Dislocation remains among the most common complications of, and reasons for, revision of both primary and revision total hip arthroplasties in the United States. Hence, there is great interest in maximising stability to prevent this complication. Highly crosslinked polyethylene has allowed us to increase femoral head size, without a clinically important increase in wear. As femoral head size increases, stability is augmented, secondary to a decrease in component-to-component impingement, which is theoretically eliminated at head sizes greater than 36mm in diameter (however osseous impingement can still occur). Larger heads sizes also greatly increase the “jump distance” required for the head to dislocate (in an appropriately positioned cup) and eliminate the need for skirts. Hence, large heads have become the mainstay for preventing and treating instability in contemporary practice. Large heads, however, have been shown to have poor performance in patients with abductor insufficiency. Constrained liners are a tantalising solution to both prevent and treat instability, as they markedly increase the force needed for a dislocation to occur. They have, however, several important negatives that the surgeon must consider before entertaining their use including:
Increased stresses at the implant bone interface which can increase the risk of loosening or cause catastrophic failure in the early post-operative period Decreased range of motion with a greater risk of impingement Usually require an open reduction if they dislocate or otherwise fail Given the limitations of constrained liners, we have moved to dual mobility articulations in most situations where we would have used a constrained liner in the past, including patients with abductor deficiency. These articulations offer anatomic sized femoral heads that greatly increase the jump distance, without many of the negatives of a constrained liner. While dual mobility is associated with its own concerns and problems (including intraprosthetic dislocation and wear) our initial results suggest that they are a viable alternative to a constrained liner, even in the most challenging situations.
Periprosthetic fractures present several unique challenges including gaining fixation around implants, poor bone quality and deciding on an appropriate treatment strategy. With the popularity of cementless stems in primary total hip arthroplasty (THA) we have seen a concomitant rise in the prevalence of intra-operative and early post-operative fractures of the femur. While initial press-fit fixation is a requirement for osseointegration to occur, there is a fine balance between optimising initial stability and overloading the strength of the proximal femur. Hence, the risk of intra-operative fractures is intimately related to the design of the femoral component utilized (metaphyseal engaging, wedge shaped designs having the highest risk) and the strength of the bone that it is inserted into (elderly females being at highest risk). These fractures typically are associated with a loose femoral component and require revision to a stem that gains primary fixation distally. We have found a high risk of complications and problems when treating these fractures in the early post-operative period with a high risk of infection, heterotopic ossification and the requirement for subsequent surgery. The Vancouver Classification is based on the location of the fracture, the fixation of the implant and the quality of the surrounding host bone. The most common pitfall in treatment is mistaking a B2 fracture (stem loose) for a B1 (stem stable); treatment of a loose implant with ORIF alone will necessarily fail.Early
Late
A “two-stage exchange” remains the gold standard for treatment of the infected THA in North America. Although there is interest in “one-stage exchange” this technique is predicated on the use of fixation of the revision implants with antibiotic loaded cement, which is not as popular in North America. Diagnosis is critical and in general consists of a screening serum ESR and CRP followed by selective aspiration if the above are abnormal and/or if the clinical history is suspicious. The aspirated fluid is sent for a synovial fluid WBC (cut-off approximately 3,000 WBC/μL), differential (cut-off 80% PMN) and culture. The basic tenets of treatment include:
Thorough debridement of all infected appearing cement and all foreign material Placement of an interval antibiotic loaded spacer (note that the addition of antibiotics to bone cement is NOT FDA approved) 4–6 g of antibiotics per pkg of cement; typically vancomycin + tobramycin Higher viscosity cement may be associated with higher elution Higher elution with combination of antibiotics Antibiotic spacers can be “articulating” or “static”. Potential advantages of an articulating spacer include greater patient comfort and an easier approach at the second stage exchange as leg length and soft tissue tension is maintained. However, these spacers are oftentimes more costly and can dislocate. May not be appropriate in cases where there is severe bone loss that cannot support partial weight bearing or if the abductors are compromised (higher risk of dislocation). The first stage is followed by approximately 6 weeks of organism specific IV antibiotics. An interdisciplinary approach with an infectious disease specialist, internal medicine and a nutritionist optimises outcomes. Our protocol then includes weekly ESR and CRP to monitor their trend. These labs are re-checked two weeks after cessation of antibiotics to ensure the trend has not changed. We have found that while the ESR and CRP are significantly lower than prior to the 1st stage, they often times DO NOT normalise and there is no specific cut-off value that predicts persistent infection. An intra-operative aspiration for synovial fluid WBC count and differential is obtained intra-operatively (cut-off values of approximately 3,000 WBC/μl and 80% PMN) and are the best tests to identify persistent infection.
