Chondromalacia Patella

Etiology

Several paths can lead to the development of chondromalacia patellae; however, the pain generator is not clearly identified and is usually multifactorial. Multiple factors have been involved, including:

Lower Limb Malalignment and Patellar Maltracking

The Q angle is the measurement of the pull of the quadriceps muscle relative to the pull of the patella tendon on the patella. A normal angle is 14 degrees in men and 17 degrees in women. This variance is created because anatomically, there is normally a wider pelvis in females than in males. The Q angle is measured by drawing a line from the center of the anterior iliac spine to the center of the patella (quadriceps pull) and a second line from the mid-portion of the patella to the tibial tubercle (patella tendon pull). An abnormally high Q angle > 20 to 25 degrees, indicates lateral pull of the patella in the trochlear groove of the femur and a mechanism of articular cartilage wear and tear. The tibial tubercle trochlear groove distance (TT-TG) is a linear equivalent of the Q angle and a more accurate measure of assessing patellar maltracking.

Patellar maltracking results in narrow contact pressure areas with increased stresses and a further increase in pain. Additionally, the alignment of the patella in the vertical plane can also be abnormal. Patella Alta (high riding), and patella Baja (low riding), are both conditions that have also been implicated as a cause of chondromalacia.

Foot and ankle anatomic variances (pes planus) that cause an increased valgus orientation of the knee cause increased lateral wear of the patellofemoral joint. For example, high-heel shoes, which create increased stress on the patellofemoral joint, can also contribute to chondromalacia.

Chondromalacia patellae can be associated with miserable malalignment syndrome, a combination of specific anatomic criteria that results in increased Q angle and patellofemoral dysplasia. These criteria include femoral anteversion, genu valgum, and external tibial torsion or pronated feet.

Muscular Weakness

Weakness of vastus medialis obliques and general core muscles weakness.

Patellar Lesions

Chondromalacia is also seen as a complication of injuries direct to the patella, immobilization (casting rehabilitative periods), and surgical procedures that lead to quadriceps atrophy. The cause is the micro-trauma created by the decreased pull of the quadriceps muscle on the patella.

Most often, chondromalacia is associated with abnormal (microtrauma) wear and tear of the patellofemoral joint's hyaline cartilage. Lateral positioning of the patella in the patella-femoral joint is a frequent cause of chondromalacia. Although a tight lateral retinaculum or a lateral synovial plica may be implicated as the cause of this positioning, an abnormal Q angle is often the cause.

Contrary to congenital increased cartilage vulnerability, which is not modifiable, iatrogenic injection of chondrotoxic medication into a joint is one that patients can avoid. Intra-articular injections of bupivacaine and high doses or frequent intra-articular injections of corticosteroid lead to softening and/or articular cartilage dysfunction.

Among the causes, patella subluxation is the most common as it is more frequently missed as there is no frank dislocation.[8]

Epidemiology

More women than men are affected, which is attributed to increased Q angles in women. There does not appear to be a hormonal cause of variation. Active young adults who participate in running sports or workers who increase stress in their patellofemoral joint by repeated stair climbing and/or kneeling have a higher incidence of chondromalacia.[9]

Pathophysiology

Normally, patellar hyaline cartilage has a bluish-white, smooth, glistening, and resilient appearance. The pathology of chondromalacia patellae starts with softening, swelling, and edema of the articular cartilage, giving it a dull or even slightly yellowish-white appearance.[10][11] The pathology characteristically starts in the middle of the medial patellar facet, or just distal to it, and starts small, measuring about half an inch or more in diameter.[11] This will then progress to cartilage fibrillation, fissuring, and fragmentation in the more advanced stages.[11][1] Some reports suggest that CMP may be reversible or progress to advanced patellofemoral joint osteoarthritis.[12]

Pathological Process in Chondromalacia Patellae

Hyaline cartilage is composed of chondrocytes that are dispersed throughout an extracellular matrix. This matrix consists of type 2 collagen, proteoglycans, and water. The chondrocytes produce proteoglycans, which are then secreted into the extracellular matrix. Hyaline cartilage is avascular. Its nutrients diffuse into the matrix from synovial fluid. It does not repair well because of the lack of blood supply. Hyaline cartilage is also devoid of lymphatic and neural tissue.

