Paul E. Beaulé, MD, Receives Kappa Delta Elizabeth W. Lanier Award

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Paul E. Beaulé, MD, FRCSC

Paul E. Beaulé, MD, FRCSC, received the 2018 Kappa Delta Elizabeth W. Lanier Award yesterday for his studies of the degenerative process associated with cam-type femoroacetabular impingement (FAI) to determine whether causation exists.

Dr. Beaulé and his coauthors—George Grammatopoulos, MD, FRCS, PhD; Andrew Speirs, PhD; Geoffrey Ng, PhD; Sasha Carsen, MD; Hanspeter Frei, PhD; Gerd Melkus, PhD; Kawan Rakhra, MD; and Mario Lamontagne, PhD—were recognized during the Your Academy 2018 event.

For several years, the researchers have been investigating the association between cam-type FAI and the development of osteoarthritis (OA) of the hip. They based their case for causality on Hill’s criteria, a group of nine principles (strength, consistency, specificity, temporality, biologic gradient, plausibility, coherence, experiment, and analogy) established in 1965 by the English epidemiologist Sir Austin Bradford Hill. Their paper outlines the results of studies undertaken to meet six of the nine criteria, as well as their argument supporting their case for meeting the remaining three criteria.

They noted that abnormalities of the bony acetabulum and/or femur can damage soft-tissue structures such as the labrum and articular cartilage. FAI limits the free arc of hip motion in one of the following ways:

  • a deep or maloriented acetabulum, resulting in “pincer FAI,” with damage localized at the labrum
  • an insufficient offset between the femoral head and neck, resulting in “cam FAI,” with damage to the cartilage through an outside-in abrasion and/or delamination
  • a combination of both

The potential relationship between proximal femoral morphology and the early onset of hip OA has long been known, primarily as a sequel to childhood disease such as slipped capital femoral epiphysis (SCFE). But many individuals with cam FAI did not have SCFE, suggesting that other forces may be at work. According to the researchers, possible contributing factors may be either extrinsic (physeal stresses during development) or intrinsic (genetic predisposition).

Meeting Hill’s criteria

The researchers examined the strength of the association between cam morphology and hip pain and degeneration. They conducted a series of studies to determine the incidence and impact of cam morphology among asymptomatic volunteers. Based on these studies, they came to the following conclusions:

  • Cam deformity is relatively common, especially among males (as many as one in four).
  • The cam deformity forms during the period of skeletal maturation and is associated with a higher level of activity and reduction in hip function (internal rotation of the flexed hip).
  • The severity of the cam deformity, as well as its location, is associated with a higher risk of hip pain development, especially if associated with lower femoral neck shaft angle, increased pelvic incidence, and increased supero-acetabular coverage.
  • Zones of proteoglycan content depletion (a sign of OA) as measured using T1ρ advanced cartilage MRI mapping correspond to the area of acetabular cartilage damage at the time of surgery as well as increased bone loading.

To delineate the temporal relationship of the association (whether the cam deformity preceded the joint degeneration or vice versa), the researchers conducted a second series of studies on pediatric volunteers. These studies were designed to define the timeline of cam development, determine whether the cam increases after physeal closure, and characterize whether the bony characteristics of the cam lesion are similar to those seen with joint degeneration.

Results of these studies showed that cam morphology develops as a function of physical activity during physeal maturation and its severity does not significantly increase after skeletal maturity. They also showed that “cam deformity is a primary malformation with intrinsic biomechanical abnormalities,” leading to the conclusion that the cam morphology precedes the degenerative process.

In their search for biologic evidence that presence of cam morphology may lead to joint degeneration, the researchers used an in vitro finite element modeling study and two in vivo observational studies, including an analysis of the cartilage layer in patients undergoing surgery. They found that the in vivo observations reinforced the findings of the in vitro study at both the bony and cartilaginous levels, leading them to conclude that “it is biologically plausible for the cam morphology to lead to joint degeneration.”

To determine whether a biologic gradient (dose-response) existed, the researchers asked, “Does the α angle correlate with degree of joint degeneration?” They reviewed their previous study on prevalence, which included measuring the α angle, and they performed a new study, focused on whether the α angle could predict acetabular cartilage delamination. Both studies found a positive correlation, confirming the biologic gradient. “Hips with a larger size of the cam morphology, as quantified by the α angle, were more likely to have significant wear degeneration and acetabular subchondral bone stiffness,” they concluded.

The issue of specificity was addressed through two studies focused on patient-specific anatomic and functional parameters. The studies provided some insights, which were validated by a third study using high-resolution T1ρ MRI.

“Since not all hips with cam morphology are symptomatic, it would be important to note (a) what ‘static’ morphological features (in addition to the cam deformity) may differentiate between symptomatic and asymptomatic hips (b) whether ‘dynamic’ differences exist between symptomatic and asymptomatic hips with cam morphology, or (c) whether asymptomatic hips with cam morphology develop signs of joint degeneration with time,” they wrote.

The results of these studies led to the following conclusions:

  • Although α angle is the strongest determinant of symptoms, other anatomic (static) parameters of the femur (neck-shaft angle), acetabulum (depth), and spine (pelvic incidence) also differ between symptomatic and asymptomatic hips with cam morphology.
  • Symptomatic patients with cam morphology exhibit different pelvic and hip kinematics and reduced sagittal range of movement.
  • Most asymptomatic individuals with cam deformity will not show progression of cartilage degeneration during longitudinal follow-up (up to 3.6 years).
  • Pelvic, hip, or combined pelvic/hip range of motion may determine those at risk.

The last of Hill’s criteria addressed in the paper was experimental evidence. “If the cam morphology (and the associated FAI) were responsible for joint degeneration, one would argue that excision of the cam lesion, thereby preventing the occurrence of FAI, would improve the outcome and stop any (further) joint degeneration from taking place,” they wrote. In fact, a study of patients who underwent surgery supported this theory.

“Surgical correction of the cam morphology FAI lead to symptomatic relief as well as improved function both subjectively and objectively (ie, squat mechanics) with concomitant improvement in two biomarkers (T1ρ and bone mineral density). More importantly, there were significant correlations between improvement in function and T1ρ (ie, lower values better cartilage) providing external validity as biomarker of arthritis.”

Making their case

To meet the three remaining Hill’s criteria for illustrating causation—consistency, coherence, and analogy of their findings—the researchers presented key findings from other studies supporting their case.

“This work therefore opens avenues on how the cam morphology should be studied, screened for, followed-up, and assessed (patient-specific) to prevent early joint degeneration,” they concluded.

“Unravelling the Hip Pistol-Grip/CAM Deformity: Origins to Joint Degeneration” will be presented during the 2018 Annual Meeting of the Orthopaedic Research Society on Sunday at the Hyatt Regency New Orleans.

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