Association Between Opioid Use and Patient-Reported Outcomes in a Randomized Trial Evaluating Basivertebral Nerve Ablation for the Relief of Chronic Low Back Pain.

BACKGROUND: Chronic low back pain (CLBP) is a primary indication for opioid therapy. OBJECTIVE: To evaluate the hypothesis that CLBP patients reporting reduced opioid use have superior functional outcomes following basivertebral nerve (BVN) radiofrequency ablation. METHODS: This post hoc analysis from a sham-controlled trial examined short-acting opioid use from baseline through 1 yr. Opioid use was stratified into 3 groups by two blinded external reviewers. Two-sample t-tests were used to compare Oswestry Disability Index (ODI) and Visual Analog Scale (VAS) measurements between those patients who increased or decreased their opioid usage compared to baseline. RESULTS: Actively treated patients with decreased opioid use at 12 mo had a mean ODI improvement of 24.9 ± 16.0 (n = 27) compared to 7.3 ± 9.8 (n = 18) for patients reporting increased opioid use (P < .001). In the sham arm, the improvements in ODI were 17.4 ± 16.1 (n = 19) and 1.2 ± 14.3 (n = 5; P = .053) for the patients reporting decreased vs increased opioid usage, respectively. Actively treated patients reporting decreased opioid use had a mean improvement in VAS of 3.3 ± 2.5 (n = 27) compared to 0.6 ± 1.8 (n = 18) for patients reporting increased opioid use (P < .001). In the sham arm, the improvements in VAS were 2.5 ± 2.6 (n = 19) and 1.4 ± 1.9 (n = 5; P = .374) for patients reporting decreased vs increased opioid use, respectively. CONCLUSION: Subjects undergoing BVN ablation who decreased opioid use had greater improvement in ODI and VAS scores compared with those reporting increased opioid usage. There is an association between functional benefit from BVN ablation and reduced opioid use.

Baseline and postfusion opioid burden for patients with low back pain.

OBJECTIVES: To evaluate opioid usage patterns for patients with low back pain (LBP) with and without spinal fusion surgery (fusion patients and nonfusion patients, respectively), including long-term prescriptions post fusion. STUDY DESIGN: Claims data of outpatient pharmaceutical prescriptions from privately insured patients. METHODS: The 3-year utilization, cost, and morphine milligram equivalents (MME) of opioid prescriptions were evaluated for patients with LBP with and without lumbar fusion. For fusion patients, opioid prescriptions before and after fusion, as well as prescription use 3, 6, and 12 months following fusion surgery, were analyzed. RESULTS: Thirty-one percent of patients with LBP had opioid prescriptions within the first 6 months of initial diagnosis, which increased to 42.1% within 3 years. More than twice as many fusion patients as nonfusion patients filled opioid prescriptions (87.2% vs 41.5%; P <.001). Fusion patients had 62% and 48% more days with opioid dosages of at least 50 and at least 90 MME/day, respectively, than nonfusion patients (≥50 MME/day, 84 days vs 52 days; ≥90 MME/day, 50 days vs 34 days; both P <.001). Opioid burden was greater for fusion patients following surgery. Fusion patients continued to have 2 months' supply with at least 50 MME/day and 1 month's supply with at least 90 MME/day at least 12 months following surgery. CONCLUSIONS: The opioid burden in the LBP population is high and is further elevated in those who subsequently undergo fusion surgery. Long-term opioid prescriptions persisted in 27% of fusion patients 12 months post surgery. Efforts to identify efficacious alternative therapies to treat LBP may reduce the societal burden of chronic opioid use.

Cost-effectiveness analysis of treatments for vertebral compression fractures.

