Please note that references are provided with the section headings as opposed to in-text to better utilize the referencing features of this website.
Description
Total knee arthoplasty (TKA), also known as total knee replacement (TKR), involves the excision and replacement of the distal surface of the femur, the proximal surface of the tibia, and often the posterior surface of the patella in cases of severe knee joint degeneration.
Image Origin: http://www.wmt.com/totalknee/physicians/learn-about/tkr/advance-post-stab-knee.asp
Anatomy[1][2]
The knee is a modified hinge synovial joint consisting of the components listed below. For a more detailed description of the anatomy of the knee, please refer to the link provided in the "Additional Web Based Resources" section of this page.
Joints
Tibiofemoral
Patellofemoral
Bones
Femur
Tibia
Patella
Ligaments
Anterior Cruciate Ligament (ACL)
Posterior Cruciate Ligament (PCL)
Medial (Tibial) Collateral Ligament (MCL)
Lateral (Fibular) Collateral Ligament (LCL)
Transverse Ligament of the Knee
Posterior Meniscofemoral Ligament (Ligament of Wrisberg)
Menisci
Medial Meniscus
Lateral Meniscus
Muscles
Quadriceps: Rectus Femoris, Vastus Lateralis, Vastus Intermedius, Vastus Medialis
Hamstrings: Semimembranosus, Semitendinosus, Biceps Femoris
Sartorius
Gracilis
Gastrocnemius
Plantaris
Popliteus
Iliotibial (IT) Band
Bursae
Subcutaneous Prepatellar
Subcutaneous Infrapatellar
Deep Infrapatellar
Suprapatellar
Popliteus
Anserine
Gastrocnemius
Semimembranosus
Arteries
Popliteal Artery
Genicular Anastamosis
Nerves
Tibial Nerve
Common Peroneal (Fibular) Nerve
Saphenous Nerve
Cutaneous Innervation
Femoral Nerve
Obturator Nerve
Posterior Femoral Cutaneous Nerve
Lateral Femoral Cutaneous Nerve
Common Peroneal (Fibular) Nerve
Tibial Nerve
Image Origins: http://www.readinghospital.org/oth/Page.asp?PageID=OTH000095 and http://anatomyhq.org/grays-anatomy/syndesmology/articulation-upper-extremity/knee-joint/
Indications[3][4]
There are no official indications for TKA. It is typically utilized as a "last resort" for patients with advanced knee osteoarthritis (OA) experiencing severe pain and disability, but it is difficult to determine at what age and at what stage of OA a patient should undergo TKA. The figure to the right depicts the Canadian prioritisation algorithm for TKA, which is based on expert consensus. Recent literature suggests that patients' and surgeons' views over who should receive a TKA vary considerably, with many patients favoring the young, active, and working as opposed to many surgeons favoring the older aged and obese. As such, the decision to undergo TKA should be mutually agreed upon by the surgeon and patient.
TKA may also be indicated for patients with post-traumatic arthritis, rheumatoid arthritis, and rarely severe patellofemoral arthritis.
Image from Dieppe, et al 2011 (cited above). Author's text accompanying image: The Canadian prioritisation algorithm for hip or knee joint replacement. The numbers indicate the relative priority given to surgery for patients fitting into each category of the algorithm; the four top priority domains are highlighted in bold italics. From Naylor and Williams.
Incidence/Prevalence[5]
Overall: The incidence of TKA has increased steadily over the past 2-3 decades and is expected to continue to increase. In 2006, 248,267 Medicare patients received a TKA, reflecting a prevalence rate of 8.7/1,000. Prevalence rates for the U.S. population in 2002 were estimated to be 136/100,000 for primary TKA and 12.5/100,000 for a TKA revision.
Age: Peak utilization rates of TKA exist in the 75-84 age group. While incidence of TKA has grown in all age groups studied, the largest increase occurred in the 45-49 age group.
Gender: Women in the United States undergo TKA more frequently than men. In 2006 women had a 9.9 utilization rate whereas men had a utilization rate of 7.3. Prevalence of TKA among the sexes appears to be approximately equal in England.
Race/Ethnicity: In the United States a disparity in TKA prevalence rates does exist with black patients undergoing TKA 39% less frequently than white patients in 2006. This disparity is greater in the male population than the female population.
Clinical Presentation
Day One of Physical Therapy from a Patient's Perspective:
Surgery[4][6][7][8]
Overview
- Pre-operative Medical Evaluation: Laboratory studies, imaging studies, electrocardiography are performed to ensure that the patient is medically sound to go into surgery.
- Antibiotics: 30 minutes prior to incision antibiotics are administered.
- Anesthesia: General or regional is used as determined by the anesthetist and patient.
- Cleaning of the Leg and Application of the Thigh Tourniquet: The tourniquet assists visualization of the knee joint but is not used in patients with a history of deep vein thrombosis.
