Staging and Comorbidities
Articular cartilage injuries are common.1–3 The spectrum of these injuries ranges from small, superficial defects (focal chondral defects) to complete degenerative delami-nation of entire condyles with or without involvement of the subchondral bone and adjacent structures (osteoarthritis). In an ideal world, focal chondral defects exist in isolation, have clearly defined borders, are solitary defects, and are located in ideally accessible anatomic locations in young patients that are physically active. These types of lesions are the standard that is currently being used to enroll patients into randomized clinical trials investigating the efficiency of articular cartilage procedures. Whereas these studies are important and necessary to compare different techniques, the reality is that most patients (95%) that are presenting with clinically symptomatic cartilage lesions do not fit these clear-cut criteria.4 This presents a dilemma to the surgeon as the cartilage lesions most commonly treated are usually less clear cut and often involve “best clinical judgment” to perform an adequate assessment. This assessment process, or “staging,” is necessary to guide both patient and physician toward a clinically feasible and satisfying solution for the knee cartilage injury patient. The staging process requires knowledge about frequency and prevalence of cartilage defects, their clinical symptoms, arthroscopic grading, and sizing as well as assessment of the joint environment. Furthermore, specific comorbidities have to be taken into account prior to performing cartilage repair procedures as many of them require additional staged or concomitant surgical procedures. In this chapter, we will sequentially discuss the most pertinent factors that influence the decision-making process in patients with symptomatic cartilage lesions of the knee.
Frequency and Prevalence of Cartilage Injuries
Damage to articular cartilage is common and can result from acute traumatic injuries, early posttraumatic degenerative changes, developmental factors affecting the subchondral bone such as osteochondritis dissecans (OCD) lesions, or acquired metabolic factors such as avascular necrosis (AVN).1–3
Articular cartilage lesions are frequently encountered in routine knee arthrosco-pies. Curl et al reported articular cartilage lesions in as many as 63% of over 35,000 knee arthroscopies in the United States.3 This high incidence was corroborated by Hjelle et al in Norway and Widuchowski et al in Poland, who reported an incidence of 61 and 60%, respectively.1,2 The average age of patients reported in these studies is high, and thus the percentage of treatable lesions in younger patients is likely much lower. In fact, upon further subanalysis of Curl′s data, 60% of the reported lesions were grade III lesions and thus were potentially treatable lesions. Only 1,750 patients out of 31,516 were under the age of 40 and had Outerbridge grade III lesions. Based upon this study, one can estimate that ∼ 5% of patients under 40 undergoing knee arthroscopies may present with a chondral lesion that would be considered optimal for current therapies. While these studies provide some data regarding prevalence of these types of lesions among patients, no information is available regarding how many of the lesions are clinically symptomatic. Interestingly, the mere presence of a lesion does not seem to lead to an increase in the osteoarthritic rate over time in large cross-sectional studies, as the long-term natural history study conducted by Widuchowski et al in 2010 suggests.5 Shelbourne et al found that 123 out of 2,700 patients with anterior cruciate li gament (ACL) injuries and cartilage lesions at the time of surgery showed lower subjective Noyes scores 8 years after ACL reconstruction compared with the patients who did not have cartilage lesions at the time of surgery.6 Another study suggests that the presence of cartilage lesions can lead to rapid progression of radiographic osteo-arthritis (OA), as documented by Messner and Maletius.7 These findings underline the importance of identifying the patient who has a clinically symptomatic cartilage lesion that may benefit from early treatment.
Lesion Location and Size
The location of cartilage lesions is spread between the three compartments of the knee. Lesions are most commonly found in the weight-bearing femoral condyle (43 to 58%). Patellar lesions are frequently encountered and account for 11 to 36% of all lesions. Trochlear lesions overall are less frequent (6 to 16%).1–3
When analyzed for the lesion size, Hjelle et al were able to show that the majority of lesions (88%) were below 4 cm.1,2
Widuchowski et al found that 60% of knees (average 39 years old) contained chondral/ osteochondral lesions, 68% of which were focal chondral lesions, 3% being OCD lesions and 29% being osteoarthritic lesions.8
History and Physical Examination
The clinical evaluation of patients with symptomatic cartilage lesions in the knee is difficult and follows the recommendations of a thorough history and physical exam of the knee joint. No true evidence-based approach is available to guide the clinician, but several factors that may be important should be pointed out.
