Overview
Articular cartilage is the smooth white layer, a few millimeters thick, that covers the ends of the femur and tibia and the back of the kneecap. It has no blood supply and no nerves, which is why it glides almost without friction and why it cannot repair itself. A focal cartilage injury is a discrete defect in an otherwise healthy surface, and is a different problem from knee arthritis, where the surface is worn thin across a whole compartment. A discrete defect can be filled; a worn surface cannot.
Left alone, load concentrates on the rim of the defect and the lesion enlarges toward arthritis. Treatment turns on the size and depth of the defect, whether the bone beneath it is involved, its location (femoral condyle or patellofemoral joint), the patient's age and demands, and whether alignment, meniscus and ligaments are healthy enough to protect a repair.
Common Symptoms
- Pain localized to one spot, reproducible by pressing on the femoral condyle with the knee bent to a particular angle
- Swelling that appears after activity rather than during it and settles over a day or two
- Catching, clicking or intermittent locking when a fragment has come loose
- Pain with impact — running, jumping, landing — and with stairs or squatting when the lesion is on the kneecap or trochlea
- In osteochondritis dissecans, a dull ache in an adolescent's knee that builds with sport and has no injury behind it
Joint-line pain with twisting is more typical of a meniscus tear; diffuse aching with morning stiffness after 50 points toward arthritis; pain around the kneecap without swelling is usually patellofemoral pain.
Causes & Risk Factors
Most focal lesions are traumatic: a pivot or direct blow shears a piece of cartilage, sometimes with a shell of bone, off the femoral condyle. An ACL tear and a kneecap dislocation both do this reliably. In adolescents, osteochondritis dissecans (OCD) is different: a segment of bone beneath the cartilage loses its blood supply and can separate with its cartilage cap, usually on the medial femoral condyle of a young athlete in impact sport. Repetitive loading, a previous partial meniscectomy and bow-legged or knock-kneed alignment concentrate load on one area. Under 40, a cartilage lesion is usually one of these focal injuries; over 50, the same MRI finding is more often early arthritis.
How It Is Diagnosed
The exam looks for an effusion and for tenderness at a specific point on the condyle, found by flexing the knee until the sore spot on the femur comes under the examiner's thumb. The Wilson test (extending the internally rotated knee to provoke pain over a medial condyle OCD lesion) is used in adolescents; patellar grind and tilt tests localize patellofemoral lesions. Ligaments, meniscus and alignment are checked because a cartilage repair fails if the knee around it is unstable or overloaded on that side.
Weight-bearing X-rays come first, including a notch view that shows OCD lesions other views miss, and long-leg alignment films if surgery is being considered. MRI sizes the lesion: cartilage thickness, depth, bone involvement, and whether a fragment has separated; in OCD, fluid tracking behind the fragment means it is unstable. Patients from outside the area can upload an existing MRI through mymedicalimages.com before a visit.
Treatment Options
Non-operative care
Small lesions, partial-thickness lesions and incidental findings are managed without surgery: a period off impact loading, quadriceps and hip strengthening, and an unloader brace when alignment is overloading the compartment. An ultrasound-guided corticosteroid injection settles a knee that keeps swelling. Stable OCD lesions in adolescents with open growth plates heal in a high proportion of cases with a few months off impact sport and are followed with repeat imaging.
Arthroscopic debridement and loose body removal
When a fragment is catching or locking the knee, an arthroscopy removes the loose piece and smooths the unstable edge. This stops the mechanical symptoms and is often the right first step in an older patient, but it does not restore the surface.
Cartilage restoration
For a full-thickness lesion in a younger, active patient, the goal is to resurface the defect. For lesions larger than about 2 cm² or involving bone (unstable OCD, a large shear fragment, a failed earlier procedure), Dr. O'Donnell's usual method is osteochondral allograft transplantation: a size-matched plug of donor cartilage and bone is press-fit into a socket prepared in the defect, restoring a mature hyaline surface in one operation. Microfracture, which perforates the bone to grow a fibrocartilage patch, is reserved for small lesions because that tissue wears under load. Malalignment is corrected with an osteotomy, and a deficient meniscus or unstable ACL is addressed, at the same time; a graft placed into an overloaded compartment does not survive. Restoration carries a long protected recovery and is offered when the alternative is early arthritis in a young patient.
