The effects of early rollback in total knee arthroplasty on stair stepping.

We investigated the effects of early compared with late (ie, in flexion) rollback on quadriceps efficiency during stair stepping. We studied 10 patients with the IB II (Zimmer, Warsaw, IN) total knee arthroplasty (TKA), designed to enforce rollback at 73 degrees of knee flexion; 9 patients with the Maxim PS (Biomet, Inc, Warsaw, IN) TKA, designed to enforce rollback between 20 degrees and 30 degrees of flexion; 8 patients with the TRAC PS (Biomet, Inc, Warsaw, IN) mobile bearing TKA, designed to enforce rollback at 8 degrees of flexion; and 21 healthy control subjects during stair stepping. We measured the external knee flexion moments, which must be largely balanced by quadriceps force acting over the quadriceps lever arm, as indicators of quadriceps efficiency. The peak external knee flexion moment generated by the IB II patients during stair stepping was 12.4% and occurred at 65 degrees of knee flexion. This moment was significantly less (P=.006) than the peak moment, 17.6%, generated by the healthy controls. Knee flexion for the IB II patients did not reach 73 degrees, and rollback was not enforced until after the peak moment (ie, maximum demands on the quadriceps) had been attained. The peak moments generated by the TRAC PS patients, 14.2%, and Maxim patients, 14.8%, were not significantly different from that of the controls. These results suggest that early as compared with late rollback returns more normal quadriceps efficiency during stair stepping.

Glycation induced crosslinking of link proteins, in vivo and in vitro.

OBJECTIVE: Reducing sugars have the ability to crosslink proteins through creation of advanced glycosylated end products (AGE). In this study, we determined the ability of AGE to induce crosslinking of link proteins and aggrecan proteoglycans. METHODS: Aggrecan proteoglycans and link proteins were purified from adult human articular cartilage and from young bovine nasal cartilage for in vivo and in vitro studies, respectively. In vitro studies concerned incubation of aggrecan aggregates or link proteins with ribose under physiological conditions. After 30 days, aggregates were centrifuged dissociatively to obtain aggrecan monomers and link proteins. Aggrecan monomers were analyzed by immunoblot assay. Incubated link proteins were analyzed by SDS-PAGE and Sephacryl-200 column chromatography. RESULTS: After extensive purification, adult human cartilage aggrecan continued to show the presence of link protein antigens by immunoblot analysis. Immunoblot analysis of purified aggrecan derived from ribose-treated aggregates also showed the presence of link protein antigens. Ribose treatment of link protein lead to polymerization that was confirmed by Sephacryl-200. CONCLUSIONS: These studies suggest that human link proteins tend to become crosslinked to aggrecan in adult cartilage. A likely cause of the crosslinking is formation of AGE due to reducing sugars.

The TRAC PS mobile-bearing prosthesis: design rationale and in vivo 3-dimensional laxity.

We present a posterior stabilized mobile-bearing prosthesis, TRAC PS, which has congruent contact from full extension to full flexion, allows for freedom of internal-external rotation, and has an automatic posterior shift in tibiofemoral contact on the tibia to maximize the quadriceps lever arm in flexion. TRAC PS has 2 radii of curvature in the sagittal plane, 1 for the distal femoral condyles and 1 for the posterior femoral condyles, as does the normal knee. The distal and posterior femoral condyles articulate congruently in the inner tracks or the outer tracks of the polyethylene bearing, respectively. Anterior or posterior sliding of the femoral condyles on the bearing or of the bearing on the tibial tray cannot occur, providing inherent anterior and posterior stability. Three-dimensional knee laxity testing was performed on 17 patients from 12 months to 25 months after total knee arthroplasty with the TRAC PS and on 18 healthy control subjects of similar ages. Normal ligament balancing and normal internal-external rotational laxity were achieved with the TRAC PS prosthesis. Anterior and posterior laxity in the patients with TRAC PS was significantly reduced compared with that of the control subjects.

The effects of the rotating-hinge total knee replacement on gait and stair stepping.

