Chondromalacia

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chondromalacia patellae

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Chondromalacia Patellae

Definition and Terminology

Chondromalacia (literally "soft cartilage") of the patella describes pathologic softening and degeneration of the articular cartilage of the patella. The term was first introduced by Aleman in 1928. It is important to distinguish it from a clinical syndrome - chondromalacia is a pathologic finding, not simply anterior knee pain. Many patients with marked articular surface changes have minimal symptoms, while others with severe anterior knee pain have minimal cartilaginous change. Terms like "patellofemoral syndrome," "anterior knee pain syndrome," and "patellofemoral arthralgia" are sometimes used synonymously but do not accurately reflect the underlying pathology.

Campbell's Operative Orthopaedics 15th Ed 2026, p. 2764
Rheumatology, 2-Volume Set 2022, p. 744

Pathology and Mechanism

The basic pathologic process in chondromalacia differs fundamentally from osteoarthritis:

Feature	Chondromalacia	Osteoarthritis
Initial lesion site	Deep layers of cartilage	Surface of cartilage
Early change	Ground substance + collagen fiber disruption (not visible grossly)	Fibrillation, visible surface loss
Surface early on	Smooth and intact	Disrupted

The biochemical basis is a decrease in sulfated mucopolysaccharides in the ground substance, demonstrable as loss of basophilia on H&E staining. The two most common anatomical sites of involvement are:

An area ~1 cm in diameter straddling the ridge separating the lateral from the medial facet
An area at the inferior part of the central ridge between medial and lateral facets

These areas, when subjected to mechanical stress (e.g., extreme range of motion), become mechanically inadequate, leading to fibrillation and progressive degeneration.

Pain source: Articular cartilage itself is avascular and has no nerve endings, so it cannot directly produce pain. Pain arises from:

Synovium - chemically irritated by cartilage debris shed into the joint
Subchondral bone - altered load transfer secondary to cartilage failure
Campbell's Operative Orthopaedics 15th Ed 2026, p. 2764-2765

Grading / Classification (Outerbridge)

Stage	Appearance
Stage 1	Softening and swelling of articular cartilage
Stage 2	Deep fissures extending to subchondral bone
Stage 3	Fibrillation of articular surface
Stage 4	Loss of articular cartilage with exposed subchondral bone

Rheumatology, 2-Volume Set 2022, p. 744

Etiology

Acute Causes

Patellar dislocation with chondral/osteochondral fracture
Direct trauma (fall or blow to the patella)
Patellar fracture producing incongruous surfaces

Chronic / Mechanical Causes

Recurrent patellar subluxation or dislocation (secondary to femoral dysplasia, patella alta, femoral anteversion, external tibial torsion)
Increased Q angle (>20° is abnormal; normal ~13° in men, ~18° in women)
Quadriceps muscle imbalance or VMO weakness
Patella alta
Excessive lateral pressure syndrome
Meniscal injury altering patellar movement

Biochemical / Disease Causes

Rheumatoid arthritis
Recurrent hemarthrosis
Alkaptonuria
Repeated intra-articular corticosteroid injections
Prolonged immobilization

Degenerative

Primary osteoarthritis
Campbell's Operative Orthopaedics 15th Ed 2026, p. 2764

Clinical Features

Anterior knee pain - the cardinal symptom
Pain worsens with descending stairs and prolonged sitting ("theater sign" or "movie sign")
Puffiness/swelling depending on degree of synovitis
Patellofemoral crepitation on examination
Retropatellar tenderness on direct palpation
Notably: arthroscopic study of 56 young adults with anterior knee pain confirmed chondromalacia patellae in 45% and synovial plica in another 45% - with no correlation between severity of chondromalacia and clinical symptom severity
Rheumatology, 2-Volume Set 2022, p. 744; Campbell's Operative Orthopaedics 15th Ed 2026, p. 2765

Investigations

Plain X-rays:

AP view: lateralized patella or trochlear hypoplasia
Lateral view: patella alta (patella:patellar tendon ratio should be ~1:1; >1:1.2 is alta)
Skyline (axial) view: patellofemoral incongruity, lateral tilt, lateral subluxation

Q angle measurement:

Line from ASIS to center of patella, subtended by line from patella center to tibial tuberosity
Normal: 13° (men), 18° (women); >20° is abnormal

CT: Assesses skeletal rotational deformity (femoral anteversion, tibial torsion)

MRI: Best for cartilage assessment; measures tibial tuberosity-trochlear groove (TT-TG) distance; demonstrates lateral patellar impact on lateral femoral condyle

Arthroscopy: Gold standard for diagnosis - allows direct visualization and probing of fibrillation and softness; confirms both degree and location of cartilage damage

Rheumatology, 2-Volume Set 2022, p. 744

Treatment

Conservative (First-line)

Physiotherapy: Isometric quadriceps strengthening (especially VMO), hamstring stretches - mainstay for idiopathic cases
Activity modification, NSAIDs
Patellar taping or bracing

Surgical - Arthroscopic

Patellar shaving (chondroplasty): Debridement of unstable chondral fragments
Drilling of subchondral bone / microfracture: Stimulates fibrocartilaginous healing (inferior to native hyaline cartilage - it is disorganized and prone to deterioration)
Lateral retinacular release/lengthening: For proven lateral tilt or subluxation on axial X-rays; partial release preferred over complete release (risk of iatrogenic medial instability); ineffective in patients with normal axial radiographs or patella alta

Surgical - Open / Realignment

Tibial tuberosity transfer (e.g., Elmslie-Trillat): For proven malalignment
Maquet procedure: Anterior elevation of tibial tuberosity to mechanically decompress patellofemoral joint
Osteotomy: For bony malalignment (femoral anteversion, tibial torsion, genu valgum)
Osteochondral allograft implantation: For focal full-thickness defects
Facetectomy
Patellectomy: Reserved for exceedingly rare advanced cases recalcitrant to all other treatment; results in significant loss of extensor mechanism power

Note on Cartilage Healing

Cartilage is avascular with very limited healing capacity. Defects breaching subchondral bone heal with fibrocartilage - disorganized, fibrous, and prone to deterioration over time. This limits the durability of surface procedures.

