Total Knee Arthroplasty

Original Editors - Lynn Wright

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Definition/Description

Total knee arthroplasty (TKA) or total knee replacement (TKR) is a common orthopaedic surgery that involves replacing the articular surfaces (femoral condyles and tibial plateau) of the knee joint with smooth metal and highly cross-linked polyethylene plastic. TKA aims to improve the quality of life of individuals with end-stage osteoarthritis by reducing pain and increasing function, and was found to improve patients' sports and physical activity. The number of TKA surgeries has increased in developed countries, with younger patients receiving TKA.

During surgery:

• There is at least one polyethylene piece, placed between the tibia and the femur as a shock absorber.
• The prostheses are usually reinforced with cement, but may be left uncemented where bone growth is relied upon to reinforce the components.
• The patella may be replaced or resurfaced. Patella reconstruction aims to restore the extensor mechanism.
• A quadriceps-splitting or quadriceps-sparing approach may be used.
• The cruciate ligaments may be excised or preserved.

There are different types of surgical approaches, designs, and fixations.

• A Unicondylar knee replacement or Patellofemoral replacement (PFR) may also be performed depending on the extent of disease.
• Several options of anaesthesia are available, and include regional anaesthesia in combination with local infiltration anaesthesia, or general anaesthesia in combination with local infiltration anaesthesia, with the possible addition of peripheral nerve blocks to either option. A tourniquet may sometimes be used during surgery.
• Computer-assisted navigation systems (CAS) or robotic surgery have been introduced in TKA surgery to facilitate surgeon hand motions in limited operating spaces (prospective studies on long term functional outcomes are needed).It allows doctors to perform many types of complex procedures with more precision, flexibility and control than is possible with conventional techniques.CAS are usually associated with minimally invasive surgery (procedures performed through tiny incisions). It is also sometimes used in certain traditional open surgical procedures.

Clinically Relevant Anatomy

The Knee is a modified hinge joint that allows flexion and extension motions, with slight amounts of internal and external rotation. Three bones form the knee joint: the upper part of the tibia, the lower part of the femur and the patella. The articular surfaces are covered with a thin layer of cartilage. Meniscii adhere to the lateral and medial surfaces of the tibial plateau and aids in shock absorption. The knee joint is reinforced by ligaments and a joint capsule.

Epidemiology /Etiology

The most common indication for a primary knee replacement, TKA, is osteoarthritis. Osteoarthritis causes the cartilage of the joint to become damaged and no longer able to absorb shock. Risk factors for knee osteoarthritis include gender, increased body mass index, history of a knee injury and comorbidities. Pain is typically the main complaint of patients with knee osteoarthritis. Pain is subjective, and involves peripheral and central neural mechanisms that are modulated by neurochemical, environmental, psychological and genetic factors.

Total knee arthroplasty is more commonly performed on women and individuals of older ages. In both the US and the UK, the majority of TKA surgeries were performed on women. Dramatic increases in TKA surgeries are projected to occur with an increasing rate of younger TKA recipients under the age of 60.However according to Hawker et al, younger people undergoing TKA for knee osteoarthritis are more likely to have morbid obesity, they smoke, and their expected outcome is to return to vigorous activities, like sport.

Diagnostic Procedures

Before a TKA surgery, a full medical evaluation is performed to determine risks and suitability. As part of this evaluation, imaging is used to assess the severity of joint degeneration and screen for other joint abnormalities. A knee radiograph is performed to check for prosthetic alignment before the closure of the surgical incision.

Pre-surgical Physiotherapy

Post-surgical rehabilitation exercises may be taught before surgery, so that patients may perform the appropriate exercises more effectively immediately after TKA surgery.  A pre-surgical training programme may also be used to optimize the functional status of patients to improve post-surgical recovery. Pre-surgical training programmes should focus on postural control, functional lower limb exercises and strengthening exercises for bilateral lower extremities.

Evidence supporting the efficacy of pre-surgical physiotherapy on patient outcome scores, lower limb strength, pain, range of movement or hospital length of stay following total knee arthroplasty is lacking.

Post-TKA Surgery

A TKA surgery typically lasts 1 to 2 hours. The majority of individuals begin physiotherapy during their inpatient stay, within 24 hours of surgery. Range of motion and strengthening exercises, cryotherapy and gait training are typically initiated, and a home exercise programme is prescribed before discharge from hospital. There is low-level evidence that accelerated physiotherapy regimens reduce the length of stay in an acute hospital.

Patients are usually discharged after a few days’ stay in hospital and receive follow-up physiotherapy, in the outpatient or home care setting, within 1 week of discharge.

The following post-operative guidelines for assessment and management are suggested for individuals who have undergone primary TKA surgery with cemented prosthesis, using a standard surgical approach. Surgeons’ instructions should always be followed.

