This research is being done to see if the amount of an enzyme in blood (called serum mast cell tryptase) changes before and after surgery. The investigators would like to see if these amounts are related to knee stiffness and pain in subjects that undergo a total knee replacement.

Arthrofibrosis (AF), characterized by pain and limited mobility, affects a notable percentage of patients post-total knee arthroplasty (TKA). Despite various treatment advancements, the condition remains challenging to manage. Prior research has indicated a relationship between elevated serum mast cell tryptase (SMCT) levels and increased fibrosis in animal models, suggesting that SMCT could serve as a biomarker for arthrofibrosis in humans. This study aims to 1) assess pre- and postoperative SMCT levels in TKA patients, 2) evaluate SMCT's association with arthrofibrosis and clinical outcomes, and 3) determine the impact of allergic or inflammatory co-morbidities on SMCT levels.

Inclusion Criteria:

• Investigators will include all patients with osteoarthritis who are surgical candidates for primary TKA. Investigators will include all eligible male or female patients between the ages of 20 years to 100 years old. All included study participants must be able to give an informed consent.

Exclusion Criteria:

• Significant femoral or tibial deformity due to congenital or traumatic etiologies, inflammatory arthritis, post-septic arthritis, osteomyelitis, prior infection of knee joint, osteoporosis, dislocated or fragmented patella
• Patients taking mast cell inhibitors and/or degranulation inhibitors for any reason.
• The presence of infections, highly communicable diseases (e.g. AIDS), active tuberculosis, venereal disease, hepatitis.
• Significant neurological or musculoskeletal disorders or disease that may adversely affect normal gait or weight bearing.
• Presence of previous prosthetic knee replacement devices (of any type)
• Metastatic disease
• Psychiatric illness
• Drug or alcohol abuse
• Inability to participate in standard postoperative rehabilitation protocol

Males or females between the ages of 20 to 100 years who are surgical candidates for primary total knee replacement.

IPD will not be shared, as Mayo Clinic is the only institution involved in this research study and results reporting will be done via summary metrics and statistical analysis. Research participants did not consent for IPD to be shared outside of Mayo Clinic.