Osteochondritis Dissecans of the Knee — Fixation

Surgical Indications

Absolute Indications

• Unstable or detached OCD lesion confirmed on arthroscopic probing (Dipaola grade II-IV) in a skeletally mature or immature patient with symptoms
• Symptomatic loose body from a displaced OCD fragment with mechanical locking or catching
• Failed non-operative management after 3-6 months of protected weight-bearing and activity modification in a juvenile patient with an unstable lesion
• Progressive lesion enlargement or instability on serial MRI despite non-operative treatment

Relative Indications

• Symptomatic stable lesion (Dipaola grade I) in a skeletally mature adult (closed physes) with persistent pain despite 3-6 months of non-operative management
• Lesion greater than 2 square cm with high T2 signal but intact cartilage — fixation may prevent detachment
• Patient approaching skeletal maturity with a juvenile lesion that has not healed — fixation before physeal closure may improve healing potential
• Adult OCD with a viable fragment and a contained bed — fixation preferred over marrow stimulation when the fragment is salvageable

Contraindications

Absolute:

• Active knee infection (septic arthritis — arthroscopy and fixation deferred until infection resolved)
• Fragment completely necrotic with no attached subchondral bone and no articular cartilage integrity — fixation will fail, proceed to salvage (microfracture, OATS, or allograft)

Relative:

• Advanced degenerative changes (Outerbridge grade IV changes elsewhere in the knee) — fixation of an OCD lesion will not alter the degenerative cascade
• Patient with poor compliance with postoperative weight-bearing restrictions
• Very small lesion (less than 1 square cm) that has healed with non-operative management

Evidence for Non-Operative Treatment

Juvenile OCD (Open Physes)

• Juvenile OCD with open physes has a significantly higher healing rate with non-operative management compared to adult OCD — reported healing rates range from 50-60% with protected weight-bearing and activity modification over 3-6 months
• The key principle is that the open physis provides ongoing growth and remodelling capacity, and the juvenile subchondral bone has better vascularity
• Immobilisation is generally not recommended — hinged knee brace with protected weight-bearing (touch-down or partial weight-bearing) and activity restriction (no competitive sports) is the standard approach
• Serial MRI every 3-4 months to monitor lesion healing: look for progressive resolution of the T2 signal line, reconstitution of the subchondral bone, and cartilage integrity
• The most common reason non-operative management fails: ongoing high-impact activity that repeatedly stresses the fragment — patient education and compliance are critical

Adult OCD (Closed Physes)

• Non-operative success in adult OCD is substantially lower than in juvenile OCD — healing rates of approximately 20-30% with protected loading in stable lesions
• Adult OCD is generally considered for non-operative management only when the lesion is stable (Dipaola grade I) and the patient has low physical demands
• Many adult stable lesions are managed non-operatively initially, but have a higher rate of eventual surgery compared to juvenile lesions

Evidence for Surgical Fixation

Arthroscopic vs Open Fixation

Arthroscopic fixation (preferred when feasible):

• Minimally invasive — avoids arthrotomy, reduces postoperative pain and scarring
• Direct visualisation of the articular surface for precise fragment reduction
• Access to the most common lesion site (lateral medial femoral condyle) is generally good through standard anteromedial and anterolateral portals
• Limitations: difficult for very large lesions, lesions on the posterior femoral condyle, or lesions requiring extensive bone grafting of the bed

Open fixation (through medial parapatellar or limited approach):

• Required for very large lesions (greater than 3 square cm), lesions with significant bone loss requiring grafting, or lesions in difficult arthroscopic locations
• Allows direct inspection of the fragment and bed, bone grafting of the crater, and placement of multiple fixation devices under direct vision
• Higher morbidity than arthroscopy: larger incision, longer recovery, risk of arthrofibrosis

Key Evidence

Osteochondritis Dissecans — Location and Classification

Classic Lesion Locations

Key Anatomical Reference Points for Fixation

• Lateral medial condyle lesions: the intercondylar notch serves as a reference; the lesion typically lies just posterior to the weight-bearing surface at the condyle's most convex point, visible with the knee in 60-90 degrees of flexion
• Lateral condyle lesions: typically on the central weight-bearing zone, accessed from the anteromedial approach
• The notch view (knee flexed 30 degrees, AP X-ray tunnel view) best demonstrates the lesion and is used for preoperative sizing and postoperative follow-up

