLDFA of 92° (normal 88°) indicates a femoral deformity (valgus angulation of the distal femur contributing to overall varus). The MPTA of 80° (normal 87°) indicates a tibial deformity (varus angulation of the proximal tibia). The MAD of +20mm confirms a significant varus malalignment. The JLCA of 3° (normal 0-2°) suggests some joint line convergence, possibly due to cartilage loss or ligamentous laxity, which needs to be considered but is not the primary bone deformity.

Since both the femur and tibia contribute to the overall varus malalignment, an isolated osteotomy at either level would not fully correct the deformity and normalize the MAD. Therefore, a bi-level osteotomy addressing both the distal femur (DFO) and proximal tibia (HTO) is the most appropriate initial surgical strategy to restore physiological alignment. Options A and B are insufficient. Option D is incorrect as supramalleolar osteotomy addresses distal tibial deformities, and JLCA is not the primary target for osteotomy. Option E is inappropriate given the significant and symptomatic deformity.

Correct Answer: C

This scenario describes a situation where both the osteotomy cut and the Angulation Correction Axis (ACA) are located at the same level, but this level is away from the true CORA (osteotomy at 5cm distal to joint line, CORA at 2cm distal to joint line). This is a direct application of Paley's Rule Three: 'When both the osteotomy cut and the ACA are located at the same level, but this level is away from the CORA, a new deformity is created.' The teaching case further explains that 'the angular deformity (the "bend" in the bone) may visually appear corrected, but the mechanical axes of the proximal and distal segments will become parallel but not collinear. This introduces a massive, iatrogenic translation, and the Mechanical Axis Deviation (MAD) will persist.' However, a master surgeon can use Rule Three intentionally: 'By deeply understanding the geometry, one can calculate the exact amount of angular overcorrection needed to force the translated mechanical axis back through the center of the knee.' The image's 'Deformity Planning and Osteotomy Considerations' section for 'Opening Wedge Sequence' (iii) shows 'Rule 3 with Overcorrection' where a 37° deformity requires a 41° correction to achieve no MAD, but causes valgus and lateral translation of the anatomic axis of the distal tibia.

Therefore, the most likely consequence is the creation of a new deformity with persistent MAD, necessitating an intentional overcorrection of the angular deformity to normalize the MAD. Option A describes Rule One. Option B describes Rule Two. Option D is incorrect as MAD will persist without overcorrection. Option E describes a consequence of closing wedge osteotomy, not opening wedge in this context.

Correct Answer: C

The teaching case explicitly states: 'The fundamental, non-negotiable goal of a frontal plane osteotomy around the knee is to shift the mechanical axis back to its neutral, physiologic position, thereby reducing the MAD to zero.' This ensures that ground reaction forces are transmitted harmoniously through the center of the hip, knee, and ankle joints, preventing premature joint degeneration.

Option A is incorrect because the mechanical axis, not just the anatomical axis, is the ultimate measure of weight transmission. A perfectly straight anatomical axis does not guarantee a neutral mechanical axis. Option B is incorrect; while JLCA is important, its elimination is not the primary goal of an osteotomy, and a normal JLCA is 0-2 degrees, not necessarily zero. Option D is incorrect; while placing the ACA at the CORA is ideal (Rule One), it's not always feasible or necessary, as Rule Two allows for correction with translation when the osteotomy is away from the CORA but the ACA is at the CORA. Option E is incorrect; limb lengthening is a secondary effect of opening wedge osteotomies and is only desirable if a limb length discrepancy exists; it is not a universal goal for all frontal plane osteotomies (closing wedge osteotomies shorten).

Paley's Rule 1 states that if the osteotomy and the axis of correction (hinge) are both placed at the CORA, the deformity corrects with pure angulation and the mechanical axes become perfectly collinear without translation.

Because the osteotomy is proximal to the tubercle, the joint line is elevated relative to the tubercle, causing a relative patella baja. Additionally, standard medial opening-wedge HTO tends to increase the posterior tibial slope because the anterior aspect of the proximal tibia opens more easily than the wider posterior aspect.

Distracting at a rate faster than 1 mm per day outpaces the body's ability to form osteoid, resulting in an atrophic regenerate and potential nonunion. Distracting too slowly (e.g., 0.25 mm/day) risks premature consolidation.

Paley's Rule 2 states that if the hinge is at the CORA but the osteotomy is away from the CORA, the mechanical axes will fully realign (collinear), but there will be an obligatory translation of the bone fragments at the osteotomy site.

In a mechanically neutral lower limb, the mechanical axis (a line from the center of the femoral head to the center of the ankle talus) passes slightly medial (1 to 8 mm) to the center of the knee joint.