Upon initial evaluation, it is important to discover the history of symptoms that may be related to a cartilage lesion. Duration of symptoms has been associated with clinical outcome in patients undergoing microfracture. Mithoefer et al could show that patients with symptoms longer than 1 year had lower overall subjective outcome results than patients with more acute cartilage injuries.9 There is a correlation of worse overall clinical outcomes after cartilage procedures in patients who receive workmen′s compensation.10,11
History of smoking and family history of OA are often considered negative predictive factors for cartilage repair procedures; however, no clear evidence exists to actually link those two isolated factors to clinical outcomes. History should include the documentation of the body mass index (BMI). Whereas a BMI up to 35 does not seem to affect the overall outcomes in patients undergoing cell-based cartilage procedures,12,13 a higher BMI clearly affects the results of patients undergoing microfracture treatment.14 Similar consideration needs to be given to the age factor. Several studies have shown that higher age influences clinical outcome negatively in patients undergoing microfracture procedures.14,15 The data for cell-based procedures are somewhat conflicting. A clear correlation between age and clinical outcome has not been shown. Basic science studies, however, suggest that chondrocytes from older donors (> 40 years of age) have a lower proteoglycan and collagen production and thus may respond more slowly and less vigorously to the challenging intra-articular environment after implantation.16 A little-researched topic that is of importance is the willingness to comply with postoperative treatment protocols and rehabilitation procedures. Current protocols are not based upon evidence but rather on anecdotal experience or small case series by individual surgeons and rehabilitation specialists.17–19 Nevertheless, it is felt that adherence to these basic protocols is important. A history of noncompliance may therefore be a warning sign to the cartilage surgeon potentially indicating the patient′s lack of understanding or a significant difference in the goals that the treatment is aiming to achieve.
Pain
Pain assessment is an important part of the preoperative exam. Localized pain may be able to pinpoint a specific area of articular cartilage damage or it may indicate injury to associated structures such as the meniscus. The shorter the history of pain, the more reliably it can be considered to indicate the affected area.
No reliable data exist about the correlation of pain with a symptomatic cartilage lesion. However, the more chronic in nature the pain is, the less likely it is that a cartilage procedure alone is going to address the problem.
Most commonly utilized are visual analog scales (VAS) or a Likert scale for pain.
In absence of any clear evidence-based guidelines regarding pain, there are some pearls of wisdom that may help the less-experienced cartilage surgeon. The ideal patient should not report maximal pain other than perhaps with heavy exertion. Likewise, patients with minimal or no pain are less likely to benefit from cartilage surgery. Typically, the patient reporting pain in the midrange is considered an acceptable patient for treatment. It is also important to assess pain with and without medication (particularly narcotic pain medication) in this context.
Physical Examination
The physical exam should evaluate the overall dynamic and static alignment, antalgic gait, range of motion, muscle envelope, as well as ligamentous stability of the tibiofem-oral and patellofemoral joint.
A crude visual gait analysis in the office usually allows for detection of an antalgic gait, quadriceps avoidance gait, or a dynamic varus or valgus thrust. Any of these findings, if present, can point the examiner toward further underlying pathologies that may have a significant impact on the chosen treatment options. A varus thrust, for example, may point out an insufficiency of the lateral ligamentous structures (posterolateral corner, lateral collateral ligament [LCL]) and a triple varus. A quadriceps avoidance gait may indicate chronic anterior instability.
Knee joint effusions are generally felt to be a significant sign for symptomatic cartilage injuries. It is important to understand, however, that intra-articular effusions can exist without pain and therefore can be present longer than the actual onset of pain.
Range of motion assessment should be a routine part of the physical examination and has to be assessed in comparison with the uninjured side. Although small deficits in knee flexion can be observed with knee joint effusions, they are not normal in patients who have no effusion. An extension deficit is an important finding as these are very difficult to correct and may indicate progression to OA already beyond the scope of cartilage repair. Significant loss of motion is considered a relative contraindication for cartilage repair procedures.
Mechanical symptoms, locking during the range of motion exam, or acute inability to flex or extend the knee joint may indicate an unstable meniscus or articular cartilage fragment or a loose body.
A clinical sign that utilizes this concept is the Wilson sign. This test was originally performed to diagnose OCD lesions in the medial femoral condyle. The knee is flexed to 90 degrees. The tibia is forced into internal rotation. Under gradual extension and external rotation of the tibia, the patient may report pain when the lesion rotates into the area of the soft spot of the medial femoral condyle.20 This test can be modified by pushing the thumb slightly into the soft spot. Another helpful test is the direct palpation of the medial and lateral patella facette. If palpation is reproducing the patient′s pain, this can be a sign for a clinically symptomatic lesion in this area and will need to be correlated with the imaging results. Cartilage lesions do not typically hurt directly at the joint line. Direct palpation at the joint line is more likely associated with meniscal pathology.
Ligamentous stability is a prerequisite for cartilage procedures. It is therefore necessary to perform a full ligament examination of the knee joint. This usually includes varus and valgus stress at 0 and 30 to test the collateral ligaments; the Lachman test; the pivot shift exam, which evaluates ACL competency; the posterior drawer test at 90 degrees of knee flexion; and the posterior sag sign, which evaluates posterior cruciate ligament (PCL) sufficiency. In case of a potential posterolateral corner injury, the dial test and the flexion rotation drawer can be performed. Often forgotten is the stability exam of the patella. The medial and lateral patella glide and tilt as well as the competency of the medial patellofemoral ligament (MPFL) and the lateral retinaculum should be assessed. The patellar apprehension test is helpful to rule out the previous patellar sub/dislocation. Q-angle and patellar stability throughout the flexion should be carefully evaluated.
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