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Predictive factors for longer operative times in patients with medial knee osteoarthritis undergoing total knee arthroplasty
Journal of Orthopaedics 20 (2020) 181–185
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Journal of Orthopaedics journal homepage: www.elsevier.com/locate/jor
Predictive factors for longer operative times in patients with medial knee osteoarthritis undergoing total knee arthroplasty☆
T
Yoshinori Ishiia,∗, Hideo Noguchia, Junko Satoa, Hana Ishiib, Ryo Ishiic, Shin-ichi Toyabed a
Ishii Orthopaedic & Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan Kanazawa Medical University, School of Plastic Surgery, 1-1 Daigaku Uchinada, Ishikawa, 920-0253, Japan c Sado General Hospital, 161 Chikusa Sado, Niigata, 952-1209, Japan d Niigata University Crisis Management Office, Niigata University Hospital, Niigata University Graduate School of Medical and Dental Sciences, 1 Asahimachi Dori Niigata, Niigata, 951-8520, Japan b
A R T I C LE I N FO
A B S T R A C T
Keywords: Medial knee osteoarthritis Operative time TKA Bone mineral density Tibiofemoral angle Body mass index
Background: Prolonged operative time has frequently been implicated as a risk factor for various complications after total knee arthroplasty (TKA). We aimed to determine whether preoperative factors such as sex, age, body mass index (BMI), prosthetic design, tibiofemoral angle (TFA), range of motion, coronal laxity, Hospital for Special Surgery score and periarticular bone mineral density (BMD) affect operative time. Methods: We evaluated 164 patients (187 knees) with medial osteoarthritis who underwent primary TKA performed by a single surgeon. The medical records of 27 males and 137 females (median age of 77 and 72 years, respectively) were retrospectively reviewed. TFA was measured on non-weightbearing, standard radiographs. We used dual-energy X-ray absorptiometry to measure BMD, and an arthrometer to evaluate total coronal laxity in each patient. Results: According to univariate analyses, there was a weak positive correlation between BMI and operative time (r = 0.265, p < 0.001), between TFA and operative time (r = 0.235, p = 0.001) and between BMD of the femur and tibia and operative time (r = 0.280, p < 0.001, r = 0.286, p < 0.001, respectively). No significant correlations were found between the other factors and operative time. Based on multivariate analyses, only BMD of the tibia and TFA were significantly correlated with operative time (β = 0.418, p < 0.001 and β = 0.182, p = 0.007, respectively). Conclusions: TFA and BMD of the tibia were the variables more strongly correlated with operative time. Surgeons should recognize preoperatively that patients who have increased TFA, higher periarticular BMD, and higher BMI may have longer operative times. Level of evidence: Level IV retrospective study.
1. Introduction The optimal total knee arthroplasty (TKA) procedure involves accurately completing each step of the operation, and fulfilling each design concept in a shorter time. It is important to perform the operation appropriately, as this is associated with good postoperative clinical outcomes. Both the correct positioning of the components and the balancing of the soft tissues in various TKA designs have been reported in numerous papers to lead to successful TKA outcomes in the long term. Meanwhile, prolonged operative time in TKA has frequently been
implicated as a risk factor for complications, including infection,1 venous thromboembolism,2 and neurologic deficit,3 and remains a potentially modifiable variable that is of interest to surgeons and hospitals interested in quality improvement. Naranje et al.4 found that only prolonged operative time was a risk factor for an increased rate of postoperative infection. Factors related to surgical time can be considered to be either surgeon-related factors or patient-related factors. Possible surgeon-related factors contributing to prolonged operative time have been previously reported, and include low surgeon procedural volume and/or low hospital procedural volume,4,5 no use of tourniquet,6 use of patient-specific instrumentation,7 computer
☆
The present work was performed at the Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361–0037, Japan. Corresponding author. Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan. E-mail addresses: [email protected] (Y. Ishii), [email protected] (H. Noguchi), [email protected] (J. Sato), [email protected] (H. Ishii), [email protected] (R. Ishii), [email protected] (S.-i. Toyabe). ∗
https://doi.org/10.1016/j.jor.2020.01.026 Received 12 December 2019; Accepted 24 January 2020 Available online 25 January 2020 0972-978X/ © 2020 Professor P K Surendran Memorial Education Foundation. Published by Elsevier B.V. All rights reserved.
Journal of Orthopaedics 20 (2020) 181–185
Y. Ishii, et al.
navigation,5 and a mini skin incision.8 In addition, young age,5 male sex,4,9,10 high body mass index (BMI),4,11 American Society of Anaesthesiologists (ASA) Class12 ≧ 3,5 previous surgery to the knee5 and a diagnosis other than osteoarthritis (OA)5 have been reported to be patient-related factors contributing to prolonged operative time. The initiation and progression of medial knee OA is affected by various factors. A logical and stepwise approach should be used for the management of the varus deformity in primary TKA for medial knee OA.13,14 Thus, it is reasonable to speculate that the more severe the deformity or contracture of the arthritic knee, and/or the higher the bone mineral density (BMD) that is recently reported to be affected by joint loading axis15 and body weight,16 the longer time it may take during surgery to correct the deformity or contracture and to osteotomize the femur and tibia. Therefore, the purpose of this study was to evaluate and clarify the factors related to operative time from skin incision to wound closure in TKA procedures performed by one experienced surgeon. We analysed preoperative factors such as sex, age, and BMI, which have previously been demonstrated to affect operative time, and other factors such as the retention of the posterior cruciate ligament (PCL), tibiofemoral angle (TFA), range of motion (ROM), coronal laxity and Hospital for Special Surgery (HSS) scores,17 as well as BMD of the femur and tibia. The clinical significance of this study was that the surgeon may be able to recognize the factors determining operative time prior to TKA. In addition, it may help the hospital administration efficiently use facilities such as the operating room.
