Cartilage Repair and Restoration
Articular cartilage is the smooth tissue covering the ends of bones in the knee, allowing them to glide against each other with minimal friction. When damaged, it becomes one of orthopedic surgery’s most challenging problems because cartilage cannot heal itself. With no blood supply, there are no cells available to migrate to the injury and rebuild tissue. Left alone, a cartilage injury doesn’t stay the same. It gets larger.
A helpful way to think about it: the joint surface is a road, and a focal cartilage defect is a pothole, a discrete hole in an otherwise intact surface. The goal of cartilage surgery is to fill that pothole before the road deteriorates further. What surgery cannot address is a fully unpaved street, meaning diffuse, global cartilage loss, which is osteoarthritis. Cartilage restoration is for younger, active patients with meaningful focal damage who want to preserve their natural joint.
Cartilage injuries can result from trauma (an ACL tear, patellar dislocation, or hard landing), a condition called osteochondritis dissecans (OCD), or years of mechanical overload from malalignment. Symptoms typically include deep knee aching, swelling after activity, and sometimes catching or locking if a loose fragment is present. Because X-rays don’t show cartilage well, an MRI is essential for diagnosis and surgical planning. Early imaging matters because smaller defects are easier to treat with better outcomes than larger ones caught late.
Video Education
Dr. Merritt has developed an in-depth video on Advanced Cartilage Treatment Surgery Information. This video helps patients understand the condition, the procedure, and what to expect.
Treatment Options
The right treatment for a cartilage injury depends on several things: how large the defect is, whether it involves bone as well as cartilage, how old the patient is, what their activity demands are, and whether there are other structural problems in the knee that need to be addressed at the same time. There is no single procedure that works for every patient, and choosing correctly requires a thorough workup.
For small, stable injuries in lower-demand patients, physical therapy and activity modification can manage symptoms without surgery. In some OCD lesions in young patients where the cartilage hasn’t fully separated, conservative treatment with rest and protected weight-bearing gives the bone a chance to revascularize and heal on its own, though this requires close monitoring.
When a traumatic event — such as a patellar dislocation or ACL injury — produces a fresh osteochondral fracture (a piece of cartilage with bone attached), my first priority is to try to save that native tissue. If the fragment is large enough and contains enough bone, I can fix it back in place with specialized screws or anchors. This is the most biological option available, and when it works, the patient keeps their own hyaline cartilage. Timing matters here — fresh fragments have a much better chance of healing than old ones.
For larger defects where the native tissue is not salvageable, I use two primary restoration procedures. The first is osteochondral allograft transplantation (OCA). This involves transplanting a plug of fresh donor cartilage and bone — sourced from a tissue bank, sized and matched to the patient’s specific anatomy — directly into the defect. The damaged area is reamed to a precise circular shape, and the donor plug is press-fitted in. Because the cartilage matrix shields the donor cells from the host immune system, these grafts do not require any immunosuppression or compatibility matching beyond anatomical sizing. The result is an immediate restoration of the joint surface with mature, durable hyaline cartilage. Studies show 10-year survival rates in the range of 72–88% for femoral condyle grafts, and about 79% of patients return to sport at their pre-injury level.
The second procedure is MACI — Matrix-Induced Autologous Chondrocyte Implantation — an FDA-approved two-stage technique that uses the patient’s own cells to regrow cartilage. In the first stage, I perform a short arthroscopy to harvest a small biopsy of healthy cartilage from a non-load-bearing area of the knee.
That biopsy goes to a laboratory, where the cartilage cells are isolated, multiplied, and seeded onto a porcine collagen membrane over the following four to six weeks.
In the second surgery, I open the knee, prepare the defect, and glue the cell-seeded membrane into place. Over the following months, those cells mature into hyaline-like cartilage that fills the defect with the patient’s own biology. MACI is particularly well-suited for medium to large defects in younger patients where a fully biological solution is preferred. Published studies show implant survival rates around 85% at five years.
One thing I emphasize to every cartilage patient: surgery on the cartilage alone may not be enough. If the knee has a torn meniscus, that needs to be addressed — the meniscus protects the cartilage surface, and operating on cartilage in a meniscus-deficient knee dramatically increases failure risk. If there is ligament instability, that creates abnormal forces across the joint that will stress the new graft.
