Articular Cartilage Defects of Knee

Introduction

Spectrum of disease entities from single, focal defects to advanced degenerative disease of articular (hyaline) cartilage
Epidemiology
- incidence
  - 5-10% of people > 40 years old have high grade chondral lesions
- location
  - chronic ACL tear
    - anterior aspect of lateral femoral chondyle and posterolateral tibial plateau
  - osteochondritis dissecans
    - 70% of lesions found in posterolateral aspect of medial femoral condyle
Pathophysiology
- mechanism of injury
  - acute trauma or chronic repetitive overload
    - impaction resulting in cartilage softening; fissuring; flap tears; or delamination
  - the cause of OCD is unknown
- pathomechanics
  - impaction forces greater than 24 MPa will disrupt normal cartilage
- cellular biology
  - cartilage injuries have limited spontaneous healing and propensity to worsen over time

Anatomy

See Articular Cartilage Basic Science

Classification

Outerbridge Arthroscopic Grading System
Grade 0	Normal cartilage
Grade I	Softening and swelling
Grade II	Superficial fissures
Grade III	Deep fissures, without exposed bone
Grade IV	Exposed subchondral bone

ICRS (International Cartilage Repair Society) Grading System
Grade 0	Normal cartilage
Grade 1	Nearly normal (superficial lesions)
Grade 2	Abnormal (lesions extend < 50% of cartilage depth)
Grade 3	Severely abnormal (>50% of cartilage depth)
Grade 4	Severely abnormal (through the subchondral bone)

Presentation

History
- commonly present with history of precipitating trauma
- some defects found incidentally on MRI or arthroscopy
Symptoms
- asymptomatic vs. localized knee pain
- may complain of effusion, motion deficits, mechanical symptoms (e.g., catching, instability)
Physical exam
- inspection
  - look for background factors that predispose to the formation of articular defects
    - joint laxity
    - malalignment
    - compartment overload
- motion
  - assess range of motion, ligamentous stability, gait

Imaging

Radiographs
- indications
  - used to rule out arthritis, bony defects, and check alignment
- recommended views
  - standing AP, lateral, merchant views
- optional views
  - semiflexed 45 deg PA views
    - most sensitive for early joint space narrowing
  - long-leg alignment views
    - determine the mechanical axis
CT scan
- indications
  - better evaluation of bone loss
- findings
  - used to measure TT-TG when evaluating the patello-femoral joint
MRI
- indication
  - most sensitive for evaluating focal defects
- views
  - Fat-suppressed T2, proton density, T2 fast spin-echo (FSE) offer improved sensitivity and specificity over standard sequences
  - dGEMRIC (delayed gadolinium-enhanced MRI for cartilage) and T2-mapping are evolving techniques to evaluate cartilage defects and repair

Studies

Laboratory
- may be used to rule out inflammatory disease

Treatment

Nonoperative
- rest, NSAIDs, physiotherapy, weight loss
  - indications
    - first line of treatment when symptoms are mild
- viscosupplementatoin, corticosteroid injections, unloader brace
  - indications
    - controversial
    - may provide symptomatic relief but healing of defect is unlikely
Operative
- debridement/chondroplasty vs. reconstruction techniques
  - indications
    - failure of nonoperative management
    - acute osteochondral fractures resulting in full-thickness loss of cartilage
  - technique
    - treatment is individualized, there is no one best technique for all defects
    - decision-making algorithm is based on several factors
      - patient factors
        
        age
        
        skeletal maturity
        
        low vs. high demand activities
        
        ability to tolerate extended rehabilitation
      - defect factors
        
        size of defect
        
        location
        
        contained vs. uncontained
        
        presence or absence of subchondral bone involvement
  - basic algorithm (may vary depending on published data)
    - femoral condyle defect
      - correct malaligment, ligament instability, meniscal deficiency
      - measure size
        
        < 4 cm2 = microfracture or osteochondral autograft transfer (pallative if older/low demand)
        
        > 4 cm2 = osteochondral allograft transplantation or autologous chondrocyte implantation
    - patellofemoral defect
      - address patellofemoral maltracking and malalignment
      - measure size
        
        < 4 cm2 = microfracture or osteochondral autograft transfer
        
        > 4 cm2 = autologous chondrocyte implantation (microfracture if older/low demand)

