Orthopedics

Feature Article 

Risk Assessment for Chronic Pain and Patient Satisfaction After Total Knee Arthroplasty

Vasileios I. Sakellariou, MD, PhD; Lazaros A. Poultsides, MD, PhD; Yan Ma, PhD; James Bae, PhD; Spencer Liu, PhD; Thomas P. Sculco, MD

Abstract

The estimated prevalence of patients who report minor or no improvement of their symptoms and pain after total knee arthroplasty (TKA) remains high, ranging from 5% to 40%. The authors sought to determine whether chronic pain and functional health are related to specific variations in demographic data, surgical techniques, or radiographic pre- and postoperative findings. They also sought to identify independent risk factors for persistent moderate-to-severe chronic pain after TKA. A total of 272 patients who underwent primary TKA from October 2006 to August 2008 with a minimum follow-up of 1 year were identified from electronic medical records. A questionnaire to identify persistent postoperative pain (36-item Short Form Health Survey [SF-36]) was mailed to these patients. Linear regression and logistic regression were used to identify predictors for SF-36 and chronic pain, respectively. Thirty-nine percent of patients reported persistent pain after TKA, with a median average pain score of 3 out of 10 and worst pain score of 5 out of 10. Independent risk factors for persistent pain are the length of the operative procedure (odds ratio [OR]=1.013), medical history of diabetes mellitus (OR=0.430), presence of preoperative flexion contracture (OR=1.089), and patellofemoral joint overstuffing (OR=0.915). Persistent postoperative pain is a common finding after TKA. Nonmodifiable risk factors could be used for risk stratification, whereas modifiable risk factors could be used as a clinical guidance for modification of some aspects of existing surgical techniques. [Orthopedics. 2016; 39(1):55–62.]

Abstract

The estimated prevalence of patients who report minor or no improvement of their symptoms and pain after total knee arthroplasty (TKA) remains high, ranging from 5% to 40%. The authors sought to determine whether chronic pain and functional health are related to specific variations in demographic data, surgical techniques, or radiographic pre- and postoperative findings. They also sought to identify independent risk factors for persistent moderate-to-severe chronic pain after TKA. A total of 272 patients who underwent primary TKA from October 2006 to August 2008 with a minimum follow-up of 1 year were identified from electronic medical records. A questionnaire to identify persistent postoperative pain (36-item Short Form Health Survey [SF-36]) was mailed to these patients. Linear regression and logistic regression were used to identify predictors for SF-36 and chronic pain, respectively. Thirty-nine percent of patients reported persistent pain after TKA, with a median average pain score of 3 out of 10 and worst pain score of 5 out of 10. Independent risk factors for persistent pain are the length of the operative procedure (odds ratio [OR]=1.013), medical history of diabetes mellitus (OR=0.430), presence of preoperative flexion contracture (OR=1.089), and patellofemoral joint overstuffing (OR=0.915). Persistent postoperative pain is a common finding after TKA. Nonmodifiable risk factors could be used for risk stratification, whereas modifiable risk factors could be used as a clinical guidance for modification of some aspects of existing surgical techniques. [Orthopedics. 2016; 39(1):55–62.]

Total knee arthroplasty (TKA) is one of the most common and successful surgical procedures that provides substantial pain relief and improves functional disability and quality of life in patients with severe knee arthritis.1–3 However, not every patient undergoing TKA experiences such an improvement in pain relief and improvement of well-being status.4,5 Pain, stiffness, decreased range of motion, and/or knee instability are some of the problems that may be addressed during the immediate postoperative period or may persist for months to years.4,5

Several recent studies have reported chronic persistent pain lasting from 6 months to 4 years after TKA. The prevalence of chronic pain varies, ranging from 5% to 44%.4–11 Risk factors for continuing pain and disability after TKA include patient age, sex, comorbidities, pain profile, psychological status, and expectations.4–11 However, these variables can only account for a minority of the variance in outcomes observed, suggesting that other risk factors must be equally as or more important.

Although significant progress has been made in improving analgesia and pain control, the effect of different surgical techniques in postoperative pain after TKA is still not well understood.12,13 The authors sought to determine whether chronic pain and functional health (expressed by using the 36-item Short Form Health Survey [SF-36] survey) are related to specific variations in demographic data, surgical techniques, or radiographic pre- and postoperative findings. They also sought to identify independent risk factors for persistent moderate-to-severe chronic pain after TKA.

