Experimental inflammatory arthritis (EIA) produced by carrageenan injection provokes a rapid bone remodeling state with cortical and cancellous bone loss. The objective of this study was to determine whether changes in cortical mechanical properties and/or geometry occur in long bones, either near or remote to the site of inflammation. EIA was induced in the right tibio-femoral joint of rabbits over 56 days. The right humerus and right femur from 15 normal and 25 arthritis group animals were excized. Semi-cylindrical specimens of the medial cortical shaft were subjected to non-destructive four-point bending tests. Transverse sections at the four contact sites of the loading jig were photographed and digitized to obtain average cross-sectional area (A) and moment of inertia (I). Moment of inertia and slope of the load/deflection curve permitted calculation of modulus of elasticity (E) for each specimen. Load/time curves were also used to calculate per cent stress remaining in relaxation experiments. Per cent stress remaining, E, A, I and \(.......CONVERSION........\)\sqrt {{\text{I/A}}} (radius of gyration) were examined for differences by bone (humerus, femur) and by treatment (N,A) using two way ANOVA. The induction of inflammatory arthritis did not significantly alter the modulus of elasticity in either the femur or humerus; however, arthritis reduced the moment of inertia from \({\text{34}}{\text{.54}} \pm {\text{2}}{\text{.88}} \times {\text{10}}^{ - {\text{12}}} {\text{m}}^{\text{4}} {\text{ to 25}}{\text{.06}} \pm {\text{1}}{\text{.80}}^{ - 12} {\text{m}}^{\text{4}} ({\text{mean}} \pm {\text{SEM,}}p < 0.05)\). This was observed in the femur (near the arthritic joint), but not in the humerus (remote from arthritic joint). Analysis of area and ratio I/A demonstrated that this geometric effect of treatment was due to reduced area without gross cross-sectional shape changes. Per cent stress remaining in the femur (but not in the humerus) was higher in the arthritis specimens than in the normal specimens \(\left( {{\text{N:}}\;{\text{80}}{\text{.86}} \pm {\text{0}}{\text{.97}}\% ;\;{\text{A:}}\;{\text{83}}{\text{.25}} \pm {\text{0}}{\text{.71}}\% ,\;{\text{p}} < 0.05} \right)\). Thus, in this arthritis model, the principal mechanical or geometric effect on cortical bone was reduction of the cross-sectional area and moment of inertia. The viscoelastic relaxation response of bone was also altered, perhaps due to loss of water or collagen degradation.

Osteopenia is responsible for substantial comorbidity in patients suffering from rheumatoid arthritis and is an important factor in the surgical management of joint disease. In animal models of bone loss stimulated by inflammatory arthritis, increased bone remodelling and altered microstructure of bone have been documented. The subchondral bone plate near the joint surface is narrow and perforated by vascular inflammatory: invasion, and in the shaft the thin cortices are weakened by giant resorption defects. Biomechanical tests and a mathematical model of bone strength suggest that cortical defects, much larger than those found in normal osteonal remodelling, are principally responsible for the experimentally observed loss of strength. Similarly, these defects may explain the increased femoral fracture risk in rheumatoid arthritis.The osteoclast, the cell resorbing bone, is demonstrated in increased number and activity in rheumatoid arthritis and in animal models. Bisphosphonates, drugs that inhibit osteoclast function, have been shown experimentally to reduce both focal and generalized osteopenia and to prevent loss of bone strength. Bisphosphonates also protect articular cartilage from damage characteristic of inflammatory arthritis. The mechanism of chondroprotection may be prevention of subchondral bone resorption by the osteoclast and also an altered distribution of bone marrow cells. Thus, bisphosphonates, currently in clinical use for other bone metabolic diseases, appear to have potential as prophylaxis and treatment for osteopenia and joint damage in inflammatory arthritis.

One suggested cause of the high turnover osteopenia of experimental inflammatory arthritis is disuse of affected joints. To compare the influence of immobilization or disuse, or both, with that of inflammatory arthritis on bone turnover, rabbits were placed into four groups. In group 1, arthritis was induced in the right knee by seven intra-articular injections of 1% carrageenan, over 49 days; in group 2, a plaster cast was applied to immobilize the right hindlimb in flexion; in group 3, arthritis was induced and the hindlimb was immobilized; and in group 4, nothing was done (control). The fluorescent label calcein was administered in drinking water (0.05%) ad libitum to all groups on days 22-36. On day 49, specimens were prepared for analysis of bone volume and new bone volume at a near site (right femur) and at remote sites (contralateral femur and ipsilateral humerus). The data were analysed by multiple regression and Bonferroni tests. In group 1, new bone volume was three times higher than in group 2 or 4 (p < 0.05 for each comparison); this indicated increased bone remodeling in the right femur. This contrasted with group 2, in which neither index of bone remodeling was changed. The combination of immobilization with arthritis resulted in more intense osseous effects of inflammatory arthritis, with a one-quarter decrease in bone volume (group 3, 30.99 +/- 2.50; group 4, 42.07 +/- 2.38, p < 0.05), as well as a 4-fold increase in new bone volume (p < 0.001) compared with group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