2.1. Preoperative clinical evaluation The HSS score17 is a physician-derived score that includes an evaluation of alignment, range of motion, and joint laxity. We measured the TFA, which is related to OA and leg alignment,19 on non-weightbearing, standard radiographs. A physical therapist measured maximum knee flexion and extension using a standard hand-held goniometer with 38-cm arms, while the patient was supine under nonweightbearing conditions. The lateral femoral condyle was used as the landmark to centre the goniometer, with the stationary arm directed toward the greater trochanter and the movable arm directed toward the lateral malleolus. The amount of knee flexion was measured and recorded to the nearest 5°. Patient clinical characteristics are summarized in Table 1. 2.2. Outcome measures and bias 2.2.1. Laxity evaluations The laxity of the medial and lateral sides was measured with a Telos arthrometer (Fa Telos; Medizinisch-Technische Gerätebau GmbH, Sulzbach, Germany) with the patient lying supine on a table on the day before surgery. On the medial/lateral stress test, a force of 150 N was applied just above the joint on the lateral or medial femoral condyle. To measure the medial and lateral angles, the femoral boundary used was the distal convex margin of the condyles. The tibial boundary was the outer margin of the condyles. The neutral, unloaded position was defined as the baseline, while the total angle that indicated the angular motion from the baseline to the loaded position between the medial and lateral sides of the knee was defined as coronal laxity.14 An experienced technician performed all of the tests. Concerning test-retest reliability, the intraclass correlation coefficients (95% CI) were 0.971 (0.928–0.988) for the maximum medial, 0.935 (0.843–0.974) for the neutral, and 0.962 (0.900–0.985) for the maximum lateral position. The standard error of the measurement (maximum error) was 0.354 (0.474) for the maximum medial, 0.525 (0.736) for the neutral, and 0.412 (0.534) for the maximum lateral position.14
2. Materials and methods This study was conducted at a single centre between October 2009 and February 2018. Informed consent was obtained from all patients, and included a description of the protocol and a discussion of potential dual-energy X-ray absorptiometry (DXA) and dynamometer-related complications. The Research Board of Healthcare Corporation Ashinokai, Gyoda, Saitama, Japan, approved the study (ID number: 2017–5), which included 164 consecutive patients (187 knees) who underwent primary TKA. We enrolled 63 patients (63 knees) who were undergoing TKA with a posterior cruciate ligament (PCL)-retaining design and 114 patients (124 knees) with a PCL-substituting design using the LCS® Total Knee System (DePuy, Warsaw, IN, USA). We analysed data from 27 males and 137 females whose preoperative diagnosis was medial knee OA. We excluded patients with rheumatoid arthritis and those who had previously undergone a tibial osteotomy. Although ASA12 class≧3 was reported to influence operative time,5 all patients in this series were ASA class 1 or 2 (Table 1).
2.2.2. Measurement with DXA DXA scans of the periarticular knee joint were acquired with a Lunar Prodigy densitometer (GE Medical Systems Lunar, Madison, WI, USA) on the day before surgery. A single operator scanned all knees. For the distal femur and proximal tibia scans, patients were placed in a supine position and each knee in turn was positioned within a supportive brace with the patella facing upward. Patients who had a flexion contracture were measured at their position of maximum knee extension. The Lunar Prodigy software was used to determine bone mineral content (g) and BMD (g/cm2) for the medial and lateral regions of interest (ROI) in both the femur and tibia. The BMD values of the femoral and tibial condyles were measured and are referred to as follows: medial femoral condyle, FM; lateral femoral condyle, FL; medial tibial condyle, TM; and lateral tibial condyle, TL. The height of the ROI extended 2 cm from the joint line because the osteotomy during TKA surgery was usually performed within a depth of 2 cm. The external border of the ROI extended to the subperiosteal surface of the femur and tibia as determined manually by a single technician. The patella served as the inner border for the medial and lateral proximal femoral ROI, while the intercondylar eminences served as the inner border for the medial and lateral proximal tibial ROI. In the femoral ROI, care was taken to avoid including the patella in the measurement. In the lateral ROI, care was also taken to avoid including the fibula in the measurement (Fig. 1). The average BMD values of the FM and FL and those of the TM and TL in each patient were analysed as BMD of the femur and tibia, respectively. Precision was calculated as the coefficient of variation between the BMD values of the scans. The precision of the measurements was 2.6% in the FM, 5.5% in the FL, 4.3% in the TM and 5.0% in the TL.15
Table 1 Preoperative patient characteristics. Parameter
Osteoarthritic Patients
Knees/Patients Gender: Female (of knees)/Male (of knees) Osteoarthritis Gradea ASA Classb Median [25th percentile, 75th percentile] Age (range) (years): Female/Male Body Height (cm) Body Weight (kg) Body Mass Index (BMI) (kg/m2) Tibiofemoral angle (°) Range of motion (°) Total coronal laxity (°) HSS scorec BMDd of Femur (g/cm2) BMDd of Tibia (g/cm2)
187/164 137 (156)/27 (31) III: 6, IV: 181 I: 16, II: 121
a b c d
72 [68, 78]/77 [70, 81] 151 [146,156] 59 [52,67] 26 [23,28] 181 [179,184] 115 [100,125] 7 [6,9] 44 [36,51] 0.958 [0.854, 1.082] 0.884 [0.734, 0.998]
Kellgren-Lawrence grade.18 American Society of Anaesthesiologists.12 HSS score: Hospital for Special Surgery Score.17 BMD: bone mineral density. 182
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Table 2 Univariate analyses: (I) Spearman's correlation coefficient for variables comparing operative time and the preoperative variables. (II) Comparison between the other factors and operative time for discrete variables analysed using the Mann–Whitney U test. (I) Characteristics
p values
R
BMI Age TFA Range of Motion Coronal Laxity HSS score BMD of femur BMD of tibia (II) Variables (knees) Gender Female: 156、Male: 31 PCL retention; PCL-R 63 vs PCL-S 124
< 0.001 0.039 0.001 0.063 0.118 0.033 < 0.001 < 0.001 p values 0.121 0.052
0.265 −0.152 0.235
−0.156 0.280 0.286
BMI, body mass index; TFA, tibiofemoral angle; HSS, Hospital for Special Surgery; BMD, bone mineral density; PCL, posterior cruciate ligament; PCL-R, PCL-retaining; PCL-S, PCL-substituting.
