Knee Osteochondral Lesion: fragment fixation or microfracture
Six-phase pathway after treatment of an osteochondral lesion of the femoral condyle or patella, detailing the substantial differences between fragment fixation (native hyaline cartilage is preserved) and microfracture (reparative fibrocartilage is formed).
Protected weight bearing 6-8 weeks · Running 4-6 months · Contact/pivoting sport 9-12 months (fixation) or 8-12 months (microfracture)
These documents are protocol templates for information and education only: they do not replace the rehabilitation prescription for the individual case. Timing, loading and progressions must always be adapted to the patient, the lesion pattern, the surgical technique used and the clinical course, in collaboration between orthopaedic surgeon, physiotherapist and, where appropriate, physiatrist. Progression is driven by objective criteria, not by the calendar alone.
Articular cartilage is the smooth lining that lets the knee surfaces glide over one another with almost no friction. When trauma or osteochondritis dissecans detaches a fragment of cartilage together with its underlying bone, this is called an osteochondral lesion: in the knee the most frequent sites are the medial femoral condyle, the lateral condyle and the patellar facet after a patellar dislocation.
Two very different surgical strategies exist, and rehabilitation changes accordingly. With fragment fixation the piece is debrided, repositioned in its bed and fixed with screws or bioabsorbable pins: native hyaline cartilage is preserved, but the bone beneath the fragment must heal like a small fracture. With microfracture (or nanofracture) the fragment cannot be salvaged: the base of the defect is perforated to let bone-marrow cells reach the surface, forming a clot and then reparative tissue — fibrocartilage — which is less resistant than native cartilage and matures slowly over 12-18 months.
In both cases the biological principle is the same and must be explained clearly to the family: motion is good, early loading is harmful. Joint fluid nourishes cartilage only when the joint moves, which is why mobilisation starts immediately; but full compressive load on a freshly fixed fragment or a fresh clot can crush or displace it. Move early, load late.
The location of the lesion matters as much as the technique. A condylar (weight-bearing) lesion requires protected loading but allows free flexion; a patellar or trochlear (gliding zone) lesion allows earlier weight bearing but requires limits on loaded flexion, because flexion is exactly what compresses the patella against the femur.
The pathway described here is a six-phase protocol template. The times given are biological minimums: phase progression happens only when objective criteria are met and, when in doubt, the surgeon’s instruction prevails — they know the lesion size, the quality of fixation and the stability seen at arthroscopy.
Key parameters
- Weight bearing (condylar lesion)
- Touch-down weight bearing (~10-15 kg) for 6 weeks, then progression of roughly 25% body weight per week to full weight bearing around week 8.
- Weight bearing (patellar/trochlear)
- Weight bearing allowed in extension with the brace locked at 0° for 4-6 weeks; it is loaded flexion that is restricted, not loading itself.
- Mobilisation
- Passive motion/CPM from day 1: 0-30° initially, then +10-15° per day as tolerated. Target 90° at 2 weeks, full ROM at 6-8 weeks.
- Fragment fixation
- Bony healing of the fragment confirmed on MRI (or CT) between weeks 8 and 12 before unrestricted full weight bearing.
- Microfracture
- Fibrocartilage maturation takes 12-18 months: loading stays controlled for longer and impact and torsion are introduced more gradually.
- Running
- Not before month 4 (fixation with documented healing) or months 5-6 (microfracture), always with a dry knee and quadriceps ≥80%.
- Return to sport
- Pivoting/contact sport at 9-12 months, with the test battery passed and no effusion after progressive loading.
