ABOS Part I Orthopaedic Review: Patellar Instability, Knee OA, & Hallux Rigidus Management | Part 22308

Correct Answer: C

This patient presents with a severe form of patellar instability characterized by multiple significant anatomical risk factors: severe trochlear dysplasia, a markedly increased TT-TG distance (normal < 15-20 mm), and patella alta. Isolated MPFL reconstruction would address the medial restraint but not the underlying bony deformities. VMO advancement and lateral retinacular release are typically insufficient for severe bony dysplasia. Tibial tubercle medialization alone would only address the TT-TG and not the trochlear dysplasia or patella alta. Therefore, a comprehensive approach involving trochleoplasty (for the severe dysplasia), MPFL reconstruction (for the medial restraint), and a tibial tubercle osteotomy for both medialization (for TT-TG) and distalization (for patella alta) is indicated for optimal outcomes and recurrence prevention. This combination addresses all major identified risk factors.

Correct Answer: C

The MPFL is recognized as the primary static restraint to lateral patellar translation, particularly in the initial 20-30 degrees of knee flexion, where the trochlear groove is shallowest. At full knee extension, the joint is less constrained, but the MPFL's role is critical. The femoral attachment is variable but typically found distal and posterior to the adductor tubercle, often blended with the adductor magnus tendon and medial gastrocnemius origin, not consistently on the medial epicondyle. The patellar attachment is usually on the superior medial patella. While avulsions can occur at either end, femoral avulsions are more common in acute dislocations.

Correct Answer: D

Severe trochlear dysplasia, especially Dejour Types B, C, or D, is consistently identified as the single most significant anatomical risk factor for recurrent patellar instability. The flattened or convex trochlear groove provides inadequate bony constraint against lateral patellar translation. Generalized ligamentous laxity is a risk factor but less potent than severe dysplasia. Dislocation at a younger age (especially under 15) is associated with higher recurrence rates, not older age. A torn MPFL is characteristic of acute dislocation, but its absence doesn't preclude recurrence if other factors exist; its presence increases recurrence risk if left untreated. A Q-angle less than 10 degrees would typically be protective or normal, not a risk factor; an increased Q-angle is a risk factor.

Correct Answer: C

Over-constraining the patella is a known complication of MPFL reconstruction, leading to patellofemoral pain and stiffness. The MPFL is isometric in the initial 0-30 degrees of flexion. Tensioning the graft with the knee in 30 degrees of flexion is crucial. If the graft is tensioned in full extension or hyperflexion, it becomes too tight in mid-flexion, causing increased patellofemoral contact pressures and potentially pain or articular cartilage damage. Fluoroscopy for femoral tunnel placement is essential to avoid violating the physis in skeletally immature patients or drilling too anterior/posterior, but it doesn't directly prevent over-tensioning. Patellar fixation is standard; lateral retinacular release is not routinely performed with MPFL reconstruction unless specific lateral tightness is present.

Correct Answer: B

A TT-TG distance of 20 mm is considered significantly elevated. Normal values are typically less than 15-20 mm, with values over 20 mm strongly correlating with patellofemoral instability due to a lateralized pull of the patellar tendon and quadriceps mechanism relative to the trochlear groove. It is a key factor indicating bony malalignment. While patella alta can coexist, TT-TG specifically measures the transverse plane relationship, not patellar height. It's a significant risk factor but doesn't necessarily dictate immediate surgery if asymptomatic or if conservative management is successful. Quadriceps imbalance can contribute but isn't directly measured by TT-TG.

Correct Answer: C

The patellar apprehension test (or 'Fairbank's test') involves attempting to laterally translate the patella with the knee in varying degrees of flexion while observing for the patient's anxiety, muscle guarding, or resistance, which signifies impending dislocation. This test is highly specific for patellar instability. The other tests are for collateral ligaments (valgus stress), ACL (Lachman), meniscal injury (McMurray), or patellofemoral pain syndrome (patellar grind), not patellar instability directly.

Correct Answer: C

For skeletally immature patients with recurrent patellar instability, MPFL reconstruction is the preferred procedure. Given the open physes, techniques that avoid or protect the growth plates are critical, such as an all-epiphyseal (transphyseal without violating growth plates) or transphyseal tunnels placed carefully to minimize growth disturbance. Tibial tubercle osteotomies and trochleoplasty are generally avoided in skeletally immature patients due to the risk of growth arrest, unless there are severe underlying bony deformities that supersede this risk (which are explicitly ruled out in this question). Conservative management has failed after the second dislocation, and lateral release alone is insufficient for MPFL rupture.

