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.

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.

Differential down-regulation of alpha-2 adrenergic receptor subtypes.

The regulation of G protein-coupled receptor expression is important in the physiology of an organism and can occur at any of the steps between gene transcription to turnover of the receptor protein itself. Agonist stimulation causes receptor desensitization, which is characterized by a rapid reduction in response to the agonist. Down-regulation often occurs after prolonged agonist treatment and is manifested as a decrease in receptor density. Short term desensitization results from a rapid (in minutes) and reversible uncoupling of the receptor-G protein complex, followed by sequestration and/or internalization of receptors from the cell surface. Receptors are not degraded as removal of agonist rapidly restores receptor function. Down-regulation, on the other hand, displays a much longer time-course (hours to days) and is characterized by a decrease in receptor density as determined by radioligand binding. Removal of agonist will only slowly reverse down-regulation, because new receptor synthesis is required in most cases (1;2). The mechanism of receptor down-regulation is not well understood, but may include an accelerated rate of removal of receptors, a decrease in the rate of appearance of receptors, or both. Our previous studies have shown significant differences in the concentration of agonist required to produce down-regulation of alpha-2 adrenergic receptor subtypes (3;4). Here we review the mechanisms and molecular determinants for receptor down-regulation as well as our own data exploring the subtype-specific differences in alpha-2 receptor down-regulation. We find that the extent and time-course of agonist-induced down-regulation occurs in a similar fashion regardless of the receptor subtype or the cell line in which it is expressed. The mechanism for receptor down-regulation in all cases is an increase in the rate of receptor disappearance.

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.

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.

General considerations in total knee arthroplasty.

Total knee replacement is a powerful but complex surgical procedure. Recognizing and addressing all planes of motion at the knee is mandatory for good results. Accurate alignment of the prosthetic component and the limb is crucial. Close attention to surgical detail and prosthetic interaction is necessary. Current prosthetic replacement fails to return the bone to its normal strain environment. Clinical results with current resurfacing components rival or exceed those obtained with conventional total hip replacement in properly selected patients.

Orthopedic grand rounds. Retained wooden foreign body in the foot detected by computed tomography.

A 20-year-old female presented with a 12-week history of a penetrating wound by a pointed wooden slat to the dorsum of her right foot. She had persistent pain, swelling, and an open wound. Initial radiographs were normal, and three surgical explorations failed to find a foreign body. Later radiographs showed erosion of the second metatarsal. Computed tomography detected and localized the wooden foreign body. Removal of the foreign body was followed by healing of the foot.

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.

Future research directions in plant signal transduction mechanisms.

Photosynthesis is the ultimate driving force behind world food production. Modern agricultural practices have done much to maximize the benefits of photosynthesis through better land management and intensive crop breeding. However, enhancement in grain production is becoming increasingly dependent on biotechnology with every improvement becoming more difficult to achieve. With several crop species nearing the physical limits of grain production, more attention will be given to methods that enable farmers to consistently attain maximum yields. These efforts focus in part on how plants respond to the biotic and abiotic stresses that can significantly reduce potential yields, including the study of plant signal transduction pathways related to stress responses. Strong evidence is emerging that these pathways share many similarities to classical mammalian receptor systems including tyrosine-kinase receptors and G protein-coupled receptors. Several putative receptor-like proteins have been identified in maize and provide vast opportunities for studying plant signal transduction mechanisms. The elucidation of plant signaling pathways combined with modern technologies will not only serve to push harvest yields closer to the maximum theoretical levels but may also provide opportunities for actually increasing the theoretical maximum.

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.

Mechanism of down-regulation of alpha-2 adrenergic receptor subtypes.

