Influence of extension stem length and diameter on clinical and radiographic outcomes of revision total knee arthroplasty

Table 2 Univariate analysis of risk factors for aseptic loosening after revision total knee arthroplasty

Potential risk factor	Loosening (n = 17)	No loosening (n = 48)	OR	95% CI	p
Age, years	69.22	71.94	0.95	0.87–1.02	0.188
Female sex	8	39	4.88	1.47–16.13	0.009^*
Bone defect severity
Femur (loosening, n = 12)
I	3	28	0.29	0.07–1.22	0.075
IIa	9	25
Tibia (loosening, n = 12)
I	1	26	0.09	0.01–0.78	0.005^*
IIa	11	27
Prosthesis before revision
Primary TKA	14	43	2.28	0.86–6.01	0.094
UKA	0	3
Revision TKA	3	1
None	0	1
Stem length, mm
Femur	100 (75–200)	100 (25–200)	0.990	0.96–1.01	0.990
Tibia	75 (25–150)	100 (25–200)	0.98	0.96–1.01	0.157
Radiographic finding
Alignment, °	5.0 (2.1–6.2)	5.8 (5.2–7.4)	0.62	0.43–0.87	0.006^*
Femur (loosening, n = 12)
CFR_0.85	8.33 (1/12)	52.83 (28/53)	0.08	0.01–0.67	0.020^*
CFR_0.7 > 2 cm	16.67 (2/12)	75.47 (40/53)	0.07	0.01–0.33	0.001^*
CFR_0.7 > 4 cm	8.33 (1/12)	45.28 (24/53)	0.11	0.01–0.91	0.041^*
CFR_max	0.69 (0.54–1.00)	0.82 (0.47–1.00)	0.94	0.89–0.98	0.010^*
CFR_0.85 length	0.0 (0.0–4.7)	1.2 (0.0–7.8)	0.37	0.13–0.97	0.045^*
CFR_0.7 length	0.0 (0.0–7.5)	3.5 (0.0–10.3)	0.50	0.31–0.79	0.003^*
Tibia (loosening, n = 12)
CFR_0.85	8.33 (1/12)	47.17 (25/53)	0.10	0.01–0.84	0.034^*
CFR_0.7 > 2 cm	41.67 (5/12)	77.36 (41/53)	0.21	0.05–0.77	0.020^*
CFR_0.7 > 4 cm	16.67 (2/12)	58.49 (31/53)	0.14	0.02–0.71	0.018^*
CFR_max	0.77 (0.60–0.88)	0.82 (0.53–1.00)	0.96	0.91–1.01	0.159^*
CFR_0.85 length	0.0 (0.0–1.7)	0.0 (0.0–12.8)	0.40	0.15–1.07	0.069^*
CFR_0.7 length	1.6 (0.0–4.3)	4.5 (0.0–4.7)	0.70	0.52–0.94	0.019^*

Data are shown as frequency (number/total) or median (interquartile range) unless otherwise specified. Bone defect severity was assessed using the Anderson Orthopaedic Research Institute classification. Alignment indicates the femoral-tibial angle. CFR was calculated as the ratio between the stem width and the medullary canal width. CFR_x stands for CFR > x. CFR_x > y indicates the stem length > y for CFR larger than x. CFR_x length indicates the stem length for which CFR > x. CFR_max indicates the maximum CFR over the entire length of the stem. CI, confidence interval; CFR, canal filling ratio; OR, odds ratio; TKA, total knee arthroplasty; UKA, uni-compartment knee arthroplasty; *: p < 0.05

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