The epidemiology of revision total hip arthroplasty in the United States

Combining C-reactive protein and interleukin-6 may be useful to detect periprosthetic hip infection

BACKGROUND

The sensitivity and specificity to detect periprosthetic infection of the different methods have been questioned, and no single laboratory test accurately detects infection before revision arthroplasty.

QUESTIONS/PURPOSES

We asked whether preoperative C-reactive protein (CRP) and interleukin-6 (IL-6) could lead to similar sensitivity, specificity, and predictive values as our previous results obtained with intraoperative frozen section (FS) in revision total hip arthroplasty (THA).

METHODS

We prospectively followed 69 patients who had undergone revision THA for failure of a primary THA. The definitive diagnosis of an infection was determined on the basis of positive histopathologic evidence of infection or growth of bacteria on culture.

RESULTS

Eleven of the 69 hips were infected. The combination of an elevated CRP and IL-6 was correlated with deep infection in all the cases and showed a sensitivity of 0.57 (0.13-1.00), a specificity of 1.00 (0.99-1.00), a positive predictive value of 1.00 (0.87-1.00), and a negative predictive value of 0.94 (0.87-1.00). FS showed a sensitivity of 0.81 (0.54-1.00), a specificity of 0.98 (0.94-1.00), a positive predictive value of 0.90 (0.66-1.00), and a negative predictive value of 0.96 (0.91-1.00). Combining CRP and IL-6 provided similar sensitivity, specificity, and positive predictive values as the FSs.

CONCLUSIONS

Our data suggest the combination of CRP and IL-6 would be a useful serologic tool to complement others when diagnosing periprosthetic infection.

Prevalence and projections of total shoulder and elbow arthroplasty in the United States to 2015

HYPOTHESIS

This study examined national trends and projections of procedure volumes and prevalence rates for shoulder and elbow arthroplasty in the United States (U.S.). This study hypothesized that the growth in demand for upper extremity arthroplasty will be greater than the growth in demand for hip and knee arthroplasty and that demand for these procedures will continue to grow in the immediate future.

MATERIALS AND METHODS

The Nationwide Inpatient Sample (1993-2007) was used with U.S. Census data to quantify primary arthroplasty rates as a function of age, race, census region, and gender. Poisson regression was used to evaluate procedure rates and determine year-to-year trends in primary and revision arthroplasty. Projections were derived based on historical procedure rates combined with population projections from 2008 to 2015.

RESULTS

Procedure volumes and rates increased at annual rates of 6% to 13% from 1993 to 2007. Compared with 2007 levels, projected procedures were predicted to further increase by between 192% and 322% by 2015. The revision burden increased from approximately 4.5% to 7%. During the period studied, the hospital length of stay decreased by approximately 2 days for total and hemishoulder procedures. Charges, in 2007 Consumer Price Index-adjusted dollars, increased for all 4 procedural types at annual rates of $900 to $1700.

CONCLUSION

The growth rates of upper extremity arthroplasty were comparable to or higher than rates for total hip and knee procedures. Of particular concern was the increased revision burden. The rising number of arthroplasty procedures combined with increased charges has the potential to place a financial strain on the health care system.

Vitamin E diffused, highly crosslinked UHMWPE: a review

Highly crosslinked UHMWPE has become the bearing surface of choice in total hip arthroplasty. First generation crosslinked UHMWPEs, clinically introduced in the 1990s, show significant improvements compared to gamma sterilised, conventional UHMWPE in decreasing wear and osteolysis. These crosslinked UHMWPEs were thermally treated (annealed or melted) after irradiation to improve their oxidation resistance. While annealing resulted in the retention of some oxidation potential, post-irradiation melted UHMWPEs had reduced fatigue strength due to the crystallinity loss during melting. Thus, the stabilisation of radiation crosslinked UHMWPEs by the diffusion of the antioxidant vitamin E was developed to obtain oxidation resistance with improved fatigue strength by avoiding post-irradiation melting. A two-step process was developed to incorporate vitamin E into irradiated UHMWPE by diffusion to obtain a uniform concentration profile. Against accelerated and real-time aging in vitro, this material showed superior oxidation resistance to UHMWPEs with residual free radicals. The fatigue strength was improved compared to irradiated and melted UHMWPEs crosslinked using the same irradiation dose. Several adverse testing schemes simulating impingement showed satisfactory behaviour. Peri-prosthetic tissue reaction to vitamin E was evaluated in rabbits and any effects of vitamin E on device fixation were evaluated in a canine model, both of which showed no detrimental effects of the inclusion of vitamin E in crosslinked UHMWPE. Irradiated, vitamin E-diffused, and gamma sterilised UHMWPEs have been in clinical use in hips since 2007 and in knees since 2008. The clinical outcome of this material will be apparent from the results of prospective, randomised clinical studies.

