Clinical Outcomes Assessment for Articular Cartilage Restoration
Articular cartilage injuries of the knee have received increasing attention because of their lack of spontaneous repair, high clinical incidence, and frequent associated symptoms. Arøen et al1 demonstrated 66% focal articular cartilage defects in 993 consecutive knee arthroscopies, with 11% of these injuries requiring repair. Currently, several established options exist for articular cartilage repair in the knee, including microfracture, osteochondral allograft and autograft transfer, and autologous chondrocyte implantation (ACI). Novel developments in tissue engineering and biomaterials research have been promoting technical modifications and enhancements of the existing techniques, with resultant second- and third-generation technologies. With the continued evolution of cartilage repair technology, clinical instruments for outcome evaluation and comparison are becoming increasingly relevant for scientists, clinicians, and patients. Recent reviews have noticed the limited quality of reported evidence and outcome measures in the orthopedic literature. A meta-analysis of 2,468 randomized trials published in the Journal of Bone and Joint Surgery from 1988 to 2000 identified only 72 (2.9%) that met all the authors’ criteria for randomized control trials (RCTs).2 Similarly, other authors3 found that, of 61 publications on cartilage repair in the knee, only 4 were RCTs and had limited Coleman Methodology Scores (average score: 43.5; range: 0 to 100). These authors also pointed out that 27 different outcome measures had been used in these publications, many of them not validated for cartilage repair.4 Outcome instruments that have been used in the past include the Lysholm Score,5,6 International Knee Documentation Committee (IKDC) scores,7 Hospital for Special Surgery knee scale,8,9 Knee Society knee scale,10 Tegner Activity Scale,5,11,12 Cincinnati knee scale,12–14 Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC),10,11,15 and Knee injury Osteoarthritis Outcome Score (KOOS).16 In addition, instruments to measure health-related quality of life (QOL) have been increasingly used in evidence-based medicine.17 Besides knee function scores, information about the quality and quantity of the repaired cartilage provides important outcome evaluation. Recent animal and human studies have concluded that currently there is no suitable substitute for histological analyses for assessment of tissue quality.18–20 However, histological assessment may not always be feasible, and less invasive assessment of repair cartilage by magnetic resonance imaging (MRI) has evolved as a useful and practical alternative for evaluation of articular cartilage repair in the knee. Therefore, the purpose of this chapter is to outline the available options for outcome assessment in knee articular cartilage repair and to present appropriate instruments and knee function measures that are validated for this specific type of procedure or provide clinically relevant functional outcome information.
Functional Outcome Evaluation
Functional outcome measures in the knee such as the Knee Society Score, Hospital for Special Surgery Score, IKDC knee examination form, and Lysholm score have originally been developed and completed by clinicians and did not reflect the patient′s perspective. More recently, patient-reported outcome (PRO) measures have turned the focus toward the patient′s outcome perspective and have been helpful in improving standardization and decreasing assessment bias by the surgeon. Surgeon-based scores often provide only a single aggregate score. Newer PROs have been designed in separate subscales to help with interpretation of the number of meaningful and cartilage repair–oriented outcomes of clinical studies over time. Subscales include specific and critical domains such as pain, joint function, and activities of daily living (ADL). Accordingly, regulatory institutions such as the Food and Drug Administration have designated pain and physical function as the primary clinically meaningful end points that provide the best evidence of efficacy.21 When possible, blinding should be used to reduce assessment bias and improve outcome objectivity. Patients in the control group may expect less benefit from the treatment than patients in the experimental group, and surgeons may be less likely to identify treatment responses in the control group. The resultant differences in assessment and interpretation of treatment responses are likely to bias the outcome results. However, effective blinding in cartilage repair studies can be challenging because the evaluated techniques or product may have differences in invasiveness (arthroscopy vs. mini-open vs. arthrotomy), treatment process (two-stage interventions vs. a single surgery), or postsurgical follow-up requirements such as variations in rehabilitation. If it is impossible to blind patients and surgeons based on the compared technologies—for example, when comparing ACI with microfracture—blinded outcome assessment should be performed by independent evaluators—that is, with blinded histological or MRI analysis—to reduce assessment bias and optimize objectivity of the study results.