Correct Answer: C

Persistent anterior knee pain, particularly with activities like stairs and squatting, after an MPFL reconstruction that successfully prevented recurrence, strongly suggests patellofemoral overload or over-constraining. This is a common complication if the MPFL graft is tensioned too tightly or fixed in an incorrect position, leading to increased patellofemoral contact pressures. Recurrence is ruled out by the history. Infection would typically present with different symptoms (fever, warmth, redness, systemic signs). Insufficient medialization would lead to continued instability, not just pain without apprehension. Graft rupture would lead to recurrence.

Correct Answer: D

The Insall-Salvati ratio (patellar tendon length to patellar diagonal length on a lateral X-ray) and modified Insall-Salvati ratio are standard measurements for assessing patellar height (patella alta or baja). The Q-angle measures quadriceps alignment, TT-TG measures tibial tubercle lateralization, Dejour classifies trochlear dysplasia, and bisect offset is used for patellar tilt on axial views. Therefore, Insall-Salvati ratio is the correct answer for patellar height.

Correct Answer: B

An open proximal tibial physis is an absolute contraindication for a standard tibial tubercle osteotomy (e.g., Fulkerson or Elmslie-Trillat) due to the significant risk of growth arrest, angular deformities, or leg length discrepancies. In skeletally immature patients, if a bony procedure is absolutely necessary, techniques that spare the physis (e.g., physis-sparing MPFL reconstruction) or physeal bridging procedures with careful monitoring are considered. Patella alta, severe trochlear dysplasia, and generalized ligamentous laxity are risk factors that may necessitate a tibial tubercle osteotomy, not contraindications. A prior MPFL reconstruction does not contraindicate a subsequent tibial tubercle osteotomy if malalignment persists.

Correct Answer: C

The patient is a 42-year-old bricklayer with medial compartment osteoarthritis, a correctable varus deformity, and a high-demand physical job. High Tibial Osteotomy (HTO) is the most appropriate initial surgical recommendation in this scenario. HTO is indicated for younger, active patients (physiological age < 60 years) with unicompartmental osteoarthritis and a varus deformity, especially those with high physical demands. It aims to shift the mechanical axis laterally, offloading the medial compartment and preserving the native knee joint, which is advantageous for patients engaged in heavy labor.

• A. Total Knee Arthroplasty (TKA) is generally reserved for older patients with more diffuse or severe osteoarthritis, or those with lower activity demands, as it involves replacing the entire joint. A 42-year-old active bricklayer would likely wear out a TKA prematurely.
• B. Medial Unicondylar Knee Arthroplasty (UKA) is an option for unicompartmental OA, but the case explicitly states that UKA is generally not recommended for patients with highly physically demanding jobs due to the risk of accelerated wear. While women may prefer UKA due to better tolerance of angular deformity, and patients with low physical demand may benefit, it is less suitable for this patient's specific occupational demands.
• D. Arthroscopic debridement and microfracture are typically considered for smaller, contained chondral defects, not for moderate medial compartment osteoarthritis with a varus deformity, which implies more widespread cartilage loss and mechanical malalignment. These procedures are unlikely to provide long-term relief for this patient's condition.
• E. Patellofemoral Arthroplasty addresses isolated patellofemoral osteoarthritis. The patient's symptoms and radiographic findings are consistent with medial compartment osteoarthritis, not primarily patellofemoral involvement.

Correct Answer: C

The case explicitly lists inflammatory arthropathy, such as rheumatoid arthritis and psoriatic arthropathy, as main contraindications for HTO. The presence of rheumatoid arthritis significantly increases the risk of poor bone healing, disease progression in other compartments, and overall unpredictable outcomes with osteotomy. Additionally, a large varus thrust with coronal subluxation of > 1 cm is also a contraindication, which this patient also exhibits (1.5 cm).

• A. Physiological age of 48 years is well within the acceptable range (< 60 years) for HTO.
• B. Varus deformity of 8 degrees is within the acceptable range (< 15 degrees) for HTO.
• D. Full range of motion is a favorable condition for HTO, as it indicates good joint mobility and less stiffness.
• E. Stable knee ligaments are a prerequisite for HTO, as ligamentous instability (e.g., incompetent MCL or ACL) is a contraindication.