We studied 7 younger and 5 older patients who had rotating-hinge total knee replacements, 10 patients who had semiconstrained total knee replacements, and 8 younger and 11 older healthy control subjects to determine the effects of the rotating-hinge device on gait and stair stepping. The younger patients with the rotating-hinge device had few significant differences from the younger control subjects during gait or stair stepping. The older patients with the rotating-hinge device had several significant differences from both the older control subjects and subjects with the semiconstrained device during gait and stair stepping. Nevertheless, the proportions of older patients with the 2 devices who were able to perform the step-on activity for the highest step were the same.

Nonenzymatic glycation of cartilage proteoglycans: an in vivo and in vitro study.

In this study we have investigated whether proteoglycans (aggrecan) are modified by nonenzymatic glycation as in collagen. Purified human aggrecan from osteoarthritic and normal human knee articular cartilage was assayed for pentosidine, a cross-link formed by nonenzymatic glycation, using reverse-phase HPLC. In addition, an in vitro study was done by incubation of purified bovine nasal cartilage aggrecan with ribose. Pentosidine was found in all the purified human aggrecan samples. 2-3% of the total articular cartilage pentosidine was found in aggrecan. Purified link protein also contained penosidine. The in vitro study led to pentosidine formation, but did not appear to increase the molecular size of the aggrecan suggesting that pentosidine was creating intramolecular cross-links. Similar amounts of glycation were found in osteoarthritic and normal cartilage. Like collagen, aggrecan and link proteins are crosslinked by nonenzymatic glycation in normal and osteoarthritic cartilage. Crosslinking could be reproduced, in vitro, by incubating aggrecan with ribose.

Effects of basic fibroblast growth factor, transforming growth factor-beta 1, insulin-like growth factor-1, and insulin on human osteoarthritic articular cartilage explants.

This study evaluated the effects of basic fibroblast growth factor, transforming growth factor-beta 1, insulin-like growth factor-1, and insulin on the incorporation of thymidine and sulfate in human osteoarthritic articular cartilage. Tissue explants were obtained from 11 patients undergoing total knee arthroplasty and were categorized as nonfibrillated or fibrillated cartilage. The explants were cultured for 22 days, with changes of medium and growth factor every 72 hours, and labeled with [3H]thymidine and [35S]sulfate. Growth factors were used in the following concentrations: basic fibroblast growth factor at 1, 10, and 100 ng/ml; transforming growth factor-beta 1 at 0.5, 5, and 50 ng/ml; insulin-like growth factor-1 at 0.15, 1.5, and 15 ng/ml; and insulin at 0.05, 0.5, and 5 micrograms/ml. Basic fibroblast growth factor decreased thymidine incorporation to 70% and sulfate incorporation to less than 20% that of the growth factor-free controls. Transforming growth factor-beta 1 had no significant effect on thymidine incorporation, whereas the concentrations studied inhibited sulfate incorporation to approximately 40% that of the controls. At the concentrations tested, insulin-like growth factor-1 had no significant effect on incorporation of either thymidine or sulfate. In contrast, insulin significantly stimulated the incorporation of both. Compared with growth factor-free controls, insulin maximally increased thymidine incorporation by a factor (+/- SEM) of 2.36 +/- 0.47 and 1.69 +/- 0.19 in nonfibrillated and fibrillated explants, respectively; sulfate incorporation was maximally increased 1.60 +/- 0.24 and 1.92 +/- 0.29-fold for nonfibrillated and fibrillated explants, respectively. Of the factors tested, insulin demonstrated the greatest promise for promoting a synthetic response that may contribute to the regeneration of osteoarthritic cartilage.

Effect of link protein and free hyaluronic acid binding region on spacing of proteoglycans in aggregates.

