Abstract
Background
Core decompression may be performed for early osteonecrosis with a goal of improving symptoms and potentially delaying the need for total hip arthroplasty. The effectiveness and complication rate of this procedure is not well understood given the relatively rare nature of hip osteonecrosis.
Purpose
The purpose of this study is to determine time to total hip arthroplasty (THA) after core compression, assess predictors of early conversion to THA, and to examine complications after hip core decompressions.
Methods
Using Current Procedural Terminology (CPT) codes, we queried the Mariner PearlDiver dataset for patients who underwent hip core decompression. Patient demographics were recorded and subsequent THA conversion within 2 years after surgery were tracked. Patient demographic factors, including age, sex, obesity, diabetes, prior fractures, steroid use, tobacco use, or alcohol use, were evaluated as possible predictors of early conversion to THA. International Classification of Diseases (ICD) codes were used to identify complications at 90 days after core decompression. Multiple linear regression was used to test if the patient demographics significantly predicted conversion to THA and complications after core decompression.
Results
Between 2010 and 2020, 555 patients underwent hip core decompression. Within 2 years of core decompression, 226 patients converted to THA (40.7%). Age was the only significant risk factor for conversion to THA. The highest proportion of patients (61.1%, 138/226) who converted to THA were between age 40–59. The 90-day complication rate was 2.9% (16/555). The most common complication was femoral neck fracture (11/16 of all complications).
Discussion
There is a high failure rate following core decompression for hip osteonecrosis with over one third of patients converting to THA within 2 years. Age was the only variable predictive of conversion to THA. The overall complication rate after core decompression is low at 90 days.
Conclusion
Patients should be counseled regarding the risk of early conversion to THA if over 40 and the potential risk of femoral neck fracture.
Key Terms: Osteonecrosis, Core decompression, Total hip arthroplasty, Femoral neck fractures
1. Introduction
Osteonecrosis of the hip is caused by interruption of blood flow to the femoral head, resulting in pain, loss of joint function, and eventual hip arthritis requiring a total hip arthroplasty (THA).1,2 This condition occurs most often in the femoral head but can affect other bones and joints. There are many risk factors for the disease the most common being use of corticosteroids, followed by alcoholism and idiopathic, other etiologies include hemoglobinopathies, dislocation of the hip, fracture of the femoral neck, as well as collagen and vascular disease.3, 4, 5
Osteonecrosis is a progressive disease that was first categorized by Ficat et al. based on radiographic and clinical presentation.6 Association Research Circulation Osseous (ARCO) updated the classification system for osteonecrosis of the femoral head.7,8 Stage I is characterized by a normal X-ray but a positive result on either magnetic resonance imaging or bone scan. Stage II shows abnormalities on the X-ray, such as subtle signs of osteosclerosis, focal osteoporosis, or cystic changes in the femoral head, without any evidence of subchondral fracture, fracture in the necrotic portion, or flattening of the femoral head. Stage III is further divided into stage IIIA, which is an early stage with femoral head depression of 2 mm or less, and stage IIIB, which is a late stage with femoral head depression of more than 2 mm. Stage IV shows X-ray evidence of osteoarthritis, including accompanying joint space narrowing, acetabular changes, and/or joint destruction.
Core decompression is a surgical treatment option that may be performed for early stage osteonecrosis with a goal of improving symptoms and potentially delaying the need for THA.1,2,9 Core decompression of the hip is employed before femoral head collapse and more advanced degeneration of the articular surface. The aim is to preserve function and structure of the hip as well as to relieve pain associated with osteonecrosis.1,2,9 Core decompression consists of drilling into the necrotic lesions, thereby decreasing pressure within the femoral head and potentially restoring blood flow.1,9 Bone grafting or other adjuncts may be used at the time of core decompression and may be performed arthroscopically.4,10, 11, 12, 13 Prior studies on core decompression have found success rates, defined as no radiographic progression or decreased pain, of 70–85% for stage I, 40–60% for stage II, and 20–40% for stage III.4,9,14, 15, 16 In all these studies, rates of success significantly dropped with larger lesions or if the femoral head had collapsed. Time to conversion to THA is variably reported in the literature, with estimates from 24 to 77 months after decompression and conversion rates between 35 and 40%.2,5,17, 18, 19, 20 The effectiveness of this procedure is generally not well understood given the relatively rare nature of hip osteonecrosis and inconsistent literature. Therefore, predictors of conversion to THA after core decompression are not well defined.
