Chondromalacia Patellae

Chondromalacia patellae is softening, fissuring and loss of the articular cartilage of the patella. It is a structural pathologic diagnosis, whereas the clinical presentation of anterior knee pain overlaps with a pain syndrome. Causes: patellar instability or dislocation, direct trauma, malalignment, overload and inflammatory arthritis.

Cartilage damage is graded by arthroscopic or MRI appearance: grade I softening and swelling, grade II fissures under 1.5 cm, grade III fissures over 1.5 cm reaching the subchondral bone (crab meat appearance), and grade IV exposed subchondral bone. Cartilage has no blood supply, so lesions do not heal. Higher grades progress to patellofemoral osteoarthritis. Young patients with focal full thickness defects are at risk of mechanical symptoms.

• Insidious anterior knee pain on stairs, squatting and after sitting, crepitus
• Patellar grind test positive, mild effusion in advanced disease
• Quadriceps wasting
• Red flags: locking from loose cartilage fragments, recurrent effusion, night pain, and instability

• Clinical assessment for pain and crepitus, and exclusion of maltracking.
• Radiographs (skyline view) for joint space narrowing under 3 mm, osteophytes and tilt.
• MRI with cartilage sensitive sequences (fat suppressed proton density, T2 mapping) to grade the lesion and show subchondral edema.
• Arthroscopy for definitive grading when treatment depends on it.

Differentials: patellofemoral pain syndrome, patellar instability, patellar tendinopathy, plica syndrome, meniscal tear, osteochondritis dissecans.

Grades I and II: exercise therapy for 12 weeks, activity modification, weight loss, and paracetamol 1 g orally every 6 hours. Add naproxen 500 mg orally twice daily with food for up to 2 weeks for flares.

Grade III and IV:

• Intra articular triamcinolone 40 mg once for a flare, or hyaluronic acid 20 mg weekly for 3 weeks.
• Arthroscopic debridement for mechanical symptoms from unstable flaps.
• Focal defect 1 to 4 cm2: microfracture (with awl holes 3 to 4 mm apart, 4 mm deep), or osteochondral autograft.
• Larger defect 2 to 10 cm2: autologous chondrocyte implantation or osteochondral allograft.
• Tibial tubercle anteromedialization for distal or lateral lesions with maltracking.
• End stage disease: patellofemoral arthroplasty or total knee replacement.
• Cefazolin 2 g IV before incision. After microfracture or cartilage repair, protected weight bearing for 6 weeks with continuous passive motion.
• Complications: fibrocartilage of poor quality, arthrofibrosis, graft failure, infection.

Follow up at 6 weeks, 3, 6 and 12 months. Counsel on weight control, low impact exercise and the lack of reversal of established damage.