MCQs – Hip Recon 7

Modern Study Review (AI-Generated)

High-Yield Summary

Acetabular reconstruction and hip preservation strategies are a staple of orthopaedic board exams, focusing heavily on host bone contact thresholds, implant selection, and surgical indications for dysplasia and AVN. The critical clinical decision often hinges on the percentage of host bone contact (<50-70%) dictating whether to use structural allograft with cage and cemented cup versus simple uncemented reconstruction. While classic teaching favors cemented cups, modern practice increasingly prefers hybrid hip replacements due to long-term acetabular failure with cemented components. Understanding implant material biomechanics, antibiotic cement elution timelines, and imaging modalities for occult fractures is essential for exam and clinical excellence.

High-Yield Decision Matrix

Active Recall Q&A

Acetabular Reconstruction & Implant Selection

Q: What is the preferred method for reconstructing a dysplastic acetabulum in a high dislocation?
A: Structural autograft using the femoral head as a shelf autograft combined with a cementless acetabular component.
Related Pearl: Autograft integration improves biological fixation and long-term implant stability compared to allograft alone.

Q: What should be considered if acetabular reconstruction has less than 50-70% host bone contact?
A: Use structural allograft with cage and cemented cup or impaction allograft with cage and cemented cup instead of simple uncemented reconstruction.
Related Pearl: Adequate host bone contact is critical for biological fixation; below threshold, mechanical support with cages is necessary.

Q: Why are hybrid hip replacements currently favored?
A: Due to the high incidence of acetabular failure at 10 years with cemented cups.
Related Pearl: Hybrid constructs combine cementless acetabular components with cemented femoral stems to optimize long-term fixation.

Q: What is the recommended minimum polyethylene thickness for acetabular cups?
A: At least 6-8 mm.
Related Pearl: Smaller cups require smaller heads; dislocation risk depends on head-to-neck ratio, not head size alone.

Q: What is the best reconstruction method for protrusio acetabuli?
A: Use an ingrowth cup with rim fit and bone graft beneath it.
Related Pearl: Rim fit provides initial mechanical stability while bone graft restores medial bone stock.

Implant Materials & Biomechanics

Q: Why are titanium hip stems considered advantageous compared to cobalt chrome stems?
A: Titanium stems have a lower modulus (less stiff) than cobalt chrome when comparing stems of equal size and shape.
Related Pearl: Stiffness depends on both material modulus and geometry; a wider titanium stem may be stiffer than a cobalt chrome stem despite lower modulus.

Q: How do ceramic heads affect long-term loosening and polyethylene wear?
A: Ceramic heads reduce long-term loosening by being harder and more polished, producing less polyethylene wear.
Related Pearl: Reduced wear debris decreases osteolysis and implant loosening risk.

Surgical Techniques & Osteotomies

Q: What surgical procedure is indicated for a young patient with hip dysplasia showing an incongruent joint, uncovering, and some joint space narrowing?
A: Chiari osteotomy.
Related Pearl: Chiari osteotomy medializes the acetabulum to improve femoral head coverage and delay arthritis progression.

Q: How does a femoral varus osteotomy affect abductor and adductor muscle forces?
A: It decreases abductor force by lateralizing the greater trochanter and increasing the lever arm; adductor force is also diminished due to femoral shortening and medialization.
Related Pearl: Altered muscle mechanics can affect gait and hip stability post-osteotomy.

Q: What is the optimal fixation device for valgus or varus intertrochanteric osteotomies?
A: Fixed angle devices.
Related Pearl: Fixed angle devices provide stable fixation and resist deforming forces during healing.

Clinical Syndromes & Imaging

Q: What clinical features define acetabular rim syndrome?
A: Groin pain, intermittent mechanical symptoms, clicking or locking; congruent but shallow acetabulum causing labral shear stress and tears.
Related Pearl: Early osteotomy can prevent progression to localized degeneration and osteoarthritis.

Q: How do Ganz type I and type II dysplasia differ?
A: Type I: acetabular incongruency, shallowness, and uncovering; Type II: acetabular congruency, shallowness, and uncovering.
Related Pearl: Differentiating types guides surgical planning and prognosis.

Q: What is the most efficient imaging modality to detect an occult hip fracture early?
A: MRI is the most efficient early diagnostic tool.
Related Pearl: Bone scans become positive later (usually after 24 hours), making MRI superior for early detection.