- Patient Positioning: The patient is positioned in supine with the knee flexed.
- Incision: See below for approaches.
- Clearing of Osteophytes and Soft Tissue
- Bone Cuts: The femur and tibia are cut perpendicular to their mechanical axes.
- Ligament Release: Release is indicated if pre-opearative deformity exists as it facilitates normal knee biomechanics.
- Assessment of Patellofemoral Tracking: The assessment determines the need for patella resurfacing and/or the need for lateral release or medial reefing.
- Components: Components are selected and fixated with or without cement.
- Tourniquet Release
- Drain Insertion and Dressing: Performed with the knee in extension.
- Foot Pulses Checked
Components
- Tibial Component: Polyethylene and Titanium. Ultra-high molecular weight polyethylene (UHWPE) is the current material of choice for the tibial tray component of TKA for its strength and low coefficient of friction. This tray is often attached to a titanium component which connects to the tibia. Decomposition of the tibial component through delamination of the polyethylene or through release of polyethylene fragments is the most frequent need for revision of the TKA. Polyethylene in the joint capsule promotes inflammation of the joint and the macrophages it attracts can resorb bone and loosen the hardware. Alternate forms of polyethylene are being explored to reduce the incidence of revision.
- Femoral Component: Metal Alloy. Most femoral components of TKAs are cobalt-chrome alloys that contain an articulation surface for the patella. A new metal alloy consisting of oxidized zirconium, also known as oxinium has been proposed. Oxinium acts like a ceramic and has a low coefficient of friction. It is thought to decrease the incidence of polyethylene wear and thus decrease the need for revision of the TKA.
- Patella Button: Polyethylene. Like the tibial tray, the patella button is comprised of polyethylene. This is applied to the posterior surface of the patella when resurfacing is indicated.
- Cement: Acrylic Polymethylmethacrylate. The gold standard cement for TKA is acrylic polymethylmethacrylate. Although initially regarded as ineffective, there is growing interest in a cementless TKA, resembling that of a total hip arthroplasty for the younger population of the patients receiving a TKA. A cementless TKA requires porous tibial and femoral components which encourage integration of new bone into the hardware and thus a stronger fixation and quicker recovery than a cement TKA.
Image Origin: http://www.medicaldiscounts.com/orthopedic_surgery.htm
Design Variations
- High Flexion Knee: A typical TKA allows a maximum of 110o of knee flexion post-surgery, which allows patients to complete nearly all functional activities. The physiologic norm for knee flexion is 135o, though. A high flexion TKA design has been introduced to potentially allow 130o of knee flexion. The femoral component in this design wraps around further posteriorly than the traditional TKA to allow for more flexion. It is popular among younger patients who often demand higher function out of their TKAs. Success of the high flexion TKA has been investigated and the literature reveals mixed results.
- Medial Pivot Knee: The medial pivot knee attempts to recreate typical knee motion in which the medial femoral condyle remains relatively stationary on the tibia during knee flexion unlike the lateral femoral condyle which translates during flexion. This design has a closer fitting articulation between medial femoral and tibial components, which limits motion more than a traditional TKA. Early follow-up studies have shown good results, but longer-term studies are needed.
- Gender Specific Knee: The traditional TKA is based on the anatomy of the male knee, which has slightly wider femoral condyles than the female knee. Components are sized based on anteroposterior (AP) diameter, which resulted in the stretching of collateral ligaments in many females receiving TKAs with components designed for the male. The gender specific knee takes into account these variations, as well as the variations in knee articulations between the sexes. While the gender specific knee has many theoretical benefits, there is not conclusive evidence that they are superior to traditional TKAs.
- PCL-Retaining Knee: Potential post-operative complications of the PCL-retaining knee include rupture of the PCL, patellofemoral malalignment, and wearing of the polyethylene tibial component with subsequent osteolysis. Despite these potential risks, survival rates of this TKA exceed 90% after 17 years.
Surgical Approaches
- Medial Parapatellar Approach: The medial parapatellar approach is the standard approach for TKA. It involves splitting the quadriceps tendon and eversion of the patella to visualize the joint space.
- Minimally Invasive/Subvastus Approach: The minimally invasive surgical approach aims to reduce injury to the skin and soft tissue by using a smaller incision and modifying surgical techniques. The patella is not everted in this approach and the extensor mechanism is preserved. This approach is difficult to perform if the patient lacks knee flexion pre-operatively or if the patient is obese. Benefits of this approach include decreased post-operative pain and quicker functional recovery, as well as a better post-operative cosmetic appearance of the knee. Potential risks include malpositioning of components due to a smaller operating window. The literature has not demonstrated definitive long-term benefit for the minimally invasive approach.
