Focal Chondral Injuries

Patient History

As in any diagnostic work-up, it is important to obtain a comprehensive history from any patient that complains of knee pain, particularly because of the overlapping symptoms of cartilage defects and intraarticular pathological conditions. Sports participation is the most common inciting event shared among those with a diagnosis of chondral lesions. Approximately half of patellofemoral FCDs occur in the setting of a traumatic injury. Patients with FCDs are usually young, active and able to carry out activities of daily living (ADLs), although they may complain of pain with specific activities, such as deep squats or cutting. Notably, an activity or ‘trauma’ may not necessarily cause the FCD but rather incite the onset of symptoms on a preexisting yet asymptomatic FCD, resulting from localised degeneration.

Pain is the most common presenting complaint for patients with FCDs. This can present acutely in the setting of injury or sudden load or insidiously in the case of repetitive microtrauma or OCD. This is classically reported with weightbearing and localised to the same compartment as the defect. Pain that worsens with flexion suggests a more posterior lesion. Patellofemoral articular defects typically present as anterior knee pain. However, it is not uncommon for patients to report pain located retropatellar, peripatellar or, in the instance of trochlear defects, posteriorly in the popliteal area. Considering that articular cartilage is aneural, the pain often originates from surrounding structures, including capsular or synovial irritation and overload of the subchondral bone resulting in loss of tissue homeostasis. Therefore, if a FCD is identified in the context of pain-free tissue homoeostasis, the structural cartilage defect may not be of clinical significance. If pain and loss of tissue homoeostasis are present, other causes of the pain must also remain on the differential despite a high clinical suspicion.

Activity-related swelling should raise suspicion for a possible FCDs. The presence of this finding in the absence of pain can help exclude other potential pathological conditions. For example, patellofemoral pain syndrome may also present as swelling with activity but is more often than not painful. Activity-related swelling and, in particular, joint effusion indicate more advanced disease. Diffuse cartilage damage more reliably presents with subtle decreases in range of motion, which has a predilection to limit flexion earlier than extension. These patients also present with diffuse rather than focal pain during activity. For the previously mentioned reasons, it is important to differentiate an isolated FCD from an ongoing osteoarthritic process that has patchy diffuse involvement of the cartilage and results in pain as a result of loss of generalised tissue homoeostasis.

To better understand the best course of treatment, it is critical to obtain a history of any previous treatments that the patient has received to the symptomatic knee, particularly previous injections (cortisone, hyaluronic acid, platelet-rich plasma (PRP)) and surgeries. Insufficient rehabilitation or inappropriately timed return to high-load activities after past surgeries is a common source of symptoms when a patient has already undergone an operation on the ipsilateral knee. This should be evaluated as a potential source of pain before considering a costly work-up or revision surgery.

Physical Examination

The physical examination should begin with a gait analysis followed by evaluation of the symptomatic knee joint for effusion, deformity, contracture, malalignment and patellar maltracking. An OCD-derived FCD at the lateral aspect of the medial femoral condyle can cause the patient to ambulate with an antalgic gait or with the affected leg in obligate external rotation (Wilson sign) as a compensatory mechanism to avoid tibial spine impingement. In patellofemoral FCDs, gait abnormalities, such as in-toeing or hip abductor weakness, are commonly seen. Additionally, it is common to see femoral anteversion and valgus malalignment of the lower extremity. Patients with FCDs usually have normal range of motion and focal tenderness over palpable areas along the lateral or medial femoral condyles. Joint line tenderness is commonly elicited when the lesion affects the femoral condyle and tibial plateau. However, it must be recognised that neither a patient’s history nor physical examination are sensitive or specific for differentiating cartilage defects from other intraarticular derangements but may only raise clinical suspicion to pursue further work-up.

