I. Occult Fractures and Bone Bruises
A. Overview and epidemiology
1. Subchondral and trabecular bone is often injured with trauma to the knee.
2. Occult fractures and "bone bruises" have become recognized with MRI technology.
3. Bone bruises are commonly encountered in conjunction with ligament or hyperextension injuries of the knee, and they are associated with 70% to 80% of anterior cruciate ligament (ACL) injuries.
4. With ACL tears, bone bruises are found on the anterior aspect of the lateral femoral condyle, near the sulcus terminalis, and on the posterolateral tibial plateau (
Figure 1).
B. Pathoanatomy
1. Bone bruises represent bleeding and edema from microscopic compression fractures of cancellous bone.
2. These injuries are thought to result from traumatic impaction between the femoral and tibial condyles.
C. Evaluation
1. History and physical examination
a. Patients typically present after trauma to the knee.
b. The physical examination is crucial in evaluating for associated ligamentous injury to the knee.
c. Occult fractures usually result in a knee effusion
[Figure 1. MRI scans of common occult bone bruises associated with ACL injuries in the sulcus terminalis of the lateral femoral condyle (A) and the posterolateral tibial plateau (B).]
and pain with weight bearing.
d. Joint effusion and local tenderness are often present.
2. Imaging
a. Plain radiographs are often negative.
b. Bone bruises and occult fractures are best seen on T2 fat-suppressed and short T1 inversion recovery MRI images.
D. Classification—Occult fractures are classified as reticular, geographic, linear, impaction, or osteochondral. The treatment protocol depends on the type and severity of the fracture.
E. Treatment
1. Nonsurgical
a. Isolated bone bruises are treated with activity modification and protected weight bearing until pain and swelling resolve. The sequelae of bone bruises are unclear, but some studies suggest that subsequent articular cartilage degeneration may occur.
b. Return to preinjury activities, including sports, occurs at an average of 3 months after injury.
c. Treatment is modified as needed with concomitant ligamentous injury.
2. Surgical
a. If an impaction-type injury results in significant displacement of the articular surface (>2 mm) in a weight-bearing portion of the knee, then reduction and stabilization should be considered.
b. Osteochondral fractures resulting in focal full-thickness loss of cartilage may require treatment as described in section IV of this chapter.
F. Rehabilitation—Rehabilitation after surgical treatment is usually guided by a physical therapist. Initially, the patient is treated with nonweight bearing for approximately 6 weeks followed by progression to normal weight bearing. Range-of-motion and strengthening exercises are begun immediately, with an emphasis on frequent and repetitive knee motion to aid in the cartilage healing process. Return to impact and sports activities usually occurs at least 4 to 6 months after surgery.
II. Blunt Injuries to Articular Cartilage
A. Overview and epidemiology
1. Blunt injury to articular cartilage likely occurs with most blunt trauma and ligamentous injuries of the knee when there is excessive impact.
2. Blunt injuries cause impaction damage to the articular surface, which may consist of softening, fibrillation, flap tears, cracking, or delamination.
B. Pathoanatomy
1. Blunt trauma can produce histologic, biochemical, and ultrastructural changes of the cartilage, even in the absence of surface disruption.
2. Overt damage to the articular surface may result as well.
3. Cartilage trauma can be suspected when bone bruises and occult bone fractures are seen.
C. Evaluation
1. History and physical examination
a. Patients present with a history of trauma and report pain and swelling; they may also report mechanical symptoms if articular damage is present.
b. Physical examination should rule out associated ligamentous injury.
c. Focal tenderness may be present over the involved area.
d. An effusion is often present.
2. Imaging
a. MRI can reveal articular cartilage damage.
b. T1-rho and T2-mapping MRI sequence techniques can accentuate MRI evaluation of articular cartilage.
D. Classification—Articular cartilage damage has been classified by Outerbridge (
Table 1) and Noyes (
Table 2).
E. Treatment
1. Nonsurgical
a. Treatment for intact articular cartilage lesions consists of protected weight bearing until pain and swelling improve.
b. Prolonged symptoms may be lessened with unloader bracing.
2. Surgical
a. Indications for surgical treatment are prolonged symptoms or overt damage to the articular surface found on imaging.
b. Arthroscopy can provide direct evaluation of cartilage damage.
c. Chondroplasty is indicated for removal of unstable flaps and loose cartilage fragments.
d. Full-thickness lesions with exposed subchondral bone can be treated as outlined in section IV of this chapter.
[Table 1. Outerbridge Grading System for Osteochondral Damage]
[Table 2. Noyes Grading System for Osteochondral Damage]
III. Osteochondritis Dissecans
A. Overview and epidemiology
1. Osteochondritis dissecans (OCD) is a lesion of the articular cartilage that usually involves the subchondral bone.
2. Delamination, sequestration, and instability of the involved area may develop.
3. The exact prevalence of OCD is unknown but has been estimated to be between 15 and 29 per 100,000.
4. OCD is more common in males, and bilateral lesions have been reported to be present in up to 25% of patients.
5. In the knee, approximately 70% of OCD lesions are found in the posterolateral aspect of the medial femoral condyle, 15% to 20% in the central lateral femoral condyle, and 5% to 10% in the patella. OCD lesions rarely affect the trochlea.
