Achondroplasia natural history study (CLARITY): 60-year experience in orthopedic surgery from four skeletal dysplasia centers

Table 7 Incidence of lower extremity procedures by birth cohort

Birth cohort	Total patients	Patients with lower extremity surgery N (%)	Age at first lower extremity surgery mean ± SD	Total number of lower extremity surgeries	Years contributed	Surgeries per 1000 patient years	Incidence rate ratio (95% CI)
2010–date	239	11 (4.6)	4.98 ± 1.03	17	813.96	20.89	Reference
2000–2009	356	65 (18.3)	7.17 ± 3.28	169	3140.49	53.81	2.58 (2.42–4.24)
1990–1999	314	100 (31.8)	8.91 ± 5.24	257	3674.43	69.94	3.35 (3.15–5.47)
1980–1989	231	68 (29.4)	9.63 ± 5.25	139	3189.94	43.57	2.09 (1.96–3.45)
< 1980	234	47 (20.1)	16.73 ± 13.79	103	7248.89	14.21	0.68 (0.64–1.14)
Total	1374	291 (21.2)		685	18,067.71

Incidence was represented by person-year (surgeries per 1000 years) and the incidence rate ratio, which standardized the number of patients and years contributed in each cohort. A total of 685 lower extremity surgeries were performed in 291 patients. Patients born between 1990 and 1999 had the highest incidence rate ratio for lower extremity surgeries

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