Resident Participation During Revision Total Knee Arthroplasty Is Not Associated With Increased Risk of 30-Day Postoperative Complication

Abstract

Background

Academic teaching institutions perform approximately one third of all orthopedic procedures in the United States. Revision total knee arthroplasty (rTKA) is a complex and challenging procedure that requires expertise and extensive planning, however the impact of resident involvement on outcomes is poorly understood. The aim of the study was to investigate whether resident involvement in rTKA impacts postoperative complication rates, operative time, and length of hospital stay (LOS).

Methods

The American College of Surgeons National Surgical Quality Improvement Program registry was queried to identify patients who underwent rTKA procedures from 2006-2012 using CPT codes 27486 and 27487. Cases were classified as resident involved or attending only. Demographics, comorbidities, and 30-day postoperative complications were analyzed. Multiple logistic regression analysis was performed to identify independent risk factors for increased 30-day postoperative complications. Wilcoxon rank sum tests were performed to determine the impact of resident involvement on operative time and LOS with significance defined as p<0.05.

Results

In total, 2,396 cases of rTKA were identified, of which 972 (40.6%) involved residents. The two study groups were similar, however the resident involved cohort had more patients with hypertension and ASA class 3 (p=0.02, p=0.04). There was no difference in complications between the cohorts (No Resident vs Resident-involved: 7.0% vs 6.7%, p=0.80). Multivariate analysis identified obesity (OR: 1.81, 95% CI: 1.18-2.79, p=0.01), morbid obesity (OR: 1.66, 95% CI: 1.09-2.57, p=0.02), congestive heart failure (OR: 5.97, 95% CI: 1.19-24.7, p=0.02), and chronic prosthetic joint infection (OR: 3.16, 95% CI: 2.184.56, p<0.01), as independent risk factors for 30-day complications after rTKA. However, resident involvement was not associated with complications within 30-days following rTKA (OR: 0.91, 95% CI: 0.65-1.26, p=0.57). Resident involvement was associated with increased operative time (p<0.001) and LOS (P<0.001).

Conclusion

Resident involvement in rTKA cases is not associated with an increased risk of 30-day postoperative complications. However, resident operative involvement was associated with longer operative time and length of hospital stay.

Level of Evidence: III

Introduction

Total knee arthroplasty (TKA) is an effective procedure that provides pain relief and improvement of function. Amid the increase in volume of primary TKA and continued expansion of indication criteria and patient selection, the volume of revision TKA (rTKA) has increased. With increasing incidence of rTKA, it is imperative that future surgeons develop an appropriate framework for preoperative planning, postoperative management, and necessary technical skills to successfully care for patients that require rTKA.¹

Academic teaching institutions perform approximately one third of all orthopedic procedures in the United States. Therefore, operative participation of residents in various settings including rTKA are a fundamental aspect of resident education. However, resident participation in surgical specialties, like orthopedic surgery, is a potential source of patient apprehension.² In addition to patient concern, training residents can significantly increase operative time especially while training junior orthopedic residents.³ While in some procedures, operative time may have minimal impacts, multiple studies have demonstrated that increased operative time increases the risk of postoperative complications in the setting of total joint arthroplasty procedures.^4-7 As a result, academic surgeons have to balance training residents while minimizing adverse events and providing efficient care, especially while performing challenging procedures that require extensive planning and skill.

Prior studies have demonstrated that resident participation does not have a significant impact on postoperative complications after various primary orthopedic procedures including primary TKA.^8-16 However, the impact of resident involvement in complex revision cases on intraoperative and postoperative outcomes is poorly understood. The aim of the study was to investigate whether resident involvement in rTKA impacts postoperative complication rates, operative time, and length of hospital stay (LOS). We hypothesize that resident participation during rTKA would not have a significant impact on postoperative complications, LOS, or operative time.