BACKGROUND: Vertebral compression fractures (VCFs) can be treated by nonsurgical management or by minimally invasive surgical treatment including vertebroplasty and balloon kyphoplasty. OBJECTIVE: The purpose of the present study was to characterize the cost to Medicare for treating VCF-diagnosed patients by nonsurgical management, vertebroplasty, or kyphoplasty. We hypothesized that surgical treatments for VCFs using vertebroplasty or kyphoplasty would be a cost-effective alternative to nonsurgical management for the Medicare patient population. METHODS: Cost per life-year gained for VCF patients in the US Medicare population was compared between operated (kyphoplasty and vertebroplasty) and non-operated patients and between kyphoplasty and vertebroplasty patients, all as a function of patient age and gender. Life expectancy was estimated using a parametric Weibull survival model (adjusted for comorbidities) for 858 978 VCF patients in the 100% Medicare dataset (2005-2008). Median payer costs were identified for each treatment group for up to 3 years following VCF diagnosis, based on 67 018 VCF patients in the 5% Medicare dataset (2005-2008). A discount rate of 3% was used for the base case in the cost-effectiveness analysis, with 0% and 5% discount rates used in sensitivity analyses. RESULTS: After accounting for the differences in median costs and using a discount rate of 3%, the cost per life-year gained for kyphoplasty and vertebroplasty patients ranged from $US1863 to $US6687 and from $US2452 to $US13 543, respectively, compared with non-operated patients. The cost per life-year gained for kyphoplasty compared with vertebroplasty ranged from -$US4878 (cost saving) to $US2763. CONCLUSIONS: Among patients for whom surgical treatment was indicated, kyphoplasty was found to be cost effective, and perhaps even cost saving, compared with vertebroplasty. Even for the oldest patients (85 years of age and older), both interventions would be considered cost effective in terms of cost per life-year gained.

Mechanics of bone/PMMA composite structures: an in vitro study of human vertebrae.

The goal of this study was to provide material property data for the cement/bone composite resulting from the introduction of PMMA bone cement into human vertebral bodies. A series of quasistatic tensile and compressive mechanical tests were conducted using cement/bone composite structures machined from cement-infiltrated vertebral bodies. Experiments were performed both at room temperature and at body temperature. We found that the modulus of the composite structures was lower than bulk cement (p<0.0001). For compression at 37( composite function)C: composite =2.3+/-0.5GPa, cement =3.1+/-0.2GPa; at 23( composite function)C: composite =3.0+/-0.3GPa, cement =3.4+/-0.2GPa. Specimens tested at room temperature were stiffer than those tested at body temperature (p=0.0004). Yield and ultimate strength factors for the composite were all diminished (55-87%) when compared to cement properties. In general, computational models have assumed that cement/bone composite had the same modulus as cement. The results of this study suggest that computational models of cement infiltrated vertebrae and cemented arthroplasties could be improved by specifying different material properties for cement and cement/bone composite.

2006 Otto Aufranc Award Paper: significance of in vivo degradation for polyethylene in total hip arthroplasty.

Our research group developed an implant retrieval program to study in vivo degradation of polyethylene. We now have evidence to support our hypothesis that degradation of radiation-sterilized polyethylene occurs in the body for not only historical gamma air sterilized liners, but also for conventional gamma inert sterilized (ArCom) and annealed highly crosslinked polyethylene (Crossfire) liners as well. Our research has also led to the discovery that the most severe manifestations of in vivo oxidation typically occur in regions of the liner experiencing minimal wear, such as the rim of the component, where the body fluids (containing oxidizing species) have access to the polyethylene. Our data from historical, ArCom, and Crossfire retrievals all point to a similar scenario in which the femoral head limits the in vivo oxidation of polyethylene at the bearing surface. Consequently, provided rim impingement does not occur, and the polyethylene locking mechanisms remain relatively isolated from oxidizing fluid, in vivo oxidation does not seem to be clinically important in the first 10 years of implantation for conventional gamma sterilized polyethylene. We conclude that in vivo degradation should be included among the list of potential long-term failure modes for modular polyethylene components for total hip arthroplasty.

In vivo degradation of polyethylene liners after gamma sterilization in air.

BACKGROUND: Ultra-high molecular weight polyethylene degrades during storage in air following gamma sterilization, but the extent of in vivo degradation remains unclear. The purpose of this study was to quantify the extent to which the mechanical properties and oxidation of conventional polyethylene acetabular liners treated with gamma sterilization in air change in vivo. METHODS: Fourteen modular cementless acetabular liners were revised at an average of 10.3 years (range, 5.9 to 13.5 years) after implantation. All liners, which had been machined from GUR 415 resin, had been gamma-sterilized in air; the average shelf life was 0.3 year (range, 0.0 to 0.8 year). After removal, the components were expeditiously frozen to minimize ex vivo changes to the polyethylene prior to characterization. The average duration between freezing and testing was 0.6 year. Mechanical properties and oxidation were measured with use of the small-punch test and Fourier transform infrared spectroscopy, respectively, in the loaded and unloaded regions of the liners. RESULTS: There was substantial regional variation in the mechanical properties and oxidation of the retrieved liners. The ultimate load was observed to vary by >90% near the surface. On the average, the rim and the unloaded bearing showed evidence of severe oxidation near the surface after long-term in vivo aging, but these trends were not typically observed on the loaded bearing surface or near the backside of the liners. CONCLUSIONS: The mechanical properties of polyethylene that has been gamma-sterilized in air may decrease substantially in vivo, depending on the location in the liner. The most severe oxidation was observed at the rim, suggesting that the femoral head inhibits access of oxygen-containing body fluids to the bearing surface. This is perhaps why in vivo oxidation has not been associated with clinical performance to date.