Transient subluxation of the femoral head after total hip replacement

Dislocation is a common and well-studied complication after total hip replacement. However, subluxation, which we define as a clinically recognised episode of incomplete movement of the femoral head outside the acetabulum with spontaneous reduction, has not been studied previously. Out of a total of 2521 hip replacements performed over 12 years by one surgeon, 30 patients experienced subluxations which occurred in 31 arthroplasties. Data were collected prospectively with a minimum follow-up of two years. Subluxation occurred significantly more frequently after revision than after primary hip replacement, and resolved in 19 of 31 cases (61.3%). In six of the 31 hips (19.4%) the patient subsequently dislocated the affected hip, and in six hips (19.4%) intermittent subluxation continued. Four patients had a revision operation for instability, three for recurrent dislocation and one for recurrent subluxation. Clinical and radiological comparisons with a matched group of stable total hips showed no correlation with demographic or radiological parameters.

Patients with subluxing hips reported significantly more concern that their hip would dislocate, more often changed their behaviour to prevent instability and had lower postoperative Harris hip scores than patients with stable replacements.

Use of morphometry to quantify osteolysis after total hip arthroplasty

BACKGROUND

Progressive osteolysis threatens the longevity of hip arthroplasties and radiographic review is recommended. Measurement of osteolytic lesions in a clinical setting has not been achieved easily in the past. Other radiologic investigations provide accurate information but cost and risk to the patient prohibit their use in routine review.

QUESTIONS/PURPOSES

We developed a simple, reliable tool to be used in hip arthroplasty review to quantify osteolytic changes seen on plain film radiographs.

METHODS

A morphometric grid was developed and tested on simulated and actual osteolytic lesions. Four health professionals measured lesions on each of two occasions. Intraclass correlation coefficients (ICC) for interobserver and intraobserver reliabilities were calculated and Bland-Altman plots were constructed for graphic analysis.

RESULTS

The ICCs for interobserver reliability on the simulated and actual osteolytic lesions were in the range 0.90 to 0.96. The values for intraobserver (test-retest) reliability were 0.97 to 0.98. The Bland-Altman plots confirmed agreement and in each case, proximity of the mean to zero indicated no significant bias.

CONCLUSIONS

The data show a morphometric grid is reliable for measuring osteolytic changes after hip arthroplasty.

CLINICAL RELEVANCE

This tool has potential to improve monitoring processes for hip arthroplasty and to be useful in future research studies. Additional work is needed to test for validity and clinical importance of the measurements obtained.

The acceleration of implant osseointegration by liposomal Wnt3a

The strength of a Wnt-based strategy for tissue regeneration lies in the central role that Wnts play in healing. Tissue injury triggers local Wnt activation at the site of damage, and this Wnt signal is required for the repair and/or regeneration of almost all tissues including bone, neural tissues, myocardium, and epidermis. We developed a biologically based approach to create a transient elevation in Wnt signaling in peri-implant tissues, and in doing so, accelerated bone formation around the implant. Our subsequent molecular and cellular analyses provide mechanistic insights into the basis for this pro-osteogenic effect. Given the essential role of Wnt signaling in bone formation, this protein-based approach may have widespread application in implant osseointegration.

Unexplained pain after THR: what should i do?

Early causes of hip pain within the first year of total hip replacement (THR) include failure of fixation, infection, instability, other sources of pain (eg, lumbar spine), and mechanical dysfunction such as psoas tendon impingement or other soft tissue irritation. Metal-on-metal THRs may present with pain due to hypersensitivity within the first 1 to 3 years after arthroplasty. Late causes of pain include loosening, wear reactions, or mechanical dysfunction such as subluxation associated with wear of the articular couple. Late hematogenous infection is often sudden in onset, but may be subtle. Other sources of pain such as spinal stenosis or lumbar degenerative disk disease may also present as hip pain. Evaluation of the painful hip should start with a careful history: is the current pain similar or different to the preoperative symptoms? A review of the preoperative radiographs will provide clues as to the extent of the pathology, and if not obvious, may suggest other sources for the pain syndrome. Careful comparison of serial radiographs is necessary to identify loosening. Serologic tests should include a sedimentation rate and C-reactive protein; if both are elevated, aspiration of the joint under radiograph control for culture is indicated. In the absence of abnormalities in the studies described above, serial Technetium bone scans performed every 6 to 12 months may suggest loosening if progressive increases in uptake are observed about a component. Malposition of the acetabular component may be associated with psoas tendon impingement (symptomatic with active flexion of the hip) and may be confirmed by computed tomography scan or a psoas tenosynogram. Hypersensitivity of metal-on-metal THRs should be suspected in the presence of early (subtle) osteolysis, and the presence of predominantly mononuclear cells on the sterile aspirate. Perseverance and patience are encouraged in the pursuit of an accurate diagnosis, and objective analysis of the data is necessary. Do not operate without sufficient cause.