Methods

Data Source

Patients undergoing rTKA were identified utilizing the American College of Surgeons National Surgical Quality Improvement Program database (ACS-NSQIP). The NSQIP database prospectively collects perioperative patient variables from private and academic hospitals across the United States.¹⁶ The data is collected by expert clinical reviewers and includes information up to 30 days following the procedure. Information collected includes patient demographics, medical comorbidities, preoperative laboratory values, operative time, length of hospital stay (LOS), and postoperative complications within 30 days of surgery. The last year that NSQIP database collected resident involvement information was 2012; therefore, data of patients who underwent rTKA from 2006 to 2012 was obtained and analyzed for this study. Patient records were retrieved and analyzed using Current Procedural Terminology (CPT) and International Classification of Diseases Ninth Revision (ICD 9) codes. Cases are de-identified and selected based on a systematic sampling process with a reported inter-observer disagreement rate of 2%.^16,17 Due to the de-identified nature of the data, this study was granted exemption from the local institutional review board (IRB).

Patient Selection, Demographics, and Comorbidities

A total of 4,309 rTKA cases were identified during the study period using CPT codes 27486 and 27487. Patients with incomplete/incongruent information regarding resident participation (n=1,781) and those with revision due to periprosthetic malignancy (n=32) were excluded from the study. After exclusion, 2,396 cases were included, of which 972 (40.6%) consisted of at least one resident involved. (Figure 1)

Figure 1.

Flowchart of Inclusion and Exclusion Criteria.

Basic patient demographics including age and sex are recorded in the database and were compared between resident involved and non-resident procedures. Age was stratified by 10-year increments with patients identified as <50 years, 50-59.9years, 60-69.9 years, 70-79.9 years, and >80 years. Body mass index (BMI) was calculated from each patients’ height and weight and was defined as normal for BMI 18 to 29.9 kg/m², obese for BMI 30 to 39.9 kg/m², and morbidly obese as BMI > 40 kg/m². Other preoperative conditions including diabetes mellitus, smoking history, chronic obstructive pulmonary disease, congestive heart failure, hypertension, and American Society of Anesthesiologist class (ASA) were compared between the two cohorts. Diabetes mellitus is categorized as insulin-dependent, non-insulin dependent, or no diabetes in the database; however, for the purposes of this study patients were categorized as having diabetes mellitus (insulin-dependent or non-insulin dependent) or not. The indication for rTKA was determined using ICD 9 codes and were categorized as component failure, prosthetic joint infection (PJI), aseptic necrosis, periprosthetic fracture, or dislocation. (Table 1).

Table 1.

Comparison of Comorbidities Between Resident Involved and Attending Only Cohorts Undergoing Revision Total Knee Arthroplasty

Comorbidities	Attending Only (n= 1,424)	Resident Involved (n= 972)	P-Value
Age, years
< 50 years	123 (8.6)	90 (9.3)	0.60
50 - 59.9 years	308 (21.6)	238 (24.5)	0.10
60 – 69.9 years	451 (31.7)	312 (32.1)	0.83
70 – 79.9 years	386 (27.1)	243 (25)	0.25
>80 years	156 (11)	89 (9.2)	0.15
Male Sex	568 (39.9)	419 943.1)	0.16
Body Mass Index, m/kg2
Normal	536 (37.6)	383 (39.4)	0.38
Obese	408 (28.7)	278 (28.6)	0.98
Morbid Obesity	480 (33.7)	311 (32.0)	0.38
Diabetes Mellitus	324 (22.8)	191 (19.7)	0.07
Smoke	168 (11.8)	113 (11.6)	0.90
Chronic Obstructive Pulmo- nary Disease	63 (4.4)	38 (3.9)	0.54
Congestive Heart Failure	5 (0.4)	4 (0.41)	0.81
Hypertension	991 (69.6)	633 (65.1)	0.02*
ASA Classification
1-No Disturb	18 (1.3)	14 (1.4)	0.71
2- Mild Disturb	589 (41.4)	427 (43.9)	0.21
3- Severe Disturb	784 (55.1)	493 (50.7)	0.04*
4- Life Threat	42 (2.9)	37 (3.8)	0.25
5- Moribund	0 (0)	1 (0.1)	0.23
Reason for Revision TKA
Component Failure	1087 (76.3)	725 (74.6)	0.33
Prosthetic Joint Infection	197 (13.8)	163 (16.8)	0.04*
Aseptic Necrosis/ Oste- olysis	27 (1.9)	12 (1.2)	0.21
Peri-prosthetic Fracture	110 (7.7)	67 (6.9)	0.44
Stiffness	3 (0.2)	5 (0.51)	0.21

