When Does a Knee Cartilage Defect Need a Bone Graft, Not Just Cartilage?
Osteochondral allograft transplantation replaces cartilage and the bone beneath it as a single donor unit, used for large lesions, bone loss, and osteochondritis dissecans that cartilage-only techniques can't address.
Overview
Osteochondral allograft transplantation, or OCA, replaces a damaged section of cartilage together with the bone beneath it, using a single, size-matched piece of donor bone and cartilage. Dr. Raffo uses OCA when a defect involves the subchondral bone itself — from osteochondritis dissecans, prior failed surgery, or a large traumatic lesion — damage cartilage-only techniques cannot fix.
Who this is for
OCA is best suited to larger lesions and lesions with meaningful bone involvement. In the literature, mean lesion size for OCA runs around 5.05 cm² and has been reported as large as 25 cm² in osteochondritis dissecans populations (Wang X, OJSM 2023; Sadr et al. 2016). It is a strong option for patients with OCD, prior failed cartilage surgery, or defects where the bone stock itself needs to be restored, not just resurfaced. OCA is not the first choice for a smaller, purely chondral defect without bone loss — a two-stage cell therapy or, if the arthritis grade fits, a single-stage scaffold may be more appropriate for that patient, and it is not indicated in a knee with diffuse arthritis rather than a focal, bone-involving lesion.
How I approach it
I turn to OCA specifically because it solves a problem that no cartilage-only technique can: restoring lost bone stock along with the cartilage surface above it. When I'm evaluating a patient with osteochondritis dissecans or a defect from prior failed surgery, the question isn't just how much cartilage is missing — it's how much bone is missing underneath it, and OCA is the only technique on this site's cartilage framework built to address both at once.
Graft freshness matters more than most patients realize, and I take it seriously in how I plan these cases. A comparative cohort found that grafts stored 19 to 24 days had 5-year survivorship of 93.1%, compared to 70.4% for grafts stored 25 to 27 days — a statistically significant difference, with late grafts carrying roughly 3.4 times greater likelihood of failure after adjusting for age and defect size (Merkely et al. 2020). Given that roughly 14 days of the standard 28-day shelf life are consumed by mandatory infectious-disease screening, the real clinical window to transplant a graft before quality declines is narrow, and I coordinate scheduling around it rather than treating graft timing as incidental.
The operation
The recipient site is prepared arthroscopically or through a small arthrotomy to define the size and depth of the defect precisely. A donor allograft — cadaveric bone and cartilage matched to the patient's anatomy — is then shaped to fit and press-fit into the prepared socket, restoring both the bony architecture and the joint surface in a single procedure. Unlike MACI, there is no separate biopsy stage; OCA is single-stage from the patient's perspective, though the graft itself has already gone through donor screening and preparation before it reaches the operating room (FDA — MACI, for comparison of two-stage structure).
Where Surgeons Disagree
Does OCA's higher reoperation rate mean it's a worse choice than MACI for a large defect?
I don't equate a higher reoperation rate with a worse outcome — reoperation and outright graft failure are different things, and for the defects OCA is used on, there often isn't a comparable alternative.
The weighted mean reoperation rate for OCA across the literature is 30.2%, which sounds high in isolation, but the weighted mean failure rate — meaning the graft itself did not survive — is considerably lower at 18.2% (Familiari et al. 2018). Survivorship at 5 years is 86.7%, and even at 15 years it remains 72.8% (Familiari et al. 2018). OCA is generally used for larger, more complex lesions than MACI in the first place — a mean of 5.05 cm² versus MACI's 4.4 cm² — so comparing raw reoperation rates without accounting for lesion complexity understates how well OCA performs given what it's being asked to fix (Wang X, OJSM 2023; Milliron/Flanigan 2025).
Where I’d be talked out of it
In a revision case, or a knee with a patellar or bipolar lesion, survivorship is measurably worse — those factors were specifically associated with worse outcomes in the systematic review — and I'll set expectations accordingly or consider whether OCA is even the right call in that specific anatomy (Familiari et al. 2018).
How strict should I be about graft storage time?
I push to transplant grafts before the 25-day mark whenever logistically possible, rather than treating the full 28-day shelf life as equally safe throughout.