A mouse model of post-arthroplasty Staphylococcus aureus joint infection to evaluate in vivo the efficacy of antimicrobial implant coatings

BACKGROUND

Post-arthroplasty infections represent a devastating complication of total joint replacement surgery, resulting in multiple reoperations, prolonged antibiotic use, extended disability and worse clinical outcomes. As the number of arthroplasties in the U.S. will exceed 3.8 million surgeries per year by 2030, the number of post-arthroplasty infections is projected to increase to over 266,000 infections annually. The treatment of these infections will exhaust healthcare resources and dramatically increase medical costs.

METHODOLOGY/PRINCIPAL FINDINGS

To evaluate novel preventative therapeutic strategies against post-arthroplasty infections, a mouse model was developed in which a bioluminescent Staphylococcus aureus strain was inoculated into a knee joint containing an orthopaedic implant and advanced in vivo imaging was used to measure the bacterial burden in real-time. Mice inoculated with 5x10(3) and 5x10(4) CFUs developed increased bacterial counts with marked swelling of the affected leg, consistent with an acute joint infection. In contrast, mice inoculated with 5x10(2) CFUs developed a low-grade infection, resembling a more chronic infection. Ex vivo bacterial counts highly correlated with in vivo bioluminescence signals and EGFP-neutrophil fluorescence of LysEGFP mice was used to measure the infection-induced inflammation. Furthermore, biofilm formation on the implants was visualized at 7 and 14 postoperative days by variable-pressure scanning electron microscopy (VP-SEM). Using this model, a minocycline/rifampin-impregnated bioresorbable polymer implant coating was effective in reducing the infection, decreasing inflammation and preventing biofilm formation.

CONCLUSIONS/SIGNIFICANCE

Taken together, this mouse model may represent an alternative pre-clinical screening tool to evaluate novel in vivo therapeutic strategies before studies in larger animals and in human subjects. Furthermore, the antibiotic-polymer implant coating evaluated in this study was clinically effective, suggesting the potential for this strategy as a therapeutic intervention to combat post-arthroplasty infections.

Septic versus aseptic hip revision: how different?

Background

The few available studies directly comparing aseptic and septic joint revision surgery report conflicting results. We investigated whether two-stage revision of septic hip prosthesis with a preformed antibiotic-loaded spacer and an uncemented prosthesis provides hip function and quality of life similar to those provided by aseptic revision surgery in the medium term, as well as the associated direct hospital costs.

Materials and methods

We prospectively evaluated the hip function (Harris hip score) and quality of life (WOMAC and SF-12 scores) of 80 patients who underwent one-stage revision for aseptic loosening (Group A, 40 patients) or two-stage revision for septic total hip prostheses (Group S, 40 patients). Patients were matched for gender, age, and bone loss. A preformed antibiotic-loaded cement spacer was used for two-stage revision, and uncemented modular prostheses were implanted at revision in both groups. The minimum follow-up was 2 years (average 4 years; range 2–6 years).

Results

We found no difference in infection recurrence or aseptic loosening rate in the two groups. Average Harris hip score increased similarly in both groups: from 19.1 to 74.0 in Group A versus 15.0–71.2 in Group S. Patient-reported quality-of-life questionnaires (SF-12 and WOMAC) at last follow-up were similar postoperatively, but the complication rate for Group S was twice that of Group A (20.8 versus 10%). Mean overall hospital-related costs of two-stage procedures were 2.2 times greater than those for aseptic revisions.

Conclusions

Two-stage revision for infected hip prostheses, using a preformed antibiotic-loaded cement spacer and uncemented revision prosthesis, offers a success rate comparable to noninfected revisions in the medium term but is associated with a higher complication rate and costs.

Risk of complication and revision total hip arthroplasty among Medicare patients with different bearing surfaces

BACKGROUND

To address the long-term problems of bearing surface wear and osteolysis associated with conventional metal-polyethylene (M-PE) total hip arthroplasty (THA), metal-metal (M-M), and ceramic-ceramic (C-C) bearings have been introduced. These bearing surfaces are associated with unique risks and benefits and higher costs. However the relative risks of these three bearings in an older population is unknown.

