The effect of hospital volume on the in-hospital complication rate in knee replacement patients.

OBJECTIVE: To examine the effect of hospital volume on in-hospital surgical outcomes for knee replacement using six years of Medicare claims data. DATA SOURCES/STUDY SETTING: The data include inpatient claims for a 100 percent sample of Medicare patients who underwent primary knee replacement during 1985-1990. We supplemented these data with information from HCFA's denominator files, the Area Resource File, and the American Hospital Association survey files. STUDY DESIGN: We estimated the probability that a patient has an in-hospital complication in the initial hospitalization for the first primary knee replacement, using a Logit model, for three definitions of complication. The models controlled for hospital volume, other hospital characteristics, patient demographics, and patient health status. We tested for the endogeneity of hospital volume. DATA COLLECTION/EXTRACTION METHODS: A panel of two orthopaedic surgeons and two internists reviewed diagnosis codes to determine whether a complication was likely, possible, or due to anemia. After removing the few observations with bad or missing data, the final population has 295,473 observations. PRINCIPAL FINDINGS: The probability of a likely in-hospital complication declines rapidly from 53 through 107 operations per year, then levels off. Statistical tests imply that hospital volume is exogenous in this patient-level data. Complication rates increased steadily through the study period. Although obesity appeared to lower the probability of a complication, a counterintuitive result, further investigation revealed this to be an artifact of the claims data limit of listing no more than five diagnoses. Controlling for this restriction reversed the effect of obesity. CONCLUSIONS: Rather than uncontrolled expansion of knee surgery to small hospitals, decentralization to regional centers where at least about 50, and preferably about 100, operations per year are assured appears to be the optimal policy to reduce in-hospital complications.

Revision rates after knee replacement in the United States.

OBJECTIVES: Each year approximately 100,000 Medicare patients undergo knee replacement surgery. Patients, referring physicians, and surgeons must consider a variety of factors when deciding if knee replacement is indicated. One factor in this decision process is the likelihood of revision knee replacement after the initial surgery. This study determined the chance that a revision knee replacement will occur and which factors were associated with revision. METHODS: Data on all primary and revision knee replacements that were performed on Medicare patients during the years 1985 through 1990 were obtained. The probability that a revision knee replacement occurred was modeled from data for all patients for whom 2 full years of follow-up data were available. Two strategies for linking revisions to a particular primary knee replacement for each patient were developed. Predictive models were developed for each linking strategy. ICD-9-CM codes were used to determine hospitalizations for primary knee replacement and revision knee replacement. RESULTS: More than 200,000 hospitalizations for primary knee replacements were performed, with fewer than 3% of them requiring revision within 2 years. The following factors increase the chance of revision within 2 years of primary knee replacement: (1) male gender, (2) younger age, (3) longer length of hospital stay for the primary knee replacement, (4) more diagnoses at the primary knee replacement hospitalization, (5) unspecified arthritis type, (6) surgical complications during the primary knee replacement hospitalization, and (7) primary knee replacement performed at an urban hospital. CONCLUSIONS: Revision knee replacement is uncommon. Demographic, clinical, and process factors were related to the probability of revision knee replacement.

Patient outcomes after knee replacement.

A prospective, observational cohort investigation was performed to help understand the impact of knee replacement on patients with knee osteoarthritis in community practice. Of those, 291 patients (330 knees) were eligible and willing to participate. Forty-eight orthopaedic surgeons referred 563 patients from 25 institutions within the state of Indiana. Demographics, patient completed health status, satisfaction, independent radiographic measures, surgeon reported intraoperative factors, hospital discharge factors, and independent physical examinations were recorded. A minimum 2-year followup was obtained in 92% of the patients. At followup, 88% were satisfied, 3% were neutral, and 9% were dissatisfied with the results of their knee surgery. The physical composite score improved from 27.4 +/- 0.4 (range, 13.3-50.3) to 37.7 +/- 0.7 (range, 12.9-61.3) at two years. Maximal improvement in physical composite score was seen in patients who had their surgery performed in institutions that performed greater than 50 knee replacements per year in patients with Medicare insurance; who had a better mental health status at baseline; who had surgery performed on Monday, Friday, or Saturday; who were older; who were treated with a posterior cruciate sparing device; and who had worse preoperative function. A lower likelihood of complications were found with surgeons who performed greater than 20 knee replacements per year; midweek surgeries; in patients with more severe preoperative knee dysfunction; patients with fewer comorbidities; patients with less preoperative stiffness; patients being treated by younger surgeons; and in patients undergoing unilateral knee replacement. Among voluntarily participating physicians, knee replacement can be a highly effective medical technology with high levels of patient satisfaction and low rates of complications.