rank correlation tests. Univariate and multivariate analyses were performed to examine preoperative factors related to TKA operative time. Spearman's rank correlation coefficient was used to investigate the association between any two variables. The Mann–Whitney U test was used to determine differences between two groups. Multiple linear regression analyses were performed to identify variables significantly associated with proximal tibial BMD. Multiple linear regression models were constructed by entering all variables shown in Table 2 and using the stepwise selection method. The strength of the correlation of the rank coefficients was defined as: strong = 0.70–1.0, moderate = 0.40–0.69, or weak = 0.20–0.39. Post hoc power analyses were performed after the study. The power of Spearman's rank correlation test with a medium effect size (0.3) and an α-error of 0.05 was 0.989, and the power of the Mann–Whitney U test with a medium effect size (0.5) and an α-error of 0.05 was 0.695 for gender of patients and 0.881 for retaining of PCL in surgery, respectively. In all tests, a p < 0.05 was considered statistically significant. All statistical analyses were performed using IBM SPSS Statistics version 23 (IBM Japan, Tokyo, Japan). Values are expressed as median [25%; 75% percentile].
Fig. 1. Bone mineral density values were measured in the femoral and tibial condyles. FM: medial femoral condyle; FL: lateral femoral condyle; TM: medial tibial condyle; and TL: lateral tibial condyle. The height of the regions of interest (ROI) extended to 2 cm below the joint line. The external border of the ROI extended to the subperiosteal surface of the femur and tibia as determined manually. The patella served as the inner border for the medial and lateral proximal femoral ROI, and the intercondylar eminences served as the inner border for the medial and lateral proximal tibial ROI. In the femoral ROI, care was taken to avoid including the patella in the measurements. In the lateral ROI, care was also taken to avoid including the fibula in the measurements.
3. Results Median operative time was 55 min [51; 60] (range; 41–116). According to univariate analyses using Spearman's correlation coefficient for continuous variables, there was a weak positive correlation between BMI and operative time (r = 0.265, p < 0.001), between TFA and operative time (r = 0.235, p = 0.001), between BMD of the femur and operative time (r = 0.280, p < 0.001) and between BMD of the tibia and operative time (r = 0.286, p < 0.001) (Table 2). However, no significant correlations were found between the other factors and operative time for continuous and discrete variables (Table 2). Based on multivariate analyses using multiple linear regression analysis with stepwise variable selection, only BMD of the tibia and TFA were significant factors associated with operative time (β = 0.418, p < 0.001 and β = 0.182, p = 0.007 respectively) (Table 3).
2.2.3. Surgical technique From initial skin incision to wound closure, a single experienced surgeon performed all of the surgeries using standardized techniques, as described previously.20 In all knees, the femoral components were fixed without cement, and the tibial components were fixed with cement. The patella was not resurfaced, and no lateral retinaculum release was performed in any case. Ligament-balancing techniques, which included the removal of peripheral osteophytes and necessary soft tissue releases, were used and confirmed with spacer blocks to ensure a balanced knee with equal flexion and extension gaps. The proper intraoperative coronal and sagittal plane laxity was confirmed manually, although no intraoperative quantitative evaluation was performed. As reported in our previous study, achieving about 4° of coronal laxity in extension and 3° of coronal laxity in flexion, measured using an arthrometer, was associated with good clinical outcomes for both prostheses.21
4. Discussion Our results revealed two important findings. First, there was a weak positive correlation between operative time and BMI, TFA and BMD of the femur and tibia on univariate analyses. Also, only TFA and BMD of the tibia showed significant correlations with operative time on multivariate analyses. Our results showed that TFA and BMD of the tibia are the most significant factors among the factors related to operative time
2.2.4. Statistical analysis Because data for certain variables did not pass the Kolmogorov–Smirnov normality test or the Shapiro–Wilk normality test, we used non-parametric Mann–Whitney U tests and Spearman's 183
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(Libaud11 mean age, 65 years; Kosashvili10 mean age, 67 years in men and 66 years in women). In addition, the relatively low number of included males may have also masked sex-associated differences, although the numbers would be sufficient to detect differences of 0.5 by power analysis. Basques et al.9 reported in a recent large-scale study that the sex-related differences in operative time were small and unlikely to be clinically significant, although men had a slightly increased operative time (+6 min) compared with women. Finally, in contrast to our hypothesis, there were no correlations between operative time and the retention of the PCL, ROM, coronal laxity or clinical scores. It seems reasonable that it would take a longer time to perform a satisfactory procedure in cases where the PCL is retained, where there is poor ROM, or where there is less coronal laxity, since meticulous soft tissue releases might be needed. In fact, Mihalko et al.13 described the necessity of stepwise medial, lateral, and/or posterior soft tissue releases, including the PCL, in knees with various degrees of medial OA and flexion contracture to obtain a well-balanced knee or a knee with good ROM. However, these three factors did not correlate with operative time, and we speculate that there may have been two reasons for this. One is a patient-related factor. Since patients with the same laxity and/or ROM had different degrees of contracture of the periarticular soft tissues including the PCL, the time necessary for each stepwise procedure was likely inconsistent. The other is a surgeonrelated factor. All surgeries in this series were performed by a single experienced surgeon in an academic practice.14–16,20,21,25 Thus, it is reasonable to assume that intraoperative efficacy was maximized with regard to meticulous soft tissue releases. That is, the surgeon's skill was unlikely to create a significant time lag regardless of the different degrees of contracture and/or laxity. Finally, with regard to HSS score,17 the lower point distributions of ROM, laxity, and alignment than those of pain or activity level might not reflect the operative time in each patient, even if the soft tissue releases or osteotomies took longer. There are several limitations of this study. First and foremost, this was a retrospective medical record and database review, which has inherent limitations. Second, the proportion of males to females was unequal. The higher prevalence of OA and TKA operations in females is a common finding in Japanese ethnic groups. This might be explained by the racial difference in disease demographics and sex-based disparities in the incidence of bow-leggedness. In addition, female predominance is common in studies of Asian patients.8,16,20,21 Third, the PCL-retaining design was less common than the substituting design. Initially, the order of implant use was quasi-randomised; patients with even medical record numbers received a PCLR implant, and patients with odd medical record numbers received a PCLS implant. Unexpectedly, the PCL-retaining design was discontinued by the manufacturing company at the end of January 2013, and the TKA procedures were performed using only the substituting design after that time. Fourth, on the short radiograph, which does not include the femoral head and ankle, it is not easy to obtain an accurate TFA. However, Ishii et al. compared TFA on short radiographs with TFA observed on long radiographs using the best correlation procedure available (r = 0.94),25 and the discrepancy between them was reported to be only 0.5° (SD 1.2°).25 Finally, unlike a previous report that measured time for each surgical step,7 the total operative duration was evaluated. Despite these limitations, the strength of this study was that less surgeon-related bias was present than in previous studies. This was because all procedures from skin incision to wound closure were performed by a single experienced surgeon who has well over the 300 TKA cases that are needed to prevent prolonged operative time due to inexperience.4
Table 3 Multivariate regression analysis.