Materials and Methods

The authors electronically identified a total of 745 patients who had undergone primary TKA in their institution from October 2006 to August 2008 with a minimum 1-year follow-up. Questionnaires and consent forms with descriptions of the study and contact telephone numbers for questions were then mailed to all patients approximately 12 months (range, 12–16 months) postoperatively. Prestamped return envelopes were included. A reminder was mailed to nonresponders after approximately 1 week. Any questionnaires not returned or returned incomplete were excluded from the study data. A total of 272 patients who returned completed questionnaires and signed consent forms were included for final analysis to determine the prevalence of persistent pain at the surgical site and to identify potential risk factors for persistent pain and patient dissatisfaction after TKA. Institutional review board approval was granted, and written informed consent was obtained from all included patients.

The primary outcome was the prevalence of persistent pain (new onset since TKA) as defined by a previously published questionnaire that was used to document incidence of persistent postoperative pain.12 Postoperative pain was evaluated using the 10-point visual analog scale (VAS) score. Pain was defined as moderate-to-severe if the VAS score was 4 or greater.

A previously published questionnaire to identify persistent postoperative pain that included the SF-36 was mailed to this group. The SF-36, a short-form functional health and well-being survey, is well documented and has been used and validated in orthopedic patients, including those who underwent TKA.3,6,14,15 Software based on SF-36 guidelines from a previous study was used to calculate the scores of 8 independent scales, 2 dimensions (physical health and mental health), and total SF-36 results.12 Scores in the SF-36 were converted to a scale from 0 to 100 (0=worst and 100=best); this conversion has been previously described and used in TKA literature.3,14,16

Perioperative information on patient demographics and surgical and radiographic data were gained by retrospective chart review. Demographic data collection included age, sex, race, body mass index (BMI), type of arthritis (ie, idiopathic osteoarthritis [OA], rheumatoid arthritis [RA], posttraumatic, other), and history of diabetes mellitus. The pain profile of the patients was also recorded, including any preexisting pain at the surgical site, preexisting pain scores, preexisting worst pain level, and type of anesthesia (ie, general or regional). The total length of in-hospital stay (LOS) and disposition after discharge (ie, home or rehabilitation) were also recorded.

Data associated with the surgical technique, including total operative time, pressure and duration of tourniquet, length of the incision, eversion of the patella, varus or valgus releases required for soft tissue balancing, administration or not of periarticular knee injections, and characteristics (type and sizes) of the knee prostheses, were also collected.

Standardized pre- and postoperative radiographs were collected from patients' electronic files to assess the pre- and postoperative alignment of the femur, tibia, and knee joint in both coronal and sagittal planes. The amount of tibial and femoral component alignment in the coronal plane was measured by the alpha and the beta joint line angle. For assessment of the alpha angle, one line was drawn parallel to the femoral condyles and a second was drawn in the femoral shaft axis. For calculation of the beta angle, one line was drawn parallel to the plateau of the metal tibial component and a second was drawn parallel the tibial shaft axis. The restoration of joint line was assessed by measuring the distance from the femoral condyles to a constant anatomic landmark at the tibial side (usually the tip of the fibular head) pre- and postoperatively. Potential overhanging of the components was also recorded.

The femoral and the tibial component angles were also measured in the sagittal plane (sagittal femoral angle and sagittal tibial angle). The femoral size (anteroposterior distance of the femoral condyles) and the anterior and posterior femoral offsets were assessed pre- and postoperatively. Femoral component flexion and extension angles were measured between a line perpendicular to the distal metal-cement interface of the femoral component and a line parallel to the femoral shaft axis. The tibial component sagittal angle was measured between a line parallel to the metal tibial plateau and the tibial shaft axis. The Insall-Salvati ratio was used for the assessment of the level of the patella. Other radiographic patellar measurements included the anterior displacement of the patella, sulcus angle, congruence angle, and patellar tilt. All measurements on pre- and postoperative radiographs are illustrated in Figure 1 and Figure 2.

Radiographic measurements on preoperative radiographs. Abbreviations: A, anatomical axis of the tibia; B, b angle of the tibia joint; C, anatomical axis of the femur; D, a angle of the femur; E, angle of the knee joint; F, femoral offset; G, anterior femoral offset; H, posterior femoral offset; I, Insall-Salvati ratio; J, anterior patella displacement; K, sulcus angle; L, congruence angle.