What the surgery does
Fragment fixation or microfracture: what really changes
The two techniques have different biological goals, and this changes loading, timing and return to sport. Neither is better in absolute terms: the choice depends on lesion size, fragment condition and patient age.
| Fragment fixation | Microfracture / nanofracture | |
|---|---|---|
| Biological goal | Preserve native hyaline cartilage and heal the bone under the fragment, like a small fracture. | Stimulate the bone marrow to produce reparative tissue (fibrocartilage) covering the defect. |
| Typical indication | Intact fragment of adequate size with salvageable underlying bone; common in adolescent osteochondritis dissecans. | Fragmented, degenerate or absent fragment; usually small lesions (indicatively <2 cm²). |
| Weight bearing | Touch-down for about 6 weeks, then progression to full weight bearing around week 8 after healing is confirmed. | Protected loading for 6-8 weeks so the clot is not crushed, with a similar but symptom-guided progression. |
| Early motion | Immediate passive motion: it nourishes cartilage and prevents adhesions. | Passive motion is even more important: movement shapes the forming repair tissue. |
| Maturation time | Bone healing in 8-12 weeks; the overlying cartilage is already mature because it is native. | Fibrocartilage matures over 12-18 months: the surface stays vulnerable for a long time. |
| Final tissue quality | Hyaline cartilage — the "real" one — with the best mechanical properties if the fragment heals. | Fibrocartilage, less elastic and less wear-resistant in the long term. |
| Return to sport | Usually 9-12 months for pivoting sports, with radiological confirmation of healing. | 8-12 months with a more gradual impact progression; better outcomes in small lesions and young patients. |
| Main risk | Non-union or fragment displacement if loading is advanced too soon. | Incomplete defect fill and tissue deterioration over time, especially in large lesions. |
Other options exist (osteochondral grafts, membranes, autologous chondrocyte implantation) with specific protocols: the two techniques most frequent in young patients are described here.
Loading timeline
Range of motion progression
Milestones at a glance
- Day 1CPM 0-30°, full extension, touch-down
- 2 weeks90° flexion, effusion controlled
- 6 weeksStart of load progression
- Weeks 8-12Full weight bearing after MRI check
- Months 3-5Strength ≥80%, single-leg control
- Months 4-8Running and plyometrics
- Months 9-12Return to sport with tests passed
Phases of the pathway
Phase 1 — Protecting the fragment and the clot
Days 0-14
Goals
- •Protect the repair: no compression on the treated area
- •Achieve and maintain full extension (0°)
- •Reduce effusion and pain, reactivate the quadriceps
What to do
- •Continuous passive motion (CPM) 2-4 hours daily in blocks, or manual passive mobilisation if CPM is unavailable: 0-30° on day 1, then 10-15° increments per day as tolerated
- •Cryotherapy and compression 15-20 minutes, 4-6 times daily; limb elevated above heart level when sitting or lying
- •Quadriceps isometrics (quad sets) and patellar mobilisation in all directions to prevent adhesions
- •Walking with two crutches, strictly respecting the prescribed load: the toes touch down for balance only, not for support
- •Ankle and gluteal contractions, exercises for the healthy limb and trunk to maintain general condition
Restrictions and precautions
- •No load beyond touch-down for condylar lesions
- •No loaded flexion for patellar/trochlear lesions
- •No resisted open-kinetic-chain quadriceps work
- •Avoid prolonged sitting with the knee flexed and the foot dependent (increases swelling)
Criteria to progress
- ☐Full active extension (0°) with no extensor lag
- ☐At least 60-90° passive flexion
- ☐Decreasing effusion, dry wounds
- ☐Safe and correct crutch use, including stairs
Note for the physiotherapist
An extension deficit in the first weeks is the hardest complication to reverse: prone hangs with the heel supported, 10 minutes 3-4 times daily, is the single highest-yield exercise of this phase.