Imaging

First-line imaging for the approach to FCDs consists of conventional cartilage radiographs – in particular, bilateral standing anteroposterior (AP), 45-degree flexion weightbearing posteroanterior (PA; Rosenberg view), and nonweightbearing lateral and patella sunrise views (Merchant view). These views allow for evaluation of pathological joint conditions, such as degenerative changes in the tibiofemoral and patellofemoral joints, trochlear dysplasia, and abnormal patella height, tilt and subluxation. The Merchant view is useful to determine joint space narrowing in OA of the patellofemoral articulation. In most cases, FCDs will not be apparent on plain radiographs because most lesions are extraosseous; however, this imaging modality can detect lesions that involve subchondral bone and lead to FCD, such as OCD. The 45-degree flexion PA radiographs are particularly helpful to diagnose fairly large OCD lesions along the posterior femoral condyles. When OCD are suspected, contralateral knee radiographs can be considered given the high incidence of bilateral involvement. Radiographic findings consistent with an OCD include an area of osteosclerotic bone, with a high-intensity line between the defect and epiphysis. Radiographs should be assessed for radiolucencies, subchondral cysts, sclerosis, fragmentation, loose bodies, joint space narrowing and physeal status because these can affect the treatment algorithm. The long-leg axial alignment radiograph is the final view implicated in suspected FCD evaluation and is of utmost importance to determine the mechanical alignment in patients with known or suspected chondral defects. The benefit of this view is that it confers the ability to determine whether the symptomatic knee requires malalignment correction with a concomitant osteotomy. It is useful to obtain these images with a radiological marker alongside the knee to allow for correction of magnification and accurate determination of appropriately sized donor tissue if needed depending on surgical approach.

Magnetic resonance imaging (MRI) is an effective imaging modality for evaluating articular cartilage and the subchondral bed. Although determining the size of a lesion on imaging is helpful for prognostic and surgical planning purposes, MRI often underestimates lesion size by as much as 60%. Moreover, the appearance of cartilage lesions on MRI is often inconsistent with clinical symptoms and arthroscopic findings. Novel MRI techniques such as the delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) and T2 relaxation time mapping have shown great potential in the evaluation of articular cartilage, although these technologies are not widely available and not routinely used for clinical purposes. dGEMRIC tags glycosaminoglycan (GAG) content in cartilage and can be helpful in the diagnosis of early knee OA and cartilage health after ligament rupture. This imaging modality also allows for measurement of compressive stiffness after cartilage repair procedures. ^,

T2 relaxation time mapping, an emerging MRI parameter that represents the internuclear reaction secondary to transverse relaxation of hydrogen ions, has demonstrated potential in measuring the collagen content of cartilage. The benefit of this test is the ability to evaluate cartilage degeneration from time of injury, thus providing information about optimal timing for surgical intervention. Such advances in imaging allows for the ascertainment of objective information, which helps to determine the optimal window and treatment methodology. However, because they are emerging technologies the authors of this chapter do not routinely use these MRI-based modalities in the evaluation of patients with FCD.

Biomarkers

Cartilage biomarker analysis is a novel diagnostic tool for detecting the presence of chondral damage. Several type II collagen degradation markers, specifically neoepitope specific for type II collagen cleavage (C2C), cartilage oligomeric matrix protein precursor (COMP) and C-propeptide of type II procollagen (CPII), as well as type II collagen synthesis markers (serum PIIANP), have been identified as potential indicators of cartilage degradation. These precursor proteins are processed by proteases before incorporation into fibrils, thus releasing markers that are then detectable in serum and urine assays. The relative levels of collagen synthesis biomarkers and degradation products can be used to gauge the extent of cartilage turnover occurring at the articular surface.

A number of assays exist that are specifically designed to detect these propeptide levels. Although initial studies have reported promising results in the detection of osteoarthritic changes in the joint, there is a paucity of literature that affirms the efficacy of the use of these biomarkers in detection of FCDs. Future studies in this area are underway to validate these biochemical markers as a tool for early detection of morphological changes within the joint with the hopes to help guide the timing and nature of future treatment.

