William J. Hozack

Why are total knee arthroplasties failing today

The incidence of failure after knee replacement is low, yet it has been reported that more than 22,000 knee replacements are revised yearly. The purpose of the current study was to determine current mechanisms of failure of total knee arthroplasties. A retrospective review was done on all patients who had revision total knee arthroplasty during a 3-year period (September 1997–October 2000) at one institution. The preoperative evaluation in conjunction with radiographs, laboratory data, and intraoperative findings were used to determine causes of failure. Two hundred twelve surgeries were done on 203 patients (nine patients had bilateral surgeries). The reasons for failure listed in order of prevalence among the patients in this study include polyethylene wear, aseptic loosening, instability, infection, arthrofibrosis, malalignment or malposition, deficient extensor mechanism, avascular necrosis in the patella, periprosthetic fracture, and isolated patellar resurfacing. The cases reviewed included patients who had revision surgery within 9 days to 28 years (average, 3.7 years) after the previous surgery. More than half of the revisions in this group of patients were done less than 2 years after the index operation. Fifty percent of early revision total knee arthroplasties in this series were related to instability, malalignment or malposition, and failure of fixation.

Transforming Growth Factor-β-mediated Chondrogenesis of Human Mesenchymal Progenitor Cells Involves N-cadherin and Mitogen-activated Protein Kinase and Wnt Signaling Cross-talk

The multilineage differentiation potential of adult tissue-derived mesenchymal progenitor cells (MPCs), such as those from bone marrow and trabecular bone, makes them a useful model to investigate mechanisms regulating tissue development and regeneration, such as cartilage. Treatment with transforming growth factor-β (TGF-β) superfamily members is a key requirement for the in vitro chondrogenic differentiation of MPCs. Intracellular signaling cascades, particularly those involving the mitogen-activated protein (MAP) kinases, p38, ERK-1, and JNK, have been shown to be activated by TGF-βs in promoting cartilage-specific gene expression. MPC chondrogenesis in vitro also requires high cell seeding density, reminiscent of the cellular condensation requirements for embryonic mesenchymal chondrogenesis, suggesting common chondro-regulatory mechanisms. Prompted by recent findings of the crucial role of the cell adhesion protein, N-cadherin, and Wnt signaling in condensation and chondrogenesis, we have examined here their involvement, as well as MAP kinase signaling, in TGF-β1-induced chondrogenesis of trabecular bone-derived MPCs. Our results showed that TGF-β1 treatment initiates and maintains chondrogenesis of MPCs through the differential chondro-stimulatory activities of p38, ERK-1, and to a lesser extent, JNK. This regulation of MPC chondrogenic differentiation by the MAP kinases involves the modulation of N-cadherin expression levels, thereby likely controlling condensation-like cell-cell interaction and progression to chondrogenic differentiation, by the sequential up-regulation and progressive down-regulation of N-cadherin. TGF-β1-mediated MAP kinase activation also controls WNT-7A gene expression and Wnt-mediated signaling through the intracellular β-catenin-TCF pathway, which likely regulates N-cadherin expression and subsequent N-cadherin-mediated cell-adhesion complexes during the early steps of MPC chondrogenesis.

Characterization of Multipotential Mesenchymal Progenitor Cells Derived from Human Trabecular Bone

The in vitro culture of human trabecular bone‐derived cells has served as a useful system for the investigation of the biology of osteoblasts. The recent discovery in our laboratory of the multilineage mesenchymal differentiation potential of cells derived from collagenase‐treated human trabecular bone fragments has prompted further interest in view of the potential application of mesenchymal progenitor cells (MPCs) in the repair and regeneration of tissue damaged by disease or trauma. Similar to human MPCs derived from bone marrow, a clearer understanding of the variability associated with obtaining these bone‐derived cells is required in order to optimize the design and execution of applicable studies. In this study, we have identified the presence of a CD73+, STRO‐1+, CD105+, CD34−, CD45−, CD144− cell population resident within collagenase‐treated, culture‐processed bone fragments, which upon migration established a homogeneous population of MPCs. Additionally, we have introduced a system of culturing these MPCs that best supports and maintains their optimal differentiation potential during long‐term culture expansion. When cultured as described, the trabecular bone‐derived cells display stem cell‐like capabilities, characterized by a stable undifferentiated phenotype as well as the ability to proliferate extensively while retaining the potential to differentiate along the osteoblastic, adipocytic, and chondrocytic lineages, even when maintained in long‐term in vitro culture.

