MCQs – Hip Recon 2

Modern Study Review (AI-Generated)

High-Yield Summary

Femoral head blood supply in early childhood relies on metaphyseal vessels before physeal closure, with the ligamentum teres artery being least important. Postoperative mortality after total hip arthroplasty (THA) is dominated by pulmonary embolism (PE), responsible for >50% of deaths within 3 months. Acetabular component positioning critically affects dislocation risk, with 10-20° anteversion optimal; neutral version predisposes to posterior dislocation. Femoral head size balances stability and wear: 26-28 mm is the best compromise. Cemented and cementless femoral components show no difference in short-term outcomes, but long-term failure is mainly due to cup loosening. Heterotopic ossification (HO) prophylaxis includes indomethacin or radiation therapy. Hip dislocation risk factors emphasize surgical and biomechanical variables over demographic factors. Conversion of hip arthrodesis to arthroplasty has best outcomes with spontaneous fusion and no prior surgeries.

High-Yield Decision Matrix

Active Recall Q&A

Femoral Head Blood Supply

Q: Which vessels are least important in the blood supply of the femoral head between ages 0-2?
A: The ligamentum teres vessels are probably the least important.
Related Pearl: The ligamentum teres artery regresses after infancy and rarely contributes to adult femoral head perfusion.

Q: Why are metaphyseal vessels important at birth for femoral head blood supply?
A: Because the femoral head is cartilaginous and the physis has not developed, allowing metaphyseal vessels to supply the head.
Related Pearl: Once the physis forms, it acts as a barrier, shifting blood supply reliance to epiphyseal vessels.

Postoperative Mortality

Q: What is the most common cause of death within 3 months after total hip or knee replacement?
A: Pulmonary embolism (PE) is the most common cause of death within 3 months postoperatively.
Related Pearl: PE accounts for over 50% of postoperative mortality after total hip arthroplasty.

Q: What are the second and third most common causes of death after total hip or knee replacement?
A: Myocardial infarction (MI) and congestive heart failure (CHF) are the second and third most common causes.
Related Pearl: Cardiovascular complications remain a significant risk in the perioperative period.

Q: What is the fatal pulmonary embolism rate after total hip replacement without prophylaxis?
A: Approximately 2%.
Related Pearl: Prophylaxis protocols have significantly reduced this rate in modern practice.

Q: What is the fatal pulmonary embolism rate after total knee replacement without prophylaxis?
A: Approximately 0.3%.
Related Pearl: Lower PE rates in TKA may relate to differences in surgical technique and patient mobilization.

Acetabular and Femoral Components

Q: What happens if the acetabulum is placed in neutral version during hip replacement?
A: The hip is most likely to dislocate posteriorly.
Related Pearl: Optimal acetabular anteversion is 10-20 degrees to minimize dislocation risk.

Q: How do cemented and cementless femoral components compare in short-term follow-up?
A: There is no difference in outcomes at 3-5 years.
Related Pearl: Long-term differences may emerge, but early fixation is comparable.

Q: What is the best pore size for cementless femoral components?
A: 200-500 microns.
Related Pearl: This pore size optimizes bone ingrowth; it differs from total knee implants which use 150-400 microns.

Q: How does increasing femoral head size from 22 mm to 32 mm affect hip stability and wear?
A: Stability increases due to greater range of motion before impingement, but volumetric wear also increases.
Related Pearl: The best compromise head size is 26-28 mm balancing stability and wear.

Long-term Outcomes and Complications

Q: What is the most common cause of long-term failure in cemented total hip arthroplasty?
A: Cup loosening.
Related Pearl: Loosening often results from polyethylene wear debris-induced osteolysis.

Q: What causes intraoperative hypotension and hypoxia during cemented total hip replacement?
A: Fat emboli during cement pressurization cause immediate effects; cement monomer peaks later (~3 minutes).
Related Pearl: Early hemodynamic changes are primarily embolic rather than chemical.

Heterotopic Ossification (HO)

Q: What are risk factors for heterotopic ossification (HO) after hip replacement?
A: DISH, hypertrophic osteoarthritis, ankylosing spondylitis, post-traumatic OA, revision surgery, Paget’s disease, and extensive soft tissue stripping.
Related Pearl: HO risk correlates with local inflammation and surgical trauma.

Q: Which factors are not associated with increased risk of heterotopic ossification after hip replacement?
A: Immobilization and rheumatoid arthritis are not risk factors.
Related Pearl: Rheumatoid arthritis patients may have less HO due to immunosuppressive therapy.

Q: What are current methods to reduce heterotopic ossification after hip replacement?
A: Indomethacin 75 mg PO daily for 6 weeks or a single dose of radiation therapy (700 rads) within 72 hours post-op.
Related Pearl: Both methods inhibit osteoprogenitor cell proliferation.

Hip Dislocation

Q: What are risk factors for hip dislocation after arthroplasty?
A: Revision surgery, posterior approach, malpositioned components, trochanteric escape or abductor weakness, leg length discrepancy (too short), impingement, neuromuscular disease (Parkinson’s, stroke, confusion), and female sex.
Related Pearl: Female patients have higher dislocation rates possibly due to soft tissue laxity.

Q: Which patient factors do not increase the risk of hip dislocation?
A: Age, height, weight, and preoperative diagnosis do not appear causative.
Related Pearl: Surgical and biomechanical factors outweigh demographic variables.

Hip Arthrodesis Conversion

Q: What is the best candidate for conversion of hip arthrodesis to arthroplasty?
A: A spontaneous fusion without prior surgical trauma.
Related Pearl: Preserved soft tissues and abductors improve stability post-conversion.

