REST-Knee: A Pilot RCT of 72-Hour Knee Immobilization and Pain Outcomes

Postoperative pain following total knee arthroplasty (TKA) remains a significant clinical challenge, particularly in the context of increasing use of outpatient surgical pathways. Optimizing early postoperative pain management is essential to improve recovery, reduce unplanned healthcare utilization, and support enhanced recovery after surgery (ERAS) principles.

This study aims to evaluate the effect of short-term postoperative immobilization using a knee extension brace (Zimmer-type) worn continuously for 72 hours following primary unilateral TKA on postoperative pain at 2 and 6 weeks, measured using the Visual Analog Scale (VAS). The study hypothesizes that maintaining the knee in full extension during the immediate postoperative period will reduce pain and improve early recovery outcomes.

Study Design

This study is a pilot randomized controlled trial with a 1:1 allocation ratio and a single-blind design, in which outcome assessors are blinded to group allocation. The study is conducted at a single center (CHUS, Estrie, Canada).

Participants undergoing primary unilateral TKA will be randomized into one of two groups:

Intervention group: immobilization of the operated knee in full extension using a Zimmer-type brace for 72 hours postoperatively, followed by standard physiotherapy care.

Control group (standard of care): no restriction in movement, with early supervised mobilization according to usual physiotherapy practice.

The study adopts a pragmatic approach, allowing variability in physiotherapy delivery to reflect real-world clinical practice and enhance external validity. Timing and frequency of physiotherapy sessions will be recorded.

Study Objectives

The primary objective of this pilot study is to assess feasibility, including:

Recruitment rate and participant flow (inclusion, exclusion, refusal) Follow-up completion rate (target ≥80%) Intervention adherence (target ≥80% compliance in the intervention group) Safety, based on postoperative complication rates (including deep vein thrombosis, wound complications, and joint stiffness) Acceptability of the intervention and study procedures among patients and healthcare providers Estimation of variance in VAS pain scores to inform sample size calculation for a future definitive trial

The clinical primary outcome is postoperative pain at 2 and 6 weeks measured using the VAS, reported as mean differences between groups with 95% confidence intervals.

Secondary clinical outcomes include:

Knee range of motion (ROM) Postoperative opioid consumption Postoperative complications Emergency department visits and hospital readmissions Health-related quality of life (EQ-5D-5L) Knee function (Knee Society Score \[KSS\] and Functional KSS) Blood loss (hemoglobin levels) Postoperative inflammation (C-reactive protein) Study Population

The study population includes adults aged 18 years and older undergoing primary unilateral TKA for knee osteoarthritis at CHUS.

Key exclusion criteria include:

Known thrombophilia or bleeding disorders History of thromboembolic events Contraindications to brace use (e.g., material allergy) Revision or constrained knee prostheses Use of continuous postoperative nerve block infusion Sample Size

The pilot study aims to recruit 106 participants (53 per group) over an 18-month period, representing approximately 15% of the estimated sample size required for a definitive trial. Data from this pilot will be used to refine sample size calculations.

Recruitment and Procedures

Eligible patients will be identified during orthopedic consultations and approached for participation. After informed consent, baseline data (demographics, clinical characteristics, and preoperative measures) will be collected.

Randomization will occur on the day of surgery. The intervention will be applied by the orthopedic surgeon.

Follow-up assessments will occur at:

2-5 days postoperatively 2 weeks 6 weeks 3 months 12 months

Data collected include patient-reported outcomes, clinical assessments, laboratory values, and healthcare utilization. Participants in the intervention group will record brace wear time and opioid consumption using daily logs.

Data Collection and Outcomes

Pain will be assessed using the Visual Analog Scale (VAS). Additional outcomes include ROM measured with a goniometer, validated questionnaires (KSS, FKSS, EQ-5D-5L), laboratory markers (hemoglobin and C-reactive protein), and postoperative complications.

Opioid consumption and brace adherence will be self-reported using patient diaries. Healthcare utilization (emergency visits and readmissions) will be collected retrospectively.

Data Analysis

Feasibility outcomes will be analyzed descriptively using an intention-to-treat approach. Recruitment, adherence, and completion rates will be reported with 95% confidence intervals.

Comparisons between groups for exploratory clinical outcomes will be conducted using appropriate statistical tests depending on data distribution. This pilot study is not powered for definitive efficacy conclusions but will provide estimates to guide a larger trial.

• Postoperative Pain (VAS) [Time frame: 2 weeks, 6 weeks, 3 months, 12 months]
• Knee Range of Motion (ROM) [Time frame: 2 weeks, 6 weeks, 3 months, 12 months]
• Opioid Consumption [Time frame: Up to 6 weeks]
• Postoperative Complications [Time frame: Up to 6 weeks]
• Healthcare Utilization [Time frame: Up to 6 weeks]
• Quality of Life (EQ-5D-5L) [Time frame: Baseline, 2 weeks, 6 weeks, 3 months, 12 months]
• Knee Function (KSS/FKSS) [Time frame: Baseline, 6 weeks, 3 months, 12 months]
• Inflammation (CRP) [Time frame: Blood test marker.]
• Hemoglobin [Time frame: 2-5 days and 6 weeks]
• Global Improvement (PGI-C) [Time frame: 2 and 6 weeks]
• Brace Compliance [Time frame: First 72 hours]
• Perceived Safety [Time frame: 2 weeks]