Diagnostic Arthroscopy

Diagnostic arthroscopy remains the gold standard for the evaluation of intraarticular pathological conditions of the knee. This minimally invasive diagnostic procedure allows for direct identification and classification of FCDs, as well as detection of any concomitant injuries or additional articular cartilage pathological condition that may need to be addressed in place of or in addition to the FCD. A simple debridement during the procedure may help improve symptomatic lesions and delay treatment of FCDs in almost 60% of patients. During arthroscopy, the chondral defect size can be measured and graded according to standardised criteria systems: the Outerbridge or International Cartilage Repair Society (ICRS) criteria ( Table 22.1 ).

The size and location of the lesion play a large role in management; therefore it is important to directly document and probe these lesions during arthroscopy. Defect size, patient factors and subchondral bone involvement ultimately contribute to the treatment decision.

Extrinsic Factors

Extrinsic factors that must be considered include malalignment, concomitant meniscal deficiency, ligament insufficiency and knee instability. If present, these concomitant extrinsic factors can be treated with the appropriate intervention simultaneously ( Fig. 22.3 ): for malalignment, a simultaneous or staged osteotomy (high tibial, distal femoral or tibial tuberosity); for meniscal deficiency, a meniscal repair or meniscal allograft transplantation; for ligament insufficiency and knee instability, a ligament reconstruction or repair, respectively. It is imperative to both identify and address the existence of these pathological conditions because failure to do so will compromise the outcomes of FCD treatment.

Extrinsic Factor I: Malalignment

Malalignment of the tibiofemoral joint can predispose the affected compartment to undue mechanical stress that accelerates the development and progression of intraarticular pathological conditions. If varus malalignment is present in the setting of medial femoral condyle disease, a valgus-producing proximal tibial osteotomy (PTO) should be performed to unload the articular surface and repair the site. Similarly, valgus malalignment can be addressed with a distal femoral osteotomy, a closing wedge PTO (CWPTO) or proximal lateral opening tibial varus osteotomy to off-load the lateral compartment. Failure to correct malalignment has been reported to lead to inferior outcomes after FCD treatment. Moreover, improved functional status and symptom relief have been reported in combined osteotomy and cartilage surgery. Kahlenberg et al. reported on 827 patients who underwent high tibial osteotomies (HTOs) and cartilage repair or restoration surgery with 2-year follow-up and demonstrated improved clinical outcomes with low rates of complications (10.3%). Malalignment should be corrected in conjunction with FCD treatment to avoid subjecting the treated lesion to inappropriate mechanical stress.

Extrinsic Factor II: Meniscal Pathological Conditions

Cartilage structure and meniscal integrity are closely intertwined. Failure to address either defect during surgery can potentiate the progression of disease. For example, if cartilage procedures are performed in patients who are meniscus deficient, increased contact pressure on the implanted cartilage, graft or developing fibrocartilage may ensue and jeopardise the procedure. In cases where the damaged meniscus is not amenable to repair or has been previously removed in a subtotal meniscectomy, a meniscus allograft transplantation (MAT) in addition to addressing the chondral defect is a viable surgical solution. Success with MAT has been demonstrated with judicious selection criteria; however, meniscal insufficiency in the setting of a FCD, typically on the femoral side, is one of the most challenging pathological conditions to treat. When performed in combination, our preferred technique for addressing the meniscus is through an arthroscopic technique, and the cartilage restoration procedure is then performed using an appropriate technique for the indicated procedure (i.e., arthroscopic for microfracture, OAT or MACI versus open for OCA). A systematic review evaluating six studies including 110 patients at a mean follow-up of 36 months found that combined MAT and cartilage restoration or repair had similar outcomes to isolated cartilage repair as determined by the Lysholm Knee Questionnaire, Knee Injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee (IKDC), Tegner Activity Scale, Modified Hospital for Special Surgery (HSS) Knee Rating Scale and 36-item Short Form Health Survey (SF-36); however, a higher reoperation rate was observed with the combined procedure. The available clinical studies reporting outcomes after combined meniscus and femoral OCA are encouraging as a viable and predictable joint preservation strategy. ^,