Computer Navigation in TKA and Implant Positioning, Function
Computer Navigation in TKA and Implant Positioning, Function
Patients in the CON group were more often female (p < 0.05), more often operated with cemented prostheses (p < 0.01) and had a higher ASA score (p < 0.01). There was no difference in age, Charnley category and diagnosis (p > 0.05, Table 1).
Coronal Plane Alignment. For the chi angle (Figure 3a), 80% of the knees in the CAOS group were within ±3° of the ideal, compared to 75% in the CON group. The difference was not statistically significant (p = 0.37). Mean measurement (Table 2) was 180.3° in the CON group and 180.7° in the CAOS group. The difference was not statistically different (p = 0.23). Mean measurements of individual femoral and tibial component (alpha and beta, respectively) differed statistically in the two groups, but all mean measurements were within ±1° of expected ideal (Table 2).
(Enlarge Image)
Figure 3.
Frontal plane alignment. Values less than 180° for chi angle and 90° for alpha or beta represent valgus. An outlier is defined as more than ±3° from ideal angle measurement. 3a: Chi (mechanical axis). Outliers are 20% for CAOS and 25% for CON (p = 0.37). 3b: Alpha (femoral component alignment). Outliers are 5% for CAOS and 18% for CON (p < 0.01). 3c: Beta (tibial component alignment). Outliers are 8% for both CAOS and CON (p = 0.58).
With conventional technique, 18% of the femoral components (alpha angle) were outside 3° of ideal, versus 5% in the navigated group (Figure 3b), and the difference was statistically significant (p < 0.01). For the tibial component (beta angle), the number of outliers was 8.4% in the CON group and 7.8% in the CAOS group (Figure 3c), which was not a statistically significant difference (p = 0.58).
Sagittal Plane Alignment. The gamma angle expressed the femoral flexion-extension. In the CON group, mean measurement was 4.4° and range 0–11°. In the CAOS group, mean and range was 7.2° and 0–16°, respectively (Figure 4a). The tibial slope (sigma) had a mean of 90 degrees and a range from 84 to 95 degrees in the conventional group. In the navigated group, mean tibial slope was 86 degrees, and the range was 79 to 95 degrees (Figure 4b).
(Enlarge Image)
Figure 4.
Sagittal plane alignment. In the CON group, ideal angles are 0–10° for gamma and 86° for sigma. In the CAOS group, the surgeon has adjusted the alignment to the patient's anatomy. Thus, the angles had a wider range compared to the conventional group. 4a: Gamma (femoral component flexion). Large angles indicate high degree of femoral component flexion. 4b: Sigma (slope of tibial component). Angles less than 90 indicate posterior slope.
Twenty randomly chosen patients (ten from each group) were measured twice by the observer and also by a second independent observer (ØG), to find the intra- and interobserver variabilities. The quality of measurements was confirmed by intraclass correlation coefficients (ICC). ICC was more than 0.8 for all angle measurements, which is considered a good reliability (Table 2).
We received questionnaires from 164 (83%) patients. The response rate was 74% in the CON group and 91% in the CAOS group. Total response rate for females was 83% and for males 83%. Median time from operation to completing the questionnaire was 3.3 (2.1–4.2) years in the CON group and 2.2 (1.5–3.7) years in the CAOS group.
In the unadjusted analysis, we observed no differences between the CON group and the CAOS group for the KOOS sub-scales pain, symptoms, ADL and QOL, with all p-values >0.2. In the sub-scale Sport and rec, the CON group scored 46.4 and the CAOS group scored 55.8 (p = 0.03) In the adjusted analysis, there were no statistical difference in any of the KOOS sub-scales, but there was a trend towards higher score in all sub-scales for patients in the CAOS group (Table 3, Figure 5). Mean KOOS ADL score was 84 in the CON group and 86 in the CAOS group at two years. This coincides with the reference data for KOOS ADL; in the age group 55–74 it is 86 for men and 77 for women. In the age group 75–84 years, it is 76 for men and 83 for women. Patients in the CAOS group also had a higher score in VAS for pain and satisfaction and ΔEQ-5D, but the differences were not statistically significant (all p-values >0.2) (Table 3, Figure 5).