QUESTIONS/PURPOSES

We compared the short-term risk of complication and revision THA among Medicare patients having a primary THA with metal-polyethylene (M-PE), metal-metal (M-M), and ceramic-ceramic (C-C) bearings.

METHODS

We used the 2005 to 2007 100% Medicare inpatient claim files to perform a matched cohort analysis in three separate cohorts of THA patients (M-PE, M-M, and C-C) who were matched by age, gender, and US census region. Multivariate Cox proportional-hazards models were constructed to compare complication and revision THA risk among cohorts, adjusting for medical comorbidities, race, socioeconomic status, and hospital factors.

RESULTS

After adjusting for patient and hospital factors, M-M bearings were associated with a higher risk of periprosthetic joint infection (hazard ratio, 3.03; confidence interval, 1.02-9.09) when compared with C-C bearings (0.59% versus 0.32%, respectively). There were no other differences among bearing cohorts in the adjusted risk of revision THA or any other complication.

CONCLUSIONS

The risk of short-term complication (including dislocation) and revision THA were similar among appropriately matched Medicare THA patients regardless of bearing surface. Hard-on-hard THA bearings are of questionable value in Medicare patients, given the higher cost associated with their use and uncertain long-term benefits in older patients.

LEVEL OF EVIDENCE

Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Reasons for revision of first-generation highly cross-linked polyethylenes

Over a 10-year period, we prospectively evaluated the reasons for revision of contemporary and highly cross-linked polyethylene formulations in amulticenter retrieval program. Two hundred twelve consecutive retrievals were classified as conventional gamma inert sterilized (n = 37), annealed (Cross fire,[Stryker Orthopedics, Mahwah, NJ] n = 72), or remelted (Longevity [Zimmer ,Warsaw, Ind], XLPE[Smith and Nephew, Memphis, Tenn], Durasul [Zimmer,Warsaw, Ind] n = 103) liners. The most frequent reasons for revision were loosening (35%), instability(28%), and infection (21%) and were not related to polyethylene formulation (P = .17). Annealed and remelted liners had comparable linear penetration rates(0.03 and 0.04 mm/y, respectively, on average), and these were significantly lower than the rate in conventional retrievals (0.11 mm/y, P ≤ .0005). This retrieval study including first-generation highly cross linked liners demonstrated lower wear than conventional polyethylene. Although loosening remained as the most prevalent reason for revision, we could not demonstrate a relationship between wear and loosening.The long-term clinical performance of first-generation highly cross-linked liners remains promising based on the midterm outcomes of the components documented in this study [corrected].

Retrospective analysis of infection rate after early reoperation in total hip arthroplasty

BACKGROUND

Infection is a devastating complication of total hip arthroplasty (THA). Unavoidable reoperation during the acute recovery phase of hip arthroplasty has the potential for an increased infection rate but the risk is not well established nor is the fate of these infected hips.

QUESTIONS/PURPOSES

We therefore report the infection rate for patients undergoing THA who returned to the operating room within 90 days of his or her index procedure for any surgical intervention on the same hip.

METHODS

We identified 60 patients undergoing THA referred to or treated at our institution who required an unplanned and unavoidable return to the operating room during the acute recovery phase. The complications of the initial surgery that resulted in reoperation included instability, periprosthetic fracture, retained hardware, and nerve exploration. We then retrospectively reviewed the medical records to determine the infection rate and implant survivorship. The minimum followup was 1 month (average, 3.7 years; range, 1 month to 7 years) and included all patients who required resection before a minimum 2-year followup.

RESULTS

The infection rate for this cohort was 20 of 60 (33%). Six of these 20 retained their implants at 2 years after the reoperation and were considered infection-free. Two-stage reimplantation or resection was eventually performed in 14 of the infected patients.

CONCLUSIONS

A high percentage of patients undergoing THA developed a deep infection after unavoidable reoperation during the acute recovery phase. The reasons for the reoperations were potentially modifiable complications and situations that deserve further investigation to delineate protocols to minimize the risk of infection in these patients.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Minimal incision surgery as a risk factor for early failure of total hip arthroplasty

BACKGROUND

Minimal incision total hip arthroplasty (MI THA) techniques were developed to decrease postoperative pain and recovery time. Although these techniques have increased in popularity, the long-term survivorship of these procedures is unknown.