Bold*: significant finding (P<0.05); ‘-’: not calculable

Outcomes

The NSQIP database tracks patients for any occurrence of various adverse events for 30 days postoperatively. Therefore, only 30-day postoperative complications were compared between the cohorts. The primary outcomes evaluated were overall complications, surgical complications, medical complications, operative time, and LOS. Overall complications were defined as any occurrence of medical or surgical complications. In this study, surgical complications were defined as any occurrence of superficial surgical site infection (SSI), deep SSI, wound dehiscence, wound infections, and neurologic deficits. Medical complications were defined as any occurrence of pulmonary embolism (PE), deep vein thrombosis (DVT), urinary tract infection (UTI), renal insufficiency, pneumonia, or sepsis.

Statistical Analysis

Pearson Chi-square tests and Fischer exact tests were performed for univariate analysis to compare patient demographics, preoperative comorbidities, indication for rTKA, and postoperative complications after rTKA between the resident involved and non-resident cohorts. A multiple binomial regression analysis was performed to control for potential confounding variables and identify independent risk factors for increased complication rates within 30-days following rTKA. Additionally, Wilcoxon rank sum test was performed to compare operative time and LOS between the cohorts. All statistical analyses were performed using R version 4.0, with statistical significance defined as p<0.05.

Results

Patient Characteristics

Overall, 2,396 cases of rTKA were included in the study, with 40.6% of the revision cases involving a resident. Patients in the resident involved cohort had a significantly higher incidence of patients with ASA class 3 and hypertension (p=0.04; p=0.02; Table 1). In regard to the indication for rTKA, the resident involved cohort had a higher incidence of PJI (16.8% vs 13.8%, p=0.04; Table 1).

Postoperative Complications

On univariate analysis, there was no significant difference in overall complication rate (6.7% vs 7.0%, p=0.80), surgical complication rate (3.1% vs 3.9%, p=0.27), or medical complication rate (4.8 vs 4.5%, p=0.70) between the resident involved and non-resident cohorts (Table 2).

Table 2.

Comparison of Complication Rates Between Resident Involved and Attending Only Cohorts following Revision Total Knee Arthroplasty

Adverse Events	Attending Only	Resident Involved	Unadjusted
	(n= 1,424)	(n= 972)	P-Value
Overall Complication Rate	99 (7.0)	65 (6.7)	0.80
Medical Complication Rate	64 (4.5)	47 (4.8)	0.70
Pulmonary Embolism	8 (0.56)	1 (0.1)	0.07
Deep Vein Thrombosis	9 (0.63)	11 (1.1)	0.19
Urinary Infection	23 (1.6)	15 (1.5)	0.89
Renal Insufficiency	4 (0.28)	1 (0.1)	0.65
Pneumonia	9 (0.63)	5 (0.51)	0.71
Systemic Infection (Sepsis, Septic Shock)	11 (0.77)	14 (1.4)	0.11
Surgical Complication Rate	56 (3.9)	30 (3.1)	0.27
Wound Infection	15 (1.1)	4 (0.4)	0.08
Wound Dehiscence	9 (0.63)	7 (0.72)	0.79
Superficial SSI	10 (0.7)	8 (0.82)	0.74
Deep SSI	18 (1.3)	11 (1.1)	0.77
Neurologic Injury	4 (0.28)	0 (0)	0.15

Bold*: significant finding (P<0.05); ‘-’: not calculable

Multivariate analysis identified obesity (OR: 1.81, 95% CI: 1.18-2.79, p=0.01), morbid obesity (OR: 1.66, 95% CI: 1.09-2.57, p=0.02), congestive heart failure (OR: 5.97, 95% CI: 1.19-24.7, p=0.02), and chronic prosthetic joint infection (OR: 3.16, 95% CI: 2.18-4.56, p<0.01), as independent risk factors for 30-day complications after rTKA (Table 3). However, resident involvement was not associated with complications within 30-days following rTKA (OR: 0.91, 95% CI: 0.65-1.26, p=0.57). (Figure 2)

Table 3.