Recovery & What to Expect
A transplanted graft has to incorporate into the surrounding bone before it can be loaded, so the early phase is slow and strictly protected. A femoral condyle graft is kept off weight for 6 to 8 weeks; a patellofemoral graft bears weight straight away in a brace locked in extension but avoids loaded bending. The osteochondral allograft protocol runs as follows.
| Phase | Timing | What happens |
|---|---|---|
| Protection & motion | Weeks 0–6 | Touch-down weight bearing on crutches (condyle) or brace locked in extension (patellofemoral). Continuous passive motion, quad sets, straight-leg raises, heel slides within limits. Full passive extension is the priority. |
| Progressive weight bearing | Weeks 6–12 | Weight bearing advanced to full by about 8–12 weeks; crutches weaned; full motion. Bike, pool, closed-chain strengthening in protected ranges. Low impact only. |
| Low-impact strengthening | Months 3–6 | Progressive resistance and single-leg work, hip and core, elliptical and swimming. No running, jumping or cutting. Advance at 80% strength of the other leg with no swelling. |
| Return to impact & sport | Months 6–12 | Criteria-based running and plyometric progression, agility and sport-specific drills. Return to sport typically 9–12 months, surgeon-cleared. |
Desk work on crutches is possible within a week or two; driving a right-knee patient waits for full weight bearing at 8 to 12 weeks; running not before 6 months and sport at 9 to 12 months. The protocol is available as a PDF: osteochondral allograft transplantation.
Frequently Asked Questions
Can knee cartilage heal on its own?
Articular cartilage has no blood supply, so a full-thickness defect does not fill back in with normal cartilage. Small partial-thickness lesions can become asymptomatic, and stable OCD lesions in adolescents with open growth plates often heal with time off impact sport. A full-thickness lesion with bone involvement in an adult does not heal, and a symptomatic one tends to enlarge.
Is a cartilage injury the same thing as arthritis?
No. A focal cartilage injury is a discrete defect in an otherwise healthy surface, usually from an injury in a patient under 40. Arthritis is thinning across a whole compartment. A focal defect can be resurfaced to protect the joint; a worn compartment is managed with injections and bracing and eventually replacement.
What is the difference between microfracture and an osteochondral allograft?
Microfracture makes small holes in the bone beneath the defect so marrow cells form a scar-cartilage patch; it suits small lesions but the patch wears under heavy load. An osteochondral allograft replaces the defect with a plug of donor cartilage and bone, restoring a true hyaline surface, and is used for larger lesions, bone involvement and failed prior procedures.
How long am I on crutches after cartilage restoration surgery?
For a femoral condyle graft, 6 to 8 weeks of touch-down weight bearing while the graft incorporates, then a gradual progression to full weight bearing by about 8 to 12 weeks. For a patellofemoral graft you bear weight from the start in a brace locked straight, with crutches only until walking is comfortable.
Can I have cartilage surgery with Dr. O'Donnell if I live outside Miami?
Yes. Start with a telemedicine consultation and upload your MRI through mymedicalimages.com. Allograft surgery is scheduled once a size-matched donor graft is available, performed as an outpatient at Bayside Surgery Center, and follow-up can be by telemedicine while you rehabilitate at home with the written protocol. See the visiting patients page.
This page is for general education and is not a substitute for a medical evaluation. Treatment recommendations depend on your individual diagnosis and goals. Kevin O'Donnell, MD sees patients from Coral Gables, Miami, Brickell, Pinecrest and Coconut Grove at 475 Biltmore Way, and out-of-town patients by telemedicine.