Phase 2 — Restoring motion under protected loading
Weeks 2-6
Goals
- •ROM 0-120° by week 6
- •Active quadriceps control without activation delay
- •Maintain muscle trophism without loading the lesion
What to do
- •Daily active-assisted and passive mobilisation, wall heel slides, stationary bike with no resistance (high saddle) once flexion exceeds 100-105°
- •Quadriceps NMES combined with voluntary contraction if inhibition persists
- •Closed-chain strengthening in offloading or in water (hydrotherapy after wound healing), hip and core work
- •Load progression only if prescribed: roughly 25% of body weight per week, using bathroom scales as feedback
Restrictions and precautions
- •No squatting beyond 30-45° for patellar/trochlear lesions
- •No loaded leg extension, no step-ups, no lunges
- •No loaded knee torsion
Criteria to progress
- ☐ROM 0-120° or within 15° of the other side
- ☐Clear quadriceps contraction with straight-leg raise and no lag
- ☐No increase in effusion in the 24 hours after sessions
- ☐Load progression achieved as prescribed
Note for the physiotherapist
For patellar lesions the safe arc depends on lesion location: distal patellar lesions are compressed at 20-30°, proximal lesions at 60-90°. Ask the surgeon which arc to avoid rather than applying a generic rule.
Phase 3 — Transition to full weight bearing
Weeks 6-12
Goals
- •Crutch weaning with symmetrical gait
- •Quadriceps strength ≥60-70% of the other side
- •Imaging confirmation of healing (fixation) or defect fill (microfracture)
What to do
- •Progressive crutch weaning: one crutch on the opposite side first, then free walking, only if there is no limp
- •Closed-chain strengthening: mini-squats 0-45°, low-load double-leg press, glute bridge, low step-ups
- •Double- then single-leg proprioception on a stable surface
- •Stationary bike with progressive resistance, freestyle swimming (avoid breaststroke for the first 12 weeks)
- •Follow-up MRI at 8-12 weeks after fixation to confirm healing before releasing load
Restrictions and precautions
- •No running, no jumping, no change of direction
- •Avoid deep squats and deep lunges
Criteria to progress
- ☐Walking without limp or aids for at least 20 minutes
- ☐Full symmetrical ROM
- ☐Dry knee: no effusion after daily activity
- ☐Quadriceps ≥60-70% on dynamometry or comparative isometric testing
Phase 4 — Strength and neuromuscular control
Months 3-5
Goals
- •Quadriceps and hamstring strength ≥80%
- •Single-leg limb alignment control (no dynamic valgus)
- •Prepare the knee for impact
What to do
- •Progressive strengthening: squats, single-leg press, step-downs, controlled lunges, single-leg bridge
- •Eccentric quadriceps and posterior chain work (age-adapted nordic hamstring)
- •Proprioception on unstable surfaces, dual task, perturbations
- •Non-impact conditioning: bike, elliptical, swimming, deep-water running
- •After microfracture: introduce progressive cyclic loading (brisk walking, hills) before true impact
Restrictions and precautions
- •Impact and plyometrics only once phase criteria are met
- •Watch for deep pain and delayed effusion: signs of overloading the repair
Criteria to progress
- ☐Quadriceps strength ≥80%
- ☐20 cm step-down performed with knee control, no valgus and no pain
- ☐No effusion 48 hours after an intense session
- ☐30-minute brisk walk and stairs without pain
Note for the physiotherapist
Effusion is the cartilage thermometer: if swelling appears after a new load, that load was too much. Drop back one level and retry after 5-7 days rather than stopping everything.
