The Reliability of the Tönnis Grading System in Patients Undergoing Hip Preservation

Abstract

Background: The presence of pre-existing osteoarthritis (OA) has been associated with poor results after hip arthroscopic surgery. There is limited evidence validating the currently available grading systems of hip OA in patients undergoing hip preservation. Purpose/Hypothesis: Our purpose was to evaluate the interobserver and intraobserver reliabilities of 2 grading systems in a group of patients undergoing hip preservation: the Tönnis grading system and a simple 4-choice Likert scale. The hypothesis was that interobserver and intraobserver reliabilities using the Tönnis grading system would be poor among surgeons experienced in hip preservation and that a 4-choice Likert scale would be more reliable. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: A total of 100 hip radiographs were reviewed by 8 experienced hip preservation surgeons. Overall, 2 rounds of reviews were performed, at least 3 weeks apart, assessing for the presence, degree, and/or location of joint space narrowing, joint space asymmetry, subchondral cysts, osteophytes, and sclerosis. The radiographs were assigned a Tönnis grade as well as a Likert grade of OA, reported as none, mild, moderate, or severe. Statistical analysis was conducted to provide Fleiss kappa values with 95% CIs. Agreement was classified as poor for <0.00, slight for 0.00-0.20, fair for 0.21-0.40, moderate for 0.41-0.60, substantial for 0.61-0.80, and almost perfect for >0.80. Results: A total of 50 patients (28 female and 22 male) with a mean age of 42.8 ± 14.2 years (range, 19-70 years) were reviewed. The Tönnis grade demonstrated an interobserver kappa value of 0.30 (95% CI, 0.26-0.34). The Likert grade demonstrated an interobserver kappa value of 0.33 (95% CI, 0.28-0.37). All other measures demonstrated interobserver kappa values classified as slight or fair except for subchondral cysts which was moderate. Intraobserver reliabilities were statistically significantly higher than interobserver reliabilities. Intraobserver reliabilities for both the Tönnis grade (κ = 0.55 [95% CI, 0.51-0.60]) and Likert grade (κ = 0.59 [95% CI, 0.55-0.63]) demonstrated similar kappa values, consistent with moderate agreement. Subchondral cysts demonstrated the strongest interobserver (κ = 0.53) and intraobserver (κ = 0.85) reliabilities. Conclusion: Interobserver and intraobserver reliabilities were fair and moderate, respectively, for grading OA. Given the limited interobserver reliability, caution should be used when interpreting and translating studies that utilize the Tönnis grade or other rating to dictate treatment algorithms.

Modern Hip Arthroscopy for FAIS May Delay the Natural History of Osteoarthritis in 25% of Patients: A 12-Year Follow-up Analysis

“…18 Anteroposterior pelvis radiographs may also not provide the ideal radiographic view to assess joint degeneration. Magnetic resonance imaging to evaluate cartilage status may have been ideal, but this was logistically and fiscally impractical to accomplish; moreover, a recent study by Pullen et al 19 showed that magnetic resonance imaging scans demonstrated strong reliability in evaluating subchondral cysts but did not improve the interobserver variability of grading hip arthritis. Ideally, this study would have included more surgeons for generalizability.…”

“…Even though this is the most commonly used metric and is consistently evaluated from a medicolegal and billing documentation standpoint, it carries a variable interrater reliability ranging from 0.55 to 0.99 12 and has recently demonstrated moderate reliability in grading osteoarthritis. 18 Anteroposterior pelvis radiographs may also not provide the ideal radiographic view to assess joint degeneration. Magnetic resonance imaging to evaluate cartilage status may have been ideal, but this was logistically and fiscally impractical to accomplish; moreover, a recent study by Pullen et al 19 showed that magnetic resonance imaging scans demonstrated strong reliability in evaluating subchondral cysts but did not improve the interobserver variability of grading hip arthritis.…”

The HAR-index: a reliable method for evaluating the risk of total hip arthroplasty conversion after hip arthroscopy for femoroacetabular impingement

“…The preoperative variables recorded for each patient included age, sex, affected side, weight, height, body mass index (BMI), visual analogue scale (VAS 0–100 mm), joint space based on the Tönnis classification [29], cartilage injury degree based on the modified acetabular labrum articular disruption (ALAD) [22], modified Harris hip score (mHHS) [16], hip outcome score activities of daily living and sport‐scale (HOS‐ADL, HOS‐SS) [34], and the Western Ontario and McMaster index (WOMAC) [37]. For those patients who required conversion to THA, time from arthroscopy to reintervention for THA was also recorded.…”