Core decompression is also not without complications. The estimated complication rate is 4.8%.4 Some of those complications include heterotopic ossifications, pain, infection, violation of cartilage as well as fractures.3,21,22 Types of fractures are rarely reported in the literature. Core decompression has been supplemented with the insertion of allografts and bone autografts to provide mechanical support of the osteonecrotic lesion and prevent collapse.2,4,10,11,23
The purpose of this study is to determine time to THA after core compression, assess predictors of early conversion to THA, and to examine complications after hip core decompressions. We hypothesize: 1. less than 25% of patients who had a hip core decompression will convert to THA at two-year follow up. 2. Age at time of core decompression will be a predictor of conversion to THA. 3. There will be less than 5% complication rate after core decompression.
2. Methods
The Mariner dataset (PearlDiver Technologies, Colorado Springs, CO) is a publicly available collection of orthopaedic patient records within the United States which includes various insurance payer types such as: United Health, Humanam Medicaid, Medicare, and self-pay patient populations. This database contains more than 144 million patients with Health Insurance Portability and Accountability Act (HIPAA) complaint records between 2010 and 2020. The International Classification of Diseases, Ninth Revision (ICD-9), ICD-10, and Current Procedure Technology (CPT) codes were used to query the dataset.
We queried data from the M91Ortho dataset, which is a subset of roughly 91 million patients within the Mariner database. To be included in this study, patients needed to have a record which contained the CPT code for hip core decompression (CPT-S2325). Patient records were then queried for subsequent THA (CPT-27130, CPT-27132, CPT-27125).
Patient demographic factors, including, age, sex, obesity, diabetes, prior fractures, steroid use, tobacco use, sickle cell disease or alcohol use, were evaluated as possible predictors of early conversion to THA. Last, International Classification of Diseases (ICD) codes were used to identify adverse events within 90 days after core decompression, such as post-op infection, heterotopic ossification, femoral neck, head, subtrochanteric, intertrochanteric fractures, or hip dislocations.
2.1. Statistical analysis
Demographics were described using mean values and standard deviation. Simple linear regression was used to test if the patient demographics significantly predicted conversion to THA. Multiple linear regression was use to determine if the impact of multiple variables on THA conversion. Similar analyses were used to test if the patient demographics predicted complications after core decompression. Cox-Survival plot was performed. Statistical significance was defined as p < 0.05. This study was exempt from the institutional review board approval due to analysis of only de-identified administrative data.
3. Results
Between 2010 and 2020, 555 patients were identified who underwent hip core decompression (Table 1). Within 2 years of core decompression, 226 patients converted to THA (40.7%) and one patient converted to hemiarthroplasty. Average age for patients converting to THA was 47.4 years compared to those who did not convert 43.4 (95% CI 1.19–6.0 years, p < 0.001). The largest proportion of patients who converted to a THA were between ages 40–59 (61.1%, 138/226; Fig. 1). Age was the only statistically significant risk factor for conversion to THA, even when controlling for other demographic variables (p < 0.01). There was no significant relationship between conversion to THA and patient sex, obesity, diabetes, prior fracture, steroid use, tobacco use, or alcohol use (p > 0.05; Table 1). Cox survival plot demonstrated a high risk of conversion to THA within two years of core decompression with the highest risk within the first 200-days (p = 0.02; Fig. 2). At two years the survival was 59.6% (95% CI 55.5%–64.0%).
Table 1.