Independent Risk Factors for Complications Within 30-days After Revision Total Knee Arthroplasty

Age, (Reference: <50 years)
50 - 59.9 years	1.36 [0.67-2.99]	0.42
60 – 69.9 years	1.56 [0.79-3.39]	0.23
70 – 79.9 years	1.40 [0.68-3.13]	0.38
> 80 years	2.10 [0.94-4.99]	0.08
Male Sex	1.19 [0.85-1.66]	0.32
Body Mass Index (Reference: 18.5 to 30 m/kg2)
Obese (30 to 34.9 m/kg2)	1.81 [1.18-2.79]	0.01*
Morbid Obesity (>34.9 m/kg2)	1.66 [1.09-2.57]	0.02*
Diabetes Mellitus	1.10 [0.73-1.66]	0.64
Smoking History	1.44 [0.86-2.34]	0.15
Chronic Obstructive Pulmonary Disease	1.37 [0.67-2.61]	0.36
Congestive Heart Failure	5.97 [1.19-24.7]	0.02*
Hypertension	0.80 [0.55-1.17]	0.24
ASA (reference: 1- No Disturb)
2- Mild Disturb	5.58 [0.45-23.5]	0.97
3- Severe Disturb	7.28 [0.19-94.1]	0.97
4- Life Threat	12.3 [0.22-31.2]	0.97
Reason for Revision TKA (reference: Component failure)
Infected Implant	3.16 [2.18-4.56]	<0.001*
Aseptic Necrosis/ osteolysis	0.42 [0.02-2.11]	0.41
Peri-prosthetic Fracture	1.14 [0.56-2.10]	0.69
Stiffness	-	0.99
Resident Involvement	0.91 [0.65-1.26]	0.57

Bold*: significant finding (P<0.05); ‘-’: not calculable

Figure 2.

Risk Factors for 30-Day Complications After Revision Total Knee Arthroplasty.

Operative Time and LOS

Resident participation in rTKA cases significantly prolonged operative times (146 vs 125 minutes, p<0.001) and increased LOS duration (resident involved vs nonresident: 4.6 vs 3.9 days, p<0.001). (Table 4)

Table 4.

Comparison of Operative Time and Length of Hospital Stay

Variable	Attending Only	Resident Involved	P-Value
	n=1,424	n= 972
Operative time, min (SD)	125.0 (60.1)	145.8 (67.1)	<0.001*
Length of hospital stay, days (SD)	3.9 (3.2)	4.6 (5.3)	<0.001*

Bold*: significant finding (P<0.05); ‘-’: not calculable

Discussion

Resident training, inside and outside of the operating room, is a fundamental pillar of academic orthopedic institutions. While maturation of the next generation of orthopedic surgeons is critical, there is concern regarding patient safety with resident participation during operative cases.² The findings of this study are valuable in informing orthopedic residents as well as resident educators. This study determined that resident participation during rTKA was not associated with increased risk of 30-day postoperative complications. However, resident participation during rTKA was associated with significantly longer operative time as well as increased length of hospital stay.

Prior studies have assessed the impact of resident participation on postoperative complications after various orthopedic,^{8,10-12,15,18-21} and non-orthopedic procedures^22-25 with conflicting findings. Haughom et al. assessed the impact of resident participation during primary TKA and concluded that resident participation in primary TKA does not increase risk for short-term morbidity or mortality.¹⁵ Similarly, resident participation was not associated with increased risk of short-term morbidity or mortality after primary total hip arthroplasty (THA).⁸ These findings have also been demonstrated for patients undergoing total shoulder arthroplasty,^10,11 knee arthroscopy,¹⁸ anterior cruciate ligament reconstruction,¹⁹ and other orthopedic procedures. The findings of the present study are consistent with prior studies and demonstrates that resident participation during rTKA was not significantly associated with 30-day medical, surgical or overall complications. However, unlike prior studies, this is the first study to assess the impact of resident participation on revision cases, which involves additional skill and challenging factors.