Arthroscopic Portal Anatomy for OCD Fixation

Standard Portals

• Anterolateral portal: primary viewing portal for lateral medial condyle OCD; instrument portal for lateral condyle OCD
• Anteromedial portal: instrument portal for lateral medial condyle OCD; viewing portal for lateral condyle OCD
• Superomedial or accessory medial portal: may be needed for screw placement perpendicular to the lesion surface on the medial condyle
• Posteromedial portal: occasionally required for far posterior lesions on the medial condyle that cannot be reached from standard anterior portals

Approach Selection

• The medial parapatellar approach (mini-arthrotomy) is used for open fixation when the lesion is large, far posterior, requires bone grafting, or when arthroscopic screw placement is not achievable at a perpendicular angle to the fragment
• The arthroscopic approach is preferred for most lesions less than 2-3 square cm with an in-situ or hinged fragment

Relevant Neurovascular Structures

• The saphenous nerve and its infrapatellar branch are at risk during medial portal placement and the medial parapatellar approach — identify and protect
• The common peroneal nerve lies posterolaterally and is at risk during posterolateral portal placement or posterior approach for far posterior condyle lesions
• The popliteal vessels are deep posterior structures — avoid posterior capsule penetration during drilling or fixation of far posterior lesions

Positioning and Preparation

Patient position: Supine on a radiolucent table, lateral post at thigh level or leg holder. A tourniquet is placed on the proximal thigh and inflated to 250 mmHg after exsanguination. The leg is draped free to allow full range of movement from full extension to at least 120 degrees of flexion.

Imaging: Fluoroscopy (C-arm) is mandatory for preoperative localisation of the lesion, intraoperative screw placement confirmation, and postoperative fixation verification. Obtain AP, lateral, and notch views to confirm lesion position and size before draping.

Equipment: Standard knee arthroscopy set with 30-degree and 70-degree arthroscopes. Headless compression screw set (Herbert-type or Acutrak, 2.0-4.5 mm diameters). Bioabsorbable pin set (PLLA or PGA, 1.5-2.7 mm). K-wires (1.2-2.0 mm) for temporary fixation and drilling. Arthroscopic reduction instruments. Fluoroscopic guidance.

Consent: Specifically counsel regarding risk of fragment fragmentation or failure of fixation, nonunion requiring revision surgery, hardware irritation requiring a second arthroscopy for removal, infection (less than 1%), stiffness and arthrofibrosis, progression to osteoarthritis, and the possibility that salvage procedures (OATS, ACI, allograft) may be needed if fixation fails.

Arthroscopic Fixation — Step-by-Step

Step 1: Diagnostic Arthroscopy and Stability Assessment

Perform a systematic diagnostic arthroscopy. Examine all compartments, paying particular attention to the OCD lesion. Document the lesion with the probe: size, location, cartilage integrity, stability on probing, and any associated loose bodies.

Classify the lesion:

• Dipaola grade I: intact articular cartilage, stable on probing, fragment in situ — consider non-operative treatment
• Dipaola grade II: articular cartilage partially breached, fragment partially detached but hinged in situ — indication for fixation
• Dipaola grade III: articular cartilage fully breached, fragment completely detached but sitting in the crater — indication for fixation
• Dipaola grade IV: empty crater with fragment displaced as a loose body elsewhere in the joint — retrieve and fix, or salvage

Step 2: Fragment Preparation and Bed Debridement

If the fragment is hinged or detached but viable (intact articular cartilage surface, attached subchondral bone), prepare it for fixation. Remove any loose fibrous tissue from the fragment's deep surface and from the crater bed using a curette and shaver.

The crater bed must be debrided back to bleeding cancellous bone — this is essential for healing. Remove all sclerotic bone from the crater base. Do not over-resect the subchondral bone plate, or the fragment will sink and the articular surface will be incongruent.

Step 3: Fragment Reduction

Reduce the fragment into its anatomical position. Use a grasper to manipulate the fragment back into the crater. If the fragment is hinged, fold it back into position from its hinge point. Confirm anatomical reduction by visualising the articular surface from multiple angles — the fragment cartilage should be perfectly flush with the surrounding articular surface, with no step-off.