BMD of tibia TFA
B
S.E.
Β
significance
95% CI for B
14.084 0.358
2.263 0.132
0.418 0.182
< 0.001 0.007
9.620 0.097
18.548 0.619
A multivariate linear regression model was constructed by entering all variables identified in Table 2 by using a stepwise selection method to identify variables significantly associated with operative time. BMD; bone mineral density; TFA, tibiofemoral angle; S.E, standard error: CI, confidence interval.
that we evaluated in this study. Second, the other factors such as sex, ROM, coronal laxity, prosthetic design, and clinical score showed no significant correlation with operative time. It may be reasonable that there was a significant correlation between both BMD and operative time, since BMD enables the quantitative evaluation of the variations in bone biomechanical characteristics of the knee before a TKA procedure.22 Petersen et al.22 stated that BMD is a recognized reflection of trabecular bone strength. Although cutting through denser bone was recognized as a factor that may prolong operative time,4 to our knowledge, this is the first study to demonstrate the correlation between actual BMD values and operative time. Based on multivariate analyses, only BMD of the tibia showed significant correlations with operative time, so measurements of the tibial side alone may be enough to evaluate the BMD for estimation of operative time. However, the measurement of BMD before TKA is not common in practice.15 Considering that body weight (BW) is reported to be the most important factor influencing proximal tibial BMD,16 BMI may take the place of BMD values and be a practical indicator of operative time in TKA. BMI is well reflected by the BW, which is measured routinely before surgery regardless of the size and level of the facilities. TFA was another significant predictive factor for operative time in this study. TFA may reflect the degree of varus deformity contributing to medial OA, and stepwise procedures such as soft tissue releases, removal of osteophytes, and osteotomy have been needed to obtain correct alignment and balanced laxity after TKA. A larger TFA indicates more varus deformity, and this may lead to a longer time required to obtain an aligned and well-balanced knee. Thus, it is reasonable that operative time may be prolonged in proportion to the severity of the TFA abnormality. In addition, since a more varus alignment was associated with higher medial-to-lateral periarticular BMD of the knee,23 a larger TFA might necessitate a longer time to cut the femur and tibia. Therefore, a large TFA may be one of the most significant factors determining operative time. Several previous studies documented the relationship between increasing BMI and prolonged operative time.4,11 Liabaud et al.11 showed a direct linear relationship between BMI and operative time in patients undergoing TKA. In addition, Naranje et al.4 reported prolonged operative times in males as compared with females with the same BMI. They hypothesized that larger BMI leads to difficulties in both exposure and closure, both of which can prolong operative time. Hamilton et al.7 reported that closure and exposure were the longest components of the 15 surgical sub-steps with traditional and patient-specific instrumentation during TKA surgery. These studies support our finding that BMI had a significant effect on the operative time in TKA. Unlike in previous studies,4,5,9,10 we found no correlations between sex or age and operative time. These previous studies showed that male or younger-aged patients may have a larger extensor mechanism mass that complicates exposure, have denser bone to cut, or some combination of these and other factors that prolong operative time compared with females. Neder et al.24 reported that males have a higher percentage of lean muscle mass than females. We speculate that the higher age in both males and females in this series may have masked sex- and age-related differences compared with those of the previous studies
5. Conclusion Patients with higher periarticular BMD, TFA (more varus deformity), and BMI should be allocated additional surgical time. Surgeons should recognize that obese patients with severe medial OA knee are those who may require a longer operative time. Finally, the current data 184
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Y. Ishii, et al.
may allow for more effective planning of operative times, which may lead to more efficient use of resources by health systems.
2.
Ethics approval and consent to participate 3.
All procedures in this study that involved human participants were performed in accordance with the ethical standards of the Research Board of Healthcare Corporation Ashinokai, Gyoda, Saitama, Japan, approved the study (ID number: 2017–5) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Written informed consent was obtained from all individual participants included in the study.
4. 5.
6.
Consent for publication
7.
Not applicable.
8.
Availability of data and materials
9.
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
10. 11.
Funding
12.
None. 13.
Authors’ contributions 14.
YI contributed to the study conception and design, drafted the article, and ensured the accuracy of the data and analysis. HN and JS contributed to the study conception and design and to the analysis and interpretation of the data. HI and RI contributed to the data collection. ST provided statistical expertise and contributed to ensuring the accuracy of the data and analysis. All authors approved the final manuscript.
15.
16.
17.
Ethical review committee statement 18.
The local institutional review board approved this study. All patients provided informed consent.
19. 20.
Declaration of competing interest 21.
Each author certifies that he or she has no commercial associations (e.g., consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.
22.
23.
Acknowledgment
24.