Figure 1:

Radiographic measurements on preoperative radiographs. Abbreviations: A, anatomical axis of the tibia; B, b angle of the tibia joint; C, anatomical axis of the femur; D, a angle of the femur; E, angle of the knee joint; F, femoral offset; G, anterior femoral offset; H, posterior femoral offset; I, Insall-Salvati ratio; J, anterior patella displacement; K, sulcus angle; L, congruence angle.

Radiographic measurements on postoperative radiographs. Abbreviations: A, anatomical axis of the tibia; B, b angle of the tibia joint; C, anatomical axis of the femur; D, a angle of the femur; E, angle of the knee joint; F, femoral offset; G, anterior femoral offset; H, posterior femoral offset; I, Insall-Salvati ratio; J, anterior patella displacement; K, sulcus angle; L, congruence angle.

Figure 2:

Radiographic measurements on postoperative radiographs. Abbreviations: A, anatomical axis of the tibia; B, b angle of the tibia joint; C, anatomical axis of the femur; D, a angle of the femur; E, angle of the knee joint; F, femoral offset; G, anterior femoral offset; H, posterior femoral offset; I, Insall-Salvati ratio; J, anterior patella displacement; K, sulcus angle; L, congruence angle.

Statistical Analysis

Logistic regression was planned to identify independent risk factors for chronic pain. Specifically, univariate logistic regression was first conducted to screen for potential predictors for chronic pain. Those variables with a P value less than .2 were included in a multivariate logistic regression. For each individual predictor, the odds ratio (OR), 95% confidence interval (CI), and P value were computed. Multivariate logistic regression models were fitted and selected using backward elimination. Similarly, linear regression analysis was performed to identify predictors for SF-36. A P value of .05 was considered statistically significant. All statistical analyses were performed using SAS version 9.3 statistical software (SAS Institute, Cary, North Carolina).

Results

A total of 745 questionnaires were mailed from the authors' institution, and 272 were returned, resulting in a response rate of 36.51%. Twenty-six patients were excluded because of a disallowed surgical procedure or incomplete survey. Overall, 107 (39.34%) of the 272 patients reported persistent pain at the operated knee. Median average pain score was 3 of 10 and worst pain was 5 of 10, according to the questionnaire.

Univariate logistic regression analysis of demographic, operative, and radiographic variables showed that (1) the presence of antalgic gait preoperatively (P=.0343), (2) patellofemoral joint over-stuffing (P=.0222), and (3) the amount of correction in the coronal plane (P=.323) are associated statistically significantly with chronic pain (Tables 14).

Univariate Analysis of Chronic Pain for Different Demographic Variables

Table 1:

Univariate Analysis of Chronic Pain for Different Demographic Variables

Univariate Analysis of Chronic Pain for Different Clinical Variables

Table 2:

Univariate Analysis of Chronic Pain for Different Clinical Variables

Univariate Analysis of Chronic Pain for Different Surgical Techniques

Table 3:

Univariate Analysis of Chronic Pain for Different Surgical Techniques

Univariate Analysis of Chronic Pain for Different Radiographic MeasurementsUnivariate Analysis of Chronic Pain for Different Radiographic Measurements

Table 4:

Univariate Analysis of Chronic Pain for Different Radiographic Measurements

Independent risk factors for persistent pain from the multivariate logistic regression are the length of the operative procedure (OR=1.013; 95% CI, 1.001 to 1.026), presence of preoperative flexion contracture (OR=1.089; 95% CI, 1.002 to 1.183), and patellofemoral joint overstuffing (OR=0.915; 95% CI, 0.855 to 0.98) (Table 5).

Regression Analysis of Chronic Pain

Table 5:

Regression Analysis of Chronic Pain

Worse SF-36 scores were found in females (P=.013), in patients with increased preoperative femoral offset (P=.0116) and posterior femoral offset (P=.0416), in patients who needed a greater amount of correction in anatomical axis of the tibia (P=.0332), when the patella was everted during the procedure (P=.0249), when a thicker polyethylene insert was used (P=.0212), and when a more constrained implant was used (P=.0473) (Tables 69).

