Where Are We Now?
During my initial orthopaedic residency training in the mid-1990s, the words “hip impingement” never appeared in any orthopaedic diagnosis. Today, hip impingement is an established condition with an emphasis on early diagnosis, well-established imaging criteria, and the understanding that the natural history of untreated symptomatic impingement may lead to early arthritis of the hip joint.
Femoroacetabular impingement (FAI) is a clinical syndrome where morphological changes in the femoral head-neck and/or acetabulum result in abnormal contact and wearing of the joint surfaces (including the labrum) that can lead to, in some symptomatic patients, joint arthritis if left untreated. A cam-type morphology is an aspherical contour of the femoral head-neck junction that may lead to abnormal contact with the acetabular rim in FAI [1, 3, 5, 8]. Given what we have come to know about the natural history of this condition during the last two decades, the topic is quite relevant.
In the current study, Hosseinzadeh and colleagues  retrospectively evaluated 16 patients (between the ages of 8 to 15 years) with cam-type FAI who had undergone CT hip evaluation . The authors found more peripheral cupping in patients with cam-type FAI than in a control group of patients without hip symptoms who did not have FAI. The epiphyseal tubercle height and length were smaller and the metaphyseal fossa was larger in hips with cam-type FAI, suggesting varying inner bone surface morphology of the growth plate. Based on these findings, I believe that surgeons should focus on developing imaging biomarkers to help predict the risk of FAI, and more importantly, those cases that are likely to become symptomatic.
Where Do We Need To Go?
Future studies should focus on identifying longitudinally which patients with radiographic FAI become symptomatic. We should then ask two questions: (1) What proportion of patients with clinically symptomatic FAI have hip symptoms that persist despite nonsurgical treatment, and (2) how many of them develop arthritis earlier compared with those of similar age, sex, and race who do not have FAI?
Despite extensive research related to the natural history of symptomatic FAI, the best management for adolescent or younger patients with FAI is still unknown. Surgical treatment of the hip in child or adolescent remains a difficult, emotional decision for families because surgery has inherent risks, including nerve injuries due to portal placement; traction and compression from positioning; labral injury; cartilage scuffing and instrument breakage; iatrogenic chondral damage; under-resection; over-resection with hip instability or, rarely, fracture; heterotopic ossification; scarring; and intraabdominal fluid extravasation—another rare occurrence. A prospective study from 2018  on adolescents with symptomatic FAI reported that most (82%) adolescent patients with FAI syndrome can be managed nonoperatively with improvement in outcome scores. Future studies should further explore that nonoperative approach, especially since a majority of the population seems to respond to that.
It appears that some morphological variations of the hip in an early growing skeleton, compounded by certain excessive sporting or repetitive loading activities, may lead to FAI morphology in adolescence . It also appears that many patients with symptomatic FAI respond to nonoperative management and activity modifications, but an important subset do not, and they need surgical intervention. Finally, some of these patients who proceed to adulthood with FAI morphologies develop symptomatic FAI in adulthood and are at risk for early hip arthrosis. Therefore, it would be helpful if we could determine which children or adolescents with FAI morphologies are the best candidates for earlier surgery, and which children and adolescents who are treated without surgery are at greatest risk to develop symptomatic FAI in adulthood.
How Do We Get There?
Ideally, prospective studies including early identification of risk factors (clinical and radiographic) and longitudinal follow-up of these subjects (with or without nonoperative intervention) would help determine the real benefit of intervention for these patients.
A multifactorial etiology (morphological alteration of a growing hip compounded by other factors like sports, diet and nutrition, tight muscles in a growing skeleton, and bone metabolism) may likely have to be explored.
Genetic influences are implicated in the etiology of FAI, and future studies could include genomic data prospectively on patients while evaluating the role of intrinsic factors contributing to the altered morphology and its progression to symptomatic FAI . It may help to closely monitor siblings and identify FAI earlier in the offspring of the patient population. Patients with documented early structural or morphological changes that meet the current FAI morphology criteria but remain asymptomatic are perhaps the most important group that will help us get the answers we need, and as such, they need close monitoring. It would be impractical and possibly a huge burden to the system to monitor them with regular imaging, but with good education (of patients and parents), it is possible to catch the subset that begins getting early symptoms of hip pain and monitor those patients more closely (clinically and radiographically). With the current technological advances, it is easy to monitor activity level and even level of hip motion and loading of the extremity with implanted chips in garments and/or shoes followed by artificial intelligence–based information collection and processing.
Future studies should focus on questions like: (1) In individuals who are genetically at risk (such as siblings of patients or children), and in patients with incidental early identification of FAI morphology, would activity modification including avoidance of at-risk sports (those with repetitive axial loading of the hip) change the clinical course of the condition? (2) For those individuals that show early symptoms, what role does activity modification, restoration of bone nutrition, metabolic health and joint forces (while addressing tight muscles in a growing skeleton), and biologics (like platelet-rich plasma) play in management?
FAI is a dynamic abutment of the joint surfaces in a hip joint of a specific individual. It is and remains a clinical diagnosis. In my opinion, arbitrary indices, angles, and numbers obtained by imaging have come to dominate surgeons’ approaches to diagnosis, perhaps leading to overdiagnosis of the condition. The goal in FAI eventually would be to replace these arbitrary indices with patient-specific diagnostic tools based on specific structural (and perhaps genomic) information. There is a world of difference between clinical and radiographic FAI, and we need to get better at distinguishing the two.
1. Ahn T, Kim CH, Kim TH. What is the prevalence of radiographic hip findings associated with femoroacetabular impingement in asymptomatic Asian volunteers? Clin Orthop Relat Res.
2. Byrd JW. Femoroacetabular impingement in athletes, part 1: cause and assessment. Sports Health.
3. Frank JM, Harris JD, Erickson BJ. Prevalence of femoroacetabular impingement imaging findings in asymptomatic volunteers: a systematic review. Arthroscopy. 2015;31:1199-204.
4. Hosseinzadeh S, Novias E, Emami A. Does the capital femoral physis bony morphology differ in children with symptomatic cam-type femoroacetabular impingement. Clin Orthop Relat Res.
5. Monazzam S, Bomar JD, Dwek JR, Hosalkar HS, Pennock AT. Development and prevalence of femoroacetabular impingement-associated morphology in a paediatric and adolescent population: a CT study of 225 patients. Bone Joint J. 2013;95B:598-604.
6. Pennock AT, Bomar JD, Johnson KP, Randich K, Upasani VV. Nonoperative management of femoroacetabular impingement: a prospective study. Am J Sports Med. 2018;46:3415-3422.
7. Pollard TC, Villar RN, Norton MR. Genetic influences in the aetiology of femoroacetabular impingement: a sibling study. J Bone Joint Surg Br.
8. Scheidt RB, Galia CR, Diesel CV, Rosito R, Macedo CA. Prevalence of radiographic markers of femoroacetabular impingement in asymptomatic adults. Rev Col Bras Cir. 2014;41:36-42.