Studies have demonstrated that early rehabilitation interventions following knee arthroplasty (TKA) can shorten the time needed to regain baseline extension/full extension and gait mechanics. As telehealth visits and home-based rehabilitation increases with advancements in technology, much of this rehabilitation is projected to be performed at home. The purpose of this study is to prospectively evaluate early post-operative knee extension and self-reported outcomes in patients using the Zero Degree Knee positioner (ZDK) compared to subjects not using the ZDK. Patients electing to undergo primary TKA will be recruited into the study and randomized to receive and follow the ZDK protocol post-operatively or standard of care rehabilitation instructions. Knee extension measurements will be recorded at 2 weeks post-op and patient-reported outcome measurements will be recorded pre-operatively and at various post-op timepoints.

Total Knee Arthroplasty (TKA) remains one of the most commonly performed elective surgical procedures in the United States. The number of TKAs performed annually has increased steadily since 2005 and is projected to be more than 3 million procedures annually by 2030. This steady growth may be attributed to the increasing geriatric population which is expected to represent 17% of the world's population by 2050. TKA aims to reduce pain and restore motion from those with knee complications, and with the geriatric population continuing to rise, TKA procedures are projected to grow over the next decade and beyond.

Historically, one of the major concerns following TKA is joint stiffness and subsequent range of motion loss. Range of motion loss, or more specifically, the inability to regain full extension (flexion contracture) have a relatively high occurrence and may lead to gait abnormalities and associated complications of the hips and low back. Early rehabilitation interventions following TKA may shorten the time needed to regain baseline extension/full extension and gait mechanics which not only is this beneficial for patient reported outcomes, but early rehabilitation interventions may reduce the economic burden associated with TKA recovery.

In-home or virtual physical therapy (PT) has also helped offload the economic burden to patients following TKA comparted to traditional in-clinic physical therapy. More importantly, the rise in in-home/virtual PT has not compromised patient outcomes, rather, it has improved them. In-home/virtual PT has reported improvements in total cost of therapy, compliance with unsupervised therapy, and hospital readmission rates.

Patient positioning has always played a vital role in the effectiveness of postoperative therapy. Historically, a continuous passive motion (CPM) machine was the standard for initiating ROM exercises, however, this modality has fallen out of favor due to the inconsistency of patient position and appropriate fitting of the device. The Zero Degree Knee (ZDK) positioning device is a knee extension pillow designed to simplify knee extension exercise following TKA surgery. Following knee surgery, the patient often experiences postoperative surgical pain which may lead to apprehension to physical therapy and engaging knee musculature. This apprehension may lead to joint stiffness and ultimately, ROM loss. The ZDK is a pillow that elevates the lower extremity and allows gravity to pull the knee passively and gently into an extended position. Additionally, the ZDK has a sliding capability that allows a patient to work on knee extension exercises along with knee flexion exercises.

In this study, the investigators aim to prospectively evaluate early post-operative knee extension and self-reported outcomes in patients using the Zero Degree Knee positioner. Patients electing to undergo primary TKA will be recruited into the study and randomized to receive and follow the ZDK protocol post-operatively or standard of care rehabilitation instructions. Knee extension measurements will be recorded at 2 weeks post-op and patient-reported outcome measurements will be recorded pre-operatively and at various post-op timepoints.

Inclusion Criteria:

• Men and women between the ages of 40-80 years
• Candidate for total knee arthroplasty
• Diagnosis of mild to advanced osteoarthritis
• The ability to walk independently at baseline

Exclusion Criteria:

• History of knee replacement in operative limb (i.e. patients undergoing revision surgery)
• Neuromuscular/skeletal or connective tissue conditions that can alter gait or joint mechanics (joint infection, gout, rheumatoid arthritis)
• Pregnant women
• Prisoners
• Non-English speakers