The biomechanical effects of kyphoplasty on treated and adjacent nontreated vertebral bodies.

It remains unclear whether adjacent vertebral body fractures are related to the natural progression of osteoporosis or if adjacent fractures are a consequence of augmentation with bone cement. Experimental or computational studies have not completely addressed the biomechanical effects of kyphoplasty on adjacent levels immediately following augmentation. This study presents a validated two-functional spinal unit (FSU) T12-L2 finite element model with a simulated kyphoplasty augmentation in L1 to predict stresses and strains within the bone cement and bone of the treated and adjacent nontreated vertebral bodies. The findings from this multiple-FSU study and a recent retrospective clinical study suggest that changes in stresses and strains in levels adjacent to a kyphoplasty-treated level are minimal. Furthermore, the stress and strain levels found in the treated levels are less than injury tolerance limits of cancellous and cortical bone. Therefore, subsequent adjacent level fractures may be related to the underlying etiology (weakening of the bone) rather than the surgical intervention.

A 10-year minimum follow-up of hydroxyapatite-coated threaded cups: clinical, radiographic and survivorship analyses with comparison to the literature.

We evaluated the clinical, radiographic, and survivorship outcomes in a series of 418 threaded hydroxyapatite-coated acetabular cups (Arc2f; Osteonics, Allendale, NJ) implanted in a consecutive series of 384 patients undergoing primary total hip arthroplasty. In all cases, the cup was screwed into the prepared acetabulum. Bone screws were used to provide secondary fixation. At a minimum 10-year follow-up, 304 cups were available for analysis. The cumulative survivorship (mechanical failure as endpoint) at that time was 99.43% +/- 0.0104. Two hundred seventy-six hips were available for full clinical and radiographic review at or after the tenth anniversary. No unstable implants were noted; all implant fixation interfaces were classified as "stable bone ingrown," and the cup migration rate was zero. Based on the survivorship achieved with this implant, our results compare favorably with survivorship reported for the best cemented and cementless acetabular implant designs.

Osteolysis: a disease of access to fixation interfaces.

Long-term clinical studies of total hip replacement suggest a direct relationship between bearing wear and periprosthetic osteolysis, particularly if polyethylene wear is greater than a threshold value of 0.1 mm per year. The current clinical trend to cross-linked polyethylene and hard-to-hard bearings attempts to ensure that bearing wear remains below this threshold. Fluid pressure generated in the hip during patient activity also has been implicated in the formation of periprosthetic lesions. Pressure fluctuation measured during manipulation of the hip at revision, or the identification of modular components that pump fluid during loading, suggest cyclic pressure may be a causative factor in bone resorption. Animal studies show the adverse effect of direct pressure on osteocytes. At more than 10 years followup, the low incidence of osteolytic lesions in retrospective reviews of successful cemented and cementless implant designs suggest that osteolysis is not an inevitable consequence of particle or pressure generation in the hip. If the quality of implant fixation prohibits fluid access to the surrounding bone, the rate of osteolysis is minimal. It is evident that whether the active factor in osteolysis is pressure, wear particles, or both, adverse periprosthetic effects can be minimized if access to the fixation interfaces in the hip is denied.

A literature review of the association between wear rate and osteolysis in total hip arthroplasty.

The establishment of a polyethylene wear rate threshold for the development of osteolysis at the hip would allow surgeons to identify patients at risk for osteolysis and to implement selective, more frequent follow-up. We reviewed publications that met certain criteria for wear and osteolysis measurement. Based on this review, the incidence of osteolysis increases as the rate of wear increases. The literature indicates that osteolysis rarely is observed at a wear rate of <0.1 mm/y. We suggest that a practical wear rate threshold of 0.05 mm/y would eliminate osteolysis. This wear threshold suggests that the new cross-linked polyethylenes would reduce osteolysis, provided that in vivo wear rates mirror those observed in vitro. To facilitate future comparison of published data, we suggest that longitudinal wear studies adopt consistent edge detection-based wear measurement techniques and uniform osteolytic lesion classification and measurement schema.