3.4 Total Knee Arthroplasty: Postoperative Nursing Care, Pain Management & Early Mobilization

Regional Analgesia: Adductor Canal Block vs. Femoral Nerve Block

Severe postoperative pain following Total Knee Arthroplasty (TKA) is a major barrier to early rehabilitation, patient satisfaction, and rapid discharge. Regional nerve blocks are the cornerstone of contemporary TKA analgesia, but the specific anatomical target profoundly impacts early mobility and patient safety.

                      REGIONAL NERVE BLOCKS IN TKA

    [Femoral Nerve Block (FNB)]              [Adductor Canal Block (ACB)]
    - High sensory analgesia                 - Targeted sensory analgesia (Saphenous n.)
    - Motor block of ALL 4 Quad muscles      - Sparing of major Quad motor branches
    - Significant Quadriceps weakness        - Preserved Quadriceps muscle strength
    - HIGH RISK of knee buckling & FALLS     - LOW Fall risk; enables same-day walking

Femoral Nerve Block (FNB) vs. Adductor Canal Block (ACB)

1. Femoral Nerve Block (FNB):

   • Anatomy: Administered in the femoral triangle, blocking the main trunk of the femoral nerve.
   • Clinical Effects: Provides dense, complete sensory analgesia to the anterior knee and femur. However, it simultaneously causes profound motor paralysis of all four heads of the quadriceps femoris (rectus femoris, vastus lateralis, vastus medialis, vastus intermedius).
   • Complications: Patients experience severe "quadriceps lag," an inability to lock the knee in full extension, leading to catastrophic knee buckling and in-hospital patient falls during early ambulation attempts. As a result, FNB has been largely replaced by motor-sparing techniques in modern clinical pathways.

2. Adductor Canal Block (ACB / Subsartorial Block):

   • Anatomy: Local anesthetic (e.g., 0.2% ropivacaine or 0.25% bupivacaine) is injected under ultrasound guidance into the adductor canal (Hunter's canal) in the mid-thigh, deep to the sartorius muscle.
   • Sensory Coverage: Selectively blocks the saphenous nerve (a pure sensory terminal branch of the femoral nerve supplying the anteromedial knee and joint capsule) and the nerve to the vastus medialis (providing sensory articular branches to the capsule), along with contributions from the posterior branch of the obturator nerve.
   • Motor Sparing: Spires the main motor branches innervating the vastus lateralis, vastus intermedius, and rectus femoris, preserving over 80% to 90% of baseline quadriceps motor strength.
   • Clinical Outcomes: Provides equivalent analgesia to FNB while drastically reducing fall risk, facilitating immediate postoperative weight-bearing ambulation on postoperative day (POD) 0, and shortening length of stay.

3. IPACK Block (Infiltration between the Popliteal Artery and Capsule of the Knee):

   • Administered to target the sensory articular branches of the tibial, common peroneal, and posterior obturator nerves innervating the posterior knee capsule.
   • Because the main tibial and peroneal motor trunks are spared, the IPACK block effectively alleviates deep posterior surgical pain without inducing foot drop or motor weakness, pairing synergistically with the ACB.

Range of Motion (ROM) Science, Extension Primacy, and the CPM Debate

The Critical Primacy of Full Knee Extension (0°)

In the acute postoperative phase, orthopaedic nurses and physical therapists prioritize achieving full active and passive knee extension (0 degrees) over deep knee flexion:

                      KNEE RANGE OF MOTION RECOVERY PRIORITIES

    [PRIMARY TARGET: FULL EXTENSION (0°)]        [SECONDARY TARGET: PROGRESSIVE FLEXION]
    - Essential for normal biomechanical gait     - 60° to 70° on POD 1
    - Prevents crippling flexion contracture      - ≥90° by discharge (sufficient for chair/stairs)
    - NO pillows under knee in bed!               - 110° to 120° by 6 to 12 weeks
    - Place pillow under heel/calf only           - Active heel slides & seated quad sets

• Biomechanical Rationale: A persistent knee flexion contracture of even 5 to 10 degrees dramatically increases the metabolic and muscular energy expenditure of the quadriceps during normal gait (by up to 50%). It creates a functional limb-length discrepancy, pelvic obliquity, compensatory lumbar lordosis, and an abnormal, fatiguing antalgic gait. Once established, flexion contractures become increasingly resistant to physical therapy due to posterior capsular tightening and hamstring contracture.
• Essential Nursing Intervention (The "No Pillow Under Knee" Rule):
  • Orthopaedic nurses must never place a pillow, rolled towel, or blanket directly beneath the operative knee when the patient is in bed.
  • Placing a pillow under the knee maintains the joint in 15° to 30° of comfortable flexion, rapidly encouraging posterior capsular scarring and permanent flexion contracture.
  • Correct Positioning: Place pillows or elevation foam strictly beneath the lower calf and heel, leaving the knee unsupported in space so gravity facilitates full passive extension.
• Flexion Milestones:
  • POD 1 target: 60° to 70° active-assisted flexion.
  • Discharge target: ≥90 degrees of knee flexion (the minimum ROM required to rise independently from a standard chair, navigate standard stairs, and use a commode).
  • Long-term target (6–12 weeks): 110° to 125° of flexion.