A medial closing-wedge osteotomy provides bone-on-bone compression over a broad surface area, allowing for faster healing and greater inherent stability. It does, however, result in slight limb shortening compared to an opening-wedge technique.

Hexapod external fixators, such as the Taylor Spatial Frame, are based on the Stewart-Gough platform mechanism. This allows for simultaneous multi-planar correction in all six degrees of freedom using a virtual hinge.

Lateral closing-wedge HTO typically requires a concomitant proximal fibular osteotomy to allow for tibial compression. The common peroneal nerve winds tightly around the fibular neck and is highly susceptible to injury during this step.

Paley's Rule 3 states that if the hinge and the osteotomy are both located away from the true CORA, angular correction is possible, but it will result in mechanical axes that are parallel rather than collinear, effectively inducing a translation deformity.

The normal femoral mechanical axis is a line from the center of the femoral head to the intercondylar notch. The anatomic axis bisects the diaphysis. The angle between these two axes is typically 5 to 7 degrees of valgus.

The latency period allows for the initial inflammatory phase of fracture healing to subside and for a highly vascularized granulation tissue network to form. Premature distraction risks pulling apart this essential cellular matrix, leading to poor regenerate.

To maintain a robust lateral hinge, the osteotomy should aim approximately 10-15 mm below the lateral joint line, typically directed toward the tip of the fibular head or the superior proximal tibiofibular joint.

The JLCA measures the angle between the articular surface of the distal femur and the proximal tibia. An increased JLCA (typically >2 degrees) indicates either asymmetric joint space narrowing (cartilage loss) or ligamentous laxity opening the joint space.

A dome osteotomy (focal dome) is highly advantageous for multi-planar deformities because it allows correction of varus/valgus, flexion/extension, and rotational alignment simultaneously through a semicircular cut without creating large bone defects or "dog ears".

Lengthening over a nail (LON) allows the external fixator to be removed immediately after the distraction phase is completed by locking the intramedullary nail. This dramatically reduces the time the patient must wear the external frame (the consolidation phase).

Paley's Osteotomy Rule 1 states that when the osteotomy and the hinge (axis of correction) are both located at the CORA, the deformity corrects with pure angulation and no translation.

Paley's Osteotomy Rule 2 dictates that if the hinge is on the CORA bisector line but the osteotomy is at a different level, the correction will result in angulation combined with translation. This allows the mechanical axis to realign correctly.

Medial opening wedge HTO performed proximal to the tibial tubercle elevates the joint line relative to the tubercle. This causes a relative decrease in patellar height, leading to patella infera.

The proximal tibia is triangular in cross-section, being narrower anteriorly. Symmetrical opening of the anterior and posterior cortices will inadvertently increase the posterior tibial slope.

The optimal rate of distraction osteogenesis is 1.0 mm per day. Dividing this into four increments of 0.25 mm provides a balance between adequate bone formation and prevention of premature consolidation.

The Fujisawa point, located approximately 62.5% of the medial-to-lateral width of the tibial plateau, is the standard target for the mechanical axis in HTO to optimally off-load the medial compartment.

The common peroneal nerve is highly vulnerable during lateral closing-wedge HTO and proximal fibular osteotomies. Injury results in foot drop due to loss of ankle dorsiflexion and toe extension.

The normal medial proximal tibial angle (MPTA) is typically 87 degrees, with an accepted normal range of 85-90 degrees. Angles significantly lower indicate tibia vara.

The normal mechanical lateral distal femoral angle (mLDFA) is 88 degrees (range 85-90 degrees). An mLDFA of less than 85 degrees typically indicates a valgus deformity originating in the distal femur.

According to Paley's Rule 3, placing both the osteotomy and the hinge axis outside the CORA and its bisector line results in a new, iatrogenic translation deformity upon angular correction.

The JLCA measures the convergence of the distal femoral and proximal tibial articular surfaces, which is normally 0-2 degrees. An increased JLCA indicates intra-articular deformity, asymmetrical cartilage loss, or collateral ligament laxity.

For a medial closing wedge distal femoral osteotomy to correct valgus, the hinge is placed on the medial cortex (the apex of the wedge). This adheres to Rule 1, producing pure angulation at the CORA.

The mechanical axis of the lower limb is defined as a straight line drawn from the center of the femoral head to the center of the tibial plafond. Deviation of this line from the center of the knee dictates the MAD.

A latency period of 5-7 days allows the fracture hematoma to organize and mesenchymal stem cells to populate the gap. This critical step is essential to set the stage for successful distraction osteogenesis.

The TSF relies on a hexapod configuration utilizing exactly six adjustable struts. This structure provides the ability to correct angulation, translation, and rotation simultaneously in all six degrees of freedom.