We thank Koji Todoroki, RT, and Tetsuya Sakurai, PT for their contributions in gathering the data from Ishii Orthopedic & Rehabilitation Clinic.
25.
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Predictive factors for longer operative times in patients with medial knee osteoarthritis undergoing total knee arthroplasty☆
T
Yoshinori Ishiia,∗, Hideo Noguchia, Junko Satoa, Hana Ishiib, Ryo Ishiic, Shin-ichi Toyabed a
Ishii Orthopaedic & Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan Kanazawa Medical University, School of Plastic Surgery, 1-1 Daigaku Uchinada, Ishikawa, 920-0253, Japan c Sado General Hospital, 161 Chikusa Sado, Niigata, 952-1209, Japan d Niigata University Crisis Management Office, Niigata University Hospital, Niigata University Graduate School of Medical and Dental Sciences, 1 Asahimachi Dori Niigata, Niigata, 951-8520, Japan b
A R T I C LE I N FO
A B S T R A C T
Keywords: Medial knee osteoarthritis Operative time TKA Bone mineral density Tibiofemoral angle Body mass index
Background: Prolonged operative time has frequently been implicated as a risk factor for various complications after total knee arthroplasty (TKA). We aimed to determine whether preoperative factors such as sex, age, body mass index (BMI), prosthetic design, tibiofemoral angle (TFA), range of motion, coronal laxity, Hospital for Special Surgery score and periarticular bone mineral density (BMD) affect operative time. Methods: We evaluated 164 patients (187 knees) with medial osteoarthritis who underwent primary TKA performed by a single surgeon. The medical records of 27 males and 137 females (median age of 77 and 72 years, respectively) were retrospectively reviewed. TFA was measured on non-weightbearing, standard radiographs. We used dual-energy X-ray absorptiometry to measure BMD, and an arthrometer to evaluate total coronal laxity in each patient. Results: According to univariate analyses, there was a weak positive correlation between BMI and operative time (r = 0.265, p < 0.001), between TFA and operative time (r = 0.235, p = 0.001) and between BMD of the femur and tibia and operative time (r = 0.280, p < 0.001, r = 0.286, p < 0.001, respectively). No significant correlations were found between the other factors and operative time. Based on multivariate analyses, only BMD of the tibia and TFA were significantly correlated with operative time (β = 0.418, p < 0.001 and β = 0.182, p = 0.007, respectively). Conclusions: TFA and BMD of the tibia were the variables more strongly correlated with operative time. Surgeons should recognize preoperatively that patients who have increased TFA, higher periarticular BMD, and higher BMI may have longer operative times. Level of evidence: Level IV retrospective study.
1. Introduction The optimal total knee arthroplasty (TKA) procedure involves accurately completing each step of the operation, and fulfilling each design concept in a shorter time. It is important to perform the operation appropriately, as this is associated with good postoperative clinical outcomes. Both the correct positioning of the components and the balancing of the soft tissues in various TKA designs have been reported in numerous papers to lead to successful TKA outcomes in the long term. Meanwhile, prolonged operative time in TKA has frequently been
implicated as a risk factor for complications, including infection,1 venous thromboembolism,2 and neurologic deficit,3 and remains a potentially modifiable variable that is of interest to surgeons and hospitals interested in quality improvement. Naranje et al.4 found that only prolonged operative time was a risk factor for an increased rate of postoperative infection. Factors related to surgical time can be considered to be either surgeon-related factors or patient-related factors. Possible surgeon-related factors contributing to prolonged operative time have been previously reported, and include low surgeon procedural volume and/or low hospital procedural volume,4,5 no use of tourniquet,6 use of patient-specific instrumentation,7 computer
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The present work was performed at the Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361–0037, Japan. Corresponding author. Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama, 361-0037, Japan. E-mail addresses: [email protected] (Y. Ishii), [email protected] (H. Noguchi), [email protected] (J. Sato), [email protected] (H. Ishii), [email protected] (R. Ishii), [email protected] (S.-i. Toyabe). ∗
https://doi.org/10.1016/j.jor.2020.01.026 Received 12 December 2019; Accepted 24 January 2020 Available online 25 January 2020 0972-978X/ © 2020 Professor P K Surendran Memorial Education Foundation. Published by Elsevier B.V. All rights reserved.
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navigation,5 and a mini skin incision.8 In addition, young age,5 male sex,4,9,10 high body mass index (BMI),4,11 American Society of Anaesthesiologists (ASA) Class12 ≧ 3,5 previous surgery to the knee5 and a diagnosis other than osteoarthritis (OA)5 have been reported to be patient-related factors contributing to prolonged operative time. The initiation and progression of medial knee OA is affected by various factors. A logical and stepwise approach should be used for the management of the varus deformity in primary TKA for medial knee OA.13,14 Thus, it is reasonable to speculate that the more severe the deformity or contracture of the arthritic knee, and/or the higher the bone mineral density (BMD) that is recently reported to be affected by joint loading axis15 and body weight,16 the longer time it may take during surgery to correct the deformity or contracture and to osteotomize the femur and tibia. Therefore, the purpose of this study was to evaluate and clarify the factors related to operative time from skin incision to wound closure in TKA procedures performed by one experienced surgeon. We analysed preoperative factors such as sex, age, and BMI, which have previously been demonstrated to affect operative time, and other factors such as the retention of the posterior cruciate ligament (PCL), tibiofemoral angle (TFA), range of motion (ROM), coronal laxity and Hospital for Special Surgery (HSS) scores,17 as well as BMD of the femur and tibia. The clinical significance of this study was that the surgeon may be able to recognize the factors determining operative time prior to TKA. In addition, it may help the hospital administration efficiently use facilities such as the operating room.
