**4.2 Magnetic resonance imaging (MRI)**

MRI is highly advantageous in imaging articular cartilage. This non-invasive modality avoids ionizing radiation, has superior sensitivity and specificity for articular cartilage, and allows for high contrast with proximate structures. Standard MRI sequences in imaging cartilage include conventional spin-echo (SE) and gradient-recalled echo (GRE), and fast SE sequences. The morphologic features of cartilage, evaluated with these standard techniques, can be semiquantitatively analyzed with the WORMS (whole-organ MRI score)(Peterfy, Guermazi et al. 2004). Also, the MOCART (magnetic resonance observation of cartilage repair tissue) has been demonstrated to be accurate, reliable, and reproducible in post-ACI assessment of cartilage restoration tissue(Marlovits, Singer et al. 2006). Fast SE sequences are included in the ICRS cartilage repair evaluation package for non-invasive assessment of cartilage following surgery. Fat-suppression techniques increase the contrast between articular cartilage and the

Management of Knee Articular Cartilage Injuries 113

fronds of articular cartilage and loose bodies. This heterogeneous definition also encompasses lavage, which removes inflammatory joint fluid containing catabolic enzymes. All potentially mechanically-irritating pathology is removed and unstable, irregular edges

Arthroscopic debridement may be indicated in certain groups of patients. The American Academy of Orthopaedic Surgeons (AAOS) Clinical Practice Guidelines (Level V evidence; Grade of Recommendation C)(Richmond, Hunter et al. 2009) recommend arthroscopic partial meniscectomy and / or loose body removal in patients with symptomatic osteoarthritis with primary complaints (mechanical symptoms) of torn meniscus or loose body. However, these guidelines do not recommend arthroscopic debridement or lavage in patients with symptomatic osteoarthritis without mechanical symptoms (Level I and II

In patients with isolated chondral defects, the post-operative rehabilitation following certain cartilage repair or restoration techniques may preclude their use. Some athletes (professional or amateur) may not be willing to forego part of a competitive season or at least one full season due to concerns of scholarships, salaries, contracts, signing bonuses, other endorsements, public image, and career length. Further, many athletes are aware of certain surgical techniques and media coverage has instilled preconceived, irrational notions about their efficacy. Thus, arthroscopic debridement may be an effective, quick method to return an athlete to sport. Do not perform microfracture or other more advanced cartilage surgery if the patient has not consented or is unwilling to undergo the rehabilitation following surgery.

Standard arthroscopic portals (working anteromedial and viewing anterolateral) are generally all that are required for this technique. Systematic diagnostic arthroscopy ensures that each location in the joint is inspected and no pathology left untreated. This includes the suprapatellar pouch, medial and lateral gutters, menisci, chondral surfaces, and cruciate ligaments within the notch. If access to the posterior compartments is indicated, the arthroscope may be placed through the notch and accessory posteromedial or posterolateral portals created to evaluate for loose bodies or posterior horn meniscal pathology. Some loose bodies may be removed with suction on an arthroscopic shaver, however others may require a grasper and either a separate incision or enlarging one of the standard portals. Degenerative chondral flaps and meniscal tears may be removed or trimmed to stable, smooth edges with a combination of arthroscopic biters, shavers, and curettes. Thorough palpation of all surfaces with a probe ensures no pathology is missed. If osteophytes are present, an arthroscopic burr may be required to contour this down as it may be a source of

Short- and mid-term outcomes of arthroscopic debridement are good to excellent (variably defined) in up to 75% of patients(Sprague 1981; Fond, Rodin et al. 2002). Patients whose primary symptom is mechanical generally have a better prognosis(Baumgaertner, Cannon et al. 1990; Ogilvie-Harris and Fitsialos 1991). Shorter duration of symptoms(Yang and Nisonson 1995; Fond, Rodin et al. 2002), normal coronal plane alignment(Baumgaertner, Cannon et al. 1990; Aaron, Skolnick et al. 2006), and no evidence of joint space narrowing(Jackson and

Dieterichs 2003; Aaron, Skolnick et al. 2006) also are predictive of better outcomes.

of articular cartilage and meniscal tissue are smoothed.

evidence; Grade of Recommendation A).

mechanical impingement and loss of motion.

**5.1.1 Surgical technique** 

**5.1.2 Outcomes** 

underlying subchondral bone. Short-tau inversion recovery (STIR) sequences are an example of a fat-suppression technique used for imaging cartilage defects.