Orthopaedic surgeon workforce and volume assessment for total hip and knee replacement in the United States: Preparing for an epidemic

The demand for health-care services in general, and musculoskeletal care in particular, is expected to increase substantially in the United States because of the growth of the population, aging of the population, public expectations, economic growth, investment in health-care interventions, and improved diagnosis and treatment. The impact of an aging population is demonstrated by the fact that, in 2000, the eleven most costly medical conditions in the United States were far more prevalent among the elderly, and the population of elderly Americans is increasing. It is not clear that the future supply of physicians will be sufficient to meet the increasing demand for health care. The supply of American physicians is limited by the aging and retirement of current physicians, medical school graduation class size of allopathic medical doctors and osteopathic physicians, and United States immigration policies, which limit the number of physicians entering the country. Furthermore, among active physicians, the “effective physician supply” is limited by gender and generational differences, lifestyle choices, changing practice patterns, and variability in physician productivity. At current physician production levels, the ratio of physicians to population will peak between 2015 and 20201. Between 2000 and 2020, the demand for orthopaedic services in this country will increase by 23% while the supply of orthopaedic surgeons will increase by only 2% during the same interval2. During the next few decades, the demand for total joint arthroplasties in the United States may not be met because of an inadequate supply of total joint arthroplasty surgeons. This hypothesis or concern is based on data and trends associated with the prevalence of total joint arthroplasty, projected volumes of total joint arthroplasty, workforce trends in total joint arthroplasty, and reimbursement for total joint arthroplasty. The purposes of this paper are to evaluate the validity of this …

Total joint arthroplasty: When do fatal or near-fatal complications occur?

Background: With the recent trend toward minimally invasive total joint arthroplasty and the increased emphasis on faster recovery and shorter hospital stays, it has become increasingly important to recognize the timing and severity of the various complications associated with elective total joint arthroplasty to ensure that early patient discharge is a safe practice. Methods: We evaluated the systemic and local complications associated with primary unilateral lower-extremity arthroplasties performed during one year in 1636 patients. A total of 966 patients had a primary total hip arthroplasty, and 670 had a primary total knee arthroplasty. All complications that occurred in the hospital and for six weeks following the index surgery were recorded. The circumstances leading to the complications and the details of the therapeutic intervention for each complication were recorded. Analyses were performed to predict the factors that predispose patients to serious complications. Results: One patient (0.06%) in the cohort died during the hospital stay. There were a total of 104 major (life-threatening) complications, including cardiac arrest (one), tachyarrhythmia (thirty-three), pulmonary edema or congestive heart failure (ten), myocardial infarction (six), hypotensive crisis (four), pulmonary embolus (twenty-five), acute renal failure (fourteen), stroke (six), bowel obstruction or perforation (three), and pneumothorax (one). There were seventeen major local complications. Ninety-four (90%) of the major complications occurred within four days after the index surgery. Although older age, increased body mass, and preexistent comorbidities were important predisposing factors for serious medical complications, 58% of the patients who had life-threatening complications develop had no identifiable predisposing factors. Conclusions: This study demonstrated that most of the complications of lower-extremity total joint replacement occur within the time-frame of the typical hospital stay. Given the serious nature of some of these complications and the inability to identify many of the patients who may be at risk, we caution against early discharge of patients from the hospital after elective total joint arthroplasty in the lower extremity. Level of Evidence: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.

Effect of femoral component offset on polyethylene wear in total hip arthroplasty.

Seventeen staged, bilateral total hip arthroplasties performed in 17 patients were reviewed to compare side-to-side polyethylene wear. Implants used on both sides were similar except for implant offset: one hip in each patient was replaced using a femoral component having a standard implant offset, whereas the other side had a lateral offset implant. The mean followup was 5.70 years (range, 2–10.2 years) on the side with a standard femoral implant and 5.67 years (range, 2–9.7 years) on the side with a lateralized femoral component. The only statistically different parameter between the sides was the femoral component offset. All other parameters affecting polyethylene wear, such as period of followup, head size, head type, cup size, cup inclination, medialization of cup, and patientrelated factors were similar on both sides. On the side with a standard femoral component, the mean actual prosthetic offset (determined by manufacturer’s specifications) was 35.2 mm and the radiologic offset was 31.5 mm. On the side with a lateralized femoral component, the actual prosthetic offset was 42.5 mm and the radiologic offset was 40.1 mm. The difference in offsets between the sides was statistically significant. The mean preoperative offset of the femur was 38.8 mm. Regression analysis revealed that only femoral component offset and cup size correlated significantly with linear wear rate. On the side with a standard femoral component, the linear wear rate was 0.21 mm per year, whereas on the side with a lateralized femoral component, the linear wear rate was 0.10 mm per year. The differences in the linear wear rates were significant. Lateralization of the femoral component in this series more closely restored preoperative hip biomechanics and significantly decreased polyethylene wear.