Demographic variation in the rate of knee replacement: a multi-year analysis.

OBJECTIVE: The aim of this study is to describe the practice variation of knee replacements (KRs) in the elderly ( > or = 65) over time from 1985-1990 in terms of the number of primary, bilateral, and revision KRs; the extent of large area variation in performance rates; and the degree to which demographic variables are the determinants of area rates. DATA SOURCES/STUDY SETTING: Data analyzed are from every hospital in the United States that performed a KR on a Medicare patient during the study period. Data were obtained from the MEDPAR, HISKEW, and denominator files of the Medicare Statistical System. STUDY DESIGN: This is a cohort study of all Medicare beneficiaries who received a KR between 1985 and 1990. The dependent variable in the analyses was the count of the KRs performed in each area. DATA COLLECTION/EXTRACTION METHODS: This is a population-based sample of Medicare enrollees in the United States. All hospitalizations for Medicare-reimbursed KRs were included in the initial data set. Exclusion criteria were used to identify the Medicare covered population with a definite KR. These criteria resulted in 7.3 percent exclusions and a final set of 414,079 KR hospitalizations. PRINCIPAL FINDINGS: The number of Medicare-funded KRs increased in each of the study years corresponding to an annual rate of increase of 18.45 percent. The likelihood of receiving a KR was a function of age, gender, and race. For each year, KRs were almost-twice as likely to be performed on women than on men. The odds of whites getting the surgery were over 1.5 times greater than for blacks. Even after adjusting for demographic factors, significant regional variation remained. CONCLUSIONS: Much about area variation and the rate of growth in KR rates remains unexplained. For answers to emerge, better data and different types of studies are required.

Prosthetic component failures in hip arthroplasty surgery.

A survey was conducted of the entire membership of the American Association of Hip and Knee Surgeons to determine their experience with total hip arthroplasty (THA) device-related failures. Forty-seven percent of the membership reviewed their preceding 5-year clinical experience and returned the survey instrument. The aggregate 5-year volume encompassed experience with more than 60,000 hip arthroplasties. The median 5-year experience per respondent was 200 metal-based sockets and 214 metal stems. The frequency distribution of the number of hip arthroplasties per respondent was skewed to the right, with fewer surgeons reporting the higher volumes of arthroplasties. In aggregate, 60,115 of the acetabular components used were metal backed. Nonmetal acetabular component usage totaled 3,219. Complete polyethylene failure was defined as fracture or complete wear through of the polyethylene portion of the component. Complete polyethylene failure was seen in 172 metal-backed sockets (29/10,000). Seventy-seven all-polyethylene sockets had complete polyethylene failure (239/10,100). A total of 87 THAs were revised for modular acetabular dissociations for a dissociation rate of 15/10,000. In aggregate, 64,483 metal-stemmed components were used. Femoral stem fractures occurred in 172 for a rate of 27/10,000. A total of 56,965 metallic femoral components were reported as being modular. Dissociation between the femoral head and neck was uncommonly seen (3/10,000). Use of ceramic femoral heads was low (5,023); however, a total of 11 ceramic head fractures were revised in the 5-year period for a failure rate of 22/10,000. The risks of catastrophic prosthetic THA failure are low but vary according to hip component and the manufacturer of the part.

Patient outcomes following unicompartmental or bicompartmental knee arthroplasty. A meta-analysis.