Univariate Analysis of SF-36 Score for Different Demographic Variables

Table 6:

Univariate Analysis of SF-36 Score for Different Demographic Variables

Univariate Analysis of SF-36 Score for Different Clinical Variables

Table 7:

Univariate Analysis of SF-36 Score for Different Clinical Variables

Univariate Analysis of SF-36 Score for Different Surgical Techniques

Table 8:

Univariate Analysis of SF-36 Score for Different Surgical Techniques

Univariate Analysis of SF-36 Score for Different Radiographic MeasurementsUnivariate Analysis of SF-36 Score for Different Radiographic Measurements

Table 9:

Univariate Analysis of SF-36 Score for Different Radiographic Measurements

Independent risk factors for SF-36 scores from the multivariate logistic regression are female sex (OR=8.1766; 95% CI, 2.8959 to 13.4573), eversion of the patella (OR= −9.4899; 95% CI, 15.1637 to −3.8162), preoperative femoral offset (OR=−0.3942; 95% CI, −0.7003 to −0.0881), and patellofemoral joint overstuffing (OR=0.5829; 95% CI, 0.0767 to 1.0892) (Table 10).

Multivariate Regression Analysis for SF-36 Score

Table 10:

Multivariate Regression Analysis for SF-36 Score

Discussion

Many patients experience significant pain 6 to 12 months after TKA despite an absence of clinical or radiographic evidence of abnormalities as identified on the standard outcome instruments. Clinical experience has shown that a large percentage of patients suffer from mild to severe persistent pain and stiffness, but these data are confounded by little correlation between surgeons' assessment of pain (the parameter used in the majority of outcome reports) and patients' self-assessments.5,15,16 The International Association for the Study of Pain has defined chronic pain as pain persisting more than 3 months postoperatively.11 Previous studies examining persistent pain after TKA during the 3- to 12-month postoperative period reported a typical prevalence of 7% to 20%.11 Studies that examined the prevalence of persistent pain ranging from 1 to 4 years after TKA reported an even greater prevalence (24% to 44%) after TKA.4,6,17 In the current study, the authors identified a 39.34% incidence of persistent moderate-to-severe pain after TKA approximately 1 year postoperatively that is similar to those reported by other authors.11,18

The use of a large sample size and validated tools for the assessment of chronic pain and postoperative functional health and well-being of the patients are strengths of this study. However, there are several limitations. As is typical of any observational study, the analysis may only identify associations between observations and cannot determine the causality and efficacy of any interventions. Another limitation is the response rate (36.51%), which may have biased the results because nonresponders may have had better or poorer outcomes than those who responded to the survey, and patients who responded may have had recall bias concerning their perioperative experience. A previous study found that nonresponders tended to have lower clinical scores and inferior functional health and well-being outcomes compared with patients who responded.19

The current authors observed the outcomes of pain and functionality at only a single time period. Their survey period of 12 to 16 months postoperatively is intermediate among studies that examined an early period (months) and those that examined a much later period (years). In the current literature there is no standardized or optimal time after surgery to measure the existence of persistent pain. Although a longitudinal study including observations at multiple time frames would be optimal and should be performed, the authors believe that the selection of the current postoperative time period (12 to 16 months) reflects more accurately the chronic pain that is directly associated with surgery; longer postoperative follow-up times may be confounded by the accentuation-type phenomenon or use of different methodologies for pain assessment.

Several authors have reported the association of poor outcomes after TKA with several demographic variables.3–5,10,11,15,16,20,21 Age, sex, obesity, and other comorbidities have been found to be determinants of some of the various outcomes after TKA. Some authors have indicated that preoperative pain, physical function, and mental state are significant factors for increased chronic postoperative pain.2–5,8,10–13,15,16,20–22 The current study found that female sex and patients with diabetes mellitus were related to worse postoperative functional health and increased persistent postoperative pain, respectively.

In the current literature, there are numerous reports on surgical techniques that demonstrate favorable short-term outcomes on pain and functionality. Mini-skin incision and quad-preserving approaches (midvastus and subvastus) have been related to lower pain and better function compared with a standard skin incision and typical medial parapatellar approach during the initial postoperative period (1 to 6 weeks).17 However, no benefit is reported beyond this early postoperative period. In the current study, the authors found that the presence of chronic pain was not related to the length of skin incision. However, the length of the operative procedure was found to be a significant risk factor for persistent chronic pain after TKA. Specifically, for every minute of extended operative time, the odds of developing chronic pain are increased by 1.013 times.