QUESTIONS/PURPOSES

We therefore investigated whether the time to revision in our referral practice was shorter for patients who underwent primary MI THA compared to primary traditional THA.

METHODS

We retrospectively reviewed 46 revision THAs performed during a 3-year period. We excluded revisions performed for infection and rerevisions. Patients with incisions less than or equal to 10 cm were defined as having had MI THA. Fifteen of the 46 patients (33%) had undergone primary MI THA. At the time of primary index THA, the mean ages of the MI and non-MI patients were 65 years and 55 years, respectively.

RESULTS

The mean time to revision was 1.4 years for the MI patients compared with 14.7 years for the non-MI patients. Twelve of the 15 patients having MI THA required revision within 2 years of primary THA compared to 4 of the 31 patients without MI surgery (OR = 26.5, 95% CI 4.4-160.0). There were no differences between the groups with regard to age, gender, or body mass index. The most common reasons for revision in the MI THA group were intraoperative fracture and failure of femoral component osseointegration.

CONCLUSIONS

Our data suggest MI THA may be a risk factor for early revision surgery and the long-term survival therefore may be lower than that for non-MI surgery.

LEVEL OF EVIDENCE

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

The validity of using administrative claims data in total joint arthroplasty outcomes research

The purpose of this study was to evaluate concordance between administrative and clinical diagnosis and procedure codes for revision total joint arthroplasty (TJA). Concordance between administrative and clinical records was determined for 764 consecutive revision TJA procedures from 4 hospitals. For revision total hip arthroplasty, concordance between clinical diagnoses and administrative claims was very good for dislocation, mechanical loosening, and periprosthetic joint infection (all kappa > 0.6), but considerably lower for prosthetic implant failure/breakage and other mechanical complication (both kappa < 0.25). Similarly, for revision total knee arthroplasty diagnoses, concordance was very good for periprosthetic fracture, periprosthetic joint infection, mechanical loosening, and osteolysis (all kappa > 0.60), but much lower for implant failure/breakage and other mechanical complication (both kappa < 0.24). Concordance for TJA-specific procedure codes was very good only for revision total knee arthroplasty patellar component revisions and tibial insert exchange procedures. Total (all-component) revisions were overcoded for hips (00.70) and undercoded for knees (00.80). Improved clinical documentation and continued education are needed to enhance the value of these codes.

Early- and late-term dislocation risk after primary hip arthroplasty in the Medicare population

From 1998 to 2007 Medicare 5% national sample dataset, 39 271 primary total hip arthroplasty (THA) patients were identified. Dislocations within 2 years (early) and after 2 years (late) of primary THA were identified. Cox regression was used to evaluate patient, hospital, and procedure characteristics for risk of dislocation, and 1540 (3.92%) and 451 (1.15%) patients were diagnosed with early and late dislocations, respectively. Dislocation rate at 6 months' follow-up decreased steadily between 1998 and 2007 from 4.21% to 2.14%. Early and late dislocation risks were lower by 35% (P < .001) and 43% (P = .01), respectively, for patients operated during 2004 and 2007 compared with 1998 and 2003. Higher Charlson index scores (i.e., more comorbid conditions) and surgeon volume were significant risk factors (P < or = .04). Decrease in dislocation risks after primary THA seems to coincide with increasing use of larger diameter femoral heads. An awareness of risk factors for dislocation can help surgeons identify high-risk patients so as to prescribe appropriate intervention strategies.

Synovial fluid biomarkers for periprosthetic infection

BACKGROUND

We have previously described a unique gene expression signature exhibited by synovial fluid leukocytes in response to bacterial infection, identifying a number of potential biomarkers for infection. However, the diagnostic performance of these potential biomarkers in an immunoassay format is unknown.

QUESTIONS/PURPOSES

We therefore evaluated the sensitivity, specificity, and accuracy of several potential synovial fluid biomarkers for infection, and compared them to current standards of testing for periprosthetic infection.

METHODS

We prospectively collected synovial fluid from 14 patients classified as having a periprosthetic infection and 37 patients classified as having an aseptic failure. The synovial fluid samples were tested for 23 potential biomarkers for periprosthetic infection. We then determined differences in biomarker levels between infected and aseptic groups, then computed the sensitivity, specificity, positive predictive value, negative predictive value and accuracy for select biomarkers, and finally compared those to current standard tests for infection.

