Damage type and strain mode associations in human compact bone bending fatigue.

When compact bone is subjected to fatigue loading, it develops matrix microdamage, which reduces the tissue's ability to resist fracture. The relative influence of different strain modes on damage and strength in compact bone has not been characterized, to our knowledge. In this study, the nonuniform strain field produced by four-point bending was used to introduce fatigue damage into tibial bending beam specimens from men 40-49 years old. The specimens were then bulk-stained with basic fuchsin to mark damage surfaces and were examined histologically and with confocal microscopy to describe damage morphologies and position relative to tension and compression-strained regions of the specimen. Histomorphometric methods were used to quantify the amounts of different types of bone microdamage. Three major types were observed. In regions subjected to tensile strains, the bone had focal regions of diffusely increased basic fuchsin staining (i.e., diffuse microdamage). Confocal microscopy of these regions showed them to be composed of extensive networks of fine, ultrastructural-level cracks. In compressive strain regions, the tissue developed linear microcracks in interstitial areas similar to those originally described by Frost. Fine, tearing-type (wispy-appearing) cracks were observed near and in the plane of the neutral axis. The paths of these fine cracks were not influenced by microstructural boundaries. Other minor damage morphologies (sector-stained osteons, delamination of regions of lamellae, and intraosteonal cracking) were observed, but their distribution was unrelated to local strain field. Thus. in fatigue of human compact bone, the principal mechanisms of matrix failure (i.e., linear microcrack, diffuse damage foci, and tearing-type damage) are strongly dependent on local strain type.

A curriculum for the ideal orthopaedic residency. Academic Orthopaedic Society.

The Academic Orthopaedic Society met in April 1994 to discuss manpower issues in orthopaedics. The members developed an approach using the Delphi system to define and obtain consensus on the characteristics of the ideal residency. Six categories of educational attributes were included: General; Clinical Management; Skills and Technical Aspects; Rehabilitation; Basic Science and Research; and Educational Environment. The following year a questionnaire was sent to more than 125 programs in an attempt to have residents and staff anonymously self score their residencies according to the standards defined by the Delphi panels. The results obtained from the 745 responders from 73 programs validate effectively the characteristics of the ideal program and also show the variation among the programs.

Treatment of overuse patellofemoral pain. Prospective randomized controlled clinical trial in a military setting.

The efficacy of treatment of overuse patellofemoral pain with an elastic knee sleeve with a silicone patellar ring was compared with a simple elastic sleeve and with no treatment in a prospective study of 395 army recruits. During 14 weeks of basic training, 84 knees were diagnosed as having overuse patellofemoral pain. Recruits treated with a simple elastic knee sleeve had a statistically significant better comfort score and more had their pain resolved by the end of training than those treated with elastic knee sleeves with a silicone patellar ring. The mean pain score at the end of training decreased more among recruits who were treated with a simple elastic knee sleeve than among recruits who received no treatment, but this difference was not significant. Among the treatment options tried, the simple elastic knee sleeve was no more effective than no treatment at all, but it was more effective than the more elaborate patellar brace.

Long-term follow-up study on the Maquet procedure with special reference to the causes of failure.

Thirty-nine patients with symptomatic osteoarthrosis (OA) of the patellofemoral joint were treated with 42 anterior tibial tubercle elevations, also known as the Maquet procedure. The patients all had symptomatic OA of the patellofemoral joint that fell into one of three categories: old patellar fracture, chronic patellar subluxation, or postpatellectomy pain. In the latter group, the OA was manifested by erosions of trochlear articular cartilage from the articulating quadriceps tendon-patellar ligament suture line. All 39 patients had a 1.5-2.5-cm tibial tubercle elevation with medial displacement, as necessary, to centralize their patellofemoral mechanisms. Follow-up period averaged 6.1 years. Seventy-nine percent (33 of 42 procedures) had good to excellent results. There was a major complication rate of 7%. Six of the nine failures were attributable to social/psychiatric reasons. Previously unrecognized tibiofemoral OA was the reason for poor results in two of the other failures, and one failure was unexplained. Patients with long-standing symptoms caused by patellofemoral OA should preoperatively be psychologically evaluated and diagnostically arthroscoped before the Maquet procedure is carried out.