Correct Answer: C

The case states that while indications for HTO and UKA are similar, women often prefer UKA because they do not tolerate the angular deformity created by HTO very well. Additionally, patients with low physical demand may benefit from UKA. This patient fits both criteria: she is female, has low physical demand, and is concerned about angular deformity. UKA offers a less invasive option with potentially better cosmetic outcomes and is suitable for her activity level.

• A. High Tibial Osteotomy (HTO), while a viable option for unicompartmental OA, might not be preferred by this patient due to the angular deformity it creates, which women may not tolerate well.
• B. Total Knee Arthroplasty (TKA) is generally considered for more severe, multi-compartmental arthritis or older, less active patients. It is an overtreatment for isolated medial compartment OA in a 55-year-old with low physical demand.
• D. Arthroscopic lavage and debridement are typically palliative and offer limited long-term benefit for established osteoarthritis with structural deformity.
• E. Distal Femoral Osteotomy is indicated for lateral compartment osteoarthritis with valgus deformity, which is not the patient's presentation.

Correct Answer: C

The case specifically mentions that closing wedge osteotomy 'may entail proximal fibular osteotomy or disruption of tibial–fibular joint. It has the risk of peroneal nerve injury'. This is a direct complication associated with the closing wedge technique due to the proximity of the fibula and the common peroneal nerve during the osteotomy and potential fibular shortening or osteotomy.

• A. Late collapse with loss of correction is a disadvantage specifically attributed to opening wedge osteotomy in the case.
• B. Need for bone graft is a disadvantage specifically attributed to opening wedge osteotomy, as the gap created needs to be filled.
• D. Decreased patellar height (patella baja) is associated with opening wedge osteotomy, whereas closing wedge osteotomy is noted to increase patellar height. Historically, patella baja was associated with lateral closing wedge HTO with cast immobilization, but more recent studies show closing wedge increases patellar height.
• E. Increased risk of non-union is not specifically highlighted as a unique complication of closing wedge HTO over opening wedge in the provided text, though it can be a general complication of any osteotomy.

Correct Answer: D

The case states that the opening wedge osteotomy 'has the disadvantage of having to use bone graft and late collapse with loss of correction'. This directly identifies 'late collapse with loss of correction' as a specific disadvantage of the opening wedge technique.

• A. Loss of bone stock making TKA technically difficult is a disadvantage specifically attributed to closing wedge osteotomy.
• B. Increased patellar height is associated with closing wedge osteotomy, while opening wedge osteotomy is noted to lower patellar height.
• C. Risk of peroneal nerve injury is a specific risk associated with closing wedge osteotomy, particularly with proximal fibular osteotomy or disruption of the tibiofibular joint.
• E. Disruption of the tibiofibular joint is mentioned as a potential consequence of closing wedge osteotomy.

Correct Answer: C

The case lists the prerequisites for HTO, including a fixed flexion deformity of < 15 degrees. This patient has a fixed flexion deformity of 20 degrees, which exceeds this prerequisite and therefore contraindicates HTO.

• A. Varus deformity of 10 degrees is within the acceptable range (< 15 degrees) for HTO.
• B. Physiological age of 62 years is slightly above the stated prerequisite of < 60 years, but 'physiological age' can be subjective. However, the fixed flexion deformity is a more definitive contraindication based on the strict criteria provided. If the patient was physiologically younger than 60 despite chronological age, this might not be an absolute contraindication, but the fixed flexion deformity is.
• D. Knee flexion of 85 degrees is just below the prerequisite of > 90 degrees flexion. While close, it could be a relative contraindication, but the fixed flexion deformity is a more direct and absolute contraindication based on the given thresholds.
• E. Medial compartment osteoarthritis is the indication for HTO, not a contraindication.

Correct Answer: C

The case explicitly states, referencing Dettoni et al., that 'They concluded that with the correct indications, both treatments produce durable and predictable outcomes in the treatment of medial unicompartmental arthrosis of the knee. There is no evidence of superior results of one treatment over the other.'

