CORR Insights®: Can Traditional Straight-leg Swaddling Influence Developmental Dysplasia of the Femoral Trochlea? An In Vivo Study in Rats

Where Are We Now?

Over the past century, our knowledge of developmental dysplasia of the hip (DDH) has grown exponentially. Current strategies for treating patellofemoral instability focus on surgical treatment well after the patellofemoral joint is formed. Except in extreme situations, such as congenital patellofemoral dislocation, patellofemoral instability is not usually clinically evident until adolescence or young adulthood [1]. At that late stage, treatment is focused on correcting bad anatomy rather than preventing it. One of the most controversial topics is the surgical management of the trochlea. Trochlear dysplasia has been shown to be a major predictor of recurrent instability [6]. In the United States, trochleoplasty has not seen wide use. However, European centers use trochleoplasty much more frequently, with multiple techniques. A case series [3] suggested that these procedures effectively reduce the likelihood of recurrent instability and dislocation, but true long-term studies—that is, studies evaluating patients for arthritis at a minimum follow-up duration of 10 years or more—have not been performed [3].

Although controversies remain, we have a much better understanding of the formation of the hip, risk factors for DDH, effective screening, and early interventions based on the plasticity of the growing hip than we do of the developing trochlea. There is a sizeable body of work suggesting the patellofemoral joint may depend on mechanical forces for proper development [4, 5]. Perhaps there are some lessons to be learned from our experience with DDH. In the knee, we’re attempting to treat a problem of which we have a poor understanding, with tools that produce unpredictable results. Fortunately, there is growing evidence, including the present study [8], suggesting that the trochlear depth may be influenced by physical forces applied during development. Certainly, it would be better if we could prevent trochlear dysplasia rather than treating it after it’s already developed. One does not need to look very hard to see some parallels between DDH and trochlear dysplasia in terms of etiology and potential opportunities for prevention and treatment.

Where Do We Need To Go?

The current work [8] provides another piece of the puzzle. It also raises many more questions as to the risk factors, prevention, and even reversal of trochlear dysplasia. What does seem clear from this study, and many of the studies cited by the authors, is that trochlear depth is likely influenced by mechanical forces very early in development. One could infer from the diversity of approaches that no one has discovered a universally predictable solution to patellofemoral instability, much less trochlear dysplasia. This should cause us to ask a few questions: Is some degree of trochlear dysplasia more likely to be present in breech infants than in those without a breech presentation? Is trochlear dysplasia preventable or modifiable during development? With respect to the hip, it is widely accepted that early treatment with a Pavlik harness can restore more normal forces across the hip. Can trochlear development be influenced by a simple orthosis, such as a Pavlik harness? Early treatment of DDH has been shown to be more than 90% effective [2]. Are there lessons to be gleaned from our collective experience in DDH with respect to the diagnosis and treatment of trochlear dysplasia?

The present article [8] attempts to identify a potentially clinically relevant risk factor—straight leg swaddling—for the development of trochlear dysplasia. These data suggest there are mechanical factors influencing the development of the patellofemoral joint and that a lack of those forces contributes to a lack of proper trochlear depth. We need to develop a more complete understanding of not only the risk factors for trochlear dysplasia but also how we might modify the natural history through early diagnosis and treatment. The kinds of noninvasive measures we use to diagnose and treat DDH may offer us some clues as to how to do this. Imagine if we could screen neonates based on clinical criteria and perform simple, noninvasive testing and early treatment with an orthosis, such as a Pavlik harness, to prevent the multiple surgical procedures and chronic instability often experienced by patients with severely dysplastic patellofemoral joints.

How Do We Get There?

The first step in developing prevention and early treatment strategies for trochlear dysplasia is to understand the process better in humans. Breech presentation has been associated with trochlear dysplasia [7], likely from knees remaining in an extended position, limiting the opposing forces between the patella and femur. Studying the trochlear development of children with breech presentation may be a good place to start. For example, investigators could measure trochlear depth via ultrasound in breech children versus that of controls without breech presentation. A step further, trochlear depth could be measured before and after Pavlik harness treatment in children with DDH.

The next steps would be to look for ways to modify the natural history through early diagnosis and treatment through noninvasive measures like those used to diagnose and treat DDH. For example, ultrasound is a noninvasive, low-cost imaging modality that could be used to serially measure trochlear morphology. We might begin with a natural history study examining trochlear development in breech infants compared with normal controls. Understanding how trochlear morphology changes over time and the factors influencing that development would provide the basis of knowledge to develop screening and prevention strategies. Without such information, we’re left treating a difficult problem well after it has occurred, which is seldom as successful as preventing it. Drawing on our collective experience of the infant hip may help us develop early recognition and treatment strategies, including the ability to prevent patellofemoral instability in some patients.