(Enlarge Image)
Figure 5.
Questionnaire outcomes. Mean outcome scores for CON and CAOS. The first 5 outcomes represent the KOOS subscales. Results are adjusted for age, sex, fixation, Charnley category and preoperative EQ-5D index score (except for ΔEQ-5D). Outcomes were measured on a scale from 0 (worst) to 100 (best).
In the analyses of the detailed questions from KOOS (Figure 6), there was also a trend towards better results for CAOS. We observed a clinically significant difference in three questions, considering how often the patient experienced knee pain (p = 0.05), ability to bend the knee fully (p = 0.09) and difficulties in getting in/out of car (p = 0.03). The observed differences were all in favor of CAOS.
(Enlarge Image)
Figure 6.
Mean differences in outcome (detailed questions from KOOS) between CON and CAOS. *Difference is equal to mean score among CON and CAOS (positive values are in favor of CAOS), Adjusted for age, gender, diagnosis, fixation method, Charnley category and preoperative EQ-5D index scores in a multiple linear regression model. With a Bonferroni correction, the significance level is set at p < 0.001. Consequently, none of the single questions in KOOS are statistically significantly in the groups. KOOS = the Knee Injury and Osteoarthritis Outcome Score; CON = conventional technique; CAOS = computer assisted orthopedic surgery; ADL = function in daily living; Sport/rec = function in sport and recreation; QOL = knee related quality of life.
The possible difference for inliers and outliers for the sigma and gamma angle were investigated in the three situations; "Can you bend your knee fully?", "Getting in/out of car?" and "Getting on/off toilet?" in the CAOS group of 103 knees. The analyses were adjusted for the same variables as before. We found no statistical significant differences except for the question "Can you bend your knee fully?" where we found p-value = 0.044. Internally validation of the statistical model by use of bootstrapping (p = 0.08) could however not confirm this finding.
The operation time was 101 minutes in the CON group and 90 minutes in the CAOS group (Table 4). The difference was statistically significant (p < 0.01). By exclusion of uncemented prostheses in both groups, there was no longer any statistically significant difference (101 min for CON, 97 min for CAOS; p = 0.37).
Results
Patients in the CON group were more often female (p < 0.05), more often operated with cemented prostheses (p < 0.01) and had a higher ASA score (p < 0.01). There was no difference in age, Charnley category and diagnosis (p > 0.05, Table 1).
Radiographs
Coronal Plane Alignment. For the chi angle (Figure 3a), 80% of the knees in the CAOS group were within ±3° of the ideal, compared to 75% in the CON group. The difference was not statistically significant (p = 0.37). Mean measurement (Table 2) was 180.3° in the CON group and 180.7° in the CAOS group. The difference was not statistically different (p = 0.23). Mean measurements of individual femoral and tibial component (alpha and beta, respectively) differed statistically in the two groups, but all mean measurements were within ±1° of expected ideal (Table 2).
(Enlarge Image)
Figure 3.
Frontal plane alignment. Values less than 180° for chi angle and 90° for alpha or beta represent valgus. An outlier is defined as more than ±3° from ideal angle measurement. 3a: Chi (mechanical axis). Outliers are 20% for CAOS and 25% for CON (p = 0.37). 3b: Alpha (femoral component alignment). Outliers are 5% for CAOS and 18% for CON (p < 0.01). 3c: Beta (tibial component alignment). Outliers are 8% for both CAOS and CON (p = 0.58).
With conventional technique, 18% of the femoral components (alpha angle) were outside 3° of ideal, versus 5% in the navigated group (Figure 3b), and the difference was statistically significant (p < 0.01). For the tibial component (beta angle), the number of outliers was 8.4% in the CON group and 7.8% in the CAOS group (Figure 3c), which was not a statistically significant difference (p = 0.58).
Sagittal Plane Alignment. The gamma angle expressed the femoral flexion-extension. In the CON group, mean measurement was 4.4° and range 0–11°. In the CAOS group, mean and range was 7.2° and 0–16°, respectively (Figure 4a). The tibial slope (sigma) had a mean of 90 degrees and a range from 84 to 95 degrees in the conventional group. In the navigated group, mean tibial slope was 86 degrees, and the range was 79 to 95 degrees (Figure 4b).