If the fragment has been free in the joint, match the fragment to the crater by size, shape, and the direction of the cancellous bone trabecular pattern. A small amount of bleeding from the crater margins confirms a viable bed.

Step 4: Temporary Fixation

Insert 1.2-1.6 mm K-wires percutaneously under fluoroscopic guidance to hold the fragment in its reduced position. Place at least two K-wires from different angles to prevent fragment rotation during definitive screw placement.

Confirm reduction with fluoroscopy (AP, lateral, notch views) and with direct arthroscopic visualisation of the articular surface. The fragment must be anatomically reduced before any definitive fixation device is placed.

Step 5: Definitive Fixation — Headless Compression Screws

Screw selection: Headless compression screws (Herbert, Acutrak, or MMP) are the most commonly used devices. Screw diameter is selected based on fragment size: 2.0-2.4 mm for small fragments (less than 1.5 square cm), 3.0-4.0 mm for medium fragments (1.5-3 square cm), 4.5 mm for large fragments (greater than 3 square cm).

Screw placement:

1. Select the screw entry point on the femoral condylar cortex — choose a trajectory that places the screw perpendicular to the fragment surface and within the fragment substance
2. Drill a guide pin over the K-wire trajectory using a cannulated drill system, under fluoroscopic control
3. Measure screw length from the pin (or use the calibrated pin) to ensure the screw threads will engage the fragment and anchor into the subchondral bone beyond the lesion
4. Insert the headless compression screw along the guide pin, countersinking the trailing thread fully beneath the cortical surface
5. Verify that the screw is fully buried below the articular cartilage by direct arthroscopic visualisation and fluoroscopy
6. Repeat for additional screws (typically 2-3 screws for a medium lesion) — space screws to distribute compression across the fragment

Step 6: Alternative Fixation — Bioabsorbable Pins

When the fragment is too small or too thin for screw fixation, when the bone is osteoporotic and will not hold screw threads, or when avoiding hardware across an open physis is critical in a juvenile patient, bioabsorbable pins (PLLA or PGA) are used.

Technique:

1. Drill guide channels through the fragment into the subchondral bone using a 1.5-2.0 mm drill
2. Insert bioabsorbable pins or nails through the pre-drilled channels using the delivery cannula
3. Bury the pin heads beneath the articular cartilage surface — tap the pins flush with a plastic impactor or counter-sink instrument
4. Confirm no pins are proud by direct arthroscopic visualisation and probe assessment
5. Typically 3-5 pins are placed depending on fragment size

Bioabsorbable devices resorb over 12-36 months (PLLA resorbs more slowly than PGA). They avoid the need for hardware removal surgery but provide less rigid fixation than metal screws.

Step 7: Subchondral Drilling for Healing Stimulation

After definitive fixation, drill 1-2 mm K-wires through the reduced fragment into the bleeding cancellous bone of the bed to create vascular channels. Place 4-8 drill holes across the fragment, targeting the interface between the fragment and the bed. This stimulates fibrovascular ingrowth and promotes bony healing across the fragment-bed junction.

For stable, in-situ lesions treated without fragment displacement, retrograde drilling from the condylar cortex away from the articular surface (through the subchondral bone) may be performed without breaching the cartilage.

Step 8: Final Assessment and Closure

Perform a final arthroscopic visualisation of the fixed fragment. Confirm:

• Anatomical reduction (no step-off, no gap at the fragment edges)
• All hardware fully countersunk below the articular cartilage
• Stable fixation (no fragment movement with probe pressure)
• No loose bodies remaining in any compartment
• Smooth range of motion — flex and extend the knee under direct visualisation to confirm no catching or impingement

Withdraw arthroscopy instruments. Close portal incisions with 4-0 nylon sutures. Apply a sterile compression dressing and hinged knee brace locked in extension.

