Symptomatic articular cartilage degeneration: the impact in the new millennium.

The symptomatic degeneration of articular cartilage and associated arthritis is among the most prevalent chronic conditions in the United States and the population most at risk is increasing. It is the leading cause of limitations in activities of daily living and is second to heart disease in causing work disability. The current and future socioeconomic impact of chronic articular cartilage disease on the healthcare system will be magnified by increasing numbers of patients who will seek relief of their symptoms and their disability to remain active. Because these individuals live longer and remain active, the proportion of their life living with symptoms and disability from articular cartilage degeneration increases. The economic, psychologic, and social impact of degenerative articular cartilage can be enormous for these individuals but it also impacts their family and society. The direct traditional medical costs and indirect economic and wage loss from arthritis in individuals the United States has reached in excess of $65 billion annually and is expected to increase as the population ages. In addition, the expenditures for complementary and alternative professional services and therapies for arthritis is increasing and is also in the billions of dollars annually. Because of these escalating costs, documenting the value of the patient and cost effectiveness to society of prevention and treatment programs for symptomatic articular cartilage degeneration will be required.

Spontaneous repair of full-thickness defects of articular cartilage in a goat model. A preliminary study.

BACKGROUND: Full-thickness defects measuring 3 mm in diameter have been commonly used in studies of rabbits to evaluate new procedures designed to improve the quality of articular cartilage repair. These defects initially heal spontaneously. However, little information is available on the characteristics of repair of larger defects. The objective of the present study was to define the characteristics of repair of 6-mm full-thickness osteochondral defects in the adult Spanish goat. METHODS: Full-thickness osteochondral defects measuring 6 x 6 mm were created in the medial femoral condyle of the knee joint of adult female Spanish goats. The untreated defects were allowed to heal spontaneously. The knee joints were removed, and the defects were examined at ten time-intervals, ranging from time zero (immediately after creation of the defect) to one year postoperatively. The defects were examined grossly, microradiographically, histologically, and with magnetic resonance imaging and computed tomography. RESULTS: The 6-mm osteochondral defects did not heal. Moreover, heretofore undescribed progressive, deleterious changes occurred in the osseous walls of the defect and the articular cartilage surrounding the defect. These changes resulted in a progressive increase in the size of the defect, the formation of a large cavitary lesion, and the collapse of both the surrounding subchondral bone and the articular cartilage into the periphery of the defect. Resorption of the osseous walls of the defect was first noted by one week, and it was associated with extensive osteoclastic activity in the trabecular bone of the walls of the defect. Flattening and deformation of the articular cartilage at the edges of the defect was also observed at this time. By twelve weeks, bone resorption had transformed the surgically created defect into a larger cavitary lesion, and the articular cartilage and subchondral bone surrounding the defect had collapsed into the periphery of the defect. By twenty-six weeks, bone resorption had ceased and the osseous walls of the lesion had become sclerotic. The cavitary lesion did not become filled in with fibrocartilage. Instead, a cystic lesion was found in the center of most of the cavitary lesions. Only a thin layer of fibrocartilage was present on the sclerotic osseous walls of the defect. Specimens examined at one year postoperatively showed similar characteristics. CONCLUSIONS: Full-thickness osteochondral defects, measuring 6 mm in both diameter and depth, that are created in the medial femoral condyle of the knee joint of adult Spanish goats do not heal spontaneously. Instead, they undergo progressive changes resulting in resorption of the osseous walls of the defect, the formation of a large cavitary lesion, and the collapse of the surrounding articular cartilage and subchondral bone. CLINICAL RELEVANCE: As surgeons apply new reparative procedures to larger areas of full-thickness articular cartilage loss, we believe that it is important to consider the potential deleterious effects of a "zone of influence" secondary to the creation of a large defect in the subchondral bone. When biologic and synthetic matrices with or without cells or bioactive factors are placed into surgically created osseous defects, the osseous walls serve as shoulders to protect and stabilize the preliminary repair process. It is important to protect the repair process until biologic incorporation occurs and the chondrogenic switch turns the cells on to synthesize an articular-cartilage-like matrix. It takes a varying period of time to fill a large, surgically created bone defect underlying a chondral surface. The repair of such a defect requires bone synthesis and the reestablishment of a subchondral plate with a tidemark transition to the new overlying articular surface. The prevention of secondary changes in the surrounding bone and articular cartilage and the durability of the new reparative tissue making up the articulating surface are issues that must be addressed in future studies.

Single-stage revision using an uncemented, porous-coated, anatomic endoprosthesis in two dogs: case report.