The Maquet procedure: effect of tibial shingle length on patellofemoral pressures.

The Maquet procedure--elevation of the anterior tibial tubercle--has been recommended for treatment of symptomatic osteoarthrosis of the patellofemoral joint. Although the operation was first described 30 years ago, it remains controversial, both on a clinical and on a biomechanical basis. In addition, deterioration of the long-term results has been suggested. One of the variables that has been ignored in both clinical and biomechanical studies has been tibial shingle length. In order to judge its effect, we examined contact pressures and areas in 15 cadaver knees with 7 and 20 cm tibial shingle lengths. We found significant patellofemoral pressure diminution only with 2 cm elevations. The short anterior tibial shingle with 2 cm of elevation tipped the patella on its superior pole, with a significant change in angle between the patella and the shingle. We suggest that this creates a potentially less than desirable biomechanical circumstance and believe it may explain the discrepancies among previously published reports.

The influence of basal cartilage calcification on dynamic juxtaarticular stress transmission.

Dynamic finite element analysis is used to elucidate the manner in which juxtaarticular stress distributions depend on the transitional mechanical properties of the calcified cartilage layer. A finite element model is used to study how these stresses change in response to the thinning of the articular cartilage layer associated with tidemark advancement. The finite element results indicate that shear stress levels within the deepest layer of articular cartilage are increased when tidemark advancement with concomitant cartilage-thinning and calcified cartilage/subchondral plate thickening is modeled. The cartilage-thinning associated with tidemark advancement, observed both clinically and experimentally, may be an explanation for what has previously been considered wear-related thinning.

Mechanical determinants of osteoarthrosis.

The joint is an organ and functions as a mechanical bearing created of biological materials. In the joint, as in all connective tissues, there is a relationship between mechanical factors and tissue behavior. Therefore, it is not surprising that joint health and osteoarthrosis are reflections of both mechanical and biological factors. Osteoarthrosis is not a disease, but organ failure caused initially by mechanical factors. The biological changes follow. There is no habitual pathophysiological cascade. Osteoarthrosis is best thought of not as a common final pathway, but as a common end stage. The hypotheses that in osteoarthrosis substructural disorganization of the matrix proceeds chondrocytic enzyme production, that impulsive loading is an essential factor in the progressive cartilage destruction, and that tidemark advancement and horizontal cartilage splitting are the primary mechanisms in progressive cartilage loss are discussed.

Relationship between lower limb dynamics and knee joint pain.

To test the hypothesis that appropriate and timely neuromuscular control of limb motions plays an important role in the preservation of joint health, we kinematically and kinetically examined the behavior of the legs of young adult subjects at heel strike during natural walking. We compared a group of 18 volunteers, who, we presumed, were preosteoarthrotic because of mild, intermittent, activity-related knee joint pain, with 14 age-matched asymptomatic normal subjects. The two groups of subjects exhibited similar gait patterns with equivalent cadences, walking speeds, terminal stance phase knee flexion, maximum (peak) swing angular velocity, and overall shape of the vertical ground reaction. However, our instrumentation detected statistically significant differences between the two groups within a few milliseconds of heel strike. In the knee pain group, the heel hit the floor with a stronger impact in this brief interval. Just before heel strike, there was a faster downward velocity of the ankle with a larger angular velocity of the shank. The follow-through of the leg immediately after heel strike was more violent with larger peak axial and angular accelerations of the leg echoed by a more rapid rise of the ground reaction force. This sequence of events represents repetitive impulsive loading, which consistently provoked osteoarthrosis in animal experiments. We refer to this micro-incoordination of neuromuscular control not visible to the naked eye as "microklutziness."

Morphologic and morphometric changes in synovial membrane associated with mechanically induced osteoarthrosis.

We sought to determine whether synovial leukocytic inflammation is a primary event in mechanically induced osteoarthrosis. Repetitive impulse loading (50 ms duration at 60 Hz for 40 minutes each day) was applied to the right hindlimbs of 24 New Zealand white rabbits for 3, 6, or 9 weeks. The synovial membrane from the medial suprapatellar area was examined qualitatively using transmission electron microscopy and quantitatively using light microscopic morphometry. The results indicate that synovial inflammation is not a primary event in this mechanically induced osteoarthrosis, but synovial hyperplasia occurs prior to histologically evident cartilage destruction at 6-9 weeks.

