The John Charnley Award: Redefining the Natural History of Osteoarthritis in Patients With Hip Dysplasia and Impingement

Abstract

Background: Structural hip deformities including developmental dysplasia of the hip (DDH) and femoroacetabular impingement (FAI) are thought to predispose patients to degenerative joint changes. However, the natural history of these malformations is not clearly delineated.

Questions/purposes: (1) Among patients undergoing unilateral THA who have a contralateral hip without any radiographic evidence of hip disease, what is the natural history and progression of osteoarthritis in the native hip based on morphological characteristics? (2) Among patients undergoing unilateral THA who have a contralateral hip without any radiographic evidence of hip disease, what are the radiographic parameters that predict differential rates of degenerative change?

Methods: We identified every patient 55 years of age or younger at our institution who received unilateral primary THA from 1980 to 1989 (n = 722 patients). Preoperative radiographs were reviewed on the contralateral hip and only hips with T?nnis Grade 0 degenerative change that had minimum 10-year radiographic followup were included. A total of 172 patients met all eligibility criteria with the following structural diagnoses: 48 DDH, 74 FAI, and 40 normal morphology, and an additional 6% (10 of the 172 patients) met all eligibility criteria but were lost to followup before the 10-year minimum. Mean age at the time of study inclusion was 47 years (range, 18-55 years), and 56% (91 of 162) of the patients in this study were female. Mean followup was 20 years (range, 10-35 years). Radiographic metrics, in conjunction with the review of two experienced arthroplasty surgeons, determined the structural hip diagnosis as DDH, FAI, or normal morphology. Every available followup AP radiograph was reviewed to determine progression from T?nnis Grade 0 to 3 until the time of last followup or operative intervention with THA. Survivorship was analyzed by Kaplan-Meier methodology, hazard ratios, and multistate modeling. Thirty-five patients eventually underwent THA: 16 (33%) DDH, 13 (18%) FAI, and six (15%) normal morphology.

Results: Degenerative change was most rapid in patients with DDH followed by FAI and normal morphology. Among patients who recently developed T?nnis 1 degenerative change, the probability of undergoing THA in 10 years based on hip morphology was approximately one in three for DDH and one in five for both FAI and normal morphology hips, whereas the approximate probability at 20 years was two in three for DDH and one in two for both FAI and normal morphology hips. The likelihood of radiographic degeneration was increased in patients with the following findings: femoral head lateralization > 8 mm, femoral head extrusion index > 0.20, acetabular depth-to-width index < 0.30, lateral center-edge angle < 25°, and T?nnis angle > 8°.

Conclusions: Degenerative change occurred earliest in patients with DDH, whereas the natural history of patients with FAI was quite similar to structurally normal hips. However, patients with cam deformities and concomitant acetabular dysplasia developed osteoarthritis more rapidly. Although the results of this study cannot be directly correlated to highly active patients with FAI, these findings suggest that correction of FAI to a normal morphology may only minimally impact the natural history, especially if intervention takes place beyond T?nnis 0. Analysis of radiographic parameters showed that incremental changes toward dysplastic morphology increase the risk of degenerative change.

DDH and FAI are structural hip deformities thought to potentiate premature degenerative change. However, the natural history of these conditions, particularly about those factors that exacerbate osteoarthritis, is poorly understood. The current investigation demonstrates that after mild degenerative change develops in the hip, patients with DDH have a higher probability of progressing to end-stage osteoarthritis or THA at 10- and 20-year followup compared with FAI and normal morphology. Furthermore, radiographic cutoffs are established by this work that are associated with increased risk of osteoarthritis progression with incremental changes toward a dysplastic morphology portending a worse prognosis.

This study has a number of limitations. First, the sample size is modest for each of the three groups included in the final analysis, which likely explains why several results only trended toward significance despite point estimates of effect that actually seemed large. As such, the true effect may be underestimated or overestimated for some analyses. However, cohorts such as this have traditionally been very difficult to obtain, which was especially true for our study with more stringent eligibility criteria than previous work on the topic. Second, all measurements and categorization were based off AP pelvis radiographs. Unfortunately, this was the only view available for every patient in the study at each followup time point. It is well recognized that alternative radiographic views and three-dimensional imaging are often used to provide more complete information about hip morphology in modern practice. Third, the natural history of DDH, FAI, and normal morphology hips in patients with contralateral THA may not replicate other populations. It is possible that these patients place more stress on their native hip or that perhaps they have intrinsically poor cartilage given the young age of their first THA. However, the contralateral THA was essential to identifying a group of patients who would undergo serial radiographic followup. More importantly, it provided an excellent means of controlling prognostic risk in the native hip under study because young patients receiving THA specifically for degenerative joint disease presumably place similar demand on their native hip during ensuing decades. This could potentially be seen as a best case scenario if we assume that patients with contralateral THA are less active. Furthermore, this would likely be more important in FAI hips in which activity and ROM resulting in impingement lead to mechanical damage of the joint. Fourth, standard radiographic followup intervals limited the precision of transition date identification. However, a sensitivity analysis of the multistate modeling was conducted with hypothetically enriched and depleted data sets. Importantly, this sensitivity analysis revealed no significant differences from our reported findings, strengthening confidence in the presented data.