B. Etiology—The cause of OCD is unknown. Inflammation, repetitive trauma, ischemia, genetics, and problematic ossification have been implicated.
C. Evaluation
1. History and physical examination
a. Patients with OCD typically present with poorly localized knee pain, often without a history of trauma or injury.
b. Pain is often associated with higher activity levels and sports participation.
c. Concomitant swelling and mechanical symptoms, such as locking or catching, suggest loose OCD fragments.
d. Physical examination often elicits tenderness over the area of the OCD, most commonly the anteromedial aspect of the knee.
2. Imaging
a. Plain radiographs should include AP, lateral, notch, and patellofemoral views. Notch and lateral views are helpful for evaluating lesion localization and size.
b. MRI
i. Provides essential further information in terms of lesion size, cartilage and subchondral bone status, signal intensity below the lesion, and the presence of loose bodies.
ii. Increased signal intensity below the lesion and disruption of the articular cartilage indicate instability of the OCD.
c. Technetium Tc 99m bone scans have also been used for evaluation of OCD lesions.
D. Classification
1. OCD lesions are typically classified as either adult or juvenile (open growth plates), depending on the maturity status of the distal femoral physis.
2. An MRI classification of OCD lesions has been described by Hefti and associates (
Table 3).
E. Treatment
1. Nonsurgical
a. Nonsurgical management is indicated for a stable OCD lesion, especially in a child or adolescent with open physes.
b. Nonsurgical management involves a period of activity modification, often with crutch-protected weight bearing. This is followed
[Table 3. MRI Classification of OCD Lesions*]
with normal weight-bearing walking and rehabilitation exercises.
c. If clinical or radiographic signs of healing are present after a minimum of 3 to 4 months, then gradual resumption of rehabilitation can be attempted. This is eventually followed by sports and impact activities as tolerated.
d. Nonsurgical management has a reported success rate of approximately 50% in juvenile OCD cases.
e. Larger lesion size, skeletal maturity, lesion location other than the medial femoral condyle, and lesion instability have been correlated with lower success rates in nonsurgical treatment of juvenile OCD.
2. Surgical
a. Surgical intervention is indicated when nonsurgical treatment of OCD fails, when OCD lesions are unstable, or when OCD is symptomatic in adults.
b. The objectives of surgical intervention are maintenance or restoration of joint congruity and rigid fixation of unstable fragments when they are salvageable.
3. Surgical procedures
a. Retrograde or anterograde arthroscopic drilling for symptomatic stable lesions can be done for symptomatic stable lesions in juvenile OCD.
b. In unstable OCD lesions, any fibrous tissue found at the base of the lesions should be debrided.
c. Options for fixation of unstable fragments that remain relatively intact and congruous include Herbert screws, cannulated screws, bioabsorbable pins/screws, or osteochondral transplants.
d. Marrow stimulation techniques, such as microfracture, drilling arthroplasty, and abrasion arthroplasty, are options for OCD fragments <2 cm in diameter deemed irreparable.
e. Osteochondral autograft transfer system (OATS), osteochondral allograft reconstruction, and autogenous chondrocyte implantation are also options for OCD lesion reconstruction.
IV. Full-Thickness (Outerbridge Grade IV) Defects
A. Overview and epidemiology
1. Articular cartilage defects can be challenging to treat because they have limited potential for self-healing.
2. They are commonly encountered at arthroscopy, with full-thickness (Outerbridge grade IV) lesions reported in 20% of arthroscopy cases.
3. In studies limited to patients younger than age 40 years with isolated grade IV defects, articular cartilage defects have been reported in 4% of arthroscopies, most commonly on the medial femoral condyle.
4. Articular cartilage injuries are associated with other intra-articular pathology such as meniscal tears, ACL tears, and patellar dislocations.
B. Pathoanatomy
1. The cause of full-thickness lesions can be acute injury or chronic repetitive overload.
2. Common mechanisms of injury include blunt trauma and shear stress.
3. The pathology can range along a continuum from contusion to fracture, ranging in depth from the superficial articular cartilage to the underlying subchondral bone.
4. Contact stress greater than 24 MPa is necessary to disrupt normal articular cartilage.
5. Although normal physical activity leads to peak articular cartilage contact stresses less than 10 MPa, other factors, such as the rate of load and the effect of repetitive load, are important in articular cartilage injury.
6. When load occurs too rapidly for fluid to shift in the matrix, high stress is generated, and chondrocyte death and fissures can develop.
7. Articular cartilage fissures can be propagated by repetitive loading.
C. Evaluation
1. History and physical examination
a. Patients commonly present with history of a precipitating traumatic event or previous surgery.
b. An effusion, motion deficits, or limb malalignment may be observed. Knee stability should be compared with the normal side.