OBJECTIVE: To describe the clinical and radiographic features of septic and aseptic failure of two femoral endoprostheses and their successful revision. STUDY DESIGN: Case report. ANIMALS OR SAMPLE POPULATION: Two skeletally mature male research dogs. METHODS: An uncemented porous-coated anatomic (PCA) endoprosthesis was implanted in a single-stage revision procedure after thorough debridement and lavage of the femoral canal. An autogenous cancellous bone graft was used in dog 2 (aseptic loosening). Serial clinical and radiographic examinations were performed postoperatively. The dogs were euthanatized 1 year (dog 1) and 2 years (dog 2) after revision surgery, and necropsy was performed. High-resolution contact radiographs and histopathologic evaluation of femoral sections were obtained. RESULTS: The cause of implant failure was septic loosening in dog 1 and aseptic loosening in dog 2. In both dogs, clinical function returned to normal after revision. Serial radiographic assessment after revision documented disappearance of the bone pedestal and the periprosthetic lucency. Cancellous hypertrophy seen adjacent to the proximal porous-coated region of the implants provided radiographic evidence of bony fixation. Histological evaluation of femoral sections documented successful implant integration with bone and fibrous tissue. CONCLUSION: Revision with an uncemented implant in a single-stage procedure was successful in the two dogs described in this report. CLINICAL RELEVANCE: This report provides a detailed description of the clinical course and serial radiographic assessment of septic and aseptic loosening of two femoral endoprostheses. Single-stage revision is a potential treatment for either condition as demonstrated by the successful outcome in these two dogs.

Improved osseointeraction of calcium phosphate-coated external fixation pins. Studies in calves.

We investigated osseointeraction of solution-precipitated calcium phosphate (SPCP)-coated transfixation pins used in external skeletal fixation of a calf stable fracture model. One group (SPCP) received centrally-threaded transfixation pins which had SPCP coating; the other group (control) received identical, but not coated, pins. Radiographs were obtained 1 and 40 days after surgery and examined for evidence of osteolysis. Bone phase 99mTc-MDP studies were performed 6 and 28 days after surgery. Calves were killed 40 days after surgery and mechanical tests performed. Dual-energy x-ray absorptiometry (DEXA) and histomorphometric analyses were done. A smaller proportion of SPCP pins (5/24) had evidence of discharge during the study compared with control pins (21/24). A smaller proportion of SPCP pins (4%) had radiographic evidence of osteolysis compared with control pins (42%). Uptake of 99mTc-MDP was similar for SPCP and control calves. Uptake was significantly greater in bone segments showing radiographic evidence of osteolysis than in bone segments not having osteolysis. Yield stress (MPa) for axial displacement was similar in the treatment groups. Bone mineral density was less in SPCP pins. Affinity index and interface histologic score were greater and osteoclastic index less in SPCP calves. Coating of transfixation pins with solution-precipitated calcium phosphate improved the osseointeraction of pin and bone during this 40-day study.

Comparison of pullout strength for seven- and nine-millimeter diameter interference screw size as used in anterior cruciate ligament reconstruction.

This study compares biomechanical properties of 7- and 9-mm diameter screws providing interference fixation in anterior cruciate ligament reconstruction. Sixteen pairs of fresh-frozen bovine knees were evaluated. Uniaxial load to failure was performed at a deformation rate of 30 mm/s along the mechanical axis of the ligament graft with the knees secured at 45 degrees of flexion in a custom jig. A video analyzer was used to measure ligament strain and bone-to-bone deformation. Ultimate force, deformation, and failure mode were recorded and compared. The 7-mm screws provided 98% yield strength, and 95% ultimate force compared with the 9-mm screws. The average femoral pullout strength was 1161 +/- 93 N in the 7-mm group and 1198 +/- 142 N in the 9-mm group. Failure mode was similar in both groups. Clinically, the usage of 7-mm screws may reduce iatrogenic injuries to the patellar tendon graft compared with larger screws. This study shows that the biomechanical advantages of 9-mm screws compared with 7-mm screws are minimal.

The effects of implant orientation, canal fill, and implant fit on femoral strain patterns and implant stability during catastrophic testing of a canine cementless femoral prosthesis.

Cementless femoral stems were placed into 12 normal greyhound femora. The implanted femora were divided into three groups by stem orientation and implant size and loaded in axial compression at a rate of 25 newtons (N) per second until failure. Rosette strain gauges were used to measure femoral principal strains at 500 N, 1,000 N, 1,500 N, and at maximum load. During maximum load, varus orientation of the femoral stem had significantly higher tensile hoop strains in the proximomedial cortex, whereas neutral orientation had higher tensile hoop strains along the cranial cortex. Femoral fractures occurred in these areas of peak tensile strain. There was no difference in maximum load between groups, therefore varus orientation did not predispose to fracture. Maximizing canal fill and implant fit increased implant stability.

Effect of age on bone formation around orthopaedic implants.

Bone and mineral metabolism are known to change with age, but studies of biologic fixation have traditionally ignored or poorly documented the effect of age on the quality and quantity of bone about implants. This study documents the effect of age on quality and quantity of biologic fixation about hydroxyapatite-coated and uncoated implants in young and old sheep. Mechanical and histologic tests demonstrate comparable fixation of implants in young and old sheep, indicating that age is not a dominant factor in the development or failure of implant osseointegration.

The response of cancellous and cortical canine bone to hydroxylapatite-coated and uncoated titanium rods.