- Computer Assisted Navigation: Computer assisted navigation has been developed to assist surgeons in proper locations of bone cuts and subsequent positioning of components. It utilizes pre-operative CT (computed tomography) scans in conjunction with fluoroscopy or digital registration during surgery to identify anatomical landmarks to guide the surgery. While this navigation system holds the potential for great benefit, its cost and cumbersome nature have prevented it from being incorporated into standard practice.
Animated Video of Surgery
Live Computer Navigated, Minimally Invasive TKA with Surgeon Narration
Complications[4]
- Thromboembolism
- Infection
- Patellofemoral complications
- Neurovascular complications
- Periprosthetic fractures
- Aseptic loosening
- Arthrofibrosis
Post-operative Treatment[9][10][11]
Inpatient: Immediately post-op to discharge
- Cryotherapy: Immediate continuous flow cryotherapy with compression has been associated with decreased pain, decreased analgesic use, and faster recovery.
- Weight-bearing as tolerated with assistive device
- Assisted walking within 24 hours
- Range of motion exercises
- Preparation for return to home
Home Health: 1-2 weeks post-op
- Range of motion exercises
- Gait training
- Stair training
- Neuromuscular electrical stimulation to the quadriceps
- Training for community participation
Outpatient:
Protocol developed by Marcus, et al to be performed two times per week for six weeks:
Warm up (15 min)
- Stationary cycling (5-10 min)
- Seated or supine AROM knee flexion and extension (2-3 min) **
- Alternating ankle dorsiflexion and plantarflexion (1-2 min)
- Passive quadriceps stretching in standing or prone (1-2 min)
- Passive hamstrings stretching in standing or sitting (1-2 min)
**Usage of continuous passive motion or a slide board has been shown to provide no additional benefit to improving ROM when compared to standard exercises.
Leg strengthening exercise (30 min)
- RENEW (Resistance Exercise via Negative, Eccentrically-induced Work) performed on the Eccentron (5-20 min)
Image from Marcus, et al 2011 (cited above). Author's text accompanying image: Recumbent eccentric stepper (Eccentron; BTE Technologies, Inc., Hanover, MD, USA). High muscle forces are generated on an eccentric stepper powered by a 3hp motor that drives the pedals. As the pedals move toward the participant (blue arrow), the rider resists by applying force to the pedals (red arrow). Because the magnitude of force produced by the motor exceeds that produced by the rider, the leg extensors (green arrows) work eccentrically (lengthening), creating negative work.
| Training Week | Time/Week | Training Duration | Rating of Perceived Exertion |
|---|---|---|---|
| 1 | 2 | 5-8 min | 7 (very very light) |
| 2 | 2 | 11-14 min | 9 (very light) |
| 3 | 2 | 17-20 min | 11 (fairly light) |
| 4 | 2 | 20 min | 11-13 (fairly light to somewhat hard) |
| 5,6 | 2 | 20 min | 13 (somewhat hard) |
- Leg press, 2x10-15 reps 70% 1RM
- Leg extension, 2x10-15 reps 70% 1RM
- Leg curl, 2x10-15 reps 70% 1RM
- Standing calf raise, 2x10-15 reps body weight
Functional task oriented exercise (5 min)
- Get up and sit down, 15 reps
- Wall sits at 60 degrees 5-10 sec holds, 15 reps
- Negotiating stairs (step-ups starting at 4" and progressing to 8"), 30 reps
- Body weight half-squatting, 15 reps
- Unilateral standing on firm or unstable surface (building to 30 sec holds), 3-5 reps
- Walking backward, forward, marching, and side stepping on a slope and/or with resistance, 30 m
Endurance Exercise (10 min)
- Treadmill walking, change of speed or on incline (5 min)
- Stationary biking, "somewhat hard effort" (5 min)
Outcomes[12][13][14]
Range of Motion
The most significant increases in knee flexion and extension ROM are seen in patients who present with severely limited ROM prior to TKA. Those who have pre-operative ROM that is mildly limited or within normal limits initially lose ROM then regain full extension ROM within a year following TKA. Flexion ROM is not fully recovered.
Pain
Patients who have lower pre-operative mental health status and who preoperatively engage in pain catastrophizing (excessive focus on pain) are at increased risk for post-operative pain.
Sport Activity
While there is evidence that patients who have undergone a TKA experienced improved ability to participate in sports, the literature is inconclusive regarding long-term benefits of TKA for sporting activity. Current recommendations limit participation to light activity (see figure on right).
Image Origin: http://orthoinfo.aaos.org/topic.cfm?topic=a00389
Select Outcome Measures
SF-36
Six Minute Walk Test (6MWT)
Lower Extremity Functional Scale (LEFS)
Arthritis Impact Measurement Scales (AIMS/AIMS2)
WOMAC
Knee Injury & Osteoarthritis Outcome Score (KOOS)
Additional Web Based Resources
American Academy of Orthopaedic Surgeons Patient Page
National Institutes of Health 2003 Consensus Statement
Knee Joint Anatomy
