Anterior Knee Pain (AKP)

Anterior knee pain refers to knee pain caused by anatomical structures in front part of the knee. AKP is a very common condition affecting high performance athletes and low demand patients.

Clinical presentation

It is more prevalent in females and starts as early as 2nd decade. Usually both knees are affected and is characterised by pain when patient sits with knees bent (cinema sign), stair climbing and with any running or jumping exercises or sport. In severe cases the knee can start to swell.

Basic anatomy

The patella (kneecap), quadriceps tendon (tendon that attaches the thigh muscle to upper pole of the patella),patellar tendon ( tendon between lower pole of patella and shin bone attachment (tibial tuberosity) and synovial plica (folds of the cell lining of the joint capsule) are the anatomical structures that cause anterior knee pain.

The most common causes are:

Softening and overload of patella chondral cartilage (used to be called chondromalacia).

Fragmentation and damage of the chondral cartilage on the under surface of the patella (kneecap) or femoral surface of the femur (trochlea).

Patellar tendinitis (runner’s or jumper’s knee)

Quadriceps tendinitis

Synovial plica impingement (pinched or swollen synovial cell lining).

Basic biomechanics

The kneecap (patella) sits over the front of the knee joint. As the knee flex from extension (bend or straighten), the underside of the patella glides into its groove (trochlea) in between the 2 condyles of the femur (thigh bone)

It has a relatively short excursion in the trochlea, but high forces are generated, especially in deceleration with heel strike. This is when the quadriceps (thigh muscle) tendon eccentrically contracts causing resultant forces over the kneecap joint cartilage.

When the forces exceed the critical load of kneecap cartilage it will start to cause breakdown collagen matrix and fragmentation the knee will start to hurt even before permanent cartilage damage occur.

Causes for cartilage overload

The kneecap in an abnormal position (too high or not central) (abnormal tracking of kneecap) Weakness of the muscles on the front and back of your thigh especially controlling deceleration as in walking down hill or down stairs Weak hip or trunk control leads to increase loads at kneecap joint

Conservative treatment options

Decrease the load on the kneecap joint by adjusting activities (change sport if possible) Core muscle training program Training program to strengthen Quadriceps muscle, focussing on eccentric training.

Surgical treatment options

Smoothing of the kneecap cartilage in cases where there is severe fragmentation with arthroscopic instruments, can bring improvement of symptoms in certain cases. But this procedure must be combined with a dedicated exercise program.

Adjustment of kneecap alignment by repositioning can deliver good results in patients with abnormal tracking or positioning of the kneecap.

In patients where overhang (lateral facet osteophyte) of the kneecap have developed, removal of that extra bone can lead to improvement in symptoms.

Kneecap replacements should be reserved for very specific indications due to the lack of favourable results of long term survival.