Demographics.
| Core Decompression | No THA Conversion | THA Conversion | |
|---|---|---|---|
| Age | 45.0 (SD 12.2) | 43.4 (SD 11.5) | 47.4 (SD 13.0) * |
| Sex (% females) | 42.5% (236/555) | 44.7% (147/329) | 39.4% (89/226) |
| Diabetes (%) | 15.5% (86/555) | 17.0% (56/329) | 13.3% (30/226) |
| Obesity (%) | 17.5% (97/555) | 16.7% (55/329) | 18.6% (42/226) |
| Sickle Cell Disease (%) | 3.0% (16/555) | 4.0% (13/329) | 1.6% (3/226) |
| Tobacco Use (%) | 31.0% (172/555) | 29.5% (97/329) | 33.2% (75/226) |
| Alcohol Use (%) | 6.1% (34/555) | 6.1% (20/329) | 6.2% (14/226) |
| Steroid Use (%) | 32.6% (181/555) | 30.4% (100/329) | 35.8% (81/226) |
| Prior Fracture (%) | 4.1% (23/555) | 4.3% (14/329) | 4.0% (9/226) |
Fig. 1.
Patient conversion to THA after core decompression by age group categories. Note: categories <29 for THA and >69 years for THA had less than 10 patients.
Fig. 2.
Cox Survival Probability plot two years after core decompression with standard deviation for the entire cohort, dotted line (p < 0.001).
The 90-day complication rate was 2.9%. The most common complication was femoral neck fracture (11/16 of all compilations at 90 days), no patients had a post operative infection, or developed heterotopic ossification. There was no significant relationship between complications after core decompression and patient age, sex, obesity, diabetes, prior fracture, steroid use, tobacco use, or alcohol use (p > 0.05).
4. Discussion
After core decompression for hip osteonecrosis nearly 40% of patients converted to THA within 2 years. Patients between 40 and 59 had the highest rates of conversion to THA. Other demographics variables did not significantly predict conversion. There were low complication rates at 90 days, however the most common complication was a femoral neck fracture.
In this study nearly 40% of patients who underwent hip core decompression converted to THA at 24 months. These results are consistent with a prior study evaluating 1134 patients with early stage of osteonecrosis, which showed 38% of patients underwent a THA at an average of 26 months following core decompression.2 Historically, core decompression, has been offered as a management option for osteonecrosis that relieves pain and delays conversion to THA. The present study adds to the growing evidence of literature that core decompression may not substantially delay THA and suggests that the highest rate of conversion is during the first 200 days.
Age was the only statistically significant predictor of early conversion to THA. It is possible that in older patients osteonecrosis may progress faster or that they had more advanced osteonecrosis at the time of core decompression. Additionally, surgeons may be more willing to offer THA to an older patient with ongoing symptoms after core decompression whereas younger patients may be counseled to avoid early conversion to THA. Few studies have examined demographic factors as predictors of core decompression failure and none to THA conversion. In a prospective study of 34 patients who underwent core decompression, Bozic et al. found significant predictors of overall failure, defined as osteonecrosis radiographic progression or subsequent surgery, included advanced preoperative radiographic stage, and use of corticosteroids.24 Another study found that four of five patients with a history of alcohol usage clinically failed, and contrary to the previous study steroid use did not predict complications.9 Although steroid and alcohol use were not significant predictors of conversion to THA in this study, use of these has been reported as common causes of osteonecrosis so it is possible that progression may ensue due to prior exposure or continued use.4 Similar to these studies we found no association with sex, obesity, diabetes, prior fracture, or tobacco use. While older patients underwent conversion to THA at a higher rate, some of this willingness to convert to THA may be related to selection bias and a lower threshold for surgeons to counsel patients towards THA at an older age.
Most of the literature has focused on evaluating radiographic parameters such as osteonecrosis staging and lesion size as predictors of conversion to THA.4,5,9,18 These studies found that higher staged osteonecrosis and larger lesions tend to have higher rates of failures and conversion to THA. In a prospective study 45 patients who received CD and were followed for an average of 24 months, Mont et al. found failure rates of 20% in Ficat stage 1, 47% in stage 2, and 58% in large lession.9 Careful risk and benefits conversation should be had with the patients of specific age groups and as older patients may be a higher risk of earlier conversion equally their osteonecrosis staging and lesion size should be considered.
