A Claims Based Natural History of the Post-operative Period after a Unilateral Total Knee
Arthroplasty
Maha Karim BS1, Samantha J Beckley PhD1, Shaun K Stinton PhD1 Thomas P Branch MDb
a ArthroResearch LLC, 441 Armour Place NE, Atlanta, GA, 30324, United States
b Ermi LLC, 2872 Woodcock Blvd. Suite 100, Atlanta, GA, 30341, United States
Address for correspondence:
Samantha Beckley, 441 Armour Place NE, Atlanta, GA, 30324, USA
Phone: +1 404-579-1546
Email: s.beckley@arthroresearch.com.
| Abstract: Objective: This study aimed to determine a claims-based timeline of unilateral total knee arthroplasty (TKA) recovery including the impact of comorbidities and post-surgical complications. Methods: Healthcare claims data were analyzed to determine the costs and recovery timeline after unilateral TKA. Costs related to: i) index surgery, ii) complication surgery, iii) TKA revision, iv) non-operative hospitalization, v) motion restoring surgery and vi) outpatient surgery were reported. The effect of comorbidities including diabetes, obesity, peripheral vascular disease, joint infection, cardiovascular disease, and joint contracture, was assessed. The effect of post-index surgical complications was determined using data from patients re-hospitalized with or without additional surgery. Perioperative complications including joint fibrosis/contracture, infection, and pulmonary embolus were also reported. Results: Index surgery median cost was $30,346 (IQR: $14,203-$350,304). Median recovery time (from Index Surgery to last physical therapy claim) was 126 days (IQR: 30-975 days). While 54% of patients completed their postoperative period in six months, 46% took over six months. Recovery periods for patients that required a complication surgery were six times longer and costs were added 14 times higher than for those without complications. Nonoperative hospitalizations for pulmonary embolus and/or infection increased the postoperative period 4 times at a cost of $25,430 per event. Conclusion: Comorbidities and complications after TKA lead to dramatically increased costs and recovery times. Knowing the timeline of recovery in the average TKA patient and in outlier patients can help manage recovery and determine appropriate interventions. |
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| Keywords: TKA, healthcare claims analysis, natural history Introduction: Total knee arthroplasty (TKA) is one of the most common and costly procedures in the United States, with over 700,000 performed in 2012—a figure expected to increase by 60% by 2050 1 . The rising prevalence of comorbidities and an aging population will likely increase TKA costs 2 . The primary goal of TKA is to improve knee function by increasing range of motion and to alleviate arthritis pain, with most patients achieving satisfactory outcomes 3 . Despite its success, some patients face prolonged recovery due to complications or lifestyle factors. Up to 21% report dissatisfaction, often requiring continued healthcare use 4-6 . For patients who struggle with recovery, both mental and emotional well-being can suffer, placing further strain on healthcare resources 7 . Secondary surgeries due to complications, revisions, and risk factors related to hospitals and patient comorbidities can drive up costs and lengthen recovery time, with revision TKAs generally showing worse outcomes and higher reoperation rates compared to primary TKA 8,9 . Avoiding these complications could lead to significant savings to the healthcare system. A study reported median first-year post-operative expenses of $5,370, with patient costs ranging from $436 to $90,066 1 . Furthermore, outliers included individuals with $76,702 of inpatient costs alone, 6.5 hospitalizations, and 33 in-patient days 1 . In another study, one year after TKA, patients averaged nearly 49 outpatient visits, with over half being for physical therapy (PT) 7 . Total costs for the year post-TKA were close to |
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| $9,000, encompassing outpatient, inpatient, and emergency care 7 Post-acute care expenses are expected to rise due to growing comorbidities, hospital factors, PT duration, and other health variables influenced by care quality 4 Common post-TKA complications include stiffness, pain, wound issues, necrosis, fractures, and neurovascular problems 8,10 Studies have shown that up to 10% of TKA patients subsequently require manipulation under anesthesia (MUA) 11 Revision rates of 3-12% have been reported 12 Examining complications related to a TKA can provide information on advancing post-operative recovery strategies. Re-hospitalizations serve as key data points, highlighting patients at risk for less favorable outcomes. Motion restoring surgeries (MRS) such as MUA, arthroscopic synovectomy, debridement, or lysis of adhesions add considerable risk, increase costs and delay recovery. Addressing these challenges may help develop protocols that reduce recovery obstacles and enhance patient outcomes. One resource for establishing TKA recovery patterns is the IBM MarketScan Commercial Claims and Encounters Database, which includes de-identified health data from reimbursed healthcare claims for over 250 employers and health plans 13 This database covers clinical utilization, expenses, insurance details, and care services for a large, insured population in the United States (30 million individuals/year) 13 The aim of this study was to perform a claims-based timeline analysis of unilateral TKA, from initial surgery to the final PT session, to establish a recovery timeline. Additionally, we |
