Cartilage damage is a common issue that can occur from injury, general wear and tear, or diseases like osteoarthritis. Cartilage is the flexible connective tissue that covers the ends of bones at joints. It acts as a shock absorber and allows bones to glide over one another smoothly. When cartilage is damaged, it can be painful and limit movement. Because cartilage has limited natural healing ability, cartilage damage can progress over time and lead to more serious joint problems. Fortunately, there are several evidence-based ways to help promote cartilage healing.
What is cartilage?
Cartilage is a type of connective tissue found throughout the body. There are three main types of cartilage:
- Hyaline cartilage – covers bone surfaces at joints and gives shape and support to structures like the nose, trachea, and ends of ribs
- Fibrocartilage – found in discs between vertebrae and at sites requiring compressive strength like knee menisci
- Elastic cartilage – gives shape and support to external ear and epiglottis in throat
The focus here will be on hyaline cartilage that lines the bones at synovial joints. Hyaline cartilage is composed mainly of water (60-85% by weight) along with collagen fibers, proteoglycans, and cells called chondrocytes. The collagen fibers provide tensile strength, proteoglycans attract water to resist compressive forces, and chondrocytes maintain the cartilage matrix.
This structure allows hyaline cartilage to smoothly distribute mechanical forces across joint surfaces. Without this cushioning, bones would grind painfully against each other during movement. Cartilage also gives joints shape and guides motion.
What causes cartilage damage?
Cartilage damage can occur for several reasons:
Injury
Trauma from sports, falls, accidents, or repetitive overuse can injure cartilage. Tears, fractures within cartilage, or damage to the underlying bone can occur.
Aging
As people get older, cartilage loses proteoglycans and becomes more brittle. It is less able to withstand mechanical stress and strain.
Diseases
Osteoarthritis causes progressive breakdown of cartilage over time. Other diseases like rheumatoid arthritis, gout, and septic arthritis also damage cartilage.
Genetics
Some genetic conditions affect cartilage development or composition and predispose it to early wear and tear.
Obesity
Excess body weight places more mechanical stress on weight-bearing joints like knees and hips, wearing down cartilage.
Why doesn’t cartilage heal well on its own?
Cartilage has a limited capacity for self-repair for several reasons:
Limited blood supply
Cartilage lacks blood vessels, nerves, and lymphatics. Blood delivers nutrients, oxygen, immune cells, and signaling molecules needed for healing. Without direct blood supply, damaged cartilage struggles to regenerate.
Low cell density
Cartilage contains far fewer cells per volume than most tissues. Chondrocytes sparsely scattered through cartilage have to maintain large extracellular matrix areas.
Slow cell turnover
Chondrocytes divide and replenish cartilage very slowly. The cell turnover time for articular cartilage is estimated at 100-400 years. This sluggish metabolism restricts healing capacity.
Unique extracellular matrix
The abundant extracellular matrix composed of collagen, proteoglycans, and water gives cartilage its distinct biomechanical properties. But it also presents a challenge for cells to remodel and integrate new tissue after injury.
What happens when cartilage is damaged?
There are several consequences when cartilage is damaged:
Loss of matrix constituents
Injuries like fractures cause immediate physical disruption and loss of cartilage tissue. Enzymes and inflammation break down matrix components.
Cell death
Trauma kills chondrocytes near the injury site. Apoptosis and necrosis reduce local cell numbers.
Matrix degradation
Chondrocytes secrete catabolic enzymes like metalloproteinases that digest surrounding damaged matrix. This can lead to further matrix breakdown over time.
Flawed repair response
Cartilage has a limited intrinsic healing response. Any new matrix formed is often biomechanically inferior fibrocartilage.
Pain and stiffness
As cartilage damage progresses, associated bone changes and joint inflammation can lead to pain, swelling, and restricted mobility.
What are symptoms of cartilage damage?
Symptoms of cartilage injury include:
- Joint pain – aching, throbbing, or sharp pain located in the affected joint. Pain often worsens with use.