• A. UKA consistently shows significantly better survivorship and functional outcomes. The review reported 'slightly better results for UKA in terms of survivorship and functional outcome,' but immediately qualified this by stating 'the differences are not remarkable' and 'no evidence of superior results of one treatment over the other.'
• B. HTO consistently shows significantly better survivorship and functional outcomes. This is incorrect, as the review suggested slightly better results for UKA, though not remarkably so.
• D. HTO is superior for high-demand patients, while UKA is superior for low-demand patients. While this is the clinical recommendation made by the candidate in the case based on practical considerations (accelerated wear of UKA in high-demand jobs), the Dettoni et al. review's conclusion was specifically about the lack of evidence for superiority in outcomes between the two treatments when indications are correct, not a direct endorsement of one over the other based on activity level in terms of overall outcome superiority.
• E. The review found no reliable data to compare the two treatments effectively. This is incorrect. The review did compare studies but noted that 'the study methods are not homogeneous' and that most papers reported on closing wedge HTOs, which limited strong conclusions, but it still drew a conclusion about the comparable efficacy.

Correct Answer: B

The case states, 'More recent studies show that closing wedge osteotomy increases patellar height, whereas opening wedge osteotomy lowers patellar height and this can have implications following TKA.' Patella baja (lowered patellar height) can significantly complicate TKA by making patellar tracking more difficult, increasing the risk of patellar impingement, and potentially affecting the choice and placement of prosthetic components.

• A. It typically leads to patella alta, making patellar tracking easier. This is incorrect. Opening wedge HTO lowers patellar height, leading to patella baja. Closing wedge HTO increases patellar height.
• C. It has no significant effect on patellar height, simplifying TKA conversion. This is incorrect, as the case explicitly states it 'can have implications following TKA.'
• D. It causes lateral patellar subluxation, requiring a lateral release. While patellar tracking issues can occur, the primary effect on patellar height is lowering it, not necessarily causing lateral subluxation as a direct consequence of the osteotomy type itself.
• E. It increases the risk of patellar fracture during TKA. While TKA after HTO can have increased risks, the direct implication on patellar height is patella baja, not necessarily an increased fracture risk as the primary concern related to patellar height.

Correct Answer: D

The case lists 'severe OA of medial compartment or lateral compartment/PFJ' as a main contraindication for HTO. If the patient had severe osteoarthritis of the patellofemoral joint, HTO would be contraindicated because it only addresses the tibiofemoral compartments and would not alleviate the patellofemoral pain.

• A. Varus deformity of 12 degrees is within the acceptable range (< 15 degrees) for HTO.
• B. Physiological age of 55 years is within the acceptable range (< 60 years) for HTO.
• C. Fixed flexion deformity of 10 degrees is within the acceptable range (< 15 degrees) for HTO.
• E. Ability to flex the knee to 100 degrees meets the prerequisite of > 90 degrees flexion for HTO.

Correct Answer: B

The case states that closing wedge osteotomy 'has the risk of peroneal nerve injury, there is also loss of bone stock making it technically difficult to perform TKA.' This loss of bone stock, particularly from the proximal tibia, can significantly complicate the preparation of the tibial plateau for TKA components, potentially requiring bone grafting or specialized implants.

• A. Increased risk of infection due to retained hardware is a general risk with any retained hardware, but 'loss of bone stock' is a more specific and direct difficulty related to the conversion itself, as highlighted in the text.
• C. Improved bone quality for implant fixation is incorrect; the loss of bone stock generally implies a more challenging bone bed for TKA.
• D. Reduced need for soft tissue balancing is incorrect; prior HTO can alter soft tissue tension and ligamentous balance, often making TKA soft tissue balancing more complex, not less.
• E. Easier restoration of the mechanical axis is incorrect; the altered anatomy and bone loss from HTO can make accurate restoration of the mechanical axis more challenging during TKA.

Correct Answer: C

The Coughlin and Shurnas classification for hallux rigidus is widely used. Stage 1 involves mild flattening of the metatarsal head, minimal osteophytes, and good joint space. Stage 2 presents with moderate osteophytes (dorsal and dorsal-medial), mild-to-moderate joint space narrowing, and flattening of the metatarsal head, with 20-50% cartilage involvement. Stage 3 is characterized by significant osteophytes, moderate-to-severe joint space narrowing, and subchondral sclerosis/cysts, with greater than 50% cartilage involvement and pain at end-range motion. Stage 4 involves ankylosis or severe degenerative changes throughout the entire joint. This patient's presentation of significant dorsal osteophyte formation, joint space narrowing, subchondral sclerosis, and limited dorsiflexion to 20 degrees, affecting approximately 50% of the joint, aligns with Stage 3 hallux rigidus.