Mechanism of disc rupture. A preliminary report.

Lumbar intervertebral disc herniation is thought to be related to senescent changes in the nucleus pulposus except in rare instances of trauma. This investigation provides the first in vitro model of disc prolapse that reliably ruptures discs under physiologically reasonable stress. Fourteen vertebral motion segments with intact posterior elements were loaded repetitively at 1.5 Hz in a combination of flexion (7 degrees), rotation (less than 3 degrees), and compression (1,334 N) for an average of 6.9 hours (range, 3.0-13.0 hours) in a materials testing machine. Loading was terminated when reaction force leveled off for more than 1 hour. Ten discs failed through annular protrusions, and four failed by nuclear extrusion through annular tears, supporting the hypothesis that intervertebral disc prolapse is peripheral in origin. The annulus fibrosus is the site of primary pathologic change.

Stress wave effects in a finite element analysis of an impulsively loaded articular joint.

A dynamic contact finite element formulation was used to study transient stresses in the impulsively loaded rabbit knee, an established experimental model of mechanically induced osteoarthrosis. The computations were used to test the hypothesis that stress wave propagation and reflection, from juxtarticular interfaces of material property discontinuity, could be responsible for markedly increased levels of transient local cartilage stress. The finite element results demonstrated intuitively credible stress wave propagation and interfacial reflection phenomena. However, the magnitude of these waves was not nearly large enough to appreciably alter the quasi-static stress distributions otherwise prevailing. Thus, local stress wave reflection from interfaces of modulus discontinuity (for example the cartilage/subchondral plate) probably does not contribute appreciably to the heightened tissue sensitivity to impulsive loading experimentally observed in this animal model.

[Synovial membrane and cartilage changes in an arthrosis model. Instability and impact stress model]. / Synovialmembran und Knorpelveränderungen im Arthrosemodell. Instabilitäts- und Stoss-Belastungsmodell.

UNLABELLED: Surgical instability and repetitive impulsive loading was used to generate degenerative changes in knee joints of rabbits. Light- and electronmicroscopy was carried out at synovial membrane and cartilage samples. The instabilised joints had early synovial inflammation, preceding overall cartilage changes. Synoviocytes were activated and showed more and dilatated cytoplasmatic organells. Invaded round cells--potentially cartilage degenerative--were seen. In the loading model no initial synovial inflammation could be seen. Focal cartilage changes were located at the weight bearing zone. Two different inductive pathways may be involved in cartilage breakdown comparing the two arthrosis models. Mechanical factors seemed to trigger cartilage changes in the loading model, an inflammatory synovial pathway is likely to initiate cartilage breakdown in the instability model. CLINICAL RELEVANCE: The synovial membrane has the key-position for the cartilage degeneration in posttraumatic joint affections. The therapeutic use of antiphlogistic substances is indicated to supreme inflammatory mediators from the synovial membrane. This therapeutic concept seemed not to be useful in primary mechanical induced osteoarthrosis.

Bone and cartilage changes following experimental varus or valgus tibial angulation.

The purpose of this work was to determine whether subchondral bone changes are an integral part of the development of osteoarthrosis of the knee following experimentally created tibial angulation. Thirty degree varus or valgus proximal tibial osteotomies were created in female New Zealand white rabbits. Bone and cartilage changes were assessed grossly, radiologically, and histologically. Thirty-four weeks following osteotomy, severe cartilage changes, including osteophytes, fibrillation, derangement of cell columns, and cloning, were evident on the overloaded condyle, accompanied by increased subchondral bone density. The pattern of cartilage deterioration was different from that found in other experimental, mechanically induced arthroses. We conclude that osteoarthrosis is a final common pathway for mechanically induced joint failure, and that progressive cartilage change is associated with increased subchondral bone density.

A prognosis for ultra high molecular weight polyethylene.

Ultra high molecular weight polyethylene (UHMPWE) is now the material of choice for total joint replacement prostheses, in combination with a metal surface against which the polymer articulates. As this material has now been in use in this application for approximately three decades and other limiting factors (e.g. loosening of the prosthesis) have been improved upon, it is appropriate to attempt a long-term prognosis.