The cartilage reacts to both the environment and physical loads. Destruction of hyaline cartilage can occur in response to chondrotoxic substances injected into a joint. It can also occur through exposure to cytokinins and proteolytic enzymes produced in response to intra-articular bacterial infections.

Hyaline cartilage degeneration also occurs in response to microtrauma wear and tear. Repeated activities that create compressive stress on the patella-femoral joint or increased loads applied to the joint can lead to chondromalacia.

Aging also affects hyaline cartilage. The number of chondrocytes in the cartilage decreases, which correlates with a reduction in the number of proteoglycans produced. This reduction leads to a decrease in the water content of the cartilage. Loss of the cartilage's elastic properties develops because of the cross-linking of collagen fibrils that also occurs with aging. The superficial zone of hyaline cartilage is the first zone to degenerate in the aging process.

The anterior fat pad and the joint capsule are most commonly involved in generating pain signals, while the subchondral bone is less likely to cause pain signals.

Pathology of chondromalacia patellae starts with softening, swelling, and edema of the articular cartilage.

Histopathology

Hyaline cartilage has four zones. The most superficial zone is a gliding surface, i.e., the articular surface of hyaline cartilage. The arrangement of its collagen fibers is parallel to the articular surface to resist shear forces. Other layers include a transitional zone that resists compressive forces and a deep zone that resists shear forces. The collagen fibers in this zone are perpendicular to the articular surface. The fourth zone is the deep calcified zone. This zone contains hydroxyapatite and calcium salts. The deep calcified zone secures the hyaline cartilage to bone.

History and Physical

Anterior knee pain is the most common chief complaint of patients with chondromalacia patellar; however, a high proportion of patients will present with insidious onset of vaguely diffuse retropatellar or prepatellar pain. This pain is usually made worse with activities that increase the stress on the patellofemoral joint, for example, stair ascending or more frequently descending, squatting, kneeling, and running, or even prolonged sitting rather, known as theatre pain. In addition to the anterior knee pain,  effusion, wasting of the quadriceps, and retropatellar crepitus have all been reported in patients with CMP despite none being specific.[13] Hence reliable diagnosis depends on the exclusion of other differential diagnoses presenting with anterior knee pain.

The varied etiological factors of chondromalacia mandate a thorough history and physical evaluation to diagnose this condition and avoid mismanagement due to misdiagnosis correctly. The history should include evaluating previous trauma, comorbid conditions, unstable joints, foot and ankle pain or dysfunction, and activity. Likewise, the physical exam should evaluate the quadriceps appearance and presence of atrophy, the orientation of the foot and ankle, as well as a specific evaluation of the patellofemoral joint.

Specific evaluation of the patellofemoral joint should include assessment of pain, effusion, quadriceps strength, patella mobility, and crepitus. Particular attention to signs of patella maltracking, which includes increased femoral anteversion, increased external tibial torsion, lateral patella subluxation, loss of medial patellar mobility, and positive patellar apprehension test.

The physical examination test, which specifically evaluates the knee for chondromalacia patellae, is Clark's test. This test evaluates patellofemoral grinding and pain by compressing the patella into the femoral trochlea and having the patient contract their quadriceps muscle-pulling the patella through the groove.

Evaluation

Conventional radiographs: Anteroposterior, lateral, and notch views. Radiographs have lower sensitivity and specificity in early grades of CMP. In advanced stages, might show chondrosis, cystic changes, advanced cartilage loss, or joint space loss. In general, radiographs can serve as guidance to the underlying etiology such as in cases of trochlear dysplasia, patella Alta, patella Baja, or lateral patellar tilt. 

CT scan: gives more information with regard to patellofemoral alignment by delineating trochlear geometry. The TT-TG distance can be measured on the CT scan. In addition, torsional deformities of the lower limb can be detected and measured.