Evaluation of the painful prosthetic joint: Relative value of bone scan, sedimentation rate, and joint aspiration

Seventy-two joint arthroplasties undergoing total hip or total knee surgery were studied prospectively with plain radiographs, three-phase bone imaging (3PBI), erythrocyte sedimentation rate (ESR), aspiration of the joint for culture, and multiple intraoperative cultures at the time of revision. Intraoperative cultures and the operative appearance were used to form a diagnosis of definite infection (unequivocal microbiology and gross sepsis), possible infection (positive microbiology or gross sepsis), or no infection (neither positive microbiology nor gross sepsis). For the preoperative diagnosis of infection, as opposed to aseptic loosening, 3PBI alone had a sensitivity of 33% and a specificity of 86%. In conjunction with plain radiographs, minimal improvement in accuracy was seen. A preoperative ESR greater than 30 had low sensitivity (60%) and a specificity of (65%). However, the ESR was statistically significantly higher in the joints with definite infection as compared to those joints without infection. The preoperative joint aspiration had a sensitivity of 67% and a specificity of 96% and, therefore, appears to be the most useful single test in the workup of a painful total joint arthroplasty.

The Noisy Ceramic Hip: Is Component Malpositioning the Cause?

Noisy ceramics bearing surfaces are a recently recognized problem in total hip arthroplasty. Component malposition as a potential cause has been proposed. Squeaking occurred in 28 (2.7%) of 999 patients undergoing ceramic on ceramic total hip arthroplasty at our institution. Patients were matched, in a 1:2 ratio by anthropometric and demographic variables and also prosthesis size and type. The acetabular position was measured using radiographs and computed tomography. There was no statistically significant difference in cup inclination (P = .25) or version (P = .38) between groups. Four hips that have been revised were available for retrieval analysis. Stripe wear and metal transfer to ceramic components were observed. Etiology of squeaking ceramic total hip arthroplasty remains elusive. Although malposition could be an important contributing factor, the latter cannot be the sole reason based on our findings. Further investigation to elucidate the etiology is warranted.

Muscle damage during MIS total hip arthroplasty : Smith-Petersen versus posterior approach

Decreased muscle damage is a reported benefit of minimally invasive surgical (MIS) approaches in total hip arthroplasty (THA). We compared the extent and location of muscle damage during THA using the MIS anterior Smith-Peterson and MIS posterior surgical approaches. THA was performed in six human cadavers (12 hips). One hip was assigned to the Smith-Peterson approach and the contralateral hip to the posterior approach. Muscle damage was graded with a technique of visual inspection to calculate a proportion of surface area damage. Less damage occurred in the gluteus minimus muscles and minimus tendon with the Smith-Peterson approach. A mean of 8% of the minimus muscle was damaged via the Smith-Peterson approach, compared to 18% via the posterior approach. The tensor fascia latae muscle was damaged (mean of 31%), as well as direct head of the rectus femoris (mean 12%) during the Smith-Peterson approach. The piriformis or conjoined tendon was transected in 50% of the anterior approaches to mobilize the femur. The posterior approach involved intentional detachment of the piriformis and conjoined tendon and measurable damage to the abductor muscles and gluteus minimus tendon in each specimen. Clinical outcome studies and gait analysis are necessary to ascertain the functional implications of these findings.

In Hospital Complications After Total Joint Arthroplasty

Total joint arthroplasty is a safe and successful procedure. However, numerous complications may present after elective arthroplasty. This study prospectively collected data on systemic and local in hospital complications after 15383 joint arthroplasties, which included 8230 total hip arthroplasties and 7153 total knee arthroplasties. In general, the incidence of complications was higher after knee arthroplasty, simultaneous bilateral surgery, and revision surgery. There were 22 (0.16%) deaths in this cohort. We identified 486 major systemic complications, the most common was pulmonary embolism (152), followed by tachyarrhythmia (92) and acute myocardial infarction (36). There were 109 major local complications, including 16 vascular injuries, 29 peripheral nerve injuries, 25 periprosthetic fractures, and 18 dislocations. Total joint arthroplasty, despite its success, can be associated with rare serious and life-threatening complications. This study provides a baseline of complications that can occur after elective joint arthroplasty.