And critically, if the leg is malaligned — bow-legged or knock-kneed — the weight-bearing line passes through the repaired area, loading it with every step. In those cases, I also perform an osteotomy: a precise cut in the tibia or femur to shift the alignment and redirect load away from the graft. Without correcting the alignment, cartilage surgery in a malaligned knee has a much higher chance of failing prematurely. Doing everything at once is more demanding surgically, but it gives the graft the mechanical environment it needs to survive long-term.
Cartilage Restoration Recovery Timeline
Drag the slider to explore each phase of your recovery
Select Your Procedure
Your surgeon will tell you which procedure applies. OCA uses donor cartilage and bone that heals through bone-to-bone integration (~6-month recovery). MACI uses your own cartilage cells grown on a scaffold (12–18-month recovery).
Recovery Timeline
Injury to Surgery:
Cartilage surgery requires one of the longer and more demanding recoveries in sports medicine, and I am always direct about that with patients up front. The reason is biology: the cartilage graft needs time to integrate and mature, and loading it too aggressively before it has done so risks failure. This is not a situation where working harder in PT always gets you back faster. Respecting the biology of healing is just as important as the effort.
Surgery to 6 weeks:
The early phase of recovery — roughly the first six weeks — is focused on protecting the graft while maintaining joint motion. Most patients are on crutches and restricted from full weight-bearing, though the specific protocol depends on where the defect is located. For defects on the trochlea (the front of the femur, where the kneecap rides), patients can often be full weight-bearing in a locked brace early, because the kneecap unloads that area during walking. For defects on the femoral condyle or tibial surface, we are much more careful about loading during the first several weeks. Motion exercises begin almost immediately — moving the joint without loading it is critical for nourishing the newly implanted cells and preventing stiffness.
6 weeks to 3 Months:
By three months, most patients are off crutches, walking without a significant limp, and have regained most or all of their range of motion. Physical therapy during this period focuses on building quad strength, improving balance, and introducing progressive functional loading. Swelling continues to resolve but remains variable — it is normal for the knee to fluctuate with activity during this phase, and it does not mean something is wrong.
3 Months to 6 Months:
Months three through five bring a shift toward functional strengthening — single-leg exercises, step-ups, light cycling with resistance. By months five to six, impact loading is introduced: a gradual walk-to-jog program, followed by progressive running as strength and comfort allow.
6 Months to 9 Months:
Return to sport for isolated cartilage procedures is typically five to six months. When the cartilage surgery was combined with an ACL reconstruction or ligament repair, the timeline extends to nine months or longer, because we’re waiting on the ligament graft to mature as well as the cartilage. For patients who had an osteotomy at the same time, the bone cut needs to heal fully before full loading is appropriate, which adds another variable to the timeline. I use criteria-based return-to-sport testing — objective measures of strength, stability, and movement quality — rather than clearing patients based on time alone.
9 Months – 1 year:
The long-term outcomes for well-selected cartilage patients are genuinely good. MACI carries approximately 85% implant survival at five years. Osteochondral allograft shows 72–88% graft survival at ten years depending on location. These are not perfect numbers — cartilage surgery is not a guarantee — but for a young patient facing years of pain in a damaged joint, the alternative of doing nothing and watching the pothole grow is a much worse trajectory. The goal is to fill the pothole while the rest of the road is still in good shape, and the earlier we do it, the better the environment for long-term success.
Injury and Surgery Resources
Dr. Merritt provides detailed instructions and protocols to guide patients through every stage of recovery.