The purpose of this study was to summarize the literature describing patient outcomes following unicompartmental and bicompartmental knee arthroplasty. Original studies were included in this meta-analysis if they enrolled 10 or more patients at the time of an initial knee arthroplasty and measured patient outcomes using a global knee rating scale. Forty-six studies on unicompartmental prostheses and 18 studies on bicompartmental prostheses met these criteria. For unicompartmental studies, the total number of enrolled patients was 2,391, with a mean enrollment of 47 patients and a mean follow-up period of 4.6 years. The mean patient age was 66 years; 67% were women, 75% had osteoarthritis, and 16% underwent bilateral knee arthroplasty. The mean postoperative global rating scale score was 80.9. The overall complication rate was 18.5% and the revision rate was 9.2%. Studies published after 1987 reported better outcomes, but also tended to enroll older patients and patients with osteoarthritis and higher preoperative knee rating scores. For bicompartmental studies, the total number of enrolled patients was 884, with a mean enrollment of 44 patients and a mean follow-up period of 3.6 years. The mean patient age was 61 years; 79% were women, 31% had osteoarthritis, and 29% underwent a bilateral arthroplasty. The mean postoperative global rating scale score was 78.3. The overall complication rate was 30% and the revision rate was 7.2%. Although bicompartmental studies reported lower mean postoperative global rating scale scores, these studies tended to enroll patients with worse preoperative knee rating scores. Recent improvements in patient outcomes following unicompartmental knee arthroplasty appear to be due, at least partially, to changes in patient selection criteria. Patient outcomes appear to be worse for bicompartmental arthroplasties than for other prosthetic designs; however, patients enrolled in these studies had more poorly functioning knees before surgery and actually had greater absolute improvements in global knee rating scores.

A biomechanical comparison of techniques of flexor tendon repair.

Achieving satisfactory digital motion after suturing severed flexor tendons remains a challenge. Although a suture technique proposed by Savage is stronger in vitro than a true Kessler repair, the Savage technique has not been previously tested in vivo. We repaired 96 severed canine tendons using either of two modifications of the Kessler technique or the Savage technique. The tensile strength of these repairs were compared at 0, 1, 3, and 6 weeks after suturing. The Savage technique provided a significantly stronger repair than the "suture locking" method in vitro and at 1 and 3 weeks after repair. We found no significant differences between the tensile strengths of the Kessler-Tajima and suture-locking methods at any time.

Tricompartmental knee replacement. A comparison of orthopaedic surgeons' self reported performance rates with surgical indications, contraindications, and expected outcomes. Knee Replacement Patient Outcomes Research Team.

The chance of a person with osteoarthritis of the knee receiving a knee replacement is highly variable. To understand better the reasons for this variation, all practicing orthopaedists in Indiana were surveyed about their management of severe knee osteoarthritis and their perception of tricompartmental knee replacement as a therapeutic option. Their perceptions of indications and outcomes of knee replacement were compared with the self reported annual number of patients for whom they performed (or referred to other surgeons for) tricompartmental knee replacements. A completed survey was returned by 220 (79%) of the 280 orthopaedists surveyed; analyses were limited to the 188 respondents who had cared for at least one patient with osteoarthritis of the knee in the prior 2 weeks (mean = 13). These surgeons reported performing (or referring patients for) a mean of 31 knee replacements in the prior year (SD 45, median 21, range 0-480 knee replacements). There was strong agreement (> 95%) among respondents for seven (21%) of 33 surgical indications and contraindications, and more general agreement (> 60%) for 21 (64%). In the five factors (15%) for which there was disagreement, there was no consistent relationship between opinions and self reported knee replacement performance rate. Surgeons reporting more knee replacements had significantly higher estimates of pain relief and functional improvement following surgery, and lower estimates of prosthesis infection and failure rates. When all responses were considered together, four decision factors correlated independently with the performance of more knee replacements, but these four factors explained only 24% of the variation in self reported knee replacement performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular determinants of the alpha-2D adrenergic receptor subtype.

The alpha-2 adrenergic receptor in the bovine pineal gland and the rodent homologues of the human alpha-2-C10 receptor express alpha-2D subtype pharmacological characteristics. The alpha-2 adrenergic receptor in the chicken pineal expresses characteristics similar to the alpha-2A subtype found in human and pig. The rodent receptors (alpha-2D) contain a serine residue at position 201 whereas the human and porcine receptors (alpha-2A) have a cysteine at this position. Our results indicate that the bovine pineal receptor has a serine at position 201, supporting the alpha-2D classification. However, the chicken pineal receptor also contains a serine at position 201 suggesting that other amino acids may be responsible for the differences in pharmacological characteristics.

Prevalence of cartilage shards in synovium and their association with synovitis in patients with early and endstage osteoarthritis.

