changes of articular cartilage after immobilization in a ...poster no. 674 • 54th annual meeting...
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Poster No. 674 • 54th Annual Meeting of the Orthopaedic Research Society
Changes of Articular Cartilage after Immobilization in a Rat Knee Experimental Model
Akira Ando, Yoshihiro Hagiwara, Eiichi Chimoto, Yoshito Onoda, Eiji ItoiOrthopaedic Surgery, Graduate School of Medicine, Tohoku University, Sendai, Japan
Introduction: Joint immobilization causes not only a limitation of motion butalso degeneration or atrophy of the articular cartilage. The amount of mechanicalstress and the preserved motion of the joint are of major importance for maintain-ing the integrity of articular cartilage (1). Though a large number of experimentalstudies regarding the articular cartilage after immobilization have been reported,changes in a joint cavity after joint immobilization have not been fully clarified (2,3). However, evaluation area varied among the previous reports. In this study, wechose three areas from each condyle of the femur and tibia to evaluate the changesthat occurred in the articular cartilage after immobilization.
Materials and Methods: Animals: Adult male Sprague-Dawley rats weighingfrom 380 to 400 g were used. Their knee joints were immobilized at 150° of flex-ion by rigid internal but extra-articular fixation for various periods (4). Sham oper-ated animals had holes drilled in the femur and tibia and screws inserted but noneof them were plated. One hundred twenty rats (3 days, 1, 2, 4, 8, and 16 weeks)were prepared for histological evaluation. We chose 3 areas (non-contact area, tran-sitional area, and contact area) from each condyle of the femur and tibia (Figure 1).
Figure 1: Gross observation of the right femoral articular cartilage. A: immobilized group at 8weeks, B: a standardized sagittal section of the medial midcondylar region of the knee in theimmobilized group at 8 weeks. Non-contact area (a and d), transitional area (b and e) and con-tact area (c and f ) were determined for histological evaluation in A and B. scale bar = 1 mm.
The specimens were fixed with paraformaldehyde. After decalcification anddehydration through a graded series of ethanol solution, the specimens wereembedded in paraffin. The embedded tissue was cut into 5 μm sagittal sections.Standardized serial sections were created in the medial midcondylar region of theknee. Each section from the 6 areas was evaluated respectively using the histolog-ical grading scheme (Modified Mankin’s score) (5). The number of chondrocytesand thickness of total articular cartilage in each area was measured on both sides ofthe condyle.
Statistics: Data for histological scores were analyzed statistically using theKruskal-Wallis test, and data for thickness and number of cells were analyzed usingone factor analysis of variance (ANOVA) with Bonferroni/Dunn post-hoc multi-ple comparisons. Differences between the experimental and control groups werecompared at each time point by Mann-Whitney’s U test (histological scores) andby unpaired t-test (thickness, number of cells). Data were expressed as mean ±standard deviation. A value of P < 0.05 was accepted as statistically significant.
Results: The surface of immobilized group became rough and a protrusion wasobserved (Figure 1A). Degenerative changes of the articular cartilage were mostsignificant in the contact area (Figure 2A).
Figure 2: Histological features in the contact area (Femur). A: immobilized group at 8 weeks.B: control group at 8 weeks. The cell staining intensity of hematoxylin and the number ofchondrocytes was decreased in the immobilized group compared with the control group. scalebars = 100 μm.
The histological grading scores of the femur were significantly greater after 1week in the contact area of the immobilized group compared with the controlgroup. The thickness in the contact area was not changed thorough all the experi-mental periods. The number of cells in the contact area was significantly reducedafter 2 weeks (Figure 3).
Figure 3: Changes of the femoral cartilage in the contact area. A: Histopathological gradingsocres, B: Thickness of articular cartilage, C: Number of chondrocytes.
Similar degenerative changes were observed in the tibial cartilage. Non-contactarea in the immobilized group seemed almost normal.
Discussion: The changes of articular cartilage became obvious as early as oneweek after immobilization. These changes may be due to a lack of mechanical stressor a lack of joint fluid circulation during immobilization. Although we do notknow the reversibility of these changes of articular cartilage, early mobilization ispreferable to avoid these cartilage changes.
References: (1) Kiviranta I et al. Histochemistry 1985; 82: 249-55. (2)Palmoski MJ, et al. Arthritis Rheum 1981; 24: 1329-37. (3) Jurvelin J, et al. ClinOrthop Relat Res 1986; 207: 246-52. (4) Hagiwara Y, et al. Ups J Med Sci 2006;111:303-313. (5) Sakakibara Y, et al. Clin Orthop Relat Res 1994; 299: 282-92.