Q: What predicts the worst outcomes in hip arthrodesis conversion to arthroplasty?
A: Multiple previous surgeries and age under 50 years.
Related Pearl: Younger patients may have higher activity demands, increasing failure risk.

Q: Does the duration of hip arthrodesis affect prognosis after conversion to arthroplasty?
A: No, length of fusion time is not a prognostic factor.
Related Pearl: Soft tissue condition and surgical history are more critical.

Acetabular Wear and Polyethylene Wear

Q: How does acetabular wear progress over time after hip replacement?
A: Wear is maximal initially as the implant “beds in,” then decreases; average wear is about 0.1 mm per year.
Related Pearl: Early creep deformation contributes to initial dimensional changes.

Q: What wear rate did Charnley report radiographically for polyethylene cups?
A: 0.15 mm per year.
Related Pearl: Radiographic wear includes creep, which overestimates true material loss.

Q: What is the primary mechanism of polyethylene wear in acetabular cups?
A: Abrasive wear dominated by molecular weight of polyethylene; creep causes shape change but not true wear.
Related Pearl: Total knee polyethylene wear is dominated by subsurface fatigue due to different joint mechanics.

Q: What is the formula for volume of wear in joint replacements?
A: Volume of wear = K × Load × Distance, where K is a material constant.
Related Pearl: Metal-on-metal has highest K; ceramic-on-polyethylene has lowest.

Q: How does femoral head size affect volumetric wear?
A: Larger heads increase the distance traveled during motion, increasing volumetric wear.
Related Pearl: This explains why bigger heads increase wear despite improved stability.

Classic Clinical Notes

• A number of questions ask about the LEAST important vessels in the blood supply of the femoral head between the ages of 0-2. The choices include the medial epiphyseal, lateral epiphyseal, superior metaphyseal, inferior metaphyseal, and medial circumflex. At birth, the metaphyseal vessels are pretty important, because the head is cartilaginous and the physis has not yet really developed. Once the physis develops it is a barrier to these vessels and the epiphyseal vessels are from the extrasynovial ascending cervical vessels become the key vessels. The best guess is then the medial epiphyseal vessels. Probably the least important of all is the ligamentum teres.

• The most common cause of death after total hip or knee replacement is pulmonary embolism. It is the most common cause of death occurring within 3 months of surgery, and is responsible for more than 50% of postoperative mortality after total hip. MI and CHF are the 2nd and 3rd most common.

• For total hip, the fatal PE rate is about 2% with no prophylaxis.

• For total knee, the fatal PE rate is about .3%.

• If the acetabulum is placed in neutral version, the hip is most likely to dislocate posteriorly. Optimum anteversion is about 10-20 degrees.

• The results of cemented and cementless femoral components are no different in short term followup (3-5 years).

• Best pore size for cementless femoral components is 200-500 microns (interestingly different from total knees – 150-400).

• Theoretically, increasing the head size from 22 to 32 increases the stability by allowing greater range of motion before impingement of the neck on the cup. An increase in the head:neck width ratio decreases the chance of impingement, but increasing the size of the head also increases volumetric wear. (Decreasing size increases the linear wear) The best compromise is probably 26-28 mm.

• The most common cause of long-term failure in cemented total hip arthroplasty is the cup loosening.

• Intraoperative hypotension and hypoxia during a cemented total hip replacement is probably due to fat emboli during pressurization of cement. The monomer can have a direct effect on the heart, but its peak levels don’t occur for 3 minutes after cementing.

• Risk of heterotopic ossification post-op hip replacement: DISH, hypertrophic OA, and ank spond, post-traumatic OA, revision surgery, Paget’s disease, and significant surgical stripping of soft tissues. Immobilization does not appear to be a risk factor. Nor does rheumatoid arthritis.

• Current methods of reducing HO include Indocid 75 mg po OD for 6 weeks, or single dose XRT of 700 rads sometime within 72 hours of surgery.

• Risk factors for hip dislocation include:
• Revision
• Posterior approach
• Faulty positioning of components
• Trochanteric escape or rupture/weakness of abductors
• Leg length too short
• Impingement – either neck against cup or femur against soft tissues or pelvis
• Neuromuscular disease – Parkinsons, stroke, confusion
• Female

• Age, height, weight, or preop diagnosis do not seem to be causative.

• For converting a hip arthrodesis to arthroplasty, it is best if there has been no surgical trauma to the area – ie a spontaneous fusion is best. On the other end of the spectrum, the multiply operated on hip that eventually gets fused is the worst candidate. Their soft tissues and abductor muscles are probably toast, and it will be very hard to keep them stable.

• Conversion of hip arthrodesis to arthroplasty has the worst results in patients with multiple previous surgeries, and age under 50. Length of time that it has been fused is not a prognostic factor.

• With regards to acetabular wear, wear is maximal right away as things get “worked in”; it then decreases with time. Wear is felt to be about 0.1 mm per year. Poly particles are a significant factor in wear.

• Charnley, using x-rays, reported a wear rate of 0.15 mm per year for cups. But in the lab, true wear is much less. Current understanding explains the difference – a large proportion of the shape change in polyethylene is a result of CREEP rather than wear. Acetabular wear is primarily abrasive,and the most crucial factor affecting the true wear rate of polyethylene cups under weightbearing conditions is the molecular weight of the material. In contrast, in the total knee where surface contours differ significantly, local contact stress and subsurface fatigue wear become the dominant mechanism of poly degradation.

• Volume of wear = K x load x distance Where K = constant for materials
• The highest K is with metal on metal; lowest K is with ceramic on poly; in between is metal on poly.
• Notice that DISTANCE is an important factor – hence, the bigger heads have more volumetric wear because with each movement, there is more distance covered.

Last Updated on January 25, 2026 by Christian Veillette