T1-weighted series illustrate anatomic features of articular cartilage well, but have poor contrast between it and synovial fluid. T2-weighted series demonstrate better contrast between cartilage and joint fluid. Proton-density-weighted series are an intermediate, providing high contrast and excellent intra-cartilaginous structure.

The biphasic extracellular matrix of articular cartilage includes both fluid and a collagenaggrecan network. The negatively-charged GAGs of aggrecan molecules allow for ions like gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA)-2 and sodium (Na+) to interact to quantitatively measure proteoglycan content(Crema, Roemer et al. 2011). dGEMRIC utilizes Gd-DTPA-2 based on the fact that its negative charge allows it to cluster where the GAG content is relatively low. Thus, since Gd-DTPA-2 concentration is measured via T1, T1 mapping after intravenous (IV) Gd-DTPA-2 allows for quantitative assessment of GAG concentration(Crema, Roemer et al. 2011). Higher Gd-DTPA-2 indicates lower GAG content, while lower Gd-DTPA-2 indicates higher GAG content.

While standard T2-weighted series provide a qualitative assessment of extracellular matrix of cartilage, T2 mapping quantitatively describes variations in relaxation time of cartilage via collagen network-water interaction. Higher T2 is seen in early stages of degenerative osteoarthritis(Dunn, Lu et al. 2004). Although T2 maps do not demonstrate any relationship between T2 and grade of defect or arthritic change (marker of severity of disease)(Koff, Amrami et al. 2007), they have demonstrated the ability to longitudinally assess cartilage repair or restoration tissue following surgery(Welsch, Mamisch et al. 2008).

Just as dGEMRIC may measure proteoglycan content, T1-rho values can also be used to assess extracellular matrix composition. The loss of articular cartilage early in osteoarthritis displays a higher T1-rho value than normal cartilage(Stahl, Luke et al. 2009). T1-rho measures not only proteoglycan content, but also collagen and other non-collagen proteins within the matrix(Mlynarik, Trattnig et al. 1999). This increased sensitivity makes it useful for detection of early arthritic change.

Sodium is a positively-charged ion that must equilibrate exactly with the negative charge imparted by GAGs in ECM of articular cartilage. Thus, normal hyaline articular cartilage exhibits high sodium content, while chondral defects and osteoarthritis exhibit lower sodium content due to loss of GAGs. This makes sodium imaging techniques attractive due to its ability to directly measure GAG content without the use of contrast material.

#### **5. Articular cartilage surgery**

Articular cartilage surgery can be broadly grouped into three categories: Palliative techniques that are, as the name implies, intended to relieve pain secondary to chondral pathology; repair techniques that invoke stimulation of the underlying subchondral bone marrow (MST), including microfracture, subchondral drilling, and abrasion arthroplasty; and restoration techniques that attempt to transfer or produce normal hyaline articular cartilage, including autologous chondrocyte implantation (ACI), osteochondral autograft / mosaicplasty, osteochondral allograft, and other cell-based surgical treatments.

#### **5.1 Palliative techniques**

Palliative techniques are minimally-invasive, arthroscopic surgeries intended to relieve pain due to articular cartilage disease. Debridement consists of removal of unstable, loose flaps or

underlying subchondral bone. Short-tau inversion recovery (STIR) sequences are an example

T1-weighted series illustrate anatomic features of articular cartilage well, but have poor contrast between it and synovial fluid. T2-weighted series demonstrate better contrast between cartilage and joint fluid. Proton-density-weighted series are an intermediate,

The biphasic extracellular matrix of articular cartilage includes both fluid and a collagenaggrecan network. The negatively-charged GAGs of aggrecan molecules allow for ions like gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA)-2 and sodium (Na+) to interact to quantitatively measure proteoglycan content(Crema, Roemer et al. 2011). dGEMRIC utilizes Gd-DTPA-2 based on the fact that its negative charge allows it to cluster where the GAG content is relatively low. Thus, since Gd-DTPA-2 concentration is measured via T1, T1 mapping after intravenous (IV) Gd-DTPA-2 allows for quantitative assessment of GAG concentration(Crema, Roemer et al. 2011). Higher Gd-DTPA-2 indicates lower GAG content,