In this study, we found a relatively low complication rate at 90-days, with the highest risk being that of femoral fractures. This is similar to what has been reported in the literature.4,9,24 In a systematic review of CD outcomes, 5% of patients had complications.4 Of these the most common complications included heterotopic ossifications (33.3%), pain (21.7%), followed by fracture (18.8%). In this study there were no cases of post-op infection or heterotopic ossification. Bozic et al. found that one patient had a fracture of the femoral neck, and the other had a hematoma.24 In an attempt to minimize complications, instead of drilling one large tract, some have suggested using multiple percutaneous drilling, and the use of mesenchymal cells, bone morphogenic proteins or bone grafting.2,3,21, 22, 23 Our findings, consistent with prior findings, suggest that core decompression is a safe procedure for the treatment osteonecrosis. However, patients must be counseled on the potential risk of fractures specially if they are current smokers or have had a prior hip fracture.
The mesenchymal cells, bone morphogenic proteins or bone grafting in conjunction to core decompression has been suggested as a way of minimizing complication, improve clinical outcomes and delay progression to THA.3,11,21,22,25 Between 2010 and 2020 only 2.7% (15/555) patients that underwent core decompression had concurrent bone grafting. Suggesting that concurrent bone grafting is still not widely used; however, the sample size is limited and conclusions cannot be drawn. In a study with 54 hips, randomized to CD or CD + vascularized fibula graft (CD + BG), Cao et al. found that patients with CD alone had more severe progression of osteonecrosis; however, it was not significantly different from CD + BG, in addition there was no difference in conversion to THA at 36months and clinical outcomes although favoring CD + BG were below the MCID.11
4.1. Limitations
This study has a larger sample size than most previously published studies; however, it should be interpreted with an understanding of its limitations. Patient records were queried based on ICD and CPT coding which may not be accurately reported by providers. In addition core decompression of the hip may also be reported under CPT-27299 (“Other Procedures on the Pelvis or Hip Joint”) which is broad and therefore not included in this analysis. Second, patients were not categorized into osteonecrosis severity stages due to the limitations of ICD coding. It is possible that patients with higher staged osteonecrosis may have converted to THA sooner and skewed the data. Third, we examined multiple demographic variables, though there may be other factors not accounted for that predict conversion to THA and complications after core decompression. Fourth, there were a limited number of patients that had concurrent bone grafting so statistical analysis could not be performed. Fifth, it is unclear how many patients were lost to follow up given the limitations of the database Last, ICD coding for core decompression did not differentiate management with adjunct mesenchymal stem cells, bone grafting, nor whether the procedure was performed arthroscopically. There has been growing evidence that use of mesenchymal stem cells or bone grafting in addition to core decompression for early osteonecrosis may increase survivorship and decrease pain when compared to core decompression alone.5,10,14,20,26
5. Conclusion
There is a high failure rate following core decompression for hip osteonecrosis with 40% of patients converting to THA within 2 years. Patients between 40 and 59 had the highest rates of conversion to THA, with higher age being predictive of early conversion. While the overall complication rate is low at 90 days, patients should be counseled regarding the risk for femoral neck fracture.
Funding/sponsorship
This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.
Institutional ethical committee approval
Not required, this study did not involve human subjects.
Author contributions
Edgar Garica-Lopez: was involved with, Conceptualization, Writing - Original Draft, Formal analysis, Methodology, Writing - Review & Editing, ChristopherAnigwe: with Methodology, Formal analysis, Writing - Review & Editing, Stephanie E.Wong: with Writing - Review & Editing, Alan L.Zhang: with Writing - Review & Editing, Drew A.Lansdown: with Conceptualization, Formal analysis, Supervision, Methodology, Writing - Review & Editing.
Declaration of competing interest
None pertaining to this work, otherwise included in the ICMJE for.
Acknowledgement
None.
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