General Health–Related Quality-of-Life Outcomes
Outcome evaluation traditionally uses both general health–related QOL measures that reflect health-related QOL in different diseases and populations such as the Short-Form 36 items and 12 items of the Medical Outcome Study (SF-36 and SF-12) and EuroQoL-5 Dimensions (EQ-5D). These general scores are different from specific outcome measures that include data related to specific diseases or organs, such as the WOMAC, IKDC, Lysholm, Cincinnati knee scale, or KOOS scores.22–24 The SF-12, SF-36, and EQ-5D are PRO scales that have been used for evaluation of cartilage defect repair. It is recommended that at least one knee- or cartilage-specific outcome instrument and one general health-related QOL measure be included in cartilage repair evaluations. Outcome measures should be reliable, responsive, and validated for cartilage repair in the knee. Reliability refers to the reproducibility of the measure, either between subjects (test–retest reliability) or between observers (interobserver reliability). A reliability coefficient of 0.8 to 0.9 is considered adequate for a patient′s group study.25 Validity questions whether an outcome instrument actually measures what it is intended to measure. Components of validity include content validity (floor and ceiling effects), criterion validity (how an instrument compares with an accepted gold standard instrument), and construct validity. Responsiveness assesses changes in the instrument value over time or treatment. Specific assessment scales that have been validated for the study of patients with chondral repair techniques include the Lysholm score,4 IKDC score,23 and KOOS.24
Disease-/Joint-Specific Outcome Measures
IKDC Subjective Knee Form
This PRO instrument assesses daily activity, symptoms, and sports function, and it has been used in different kinds of disorders of the knee (meniscal injuries, patellofemoral syndrome, osteoarthritis, and, recently, chondral lesions). The original instrument was developed in 1987 and the Subjective Knee Form was added in 2000.26 It consists of 18 items that are summed and expressed as a percentage from 0 to 100, with 100 representing an absence of symptoms and higher levels of functioning. It is part of the International Cartilage Repair Society (ICRS) cartilage injury evaluation package, and it is also in the ICRS Socrates software program. The user manual and the Excel file scoring are available from the American Orthopedic Society for Sports Medicine (www.sportsmed.org/research/IKDC_Forms). The IKDC has been shown to have an internal consistency of 0.92 and a test–retest correlation of 0.94.27 Women have been found to exhibit lower mean scores than men. It is recommended in studies of patients younger than 18 years and those age 35 years or older to adjust the Subjective Knee Form scores for age differences in both men and women.28 Hambly and Griva23 recently determined that the IKDC contains the most relevant items and is more effective than KOOS for monitoring the short- and medium-term outcomes given that KOOS focuses on longer-term consequences.
Knee Injury and Osteoarthritis Outcome Score
The KOOS is a knee-specific instrument created to evaluate the symptoms and function in subjects with a variety of knee injuries that could possibly result in osteoarthritis. It is based on an extension of the WOMAC. It comprises 42 items containing five separately scored subscales: pain (9), other symptoms (7), ADL (17), function in sport and recreation (Sport/Rec) (5), and knee-related QOL (4). Each subscale is scored from 0 to 100 on a worst-to-best scale. The original 24 items of the WOMAC were included in the KOOS, but the Sport/Rec and QOL subscales are unique to the KOOS. Psychometric properties were tested (reliability, construct validity, and responsiveness) for use in clinical studies of patients requiring several orthopedic interventions, including cartilage defect surgery.24 Content validity testing has demonstrated excellent internal consistency and reliability (reliability coefficient: 0.74 to 0.97) and test–retest reliability (reliability coefficient: 0.78 to 0.82) for the KOOS subscales.29 The KOOS is also included in the ICRS Socrates outcomes software package and can be downloaded from http://koos.nu.
Lysholm Scoring Scale
This scale was originally designed in 1982 to assess ligament injuries of the knee and modified for patient self-completion in cartilage damage evaluation in 2004.4 It is a condition-specific outcome measure that contains eight domains evaluated in points: limp (5), locking (15), pain (25), stair climbing (10), support (5), instability (25), swelling (10), and squatting (5), for a total score of 0 to 100, from worst to best. The overall scale has demonstrated acceptable test–retest reliability (average coefficient 0.91) and internal consistency (coefficient 0.71).4 Smith et al30 evaluated the validity of the Lysholm score for articular cartilage injury with the Rasch model (a measurement model that sets strict standards for the quality of measurement derived from the scale). They concluded that the Lysholm score demonstrated acceptable psychometric parameters to justify its use in outcomes assessment for chondral disorders.