- Joint swelling – fluid accumulation and inflammation cause swelling and thickening.
- Stiffness – difficulty moving the joint through full range of motion due to pain or mechanical restriction.
- Locking or catching – joint feels stuck or caught when moving. A piece of cartilage may be catching inside the joint.
- Instability – damaged cartilage disrupts joint biomechanics, leading to looseness or buckling.
- Crepitus – a popping, cracking, grating, or crunching sound when moving the joint.
- Tenderness – soreness when pressing on the damaged cartilage area.
Symptoms are often worse after activities that stress the damaged joint and ease with rest. Swelling may cause joints to feel stiff and tight, especially when first getting up after resting.
How is cartilage damage diagnosed?
To diagnose cartilage injury, doctors consider symptoms and perform a physical exam plus imaging tests:
Physical exam
The doctor will assess joint swelling, tenderness, range of motion, alignment, fluid, and stability. Moving the joint in different directions can help pinpoint the location of damage.
Imaging tests
Common imaging tests include:
- X-ray – Shows bone alignment and fractures but does not visualize cartilage directly.
- MRI – Provides detailed images of bone and soft tissues like cartilage. MRIs accurately show cartilage tears and thinning.
- Arthroscopy – A camera inserted into the joint gives the clearest view of cartilage surfaces to identify damage.
Blood tests may also be ordered to check for underlying inflammatory causes.
Goals for cartilage healing
The main goals when trying to heal damaged cartilage include:
Reduce pain and inflammation
Controlling pain and inflammation alleviates symptoms in the short term. Anti-inflammatory medications and joint injections can help achieve this.
Stimulate cell growth
Promoting chondrocyte proliferation and matrix production improves intrinsic cartilage repair. Growth factors, stem cells, and scaffolds aim to stimulate cartilage growth.
Stabilize and integrate repair tissue
Integrating new repair tissue with native cartilage and restoring smooth joint surfaces are challenges. Using biomechanically sound scaffolds, cell sources, and biophysical stimuli may enhance integration.
Restore joint function
The ultimate goal is reducing pain and stiffness to improve joint function and quality of life long-term. All aspects of treatment should facilitate returning to daily activities.
Conservative treatment approaches
Several conservative treatment strategies can promote cartilage healing without surgery:
Rest and modification of activities
Giving injured joints adequate rest periods allows inflammation to resolve and prevents overloading damaged cartilage. Transitioning to lower-impact activities protects cartilage.
Physical therapy
Exercises improve joint mobility and muscle strength to support joints. Therapists develop customized programs targeting specific deficits.
Bracing and assistive devices
Braces and canes redistribute joint forces away from damaged cartilage to ease symptoms. Unloader braces reduce pressure on one knee compartment, for example.
Weight loss
Losing excess body weight reduces mechanical stress on cartilage in weight-bearing joints. Even modest weight loss can improve joint function.
Medications
Anti-inflammatory drugs like NSAIDs, analgesics, and corticosteroid injections reduce pain and inflammation. Other drugs aim to slow cartilage breakdown.
Nutraceuticals
Supplements provide building blocks for cartilage repair and exert anti-inflammatory effects:
- Glucosamine and chondroitin – Precursors for proteoglycans and glycosaminoglycans in cartilage matrix
- MSM – Supplies sulfur for cartilage integrity
- Collagen – Promotes collagen formation
- Turmeric – Anti-inflammatory effects
However, high quality studies are needed to determine efficacy.
Prolotherapy
Injections of dextrose or platelet-rich plasma may stimulate inflammation and matrix growth. Evidence is inconsistent but it is low risk.
Emerging biophysical treatments
Exciting biophysical therapies leverage mechanical, ultrasound, or electromagnetic signals to stimulate cartilage healing:
Low-intensity pulsed ultrasound (LIPUS)
- Delivers acoustic pressure waves that may enhance chondrocyte proliferation and matrix production.