Phase 5 — Running, impact and plyometrics
Months 4-8 (fixation) / 5-9 (microfracture)
Goals
- •Continuous running without symptoms or effusion
- •Symmetrical impact absorption in jumping
- •Strength ≥90%
What to do
- •Interval return-to-running programme (walk/run) on even ground, 10% weekly volume progression
- •Graded plyometrics: partially unloaded double-leg, full double-leg, single-leg, jumps with controlled landing
- •Linear agility, then wide and finally sharp changes of direction
- •Strength work maintained 2-3 times weekly alongside field work
Restrictions and precautions
- •No contact, no full-intensity sport-specific drills
- •Stop impact work if effusion or pain lasting more than 24 hours appears
Criteria to progress
- ☐20-30 minutes of continuous running with no pain and no next-day swelling
- ☐Progressive hop tests with LSI ≥85-90%
- ☐Step landing with aligned, cushioned and symmetrical knee
- ☐Quadriceps and hamstrings ≥90%
Phase 6 — Return to sport and maintenance
Months 8-12 and beyond
Goals
- •Graded return to full training and then competition
- •Long-term cartilage protection
What to do
- •Graded reintegration: partial non-contact training → full training → part of a match → competition
- •Year-round preventive neuromuscular programme (FIFA 11+ or equivalent)
- •Body-weight management, weekly load monitoring, avoid clustered high-impact double sessions
- •Clinical review and, where indicated, MRI at 12 months for large lesions or after microfracture
Criteria to progress
- ☐Test battery passed with LSI ≥90% on all items
- ☐No effusion and no pain in the preceding 4 weeks
- ☐Surgeon clearance, with consistent imaging in large lesions
- ☐Subjective confidence in the knee (ACL-RSI or analogue scale ≥8/10)
Return to sport / full activity
Non-contact sport at 6-8 months; pivoting and contact sport at 9-12 months. Microfracture usually needs a slower impact progression because fibrocartilage matures for up to 12-18 months.
- ☐Quadriceps and hamstring strength with LSI ≥90% (dynamometry or comparable isometric testing)
- ☐Hop test battery (single, triple, crossover, 6 m timed) with LSI ≥90%
- ☐No effusion in the preceding 4 weeks, even after high loads
- ☐Double- and single-leg landing without dynamic valgus (video-assessed drop jump)
- ☐No deep pain or painful crepitus in squatting and stair descent
- ☐Subjective IKDC or KOOS-Sport ≥90 and adequate confidence
In the growing patient with osteochondritis dissecans the radiological criterion is decisive: impact should be authorised only with signs of lesion healing. For large lesions (>2-3 cm²) or weight-bearing sites, advising lower-impact sporting choices in the long term is reasonable.
Red flags: stop and contact us
- •Sudden locking or the sensation of a loose body inside the knee (possible fragment displacement)
- •Effusion that returns after every session or does not settle within 48 hours
- •Deep, dull pain that increases with loading and does not settle with rest
- •Sudden loss of previously achieved extension
- •Fever, redness, local warmth or wound discharge (suspected infection)
- •Calf pain and swelling, chest pain or breathlessness (suspected deep vein thrombosis or embolism)
Guidelines and literature
- Chahla J et al. Osteochondritis Dissecans of the Knee: Current Concepts Review. Orthop J Sports Med.
- Andrade R et al. Return to sport following cartilage repair of the knee: a systematic review. Br J Sports Med 2016.
- Mithoefer K et al. Guidelines for the Design and Conduct of Clinical Studies in Knee Articular Cartilage Repair / Return to sport after articular cartilage repair. Am J Sports Med.
- ROCK Study Group (Research in OsteoChondritis of the Knee) — classification and treatment algorithms.
- Edmonds EW, Polousky J. A review of knowledge in osteochondritis dissecans. Clin Orthop Relat Res 2013.
Key exercises, step by step
Each exercise belongs to a specific phase: do not anticipate them. Dosage is indicative and must be adapted by your physiotherapist.
1. Quadriceps isometric contraction (quad set)
From day 1
- •Lie on your back with the leg straight and a rolled towel under the ankle.
- •Push the knee down by tightening the thigh, as if flattening the bed.
- •The heel lifts slightly: that means you are reaching full extension.
Dosage: 10 contractions of 5 seconds, 4-6 times a day
2. Straight-leg raise
From day 1-2
- •Lying on your back, first tighten the thigh until the knee locks straight.
- •Lift the straight leg about 30 cm, hold 3 seconds and lower slowly.
- •If the knee bends while lifting, the quadriceps is not ready yet: go back to quad sets.
Dosage: 3 sets of 10, twice a day
3. Vastus medialis activation
Weeks 1-6
- •Sitting with a pillow under the slightly bent knee.
- •Extend the knee by pushing the heel forward, keeping the thigh on the pillow.
- •Focus on the teardrop muscle above the inner side of the knee.