Surgical Techniques

Debridement / Chondroplasty
- overview
  - goal is to debride loose flaps of cartilage
  - removal of loose chondral fragments may relieve mechanical symptoms
  - short-term benefit in 50-70% of patients
- benefits
  - include simple arthroscopic procedure, faster rehabilitation
- limitations
  - problem is exposed subchondral bone or layers of injured cartilage
  - unknown natural history of progression after treatment
Fixation of Unstable Fragments
- overview
  - need osteochondral fragment with adequate subchondral bone
- technique
  - debride underlying nonviable tissue
  - consider drilling subchondral bone or adding local bone graft
  - fix with absorbable or nonabsorbable screws or devices
- benefits
  - best results for unstable osteochondritis dissecans (OCD) fragments in patients with open physis
- limitations
  - lower healing rates in skeletally mature patients
  - nonabsorbable fixation (headless screws) should be removed at 3-6 months
Marrow Stimulation Techniques
- overview
  - goal is to allow access of marrow elements into defect to stimulate the formation of reparative tissue
  - includes microfracture, abrasion chondroplasty, osteochondral drilling
- microfracture technique
  - defect is prepared with stable vertical walls and the calcified cartilage layer is removed
  - awls are used to make multiple perforations through the subchondral bone 3 - 4 mm apart
  - protected weight bearing and continuous passive motion (CPM) are used while mesenchymal stem cells mature into mainly fibrocartilage
- benefits
  - include cost-effectiveness, single-stage, arthroscopic
  - best results for acute, contained cartilage lesions less than 2 cm x 2cm
- limitations
  - poor results for larger defects >2 cm x 2cm
  - does not address bone defects
  - requires limitation of weight bearing for 6 - 8 weeks
Osteochondral autograft / Mosaicplasty
- overview
  - goal is to replace a cartilage defect in a high weight bearing area with normal autologous cartilage and bone plug(s) from a lower weight bearing area
  - chondrocytes remain viable, bone graft is incorporated into subchondral bone and overlying cartilage layer heals.
- technique
  - a recipient socket is drilled at the site of the defect
  - a single or multiple small cylinders of normal articular cartilage with underlying bone are cored out from lesser weight bearing areas (periphery of trochlea or notch)
  - plugs are then press-fit into the defect
- limitations
  - size constraints and donor site morbidity limit usage of this technique
  - matching the size and radius of curvature of cartilage defect is difficult
  - fixation strength of graft initially decreases with initial healing response
    - weight bearing should be delayed 3 months
- benefits
  - include autologous tissue, cost-effectiveness, single-stage, may be performed arthroscopically
Osteochondral allograft transplantation
- overview
  - goal is to replace cartilage defect with live chondrocytes in mature matrix along with underlying bone
  - fresh, refrigerated grafts are used which retain chondrocyte viability
  - may be performed as a bulk graft (fixed with screws) or shell (dowels) grafts
- technique
  - match the size and radius of curvature of articular cartilage with donor tissue
  - a recipient socket is drilled at the site of the defect
  - an osteochondral dowel of the appropriate size is cored out of the donor
  - the dowel is press-fit into place
- benefits
  - include ability to address larger defects, can correct significant bone loss, useful in revision of other techniques
- limitations
  - limited availability and high cost of donor tissue
  - live allograft tissue carries potential risk of infection
Autologous chondrocyte implantation (ACI)
- overview
  - cell therapy with goal of forming autologous "hyaline-like" cartilage
- technique
  - arthroscopic harvest of cartilage from a lesser weight bearing area
  - in the lab, chondrocytes are released from matrix and are expanded in culture
  - defect is prepared, and chondrocytes are then injected under a periosteal patch sewn over the defect during a second surgery
- benefits
  - may provide better histologic tissue than marrow stimulation
  - long term results comparable to microfracture in most series
  - include regeneration of autologous tissue, can address larger defects
- limitations
  - must have full-thickness cartilage margins around the defect
  - open surgery
  - 2-stage procedure
  - prolonged protection necessary to allow for maturation
Patellar cartilage unloading procedures
- Maquet (tibia tubercle anteriorization)
  - indicated only for distal pole lesions
  - only elevate 1 cm or else risk of skin necrosis
  - contraindications
    - superior patellar arthrosis (scope before you perform the surgery)
- Fulkerson alignment surgery (tibia tubercle anteriorization and medialization
  - indications (controversial)
    - lateral and distal pole lesions
    - increased Q angle
  - contraindications
    - superior medial patellar arthrosis (scope before you perform the surgery)
    - skeletal immaturity
Matrix-associated autologous chondrocyte implantation
- overview
  - example is "MACI"
  - cells are cultured and embedded in a matrix or scaffold
  - matrix is secured with fibrin glue or sutures
- benefits
  - only FDA approved cell therapy for cartilage in the USA
  - include ability to perform without suturing, may be performed arthroscopically
- limitations
  - 2-stage procedure
  - Expense

LEFT TIBIA OSTEOCHONDRAL AND METAPHYSEAL LESIONS IN A 39M (C101043)

Cartilage lesion with mild valgus mechanical alignment (C1827)

Patellar chondropathy (C1731)