RESULTS

Twelve synovial fluid biomarkers had substantially higher average levels in the synovial fluid of infected versus aseptic patients. Synovial fluid levels of IL-1 were a mean of 258 times higher in patients with a periprosthetic infection compared to patients having revision for aseptic diagnoses. Synovial fluid IL-1 and IL-6 levels correctly classified all patients in this study with a sensitivity, specificity, positive predictive value, negative predictive value and accuracy equal to 1. Several markers tested in this study outperformed the ESR and CRP tests.

CONCLUSIONS

Patients with a periprosthetic infection have elevated levels of numerous synovial fluid biomarkers, when compared to patients with aseptic diagnoses. Several of these biomarkers exhibited nearly ideal sensitivity, specificity, and accuracy in this study, suggesting that synovial fluid biomarkers could be a valuable tool for diagnosing periprosthetic infection.

LEVEL OF EVIDENCE

Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Revision hip arthroplasty: infection is the most common cause of failure

BACKGROUND

Revision total hip arthroplasty (THA), although relieving pain and restoring function, fails in some patients. In contrast to failures in primary THA, the frequency of the causes of failure in revision THA has been less well established.

QUESTIONS/PURPOSES

We therefore determined the rate of each failure mode and the survivorship of revision THAs.

METHODS

We retrospectively reviewed the charts of 1366 revision THAs performed between 2000 and 2007. There were 609 (44.5%) men and 757 (55.5%) women with a mean age of 66 years. The indications for the revision surgery were mainly aseptic loosening (51%), instability (15%), wear (14%), and infection (8%). The minimum followup was 1 day (mean, 5.5 years; range, 1 day to 9 years).

RESULTS

Two hundred fifty-six of the revisions (18.7%) failed with an average time to failure of 16.6 months (range, 1 day to 7.5 years). Among 256 failed hips, infection was the most common cause of failure (30.2%) followed by instability (25.1%) and aseptic loosening (19.4%). At 5 years, the survivorships of septic and aseptic groups were 67% and 84.8%, respectively. Revision for infection or instability appears to have a considerably lower survivorship when compared to revision for aseptic causes.

CONCLUSIONS

The lower survivorship of revision for infection or instability highlights the importance of implementing better preventative methods that can minimize the impact of these two major causes of failure.

LEVEL OF EVIDENCE

Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Arthroscopic treatment of unstable total hip replacement

Hip arthroscopy may be useful in the diagnosis and treatment of apparently well-implanted but unstable total hip replacement prostheses. We present 2 cases of arthroscopically assisted capsular tightening in unstable total hip replacements. Both cases had significant capsular laxity. Case 2 had impingement of the lower part of the acetabulum with the lesser trochanter that caused hip dislocation. Early revision surgery can be avoided with the use of this technique in selected cases of unstable total hip replacements.

Mechanical properties, oxidation, and clinical performance of retrieved highly cross-linked Crossfire liners after intermediate-term implantation

Sixty Crossfire (Stryker Orthopaedics, Mahwah, NJ) liners were consecutively revised after an average of 2.9 years (range, 0.01-8.0 years) for reasons unrelated to wear or mechanical performance of the polyethylene. Femoral head penetration was measured directly from 42 retrievals implanted for more than 1 year. Penetration rate results (0.04 mm/y, on average; range, 0.00-0.13 mm/y) confirmed decreasing wear rates with longer in vivo times. Overall, we observed oxidation levels at the bearing surface of the 60 liners (0.5, on average; range, 0.1-1.7) comparable to those of nonimplanted liners (0.5, on average; range, 0.3-1.1) and preservation of mechanical properties. We also measured elevated oxidation of the rim (3.4, on average; range, 0.2-8.8) that was correlated with implantation time. Rim surface damage, however, was observed in only 3 (5%) of 60 cases. Retrieval analysis of the 3 rim-damaged liners did not reveal an association between surface damage and the reasons for revision.

Improving the accuracy of acetabular component orientation: avoiding malposition

Improper acetabular component orientation negatively affects the outcome of total hip arthroplasty through increasing dislocation rates, component impingement, bearing surface wear, and the number of revision surgeries. Leg length, hip biomechanics, pelvic osteolysis, and acetabular component migration are also affected by malposition. With conventional techniques, numerous variables, such as patient size, deformity and/or position, and decreased visualization, contribute to inter- and intrasurgeon acetabular component variability during surgery regardless of surgeon experience and practice volume. New acetabular component implantation techniques, such as patient-specific morphology, that incorporate anatomic landmarks may provide more accurate and individualized target zones. These techniques, coupled with the use of quantitative technology such as computer-aided navigation, may improve the precision of acetabular component placement.

National revision burden for lumbar total disc replacement in the United States: epidemiologic and economic perspectives

STUDY DESIGN

Retrospective cohort study using a nationally representative inpatient database.

