Mini-open Femoroacetabular Osteoplasty in Patients With Tönnis Grade 2 or Higher Osteoarthritis is Associated With a Higher Risk of Subsequent Conversion to THA
Authors: Abdelaal Mohammad S. , Sutton Ryan M. , Sherman Matthew B. , Parvizi Javad 
Published: January 2024

Abstract

Background
The severity of degenerative changes of the hip is known to adversely impact the outcomes of the treatment of femoroacetabular impingement (FAI). Although the operative indications for FAI have expanded to include patients with moderate degrees of hip osteoarthritis, the exact stage of hip osteoarthritis at which surgery for FAI can offer clinical benefits is still uncertain.

Questions/purposes
(1) How does the survivorship free from conversion to THA and survivorship free from revision differ between patients with preexisting Tönnis Grades 2 or 3 changes and those without advanced degenerative changes (Tönnis Grade 0 or 1) after mini-open femoroacetabular osteoplasty? (2) What are the differences in hip-specific and general health outcome scores between the two groups after mini-open femoroacetabular osteoplasty?

Methods
From December 2003 to April 2019, we treated 901 patients for FAI, and their clinical data were systematically recorded in a longitudinally maintained database. Mini-open femoroacetabular osteoplasty was our preferred surgical approach because of the surgeon's extensive experience with the technique. Among the entire dataset, 6% of patients (51 individuals) had Tönnis Grade 2 or higher hip osteoarthritis, while the remaining 94% (850 patients) had no or mild degenerative changes (Tönnis Grade 0 or 1). In the Tönnis Grade 2 or 3 group, three patients were lost before the minimum 2-year follow-up duration, leaving 4% (48 patients) who qualified for inclusion in the study. For the matched group with Tönnis Grade 0 or 1, 5% (45 patients) were excluded because of incomplete data, and a further 7% (58 patients) were excluded because they did not have 2 years of follow-up, leaving 83% (747 patients) who were eligible for the matching process. Matching was based on patient age (within 1 year), gender, and BMI (within one unit). Matching resulted in the inclusion of 144 randomly selected control patients in this retrospective, comparative study. General indications for femoroacetabular osteoplasty included symptoms of pain and restricted hip motion in young, active patients with signs of FAI evident on physical examination and radiographs. Patient demographics, medical history, radiographic parameters, and intraoperative findings were compared between the two groups to establish baseline differences and identify potential confounding variables. There was no difference in the mean ± standard deviation age between the cohort of interest and control group (39 ± 10 years and 38 ± 11 years, respectively; p = 0.67). There was no difference in the mean follow-up duration (7 ± 3 years versus 8 ± 2 years; p = 0.25) or the preoperative symptomatic period between the study and control groups (2 ± 2 years versus 3 ± 6 years; p = 0.09). There was no difference in the prevalence of dysplasia, slipped capital femoral epiphysis, Perthes disease, or avascular necrosis of the hip between the two groups. Intraoperatively, the groups did not differ in terms of labral repair (65% [31 of 48] versus 78% [113 of 144]; p = 0.08) and labral transplantation (2%; p > 0.99 for both); however, labral resection was performed more frequently in the study group (63% [30 of 48] versus 42% [60 of 144]; p = 0.002). At a minimum of 2 years of follow-up, survivorship free from conversion to THA and survivorship free from revision surgeries, as well as the latest clinical and functional outcome scores (SF-36, Hip Disability and Osteoarthritis Outcome Score, and modified Harris hip score), were compared between groups.

Results
Survivorship free from conversion to THA at 5 years was lower among patients with preexisting Tönnis Grades 2 or 3 changes than it was among patients matched for age, gender, and BMI who did not have advanced degenerative changes (Tönnis Grade 0 or 1) after mini-open femoroacetabular osteoplasty (75% [95% confidence interval 64% to 88%] versus 92% [95% CI 87% to 96%]; p < 0.001). No patients in either group underwent reoperation other than conversion to THA. Although the groups did not differ at baseline in terms of their outcomes scores, the group with more visible arthritis had lower postoperative Hip Disability and Osteoarthritis Outcome Scores than the control group (60 ± 21 points versus 86 ± 11 points, mean difference 26 points [95% CI 10 to 41]; p =0.004). There were no other between-group differences in outcome scores after surgery.

Conclusion
In our study, approximately 25% of patients undergoing mini-open femoroacetabular osteoplasty with Tönnis Grade 2 or higher osteoarthritis underwent conversion to THA within 5 years. Some postoperative functional scores were lower in patients with advanced arthritis than in matched patients with no or mild arthritis. We emphasize the importance of exercising caution when considering femoroacetabular osteoplasty in patients in whom advanced arthritis is already evident at the time of presentation.

Level of Evidence
Level III, therapeutic study.