Study Examines Total Knee Replacement in Patients Under 21

A new study from researchers at Hospital for Special Surgery (HSS) has evaluated trends in the use of total knee arthroplasty (TKA) in patients under 21 in the United States. The study was reported at the American College of Rheumatology (ACR) Convergence 2022 meeting (abstract number 08780).

According to Cynthia A. Kahlenberg, MD, MPH, an orthopedic surgeon at HSS and a coauthor of the study, TKA is rarely performed in patients under 21 years old but may be done in this population due to conditions such as inflammatory arthritis or juvenile idiopathic arthritis (JIA), malignant or non-malignant tumors, or trauma. However, the number of patients under the age of 21 undergoing TKA in the U.S. is unknown. In one of the largest U.S. studies of an institutional arthroplasty registry, only 19 TKAs were performed in patients under the age of 21 out of approximately 30,000 primary TKAs over 34 years—a majority of which were for JIA.

The researchers retrospectively analyzed the Kids’ Inpatient Database (KID), a national weighted sample of all inpatient hospital admissions of patients under 21 years old in approximately 4,200 hospitals in 46 states. The researchers used International Classification of Diseases, Ninth Revision (ICD-9) and ICD-10 codes to identify patients undergoing TKA from 2000-2016 and determine primary diagnosis. Descriptive statistics such as means and percentages, along with their 95% confidence intervals (95% CI), were calculated using the appropriate sample weights as recommended by the Agency for Healthcare Research and Quality for use with the KID dataset.

The total weighted number of TKAs performed in patients younger than 21 from 2000-2016 was 1,331; the number of TKAs performed per year in this age group remained relatively stable. The mean age of patients undergoing TKA was 14.8 years (95% CI, 14.4-15.2); 48.8% of the cohort was female. Among tumor patients, a higher proportion identified as Hispanic (22.1%) or other race (12.6%) compared to the non-tumor cohort; 70.3% of TKAs were performed for a primary diagnosis of a tumor; and the number of TKAs for malignant tumors increased slightly over the study period. In contrast, use of TKA for inflammatory arthritis / JIA decreased by more than 70% over the study period, likely due to improvements in medical management of inflammatory arthritis / JIA patients. The majority of TKAs were performed in urban teaching hospitals and in facilities with a large bed size, which likely reflects the complexity and rarity of these procedures.

“This was one of the first studies to take an in-depth look at TKA in this very young population,” said Dr. Kahlenberg. “Our study was able to confirm that tumors were the most common reason for knee arthroplasty in this population.”

“I think the biggest takeaway as a rheumatologist is that we are doing a good job treating these patients and over the years the treatments for inflammatory arthritis are really working well in this young population,” said Bella Mehta, MBBS, MS, rheumatologist at HSS and senior study author.

About HSS

HSS is the world’s leading academic medical center focused on musculoskeletal health. At its core is Hospital for Special Surgery, nationally ranked No. 1 in orthopedics (for the 13th consecutive year), No. 3 in rheumatology by U.S. News & World Report (2022-2023), and the best pediatric orthopedic hospital in NY, NJ and CT by U.S. News & World Report “Best Children’s Hospitals” list (2022-2023). In a survey of medical professionals in more than 20 countries by Newsweek, HSS is ranked world #1 in orthopedics for a third consecutive year (2023). Founded in 1863, the Hospital has the lowest complication and readmission rates in the nation for orthopedics, and among the lowest infection rates. HSS was the first in New York State to receive Magnet Recognition for Excellence in Nursing Service from the American Nurses Credentialing Center five consecutive times. An affiliate of Weill Cornell Medical College, HSS has a main campus in New York City and facilities in New Jersey, Connecticut and in the Long Island and Westchester County regions of New York State, as well as in Florida. In addition to patient care, HSS leads the field in research, innovation and education. The HSS Research Institute comprises 20 laboratories and 300 staff members focused on leading the advancement of musculoskeletal health through prevention of degeneration, tissue repair and tissue regeneration. The HSS Innovation Institute works to realize the potential of new drugs, therapeutics and devices. The HSS Education Institute is a trusted leader in advancing musculoskeletal knowledge and research for physicians, nurses, allied health professionals, academic trainees, and consumers in more than 145 countries. The institution is collaborating with medical centers and other organizations to advance the quality and value of musculoskeletal care and to make world-class HSS care more widely accessible nationally and internationally. www.hss.edu.