Effects of acute femoral head ischemia on the growth plate and metaphysis in a piglet model of Legg-Calvé-Perthes disease.

OBJECTIVE: To determine the effects of acute (≤7 days) femoral head ischemia on the proximal femoral growth plate and metaphysis in a piglet model of Legg-Calvé-Perthes disease (LCPD). We hypothesized that qualitative and quantitative histological assessment would identify effects of ischemia on endochondral ossification. DESIGN: Unilateral femoral head ischemia was surgically induced in piglets, and femurs were collected for histological assessment at 2 (n = 7) or 7 (n = 5) days post-ischemia. Samples were assessed qualitatively, and histomorphometry of the growth plate zones and primary spongiosa was performed. In a subset of samples at 7 days, hypertrophic chondrocytes were quantitatively assessed and immunohistochemistry for TGFß1 and Indian hedgehog was performed. RESULTS: By 2 days post-ischemia, there was significant thinning of the proliferative and hypertrophic zones, by 63 µm (95% CI -103, -22) and -19 µm (95% CI -33, -5), respectively. This thinning persisted at 7 days post-ischemia. Likewise, at 7 days post-ischemia, the primary spongiosa was thinned to absent by an average of 311 µm (95% CI -542, -82) in all ischemic samples. TGFß1 expression was increased in the hypertrophic zone at 7 days post-ischemia. CONCLUSIONS: Alterations to the growth plate zones and metaphysis occurred by 2 days post-ischemia and persisted at 7 days post-ischemia. Our findings suggest that endochondral ossification may be disrupted at an earlier time point than previously reported and that growth disruption may occur in the piglet model as occurs in some children with LCPD.

Quantitative T2 and T1ρ mapping are sensitive to ischemic injury to the epiphyseal cartilage in an in vivo piglet model of Legg-Calvé-Perthes disease.

OBJECTIVE: To determine if the quantitative MRI techniques T2 and T1ρ mapping are sensitive to ischemic injury to epiphyseal cartilage in vivo in a piglet model of Legg-Calvé-Perthes disease using a clinical 3T MRI scanner. We hypothesized that T2 and T1ρ relaxation times would be increased in the epiphyseal cartilage of operated vs contralateral-control femoral heads 1 week following onset of ischemia. DESIGN: Unilateral femoral head ischemia was surgically induced in eight piglets. Piglets were imaged 1 week post-operatively in vivo at 3T MRI using a magnetization-prepared 3D fast spin echo sequence for T2 and T1ρ mapping and a 3D gradient echo sequence for cartilage segmentation. Ischemia was confirmed in all piglets using gadolinium contrast-enhanced MRI. Median T2 and T1ρ relaxation times were measured in the epiphyseal cartilage of the ischemic and control femoral heads and compared using paired t-tests. Histological assessment was performed on a subset of five piglets. RESULTS: T2 and T1ρ relaxation times were significantly increased in the epiphyseal cartilage of the operated vs control femoral heads (ΔT2 = 11.9 ± 3.7 ms, 95% CI = [8.8, 15.0] ms, P < 0.0001; ΔT1ρ = 12.8 ± 4.1 ms, 95% CI = [9.4, 16.2] ms, P < 0.0001). Histological assessment identified chondronecrosis in the hypertrophic and deep proliferative zones within ischemic epiphyseal cartilage. CONCLUSIONS: T2 and T1ρ mapping are sensitive to ischemic injury to the epiphyseal cartilage in vivo at clinical 3T MRI. These techniques may be clinically useful to assess injury and repair to the epiphyseal cartilage to better stage the extent of ischemic damage in Legg-Calvé-Perthes disease.

IL6 receptor blockade preserves articular cartilage and increases bone volume following ischemic osteonecrosis in immature mice.

OBJECTIVE: Juvenile ischemic osteonecrosis (JIO) of the femoral head is one of the most serious hip disorders causing a permanent deformity of the femoral head in childhood. We recently reported that interleukin 6 (IL6) is predominantly increased in the hip synovial fluid of patients with JIO and that articular chondrocytes are primary source of IL6. This study investigated whether an inhibition of IL6 receptor improves cartilage preservation and bone healing in JIO. METHOD: A small animal model (i.e., 6-week-old mouse) of JIO was treated with either saline or tocilizumab, an IL6 receptor blocker, for 6 weeks. RESULTS: TUNEL-positive chondrocytes in the articular cartilage were reduced by the tocilizumab treatment, concomitant with the increase in cartilage matrix. The levels of a cartilage anabolic marker Sox9 was significantly increased in the articular cartilage of mice treated with tocilizumab. Micro-CT assessment showed tocilizumab treatment significantly increased trabecular epiphyseal bone volume (P = 0.001, n = 10), thickness (P = 0.007) and number (P = 0.014) and decreased bone separation (P = 0.002) and its deformity (P = 0.003). A bone formation marker, BMP2, and an angiogenic marker, vascular endothelial growth factor (VEGF), were both significantly increased by tocilizumab treatment under hypoxia using human chondrocytes while the bone resorption marker, RANKL/OPG ratio, was reduced. CONCLUSION: Tocilizumab treatment following ischemic osteonecrosis has cartilage anabolic effect and increases bone volume in JIO mouse model. The findings lead to a possible application of tocilizumab for preclinical study using a large animal model of JIO and a clinical trial to validate this treatment.

Regeneration of the proximal tibial epiphysis after infantile osteomyelitis: report of three cases with an eight- to 22-year follow-up.

We reviewed three infants with destructive osteomyelitis involving the proximal tibial epiphysis at a follow-up of eight to 22 years. All cases showed early radiographic destructive changes in the medial or lateral aspects of the epiphysis and metaphysis. Despite the ominous early appearance of the epiphysis, all cases showed spontaneous re-ossification of the epiphysis with restoration of the tibial condyle and preservation of joint congruity. The patients, however, developed a valgus or varus deformity which was treated satisfactorily with one to three proximal tibial osteotomies. The potential for regeneration of the epiphysis following infantile osteomyelitis of the proximal tibia suggests these cases should be treated expectantly with regard to joint congruity.