2.1. Preoperative clinical evaluation The HSS score17 is a physician-derived score that includes an evaluation of alignment, range of motion, and joint laxity. We measured the TFA, which is related to OA and leg alignment,19 on non-weightbearing, standard radiographs. A physical therapist measured maximum knee flexion and extension using a standard hand-held goniometer with 38-cm arms, while the patient was supine under nonweightbearing conditions. The lateral femoral condyle was used as the landmark to centre the goniometer, with the stationary arm directed toward the greater trochanter and the movable arm directed toward the lateral malleolus. The amount of knee flexion was measured and recorded to the nearest 5°. Patient clinical characteristics are summarized in Table 1. 2.2. Outcome measures and bias 2.2.1. Laxity evaluations The laxity of the medial and lateral sides was measured with a Telos arthrometer (Fa Telos; Medizinisch-Technische Gerätebau GmbH, Sulzbach, Germany) with the patient lying supine on a table on the day before surgery. On the medial/lateral stress test, a force of 150 N was applied just above the joint on the lateral or medial femoral condyle. To measure the medial and lateral angles, the femoral boundary used was the distal convex margin of the condyles. The tibial boundary was the outer margin of the condyles. The neutral, unloaded position was defined as the baseline, while the total angle that indicated the angular motion from the baseline to the loaded position between the medial and lateral sides of the knee was defined as coronal laxity.14 An experienced technician performed all of the tests. Concerning test-retest reliability, the intraclass correlation coefficients (95% CI) were 0.971 (0.928–0.988) for the maximum medial, 0.935 (0.843–0.974) for the neutral, and 0.962 (0.900–0.985) for the maximum lateral position. The standard error of the measurement (maximum error) was 0.354 (0.474) for the maximum medial, 0.525 (0.736) for the neutral, and 0.412 (0.534) for the maximum lateral position.14
2. Materials and methods This study was conducted at a single centre between October 2009 and February 2018. Informed consent was obtained from all patients, and included a description of the protocol and a discussion of potential dual-energy X-ray absorptiometry (DXA) and dynamometer-related complications. The Research Board of Healthcare Corporation Ashinokai, Gyoda, Saitama, Japan, approved the study (ID number: 2017–5), which included 164 consecutive patients (187 knees) who underwent primary TKA. We enrolled 63 patients (63 knees) who were undergoing TKA with a posterior cruciate ligament (PCL)-retaining design and 114 patients (124 knees) with a PCL-substituting design using the LCS® Total Knee System (DePuy, Warsaw, IN, USA). We analysed data from 27 males and 137 females whose preoperative diagnosis was medial knee OA. We excluded patients with rheumatoid arthritis and those who had previously undergone a tibial osteotomy. Although ASA12 class≧3 was reported to influence operative time,5 all patients in this series were ASA class 1 or 2 (Table 1).
2.2.2. Measurement with DXA DXA scans of the periarticular knee joint were acquired with a Lunar Prodigy densitometer (GE Medical Systems Lunar, Madison, WI, USA) on the day before surgery. A single operator scanned all knees. For the distal femur and proximal tibia scans, patients were placed in a supine position and each knee in turn was positioned within a supportive brace with the patella facing upward. Patients who had a flexion contracture were measured at their position of maximum knee extension. The Lunar Prodigy software was used to determine bone mineral content (g) and BMD (g/cm2) for the medial and lateral regions of interest (ROI) in both the femur and tibia. The BMD values of the femoral and tibial condyles were measured and are referred to as follows: medial femoral condyle, FM; lateral femoral condyle, FL; medial tibial condyle, TM; and lateral tibial condyle, TL. The height of the ROI extended 2 cm from the joint line because the osteotomy during TKA surgery was usually performed within a depth of 2 cm. The external border of the ROI extended to the subperiosteal surface of the femur and tibia as determined manually by a single technician. The patella served as the inner border for the medial and lateral proximal femoral ROI, while the intercondylar eminences served as the inner border for the medial and lateral proximal tibial ROI. In the femoral ROI, care was taken to avoid including the patella in the measurement. In the lateral ROI, care was also taken to avoid including the fibula in the measurement (Fig. 1). The average BMD values of the FM and FL and those of the TM and TL in each patient were analysed as BMD of the femur and tibia, respectively. Precision was calculated as the coefficient of variation between the BMD values of the scans. The precision of the measurements was 2.6% in the FM, 5.5% in the FL, 4.3% in the TM and 5.0% in the TL.15
Table 1 Preoperative patient characteristics. Parameter
Osteoarthritic Patients
Knees/Patients Gender: Female (of knees)/Male (of knees) Osteoarthritis Gradea ASA Classb Median [25th percentile, 75th percentile] Age (range) (years): Female/Male Body Height (cm) Body Weight (kg) Body Mass Index (BMI) (kg/m2) Tibiofemoral angle (°) Range of motion (°) Total coronal laxity (°) HSS scorec BMDd of Femur (g/cm2) BMDd of Tibia (g/cm2)
187/164 137 (156)/27 (31) III: 6, IV: 181 I: 16, II: 121
a b c d
72 [68, 78]/77 [70, 81] 151 [146,156] 59 [52,67] 26 [23,28] 181 [179,184] 115 [100,125] 7 [6,9] 44 [36,51] 0.958 [0.854, 1.082] 0.884 [0.734, 0.998]
Kellgren-Lawrence grade.18 American Society of Anaesthesiologists.12 HSS score: Hospital for Special Surgery Score.17 BMD: bone mineral density. 182
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Table 2 Univariate analyses: (I) Spearman's correlation coefficient for variables comparing operative time and the preoperative variables. (II) Comparison between the other factors and operative time for discrete variables analysed using the Mann–Whitney U test. (I) Characteristics
p values
R
BMI Age TFA Range of Motion Coronal Laxity HSS score BMD of femur BMD of tibia (II) Variables (knees) Gender Female: 156、Male: 31 PCL retention; PCL-R 63 vs PCL-S 124
< 0.001 0.039 0.001 0.063 0.118 0.033 < 0.001 < 0.001 p values 0.121 0.052
0.265 −0.152 0.235
−0.156 0.280 0.286
BMI, body mass index; TFA, tibiofemoral angle; HSS, Hospital for Special Surgery; BMD, bone mineral density; PCL, posterior cruciate ligament; PCL-R, PCL-retaining; PCL-S, PCL-substituting.