Correct Answer: B

The flexor hallucis brevis (FHB) is an intrinsic foot muscle with two heads (medial and lateral) that insert into the base of the proximal phalanx, encasing the sesamoids. It is the primary flexor of the great toe MTP joint and plays a critical role in stabilizing the MTP joint during gait, particularly during the push-off phase by facilitating the 'windlass mechanism'. Impairment of this mechanism due to MTP joint stiffness (hallux rigidus) alters normal gait biomechanics. Abductor hallucis abducts and flexes, adductor hallucis adducts and flexes, while lumbricales and flexor digitorum brevis act on lesser toes.

Correct Answer: C

For Stage 2 hallux rigidus, where there is moderate joint space narrowing and moderate osteophyte formation, but still reasonable cartilage (50-75% intact), a dorsal cheilectomy is typically the first-line joint-preserving surgical option. It involves removing the dorsal osteophytes and often a portion of the dorsal metatarsal head to decompress the joint and improve dorsiflexion. Moberg osteotomy is often performed in conjunction with a cheilectomy, or for more advanced cases, to improve dorsiflexion via a plantarflexion osteotomy of the proximal phalanx. Arthrodesis and arthroplasty are generally reserved for more advanced stages (Stage 3 and 4) or failed conservative/joint-sparing procedures. Metatarsal head resection arthroplasty (Keller arthroplasty) is largely historical due to associated complications like transfer metatarsalgia and instability.

Correct Answer: C

A Moberg osteotomy, a dorsal closing wedge osteotomy of the proximal phalanx, effectively plantarflexes the proximal phalanx relative to its articular surface. This maneuver indirectly increases functional dorsiflexion at the MTP joint by changing the resting position of the proximal phalanx, thereby reducing impingement and improving the toe-off phase of gait. It is typically performed in conjunction with a cheilectomy for Stage 2 or early Stage 3 hallux rigidus, or when isolated cheilectomy is insufficient to restore adequate dorsiflexion. It does not primarily offload the metatarsal head, correct hallux valgus (though some subtle correction might occur), or directly enhance intrinsic muscle function.

Correct Answer: C

For Stage 4 hallux rigidus, characterized by severe degenerative changes or ankylosis, joint-preserving procedures like cheilectomy or Moberg osteotomy are inappropriate as they cannot address the diffuse damage. First MTP joint arthrodesis (fusion) is considered the gold standard for severe hallux rigidus, especially in active patients, or when other procedures have failed. It provides reliable pain relief and a stable, pain-free platform for push-off, though it sacrifices MTP joint motion. While interpositional arthroplasty or MTP joint implants might be considered for less active patients or those unwilling to sacrifice motion, arthrodesis typically offers the most predictable and durable pain relief for severe end-stage disease. A sedentary patient might be a candidate for arthroplasty, but for reliable pain relief and functional improvement, especially with complete obliteration, arthrodesis is still considered the gold standard for overall success.

Correct Answer: C

In the early stages of hallux rigidus, the most common and often first radiographic sign is the formation of a dorsal osteophyte on the first metatarsal head. This osteophyte impinges on the base of the proximal phalanx during dorsiflexion, leading to restricted motion and pain. Complete ankylosis is a late-stage finding. Subchondral cysts and significant valgus deformity are less specific or later findings. Bone marrow edema is an MRI finding, not typically a primary radiographic finding for early diagnosis.

Correct Answer: C

Previous infection in the surgical field is a strong contraindication for any joint replacement procedure, including MTP joint arthroplasty with an implant, due to the high risk of recurrent infection and subsequent implant failure. Older, less active patients are often considered good candidates for arthroplasty as motion preservation is prioritized over the robust stability of an arthrodesis. Rheumatoid arthritis can be an indication for arthroplasty, especially with polyarticular involvement. Failed cheilectomy is a common indication for salvage procedures like arthroplasty or arthrodesis. Moderate hallux valgus may need concomitant correction but isn't a direct contraindication to implant arthroplasty itself, though some implants may not be suitable.