In the current literature, little is known about the association of chronic pain with pre- and postoperative radiographic assessment of the knee joint. Valdes et al23 reported that there is an inverse relationship between preoperative radiographic severity and postoperative pain in patients with osteoarthritis who had undergone total joint arthroplasty. Dennis et al24 found that decreased patellar component size, decreased composite patellar thickness, shorter pre- and postoperative patellar tendon length, and increased posterior femoral condylar offset are predisposing factors for painful patellar crepitus after TKA. These findings are in accordance with the current authors' results; they found that increased preoperative femoral offset and posterior femoral offset, as well as an increase in the anterior displacement of the patella postoperatively, are associated with the development of chronic postoperative pain. Many of these factors associated with an increased incidence of postoperative painful knee may increase quadriceps tendon contact forces against the superior aspect of the intercondylar box, increasing the risk of fibrosynovial proliferation development of painful crepitus.24

The effect of stuffing the patellofemoral compartment on the outcome of TKA has been studied by Pierson et al.25 They reported that pre- to postoperative changes in anterior patellar displacement, anteroposterior femoral size, combined anteroposterior patellofemoral size, anterior femoral offset, and posterior femoral offset have no clinically meaningful effect on the range of motion of the knee or on any Knee Society score.25 The current study showed that the presence of preoperative flexion contracture and patellofemoral joint overstuffing are individual risk factors for chronic pain after TKA.

Conclusion

Persistent postoperative pain is a common finding after TKA. The incidence of postoperative pain after TKA is relatively high, with more than one-third of patients in this study reporting persistent pain 1 year postoperatively. The development of persistent pain was associated with a significantly lower health-related quality of life, as measured by the SF-36.

Risk factors identified in this study included operative time, medical history of diabetes mellitus, preoperative flexion contracture, and patellofemoral overstuffing. Nonmodifiable risk factors could be used for risk stratification, whereas modifiable risk factors could be used as a clinical guide to appropriately select or modify well-established surgical techniques. Large multi-centric longitudinal surveys including a nonoperative control group are needed to confirm and validate these preliminary findings.

References

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Univariate Analysis of Chronic Pain for Different Demographic Variables

VariableEstimateWald 95% CIP
Sex−0.3711−0.6778 to −0.0643.4212
Ethnicity−0.4055−2.1947 to 1.3837.9999
Age−0.6712−1.1735 to −0.1688.2330
Obesity−0.6343−1.0441 to −0.2245.2871
DM0.1542−0.6169 to 0.9252.1012

Univariate Analysis of Chronic Pain for Different Clinical Variables

VariableEstimateWald 95% CIP
Flexion−0.6772−1.9268 to 0.5724.7415
Extension−0.5644−0.8254 to −0.3034.0722
Crepitus−0.3335−0.7041 to 0.0371.0778
Antalgic gait−0.4906−0.9450 to −0.0363.0343

Univariate Analysis of Chronic Pain for Different Surgical Techniques

VariableEstimateWald 95% CIP
Arthrotomy−0.3773−0.8967 to 0.1421.6999
Patellar eversion−0.5328−1.0080 to −0.0576.6845
Length incision−0.4495−0.7411 to −0.1579.9035
Soft tissue releases−0.3795−1.0850 to 0.3260.9799
Varus valgus releases−0.3185−0.9624 to 0.3255.7791
Pericap injections−1.0986−2.6989 to 0.5017.4189
Tourniquet pressure−0.0031−0.0100 to 0.0039.3843
Tourniquet time−0.0044−0.0189 to 0.0100.5484
Operative time0.0097−0.0001 to 0.0195.0513
EBL0.0005−0.0019 to 0.0028.6948
Level of constraint−1.6094−3.1276 to −0.0912.1429
Femoral size−0.0773−0.2486 to 0.0939.3761
Tibial size−0.1045−0.2767 to 0.0678.2346
PE thickness0.1414−0.0035 to 0.2862.0558
Patellar size−0.0565−0.1388 to 0.0258.1784
LOS0.0786−0.1277 to 0.2849.4552

