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Cam Deformity and Acetabular Dysplasia as Risk Factors for Hip Osteoarthritis//November 2018

A paper by Saberi-Hosnijeh et al, 2016 looking at acetabular dysplasia and cam deformity as risk factors for developing hip osteoarthritis has highlighted the following:

  • Recent studies have supported the hypothesis that mild acetabular dysplasia is associated with an increased risk of incidence of hip OA.
  •  In dysplasia, the femoral head articulates with a specific small area of the shallow acetabulum. Therefore, the joint stresses are localised to a more focal small area on both the femur and the acetabulum. The cumulation of these joint stresses and increased shearing forces results in articular surface contact stress above a critical threshold, therefore causing joint degeneration and early onset of OA.
  • A few studies have also found a significant association between cam deformity and the risk of developing hip OA. Which has then lead to a  total hip replacement (THR) being required within 2–20 years of follow‐up. 
  • Cam impingement is characterised by excess bone formation at the anterolateral head–neck junction creating a nonspherical femoral head known as a cam deformity.
  • The cam deformity on the femoral head articulates earlier with the acetabulum during flexion and internal rotation of the hip and results in the cam being forced into the acetabulum. This leads to structural damage of the acetabular rim, resulting in labral tears and cartilage delamination. This damage may gradually lead to hip OA. 
  • A significant association between acetabular dysplasia and development of OA was only seen in the female group. This could be due to differences in alignment of the lower extremity in women compared with men, which results in changes to dynamic and mechanical joint loading of the hip. Women often have abnormal underlying joint laxity, estrogen metabolism, and pregnancy‐associated pelvic instability which might explain the difference.

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What we have been reading this month- October 2018

This week we have been reading an interesting journal in Osteoarthritis and Cartilage by Vafaeian et al, 2017. It is titled: Finite element analysis of mechanical behaviour of human dysplastic hip joints: a systematic review.

This systematic review highlights a few key facts:

  • DDH is present in 1-3/1000 live births.
  • DDH accounts for one-third of hip replacement surgeries in patients under 60 years old.
  • DDH which is left untreated can lead to the following symptoms: mechanical instability, muscle imbalance, limited mobility, subluxation, abnormal joint loading which can cause increased cartilage shearing and development of osteoarthritis.
  • The earlier DDH is addressed the less likely the joint is to degenerate and develop osteoarthritis.
  • The labrum plays a key role in hip stability in the normal hip. In the dysplastic hip the mechanical contribution of the labrum has been found to be between 2-11  times greater.
  • Therefore in dysplastic hips there is increased load and shearing forces on the labrum, which eventually results in anterosuperior tearing of the labrum. Labral symptoms can be one of the first issues that a patient experiences- which leads to a diagnosis of hip dysplasia.
  • There is evidence of increased stress on the lateral acetabular roof, which is often where the first signs of osteoarthritis occur and sclerosis is often noted on x-ray.