rank correlation tests. Univariate and multivariate analyses were performed to examine preoperative factors related to TKA operative time. Spearman's rank correlation coefficient was used to investigate the association between any two variables. The Mann–Whitney U test was used to determine differences between two groups. Multiple linear regression analyses were performed to identify variables significantly associated with proximal tibial BMD. Multiple linear regression models were constructed by entering all variables shown in Table 2 and using the stepwise selection method. The strength of the correlation of the rank coefficients was defined as: strong = 0.70–1.0, moderate = 0.40–0.69, or weak = 0.20–0.39. Post hoc power analyses were performed after the study. The power of Spearman's rank correlation test with a medium effect size (0.3) and an α-error of 0.05 was 0.989, and the power of the Mann–Whitney U test with a medium effect size (0.5) and an α-error of 0.05 was 0.695 for gender of patients and 0.881 for retaining of PCL in surgery, respectively. In all tests, a p < 0.05 was considered statistically significant. All statistical analyses were performed using IBM SPSS Statistics version 23 (IBM Japan, Tokyo, Japan). Values are expressed as median [25%; 75% percentile].
Fig. 1. Bone mineral density values were measured in the femoral and tibial condyles. FM: medial femoral condyle; FL: lateral femoral condyle; TM: medial tibial condyle; and TL: lateral tibial condyle. The height of the regions of interest (ROI) extended to 2 cm below the joint line. The external border of the ROI extended to the subperiosteal surface of the femur and tibia as determined manually. The patella served as the inner border for the medial and lateral proximal femoral ROI, and the intercondylar eminences served as the inner border for the medial and lateral proximal tibial ROI. In the femoral ROI, care was taken to avoid including the patella in the measurements. In the lateral ROI, care was also taken to avoid including the fibula in the measurements.
3. Results Median operative time was 55 min [51; 60] (range; 41–116). According to univariate analyses using Spearman's correlation coefficient for continuous variables, there was a weak positive correlation between BMI and operative time (r = 0.265, p < 0.001), between TFA and operative time (r = 0.235, p = 0.001), between BMD of the femur and operative time (r = 0.280, p < 0.001) and between BMD of the tibia and operative time (r = 0.286, p < 0.001) (Table 2). However, no significant correlations were found between the other factors and operative time for continuous and discrete variables (Table 2). Based on multivariate analyses using multiple linear regression analysis with stepwise variable selection, only BMD of the tibia and TFA were significant factors associated with operative time (β = 0.418, p < 0.001 and β = 0.182, p = 0.007 respectively) (Table 3).
2.2.3. Surgical technique From initial skin incision to wound closure, a single experienced surgeon performed all of the surgeries using standardized techniques, as described previously.20 In all knees, the femoral components were fixed without cement, and the tibial components were fixed with cement. The patella was not resurfaced, and no lateral retinaculum release was performed in any case. Ligament-balancing techniques, which included the removal of peripheral osteophytes and necessary soft tissue releases, were used and confirmed with spacer blocks to ensure a balanced knee with equal flexion and extension gaps. The proper intraoperative coronal and sagittal plane laxity was confirmed manually, although no intraoperative quantitative evaluation was performed. As reported in our previous study, achieving about 4° of coronal laxity in extension and 3° of coronal laxity in flexion, measured using an arthrometer, was associated with good clinical outcomes for both prostheses.21
4. Discussion Our results revealed two important findings. First, there was a weak positive correlation between operative time and BMI, TFA and BMD of the femur and tibia on univariate analyses. Also, only TFA and BMD of the tibia showed significant correlations with operative time on multivariate analyses. Our results showed that TFA and BMD of the tibia are the most significant factors among the factors related to operative time
2.2.4. Statistical analysis Because data for certain variables did not pass the Kolmogorov–Smirnov normality test or the Shapiro–Wilk normality test, we used non-parametric Mann–Whitney U tests and Spearman's 183
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(Libaud11 mean age, 65 years; Kosashvili10 mean age, 67 years in men and 66 years in women). In addition, the relatively low number of included males may have also masked sex-associated differences, although the numbers would be sufficient to detect differences of 0.5 by power analysis. Basques et al.9 reported in a recent large-scale study that the sex-related differences in operative time were small and unlikely to be clinically significant, although men had a slightly increased operative time (+6 min) compared with women. Finally, in contrast to our hypothesis, there were no correlations between operative time and the retention of the PCL, ROM, coronal laxity or clinical scores. It seems reasonable that it would take a longer time to perform a satisfactory procedure in cases where the PCL is retained, where there is poor ROM, or where there is less coronal laxity, since meticulous soft tissue releases might be needed. In fact, Mihalko et al.13 described the necessity of stepwise medial, lateral, and/or posterior soft tissue releases, including the PCL, in knees with various degrees of medial OA and flexion contracture to obtain a well-balanced knee or a knee with good ROM. However, these three factors did not correlate with operative time, and we speculate that there may have been two reasons for this. One is a patient-related factor. Since patients with the same laxity and/or ROM had different degrees of contracture of the periarticular soft tissues including the PCL, the time necessary for each stepwise procedure was likely inconsistent. The other is a surgeonrelated factor. All surgeries in this series were performed by a single experienced surgeon in an academic practice.14–16,20,21,25 Thus, it is reasonable to assume that intraoperative efficacy was maximized with regard to meticulous soft tissue releases. That is, the surgeon's skill was unlikely to create a significant time lag regardless of the different degrees of contracture and/or laxity. Finally, with regard to HSS score,17 the lower point distributions of ROM, laxity, and alignment than those of pain or activity level might not reflect the operative time in each patient, even if the soft tissue releases or osteotomies took longer. There are several limitations of this study. First and foremost, this was a retrospective medical record and database review, which has inherent limitations. Second, the proportion of males to females was unequal. The higher prevalence of OA and TKA operations in females is a common finding in Japanese ethnic groups. This might be explained by the racial difference in disease demographics and sex-based disparities in the incidence of bow-leggedness. In addition, female predominance is common in studies of Asian patients.8,16,20,21 Third, the PCL-retaining design was less common than the substituting design. Initially, the order of implant use was quasi-randomised; patients with even medical record numbers received a PCLR implant, and patients with odd medical record numbers received a PCLS implant. Unexpectedly, the PCL-retaining design was discontinued by the manufacturing company at the end of January 2013, and the TKA procedures were performed using only the substituting design after that time. Fourth, on the short radiograph, which does not include the femoral head and ankle, it is not easy to obtain an accurate TFA. However, Ishii et al. compared TFA on short radiographs with TFA observed on long radiographs using the best correlation procedure available (r = 0.94),25 and the discrepancy between them was reported to be only 0.5° (SD 1.2°).25 Finally, unlike a previous report that measured time for each surgical step,7 the total operative duration was evaluated. Despite these limitations, the strength of this study was that less surgeon-related bias was present than in previous studies. This was because all procedures from skin incision to wound closure were performed by a single experienced surgeon who has well over the 300 TKA cases that are needed to prevent prolonged operative time due to inexperience.4
Table 3 Multivariate regression analysis.