Perhaps the most valuable information for surgeons comes from the multistate modeling (Table 4). It shows that for a patient who recently developed T?nnis 1 degenerative change, the probability of undergoing THA in 10 years based on hip morphology is roughly one in three for DDH and one in five for both FAI and normal morphology hips, whereas the approximate probability at 20 years for the same patient is two in three for DDH and one in two for both FAI and normal morphology hips. Thus, early joint preservation intervention on patients with DDH seems more likely to positively influence the natural history of their hip than intervention on patients with FAI, provided they do not have a large cam deformity with concomitant acetabular dysplasia. As mentioned, two reports have similarly examined the natural history of FAI and DDH. Hartofilakidis and colleagues [10] retrospectively evaluated 96 hips with radiographic evidence of FAI and no degenerative change in the hip. Murphy and colleagues [15] retrospectively evaluated 286 young patients who received THA for dysplasia. Both of these studies lacked a control group and did not describe progression of osteoarthritis over time; furthermore, in the Murphy et al. study, a substantial portion of included patients had signs of degenerative change in the hip under study at the time of inclusion. However, results of these two studies were quite similar to ours with respect to rates of end-stage degeneration and eventual need for THA. A total of 40.2% of Murphy et al.’s group underwent THA compared with 28.6% at 20 years and 43.3% at 30 years in our study for patients with dysplasia. The followup time is unclear in the Murphy et al. study; however, the higher percentage may be accounted for by the fact that some patients had signs of degenerative change at the time of study inclusion. Hartofilakidis et al.’s group showed a 17.7% rate of endstage arthritis (12.5% received THA) with mean followup of 18.5 years (range, 10–40 years) compared with 19.8% at 20 years and 26.2% at 30 years with mean followup of 20 years (range, 10–35 years) in our study for patients with FAI.

Our data suggest that patients with radiographic features of dysplasia were at highest risk of progression in the entire cohort. This is in line with the report by Murphy and colleagues [15] who documented radiographic features consistent with more severe dysplasia in patients from their study who eventually developed osteoarthritis. At the other end of the spectrum, our data also demonstrated that among patients with FAI, an increased femoral head extrusion index was the strongest radiographic measure to portent joint degeneration. Patients classified with FAI and increased femoral head extrusion indices fit with the cam subtype of FAI. We also found that patients with cam-type FAI and concomitant low lateral center-edge angles or high T?nnis angles (both representing acetabular dysplasia) were at increased risk of osteoarthritis progression. Co-occurrence of acetabular dysplasia and FAI has been documented previously with authors positing that the combination increases the risk of intraarticular pathology [2, 6, 11, 12, 16]. Tannast and colleagues [20] recently published modified reference values for acetabular overcoverage and undercoverage based on a cohort managed with hip preservation surgery, postulating that previous cutoffs may not provide optimal accuracy. Examining this from a different perspective, we attempted to understand if current diagnostic cutoffs of radiographic parameters are predictive of osteoarthritis progression. The data for femoral head extrusion index, femoral head lateralization, acetabular depth-to-width index, and T?nnis angle suggest that risk of degeneration actually begins increasing with less extreme values than are suggestive of cutoffs for dysplasia (Table 5). These new proposed radiographic cutoffs provide an opportunity to modify natural history prognostication for patients.

In summary, these data can serve as an adjuvant prognostic tool for surgeons, enabling more informed patient counseling and decisions on how to manage disease as well as if or when to intervene. For example, although results from this study cannot be directly correlated to highly active patients with FAI, the predictive tables indicate that correction of FAI to a normal morphology may only minimally impact the natural history, especially if intervention takes place beyond T?nnis 0. Positive corrections are most likely to take place in patients with large cam lesions and shallow sockets. However, the data also indicate that correction of DDH to normal morphology at early T?nnis stages seems more likely to alter a patient’s natural history with earlier intervention providing greater benefit. Future studies should formally evaluate these questions by using a similar multistate modeling approach between patients with structural hip deformity who did and did not receive joint preservation surgery. This study also identified radiographic parameters that predict more rapid degenerative change, both in continuous and categorical fashions, subclassified by hip morphology. Specifically, incremental changes toward dysplastic morphology portend a worse prognosis. Although this study provides new information, perhaps the greatest weakness is the statistical uncertainty around many of the point estimates. Similar efforts at other centers would be valuable to either validate or adjust and improve precision of these results.