Post-surgical Physiotherapy

Physiotherapy interventions are effective tools for improving patient's physical function, range of motion and pain in a short-term follow-up following total knee replacement. According to Fatoye and colleagues long term benefit and cost-effectiveness of physiotherapy interventions after a total knee replacement needs further study.

Subjective Assessment

Assessment should include, but is not limited to:

• Operative and post-operative complications, if any
• History of knee and other musculoskeletal complaints, if any
• Past medical history and relevant comorbidities
• Social factors and home set-up
• Progress of in-home exercises post-TKA surgery
• Pain and other symptoms/ discomfort (e.g. numbness, swelling)
• Expectations from surgery and rehabilitation
• Specific functional goals

Objective Assessment

In the objective assessment following Total Knee Arthroplasty (TKA), it is crucial to comprehensively evaluate various factors that contribute to the patient's recovery. It should include, but is not limited to:

• Observation of surgical wound or scar
• Check for signs of infection:
  • Redness, discharge (pus/ odour), adhesions of the skin, abnormal warmth and swelling, expanding redness beyond the edges of the surgical incision, fever or chills
  • Suspicion of infection warrants medical referral
• Knee swelling (circumference measurement)
• Vital signs and relevant laboratory findings (as relevant/in the acute setting)
• Check for deep vein thrombosis (DVT) (please see the Complications and Contraindications Section below for more information on identifying DVTs)
• Palpation:
  • For increased warmth and swelling
• Assessment of Muscle Function and Tone:
  • For muscle activation (e.g. quadriceps; vastus medialis oblique).
  • Assessing hypertonia, particularly in the hip adductors:
    • Impact on Rehabilitation:
      • Influences gait pattern and postural stability.
      • May lead to altered gait, increasing stress on the knee joint.
      • Essential to address for comprehensive rehabilitation.

• Lower limb range of motion:
  • Active and passive knee range of motion in supine or semi-reclined position (see treatment milestones below for more details)
• Lower limb muscle activation and strength
• Gait:
  • Timed up and go test (TUG) or 10-metre walk test may be used (depending on individuals’ ability and tolerance)
  • Assess for guarding in knee flexion, avoidance to weight bear on the operative leg, antalgic patterns etc.

Outcome Measures

• Knee disability and Osteoarthritis Outcome score (KOOS)
• Oxford Knee Score
• Patient satisfaction
• Walking tests: Timed up and go test (TUG), Six minute walking test
• Visual Analogue Scale (VAS)
• Knee range of motion
• Western Ontario and McMaster Universities Osteoarthritis Index score (WOMAC)

Post-surgical Physiotherapy Treatment Strategies & Goals

Phase I: Up to 2-3 weeks post-surgery

• Patient education: pain science, pain management, the importance of home exercises, setting rehabilitation goals and expectations
• Achieve active and passive knee flexion to 90 degrees, and full knee extension
  • Keep passive knee flexion range of motion testing to less than 90 degrees in the first 2 weeks to protect surgical incision and respect tissue healing
• Aim to achieve minimal pain and swelling
• Achieve full weight bearing
• Aim for independence in mobility and activities of daily living

During the early phase of rehabilitation, it is important to establish a therapeutic alliance and provide education on pain management strategies. Pain education may include appropriate usage of pain medication, cryotherapy and elevation of the operated limb. There is evidence that cryotherapy improves knee range of motion and pain in the short-term. Icing after exercise may be helpful, but low quality evidence makes specific recommendations for the use of cryotherapy difficult. Patients should be informed to avoid resting with a pillow under the knee as this may lead to contractures.

It is important to review the patient’s home exercise program during the first physiotherapy session as home exercises are a critical component of recovery. Post-surgical exercises given by the surgeon and inpatient physiotherapist should be reviewed. In the early phase, patients can be taught to use the stairs with their non-operated leg leading on the ascent, and their operated leg leading on the descent.

Common Bed and Chair Exercises

• Ankle plantarflexion/dorsiflexion
• Inner range quadriceps strengthening using a pillow or rolled towel behind the knee
• Isometric knee extension in the outer range
• Knee and hip flexion/extension
• Straight leg raises
• Isometric buttock contraction
• Hip abduction/adduction
• Bridging

Phase II: 4-6 weeks post-surgery

• Aim to have no quadriceps lag, with good, voluntary quadriceps muscle control
• Achieve 105 degrees active knee flexion range of motion
• Achieve full knee extension
• Aim for minimal to no pain and swelling

Physiotherapy sessions may be scheduled one to two times weekly, This frequency may increase or decrease depending on an individual's progress. Achieving full knee extension is essential for functional tasks such as walking and stair climbing. Knee flexion range of motion is required for comfortable walking (65 degrees), stair climbing (85 degrees), sitting and standing (95 degrees). In this phase, tissue mobilisation techniques may be used to improve scar mobility.