Correct Answer: B

When performing a dorsal cheilectomy, the goal is to remove the dorsal osteophytes and approximately 10-15% of the dorsal articular cartilage of the metatarsal head. This amount is generally considered sufficient to decompress the joint, improve dorsiflexion, and prevent impingement without excessively shortening the metatarsal or destabilizing the joint. Removing only the visible osteophyte might be insufficient if impingement persists. Resecting 30-40% or the entire dorsal third is excessive and can lead to instability, transfer metatarsalgia, or shortening.

Correct Answer: C

For a young, active professional athlete with severe hallux rigidus (Stage 3-4), a first MTP joint arthrodesis is the most appropriate and recommended option. While it sacrifices motion, it provides a highly stable, pain-free, and durable platform capable of withstanding high-impact activities required by athletes. Cheilectomy with Moberg is generally for earlier stages (Stage 2-3). Keller arthroplasty (resection of proximal phalanx base) is largely abandoned due to high rates of complications like transfer metatarsalgia and instability. Silicone implants have a high failure rate in active patients and are prone to synovitis and osteolysis. Interpositional arthroplasty may be considered for less active patients but does not provide the same level of stability and predictable outcomes for high-demand individuals.

Correct Answer: A

The optimal position for first MTP joint arthrodesis is crucial for gait and footwear. While there is some debate, generally, the joint should be fused in 10-15 degrees of dorsiflexion (relative to the weight-bearing surface) and 10-15 degrees of valgus. This position accommodates normal toe-off during gait, allows for comfortable shoe wear, and helps prevent transfer metatarsalgia to the lesser toes. Fusing in too much dorsiflexion can lead to dorsal impingement in shoes, while too much plantarflexion impairs push-off and can cause shoe fitting issues. Excessive valgus or varus can also cause problems. The options often vary, but 10-15 degrees dorsiflexion and valgus is a good range.

The optimal position for 1st MTP arthrodesis is 10-15 degrees of dorsiflexion relative to the floor, 10-15 degrees of valgus, and neutral rotation. This position allows for adequate toe clearance during the swing phase and normal toe-off during gait.

The MPFL originates in a saddle-like groove situated between the medial epicondyle and the adductor tubercle on the medial femur (Schöttle's point). Non-anatomic femoral tunnel placement is a primary cause of postoperative MPFL graft failure.

Uncorrectable varus deformity, typically greater than 15 degrees, is a contraindication for medial UKA. Other classic contraindications include ACL deficiency, inflammatory arthritis, and a fixed flexion contracture > 15 degrees.

The patient has Grade 4 hallux rigidus, characterized by pain in the mid-range of motion and extensive degenerative changes. First MTP arthrodesis is the gold standard surgical treatment to predictably relieve pain for Grade 4 disease.

A TT-TG distance > 20 mm is an indication for a medializing tibial tubercle osteotomy (Fulkerson procedure) to correct the abnormal lateral extensor mechanism vector. MPFL reconstruction is performed concurrently to restore the torn primary medial soft-tissue restraint.

In a valgus-producing HTO for medial compartment OA, the target mechanical axis is typically shifted to the lateral compartment, approximately 62% of the tibial plateau width from medial to lateral (Fujisawa point). This effectively unloads the diseased medial compartment.

The dorsomedial cutaneous nerve (a branch of the superficial peroneal nerve) crosses the 1st MTP joint dorsomedially. It is at high risk of iatrogenic injury during dorsal surgical approaches for a cheilectomy.

The MPFL is the primary restraint to lateral patellar translation in early flexion (0 to 30 degrees). Beyond 30 degrees of flexion, the patella engages the trochlea, and the bony architecture becomes the primary stabilizer.

Oral NSAIDs, topical NSAIDs, and supervised exercise/weight loss have "Strong" recommendations for treating symptomatic knee OA. Intra-articular hyaluronic acid and glucosamine/chondroitin are explicitly not recommended by current AAOS guidelines.

The Moberg procedure is a dorsal closing-wedge osteotomy of the base of the proximal phalanx. It does not increase the total arc of motion but shifts the existing restricted motion into greater dorsiflexion to improve ground clearance during gait.

Dejour Type B trochlear dysplasia is characterized by a flat trochlea, presenting as a "crossing sign" and a "supratrochlear spur" on a true lateral radiograph. Type C exhibits a crossing sign and double contour, while Type D has all three signs.

