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    Interventional procedure overview of focal resurfacing implants to treat articular cartilage damage in the knee

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    Description of the procedure

    Indications and current treatment

    The knee joint comprises the distal end of the femur, proximal end of the tibia, and the patella. Cartilage covers the ends of these bones. There are 2 types of cartilage in the knee – articular (or chondral) and meniscal. Damage because of injury or disease to a focal area of articular cartilage, particularly in the main weightbearing areas, can cause pain, stiffness in the knee, and reduced mobility. Cartilage tissue has very limited self-healing potential and, if left untreated, cartilage damage can progress to osteoarthritis.

    Treatment for people with focal articular cartilage damage typically involves arthroplasty or biological treatment. Arthroplasties include total (TKA), bicompartmental, unicompartmental (UKA), and patellofemoral knee arthroplasties. Biological treatments include microfracture, osteochondral autograft transfer system (OATS), and autologous chondrocyte implantation.

    What the procedure involves

    Focal articular resurfacing is aimed at older people for whom biological treatments may not be suitable, but who may be too young to be considered for arthroplasty.

    Before surgery, the articular cartilage damage is assessed using a pre-planned MRI, an arthroscopy, or both. Then, either the implant is adapted to fit the damaged area (Episealer implant), or an implant is selected from a catalogue to closely match the damaged area (HemiCAP/UniCAP/BioPoly implants). The procedure is done under regional (spinal) or general anaesthesia. An incision is made to access the damage site. The damaged area is prepared by removing the damaged bone and cartilage, and drilling a hole for the stem of the implant. The implant is then press-fitted into the damaged area with or without the use of bone cement. The surface of the implant is slightly recessed below the surrounding articular cartilage. The implant may be metal or a polymer.

    Rehabilitation after surgery depends on the person and implant, but typically includes either an immediate (as tolerated) or gradual return to full weight bearing and range of motion.

    The aim of this procedure is to alleviate pain, allow immediate weight bearing, preserve physiological joint function, slow progression to osteoarthritis, and reduce or delay the need for TKA/UKA.

    Outcome measures

    Cartilage defects are typically assessed by the International Cartilage Regeneration and Joint Preservation Society (ICRS) grading:

    • 0 – Normal cartilage

    • 1 – Nearly normal cartilage, superficial defect

    • 2 – Abnormal, defect extending down to <50% of cartilage depth

    • 3 – Severely abnormal, defect extending down >50% of cartilage depth but not through subchrondal bone

    • 4 – Severely abnormal, depth of cartilage defect extends through subchrondal bone

    Several instruments are used to assess patient-reported outcomes:

    • The Knee Injury and Osteoarthritis Outcome Score (KOOS) is a self-administered, 42-item instrument. Higher scores indicate better health. The publisher of the KOOS (http://www.koos.nu/) notes that the minimal clinically important difference (MCID) is likely dependent on the patient population studied, but an MCID of 8 to 10 is appropriate. The KOOS is subdivided into 5 components:

      • Pain, Other symptoms, Function in daily living, Function in sport and recreation, and knee related QoL.

    • The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a self-administered, 24-item instrument. Higher scores indicate better health. An MCID of 10 to 15 has been reported for people who had TKA. The WOMAC is subdivided into 3 components:

      • Pain, Stiffness, and Physical function.

    • In addition, the KOOS contains the WOMAC and WOMAC scores can be calculated from KOOS.

    • The Tegner Activity Scale documents the level of activity of participants before and after injury on an 11-point scale. Higher scores indicate a higher level of activity. A summary of the scale with an example activity follows:

      • 10 – Competitive football (elite level)

      • 9 – Competitive football (lower divisions)

      • 8 – Competitive badminton

      • 7 – Competitive tennis; recreational football

      • 6 – Recreational tennis; jogging at least 5 times per week

      • 5 – Heavy labour; competitive cycling

      • 4 – Moderately heavy labour; recreational cycling; jogging at least 2 times per week

      • 3 – Light labour; competitive and recreational swimming

      • 2 – Walking on uneven ground

      • 1 – Sedentary work

      • 0 – Sick leave or disability pension because of knee problems

    • The Visual Analogue Scale (VAS) is an instrument that is often used to assess pain. The simplest VAS is a straight line of fixed length. The scale ranges from least pain to most pain and the participant marks line corresponding to the level of pain they feel. A ruler is used to measure the distance from the end of the line to the participant's mark. Higher scores indicate worse pain. An MCID of 22 mm has been reported for the improvement in pain in people who had TKA. Note that the units (centimetres or millimetres) used to report VAS are not always well described.

    • The 36-item Short Form Survey (SF-36) is a 36-item, self-administered instrument. Higher scores indicate better health. An MCID of 11 to 16 points has been reported for people who had TKA. The SF-36 covers 8 domains of health:

      • Vitality, Physical functioning, Bodily pain, General health perceptions, Physical role functioning, Emotional role functioning, Social role functioning, and Mental health.