While standard T2-weighted series provide a qualitative assessment of extracellular matrix of cartilage, T2 mapping quantitatively describes variations in relaxation time of cartilage via collagen network-water interaction. Higher T2 is seen in early stages of degenerative osteoarthritis(Dunn, Lu et al. 2004). Although T2 maps do not demonstrate any relationship between T2 and grade of defect or arthritic change (marker of severity of disease)(Koff, Amrami et al. 2007), they have demonstrated the ability to longitudinally assess cartilage

Just as dGEMRIC may measure proteoglycan content, T1-rho values can also be used to assess extracellular matrix composition. The loss of articular cartilage early in osteoarthritis displays a higher T1-rho value than normal cartilage(Stahl, Luke et al. 2009). T1-rho measures not only proteoglycan content, but also collagen and other non-collagen proteins within the matrix(Mlynarik, Trattnig et al. 1999). This increased sensitivity makes it useful

Sodium is a positively-charged ion that must equilibrate exactly with the negative charge imparted by GAGs in ECM of articular cartilage. Thus, normal hyaline articular cartilage exhibits high sodium content, while chondral defects and osteoarthritis exhibit lower sodium content due to loss of GAGs. This makes sodium imaging techniques attractive due

Articular cartilage surgery can be broadly grouped into three categories: Palliative techniques that are, as the name implies, intended to relieve pain secondary to chondral pathology; repair techniques that invoke stimulation of the underlying subchondral bone marrow (MST), including microfracture, subchondral drilling, and abrasion arthroplasty; and restoration techniques that attempt to transfer or produce normal hyaline articular cartilage, including autologous chondrocyte implantation (ACI), osteochondral autograft /

Palliative techniques are minimally-invasive, arthroscopic surgeries intended to relieve pain due to articular cartilage disease. Debridement consists of removal of unstable, loose flaps or

to its ability to directly measure GAG content without the use of contrast material.

mosaicplasty, osteochondral allograft, and other cell-based surgical treatments.

repair or restoration tissue following surgery(Welsch, Mamisch et al. 2008).

of a fat-suppression technique used for imaging cartilage defects.

providing high contrast and excellent intra-cartilaginous structure.

while lower Gd-DTPA-2 indicates higher GAG content.

for detection of early arthritic change.

**5. Articular cartilage surgery** 

**5.1 Palliative techniques** 

fronds of articular cartilage and loose bodies. This heterogeneous definition also encompasses lavage, which removes inflammatory joint fluid containing catabolic enzymes. All potentially mechanically-irritating pathology is removed and unstable, irregular edges of articular cartilage and meniscal tissue are smoothed.

Arthroscopic debridement may be indicated in certain groups of patients. The American Academy of Orthopaedic Surgeons (AAOS) Clinical Practice Guidelines (Level V evidence; Grade of Recommendation C)(Richmond, Hunter et al. 2009) recommend arthroscopic partial meniscectomy and / or loose body removal in patients with symptomatic osteoarthritis with primary complaints (mechanical symptoms) of torn meniscus or loose body. However, these guidelines do not recommend arthroscopic debridement or lavage in patients with symptomatic osteoarthritis without mechanical symptoms (Level I and II evidence; Grade of Recommendation A).

In patients with isolated chondral defects, the post-operative rehabilitation following certain cartilage repair or restoration techniques may preclude their use. Some athletes (professional or amateur) may not be willing to forego part of a competitive season or at least one full season due to concerns of scholarships, salaries, contracts, signing bonuses, other endorsements, public image, and career length. Further, many athletes are aware of certain surgical techniques and media coverage has instilled preconceived, irrational notions about their efficacy. Thus, arthroscopic debridement may be an effective, quick method to return an athlete to sport. Do not perform microfracture or other more advanced cartilage surgery if the patient has not consented or is unwilling to undergo the rehabilitation following surgery.

#### **5.1.1 Surgical technique**

Standard arthroscopic portals (working anteromedial and viewing anterolateral) are generally all that are required for this technique. Systematic diagnostic arthroscopy ensures that each location in the joint is inspected and no pathology left untreated. This includes the suprapatellar pouch, medial and lateral gutters, menisci, chondral surfaces, and cruciate ligaments within the notch. If access to the posterior compartments is indicated, the arthroscope may be placed through the notch and accessory posteromedial or posterolateral portals created to evaluate for loose bodies or posterior horn meniscal pathology. Some loose bodies may be removed with suction on an arthroscopic shaver, however others may require a grasper and either a separate incision or enlarging one of the standard portals. Degenerative chondral flaps and meniscal tears may be removed or trimmed to stable, smooth edges with a combination of arthroscopic biters, shavers, and curettes. Thorough palpation of all surfaces with a probe ensures no pathology is missed. If osteophytes are present, an arthroscopic burr may be required to contour this down as it may be a source of mechanical impingement and loss of motion.