- One study showed twice daily LIPUS for 8 weeks increased cartilage thickness in knee osteoarthritis.
Extracorporeal shockwave therapy (ESWT)
- Focused shock waves induce mechanotransduction pathways to boost cartilage growth and repair.
- Systematic review found ESWT improved function and reduced pain in 73% of knee osteoarthritis patients.
Pulsed electromagnetic field (PEMF) therapy
- PEMF mats deliver electromagnetic signals that may stimulate cartilage cell metabolism.
- One RCT found PEMF therapy decreased pain after 6 weeks of treatment in knee osteoarthritis.
Dynamic tissue stimulation
- Portable devices mechanically load joints to drive chondrocyte activity and matrix formation.
- A small study showed dynamic tissue stimulation increased cartilage thickness and lessened pain.
Surgical approaches for cartilage repair
When conservative treatment fails, surgical procedures aim to repair cartilage damage:
Microfracture
- Making tiny fractures in subchondral bone allows blood and bone marrow cells to enter cartilage defect.
- Forms fibrocartilage repair tissue but is prone to thinning over time.
Autologous chondrocyte implantation (ACI)
- Harvests and cultures the patient’s own chondrocytes, then replants them under a collagen membrane cover.
- Shows good long-term outcomes for isolated cartilage defects in otherwise healthy joints.
Osteochondral allograft
- Transplants bone and cartilage from a cadaver donor into the cartilage defect.
- Ideal for large defects but availability of graft tissue is limited.
Subchondroplasty
- Injects bone substitute into bony lesions beneath cartilage defects to stabilize the joint surface.
- Improves function and reduces pain in localized cartilage damage.
Knee joint distraction
- External fixation device slightly separates femur and tibia to unload knee cartilage for 6-8 weeks.
- Allows repair cells to repopulate softened cartilage matrix.
Cutting edge cartilage regeneration approaches
Exciting new techniques aim to truly regenerate cartilage and restore its biomechanical properties:
Cell sources – stem cells and chondroprogenitors
- Using allogeneic mesenchymal stem cells or specific chondroprogenitors may improve on limitations of autologous chondrocytes.
- Induced pluripotent stem cells (iPSCs) can now be derived from the patient then guided toward chondrocytes.
3D-printed scaffolds
- Mimicking native cartilage architecture and mechanical properties may better integrate repair tissue.
- Scaffolds can also deliver therapeutic cells and growth factors.
Gene therapy
- Delivering genes locally to stimulate chondrocyte matrix synthesis and reduce catabolic enzymes.
- In animal models, gene therapy formed repair cartilage more similar to native tissue.
Developmental pathways
- Guiding endogenous or transplanted stem cells toward cartilage tissue using developmental proteins like FGF, Wnt, TGF-beta.
- Harnesses innate signaling pathways involved in cartilage formation.
Summary table
Here is a summary of the major options discussed for promoting cartilage repair and regeneration:
| Treatment category | Specific approaches | Mechanisms |
|---|---|---|
| Conservative treatments | – Activity modification – Physical therapy – Oral medications – Injections – Nutraceuticals – Biophysical stimulation |
– Reduce inflammation – Optimize biomechanics – Provide building blocks – Stimulate intrinsic healing |
| Surgical treatments | – Microfracture – ACI – Osteochondral graft – Subchondroplasty – Joint distraction |
– Stimulate blood/marrow influx – Transplant cell population – Replace damaged tissue – Stabilize bone/cartilage – Unload to allow healing |
| Regenerative medicine | – Stem cells – Scaffolds – Gene therapy – Developmental signaling |
– Direct differentiation – Support 3D growth – Enhance local cells – Recapitulate development |
Conclusion
Cartilage lacks innate regenerative capacity, but emerging biophysical and regenerative techniques show promise to truly restore damaged joint surfaces. Conservative treatments currently remain the mainstay to manage symptoms in the short-term. While more research is still needed, regenerative medicine approaches offer hope for dramatically improving the body’s ability to heal damaged cartilage in the future.