The data here is specific and persuasive. Grafts transplanted at 19 to 24 days of storage had 93.1% survivorship at 5 years versus 70.4% for grafts stored 25 to 27 days (P = .027), and ROC analysis supported transplanting before 25 days as the meaningful cutoff (Merkely et al. 2020). That's not a marginal difference — it's over 20 percentage points of survivorship tied to roughly a week of storage time.
Where I’d be talked out of it
Graft availability and donor matching are not always within my control, and if the only appropriately sized graft available falls later in that window, I discuss the tradeoff honestly with the patient rather than delaying surgery indefinitely in search of a fresher graft that may not materialize.
Risks and honest tradeoffs
OCA carries a meaningfully higher reoperation rate than some other cartilage techniques, at a weighted mean of 30.2%, though the outright failure rate is lower at 18.2% (Familiari et al. 2018). In the OCD-specific population, reoperations occurred in 23% of knees and allograft failure in 8%, split between revision OCA, unicompartmental replacement, and total knee replacement (Sadr et al. 2016). Complications in athletes running OCA specifically included graft failure in 6% of cases, accounting for over half of all complications reported in that population (Touhey et al. 2025). Worse survivorship is specifically associated with revision (non-primary) cases, patellar lesions, and bipolar lesions, which is important context when comparing outcomes across different patients (Familiari et al. 2018).
Recovery and rehabilitation
OCA requires a more protected recovery than a cartilage-only procedure because the graft includes bone that must incorporate into the patient's own skeleton, not just soft tissue that must heal.
- 0–6 weeks: Protected, limited weight-bearing to allow the bony portion of the graft to begin incorporating.
- 6–12 weeks: Progressive weight-bearing as incorporation advances, guided by follow-up imaging.
- 3–6 months: Return to low-impact conditioning for most patients.
- 11 months (mean): Athletes return to sport at a mean of 11.1 months, with a reported range of 6 to 26 months (Touhey et al. 2025).
0–6 weeks
Protected, limited weight-bearing to allow the bony portion of the graft to begin incorporating.
6–12 weeks
Progressive weight-bearing as incorporation advances, guided by follow-up imaging.
3–6 months
Return to low-impact conditioning for most patients.
11 months (mean)
Athletes return to sport at a mean of 11.1 months, with a reported range of 6 to 26 months (Touhey et al. 2025).
Alternatives I considered
For a similarly large lesion without meaningful bone involvement, I consider MACI instead, since it avoids the logistics of donor tissue and graft storage timing altogether. For a smaller lesion — within the 1 to 7 cm² labeled range — in a knee that also has mild-to-moderate arthritis, Agili-C's FDA indication may fit better than committing a patient to an allograft procedure.
Ready to be seen?
Appointments are booked through Maryland Orthopedic Specialists, where Dr. Raffo practices.
Frequently Asked Questions
Clinical References
- 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.
- Wang X, et al. Clinical outcomes and survivorship of osteochondral allograft transplantation of the knee: a single-arm meta-analysis. Orthop J Sports Med. 2023.
- Sadr KN, Pulido PA, McCauley JC, Bugbee WD. Osteochondral allograft transplantation in patients with osteochondritis dissecans of the knee. Am J Sports Med. 2016;44(11):2870-2875.
- Touhey DC, et al. Return to sport after osteochondral allograft transplantation of the knee: a systematic review. Am J Sports Med. 2025.
- Merkely G, et al. Shorter storage time is strongly associated with improved graft survivorship at 5 years after osteochondral allograft transplantation. Am J Sports Med. 2020;48(13):3170-3176.
- Milliron E, Flanigan DC, et al. Matrix-induced autologous chondrocyte implantation: a review of the first 5,000 cases in the United States. Cartilage. 2025.
- US Food and Drug Administration. MACI (autologous cultured chondrocytes on porcine collagen membrane).
Related Procedures
Knee Cartilage Restoration
The right cartilage procedure depends on lesion size, whether bone is involved, containment, alignment, age, and whether arthritis is already present — not on which implant is newest.
Learn more kneeMACI (Matrix-Induced Autologous Chondrocyte Implantation)
MACI is a two-stage cartilage repair that uses a patient's own cultured chondrocytes on a collagen membrane, best suited to larger, contained cartilage defects without significant bone loss.
Learn more kneeCartiHeal Agili-C Implant
Agili-C is a single-stage, off-the-shelf cartilage scaffold and the only FDA-approved cartilage implant labeled for use in knees with mild-to-moderate arthritis, though long-term data beyond 2 years remains limited.
Learn more