#### **5.1.2 Outcomes**

Short- and mid-term outcomes of arthroscopic debridement are good to excellent (variably defined) in up to 75% of patients(Sprague 1981; Fond, Rodin et al. 2002). Patients whose primary symptom is mechanical generally have a better prognosis(Baumgaertner, Cannon et al. 1990; Ogilvie-Harris and Fitsialos 1991). Shorter duration of symptoms(Yang and Nisonson 1995; Fond, Rodin et al. 2002), normal coronal plane alignment(Baumgaertner, Cannon et al. 1990; Aaron, Skolnick et al. 2006), and no evidence of joint space narrowing(Jackson and Dieterichs 2003; Aaron, Skolnick et al. 2006) also are predictive of better outcomes.

Management of Knee Articular Cartilage Injuries 115

creation of smooth, vertical walls of the defect and removal of the calcified cartilage layer

Microfracture is generally indicated for a full-thickness, chondral defect (after debridement of the defect to stable rims with exposed bone) of the femoral condyles, trochlea, patella, or tibial plateau. The pioneer of microfracture (Steadman) has successfully utilized microfracture in degenerative arthritis(Miller, Steadman et al. 2004). Although microfracture has been used in high-performance athletes (NFL) with excellent outcomes and return-toplay(Steadman, Miller et al. 2003), other studies have shown less success in highperformance professional athletes, with low rates of return-to-sport and decreased performance if able to return(Cerynik, Lewullis et al. 2009; Namdari, Baldwin et al. 2009). Outcomes of microfracture are mixed. Long-term outcomes have been successful (mean 11 years, range 7 to 17 years) in patients less than 45 years age, without malalignment or meniscal or ligamentous pathology, graded by both subjective and objective outcome measures(Steadman, Briggs et al. 2003). Recent systematic reviews have shown excellent short-term clinical outcomes following microfracture(Mithoefer, McAdams et al. 2009; Harris, Siston et al. 2010). However, after 18 to 24 months, outcomes tend to deteriorate, especially in patients with defects larger than 2 to 4 cm2, longer pre-operative duration of symptoms, prior surgeries to the knee, and older age (Mithoefer, McAdams et al. 2009; Harris, Brophy et al. 2010; Harris, Siston et al. 2010). Further, microfracture may compromise future outcomes following ACI. A three times greater risk of failure after ACI has been shown in those patients with previous microfracture versus those without(Minas, Gomoll et al. 2009). In general, it appears that microfracture is best suited for younger patients with small defects who have normal alignment and a short pre-operative duration

directly beneath the tidemark(Frisbie, Morisset et al. 2006).

of symptoms and are willing to comply with post-operative rehabilitation.

Cartilage restoration techniques either transfer (mosaicplasty, osteochondral autograft and allograft) or attempt to produce (cell-based treatments such as ACI) normal hyaline articular

Osteochondral autograft (OAT) and mosaicplasty are two similar techniques that harvest an osteochondral plug(s) from a "less weight-bearing" part of the knee and transplant them to a defect on a more weight-bearing, articulating location. Given the three-dimensional complexity of the articular surfaces of the knee, one can anticipate that stable congruity of the transplanted plug is paramount to the procedure's technical success. This procedure (Figure 10) can place one or many plugs of variable sizes to fill a defect. If one plug is used and is flush with surrounding cartilage, no fibrocartilaginous tissue from the underlying subchondral bone will be formed. If more than one plug is used, however, the intervening areas fill with fibrocartilage. Since this is an osteochondral transplant, chondral *and* osteochondral defects may be treated without the need for bone grafting (as opposed to other cartilage surgery). This technique, however, is limited by donor-site supply. This has prompted most authors to limit the size transplanted to no greater than 4 or 5 cm2. Despite concerns for donor-site morbidity following harvest, long-term donor-site complaints (measured by Bandi score) are minor and present in small numbers of patients, including high-level athletes (3% - 5%)(Hangody, Vasarhelyi et al. 2008; Hangody, Dobos et al. 2010).

**5.3 Cartilage restoration techniques** 

**5.3.1 Osteochondral autograft / mosaicplasty** 

cartilage.