Campbell's Operative Orthopaedics 15th Ed 2026, p. 2765-2766

Recent Evidence (2025)

Two recent systematic reviews are relevant:

A 2025 meta-analysis (PMID: 41928743) found that Traditional Chinese Medicine topical therapy combined with intra-articular sodium hyaluronate injection showed clinical efficacy in patellar chondromalacia.
A 2025 systematic review (PMID: 41009572) evaluated platelet-rich plasma (PRP) for patellofemoral arthritis and anterior knee pain, representing emerging biologic options.

These do not contradict standard conservative/surgical management but suggest adjunct injectables (hyaluronate, PRP) may have a role in symptom management.

For every flexion of legs there is knuckles every time on the left leg but it isn't happening in the right leg

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knee cracking popping sound every flexion unilateral causes crepitus

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Unilateral Knee Cracking/Popping on Every Flexion

What you're describing - a cracking, popping, or knuckling sound/sensation in the left knee every time you bend it, while the right knee is silent - is medically called crepitus. The fact that it happens every single time you flex, only on one side, is worth paying attention to.

What Is Crepitus?

Crepitus is an audible or palpable crackling, popping, or grinding at a joint during movement. It comes from different sources and carries different levels of significance depending on whether it is:

Painless - usually benign
Painful - warrants investigation

"If the click is painless, it has hardly any significance. If the click is associated with discomfort or pain, one should carefully examine to detect pathology."

S. Das: A Manual on Clinical Surgery, 13th Ed

Common Causes of Consistent Unilateral Knee Cracking

1. Patellofemoral Syndrome / Chondromalacia Patellae (Most Likely)

The most common cause of crepitus with every knee flexion. The kneecap (patella) tracks over the femur slightly improperly, causing grinding of the softened cartilage on its undersurface. This is especially common in:

Young active individuals and adolescents
Females (due to wider Q angle)
People who sit for long periods, climb stairs, or squat frequently

The crepitus is felt/heard because cartilage debris and irregular surface friction produce vibration. The unilateral nature fits - one knee may have different anatomy, alignment, or muscle balance than the other.

Tintinalli's Emergency Medicine, p. 2687; Rheumatology 2022, p. 744

2. Synovial Plica Syndrome

Plicae are folds of synovial tissue inside the knee that are remnants of fetal development. In some people they persist and become thickened/irritated. A snapping medial plica can produce a consistent, reproducible click or snap with every flexion cycle - often felt on the inner side of the knee. It is frequently unilateral and is famously difficult to distinguish from other causes of anterior knee pain.

Tintinalli's Emergency Medicine, p. 2695

3. Meniscal Pathology

A torn or degenerated meniscus can produce a click or snap with knee movement - usually during specific arcs of motion. A meniscal click is described as "a tiny, singular noise that occurs during one cycle of extension and flexion." If you notice the cracking happens at a consistent point in the bending motion (e.g., at 30-40° flexion), this raises suspicion for a meniscal tear.

4. Loose Body in the Joint

A small fragment of bone or cartilage floating inside the knee can produce a mechanical click or catch with movement. This would usually also cause intermittent locking, catching, or giving-way.

5. Snapping Tendon

Extra-articular tendons (e.g., the semitendinosus) can slip over bony prominences and produce a snapping sound that mimics an intra-articular click. Usually felt at the back or side of the knee.

S. Das: Clinical Surgery, 13th Ed, p. 4751-4752

6. Gas Cavitation (Benign)

The classic "knuckle cracking" mechanism - dissolved gases forming and collapsing in the synovial fluid. This is harmless but typically does not happen on every single flexion (there is a refractory period needed to rebuild gas). If your cracking happens every single time without fail, this is less likely the cause.

Why Only the Left Knee?

The asymmetry suggests a structural or anatomical difference between your two knees, not a systemic cause. This could be:

Slight difference in patellar alignment or Q angle between sides
A prior unnoticed minor injury to the left knee
One-sided muscle imbalance (e.g., weaker left VMO/quadriceps)
A structural plica only on the left side
Asymmetric cartilage wear

Red Flags - See a Doctor if You Have Any of These

Symptom	Concern
Pain with the cracking	Cartilage damage, plica, meniscal tear
Swelling or effusion	Joint inflammation or injury
Locking / knee getting stuck	Loose body or bucket-handle meniscal tear
Giving way / instability	Ligament or meniscal pathology
Worsening over time	Progressive chondromalacia or early OA

What to Do

If it is painless:

Monitor it; most likely benign (patellofemoral or plica)
Strengthen your quadriceps (especially VMO) and hip abductors - this improves patellar tracking
Avoid prolonged deep knee flexion positions

If it is painful or associated with any red flag above:

See a doctor/orthopedic surgeon
Investigation: clinical exam + X-ray (axial/skyline view) as first step, followed by MRI if needed (best for cartilage and menisci)
Arthroscopy if diagnosis remains unclear - it is the gold standard for direct visualization of patellar cartilage and plicae

Given your description (cracking every single flexion, only on the left side), the most likely causes in order are: patellofemoral crepitus (chondromalacia) > synovial plica > meniscal pathology. A clinical exam will quickly help narrow this down.

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