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The patella or knee cap is an integral part of the quadriceps mechanism. It articulates with the lower end of the femur (thigh bone). Its main action is to improve the mechanical efficiency at the knee by increasing the lever arm of the quadriceps (which is the anti-gravity muscle at the knee). As such it is subjected to high loads. The contact forces in the patello-femoral joint are 4-8 times the body weight.
Because of such loads, disorders of the patello-femoral joint are quite common. These are of two main types: 1) Pain due to cartilage damage or overloading of the extensor mechanism; 2) Instability of the knee cap.
This is also called patello-femoral syndrome, anterior knee pain, runner’s knee or jumper’s knee.
- Pain: The pain occurs in the front of the knee or around the knee cap. This is typically associated with climbing or getting down the stairs: kneeling, squatting or high-impact activities. Pain after a period of rest is very typical.
- Sensation of catching or grating or roughness when patient bends the knee
- Giving way of the knee due to reflex quadriceps inhibition
- Sensation of locking of the knee (pseudo-locking)
- Swelling in the knee (fluid collection or effusion)
- Excessive body weight (obesity)
- Activities: running, jogging, sitting on floor, squatting, kneeling, stair-climbing and high-impact activities
- Muscle imbalance – tight lateral patellar retinaculum
- Mal-alignment of the knee or knee-cap: knock-knee deformity, high or low placement of the knee-cap, torsional deformity (rotational mal-alignment) of the femur and tibia; flat-feet
- Softening or fraying of the cartilage of the knee cap – called chondromalacia patellae
- Inflammation of the attachment of the quadriceps muscle or patellar tendon to the patella (tendinitis)
- Inflammation of fat pad in the front of the knee (occurs rarely)
- In growing children there can be inflammation and fragmentation of the ossification centre (growing end) of the tibial tuberosity (the bony prominence where the patellar tendon attaches). This is called Osgood Schlatter Disease. This is different from the typical patello-femoral pain seen in adults.
- Rest, ice-packs, crepe bandage (compression) and elevation – RICE protocol – especially in case of acute injuries
- Anti-inflammatory medications (NSAIDs)
- Modification of activities: avoid squatting, kneeling, excessive usage of stairs and high-impact exercises
- Use of knee support (brace), proper footwear for running,
- Patellar taping (kinesio tape application usually done by physiotherapist)
- Physiotherapy: ultra-sonic massage, hot packs
- Exercises: to strengthen the quadriceps, especially the inner part; and exercises to stretch tight lateral retinaculum
- Surgery: if there is no relief from the above measures, surgery may be advised. Usually, the loose and frayed cartilage is removed by arthrocsopic surgery. Rarely, surgery may be necessary to correct the tracking of the knee-cap or correct the alignment of the knee.
When the knee cap does not slide correctly in the femoral groove it is called mal-tracking. This can be due to imbalance of the muscle or ligaments (tight lateral retinaculum, high-riding patella) or bony abnormalities (shallow femoral groove, mis-shapen patella, knock-knee deformity or rotational mal-alignment of the thigh-bone or leg-bone).
Dislocation can also occur in a well-aligned knee-cap as a result of injury (typically during contact sports). This is less likely to recur if treated properly. This type of dislocation can be associated with injury to the cartilage of the kneecap or the femur (osteo-chondral fracture) which may require surgery.
Immediate treatment: The immediate treatment of a dislocated knee-cap is reduction. This can be achieved in the majority of cases by pushing the kneecap back into its position with or without anaesthesia.
Traumatic dislocation: Traumatic dislocation in a previously normal knee can be treated by resting in a knee brace or cast for 3-6 weeks. If an osteo-chondral fracture is suspected a CT scan or MRI scan is advised. Large osteo-chondral defects need surgery to re-position the fragment and fix it. In this case, immobilization of the knee may be required for 6 weeks. Extensive tearing of the quadriceps mechanism may also require surgery.
Recurrent Dislocation: In case of recurrent dislocation surgery is required to address the underlying problem. This may require soft tissue procedures, bony procedures or a combination of these.
- Release of tight muscular or fascial bands on the outer side of the kneecap (lateral retinacular release)
- Repair or augmentation of the weak supports on the inner side of the kneecap (vastus medialis obliquus advancement, medial patello-femoral ligament reconstruction)
- In habitual dislocation, the entire quadriceps mechanism needs to be repositioned
- Repositioning of patellar tendon attachment (tibial tuberosity advancement)
- Deepening of the patellar groove (trochleoplasty)
- Correction of knock-knee (angular osteotomy)
- Correction of rotational mal-alignment (derotation osteotomy of femur), etc.
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