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| sought to quantify the impact of comorbidities and post-surgical complications on this recovery trajectory. Methods: Study Population Healthcare claims data from the IBM MarketScan database (2015–2018) focusing on patients with orthopedic CPT codes, covering 11 million unique patients and 1 billion claims, were used for this study. This retrospective study was determined to be exempt from IRB review. Patients were eligible if they had at least two consecutive years of continuous coverage . TKA patients were identified by CPT code 27447. Bilateral TKA patients (simultaneous or staged) were excluded as these data would confound the post-operative recovery period and skew recovery time and costs. The post-operative period was defined as the timeline from the index TKA surgery to the last HCPCS CPT charge for PT. Only patients with at least one PT CPT charge (codes >=97000 & <98000) post-surgery were included. Cost Analysis Costs associated with the index surgery represent all healthcare dollars spent during inpatient hospitalization or within eight days of outpatient surgery. Subsequent procedures were grouped into categories: i) complication-related surgery, ii) TKA revision, iii) non-operative hospitalization, and vi) motion-restoring surgery. Total costs in each group represent all healthcare dollars spent including the cited index surgery and any additional post-index surgery events. Therefore, these costs are a true representation of the event and the risk of related subsequent events. Standard CPT codes for post-operative costs, such as PT (>=97000 & |
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| <98000), physician visits (>=99200 & <99300, plus injection CPT codes 20610/20611), and radiology, were also analyzed (Addendum #1). Costs unrelated to TKA were excluded from the analysis by absence of knee-related ICD 9/10 codes. All reported costs reflect insurance-paid amounts. Comorbidities The study analyzed how comorbidities affect recovery timelines. Data subsets were created for patients with diabetes (codes 25.0 & E11.9), obesity (codes 278., E66., & Z68.4), peripheral vascular disease (PVD, codes 440.:444., 785., & I73.9), joint infection (codes 711., 996., M00., M01, & M02), cardiovascular disease (CVD, codes 390.:459., I11, I20, I21, & I25), and knee contracture ICD 9/10 codes 718.46 & M24.56). The median costs and 25-75% cost range were calculated for each group. Infection (Addendum #6) and pulmonary embolus (Addendum #7) incidence rates associated with each comorbidity were also included. Index Surgery All costs associated with the index surgery were included as identified by the case identifier (CaseID) for inpatient surgery. If the index surgery was performed in an outpatient setting (without a CaseID), all costs over an eight day period were included in the total index costs as submitted claims were spread out over time. If the TKA started as an outpatient and then was transferred to a hospital creating a new CaseID within 8 days, these costs were included in the outpatient index surgery costs. All patients who had inpatient surgery and were subsequently transferred to an inpatient rehabilitation hospital were counted as two separate hospitalizations. The inpatient rehabilitation hospitalization was considered a nonoperative hospitalization. |
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| Additional Postoperative Surgeries The impact of post-surgical complications on recovery was analyzed, focusing on rehospitalizations with and without additional surgeries, including TKA revisions (Addendum #2), MRS (Addendum #3), and other complication-related surgeries (Addendum #4). Hospitalizations were identified by a new CaseID linked to or following the index surgery. Perioperative complications such as joint contracture (Addendum #5), infection (Addendum #6), and pulmonary embolus (Addendum #7) were also analyzed. Presentation of Recovery Pathway A best-case recovery pathway assumes an uncomplicated post-operative course, where the patient undergoes the index surgery, is discharged, attends PT, and recovers within six months. It is generally accepted that a disability such as an injury or surgery changes from acute to chronic at the six month mark, and most states and insurance providers cap temporary or short-term disability insurance at six months. To illustrate complicated recoveries, a multiple-pathway chart (Figure 1) shows the aggregate impact of multiple post-operative events, particularly focusing on the added risks associated with MRS decisions. This chart does not represent a timeline but highlights the cumulative risk impact of successive complications during the post-operative period. Data Analysis Data were analyzed using the R statistical programming language (version 4.3.3). Given the large sample size, results are presented as medians with a 25-75% interquartile range (IQR). |