Open Fixation — Technique

Indications for Open Approach

• Lesion size greater than 3 square cm requiring bone grafting
• Far posterior condyle lesions not accessible arthroscopically
• Fragment with significant bone loss requiring autograft or allograft bone graft to fill the bed
• Failed arthroscopic fixation attempt
• Complex revision fixation with bone loss

Approach

Use a medial parapatellar approach for medial condyle OCD and a lateral parapatellar approach for lateral condyle OCD. Displace the patella laterally or medially. Inspect the lesion directly. The remainder of the fixation technique mirrors the arthroscopic approach — debride the bed, reduce the fragment, place K-wires, insert headless compression screws or bioabsorbable pins, drill for healing stimulation, and confirm the reduction and hardware burial.

In open fixation, bone grafting of the bed is straightforward: pack morsellised cancellous autograft (from the distal femur or proximal tibia) into any cavity between the fragment and the bed before final screw compression.

Postoperative Rehabilitation Protocol

Phase 1: Protected Weight-Bearing (Weeks 0-6)

• Hinged knee brace locked in extension for ambulation — unlock for controlled ROM exercises
• Weight-bearing: toe-touch only (15-20% body weight) for the first 2 weeks, progressing to 50% partial weight-bearing at weeks 2-4, then full weight-bearing by week 6
• Range of motion: begin gentle passive flexion to 90 degrees within the first 2 weeks; progress to full flexion by week 6; maintain full extension from day 1 (no flexion contracture)
• No active quadriceps exercises against resistance — active-assisted and passive only for the first 4 weeks to reduce shear stress on the fixed fragment
• Cryotherapy and elevation to control swelling
• CPM machine (optional): 0-90 degrees for 4-6 hours per day during the first 2-4 weeks — may promote cartilage nutrition

Phase 2: Progressive Loading (Weeks 6-12)

• Full weight-bearing without brace (unless bioabsorbable fixation was used — extend protected weight-bearing to 8-12 weeks for bioabsorbable devices)
• Progressive closed-chain strengthening: mini-squats (0-45 degrees), leg press, stationary cycling
• Open-chain exercises avoided until 12 weeks — they generate shear forces across the femoral condyle fixation site
• Pool-based rehabilitation (buoyancy reduces loading) for proprioception and gait retraining
• No running, jumping, or pivoting activities until at least 4-6 months

Phase 3: Return to Activity (Months 4-9)

• Straight-line running from 4 months if asymptomatic and MRI shows healing
• Sport-specific drills from 5-6 months
• Full return to competitive sport at 6-9 months, guided by clinical examination and repeat MRI confirmation of fragment healing
• Juvenile patients may progress faster (return to sport at 4-6 months) if healing is confirmed on MRI and the physis is still open
• Adult patients generally require 6-9 months before full return to impact sports

Follow-up Imaging

• 6-week radiographs: check screw position, fragment reduction, and early signs of healing
• 3-month radiographs and MRI: assess bony healing across the fragment-bed interface; persistent gap or fluid signal at the interface suggests nonunion
• 6-month MRI: confirm complete healing before clearing return to sport
• 12-month radiographs and MRI: final healing assessment; hardware removal consideration if metal screws are symptomatic or prominent

Salvage Procedures When Fixation Fails

When Fixation Is Not Possible or Fails

If the fragment is unsalvageable (necrotic, fragmented, too small) or if fixation has failed (nonunion, fragmentation), the following salvage options are available, listed in order of lesion size and patient age suitability:

Microfracture (marrow stimulation): suitable for lesions less than 2-3 square cm; produces fibrocartilage fill; first-line salvage for small defects. Best outcomes in younger patients (under 30-35).

Osteochondral autograft transfer (OATS / mosaicplasty): for lesions 1-4 square cm; cylindrical autograft plugs harvested from the non-weight-bearing periphery of the femoral condyle (typically the lateral supracondylar ridge). Provides hyaline cartilage. Donor-site morbidity limits harvest area.

Autologous chondrocyte implantation (ACI): for lesions 2-10 square cm; two-stage procedure (arthroscopic biopsy, then open implantation). Provides hyaline-like cartilage. Expensive, long rehabilitation (12-18 months).

Osteochondral allograft: for large defects (greater than 4 square cm) or failed prior procedures; fresh allograft from a matched donor; risk of disease transmission and graft incorporation failure. Often the best option for very large lesions in young patients when other procedures have failed.