Phase III: 6-8 weeks post-surgery

• Strengthening exercises to ensure hypertrophy beyond neural adaptation
• Lower limb functional exercises
• Balance and proprioception training

While primary TKA has been reported to reduce falls incidence and improve balance-related functions such as single limb standing balance, the sub-optimal recovery of proprioception, sensory orientation, postural control, and strength of the operated limb post-TKA is well documented. Literature highlights the importance of proprioceptive training, and pre-operative training that involves the non-operated limb. Balance exercises may include single leg balancing, stepping over objects, lateral step-ups, and standing on uneven surfaces. Post-surgical balance and proprioceptive training that involves single limb standing may begin when adequate knee control is achieved on the operated limb, which typically occurs around 8 weeks post-TKA.

Individualised rehabilitation programmes that include strengthening and intensive functional exercises, given through land-based or aquatic programmes, may be progressed as clinical and strength milestones are met. Owing to the highly individualised characteristics of these exercises, supervision by a trained physiotherapist is beneficial.

Phase IV: 8-12 weeks, up to 1 year post-surgery

• Aim for independent exercise in the community setting
• Continue regular exercise involving strengthening, balance and proprioception training
• Incorporate strategies for behaviour change to increase overall physical activity

Discharge Criteria

Discharge planning should be individualised, and criteria may include:

• Achieving a minimum 110 degrees active knee flexion and full knee extension
• Achieving ambulation goals
• Achieving compliance and competency with a home exercise programme
  • Commitment to an independent exercise program for 6-12 months post-operatively should be recommended
  • Exercise programme should include strength training 2-3 times/ week

Complications and Contraindications

Following TKA surgery, these complications may occur:

• Infection
• Nerve damage
• Bone fracture (intra-operative or post-operative)
• Persistent / chronic pain
• Increased Falls risk
• Deep vein thrombosis (DVT)
  • A common complication after knee or hip replacement surgery that can cause significant morbidity and mortality
  • Incidence of DVT after knee or hip replacement has been reported at 18%
  • Larger studies have reported that patients with hypercoagulable diagnosis / conditions are at greater risk of DVT within 6 months of joint replacement surgery
  • Identifying DVTs:
    • Clinicians should be familiar with signs and symptoms of DVT such as chest pain, shortness of breath, skin redness or discolouration, warmth or increased skin temperature in the affected area, pain, tenderness, swelling (usually unilateral) and visible veins. However, please note that some patients with DVT could be asymptomatic.
    • Please also note that Homan’s sign is a clinical test that has previously been used to assess for DVT. The patient is positioned in supine or semi-reclined, and the clinician passively dorsiflexes the ankle and squeezes the calf. However, Homan's sign is not considered a reliable test.
    • The Wells criteria and the Geneva score are two of the more commonly standardised clinical decision rules used to assess the pretest probability of DVT. The Wells score, in conjunction with the D-dimer test, has been validated. You can find out more about the Wells criteria and Geneva score here: Advances in the diagnosis of venous thromboembolism: a literature review.
    • Suspicion of DVT warrants urgent medical referral. Definitive diagnosis typically requires D-dimer tests and ultrasound imaging (e.g. compression ultrasonography).
• Stiffness
  • Most common complaint following primary TKA
  • Affects approximately 6 to 7% of patients undergoing surgery
  • Contemporary literature supports defining “acquired idiopathic stiffness” as having a range of motion of  <90° persisting for >12 weeks after primary TKA, in the absence of complicating factors including pre-existing stiffness.
  • Stiffness causes significant functional disability and lower satisfaction
  • Females and obese patients are reported to have increased risk
  • Evidence does not recommend routine use of continuous passive motion (CPM) as long term clinical and functional effects are insignificant, and not superior to traditional mobilisation techniques

• Prosthesis-related complications: loosening or fracture of prosthesis components, joint instability and dislocation, component misalignment and breakdown
  • While more research is needed for the long term failure rates of TKA implants, available arthroplasty registry data shows that 82% of TKA surgeries and 70% of unilateral knee replacement surgeries last 25 years in patients with osteoarthritis
  • Polyethylene wear is a common cause for revision surgery
• High-risk activities that may not be permitted, or require clearance with the orthopaedic surgeon, post-surgery:
  • Singles tennis, squash/racquet ball
  • Jogging
  • High impact aerobics
  • Mountain biking
  • Soccer, football, volleyball, baseball/softball, handball, basketball
  • Gymnastics
  • Water-skiing/ water sports
  • Skiing
  • Skating