Surgery Information
Studies Cited
- Familiari F, Cinque ME, Chahla J, et al. Clinical Outcomes and Failure Rates of Osteochondral Allograft Transplantation in the Knee: A Systematic Review. Am J Sports Med. 2018;46(14):3541-3549. PubMed
- Saris D, Price A, Widuchowski W, et al. Matrix-Applied Characterized Autologous Cultured Chondrocytes Versus Microfracture: Five-Year Follow-up of a Prospective Randomized Trial (SUMMIT). Am J Sports Med. 2018;46(6):1343-1351. PubMed
- Crawford ZT, et al. Outcomes Associated with Return to Sports Following Osteochondral Allograft Transplant in the Knee: a Scoping Review. Curr Rev Musculoskelet Med. 2019. PubMed
Common Cartilage Repair and Restoration Questions
Injury Information
A: The ideal cartilage surgery candidate is a younger, active patient — typically under 50 — with a focal, well-defined defect on MRI, a mechanically stable knee (or one that can be made stable with concurrent procedures), and the commitment to complete a long and demanding rehabilitation. Age is not a strict cutoff, but the biological environment for healing diminishes with age, and the calculus between restoration surgery and replacement shifts. If you have significant knee pain and an MRI showing cartilage damage, come in for a consultation. I’ll look at the full picture and tell you honestly what the options are and what I think makes the most sense for your specific situation.
A: It depends on the severity and distribution. Cartilage restoration is designed for focal defects — discrete areas of damage in a joint that is otherwise reasonably intact. If the arthritis is mild and confined to a focal area, and the rest of the joint surface is healthy, cartilage surgery may still be appropriate. If the cartilage loss is widespread throughout the compartment, restoration is generally not the right answer — joint replacement becomes the more durable option. That is the honest conversation I have with every patient: we’re good at filling potholes, but we cannot repave an entire road.
A: Yes, revision cartilage surgery is possible, and OCA transplantation in particular has a strong track record as a salvage procedure after prior cartilage repairs have failed. The key is understanding why the first surgery failed — whether it was the wrong procedure for the anatomy, a problem with the mechanical environment, an undertreated meniscus or alignment issue, or premature return to activity. A thorough workup before revision surgery is essential, and I will want to review all prior imaging and operative reports before making a plan.
A: The meniscus acts as a shock absorber and load distributor in the knee. When it is missing or significantly damaged, the forces across the cartilage surface increase substantially. Doing cartilage restoration in a knee with a deficient meniscus exposes the graft to higher stress than it was designed to handle. If you have a meniscus tear, I will want to repair or address it at the same time as the cartilage surgery. Similarly, if there is ligamentous instability — an untreated ACL tear, for instance — the abnormal joint motion will stress the graft with every step. The whole mechanical environment of the knee has to be in order for cartilage surgery to succeed long-term.
A: If your leg is malaligned — bow-legged or knock-kneed — the weight-bearing axis passes directly through the area we’re trying to repair. Every step loads the graft with forces it is not yet ready to handle, which dramatically increases the chance of early failure. An osteotomy corrects that alignment by cutting and repositioning the bone so that weight is redistributed away from the repaired area and onto the healthy side of the joint. I think of it as building the graft a protected environment where it can heal properly. It adds recovery time, but for patients who need it, skipping the osteotomy is one of the most common reasons cartilage surgery fails.
A: No, and this surprises many patients. The cartilage matrix effectively shields the donor cells from the host immune system, which means osteochondral allografts do not require tissue typing, compatibility matching, or immunosuppressant medications. This is one of the major advantages over organ transplantation. The graft is matched based on anatomical size — we want the donor’s joint geometry to match yours as closely as possible — but not on immune compatibility.
A: Common symptoms include deep aching pain in the knee, swelling that worsens with activity, and sometimes a catching or locking sensation if a loose piece of cartilage is moving around the joint. X-rays are generally not helpful for diagnosing cartilage injuries because they don’t show soft tissue. An MRI is the right study — it can define the size, location, and depth of a defect and give me enough information to plan treatment.
A: A cartilage injury is a focal defect — a discrete area of damage in an otherwise intact joint surface. Arthritis is diffuse, widespread loss of cartilage across the whole compartment or joint. I describe it to patients as the difference between a pothole and an unpaved road. Cartilage surgery is designed to fill the pothole. Once the entire road is gone, we’re talking about joint replacement, not cartilage restoration.
A: Cartilage has no blood supply — and blood is what carries the stem cells, growth factors, and nutrients that allow most tissues to repair themselves after injury. Without blood flow, there is nothing to initiate or carry out the healing process. A cartilage injury left alone does not regenerate. It may become symptomatic over time as the defect expands or a loose fragment develops. This is why early diagnosis and intervention matters.