It has been suggested that incorporation of shards of fibrillated cartilage into the synovium is a cause of synovitis in osteoarthritis (OA). We examined the prevalence with which fragments of cartilage are seen in synovium, and their association with synovitis, in patients with endstage OA and early OA of the knee. Samples of synovium were obtained from 12 patients with endstage OA who were undergoing knee joint replacement and 30 with only mild/moderate radiographic changes of OA who exhibited articular cartilage changes of OA at arthroscopy. The presence of cartilage shards was sought in synovium from the medial and lateral tibiofemoral compartments and the suprapatellar pouch of each patient. Comparable volumes of the synovial lining from patients with endstage and early OA were examined, and tissue mononuclear cell infiltration was graded as an indicator of synovitis. Cartilage shards were seen in synovium from 7 of 12 patients with endstage OA, all of whom had synovitis. No topographic relationship was found between shards and mononuclear cell infiltration. In contrast, cartilage fragments were not seen in synovium from any of the 30 patients with early OA, although 9 of them had full thickness cartilage ulcers and 17 had evidence of synovitis.

Gross polyethylene failure in total knee arthroplasty.

A total of 12 total knee replacements in nine patients with evidence of gross polyethylene failure at the time of revision surgery were identified. There were nine tibial and three patellar component failures. The average time from index to revision arthroplasty was 6 years (range: 0.75 to 9.63). A retrospective cohort group was identified based on date of operation. The average patient weight of the initial group was 89.6 kg (range: 76 to 104 kg), compared with 74.8 kg (range: 47 to 108 kg) (P = .045) in the control group. There was a male sex preponderance in the failure group (P = .045). The average height of the study group was 176 cm, compared to 161 cm for the control group (P = .003). Using the modified OASDI scale, the failure group had a higher activity level (P = .023). Pre-revision limb alignment in patients with failed TKA was statistically different from controls and served as an indication of polyethylene failure (P = .04). The selection of modular prosthetic component systems that allow for easy polyethylene revision is indicated in the high risk patient group identified. Close follow up is needed to minimize the sequela of polyethylene failure.

A comparison of tricompartmental and unicompartmental arthroplasty for the treatment of gonarthrosis.

An historical prospective study was performed to compare two surgical management alternatives in the treatment of patients with knee arthritis. There were 120 unicompartmental and 81 tricompartmental knee arthroplasties in 98 and 66 patients, respectively. All living patients were available for follow-up observation, and survivorship data on all arthroplasties were obtained. The average follow-up interval was 78 months (range, eight-162 months) in the unicompartmental series and 68 months (range, two- 186 months) in the tricompartmental group. Patients receiving the unicompartmental arthroplasty were treated with nonmetal-backed polyethylene tibial components. Prosthetic survivorship was 92% at ten years in the unicompartmental patient group. There were no statistically significant differences in aseptic loosening between these two patient groups. In appropriately selected patients unicompartmental arthroplasty was associated with better range of motion and ambulatory function than patients being treated with tricompartmental knee replacement.

Synovial inflammation in patients with early osteoarthritis of the knee.

While synovitis is common in advanced osteoarthritis (OA), its prevalence and severity in patients with early or mild OA are uncertain. In our study synovial biopsies from patients with arthroscopic evidence of OA whose radiographs were normal, or showed only mild/moderate changes of OA, were examined to determine the prevalence and severity of lining cell proliferation and mononuclear cell infiltration. Synovitis was present in only 16 of 29 patients (55%) who underwent arthroscopy because of chronic knee pain and were found to have OA; no synovium from 50% of the 22 patients in this group with full thickness cartilage ulceration showed infiltration with mononuclear cells. Similarly, no evidence of synovitis was seen in biopsies from 7 of 14 additional patients with OA who did not have knee pain but who underwent arthroscopy to evaluate joint instability. An association was seen between synovial mononuclear cell infiltration and thickness of the synovial lining cell layer (p less than 0.03), but lining cell hyperplasia was found in samples from only 12% of the patients with OA in our series. The severity of OA cartilage lesions was unrelated to severity of synovitis and no topographic relationship was found between cartilage ulceration and synovitis.

Gait alterations in dogs after transection of the anterior cruciate ligament.