In the presence of an incompetent PCL but intact collateral ligaments, a posterior-stabilized (PS) design is indicated. The cam-and-post mechanism substitutes for the absent PCL to prevent anterior translation of the femur on the tibia during flexion.

The MPFL provides maximum restraint to lateral patellar translation at 0 to 30 degrees of flexion. The graft should be tensioned at 20-30 degrees of flexion just enough to restore normal tracking; over-tensioning leads to medial cartilage overload and loss of knee flexion.

A TT-TG distance > 20 mm is a primary indication for a medializing tibial tubercle osteotomy to correct the lateralized extensor mechanism. It is typically combined with MPFL reconstruction to restore the primary medial soft-tissue restraint.

The AAOS strongly recommends against the use of intra-articular hyaluronic acid (viscosupplementation) for symptomatic osteoarthritis of the knee due to a lack of clinically significant efficacy in high-quality studies.

The gold standard treatment for end-stage hallux rigidus is 1st MTP arthrodesis. The ideal fusion position is 10-15 degrees of valgus and 10-15 degrees of dorsiflexion relative to the floor to allow for normal toe-off during the gait cycle.

In a medial opening wedge HTO, the posterior tibial cortex is naturally wider than the anterior cortex. Failing to open the posterior gap more than the anterior gap (typically a 2:1 ratio) inadvertently increases the posterior tibial slope, increasing strain on the ACL.

In the Dejour classification of trochlear dysplasia, Type B is characterized by a flat trochlea, the presence of a "crossing sign" (the trochlear floor crosses the anterior border of the condyles), and a supratrochlear spur.

Inflammatory arthropathies, such as rheumatoid arthritis, are classic contraindications for unicompartmental knee arthroplasty due to the global, progressive nature of the joint destruction. Obesity and mild asymptomatic patellofemoral changes are no longer strict contraindications.

A dorsal cheilectomy involves removing the dorsal osteophytes along with a portion of the dorsal articular cartilage. Resection is typically limited to the dorsal 30% of the metatarsal head to preserve stability and avoid transferring weight to compromised cartilage.

A rigid Morton's extension (a stiff plate extending under the first MTP joint) restricts motion at the first MTP joint, reducing pain during the toe-off phase of gait. It is highly effective for conservative management of hallux rigidus.

The Caton-Deschamps index relies on articular margins rather than the inferior pole, making it useful even if a patient has had Osgood-Schlatter disease or previous distal pole excision. A value greater than 1.2 indicates patella alta.

A knee that is tight in extension but balanced in flexion indicates an isolated tight extension gap. Corrective measures include resecting more of the distal femur or releasing the posterior capsule, which affects only the extension space.

Patellar clunk syndrome occurs primarily in posterior-stabilized TKA designs when a fibrous nodule forms on the deep surface of the distal quadriceps tendon. As the knee extends from flexion, the nodule catches on the superior edge of the femoral intercondylar box.

For valgus knee osteoarthritis in a young, active patient, the deformity is primarily in the distal femur. A medial closing wedge (or lateral opening wedge) distal femoral osteotomy correctly addresses the mechanical axis while sparing the joint for future arthroplasty.

Obligatory patellar dislocation occurs when the patella dislocates in extension and reduces in flexion, commonly associated with tight lateral structures or underlying dysplasia. Habitual dislocation occurs in flexion and is often caused by a short quadriceps mechanism.

The anatomic femoral origin of the MPFL lies in a small saddle or groove situated slightly distal to the adductor tubercle and proximal/posterior to the medial epicondyle.

Silastic (silicone) implants for hallux rigidus have largely fallen out of favor due to the high risk of silicone synovitis. This foreign body reaction leads to aggressive particulate-induced osteolysis and severe bone loss.

The J-sign describes the sudden lateral deviation (in an inverted 'J' shape) of the patella during terminal knee extension. It occurs because the patella loses the bony restraint of the trochlear groove, often exacerbated by patella alta or excessive TT-TG distance.

The MPFL femoral footprint is located within a saddle-like sulcus posterior and proximal to the medial epicondyle, and distal to the adductor tubercle. Schöttle's point radiographically defines this origin just anterior to the posterior femoral cortex line and distal to Blumensaat's line.