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| Results: Study Group Demographics The study group was composed of 10,936 patients with a median age of 57 years, ranging from 14 to 62 years (Figure 2) and 60.4% were female. There were no heights or weights available. Index Surgery Costs Of the 10,936 surgeries, 10,305 were inpatient only, 553 were outpatient and 78 started as outpatient, but ended as inpatient. The index surgery median cost was $30,346 (IQR:$24,292-$37,742). Inpatient surgery median cost was $30,614 (IQR:$24,481-$37,840). Outpatient surgery median cost was $25,882 (IQR:$20,788-$31,731). If the patient started as an outpatient but ended as an inpatient the median cost was $27,690 (IQR:$21,943-$34,837). Recovery Period The median length of post-operative recovery for a unilateral TKA was 126 days (IQR:30-975 days). Only 54% of patients completed their postoperative period in six months with 46% of patients taking over six months to complete PT (Figure 3). Patients recovering in under six months spent a median of 55 days in PT, compared to 727 days for those taking longer. The additional postoperative costs incurred after six months for patients undergoing PT beyond that point have a median of $2,892 (IQR:$1,647-$6,262). Complicating Events |
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| After MRS, the median number of days in structured PT and the costs of postoperative care both nearly tripled (Table 1). The median recovery period and cost for patients that required a complication surgery after a unilateral TKA were six times longer and added 14 times the cost in comparison to patients that did not require any complication surgeries (Table 1). Revision surgery had the same impact (Table 1). Nonoperative hospitalizations for pulmonary embolus and/or infection increased the postoperative period nearly 3.5 times (434 days vs. 126 days) at a median cost of $25,430 (IQR:$15,368-$52,618) per event (Table 1). The cumulative effect on medical care costs and recovery time as a result of multiple events in the postoperative period can be seen in Figure 4 and Table 2. In particular, the decision to perform a MRS substantially impacted the risk of requiring a TKA revision, with patients undergoing MRS being 3.3 times more likely to need a revision compared to those without MRS (11% vs. 3.3%). A single TKA with no complications, revisions or MRS had a median postoperative cost of $3,745. We found that 12.2% of single TKAs required a secondary surgery. This median cost surged to $53,254 (IQR:$37,642-$81,886) with a revision surgery. Out of the 10,936 patients that were observed with a unilateral TKA, 9,957 patients did not undergo a MRS. These patients had a median of 111 PT days (IQR:49-693 days) and the median postoperative cost was $3,909. The median cost with a MRS in this group of patients was $11,249 (IQR:$7,478-$19,396) with a median of 321 PT days (IQR:100-768 days). Joint Contracture The presence of joint contracture at the time of index surgery had no impact on recovery costs or time to recover whereas the development of joint contracture after the index surgery had |
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| a major impact. The median cost and recovery time for the subset of patients that developed a joint contracture post operatively were 2.64 times more expensive and 2.61 times longer than in patients with who did not develop a contracture (Table 3). Impact of Comorbidities on Recovery The effect of the presence of PVD, diabetes, obesity and CVD is shown in Table 4. The clinical impact of these conditions on recovery was small. It is important to note that there were a larger number of pulmonary embolus events present in patients with PVD and CVD in comparison to those without the comorbidities. Discussion: The primary outcome of this study was the establishment of a benchmark for the postoperative period following unilateral TKA. This baseline provides a standardized framework to monitor and manage patient progress during the early recovery phase. The median postoperative recovery time was 126 days. Notably, 46% of patients required more than six months to complete their postoperative care (Figure 3). These large variations in recovery timelines underscore the complexity of TKA recovery. A second key finding was that critical postoperative events including MRS, complication surgery, revision surgery, and non-operative hospitalizations substantially affected both recovery duration and healthcare costs. The study observed marked cost increases associated with these events with an increase of 187% for MRS, 1,316% for complication surgeries, 1,203% for revision surgeries, and 521% for non-operative hospitalizations. The greatest financial burden |
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| was associated with patients who experienced complications, while the longest recovery times in terms of median PT days were observed in patients requiring revision surgery. These findings highlight the considerable financial impact of postoperative complications and emphasize the need for effective management strategies to minimize cost escalations. The third important finding in this study was that the diagnosis of a knee contracture (M24.56) in the postoperative period after a unilateral TKA led to a considerable increase in costs and time to recover. This is likely a result of the necessity of prolonged treatment to address the contracture. For example, stiffness is one of the leading causes for TKA revisions 14 . Interestingly, the presence of a knee contracture before surgery had no impact on the claims based outcome. While some studies reported that a preoperative knee contracture is a predictor