In the current climate of cost-effective, value-based outcomes, length of procedure and postoperative hospital stay have become important parameters that have been assessed.²⁶ This has been emphasized to the degree that there is now a growing trend to perform common inpatient procedures on an outpatient or short-stay basis. In fact, in January 2018, the Center for Medicare and Medicaid Services (CMS) removed primary TKA as an inpatient only procedure in order to facilitate cost-effective care for Medicare and Medicaid patients.^27,28

The present study determined that resident participation was associated with longer operative time for rTKA when compared to non-resident cases. The fact that resident involvement in surgical procedures increases operative time is known. In 2016, Allen and colleagues evaluated 29,134 cases covering 246 procedures (including various surgical specialties) and found that overall involving, cases involving a resident consisted of significantly longer operative times.²⁹ Orthopedic specific studies agree with these findings.^8,15,20,30 Beletsky et al. retrospectively assessed the impact of resident participation during common sports medicine procedures. This study reported that resident participation was on average 15 minutes longer compared to the attending only cases (p<0.01).¹³ Haughom et al. determined that in primary THA, resident involvement significantly increased operative time.¹⁵ Similarly, resident participation was associated with increased operative time during primary TKA.¹⁵ However, even after multivariate regression analysis, these studies reported no difference in risk of complications associated with resident involvement.

Multiple studies have demonstrated the impact of operative length and postoperative complications. Duchman et al. recently investigated how the length operative time impacts postoperative complications. By utilizing the NSQIP database, they reported that an operative time consisting more than 120 minutes was an independent predictor of any complication, including wound complications. Additionally, multi-variate analysis showed that a subsequent increase of operative time by 30-minutes, beyond 120 minutes, significantly added additional risk of complications.⁴ The previously mentioned studies investigating resident involvement in primary TKA and THA procedures demonstrated with sub-analysis, that increased operative time increased the risk for postoperative complications.

Prior studies have conflicting information regarding the impact of resident participation in LOS. Recently, Perfetti et al. determined that academic teaching departments had 10% shorter LOS (p<0.001) compared to non-academy centers for elective lumbar laminectomy and discectomy for degenerative lumbar conditions.³¹ However, Nandyala et al. noted a significantly longer LOS for elective lumbar spine surgery at academic teaching institutions.³² However, the previously mentioned studies have established that resident participation during primary THA or TKA do not have a significant impact on LOS.^8,15 Contrary to these previous studies findings, the current study demonstrated that rTKA cases involving a resident consisted of longer LOS. However, this was by only ~17 hours, limiting the significance of these findings. Additionally, our increased LOS might be due to additional factors, including increased operative time, which has been previously correlated with increased LOS.³³

There are limitations that must be considered when interpreting the findings of the study. First, the retrospective nature of the study limits causal conclusions and only associations can be ascertained. Second, the NSQIP database is limited to 30-day postoperative complications; therefore, we were unable to assess complications that occur past this time point. Third, NSQIP does not collect relevant orthopedic information such as radiographic findings, type of implants used in primary TKA, type of implants used for rTKA, chronicity of symptoms, or patient reported outcome measures that may play an important role for postoperative complications. Fourth, NSQIP does not detail the extent of resident participation during the surgery and only reports whether a resident was listed during the case. Additionally, stratification of resident by year in residency was not available for all years. Therefore, associations between year of residency and 30-day complications was not studied. Lastly, NSQIP is the largest available database with information regarding resident participation during operative procedures. Therefore, the lack of short-term complications for the resident involved cohort may be secondary to a type II error.

Conclusion

Resident involvement in rTKA cases is not associated with an increased risk of 30-day postoperative complications. However, resident operative involvement was associated with longer operative time and length of hospital stay.