We calculated mean peak vertical forces (MFz) of each limb of 9 adult mongrel dogs before and 2 weeks, 6 weeks, and 12 weeks after left anterior cruciate ligament transection (ACLT). Five additional dogs were studied before and 2 weeks and 6 weeks after sham ACLT. The gaits of 3 dogs that had undergone ACLT 2.5 years previously were also analyzed. Preoperatively, there were no differences in the MFz of the right and left hind limbs of the 9 dogs; we found that each limb exerted approximately 70% of the dog's static body weight on the force plate. Two weeks following ACLT, the MFz of the operated limbs decreased to 25% of the static body weight, while at 6 weeks and 12 weeks after surgery, the MFz generated by the operated limbs rose to about 32% and 37% of static body weight, respectively. No change was noted in the MFz of the contralateral hind limbs. In the 3 dogs that had undergone ACLT 2.5 years earlier, the MFz in the unstable stifle joint was 50% of static body weight. At both 2 weeks and 6 weeks after surgery, the MFz values for all 4 limbs of the animals subjected to sham ACLT were comparable with baseline values. These observations indicate that the osteoarthritic changes seen in the unstable limb are associated with decreased loading of that limb, without increased (compensatory) loading of the contralateral hind limb.

Fracture of the femoral neck after internal fixation.

A case of femoral neck fracture despite the presence of a previously inserted sliding screw and sideplate is reported. Internal fixation in itself did not prevent subsequent fracture. A critical factor in the mechanism of this fracture was the patient's underlying disease, felt to be alcoholic osteomalacia.

Titanium fibermetal segmental replacement prostheses. A radiographic analysis and review of current status.

Thirteen patients with titanium fibermetal segmental bone/joint prostheses at a minimum follow-up period of six months were reviewed. Detailed radiographic data were analyzed quantitatively in terms of stem/bone interface radiolucency and bone bridging over the segmental portion of the prosthesis at predefined zones. Although stem radiolucent lines were common in this series, only one case had clinical loosening and required reoperation. There were two cases of stem fracture; one achieved extracortical bone union without revision, and the other case required implant removal and revision. Analysis of the retrieved specimen revealed histologic evidence of bony ingrowth. The use of a long side plate for initial implant fixation might have been partially responsible for this complication because of inhibition of new bone formation over the porous-coated segment. Sequential study of radiograms at different follow-up time periods with the same zonal analysis criteria revealed that no progression of radiolucency occurred at the bone/prosthesis interface, and bone formation over the segmental portion either increased or stabilized with time. The patients' functional results and implant performance seemed to indicate that the porous-coated segmental prosthetic system was effective in bridging skeletal/joint defects. However, further improvements are needed in prosthetic design and implant quality control in order to minimize device-related complications.

In vivo construction of a metal-backed, high-molecular-weight polyethylene cup during McKee-Farrar revision total joint arthroplasty. A case report.

The need for revision total hip arthroplasty after metal-to-metal articulating prostheses is well known. An alternative to conventional acetabular revision in the clinical circumstance of isolated femoral component loosening is in vivo construction of a metal-backed, high-molecular-weight polyethylene (HMWPE) acetabular component. This surgical approach reduces the likelihood of intraoperative acetabular bone loss, should minimize subsequent loosening, and virtually eliminates the source of metallic wear debris. Follow-up evaluation after 3 years revealed maintenance of the acetabular component position and a satisfactory clinical result. In vivo construction of a metal-backed HMWPE acetabular component is an effective alternative in the management of this potentially difficult orthopedic problem.

The effect of load alteration on the biological and biomechanical performance of a titanium fiber-metal segmental prosthesis.

The effect of overloading and underloading on tissue ingrowth into the porous-coated titanium segmental prosthesis was studied in a canine femoral model. The prosthesis has modular components that are connected by a conical coupling joint. One of the dog's hind legs was immobilized and suspended for three weeks using an external fixator to minimize loading and prevent weight-bearing, while the contralateral leg was allowed to bear weight freely, simulating an overloading situation. Five dogs reached the final study period of twelve weeks without complication. There were no significant differences between the non-weight-bearing and weight-bearing sides on radiographic assessments. However, the immobilized side had significantly higher stem-push-out strength and energy to failure. Bone ingrowth was variable, and a fibrous layer was commonly demonstrated at the prosthetic stem-bone interface. The orientation of the fibrous tissue was more organized, in a penetrating pattern, on the immobilized side. The mean concentration of titanium was insignificant in all tissue examined. Reduced implant loading for the porous-coated segmental bone prosthesis during the initial period of implantation was found to be beneficial as compared with an overloading situation in achieving intramedullary fixation.