Aging of articular cartilage results in accumulation of aggrecan fragments of various sizes that retain their ability to aggregate even though they may have relatively few glycosaminoglycan chains. Residual binding of partially degraded aggrecan may prevent binding of newly synthesized aggrecan subunits that have greater numbers of glycosaminoglycan chains. This study was undertaken to determine the effects of various relative molar ratios of intact aggrecan, link proteins, and hyaluronic acid binding region fragments on the structure of reconstituted aggregates. High molar ratios of link proteins relative to aggrecan decreased the spacing between adjacent aggrecan subunits; low molar ratios of hyaluronic acid binding region relative to aggrecan (4:1 or less) had no significant effect on spacing, and high molar ratios resulted in an increase in the spacing and a decrease in the percentage of aggrecan subunits found in aggregates. These data suggest that the density of aggrecan subunits on the aggregate is determined primarily by steric hindrance of the glycosaminoglycan chains of the aggrecan subunits and that, to a limited extent, partial degradation of aggrecan in an aggregate allows attachment of more aggrecan subunits.

Knee laxity in symptomatic osteoarthritis.

Twenty-two patients with primary osteoarthritis (OA) of the knee were studied to determine the effects of OA on laxity of the knee joint. Laxity was measured with a Genucom Knee Analysis System. Ten knees had mild OA (> 50% preservation of joint space). Fifteen knees had moderate OA (some preservation of joint space, but < 50%). Eighteen knees had severe OA (no joint space). A group of 18 knees from 9 healthy (asymptomatic) subjects of ages similar to those of the OA patients were used as controls. Compared to control knees, severe OA knees had less total anteroposterior (AP) translation (12.2 versus 6.6 mm, p < 0.025) and less total tibial rotation (79 versus 59 degrees, p < 0.01). Compared to early OA knees, knees with severe OA had 57% less average total AP translation (15.2 versus 6.6 mm, p < 0.01), 31% less total varus/valgus rotation (15 degrees versus 10.4 degrees, p < 0.016), and 26% less total internal/external tibial rotation (80.1 degrees versus 59 degrees, p < 0.007). These data indicate that osteoarthritic knees tend to have less laxity than normal knees, probably because of a combination of contracture of the ligaments and pressure of osteophytes against ligaments and other capsular structures.

Cementless total hip arthroplasty in patients with steroid-induced avascular necrosis of the hip. A 62-month follow-up study.

Twenty cementless porous-coated primary total hip arthroplasties (THA) were performed on 15 patients, all of whom were diagnosed with steroid-induced avascular necrosis (AVN). The average age of the patients at the time of surgery was 45 years. Minimum follow-up period for all patients was 24 months (average follow-up period: 62 months). Patients were rated using the modified Harris hip score, as well as serial radiographs. The average hip score at follow-up examination was 88, with 17 of the 20 hips having good or excellent clinical results. No revisions of the prostheses were performed. Using radiographic criteria, 12 femoral components met the criteria for bone ingrowth, seven were considered stable with fibrous fixation, and one femoral component was loose. When good initial femoral component fit was achieved, bone ingrowth reliably followed. Three acetabular components showed migration on serial radiographs. A high rate of acetabular component wear and osteolysis was noted. Avascular necrosis has been shown to adversely affect the outcome of hip arthroplasty surgery. Previous studies of patients with advanced AVN undergoing cemented THA report a high incidence of component loosening. Literature on the results of cementless THA in this patient group is sparse. The study demonstrates encouraging clinical results for cementless THA in steroid-induced AVN. Reliable femoral component fixation occurred if a good initial component fit was achieved; however, long-term acetabular loosening and wear remain serious concerns.

Chemical stabilization of cartilage matrix.

Severe destruction of articular cartilage in osteoarthritis manifests clinically when repair processes cannot keep up with the catabolic processes. Loss of proteoglycans, which give the tissue its ability to undergo reversible deformation, precedes and probably contributes significantly to breakdown of the matrix in the most superficial layers of articular cartilage. In this study, we have examined the ability of dithiobis[succinimidyl propionate], a bifunctional reagent with a 1.2-nm span that cross-links proteins at lysine amino acid, and poly-L-lysine of high molecular weight (average MW 360,000) to reduce passive loss of proteoglycans and collagen from thin slices (40 and 200 microns) of bovine nasal and human patellar cartilage incubated for 7 days in buffer at 4 degrees C. We present evidence that treatment of thin slices of cartilage with either of these agents is effective in reducing the loss of proteoglycans and collagen from the cartilage matrix and we define conditions (length of treatment and concentrations required) under which the stabilization of the cartilage matrix is optimized. Chemical stabilization of cartilage matrix may become an important modality of treatment in osteoarthritis by protecting the environment around chondrocytes during the repair process.