Because of the recent trend in total hip arthroplasty to achieve direct contact of the endoprosthesis with cortical bone, comparison of bone apposition from cortical bone and cancellous bone was performed. The response of cortical and cancellous bone to hydroxylapatite was also compared. Implants in cortical bone demonstrated a higher interface shear strength and more bone apposition than those in cancellous bone over all time periods tested. Hydroxylapatite coating increased the interfacial shear and bone apposition in cortical bone at all time periods and in both the 3- and 6-week cancellous bone models. The potential effect of stress shielding (and subsequent bone resorption) by femoral stems ingrown with cortical bone is discussed.

Femoral strain distribution and subsidence after physiological loading of a cementless canine femoral prosthesis: the effects of implant orientation, canal fill, and implant fit.

Twelve normal greyhound femora were divided into three groups. In group one, femoral stems were placed in neutral position with maximal fill. Group two had undersized femoral stems placed in neutral position. Group three had undersized femoral stems placed in varus position. Intact and implanted femora were loaded from 10 newtons (N) to 300 N in axial compression at a rate of 25 N/s for 10 replications. A strain gauge analysis showed that the strain distribution of all implanted femora were substantially different from intact femora, but femora with large implants placed in neutral position had the least amount of deviation from normal. An undersized stem in neutral position had significantly less compressive longitudinal strains along the proximomedial and proximocranial cortices. An undersized stem in varus position improved implant fit along the proximomedial and distolateral cortices, which resulted in increased tensile hoop strains. There were multiple significant correlations between the strain data and implantation variables (implant alignment, canal fill, and implant fit). Subsidence was significantly greater for the undersized implant in neutral position. There was not a difference in subsidence between the large neutral and varus groups. The most important variable that decreased subsidence was increased lateral implant fit (r = -0.86, P = .0003).

Total hip arthroplasty for treatment of canine hip dysplasia.

Cemented THA is an established procedure for treating arthropathies of the hip in large, healthy mature dogs. CHD with secondary osteoarthritis is the most common indication. Although comparative studies between THA and excision arthroplasty have not been reported, our experience with both procedures and studies in the literature support THA as the best available treatment for crippling degenerative joint disease secondary to CHD in large, mature dogs. Negative aspects of the procedure include high cost, the potential of significant complications, and the sophisticated surgical technique required. Improvements in patient selection, design of implants, surgical technique, and postoperative care have decreased the incidence of complications and improved the success rate to over 90%. However, concerns in human applications about cement disease and the desire to increase the functional life of the prosthesis have renewed interest in cementless systems. Advantages of cementless THA are fixation via bony ingrowth and avoidance of problems associated with PMMA. Important technical aspects of cementless THA relate to optimal fit and fill so that the prosthesis is stable, bone ingrowth is promoted, and weight-bearing forces are transferred to the proximal femur physiologically. Problems recognized with cementless systems include fissure fracture, bone resorption, and excessive motion between the implant and bone. Currently, investigations are being conducted to develop prosthetic materials that more closely match the stiffness of bone, stem designs that provide optimal fit and maintain normal strain patterns in the bone, and coating materials that promote permanent fixation by bone ingrowth. Early clinical results in humans and research results in dogs have been encouraging but have not withstood the test of time. Results of cementless techniques must be compared to the standards set by cemented THA over the last 20 years in humans and the last 10 years in dogs.

Inhalation of 1-nitropyrene associated with ultrafine insoluble particles or as a pure aerosol: a comparison of deposition and biological fate.

A large number of the environmental particulate pollutants in the atmosphere, including diesel engine exhaust, have a complex mixture of organic compounds associated with them. Organic solvent extracts of many of these particulate pollutants have been shown to contain mutagenic activity which does not require metabolic activation in the Ames bioassay. Much of this direct-acting mutagenic activity has been attributed to nitroaromatic compounds present in these extracts. In the studies reported here, the direct-acting mutagen, [3H]nitropyrene (3H-NP), was used as a model nitroaromatic compound. Rats were exposed to this radiolabeled compound by nose-only inhalation either as a coating (approximately 6% by mass) on relatively inert, ultrafine 67Ga2O3 particles or as a homogeneous ultrafine aerosol. The tissue deposition, retention, and biological fate of each aerosol were investigated and compared. Respiratory tract clearance of 3H radioactivity from each exposure was very rapid with no apparent differences seen in the lung retention of this inhaled compound between each exposure over the course of these studies. Higher 3H-radioactivity levels were seen in stomach and large intestines of rats exposed to the 67Ga2O3-associated 3H-NP than in the same tissues from rats exposed to the pure 3H-NP aerosol. Rats exposed to the 3H-NP-67Ga2O3 aerosol excreted the majority of the deposited 3H radioactivity in the feces (75 +/- 18%), whereas pure 3H-NP exposed animals excreted a major portion of the radiolabeled in the urine (76 +/- 18%). It appeared that the major portion of the pure 3H-NP aerosol was cleared from the respiratory tract by direct absorption into blood, while the 67Ga2O3-associated 3H-NP was cleared by both blood absorption and mucociliary clearance followed by ingestion and fecal excretion. These differences in the deposition and biological fate between the particle-associated NP and the pure NP aerosol may have important implications in terms of the metabolic fate of inhaled nitroaromatic compounds and the health risks associated with human exposures to particulate environmental pollutants that contain this class of compounds.