2. Imaging
a. Radiographs
i. Radiographs can underestimate isolated chondral lesions but may demonstrate joint-space narrowing, osteophytes, sclerosis, and cysts.
ii. Weight-bearing AP and lateral views and an axial view of the patellofemoral joint should be reviewed; the ability to detect subtle narrowing or an isolated chondral defect on the flexion surface may be improved with a semiflexed PA view.
iii. Long-leg alignment views are used to determine the mechanical axis. If the mechanical axis traverses the involved compartment (varus knees with medial compartment lesions or valgus knees with lateral compartment lesions), realignment may need to be considered as an initial procedure or as an adjunct to a cartilage restorative procedure.
b. MRI can be used to evaluate articular cartilage morphology.
D. Classification
1. Arthroscopy is the ideal method for evaluating articular cartilage in vivo; however, there are more than 50 arthroscopic grading scales for articular cartilage of the knee.
2. The location, size, and severity of the lesion are important domains for measurement.
3. To date, none of the measurement scales have undergone adequate validity or reliability testing, particularly during their development.
4. Nonetheless, the most widely used system is the modified Outerbridge classification (
Table 4).
E. Treatment
1. Nonsurgical
a. Nonsurgical management is attempted initially. It consists of activity modification, ice, and compression, as well as a multimodal approach of medications (eg, acetaminophen, nonsteroidal anti-inflammatory drugs) and/or nutraceuticals (eg, glucosamine, chondroitin sulfate).
[Table 4. Modified Outerbridge Grading System for Full-Thickness Articular Cartilage Defects]
b. Physical therapy can be helpful, particularly if there is notable atrophy of the quadriceps on examination. A physical therapy program that starts with quadriceps isometrics and progresses to open-chain and closed-chain exercises is often used.
c. Weight loss, corticosteroid injections, viscosupplementation, and unloader braces can be useful for selected patients.
2. Surgical
a. Surgical options can be broadly categorized as cartilage reparative marrow stimulation techniques versus restorative techniques.
b. Reparative marrow stimulation techniques initiate hematoma formation, stem cell migration, and eventual vascular ingrowth. They produce a fibrocartilage repair tissue that contains predominantly type I collagen, as opposed to native hyaline cartilage, which consists primarily of type II collagen.
c. Three methods of reparative marrow stimulation have been described: drilling, abrasion chondroplasty, and microfracture (
Figure 2, A).
d. Cartilage restorative techniques aim to fill the defect with hyaline cartilage by means of autogenous chondrocyte implantation (Figure 2, B) or with osteochondral plugs (mosaicplasty) (Figure 2, C).
e. To date, six randomized or quasirandomized controlled clinical trials have compared different surgical procedures for articular cartilage defects.
i. Inferences from these studies are limited by heterogeneity in terms of postoperative rehabilitation, weight-bearing status, co-interventions, and the delivery system used for
[Figure 2. Marrow stimulation and cartilage restoration. A, Arthoscopic view of a microfracture of the femoral condyle after the tourniquet has been released, with blood flowing from the penetration of the subchondral bone. B, Photograph of a periosteal patch sewn in place, with fibrin glue around the periphery. C, Photograph of an osteochondral autograft, with two plugs in place flush with the femoral condyle.]
chondrocyte implantation; however, at 1- to 2-year follow-up, all studies showed improvement in outcome from baseline regardless of technique.
ii. The highest quality trial performed by Knutsen and associates (2004) reported favorable results for microfracture.
f. A recent Cochrane review (2006) concluded that there was little evidence that autogenous chondrocyte transplantation was more effective than other cartilage resurfacing interventions.
g. Given these results, and the fact that microfracture can often be performed easily without an arthrotomy and avoids a staged second procedure, microfracture should be considered the primary treatment option for full-thickness articular cartilage lesions.
Top Testing Facts
1. Bone bruises are associated with 70% to 80% of ACL injuries. They occur on the posterolateral tibia and anterior lateral femoral condyle near the sulcus terminalis.
2. Bone bruises represent bleeding and edema from microscopic compression fractures of cancellous bone. They are best seen on T2 fat-suppressed and short T1 inversion recovery MRI images.
3. Approximately 70% of OCD lesions in the knee are found in the posterolateral aspect of the medial femoral condyle.
4. Location, size of the lesion, skeletal maturity, and stability of the lesion are important features to consider in managing OCD lesions.
5. A trial of nonsurgical management is indicated for stable OCD lesions, especially in a child or adolescent with open physes.
6. Surgical intervention is indicated when nonsurgical treatment of OCD fails, when OCD lesions are unstable, or when OCD is symptomatic in adults.
7. In unstable OCD lesions, any fibrous tissue found at the base of the lesions should be debrided. Unstable fragments may be fixed with screws or osteochondral transplants.
8. Full-thickness articular cartilage defects in patients younger than age 40 years are encountered in 4% of arthroscopies and are most common on the medial femoral condyle.
9. Marrow stimulation methods of cartilage resurfacing result in fibrocartilage tissue that is composed of predominately type I collagen.
10. Microfracture should be considered the primary treatment option for full-thickness articular cartilage lesions.
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