Cheilectomy is the surgical treatment of choice for Grade 1 and 2 hallux rigidus with preserved mid-arc motion and pain exclusively at terminal dorsiflexion. It removes the dorsal osteophytes and the dorsal one-third of the metatarsal head to improve impingement.

The ideal candidate for an HTO is a young, active patient with isolated unicompartmental osteoarthritis, correctable malalignment, and intact ligaments. Contraindications include inflammatory arthritis, flexion contractures >15 degrees, patellofemoral arthritis, and lateral compartment disease.

A TT-TG distance > 20 mm is considered pathologic and represents an indication for a medializing tibial tubercle osteotomy (e.g., Elmslie-Trillat or Fulkerson) in the setting of recurrent patellar instability. Normal values are typically 9-13 mm.

The Keller arthroplasty involves resecting the base of the proximal phalanx, which risks detaching the insertion of the flexor hallucis brevis. This loss of plantar intrinsic stability allows the extensor hallucis longus to overpower the digit, causing a cock-up deformity.

Inflammatory arthropathy is an absolute contraindication for UKA due to the systemic, progressive nature of the disease affecting all compartments. Correctable varus <15 degrees, flexion contracture <15 degrees, and asymptomatic patellofemoral changes are acceptable parameters for UKA.

Dejour Type B dysplasia is characterized by a flat trochlea, marked radiographically by a crossing sign and a supratrochlear spur. Type A has a shallow groove (crossing sign only), Type C has a convex lateral facet (crossing sign + double contour), and Type D has a cliff pattern.

Optimal positioning for a 1st MTP arthrodesis is 10-15 degrees of valgus, 10-15 degrees of dorsiflexion relative to the floor (which equates to about 25-30 degrees relative to the first metatarsal), and neutral rotation.

MPFL grafts should be fixed at approximately 30 degrees of knee flexion with minimal tension (just enough to eliminate slack). Over-tensioning can lead to medial patellofemoral compartment overload, anterior knee pain, and restricted flexion.

A TT-TG distance greater than 20 mm is a standard indication for a medializing tibial tubercle osteotomy (TTO). Combined anteromedialization (Fulkerson osteotomy) addresses the lateralized vector and unloads the patellofemoral joint, typically coupled with an MPFL reconstruction.

Cheilectomy, which involves excision of the dorsal osteophyte and dorsal one-third of the metatarsal head, is highly successful for Grade 1 and 2 hallux rigidus where the plantar cartilage remains viable. Arthrodesis is reserved for advanced stages (Grade 3 or 4) or failed cheilectomies.

The AAOS strongly recommends against the use of intra-articular hyaluronic acid (viscosupplementation) for patients with symptomatic osteoarthritis of the knee. This is based on multiple high-quality randomized controlled trials demonstrating a lack of clinically significant efficacy compared to placebo.

In skeletally immature patients, the anatomic femoral origin of the MPFL is typically located just distal to the distal femoral physis. Care must be taken to utilize soft tissue techniques or place fixation distal to the growth plate to prevent angular deformity or growth arrest.

Optimal positioning for a 1st MTP arthrodesis is 10 to 15 degrees of valgus and 10 to 15 degrees of dorsiflexion relative to the floor (approximately 15-20 degrees of dorsiflexion relative to the first metatarsal). This specific alignment allows proper weight transfer during the toe-off phase of the gait cycle.

A fixed angular deformity (e.g., fixed varus greater than 10 degrees) that cannot be passively corrected is an absolute contraindication to UKA, as the procedure relies on intact soft-tissue envelopes for balancing. Age, BMI, and even ACL deficiency (in specific scenarios) are considered relative or controversial contraindications.

Schottle's point is located 1 mm anterior to the posterior femoral cortical line and 2.5 mm proximal to the posterior border of Blumensaat's line. It serves as a reliable and reproducible radiographic landmark for the anatomic femoral origin of the MPFL.

The Moberg procedure is a dorsal closing wedge osteotomy of the base of the proximal phalanx. While it does not increase the total arc of motion of the MTP joint, it shifts the available motion into more dorsiflexion, thereby relieving pain during the terminal stance phase of gait.

High Tibial Osteotomy (HTO) is the ideal surgical treatment for young, highly active patients with isolated medial compartment osteoarthritis and varus malalignment. It unloads the medial compartment, significantly delaying the need for arthroplasty while allowing the patient to maintain a demanding lifestyle.