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Abstract
Purpose To evaluate the safety and effectiveness of percutaneous acetabuloplasty in treating the pain and disability related to metastatic lesions of the acetabulum.
Materials and methods This institutional review board approved retrospective study examined 11 patients who underwent percutaneous acetabuloplasty in our hospital from April 2007 to June 2010. All patients gave informed consent prior to the procedure, and all records were HIPAA compliant. Chart review was performed to collect patient demographics and to assess pre- and post-treatment patient performance on the Visual Analog Scale, Functional Mobility Scale and Analgesic Scale. Paired testing comparing the pre- and post-treatment scores for each patient was performed using the Wilcoxon signed rank test.
Results There were 11 procedures: 10 performed under CT guidance and one using fluoroscopic guidance. There was a statistically significant decrease in patient Visual Analog Scale score (p=0.001) and Functional Mobility Scale score (p=0.03) after treatment. There was no change in median Analgesic Scale scores pre- and post-treatment although paired testing revealed a trend towards reduced analgesic use postoperatively (p=0.06). There were no clinically significant complications in this series.
Conclusion Percutaneous acetabuloplasty appears to be safe and effective for improving the pain and decreased mobility secondary to metastatic lesions of the acetabulum.
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Introduction
Metastatic bone lesions commonly produce severe and debilitating pain that is poorly controlled by analgesic medication.1 Due to the presence of widespread disease, treatments for these lesions focus on palliation rather than cure.2 A common site of metastasis is the acetabulum, with approximately 45% of metastatic lesions arising in the ileum.3 Given the proximity to the hip joint, acetabular lesions produce pain with weight bearing that can significantly impair functional mobility and can predispose to pathologic fracture.
Several procedures have been used to alleviate symptoms arising from acetabular metastases. External beam radiation therapy has been demonstrated to decrease the rate of tumor growth. However, there is a marginal decrease in pain, with 20–30% of patients experiencing no pain relief at all.4 Reconstructive surgery may be effective but is not well tolerated in this patient population and carries a substantial risk of complications.5 Percutaneous ablation techniques, such as radiofrequency ablation (RFA) and cryoablation, have been shown to produce significant pain reduction but do not address the increased risk of pathologic fracture in this weight bearing region.6 Percutaneous acetabuloplasty is an image guided intervention in which acrylic cement is injected directly into the lesion in order to provide pain relief and potential structural support.6 7 Anecdotal reports suggest immediate and long term pain relief using this approach.3
In this consecutive case series, we sought to evaluate the safety of acetabuloplasty and to assess whether patients who underwent this procedure experienced a significant improvement in pain, mobility and analgesic use.
Materials and methods
This institutional review board approved retrospective study included all 11 patients who underwent percutaneous acetabuloplasty in our department from April 2007 to June 2010. Treatments were performed by two experienced interventionists (JAH, AY). Chart review was performed to collect patient demographics and to assess patient performance on the Visual Analog Scale (VAS), Functional Mobility Scale (FMS) and Analgesic Scale (AS) both pre- and post-procedure. The VAS uses a combination of illustrated faces and numbers to represent pain level on a scale from 0 to 10, with 0 representing no pain and 10 representing the worst pain the patient has ever experienced. The scale has been validated in numerous studies and represents a standard assessment of pain.8 9 Similarly, the FMS is a validated measure of patient mobility that ranges from 0 to 5, with 0 representing full activity and 5 representing a bedridden patient (table 1).10 The Analgesic Scale (AS) documents the patient's use of pain medication on a scale from 0 to 5, with 0 representing no medication use and 5 representing parenteral narcotic use (table 1). These assessments were performed during routine 3 week follow-up visits in our interventional radiology clinic. All scales were quantified through patient self-report using our standard paper questionnaire. The clinic visits were conducted by our nurse practitioner in conjunction with the treating physician. All records were HIPAA compliant.
Description of the Functional Mobility Scale and Analgesic Scale
Procedural details
Referrals for percutaneous acetabuloplasty were intended for pain relief. All patients were assessed for procedural risk using CT or MR imaging to evaluate lesion extent, including cortical destruction of the articular surface as well as proximity of neurovascular structures. Lesions that were predominantly sclerotic were not treated due to anticipated difficulty of needle placement. All patients gave informed procedure consent. Four acetabuloplasty procedures in this series were previously described in a short case report.7
Of the 11 cases evaluated in this study, 10 were performed under CT guidance. The first case in this series was performed using fluoroscopic guidance due to the patient's short stature which allowed her to fit within the biplane fluoroscopy system. The first six cases were done under general anesthesia with endotracheal intubation. With increased operator experience and comfort with the procedure, the remaining cases were performed using intravenous moderate sedation (combined fentanyl and midazolam in appropriate dosages). All patients received intravenous antibiotics (cefazolin or clindamycin) prior to the procedure. Seven patients were positioned supine, two prone and two semi-prone oblique based on lesion location and needle approach. Needle placement into the acetabulum was via an anterolateral or lateral approach in order to avoid damage to either the sciatic nerve or femoral artery and vein (see figure 1).