Univariate Analysis of Chronic Pain for Different Radiographic Measurements

MeasurementEstimateWald 95% CIP
Coronal knee angle
  Preop0.0152−0.0187 to 0.0491.3802
  Postop0.0237−0.0575 to 0.1048.5678
  Difference−0.0133−0.0455 to 0.0190.4202
Anatomical axis femur
  Preop0.0470−0.0568 to 0.1507.3749
  Postop−0.0995−0.2096 to 0.0106.0766
  Difference−0.0880−0.1686 to −0.0074.0323
Anatomical axis tibia
  Preop−0.0052−0.0830 to 0.0726.8961
  Postop−0.1139−0.2410 to 0.0132.0790
  Difference−0.0249−0.0995 to 0.0497.5127
Insall-Salvati ratio
  Preop−0.0266−0.0633 to 0.0102.1561
  Postop−0.0170−0.0497 to 0.0157.3082
  Difference1.0010−1.0750 to 3.0770.3446
Anterior patellar height
  Preop−0.0714−0.1326 to −0.0102.0222
  Postop−0.0961−0.1589 to −0.0333.0027
  Difference−0.0231−0.0773 to 0.0311.4028
Sulcus angle
  Preop0.0276−0.0094 to 0.0646.1437
  Postop0.0194−0.0071 to 0.0458.1519
  Difference0.0075−0.0153 to 0.0303.5191
Congruence angle
  Preop0.0015−0.0097 to 0.0126.7949
  Postop−0.0042−0.0183 to 0.0100.5638
  Difference−0.0023−0.0117 to 0.0072.6373
Postop patellar tilt−0.0285−0.0949 to 0.0379.3998
Femoral offset
  Preop−0.0132−0.0459 to 0.0195.4294
  Postop−0.0266−0.0657 to 0.0125.1824
  Difference−0.0266−0.0657 to 0.0125.1824
Anterior offset
  Preop−0.0209−0.1423 to 0.1005.7355
  Postop−0.0467−0.1529 to 0.0595.3888
  Difference−0.0241−0.1107 to 0.0626.5861
Posterior offset
  Preop−0.0131−0.0681 to 0.0419.6412
  Postop−0.0131−0.0681 to 0.0419.6412
  Difference0.0005−0.0461 to 0.0471.9839
Component alignment
  Femoral−0.0234−0.0831 to 0.0363.4425
  Tibial−0.0359−0.1333 to 0.0616.4709
Joint line
  Preop−0.0343−0.0845 to 0.0160.1813
  Postop0.0100−0.0423 to 0.0624.7071
  Difference0.0488−0.0003 to 0.0980.0513
Overhanging implant
  Femur−0.1911−0.6207 to 0.2386.3835
  Tibia−1.0986− 3.3618 to 1.1646.3414

Regression Analysis of Chronic Pain

VariableEstimateWald 95% CI
ROM extension1.0891.002 to 1.183
Length of procedure1.0131.001 to 1.026
Preop anterior patellar displacement0.9150.855 to 0.980
Diabetes mellitus 0 vs 10.4300.167 to 1.105

Univariate Analysis of SF-36 Score for Different Demographic Variables

VariableEstimateWald 95% CIP
Flexion0.06010.1271 to 0.02.0601
Extension−0.4932−1.1309 to 0.1446.1296
VAS admission−0.6457−1.4474 to 0.1559.1144

Univariate Analysis of SF-36 Score for Different Clinical Variables

VariableEstimateWald 95% CIP
Sex7.80623.0498 to 12.5625.0013
Ethnicity7.6375−34.6708 to 49.9458.7235
Age5.9955−3.4488 to 15.4397.2134
Obesity3.0028−1.8903 to 7.8959.2291
DM6.1651−1.7940 to 14.1243.1290

Univariate Analysis of SF-36 Score for Different Surgical Techniques

VariableEstimateWald 95% CIP
Arthrotomy−3.6549−9.4343 to 2.1246.2152
Patellar eversion−6.0983−11.4258 to −0.7709.0249
Length incision−0.7249−6.0139 to 4.5641.7882
Soft tissue releases3.1350−4.4657 to 10.7357.4189
Varus valgus releases4.6943−2.2772 to 11.6657.1869
Pericap injections−1.2366−15.1164 to 12.6431.8614
Tourniquet pressure0.0148−0.0526 to 0.0822.6673
Tourniquet time0.0896−0.0524 to 0.2316.2162
Operative time0.0051−0.0888 to 0.0990.9151
EBL0.0069−0.0159 to 0.0297.5523
Level of constraint−11.4941−22.8524 to −0.1358.0473
Femoral size−0.0342−1.6679 to 1.5995.9672
Tibial size−0.4664−2.0945 to 1.1617.5745
PE thickness−1.5932−2.9483 to −0.2382.0212
Patellar size0.2313−0.5622 to 1.0249.5678
LOS−1.9813−3.9829 to 0.0202.0524

