Core Decompression With or Without Cement Packing for ONFH

A prospective randomized controlled trial comparing the results of CD vs. CD + PMMA packing in pre-collapse ONFH was set up.

Consecutive symptomatic patients aged >14 years with Association Research Circulation Osseous (ARCO) Stage I and II ONFH diagnosed using MRI and radiographic imaging were enrolled in this study.

Exclusion criteria were pre-existing collapse, sub-chondral fracture or degenerative changes of the hip.

After obtaining informed written consent, patients are asked to complete the Harris Hip Score (HHS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and a health status questionnaire Short Form-36 (SF-36).

The femoral heads enrolled into the study are randomized using a computer-generated card draw system to one of following: core decompression (CD) or core decompression with PMMA cement packing (CD + PMMA).

Allocation concealment was practiced with the use of opaque envelopes. Patients with bilateral involvement who had been randomized to one treatment modality for one femoral head were automatically selected to receive the other treatment modality for the contralateral femoral head.

Blinding of either surgeon or patient is impossible.

The patients were followed up after surgery every 3-4 months for the first 2 years after which the patients were seen annually. Completed questionnaires and radiographs were obtained at each visit.

Statistical Analysis The date of index procedure (CD or CD + PMMA) was used as start date for the purpose of statistical analysis. Progression Free Survival was defined as the time to radiographic progression and Conversion Free Survival (CFS) as the time to a THA. In case of patients who did not have radiographic progression, the date of their last follow up or death was used for the analysis. The SAS software will be used for all the analyses. The Log rank and Gerhan-Wilcoxon tests were used to compare Kaplan-Meier survival curves for the time from the date of the index procedure to radiographic progression (subchondral collapse) or conversion to THA for separate groupings based on age at index procedure (<40 , >40 yrs), smoking (Y/N), location (central, medial, lateral), percent involvement (<15% [mild], 15% to 30% [moderate], or >30% [severe]), index of necrotic extent (<40 or >40), and modified index of necrotic extent (<40 or >40). Whenever factors were found to affect the survival curves mainly in the initial year the Gerhan-Wilcoxon test was used as the test of significance. The Kaplan-Meier curves were also compared for the main cohorts of CD vs. CD + PMMA. Cox proportional hazards regression was used to compare factors (age, smoking, location, percent involvement, index of necrotic extent, and modified index of necrotic extent) with regards to their ability to predict the time to progression or revision to THA. Mixed multilevel regression modeling was used to test for group differences in the change in self-rated health survey scores over time from baseline over the post-operative period. The hierarchical linear modeling approach has a number of advantages over traditional repeated measures approaches for modeling change over time, including allowance for missing data and for varying measurement times across subjects. Separate models were generated for SF-36, Harris Hip Score and WOMAC scores over two-year and over 5-year post-operative time periods.