Dosage: 3 sets of 12, once or twice a day
4. Load progression using scales
Crutch-weaning phase
- •Place the operated foot on bathroom scales while standing between crutches.
- •Learn what 20 kg, 40 kg and half your body weight feel like: memorise the sensation.
- •Increase one level per week, only if pain and swelling do not appear.
Dosage: 5 minutes of load training per day
5. Mini-squat 0-45°
From the full weight-bearing phase
- •Standing, feet hip-width apart, weight evenly distributed.
- •Bend the knees to about 45°, keeping the knees aligned over the feet.
- •Rise by pushing through the heels, without letting the knee collapse inwards.
Dosage: 3 sets of 12, 3-4 times a week
6. Glute bridge
From week 2
- •Lie on your back, knees bent, feet flat on the floor.
- •Lift the pelvis by squeezing the glutes until shoulders, hip and knee are aligned.
- •Lower slowly without arching the back.
Dosage: 3 sets of 12-15, on alternate days
7. Single-leg balance
From the full weight-bearing phase
- •Stand on one leg, knee slightly bent, looking ahead.
- •Progress: eyes open → eyes closed → soft surface → catching a ball.
- •The pelvis must stay level: if it drops on one side, the gluteus medius is weak.
Dosage: 3 x 30 seconds per side, daily
8. Controlled step-down
Strength phase (from month 3)
- •Stand on a 15-20 cm step on the operated leg.
- •Lower slowly with the other foot, touching the floor with the heel, over 3 seconds.
- •The standing knee must stay aligned over the foot: if it collapses inwards, lower the step.
Dosage: 3 sets of 8-10 per side, 3 times a week
9. Low-impact conditioning
All intermediate phases
- •Stationary bike with high saddle and minimal resistance, swimming (avoiding breaststroke early), elliptical.
- •These maintain general fitness without compressing the repaired area.
- •The rule is always the same: no swelling the next day.
Dosage: 20-30 minutes, 3-5 times a week
10. Progressive plyometrics
Impact phase
- •Start with two-foot hops on the spot, landing softly with bent knees.
- •Progress to front-back and lateral hops, then single-leg.
- •Landings must be silent: noise means insufficient shock absorption.
Dosage: 2-3 sets of 10-20 contacts, 2-3 times a week
Frequent questions
Why can I bend the knee but not put weight on my foot?
Because motion and load do different things. Motion circulates the joint fluid that nourishes cartilage and prevents adhesions; loading, on the other hand, compresses the repaired area. In the early weeks we want the first without the second.
Is fibrocartilage "worse" than normal cartilage?
It is repair tissue: it covers the defect and works well for years in many patients, but it is less elastic and less wear-resistant than hyaline cartilage. That is why we are more cautious with impact and torsion after microfracture and avoid rushing.
Is the CPM machine really necessary?
Useful but not essential: the goal is that the knee moves many times a day without load. If CPM is unavailable, the same result is achieved with manual passive mobilisation and repeated heel slides several times a day.
Can my child attend PE at school?
For the first 3-4 months they should be excused from running, jumping and team games. They can take part with alternative roles (refereeing, upper-limb exercises) and return gradually once the impact phase has been completed with criteria met.
Is swelling in the evening normal?
Mild evening swelling in the first weeks is common. It becomes a warning sign when it increases day by day, appears after every session, or does not settle within 24-48 hours with ice and elevation: in that case the weekly load is excessive and should be reduced by one level.
Can I do physiotherapy only once a week?
The physiotherapy session is for setting up, correcting and progressing the programme. The result, however, depends on the exercises performed at home every day: a short daily home programme is worth more than an isolated weekly session.
Knee Osteochondral Lesion: fragment fixation or microfracture — Dott. Daniele Priano, Pediatric Orthopaedics · ortopediaevolutiva.com/en/rehabilitation/knee-osteochondral-lesion · Information document: it does not replace an in-person assessment.
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Email: daniele.priano@ortopediaevolutiva.com