(Enlarge Image)
Figure 4.
Sagittal plane alignment. In the CON group, ideal angles are 0–10° for gamma and 86° for sigma. In the CAOS group, the surgeon has adjusted the alignment to the patient's anatomy. Thus, the angles had a wider range compared to the conventional group. 4a: Gamma (femoral component flexion). Large angles indicate high degree of femoral component flexion. 4b: Sigma (slope of tibial component). Angles less than 90 indicate posterior slope.
Twenty randomly chosen patients (ten from each group) were measured twice by the observer and also by a second independent observer (ØG), to find the intra- and interobserver variabilities. The quality of measurements was confirmed by intraclass correlation coefficients (ICC). ICC was more than 0.8 for all angle measurements, which is considered a good reliability (Table 2).
Questionnaire
We received questionnaires from 164 (83%) patients. The response rate was 74% in the CON group and 91% in the CAOS group. Total response rate for females was 83% and for males 83%. Median time from operation to completing the questionnaire was 3.3 (2.1–4.2) years in the CON group and 2.2 (1.5–3.7) years in the CAOS group.
In the unadjusted analysis, we observed no differences between the CON group and the CAOS group for the KOOS sub-scales pain, symptoms, ADL and QOL, with all p-values >0.2. In the sub-scale Sport and rec, the CON group scored 46.4 and the CAOS group scored 55.8 (p = 0.03) In the adjusted analysis, there were no statistical difference in any of the KOOS sub-scales, but there was a trend towards higher score in all sub-scales for patients in the CAOS group (Table 3, Figure 5). Mean KOOS ADL score was 84 in the CON group and 86 in the CAOS group at two years. This coincides with the reference data for KOOS ADL; in the age group 55–74 it is 86 for men and 77 for women. In the age group 75–84 years, it is 76 for men and 83 for women. Patients in the CAOS group also had a higher score in VAS for pain and satisfaction and ΔEQ-5D, but the differences were not statistically significant (all p-values >0.2) (Table 3, Figure 5).
(Enlarge Image)
Figure 5.
Questionnaire outcomes. Mean outcome scores for CON and CAOS. The first 5 outcomes represent the KOOS subscales. Results are adjusted for age, sex, fixation, Charnley category and preoperative EQ-5D index score (except for ΔEQ-5D). Outcomes were measured on a scale from 0 (worst) to 100 (best).
In the analyses of the detailed questions from KOOS (Figure 6), there was also a trend towards better results for CAOS. We observed a clinically significant difference in three questions, considering how often the patient experienced knee pain (p = 0.05), ability to bend the knee fully (p = 0.09) and difficulties in getting in/out of car (p = 0.03). The observed differences were all in favor of CAOS.
(Enlarge Image)
Figure 6.
Mean differences in outcome (detailed questions from KOOS) between CON and CAOS. *Difference is equal to mean score among CON and CAOS (positive values are in favor of CAOS), Adjusted for age, gender, diagnosis, fixation method, Charnley category and preoperative EQ-5D index scores in a multiple linear regression model. With a Bonferroni correction, the significance level is set at p < 0.001. Consequently, none of the single questions in KOOS are statistically significantly in the groups. KOOS = the Knee Injury and Osteoarthritis Outcome Score; CON = conventional technique; CAOS = computer assisted orthopedic surgery; ADL = function in daily living; Sport/rec = function in sport and recreation; QOL = knee related quality of life.
The possible difference for inliers and outliers for the sigma and gamma angle were investigated in the three situations; "Can you bend your knee fully?", "Getting in/out of car?" and "Getting on/off toilet?" in the CAOS group of 103 knees. The analyses were adjusted for the same variables as before. We found no statistical significant differences except for the question "Can you bend your knee fully?" where we found p-value = 0.044. Internally validation of the statistical model by use of bootstrapping (p = 0.08) could however not confirm this finding.
Operation Time
The operation time was 101 minutes in the CON group and 90 minutes in the CAOS group (Table 4). The difference was statistically significant (p < 0.01). By exclusion of uncemented prostheses in both groups, there was no longer any statistically significant difference (101 min for CON, 97 min for CAOS; p = 0.37).
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