of a postoperative contracture, others reported non-clinically significant differences in International Knee Society scores and range of motion between patients with and without a knee contracture before surgery 15,16 . A previous study identified various factors contributing to pain and discomfort following TKA, including demographic characteristics, psychological conditions, and the genetic expression of profibrotic markers, all of which can restrict a patient’s range of motion 17 . These challenges may result in slower or more difficult recoveries, especially in patients with underlying conditions such as obesity, diabetes, or knee contractures. Another study reported that abnormal tissue scarring occurred in an estimated 3% to 10% of patients with arthrofibrosis, which allows dense fibrous tissue to form and prohibits normal range of motion in these adults 18 . These limitations can slow progress in recovery for patients and lead to higher medical costs associated with the factors that affect post-surgical outcomes. |
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| The fourth key finding in this study was the impact of comorbidities on the cost and recovery time following unilateral TKA. Recovery time increased more substantially (43–204%) compared to cost (7–23%). The presence of PVD and CVD were associated with the largest increases in cost and recovery time, as well as a higher risk of postoperative pulmonary embolus, a leading cause of death after TKA 19 . These findings align with earlier research suggesting that greater comorbidity (excluding diabetes) worsens patient-reported outcomes 20 and that CVD is associated with increased postoperative complications 21 . Comorbidities and related adverse events prolong recovery and necessitate additional interventions, intensive rehabilitation, extended hospital stays, and specialized care, contributing to higher costs and longer recovery times. There are multiple limitations with a HCPCS claims-based analysis. There is the presence of standard coding inconsistencies, particularly since this study spans the change from ICD 9 to ICD 10 codes. In this study, the post-operative period definition assumes that the patient is finished with medical care after the last recorded PT visit. Another limitation of this study was that the database claims did not include the cost of prescribed drugs which would add healthcare dollars to the total costs. Conclusion: This study established a claims-based timeline or “Natural History” for recovery after unilateral TKA, highlighting the influence of comorbidities and post-surgical complications on recovery duration and costs. Patients undergoing MRS were found to substantially extend recovery timelines and increase expenses, while also elevating the likelihood of further |
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| complications, including revision surgeries. Comorbidities, such as cardiovascular and vascular disease, were linked to delayed recovery and higher risks of adverse events like pulmonary embolism. These findings underscore the need to minimize complications like MRS to enhance recovery trajectories and improve outcomes. References 1. Inacio MCS, Paxton EW, Graves SE, Namba RS, Nemes S. Projected increase in total knee arthroplasty in the United States - an alternative projection model Osteoarthritis Cartilage, 25 (11) (2017), pp. 1797-1803 2. Klug A, Gramlich Y, Rudert M, et al. The projected volume of primary and revision total knee arthroplasty will place an immense burden on future health care systems over the next 30 years. Knee Surg Sports Traumatol Arthrosc. 2021;29(10):3287-3298. doi:10.1007/s00167-020-06154-7 3. Bourne RB, Chesworth BM, Davis AM, Mahomed NN, Charron KD. Patient satisfaction after total knee arthroplasty: who is satisfied and who is not? Clin Orthop Relat Res. 2010 Jan;468(1):57-63. doi: 10.1007/s11999-009-1119-9. PMID: 19844772; PMCID: PMC2795819.) 4. Falvey JR, Bade MJ, Forster JE, et al. Home-Health-Care Physical Therapy Improves Early Functional Recovery of Medicare Beneficiaries After Total Knee Arthroplasty. J Bone Joint Surg Am. 2018;100(20):1728-1734. doi:10.2106/JBJS.17.01667 5. Marsh J, Joshi I, Somerville L, Vasarhelyi E, Lanting B. Health care costs after total knee arthroplasty for satisfied and dissatisfied patients. Can J Surg. 2022;65(5):E562-E566. Published 2022 Sep 1. doi:10.1503/cjs.006721 6. Kim et. al. Causes and predictors of patient's dissatisfaction after uncomplicated total knee arthroplasty. J Arthroplasty 2009. 24(2):263-71. 7. Hung A, Li Y, Keefe FJ, et al. Ninety-day and one-year healthcare utilization and costs after knee arthroplasty. Osteoarthritis Cartilage. 2019;27(10):1462-1469. doi:10.1016/j.joca.2019.05.019 8. Roman MD, Russu O, Mohor C, et al. Outcomes in revision total knee arthroplasty (Review). Exp Ther Med. 2022;23(1):29. doi:10.3892/etm.2021.10951 9. Stoicea N, Magal S, Kim JK, Bai M, Rogers B, Bergese SD. Post-acute Transitional Journey: Caring for Orthopedic Surgery Patients in the United States. Front Med (Lausanne). 2018 Dec 7;5:342. doi: 10.3389/fmed.2018.00342. PMID: 30581817; PMCID: PMC6292951. 10. Healy WL, Della Valle CJ, Iorio R, et al. Complications of total knee arthroplasty: standardized list and definitions of the Knee Society. Clin Orthop Relat Res. 2013;471(1):215-220. doi:10.1007/s11999-012-2489-y |
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