The deformity is localized to the distal femur as evidenced by the abnormal mLDFA. Since the child has widely open physes, medial distal femoral hemiepiphysiodesis (guided growth) is the optimal treatment to gradually correct the valgus.

Osteotomy of the middle third of the fibula is safest. A proximal osteotomy heavily risks the common peroneal nerve, while a very distal osteotomy can compromise the syndesmosis and ankle stability.

Paley's Rule 1 states that when the osteotomy and the ACA are both located at the CORA, the deformity corrects with pure angulation and no translation.

Paley's Rule 2 dictates that if the ACA is at the CORA but the osteotomy is at a different level, the mechanical axis will realign, but the bone ends will translate at the osteotomy site.

Because of the triangular shape of the proximal tibia, the anterior gap should be approximately half the size of the posterior gap to maintain the native posterior tibial slope during an opening-wedge HTO.

Medial opening-wedge HTO typically decreases patellar height (creates patella baja/infera) by distalizing the tibial tubercle relative to the joint line, whereas lateral closing-wedge HTO tends to increase patellar height (patella alta).

The latency period (typically 5-10 days) allows a hematoma to form and mesenchymal stem cells/angiogenesis to organize within the corticotomy gap, laying the foundation for the fibrovascular bridge needed for successful regenerate bone formation.

Normal mLDFA is 87 degrees (85-90) and normal MPTA is 87 degrees (85-90). An MPTA of 81 degrees indicates proximal tibial varus, meaning the deformity is primarily tibial.

The JLCA measures the angle between the distal femoral and proximal tibial articular lines. A widening >2 degrees suggests intra-articular deformity, cartilage loss, or collateral ligament laxity contributing to the malalignment.

Fibular osteotomies are typically performed at the junction of the middle and distal thirds of the fibula to minimize risk to the common peroneal nerve proximally and preserve the distal syndesmotic stability.

The classic Ilizarov protocol recommends a rate of 1.0 mm per day, divided into four increments of 0.25 mm. This rhythm balances the risk of premature consolidation with the risk of poor regenerate bone formation.

Infantile Blount's disease is a three-dimensional deformity characterized by proximal tibial varus, internal tibial torsion, and procurvatum (flexion deformity of the proximal tibia).

A prolonged latency period (e.g., 14 days) or a distraction rate that is too slow can allow the corticotomy site to heal prematurely before adequate length is achieved, leading to premature consolidation.

Hexapod frames utilize a computer program to calculate strut adjustments, allowing simultaneous correction of translation, angulation, and rotation (six degrees of freedom) without physically changing the frame hinges.

According to Osteotomy Rule 1, when the osteotomy and the ACA both pass through the CORA, the mechanical axes realign completely without any translational deformity.

The normal mLDFA is 88 degrees (range 85-90) and MPTA is 87 degrees. An mLDFA of 81 degrees indicates a valgus deformity originating in the distal femur, requiring a distal femoral osteotomy.

The Fujisawa point is traditionally located at 62-62.5% of the tibial width from the medial edge. Shifting the mechanical axis to this point optimally unloads the arthritic medial compartment.

Due to the triangular shape of the proximal tibia, opening the osteotomy equally anteriorly and posteriorly increases the posterior tibial slope. To maintain the native slope, the anterior gap should be approximately half the size of the posterior gap.

Opening-wedge HTO performed distal to the tibial tubercle distalizes the tubercle relative to the joint line. This results in patella baja and can increase patellofemoral contact pressures.

A latency period of 5-7 days allows the initial fracture hematoma to organize and mesenchymal cells to proliferate. This ensures robust callus formation before distraction begins.

Ilizarov demonstrated that a distraction rate of 1.0 mm per day is optimal. Dividing this into multiple smaller increments (e.g., four 0.25 mm increments) provides a smoother environment for regenerate formation and less soft tissue tension.

This describes Paley's Rule 2. Placing the ACA at the CORA but cutting the bone elsewhere perfectly aligns the proximal and distal mechanical axes, but creates a translational step-off at the osteotomy site.

The Taylor Spatial Frame utilizes a hexapod (Stewart-Gough) platform. Its six adjustable struts allow for the simultaneous gradual correction of all six degrees of freedom (angulation, translation, and rotation in x, y, and z axes).

In a closing-wedge osteotomy, to prevent unintended changes in the sagittal plane (flexion/extension), the hinge axis must be perfectly parallel to the joint line in the axial plane.

Inflammatory arthropathy (like rheumatoid arthritis) is a contraindication for joint-preserving osteotomies because the disease affects all compartments systemically, leading to predictable early failure.