OBJECTIVE

To quantify the national revision burden for lumbar total disc replacements (TDRs) in the United States following Food and Drug Administration approval, for comparison with lumbar fusion and other common orthopedic procedures, including hip and knee replacement.

SUMMARY OF BACKGROUND DATA

Previous studies of revision lumbar TDR surgery have been based on IDE studies. The epidemiology and costs of TDR revision surgery from a national perspective have not yet been reported.

METHODS

The Nationwide Inpatient Sample was used to identify primary and revision TDR and anterior fusion procedures in 2005 and 2006. Surgeries were identified in the Nationwide Inpatient Sample using ICD9-CM codes. The prevalence of TDR and fusion surgery was calculated as a function of age, gender, race, census region, primary payer class, and type of hospital. Average length of stay and total hospitalization costs were also computed for each type of procedure.

RESULTS

During the study period, there was a national total of 7172 TDR and 62,731 anterior fusion surgeries, including both primary and revisions. Overall, TDR patients were younger and had less comorbidity than fusion surgery patients. The average revision burden for lumbar TDR and anterior fusion was 11.2% and 5.8%, respectively. The average length of stay for primary lumbar TDR was significantly shorter compared to revision TDR, primary anterior fusion, and revision anterior fusion (P < 0.0001). Both the primary and the revision surgery using the TDR surgery involved significantly lower total hospital costs relative to anterior fusion surgery (P < 0.0001). Including revision, the average costs per TDR procedure were lower than anterior and posterior lumbar fusion.

CONCLUSION

Although the revision burden for TDR was significantly higher than fusion surgery, the TDR revision burden fell within the revision burden range of hip and knee replacement, which are generally considered successful and cost-effective procedures. Economically, the higher revision burden for TDRs was offset by lower costs for both the primary as well as the revision procedures relative to fusion.

Metal-on-metal hip arthroplasty: does early clinical outcome justify the chance of an adverse local tissue reaction?

Larger diameter metal-on-metal (MOM) bearing hips offer the possibility of low wear and reduced risk of dislocation. We reviewed the first 126 patients (131 hips) who had a large-head (36-mm) MOM bearing surface to report the early clinical outcome and especially to determine the occurrence of dislocation and wear-related concerns. The minimum followup was 5 years (mean, 5.6 years; range, 5-7 years). We found a 98% survivorship free of component revision. No hips had been revised for dislocation. Three hips (2%) had small femoral osteolytic lesions. Because this series of patients did not completely represent our experience with this bearing surface, we queried our database for the 828 patients (945 hips) that had the same bearing surface from April 2001 to December 2008. Three patients (0.3%) had a local reaction to the MOM bearing surface on revision-retrieved tissue. All three patients presented with elevated inflammatory indices, and a purulent-appearing joint effusion at revision. The possibility of infection and the delay in diagnosing a reaction to the MOM bearing with pathology complicated management of these three patients. We continue to use this bearing surface because the 5-year results are comparable to other bearing surfaces, however, we counsel patients that a local adverse reaction to the MOM bearing surface may be a factor contributing to reoperation.

LEVEL OF EVIDENCE

Level IV, retrospective clinical cohort. See Guidelines for Authors for a complete description of levels of evidence.

Outcomes of isolated acetabular revision

Isolated acetabular revision can be associated with variable patient outcomes; there is a risk of hip instability. We evaluated 42 isolated acetabular revision operations and investigated the impact of patient age, diagnosis, bone stock, bone loss, bone augmentation, and obesity on pain and the Harris hip score. Preoperative radiographs were graded according to Paprosky et al. Postoperative radiographs were graded according to Moore et al. and for implant position, prosthetic fixation, and osteolysis. Complications, patient outcome, reoperations, and acetabular rerevisions were recorded. All patients had complete clinical and radiographic followup with a minimum followup of 2 years (mean, 6.4 years; range, 2-13 years). The mean pain score and the mean Harris hip score improved postoperatively. There was one infection 6 months after operation. There were no dislocations. There were three acetabular rerevisions (7%) for aseptic loosening. Patient age, preoperative diagnosis, bone loss, and pelvic bone augmentation had no influence on pain or Harris hip scores. Before operation, obese patients tended to have less pain than nonobese patients but at followup obese patients had less improvement in pain scores than nonobese patients.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Influence of cement penetration and graft density on stem stability in impaction allografting: a finite element study

BACKGROUND

Excessive stem migration is often problematic after impaction allografting. The mechanisms responsible for migration are not known, but achieving a dense graft bed has traditionally been believed to be essential for stem stability. When the stem is cemented into the allograft bed, however, the graft becomes infiltrated with bone cement. Extensive cement penetration into the graft has been observed in previous studies, resulting in regions of cement-endosteum contact.