Evidence of proteoglycan/proteoglycan interactions within aggregates.

Nonaggregated proteoglycan monomers, digested fragments of the monomers, as well as link proteins have been shown to self-associate. These associations have not been shown to occur on the aggregate. However, previous reports, using the Kleinschmidt technique of monolayer electron microscopy, have noted proteoglycan subunits on the aggregate that appear to interact, either as branched proteoglycans or as proteoglycan subunits that appear to share the same attachment site on the hyaluronic acid chain. Branching and shared attachments were noted in all aggregates analyzed in this study. Increasing the average space between proteoglycan subunits on the reconstituted aggregate resulted in a significant decrease in branched proteoglycans, indicating either a weak association occurring on the aggregate, or an artifact created by a three-dimensional structure being reduced to a two-dimensional monolayer image. The shared attachments were independent of both the presence of link proteins and changes in spacing between proteoglycans, suggesting a proteoglycan-proteoglycan interaction occurring before aggregation. The interactions were not influenced by proteoglycan concentration at the time of aggregation. Link proteins, however, did increase the number of proteoglycans on the aggregate that could be cross-linked with a bifunctional reagent, suggesting that link proteins facilitate proteoglycan-proteoglycan interactions.

Paraxial macrodystrophia lipomatosa of the medial right lower limb.

We report the orthopaedic management of a child with macrodystrophia lipomatosa of the medial aspect of the right lower limb. Bony and soft tissue overgrowth of the medial aspect of the lower limb resulted in valgus deformities at the subtalar joint, ankle, knee, and hip. The paraxial distribution, which has not been previously reported, suggests that the condition may be caused by alteration of somatic cells during limb bud development.

The effect of marginal osteophytes on reduction of varus-valgus instability in osteoarthritic knees.

The varus-valgus stability of 20 knees with unicompartmental osteoarthritis was studied in vivo at the time of total knee replacement. Intact osteoarthritic knees had an average of 11.0 degrees of varus-valgus motion. Removal of osteophytes from the osteoarthritic compartment significantly increased the motion to 13.1 degrees (P less than 0.05), while subsequent removal of osteophytes from the nonosteoarthritic compartment further increased motion to 14.7 degrees (P less than 0.025). In primarily unicompartmental osteoarthritis, marginal osteophytes appear to stabilize osteoarthritic knees, but can cause fixed deformity.

In situ cross-linking of cartilage proteoglycans.

Although the in vitro interactions between purified cartilage matrix components have been studied extensively, little is known about these interactions in situ. In this study, cartilage was treated with a cross-linking reagent with a span of 1.2 nm between its reactive terminal groups in order to preserve the native relationships between closely associated matrix components throughout extraction, purification, and preparation for electron microscopy. After in situ cross-linking, electron microscopy and gel chromatography revealed that about one-half of the guanidine hydrochloride extractable proteoglycans were polymeric, usually with two to five proteoglycan subunits in each polymer. Cross-linking consistently involved the thin segments of the proteoglycan subunits. Some of the proteoglycan polymers were capable of binding hyaluronic acid and were parts of aggregates under associative conditions. SDS-polyacrylamide gel electrophoresis revealed that link proteins were present within the polymers, and studies in which purified proteoglycans were cross-linked in vitro confirmed that the link proteins increased the proportion of polymeric proteoglycans. These findings suggest that individual proteoglycans within cartilage have intimate associations with other proteoglycans that are mediated by link proteins.

In vitro reconstruction of a cartilage matrix granule network.