Arthrography with plain radiographs or CT arthrography:  Despite low sensitivity, may demonstrate inhibited contrast in areas of chondromalacia. Also, my sport successfully focal areas of cartilage or irregular cartilage or lost cartilage but again in advanced stages.[14]

MRI scan: is the modality of choice for articular cartilage assessment with the best appearances on the T2 sequences, where abnormal cartilage shows high signal intensity. Non-invasive and more reliable and with a higher detection rate than arthroscopy.[15][16]

Radiologically, patellofemoral congruency can be assessed by multiple variables: sulcus angle, trochlear depth, patellar angle, and evaluating patellar tilt by measuring lateral patellar tilt angle. In an MRI study for patients with CMP, both the lateral patellar tilt angle and trochlear depth were significantly decreased, sulcus angle was significantly higher. And there was no correlation reported between patella angle and CMP.[17] Another MRI study reported that patients with CMP  had lower lateral patellar tilt angle, lower trochlear depth, and higher sulcus angle. The ratio of the trochlear sulcus angle to trochlear depth was also suggested as a powerful predictor for early cases of CMP.[18] Additionally, tibial slope and patellar height were important factors in predicting CMP.[5]

Another MRI study evaluated the correlation between obesity and CMP and reported that subcutaneous knee fat thickness was significantly higher in CMP patients in comparison with normal populations. Additionally, a significant correction was reported between subcutaneous knee fat thickness and the grade of CMP. Female patients were found to have thicker subcutaneous knee fat and more serious CMP than male patients.[19]

Arthroscopy: This is the most efficient modality in diagnosing chondromalacia, and determining the location and size of cartilage lesions as well as patella position. However, due to its invasiveness, non-invasive methods are essential for the diagnosis.[13][20]

Treatment / Management

A trial of longstanding conservative management for at least one year should be the first line of treatment. This includes rest, activity restriction, and nonsteroidal anti-inflammatory medication, which is proven to be more effective than steroids. Rehabilitation with physiotherapy should focus on closed chain short arc quadriceps exercises and specific strengthening of vastus medialis obliqus, core muscle strengthening, and strengthening of hip external rotators. Quadriceps muscle strengthening with different exercises significantly reduces anterior knee pain in early cases of CMP.[21][22](A1)

Management of the patient with chondromalacia patellae is difficult, and there is no one specific form of treatment that is universally accepted as a standard of care. Medical management should be based on the physical exam findings. It can include patella stabilizing braces, physical therapy for quadriceps strengthening, orthotics that decrease pronation of the foot, and nonsteroidal anti-inflammatory medication. The use of platelet-rich plasma (PRP) is sometimes advocated, but it is not the standard of care. PRP has not been shown to improve patient outcomes consistently. Likewise, prolotherapy has been recommended by some authors, but it is not the standard of care and has not been shown to improve patient outcomes consistently.

Operative Management

Failure of conservative management will result in exploring alternative surgical options. Even though multiple effective options are available, care should be taken when recommending the best procedure, considering the patient's age and severity of CMP. Each procedure has its own merits, indications, and limitations. Available options include patellar cartilage excision, shaving, drilling, proximal soft tissue, and distal bony patellar realignment surgery. The most effective and most straightforward surgery with avoidance of quadriceps fibrosis and dysfunction is a patellar tendon medial realignment with lateral release and reefing of the medial quadriceps expansion. [23]

Arthroscopic Evaluation and Debridement:

Indicated for diseased cartilage or chondral abrasion, fibrillation, or traumatized cartilage areas (Outerbridge grade II, III, and IV chondromalacia patellofemoral joint).[24]

Debridement is either mechanical or radiofrequency.[25]

Arthroscopic or Open Lateral Retinacular Release

Indicated for lateral patellar tilt and presence of tight lateral retinacular capsule and loose medial capsule.

Patellar Realignment Surgery

This is based on restoring the biomechanical force axis of the patellofemoral joint, which would improve its function; however, it would result in patellofemoral joint degeneration to a degree. [26] Indicated for severe symptoms refractory to conservative management, including physiotherapy.

Various techniques have been described in the literature covering tibial tuberosity osteotomy, tibial tuberosity anteversion, and tibial tuberosity elevation.

Maquet (anterior tubercle elevation): Not more than 1 cm is elevated to avoid the risk of skin necrosis.

Fulkerson (anterior-medialization):

This is indicated in cases of patellar instability with the presence of an increased Q angle.