(A) Axial T1 weighted image of a right acetabular metastasis (red arrow) demonstrating the location of the right sciatic nerve (green arrows) immediately posterior to the acetabulum. (B) Axial T1 weighted image of the left acetabulum in another patient demonstrating the anteromedial location of the femoral artery (green arrows) and vein in relation to the acetabular metastasis (red arrow).
In the CT guided procedures, an intraprocedural scan was performed in order to plan the needle approach and mark the skin entry site for placement of the trocar. Local anesthesia was used at the entry site with either 0.25% bupivacaine or 1% lidocaine (with 2% bicarbonate). The periosteum was also anesthetized via a 20 gauge spinal needle. Eleven or 13 gauge straight needles were placed into the lesion using intermittent CT scanning. In one case, a biopsy was performed using a 15 gauge biopsy needle to confirm the pathology. After needle placement, polymethyl methacrylate (PMMA) was mixed and injected through the trocar into the lesion using a screw injector with intermittent CT scanning to assess cement distribution and unwanted cement migration. There was no explicit criterion for adequate cement filling within the lesion although in general we sought filling of the weight bearing surface and at least 50% of the lesion. Post-procedure CT images were used to evaluate final filling of the lesion and to look for potential complications, such as cement extravasation into the joint space or soft tissues. Figures 2 and 3 demonstrate various stages of the procedure.
CT images of the left acetabulum reveal a lytic lesion (arrow) with preservation of the articular cortex. (A) Coronal view. (B) Axial view. (C) Sagittal view.
CT guided percutaneous acetabuloplasty. (A) Anterolateral approach of the needle into the lytic metastasis. (B) Injection of polymethyl methacrylate cement into the anterior aspect of the lesion. (C) Lateral entrance of a second needle into the posterior aspect of the metastasis. (D) Final cement filling within the majority of the lytic lesion.
Early in our experience, we performed RFA just prior to cement placement in one case. This patient underwent a second acetabuloplasty 5 months later for the same lesion to provide more complete cement filling within the lesion. For the second procedure, the indication on the part of the referring physician was to provide further structural stabilization, rather than pain relief. Therefore, only the first procedure was included in the analysis. No other ablation procedures were performed in this series due to the perceived lack of added benefit on the part of the operators.
Statistical analysis
Continuous variables such as age were tested for normality using the Kolmogorov–Smirnov test. Summary statistics were given as mean±SD for normal data or median (IQR) for non-normally distributed data. Ordinal variables such as the VAS, FMS and AS scores were reported as median (IQR). Paired testing comparing the pre- and post-treatment scores for each patient was performed using the Wilcoxon signed rank test. Categorical variables were reported as percentages. Statistical significance was defined as p<0.05. Statistical analysis was performed with MedCalc software V.11.0 (Mariakerke, Belgium).
Results
Table 2 lists the demographic and clinical data for the study cohort. The patient cohort was 36.4% (4/11) female and had an average age of 62.1±14.5 years. All acetabular bone lesions were metastatic, with non-small cell lung cancer (two patients) and renal cell carcinoma (two patients) occurring most frequently. Seven procedures were performed on the right acetabulum.
Summary data for 11 patients who underwent percutaneous acetabuloplasty, including pre- and post-treatment Visual Analog, Functional Mobility and Analgesic Scale scores
All patients underwent successful cement placement within their acetabular lesions. In patient No 1, severe muscle cramping after placement onto the CT table led to termination of the planned procedure. This patient returned 2 days later and underwent successful acetabuloplasty. Otherwise, all procedures were void of complications.
Table 2 lists the pre- and post-treatment VAS, FMS and AS scores for each patient. The average time to follow-up was 20.9±11.4 days. The median pre- and post-treatment VAS scores were 7 (IQR 5.25–8) and 1 (IQR 0–1.75), respectively. In paired analysis, there was a statistically significant decrease in patient VAS scores (improved pain) after treatment (p=0.001). All patients reported an improvement in pain, with nine (81.8%) patients having a final VAS score of ≤2.
The median pretreatment FMS score was 2 (IQR 2–3) compared with the median post-treatment score of 1 (IQR 0.25–2). There was a statistically significant decrease in FMS score (increased mobility) within patients (p=0.03), with six (54.5%) reporting an increase in their mobility while the remaining patients reported no change.
There was no change in the median AS scores pre- (4 (IQR 4–4)) and post-treatment (4 (IQR1–4)). However, there was a trend towards reduced within patient analgesic use (p=0.06). Five (45.5%) patients reported a decrease in their analgesic use, four of whom were able to discontinue oral narcotic medication. Six (54.5%) patients reported no change. A graphical representation of the above data can be seen in figure 4.