Long-term exposure to agonist down-regulates receptor expression for many G protein-coupled receptors. This decrease in receptor density could occur through either an increase in receptor degradation or a decrease in receptor synthesis. We studied the mechanism of down-regulation of the alpha-2A and alpha-2B adrenergic receptor subtypes transfected into the Chinese hamster ovary cell line as well as the alpha-2A receptor endogenous to the HT29 cell line. The rate constants for receptor appearance and disappearance were calculated from the recovery of receptor expression after irreversible inactivation of the existing receptor population with an alkylating agent. In the presence of the agonist norepinephrine, the receptor subtypes in all three cell lines down-regulated to about 50% with a half-time of 2.5 hr. When recovering in the presence of norepinephrine after irreversible inactivation, the rate of receptor degradation increased approximately 2-fold for all three cell lines with little change in the rate of synthesis. During this recovery, the transfected alpha-2A receptor exhibited a half-life of 3.0 hr, which agrees with the 2.7-hr half-time of down-regulation in the presence of norepinephrine. In contrast, the transfected alpha-2B receptor and the endogenous alpha-2A receptor had a half-life of 1.2 hr and 8.9 hr, respectively. For only the endogenous alpha-2A receptor, pertussis toxin increased the half-time of down-regulation to 9.8 hr, similar to the 8.9-hr receptor half-life in the presence of norepinephrine during recovery after irreversible inactivation. Our results indicate that the mechanism of down-regulation of the alpha-2A and -2B adrenergic receptor subtypes is an increase in the rate of receptor degradation.

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.

Component wear of total knee prostheses using Ti-6A1-4V, titanium nitride coated Ti-6A1-4V, and cobalt-chromium-molybdenum femoral components.

A knee simulator was used to study the wear of carbon fiber reinforced UHMWPE (Poly Two) (Poly Two is a registered trademark of Zimmer, USA) tibial and patellar components against Ti-6A1-4V, titanium nitride (TiN)-coated Ti-6A1-4V, and cobalt-chromium-molybdenum femoral components. The prostheses tested were regular sized Miller-Galante total knees mounted on 316L stainless steel fixtures using bone cement. An environmental chamber surrounded the knee and maintained bovine serum lubricant at 37 degrees C. The specimens were tested using consecutive blocks of 464 level walking steps, 8 ascending stairs and 8 descending stairs for a total of 100,000 steps. The wear mechanisms found on the tibial components were scratching, carbon-fiber associated damage, surface deformation, pitting, minor abrasion, and delamination. Three forms of carbon fiber associated damage were identified; fibers pulled from the surface, broken fibers, and UHMWPE removed from the surface fibers. The SEM evaluation revealed a pit forming mechanism. No correlation was found between femoral component material and tibial surface damage. Visual examination of the femoral components revealed no signs of wear or scratching on the cobalt-chromium-molybdenum or TiN-coated Ti-6A1-4V components. There were, however, many light surface scratches on the uncoated Ti-6A1-4V components, which were also observed in a supplementary test of an uncoated Ti-6A1-4V component tested with a conventional polyethylene tibial component.

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.

Unicompartmental knee arthroplasty. A multicenter investigation with long-term follow-up evaluation.

Nonmental-backed, cemented, unicompartmental knee arthroplasty has a survivorship rate in this multicenter investigation at ten years of 91.4% (+/- 2.8). High levels of patient weight were associated with increased need for revision arthroplasty. Overall, men had a lower revision rate (2.4%) compared with women (3.9%). Valgus postoperative alignment was minimally associated with progression of disease as a cause for revision. No difference in revision rates between medial and lateral compartmental arthroplasty was noted. The theoretical clinical benefits of the use of metal-backed tibial components will need to be reevaluated in light of these findings.

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.

Stiffening of the femoral head due to inter-trabecular fluid and intraosseous pressure.

The mechanical properties of cancellous bone, as measured from bone plug samples have been widely documented. However, few tests have been attempted to explore the effects the intertrabecular contents may have on the load bearing capabilities. In this study, canine femoral heads were subjected to dynamic compressive strain cycles. The femoral heads were tested intact, as well as with disrupted boundary conditions of the continuous, intraosseous fluid space. A significant reduction in mechanical stiffness was observed when the fluid compartment boundary was disrupted by drilling a hole part way into the femoral neck. A finite element model of a typical femoral head showed that the stiffness change was not due to removal of material from the neck, hydraulic effects notwithstanding. Refilling the hole in the neck with saline solution and sealing the boundary restored the stiffness to the intact baseline level. However, an increase in the fluid pressure did not cause a statistically significant increase in the stiffness of the femoral head.

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.