Contraindicated in skeletal immaturity and in the presence of superomedial arthrosis ( It is recommended to perform an arthroscopic evaluation before surgery)

Elmslie-Trillat osteotomy

MPFL reconstruction

Patellectomy: either partial or total patellectomy. However, this procedure would be indicated only if a patient has excellent quadriceps function preoperatively and would be compliant to exercise regularly postoperatively. Total patellectomy is considered a radical procedure for managing  CMP. It is associated with greater damage to the surrounding ligaments and quadriceps femoris. Additionally, it changes the leverage effect of the extensor muscles. Several other complications have been reported in later stages after total patellectomy, such as instability of the extensor tendon and patellar tendon acute rupture. Hence partial rather than total patellectomy was usually performed in managing CMP.[27][28][29](A1)

Salvage procedures (Historical)

Patellar resurfacing: the McKeever prosthesis initially had a beneficial long-term effect for cases of severe CMP with advanced patellofemoral osteoarthritis; however, this procedure was abandoned due to multiple complications such as patellar tendon lesions, secondary patella fracture, avascular necrosis, patellofemoral joint instability, and prosthetic loosening.[30][24]

Other Treatment Modalities

Cell therapy:[31][32](B3)

Autologous chondrocyte implantation was first reported in 1994 for treating cartilage defects in knee osteoarthritis.[33] In the last two decades, cell therapy for osteoarthritis has emerged as a treatment. Multiple reviewers consider CMP a mesenchymal disease; therefore, cell therapy would have a positive therapeutic effect. Emerging modalities include autologous chondrocyte transplantation and injection of mesenchymal stem cells.

Mesenchymal stem cells (MSCs):

Intraarticular injections of MSCs from different sources were proven safe and clinically effective in treating chondromalacia patellar.

It has the advantages of being less invasive, providing symptomatic relief, and reducing inflammatory changes.

The mechanism of MSC injection is still an area of research, but it does have promising results.[23]

Differential Diagnosis

• Chondromalacia patellae/osteochondral defect
• Osteochondritis dessicans of the patellofemoral joint
• Patellofemoral osteoarthritis
• Patellofemoral pain syndrome
• Lateral patellar compression syndrome
• Plica syndrome
• Quadriceps tendonitis/tendinopathy
• Patellar tendonitis/ tendinopathy
• Saphenous neuroma
• Postoperative neuroma
• Patellar fat pad inflammation
• Hoffa disease
• Patella Alta
• Patella Baja
• Patella instability
• Bi-partite patella

Staging

Outerbridge classification of chondromalacia patellae (5 grades from 0 to IV):[11]

Grade 0: Normal cartilage

Grade I: Intact articular surface but soft, swollen, and oedematous

Some fibrillation and heterogeneity of the cartilage may be noted, which is translated on the MRI as high signal intensity

Grade II: Fissures and fragmentation of the articular surface ( an area half an inch or less in diameter)

Grade III: Focal, partial thickness cartilaginous defect. (an area more than half an inch in diameter)

Grade IV: Full thickness defect down to the subchondral bone

Commonly, these grades are assessed with an arthroscopic evaluation of the knee. MRI radiography can also classify the degree of articular cartilage wear, but it is not as accurate as the visual assessment done at arthroscopy[34][35][36][7][37]

In the Asian population, Ye et al. considered further classified CMP into an early stage (grade 1–2 Outerbridge) and an advanced stage (grade 3–4), and they assumed that with the early stage, patella cartilage can self-repair in comparison to an advanced stage when it progresses to patellofemoral joint osteoarthritis[38]

Prognosis

Chondromalacia patellae may be reversible, or it could progress to the development of patellofemoral osteoarthritis. Patients with knee pain resulting from chondromalacia patella often achieve full recovery. Depending on the case, recovery can occur in as little as a month or take years. Teenagers often achieve long-term recovery because their bones are still growing, and their symptoms generally ameliorate after reaching adulthood.[39]

Complications

Complications in patients with chondromalacia patella may result secondary to the effects of NSAIDs (e.g., GI symptoms) use or bracing, where occasional dermatologic reactions result from the skin's reaction to the brace material. Therapeutic exercises rarely result in symptomatic aggravation. If a specific activity correlates with aggravation of symptoms, then the patient and clinician or therapist should work together to modify the activity ( r.g., alter the frequency, duration, or intensity of the activity or cease the activity temporarily if necessary.)