The Continuous Passive Motion (CPM) Evidence Evolution

Historically, Continuous Passive Motion (CPM) machines were prescribed routinely for every postoperative TKA patient to mechanically cycle the knee through programmed flexion-extension arcs while in bed.

• Current Evidence & Clinical Practice Guidelines: Extensive Cochrane systematic reviews and the American Association of Hip and Knee Surgeons (AAHKS) / AAOS clinical practice guidelines have demonstrated that routine CPM usage:
  1. Does not improve long-term active knee range of motion or functional outcomes.
  2. Does not reduce postoperative pain scores or opioid consumption.
  3. Does not decrease hospital length of stay.
  4. Does not decrease the incidence of postoperative manipulation under anesthesia (MUA) for arthrofibrosis.
  5. Significantly increases healthcare equipment costs, fosters passive patient dependency, and can reduce time spent performing active, weight-bearing functional physical therapy.
• Current Standard: Active, patient-driven, task-oriented physical therapy (active heel slides, seated active-assisted knee flexion, quadriceps sets, straight leg raises, and early progressive over-ground ambulation) is the universally recommended standard.

Early Mobilization Protocols, VTE Prophylaxis, and Wound Surveillance

Early Mobilization and Quadriceps Lag Surveillance

Early out-of-bed mobilization within 4 to 24 hours postoperatively (POD 0 or POD 1) is a foundational component of Enhanced Recovery After Surgery (ERAS) pathways:

• Physiologic Benefits: Accelerates return of bowel motility, prevents pulmonary atelectasis and pneumonia, enhances muscle pump activity to lower venous stasis, decreases hospital length of stay, and reduces patient anxiety.
• Quadriceps Lag Assessment: Before permitting initial ambulation, the nurse and physical therapist must evaluate the patient for a quadriceps extension lag (the inability to actively extend the knee fully to the same degree achievable passively, tested by having the patient perform an active straight leg raise). If a substantial quadriceps lag is present (often secondary to residual block or reflex arthrogenic muscle inhibition), a knee immobilizer or hinged knee brace locked in full extension must be applied during weight-bearing ambulation to prevent sudden knee buckling and falls.

Multimodal Venous Thromboembolism (VTE) Prophylaxis

Major orthopaedic procedures carry a high baseline risk of deep vein thrombosis (DVT) and pulmonary embolism (PE) due to surgical endothelial injury, intraoperative tourniquet venous stasis, and systemic hypercoagulability (Virchow's Triad). Current AAOS and ACCP guidelines recommend dual mechanical and chemical prophylaxis:

                      MULTIMODAL VTE PROPHYLAXIS PROTOCOL

    [Mechanical Prophylaxis]                 [Pharmacologic Prophylaxis]
    - Intermittent Pneumatic Compression     - Standard Risk: Aspirin (81 mg BID or 325 mg BID)
      (SCDs) continuously while in bed       - High Risk: DOACs (Apixaban 2.5 mg BID, Rivaroxaban 10 mg)
    - Early out-of-bed ambulation            - Alternative: LMWH (Enoxaparin 30 mg SC q12h / 40 mg daily)
    - Active ankle pump exercises            - Duration: 14 to 35 days postoperatively

1. Mechanical Prophylaxis: Intermittent Pneumatic Compression Devices (SCDs) applied bilaterally to the calves while the patient is in bed, combined with early ambulation and hourly active ankle pumping exercises.
2. Pharmacologic Prophylaxis:
   • Standard-Risk Patients: Enteric-coated Aspirin (81 mg PO BID or 325 mg PO BID) for 4 to 6 weeks has emerged as a safe, highly effective agent with significantly lower major bleeding and wound complication rates than potent anticoagulants.
   • High-Risk Patients (prior VTE, active malignancy, severe obesity, thrombophilia): Direct Oral Anticoagulants (DOACs such as Apixaban 2.5 mg PO BID or Rivaroxaban 10 mg PO daily) or Low-Molecular-Weight Heparin (LMWH, Enoxaparin 30 mg SC q12h or 40 mg SC daily) for 14 to 35 days.

Wound Care, Cryotherapy, and Infection Surveillance

• Cryotherapy: Application of localized cold therapy (ice packs or continuous motorized circulating cold compression units) applied for 20 minutes on and 20 minutes off reduces tissue metabolic rate, diminishes localized edema, and blunts nociceptive C-fiber firing.
• Advanced Wound Dressings: Modern practice favors sterile, occlusive, silver-impregnated or hydrocolloid waterproof island dressings left undisturbed for 5 to 7 days postoperatively. Minimizing dressing changes substantially decreases the introduction of airborne nosocomial pathogens.
• Surgical Site Infection (SSI) Surveillance: Daily inspection through transparent borders for excessive strike-through drainage, spreading erythema (>2 cm from incision margin), localized heat, induration, foul odor, or persistent wound drainage beyond 48 to 72 hours postoperatively (which represents an absolute indication for orthopaedic surgical evaluation).