The cartilage extracellular matrix contains electron-dense granules and fine filaments when studied electron microscopically after staining with ruthenium red. The matrix granules contain proteoglycans, while the filaments are thought to represent hyaluronic acid. In the present study partial extraction of proteoglycans from the cartilage prior to staining reduced the density of matrix components to allow visualization of a well-developed network involving the matrix granules and hyaluronic acid filaments. The matrix granules frequently had multiple filamentous attachments and the network appeared to be formed by intersecting filaments with the matrix granules at points of intersection. A similar network was created in Sepharose CL-2B beads when proteoglycans, link proteins, and hyaluronic acid were concentrated in the beads. Elimination of any one of these components resulted in failure to form a complete network. Purified proteoglycan monomers alone were sufficient to create matrix granules in the beads. Filaments were seen only when hyaluronic acid was added to the beads. The nature of the network suggests that some type of association between separate aggregates is occurring both within cartilage and within the Sepharose CL-2B beads.

Orthopedic surgeons' attitudes and practices concerning treatment of patients with HIV infection.

Concern regarding an occupational risk of acquiring human immunodeficiency virus (HIV) infection may influence surgeons' willingness to operate. A questionnaire survey of all orthopedists in the five cities with the most cases of acquired immunodeficiency syndrome (AIDS) was conducted to assess attitudes and practices. Questionnaires were completed anonymously by 325 of 510 orthopedists. In the previous year, 43 percent had examined or operated on an HIV-infected patient, and at least 90 percent who had had an opportunity to operate on an HIV-infected patient had chosen to do so. Decisions to operate did not appear to be based on hospital requirements, perceived ethical obligations, or knowledge of HIV transmissibility. Most orthopedists (85 percent) claimed the right to order preoperative HIV testing of high-risk patients, but such testing was ordered infrequently. Although most orthopedists believed they could not be compelled to operate and that ethically they could refuse when their health was threatened, they almost always were willing to treat HIV-infected patients.

Extracorporeal hemolysis in orthopedic patients. Report of two cases.

Two patients who had extracorporeal hemolysis of their blood transfusions are reported. In both cases, accidental overheating and hemolysis of the transfused blood caused a gross hemoglobinuria. Because the etiology of the hemolysis was not readily apparent at the time, both patients were managed as though they had had an acute hemolytic transfusion reaction. Because there was no activation of the complement cascade by antigen-antibody complexes, both patients suffered no ill effects. Differentiation of extracorporeal hemolysis from hemolytic transfusion reactions requires a careful inspection of all blood administration equipment, as well as an analysis of the untransfused blood in both bag and tubing. Patients undergoing orthopedic procedures account for 15% of all blood transfused in the United States. Awareness of adverse effects of transfusion is therefore important to orthopedic surgeons.

Acute septic arthritis in chronic osteonecrosis of the hip.

Osteonecrosis is not well documented as a predisposing factor of septic arthritis despite such a relationship having obvious clinical significance. We report 4 patients with involvement of 5 hips with septic arthritis in established osteonecrotic joints. The etiologies of the osteonecrosis in our study included corticosteroid therapy, sickle cell disease and one case of idiopathic osteonecrosis. Osteonecrosis appears to render the hip more susceptible to hematogenously derived bacterial infection. In some cases, removal of the necrotic tissue may be necessary to cure the infection.

Mechanical disruption of human patellar cartilage by repetitive loading in vitro.

Plugs of cartilage and subchondral bone from patellae were subjected to cyclic compression consisting of rapid ramp loading for 0.3 seconds followed by a 2.7 second pause. At 1000 psi cyclic load, surface abrasion of the cartilage was noted at 250 cycles of compression. Primary fissures, which penetrated to the calcified cartilage, developed at 500 cycles. Secondary fissures, emanating from the primary fissures at 30 degrees-90 degrees angles, and penetrating to varying depths, were observed at 1000 cycles. Coalescence of fissures and undermining of cartilage fragments were noted at 8000 cycles. With greater loads, the same sequence of events occurred with fewer cycles except that primary fissures appeared before the surface was abraided. Fissure formation did not occur in specimens subjected to loads of 250 psi to 500 psi even if the superficial 100 micron of cartilage was removed and specimens were loaded for 120,860 cycles. The deeper layers of cartilage appear to be of prime importance in resisting fissure formation.