Chondromalacia patellae is caused by softening of the cartilage of the patella. This can cause loss of smoothness of the articular cartilage on the posterior side of the patella. Chondromalacia patellae tends to affect 2 age groups: teenagers (especially girls) and those over 40:

• In the older age-group the articular cartilage breaks down as part of the natural ageing process leading to osteoarthritis in the knee.
• In teenagers the articular cartilage "softens" from excessive and uneven pressure on it as a result of structural changes with rapid growth, and muscle imbalance around the knee.

The term chondromalacia patellae is less often used now because confirmation of the diagnosis requires MRI or arthroscopy. The term patellofemoral pain syndrome is therefore more commonly used. Patellofemoral pain syndrome usually responds to physiotherapy treatment and so investigations to confirm the diagnosis are often not required.

Epidemiology

• Chondromalacia patellae is a common cause of knee pain in adolescents and young adults.
• Over half of all cases are bilateral.¹
• Flat feet and hypermobility increase the risk.¹
• Chondromalacia patellae is more common in servicemen in their 20's.

Presentation

See also separate article Knee Assessment (History and Examination).

Symptoms

• Pain along anterior aspect of knee with walking, running, or jumping.
• Anterior pain when getting up from sitting position, going up and down stairs, and when squatting.
• Recurrent effusion, especially after activity.
• May complain of grating or crepitation.
• Rarely, symptoms at rest.

Signs

• Crepitation as the patella is passively moved within the femoral groove.
• Pain and recurrence of symptoms with passive movement of and simultaneous pressure to patella within the femoral groove.
• Q-angle greater than 15° (The Q-angle is a line created from the anterior superior iliac spine to the mid patella and a line from the mid patella to the tibial tubercle when the knee is in full extension. An average Q-angle for a male is 14°, while that for a female is 17°. Q-angles larger than average can indicate abnormal patellar tracking).
• Tenderness on palpation of borders and underside when patella is lifted out of the groove.
• Genu valgum deformity.
• External tibial torsion with external rotation of the tibial tubercle.
• Femoral anteversion combined with external tibial torsion (miserable mal-alignment syndrome).

Investigations

• X-rays may show:
  • Patella alta (elevated patella)
  • Shallow femoral groove
  • Shallow patellar angle
  • Tilting or gliding of patella on "skyline view"
• MRI can give much more detail of soft tissues.²

Differential diagnosis

Other causes of knee pain, e.g.:

• Children and adolescents: Osgood-Schlatter's disease, Jumper's knee (patellar tendonitis), referred pain from slipped capital femoral epiphysis osteochondritis dissecans.
• Adults: trauma: ligamentous sprains (anterior cruciate, medial collateral, lateral collateral); meniscal tear; inflammatory arthropathy (rheumatoid arthritis, Reiter's syndrome); septic arthritis.
• Older adults: osteoarthritis, gout, pseudogout.

Management

• In the early stages conservative treatment is effective. It includes modification of training, patellar taping/strapping techniques, quadriceps strengthening,³ NSAIDs, and rest. A physiotherapist can give advice.
• Modify exercise to eliminate activities which aggravate symptoms. Swimming is non-weight-bearing and exercises the cardiovascular system.
• Taping and strapping techniques can provide relief of pain.
• The quadriceps must be strengthened once the pain has subsided. Muscular imbalance may be the cause of the patellar mal-alignment and building of the appropriate muscles can assist realignment of the patella and reduce or eliminate symptoms with time.
• Orthotic inserts can provide relief if the symptoms result from tibial torsion or femoral anteversion.
• Simply removing the repetitive injury allows healing.

Drugs

• NSAIDs and simple analgesics help to relieve discomfort.

Surgical

If conservative measures fail there are a number of possible surgical procedures:⁴

• Shaving: with early degenerative changes an option is to shave the damaged cartilage down to the normal cartilage underneath and so smooth the gliding surface. The success of the treatment depends on the severity of the cartilage damage.
• Drilling: More localised degeneration might respond better to drilling small holes through the damaged cartilage to facilitate growth of healthy tissue up through the holes from the layers underneath. This procedure has not so far been proved to be effective.

Simply removing damaged cartilage is not enough.⁵ The biomechanical problem needs addressing and there are various procedures to aid re-alignment:

• Tightening of the medial capsule: If the medial capsule is lax it can be tightened to pull the patella back into correct alignment.
• Lateral release:⁶ A very tight lateral capsule will pull the patella laterally. Release of the lateral patellar retinaculum allows the patella to track correctly in the femoral groove.
• Medial shift of the tibial tubercle: Moving the insertion of the quadriceps tendon medially at the tibial tubercle allows the quadriceps to pull the patella more directly and decreases the amount of wear on the underside of the patella.

Other surgical techniques include:

• Removal of a portion of the patella.
• Complete removal of the entire patella is only for the severest cases. Removal of the patella leaves the patient with persistent weakness and quadriceps atrophy.
• The Maquet procedure involves anterior displacement of the tibial tubercle by about 2.5cm and inserting a bony block. This decreases the force on the patella as it passes over the femoral condyles by up to 50% and changes the weight-bearing position of the patella.
• The damaged cartilage is replaced by a polyethylene cap prosthesis. Early results have been good, but eventual wearing of the opposing articular surface is inevitable.

Prognosis

• In the older group there will probably be progression to osteoarthritis.
• In the younger group, if appropriate action is taken at an early stage, exercise adjusted accordingly and the quadricep muscles built up, then the outlook is good. It usually resolves by age 30 years and rarely progresses to osteoarthritis in the young.⁷

Document references

1. al-Rawi Z, Nessan AH; Joint hypermobility in patients with chondromalacia patellae.; Br J Rheumatol. 1997 Dec;36(12):1324-7. [abstract]
2. McCauley TR, Kier R, Lynch KJ, et al; Chondromalacia patellae: diagnosis with MR imaging.; AJR Am J Roentgenol. 1992 Jan;158(1):101-5. [abstract]
3. Desnica Bakrac N; Dynamics of muscle strength improvement during isokinetic rehabilitation of athletes with ACL rupture and chondromalacia patellae.; J Sports Med Phys Fitness. 2003 Mar;43(1):69-74. [abstract]
4. Jensen DB, Albrektsen SB; The natural history of chondromalacia patellae. A 12-year follow-up.; Acta Orthop Belg. 1990;56(2):503-6. [abstract]
5. Vuorinen OP, Paakkala T, Tunturi T, et al; Chondromalacia patellae. Results of operative treatment.; Arch Orthop Trauma Surg. 1985;104(3):175-81. [abstract]
6. Christensen F, Soballe K, Snerum L; Treatment of chondromalacia patellae by lateral retinacular release of the patella.; Clin Orthop Relat Res. 1988 Sep;(234):145-7. [abstract]
7. Bentley G; Anterior knee pain: diagnosis and management.; J R Coll Surg Edinb. 1989;34(6 Suppl):S2-3. [abstract]

Internet and further reading

• Chondromalacia Patellae - MedlinePlus
• Chondromalacia Patellae - Wheeless Textbook

Acknowledgements