Surgery Information
A: Cartilage procedures are performed as outpatient surgery — you go home the same day in most cases. You’ll arrive about 90 minutes before your scheduled start time. Surgery typically takes between 45 minutes and 1.5 hours depending on complexity and whether additional procedures are performed at the same time. You’ll wake up with your knee in a brace locked straight. Plan to have someone drive you home and stay with you the first night. The first priority after surgery is ice, elevation, and keeping swelling under control.
A: Yes. MACI received FDA approval for the treatment of symptomatic, full-thickness cartilage defects of the knee in adults. It has been studied extensively and has published five-year data showing approximately 85% implant survival. I have been performing MACI for years and it is one of the procedures I feel most strongly about for the right patient — a young, active person with a focal defect who wants a biological solution using their own cells.
A: Both are cartilage restoration procedures, but they work differently. Osteochondral allograft (OCA) uses a plug of donor cartilage and bone from a tissue bank, transplanted directly into the defect in a single surgery. It is particularly well-suited for large or deep defects involving bone. MACI is a two-stage procedure using the patient’s own cells: I harvest a small cartilage biopsy, send it to a lab where the cells are grown on a membrane over four to six weeks, then implant that membrane at a second surgery. MACI uses your own biology and works best for medium to large defects without significant bone involvement. The right choice depends on defect size, depth, age, and patient preference.
A: Osteochondritis Dissecans (OCD) is a condition where a localized area of bone beneath the cartilage loses its blood supply, causing that segment of bone — and the cartilage above it — to progressively separate from the rest of the joint. It most commonly affects the femoral condyle in adolescents and young adults. Whether surgery is needed depends on how stable the lesion is, whether the cartilage has separated, and the age of the patient. Stable lesions in skeletally immature patients sometimes heal with rest and protected weight-bearing. Unstable lesions or those with a detached fragment almost always need surgical fixation or replacement.
Post-Op Recovery
A: MACI has approximately 85% implant survival at five years in published studies. Osteochondral allograft shows 72–88% survival at ten years depending on the location of the graft. Studies on femoral condyle allografts show roughly 79% of patients returning to sport at their pre-injury level. These are genuinely good numbers for a young patient facing years of pain and functional limitation. The best long-term results come when surgery is done at the right time, the mechanical environment is optimized, and the patient commits fully to the rehab protocol.
A: For an isolated cartilage procedure, return to sport is typically five to six months. For complex reconstructions that also include an ACL or multi-ligament repair, I plan for nine months or more, because the ligament graft needs that time to mature regardless of how the cartilage is doing. I use criteria-based return-to-sport testing — quad strength symmetry, movement quality, functional testing — rather than clearing people based on time alone. A cartilage repair that gets loaded too aggressively too soon is a cartilage repair that fails.
A: If your work or school is desk-based, most patients can return within two weeks, working around the crutches and brace. Physically demanding jobs — nursing, construction, anything requiring prolonged standing or lifting — take considerably longer. With an isolated cartilage repair, full return to physical work is generally around four to six months. With a combined osteotomy, expect longer. We’ll adjust work restrictions based on what your job actually requires and how you’re progressing through rehab.
A: Pain is generally manageable. We use a combination of nerve block anesthesia at surgery, intraoperative local anesthetic, and a post-operative pain protocol to minimize narcotic use. Pain is typically worst in the first several days and improves steadily as swelling decreases. Ice and elevation are your most effective tools in the first week. Most patients are off prescription pain medications within five to seven days. One important note: avoid anti-inflammatory medications like ibuprofen or naproxen for the first three months after surgery — these can interfere with bone healing, which matters especially if an osteotomy was performed.
A: For most cartilage procedures on the weight-bearing surfaces of the knee, I protect the graft with limited weight-bearing for approximately six weeks. The specific protocol depends on the defect location — patellofemoral lesions (where the kneecap rides) are often allowed to bear more weight earlier than condylar lesions on the weight-bearing surface. If an osteotomy was performed at the same time, crutch use typically extends to eight to ten weeks to allow the bone to heal. Your physical therapist will guide the transition based on how you’re progressing.
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