BMD of tibia TFA
B
S.E.
Β
significance
95% CI for B
14.084 0.358
2.263 0.132
0.418 0.182
< 0.001 0.007
9.620 0.097
18.548 0.619
A multivariate linear regression model was constructed by entering all variables identified in Table 2 by using a stepwise selection method to identify variables significantly associated with operative time. BMD; bone mineral density; TFA, tibiofemoral angle; S.E, standard error: CI, confidence interval.
that we evaluated in this study. Second, the other factors such as sex, ROM, coronal laxity, prosthetic design, and clinical score showed no significant correlation with operative time. It may be reasonable that there was a significant correlation between both BMD and operative time, since BMD enables the quantitative evaluation of the variations in bone biomechanical characteristics of the knee before a TKA procedure.22 Petersen et al.22 stated that BMD is a recognized reflection of trabecular bone strength. Although cutting through denser bone was recognized as a factor that may prolong operative time,4 to our knowledge, this is the first study to demonstrate the correlation between actual BMD values and operative time. Based on multivariate analyses, only BMD of the tibia showed significant correlations with operative time, so measurements of the tibial side alone may be enough to evaluate the BMD for estimation of operative time. However, the measurement of BMD before TKA is not common in practice.15 Considering that body weight (BW) is reported to be the most important factor influencing proximal tibial BMD,16 BMI may take the place of BMD values and be a practical indicator of operative time in TKA. BMI is well reflected by the BW, which is measured routinely before surgery regardless of the size and level of the facilities. TFA was another significant predictive factor for operative time in this study. TFA may reflect the degree of varus deformity contributing to medial OA, and stepwise procedures such as soft tissue releases, removal of osteophytes, and osteotomy have been needed to obtain correct alignment and balanced laxity after TKA. A larger TFA indicates more varus deformity, and this may lead to a longer time required to obtain an aligned and well-balanced knee. Thus, it is reasonable that operative time may be prolonged in proportion to the severity of the TFA abnormality. In addition, since a more varus alignment was associated with higher medial-to-lateral periarticular BMD of the knee,23 a larger TFA might necessitate a longer time to cut the femur and tibia. Therefore, a large TFA may be one of the most significant factors determining operative time. Several previous studies documented the relationship between increasing BMI and prolonged operative time.4,11 Liabaud et al.11 showed a direct linear relationship between BMI and operative time in patients undergoing TKA. In addition, Naranje et al.4 reported prolonged operative times in males as compared with females with the same BMI. They hypothesized that larger BMI leads to difficulties in both exposure and closure, both of which can prolong operative time. Hamilton et al.7 reported that closure and exposure were the longest components of the 15 surgical sub-steps with traditional and patient-specific instrumentation during TKA surgery. These studies support our finding that BMI had a significant effect on the operative time in TKA. Unlike in previous studies,4,5,9,10 we found no correlations between sex or age and operative time. These previous studies showed that male or younger-aged patients may have a larger extensor mechanism mass that complicates exposure, have denser bone to cut, or some combination of these and other factors that prolong operative time compared with females. Neder et al.24 reported that males have a higher percentage of lean muscle mass than females. We speculate that the higher age in both males and females in this series may have masked sex- and age-related differences compared with those of the previous studies
5. Conclusion Patients with higher periarticular BMD, TFA (more varus deformity), and BMI should be allocated additional surgical time. Surgeons should recognize that obese patients with severe medial OA knee are those who may require a longer operative time. Finally, the current data 184
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may allow for more effective planning of operative times, which may lead to more efficient use of resources by health systems.
2.
Ethics approval and consent to participate 3.
All procedures in this study that involved human participants were performed in accordance with the ethical standards of the Research Board of Healthcare Corporation Ashinokai, Gyoda, Saitama, Japan, approved the study (ID number: 2017–5) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Written informed consent was obtained from all individual participants included in the study.
4. 5.
6.
Consent for publication
7.
Not applicable.
8.
Availability of data and materials
9.
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
10. 11.
Funding
12.
None. 13.
Authors’ contributions 14.
YI contributed to the study conception and design, drafted the article, and ensured the accuracy of the data and analysis. HN and JS contributed to the study conception and design and to the analysis and interpretation of the data. HI and RI contributed to the data collection. ST provided statistical expertise and contributed to ensuring the accuracy of the data and analysis. All authors approved the final manuscript.
15.
16.
17.
Ethical review committee statement 18.
The local institutional review board approved this study. All patients provided informed consent.
19. 20.
Declaration of competing interest 21.
Each author certifies that he or she has no commercial associations (e.g., consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.
22.
23.
Acknowledgment
24.
We thank Koji Todoroki, RT, and Tetsuya Sakurai, PT for their contributions in gathering the data from Ishii Orthopedic & Rehabilitation Clinic.
25.
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