The purpose of this study is to assess the reliability and validity of the Brooker grading of heterotopic ossification. Anteroposterior hip radiographs of 77 patients, taken 6 months following total hip arthroplasty, were blindly evaluated twice by two surgeons using the Brooker scale. Patients were also evaluated with the Harris hip scale, and range of motion of the hip was determined. All inconsistencies in heterotopic ossification grading were reviewed by the same two surgeons who developed six points of clarification to minimize ambiguities in the Brooker grading criteria. A second set of 76 radiographs were reviewed by the two surgeons using this modified Brooker index. The intraobserver reliability of the two readers was good, with agreements of 77 and 86% and weighted kappa values of 0.63 and 0.69, respectively. The two surgeons demonstrated fair interobserver reliability on the first reading (agreement of 68% and weighted kappa of 0.57) that improved to a good level of reliability (agreement of 77% and weighted kappa of 0.68) using the revised Brooker index. The grade of heterotopic ossification was correlated (r = -.25, P = .005) with the aggregate range of hip motion, but had no relationship to the patient's Harris rating. In conclusion, the grading of heterotopic ossification is reliable. Although the severity of heterotopic ossification did not correlate with the Harris scale, the relationship between heterotopic ossification and range of motion indicates that the Brooker index is also a valid measurement.

OBJECTIVE:To compare the frequency and severity of heterotopic ossification (HO) in patients with osteoarthritis or rheumatoid arthritis who undergo cemented or noncemented total hip arthroplasty.DESIGN:A prospective case study.SETTING:A university referral centre.PATIENTS:One hundred and sixty one patients underwent 184 total hip arthroplasties. The 184 hips were categorized as follows: cemented total hip arthroplasty--60 osteoarthritis hips, 26 hips affected by rheumatoid arthritis; noncemented total hip arthroplasty--67 osteoarthritic hips, 31 hips affected by rheumatoid arthritis.INTERVENTIONS:Total hip arthroplasty. A standard approach was used to implant either a cemented or noncemented prosthesis. Radiographs were obtained of each hip preoperatively, immediately postoperatively and 6 weeks, 3 months, 6 months and 1 year postoperatively.MAIN OUTCOME MEASURES:Radiographs were graded in blind fashion for HO, according to the criteria of Brooker. Modified Harris hip scores were calculated at 1 and 2 years postoperatively.RESULTS:HO (incidence of Brooker grades 2, 3 and 4) was greater after cemented (22%) than noncemented (9%) total hip arthroplasty in osteoarthritic hips (p < 0.05), but there was no significant difference between the two types of prosthesis in hips affected by rheumatoid arthritis. When both types of prosthesis were considered together there was no significant difference in the incidence of HO between osteoarthritic hips (15%) and hips affected by rheumatoid arthritis (12%). With respect to Harris hip score, the presence of grade 4 HO was associated with a significantly (p < 0.05) lower score (50.6) than grade 3 (89.4) and grade 2 (91) HO.CONCLUSIONS:Cemented total hip arthroplasty increases the frequency of HO only in osteoarthritic hips. Compared with Brooker's grades 2 and 3 HO, grade 4 HO significantly lowers the Harris hip score after total hip arthroplasty.

With use of the intravital bone label calcein, we previously identified, by histomorphometry, greatly increased new bone formation and juxtaarticular osteopenia (a high turnover state) in carrageenan-induced experimental inflammatory arthritis of the knee in rabbits. In Part I of this paper, we showed that a large increase in new bone formation after a stable incomplete distal femoral condylar osteotomy of normal bone in the rabbit does not increase bone volume (BV) in normal tissue adjacent to the osteotomy (zone 1). In this study, we performed an osteotomy of bone made osteopenic by experimental inflammatory arthritis. After 4 weeks of healing, we examined new bone formation and BV in five zones around the osteotomy. In zone 0 (the osteotomy gap), new bone formation filled the gap to normal BV, as we found for the normal/osteotomy group. In zone 1 (adjacent to but excluding the osteotomy gap), we found greatly increased new bone formation and a return to normal BV, increased from the osteopenic level induced by experimental inflammatory arthritis. In this model, osteotomy apparently reversed the bone-wasting process of inflammatory arthritis. This effect was not observed in other zones: the lateral condyle that had not been operated on, the metaphysis, or the diaphysis.

We performed a simple, undisplaced, incomplete osteotomy of the distal medial condyle of mature New Zealand White rabbits and permitted healing without fixation for 4 weeks. During the recovery period, the rabbits received the bone label calcein in their drinking water. From ground stained and unstained sections, we determined histomorphometric parameters in five zones: osteotomy gap, juxtaosteotomy, lateral condyle, metaphysis, and diaphysis. At 4 weeks, newly formed cancellous bone had obliterated the osteotomy gap. Osteotomy also stimulated new bone formation in cancellous bone of the medial condyle around the osteotomy. At that site, we found a fivefold increase in new bone without a change in bone volume (BV). Stimulation of bone formation was not observed in cancellous bone of the lateral condyle that had not been operated on or in cortical bone of the metaphysis or diaphysis. The maintenance of BV, despite increased new bone formation in the osteotomized medial femoral condyle, was probably due to a local acceleration of bone remodeling.