Activity-Related Outcome Evaluation
The evaluation of postintervention activities presents a useful and practical outcome measure after articular cartilage repair in the knee in athletically active patients. Activity rating scales that have been used to provide quantitative analysis after cartilage repair procedures are the Tegner Activity Scale and Marx Activity Rating Scale. Activity rating instruments are used to compare the activity levels before injury, before surgery, and after surgery. Besides these activity scales, return to sports activity presents an outcome parameter that is often considered particularly relevant for the subjective measurement of success in athletes undergoing cartilage repair procedures.
Tegner Activity Scale
The Tegner Activity Scale was constructed by grading sports activities according to their difficulty and was originally developed for patients with anterior cruciate ligament (ACL) surgery but has been widely used for other knee problems, including articular cartilage injury. The Tegner score uses a numerical scale ranging from 0 to 10.31 Rating can be performed by the patient or clinician, with each numerical value indicating the ability to participate in a specific sports activity. The score differentiates between recreational and competitive sports participation and includes up to 170 different athletic activities that can be rated. An activity level of 10 corresponds to participation in competitive sports, including soccer, football, and rugby at a professional level. An activity level of 6 points equals participation in recreational sports and has been shown to be the median activity level in a normal population. A score of 0 is assigned to a person who is disabled from sports participation. The Tegner score has been evaluated for validity and reliability only after ACL injury,32 but its responsiveness for articular cartilage repair was successfully demonstrated with an effect size of 0.67.24 Tegner Activity Scale scores have been found to decrease with age.
Marx Activity Rating Scale
The Marx Activity Rating Scale uses four questions to measure the frequency with which patients pivot, run, decelerate, and cut. It was developed to provide a standardized measure of athletic activity levels and is independent of the particular sport played by the athlete. It uses scores between 0 and 16 (a score of 0 refers to patients who do these activities less than once a month, and a score of 16 indicates those who do each activity four or more times a week). It has not been formally validated for cartilage injury in the knee, but its responsiveness after cartilage repair procedures has been established.33 Similar to the Tegner score, it is correlated inversely with the age of the athlete.
Return to Sports Activity
For most athletes, the ability to return to their sport is the most important measure of a successful treatment outcome. Providing an athlete with accurate information about the ability to engage in a particular sport allows for appropriate expectations of the patient and presents a critical component of the pre-treatment counseling. The goals and expectations are often variable between individual athletes and sports, but especially between recreational and competitive or even professional athletes.34 The higher prevalence (35%) of articular cartilage lesions among recreational and professional athletes, compared with the general population (5 to 11%) emphasizes the relevance of this aspect of outcome evaluation.35 Average rates for return to sports activity in the athletic population have been reported after autologous chondrocyte transplantation (ACT) (74%),36–38 microfracture (68%),39 osteochondral autologous transfer40 (91%), and osteochondral allograft transplantation40 (88%). A recent systematic review of cartilage repair techniques demonstrated that 65% of athletes returned to the preinjury level after cartilage repair without significant difference between individual techniques.41,42 Several next- generation techniques have been developed, including matrix-associated chondrocyte implantation (MACI)43 and scaffold-enhanced microfracture,44 with similar rates for return to sports compared with the first-generation techniques.36,42,45 Besides the ability to return to sports, the ability to continue to play presents another important outcome parameter. Although durability of athletic activity was observed in 87% of athletes treated with ACT after 52 months, continued sports activity was observed in only 53% after treatment with microfracture.36,42,45 Cartilage injury in athletes is often associated with other injuries such as ACL rupture,46 and several factors have been shown to affect the ability return to sports after cartilage repair. Delay in surgical treatment of more than 12 months,45,47 lesion size of more than 2 cm,2,40,45 and patient age younger than 25 years are associated with better return-to-sports activity after cartilage repair.36
Related posts:
Postoperative Management of Patients with Articular Cartilage Repair
Biomechanical Outcomes of Cartilage Repair of the Knee
Postoperative Management of Patients with Articular Cartilage Repair
Magnetic Resonance Imaging of Cartilage Repair Techniques
ACI and MACI
Particulated Articular Cartilage: CAIS and DeNovo NT
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