METHODS

This study explored the effects of graft density and cement penetration on stem motion using a finite element model that was validated against experimental data.

FINDINGS

Cement penetration has a considerable stabilizing effect on stem motion, whereas graft density is important only when there is no cement-endosteum contact. Stem migration can be attributed primarily to slippage at the endosteum and stem-cement interfaces rather than to shear failure within the graft.

INTERPRETATION

Partial cement penetration to the endosteum increases the likelihood of meeting clinical requirements of early implant stability, particularly when a dense graft bed cannot be achieved.

Ultrasound-based navigation and 3D CT compared in acetabular cup position

Intraoperative landmarks are used in image-free navigation systems. The ultrasound-based navigation systems try to overcome the problems of positional deviation associated with soft tissue. Our study analyzed the accuracy of ultrasound-based navigation of cup positioning compared with postoperative 3-dimensional (3D) computed tomography scans of cup positioning. Twenty-five ultrasound-navigated total hip arthroplasties (THAs) were analyzed. The difference between the intraoperative cup orientation (navigation) and the postoperative cup position (CT) was evaluated. The average difference between intraoperative navigation and postoperative CT measurements was 2.8 degrees (SD+/-1.8 degrees ) for abduction and 2.2 degrees (SD+/-1.6 degrees ) for anteversion. Therefore, we recommend ultrasound-based navigation as an exact tool for cup positioning in THA.

The dislocator, early and late: the role of large heads

Dislocation after total hip arthroplasty (THA) is a potentially devastating complication that can be difficult to manage. Many patient and mechanical factors have been associated with an increased risk of dislocation. Conservative treatments such as abduction bracing have not proven effective at treating this difficult problem. Surgical options include the use of larger femoral heads, unconstrained tripolar femoral heads, and constrained devices. While each device has its merits, there is no one-size-fits-all solution to this problem. With the development of highly cross-linked polyethylene and its superior wear characteristics and mechanical properties, the use of larger femoral heads is now available. Twenty-six hips in 25 patients who underwent revision surgery for recurrent dislocation were treated with a femoral head =/>36 mm in diameter. The direct lateral surgical approach was used in 24 hips, and the posterior and anterior supine intermuscular approaches were used in 1 hip each. One patient died 5 years after revision surgery, and 3 patients have not returned for clinical follow-up over the past 2 years. Four hips subsequently suffered a repeat dislocation, for a dislocation rate of 17%. Two patients underwent a subsequent surgery: 1 irrigation and debridement and 1 hardware removal. There have been no other revisions to date. Mean time to follow-up is 17.2 months. While the use of large femoral heads for the treatment of dislocation is warranted, continued follow-up is necessary.

Metal-metal bearing surfaces in hip arthroplasty

There is no mystery regarding the allure of metal-metal bearings: high stability and low wear potential. The special risks associated with these bearings are coming into focus and include a macrophage response to excessive metal particles (metal reactivity) and a lymphocyte-dominated reaction (metal sensitivity). The most common presentation of an adverse local tissue reaction (ALTR) is persistent pain. The incidence of ALTR has not been completely defined, but the risk appears to be increased in resurfacing, in women, and in bilateral cases. The differential diagnosis includes septic and aseptic loosening, and the evaluation should include aspiration. The diagnosis is confirmed by histological examination.

Prosthetic joint infection risk after total hip arthroplasty in the Medicare population

Periprosthetic joint infection is one of the most challenging complications of total joint arthroplasty. We evaluated the incidence of early-onset (less than 2 years) and late-onset (greater than 2 years) periprosthetic joint infection after primary total hip arthroplasty (THA). The Medicare 5% national sample data set (1997-2006) was used to longitudinally follow primary THA patients. Deep infections were identified with the International Classification of Diseases, Ninth Revision, Clinical Modification code 996.66. Kaplan-Meier survivorship curves were compiled with infection as the end point. Cox regression was used to evaluate patient and hospital characteristics. Eight hundred eighty-seven THA infections were identified from 39,929 THA patients. The incidence of infection was 1.63% within 2 years and 0.59% between 2 and 10 years. Comorbidities, sex, procedure duration, and socioeconomic status were found to be significant risk factors. This is the first study to establish the incidence and risk factors associated with early onset and delayed periprosthetic joint infection in the Medicare patient population.