AVN & Medical Management

Q: For which Ficat stages of AVN is core decompression most effective?
A: Greatest success in Ficat I; also recommended for Ficat II and early III.
Related Pearl: Early intervention before collapse improves outcomes by preserving subchondral bone integrity.

Q: What are the risks associated with NSAID use in orthopaedic patients?
A: Risks include GI bleeding, increased blood pressure, bone marrow suppression, liver damage, and kidney damage.
Related Pearl: Regular monitoring with blood count and chemistries every 6 months is essential to detect adverse effects early.

Pathology & Histology

Q: What histological features characterize a failing cement-bone interface?
A: Presence of plump active macrophages with intracellular and extracellular polyethylene particles and a fibrous membrane.
Related Pearl: This inflammatory response contributes to osteolysis and implant loosening.

Biomechanics & Stability

Q: What is the effect of shortening the hip on soft tissue tension and dislocation risk?
A: Shortening decreases soft tissue tension around the hip and increases the risk of dislocation.
Related Pearl: Maintaining appropriate soft tissue tension is critical for hip stability post-reconstruction.

Classic Clinical Notes

• The preferred method of reconstructing a dysplastic acetabulum in a high dislocation is with structural autograft and cementless acetabular component. (Use the femoral head as the shelf autograft).

• For antibiotic loaded cement, the local level of antibiotic ceases to be significant at 6 weeks.

• Compared to cobalt chrome, titanium hip stems are advantageous because they are less stiff (when comparing stems of equal size and shape). The stiffness depends on a material factor (modulus) and a geometric factor (size and shape). Titanium does have a lower modulus than cobalt chrome, but in order to make an estimation of stiffness you have to know the size and shape characteristics, particularly the radius. Even though titanium has a lower modulus, if the titanium stem were wider, it may still be stiffer than a cobalt chrome stem. NOTE THE DIFFERENCE BETWEEN THE TWO.

• If you shorten the hip, you decrease the soft tissue tension about the hip and increase the risk of dislocation.

• Core decompression for AVN has the greatest chance of success in Ficat I. Is also recommended for II and early III.

• Patients on NSAIDS have risks of GI system (bleeding), increased blood pressure, bone marrow suppression, liver damage, and kidney damage. They should have a blood count and chemistries every 6 months.

• The most efficient way of determining whether someone has an occult hip fracture is an MRI (if early). Bone scanning tends to be hotter a day later I think.

• Ceramic heads may reduce long term loosening because they are more polished than metal heads and thus produce less poly wear. They are harder (allows them to be more polished) and do deform less.

• For the young patient with dysplasia, an incongruent joint that is uncovered, with some joint space narrowing – do a Chiari.

• When doing the acetabular reconstruction, if there is less than 50-70% host bone contact, you have to think about doing something other than a simple uncemented reconstruction – options include structural allograft with cage and cemented cup, or impaction allograft with cage and cemented cup.

• Hybrid hip replacements are en vogue because of the high incidence of acetabular failure at 10 years with cemented cups.

• A femoral varus osteotomy will decrease the abductor force by lateralizing the GT and increasing the lever arm of the abductors. Although you might lateralize the shaft and put the adductors on more stretch, in reality you tend to shorten the femur and thus there is more slack in the adductors – hence adductor force is also diminished. Also, you often tend to medialize the shaft when you apply the fixation.

• For acetabular cups, it is felt that the poly should be at the very least 6-8 mm. Smaller head sizes should be used with smaller cups. The size of the head in and of itself does not affect dislocation rates – it is the ratio of the head:neck width. So if the cup is going to be small, you better plan on a smaller head.

• For fixing valgus or varus intertrochanteric osteotomies, the optimal fixation device is some sort of fixed angle device.

• In the failing cement-bone interface, the histology is of PLUMP active MACROPHAGES with intracellular and extracellular polyethylene, and a fibrous membrane.

• For protrusio – best reconstruction is to use an ingrowth cup with rim fit and bone graft beneath it.

• Acetabular rim syndrome is seen in young patients with groin pain, intermittent mechanical symptoms, and a sensation of clicking or locking. They often have a congruent but shallow acetabulum which leaves part of the femoral head uncovered – this causes shear stress on the labrum which will eventually tear, and lead to progressive localized degeneration. This is a good indication for osteotomy. A Ganz type I dysplasia has acetabular incongruency, shallowness, and uncovering. A Ganz type II dysplasia has acetabular congruency, shallowness, and uncovering.

Last Updated on January 25, 2026 by Christian Veillette