Univariate Analysis of SF-36 Score for Different Radiographic Measurements

MeasurementEstimateWald 95% CIP
Coronal knee angle
  Preop0.1543−0.1741 to 0.4827.3571
  Postop0.0162−0.7773 to 0.8097.9681
  Difference−0.1269−0.4379 to 0.1841.4240
Anatomical axis femur
  Preop0.0541−0.9426 to 1.0508.9153
  Postop0.2569−0.7819 to 1.2958.6278
  Difference0.1979−0.5515 to 0.9474.6047
Anatomical axis tibia
  Preop−0.4715−1.2229 to 0.2798.2187
  Postop0.9178−0.2727 to 2.1082.1308
  Difference0.77880.0620 to 1.4956.0332
Insall-Salvati ratio
  Preop−0.0426−0.3841 to 0.2989.8068
  Postop−0.0416−0.3548 to 0.2716.7945
  Difference−8.0904−28.0695 to 11.8886.4274
Anterior patellar height
  Preop−0.0897−0.6632 to 0.4838.7592
  Postop0.5364−0.0155 to 1.0883.0568
  Difference0.4763−0.0500 to 1.0026.0761
Sulcus angle
  Preop−0.1464−0.5023 to 0.2095.4200
  Postop−0.0557−0.3114 to 0.2000.6695
  Difference0.0339−0.1875 to 0.2554.7638
Congruence angle
  Preop−0.0310−0.1406 to 0.0786.5788
  Postop−0.0190−0.1599 to 0.1219.7915
  Difference0.0068−0.0871 to 0.1007.8874
Postop patellar tilt−0.2229−0.8576 to 0.4118.4913
Femoral offset
  Preop−0.3347−0.6479 to −0.0214.0363
  Postop−0.0081−0.3879 to 0.3717.9668
  Difference0.2881−0.0319 to 0.6081.0777
Anterior offset
  Preop0.0037−1.1662 to 1.1735.9951
  Postop0.0202−1.0157 to 1.0560.9695
  Difference0.0776−0.7581 to 0.9133.8556
Posterior offset
  Preop−0.5487−1.0765 to −0.0210.0416
  Postop0.1000−0.4352 to 0.6352.7142
  Difference0.3872−0.0580 to 0.8325.0883
Component alignment
  Femoral−0.2531−0.8278 to 0.3217.3881
  Tibial−0.3812−1.3281 to 0.5656.4300
Joint line
  Preop−0.3649−0.8487 to 0.1189.1393
  Postop−0.2710−0.7776 to 0.2356.2945
  Difference0.1825−0.2831 to 0.6481.4422
Overhanging implant
  Femur3.7490−1.5928 to 9.0907.1690
  Tibia−4.6428−24.2840 to 14.9984.6432

Multivariate Regression Analysis for SF-36 Score

ParameterdfEstimateStandard ErrorWald 95% CIWald Chi-SquarePa
Intercept1107.367712.182783.4900 to 131.245577.67<.0001
Sex 118.17662.69432.8959 to 13.45739.21.0024
Sex 200.00000.00000.0000 to 0.0000..
Patellar eversion 11−9.48992.8948−15.1637 to −3.816210.75.0010
Patellar eversion 200.00000.00000.0000 to 0.0000..
Preop femoral offset1−0.39420.1562−0.7003 to −0.08816.37.0116
Difference in anterior patellar height10.58290.25830.0767 to 1.08925.09.0240
Scale118.55110.903116.8630 to 20.4083
Authors

The authors are from the Hospital for Special Surgery, Weill Cornell Medical College, New York, New York.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Vasileios I. Sakellariou, MD, PhD, Hospital for Special Surgery, Weill Cornell Medical College, 535 E 70th St, New York, NY 10021 ( b_sakellariou@yahoo.com).

Received: April 09, 2015
Accepted: May 26, 2015

10.3928/01477447-20151228-06

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