Within patient changes in (A) Visual Analog Scale, (B) Functional Mobility Scale and (C) Analgesic Scale scores from pre- to post-treatment.
Discussion
This consecutive case series supports the safety and clinical effectiveness of percutaneous acetabuloplasty for improving the pain and decreased mobility secondary to metastatic lesions of the acetabulum. Specifically, there was a statistically significant reduction in within patient VAS and FMS scores following acetabuloplasty. Furthermore, there was a trend towards decreased analgesic use.
The treatment effect was most pronounced for pain relief, with all patients reporting improvement. For mobility and analgesic use, improvements were seen in approximately half of the cases. While the modest improvement in analgesic requirement appears discrepant with the dramatic pain response, it may be that our patients required analgesic medication, in some measure, for their systemic disease. As such, analgesic use may not be an accurate indicator of acetabular pain status.
Our findings confirm previous anecdotal reports of pain improvement following acetabuloplasty,7 11–13 and are in agreement with a recent study demonstrating statistically significant improvements in pain and hip function following cement placement.14 All patients in that study experienced pain reduction, with complete pain relief in 59%. Similar to these studies, we have found that pain relief is durable for at least several weeks following the procedure (mean follow-up 20.9±11.4 days). The mechanism of pain relief is unclear but may be related to PMMA mediated tumor eradication or neurolysis of pain fibers. It has also been proposed that cement reconstruction of the weight bearing portion of the joint results in improved biomechanics and pain.15 This idea is supported by our findings of increased patient mobility post-procedure.
Importantly, there were no clinically significant complications in our series. Previously reported complications include transient local pain, venous cement injection and cement extravasation into the joint space and the soft tissues.14 Cement leakage into the joint space is of foremost concern, especially when the articular cortex is compromised. Careful observation is critical during cement injection, and injection should be stopped as soon as leakage is observed. Fluoroscopy allows real time visualization during cement placement while CT guidance requires intermittent imaging after small injections of PMMA. Other potential complications of the procedure include injury to neurovascular structures and infection, which may be prevented by using a lateral needle approach, sterile operative technique and antibiotics.
Another percutaneous treatment option is RFA, which has been shown to significantly reduce pain from lytic metastatic lesions, including those in the acetabulum.4 However, ablation techniques do not address the increased risk of pathologic fracture in weight bearing regions such as the acetabulum. Cement placement has the theoretic advantage of structural stabilization, which is the primary reason for choosing acetabuloplasty over these other percutaneous approaches.6 14 In our limited follow-up period, there were no instances of pathologic fractures despite increased weight bearing.
RFA may be combined with percutaneous acetabuloplasty and is thought to improve cement filling and decrease cement extrusion by creating an ablation cavity for cement injection.7 16 This approach was used in one patient in this series. A recent study reported on 53 combined RFA and cementoplasty procedures, of which 14 were in the acetabulum.17 The authors found a significant improvement in within patient pain. However, no comparisons were made to RFA or cementoplasty alone. Furthermore, there were 19 instances of cement leakage, with two during acetabular treatment. One case was an asymptomatic cement extravasation into the joint space and in the other case cement contacted the sciatic nerve resulting in transient sensory disturbance and leg weakness.
Other management options for acetabular metastases include external beam radiation therapy and open reconstructive surgery. However, their efficacy remains controversial.5 11 18 19 Furthermore, radiation therapy does not adequately address the weakened bone leaving a persistent risk for pathologic fracture, while open surgery carries a significant risk of complications and morbidity, and may not be well tolerated in severely debilitated cancer patients.5 20 The decision to pursue these therapies is highly dependent on the patient's medical condition and the location of the lesion.21
Our study is limited primarily by the small sample size. However, despite this, we were able to demonstrate significant improvements in pain and mobility. An additional limitation is the variable and short term follow-up. Previous studies have demonstrated pain relief for up to 2 years following percutaneous acetabuloplasty.22 Finally, the lack of a concurrent control group prevents us from assessing potential mechanisms of pain relief and improvement in disability.
Acetabuloplasty appears to be an effective palliative treatment tool for improving the pain and disability related to acetabular metastatic lesions. With adequate imaging and technique, it carries a low risk of complications, making it an attractive treatment option for patients with systemic malignancies who are often poor candidates for open reconstructive procedures.
References
Footnotes
Linked article 005082.
Competing interests Joshua Hirsch is a consultant for CareFusion. CareFusion makes products that could be used in acetabuloplasty.
Ethics approval This study was conducted with the approval of the Massachusetts General Hospital Institutional Review Board.
Provenance and peer review Not commissioned; externally peer reviewed.