A dislocation of the patella (kneecap) commonly occurs during deceleration, for example when slowing from a run to a walk. The patella slides partially out of the groove between the femoral condoles but does not limit mobility. Pain and swelling may accompany this condition. Athletes who have a muscle imbalance or a structural deformity, such as a high patella, have a higher chance of dislocation.
If the outer muscle of the quadriceps, vast us laterals, is stronger than the inner muscle, vast us medials, the imbalance may cause an uneven tension on the patella, pulling it out of alignment. In addition, the lateral femoral condyle and patella may be bruised. This happens with forceful contractions such as planting, changing direction or landing from a jump.
Cause of injury
Strength imbalance between the outer and inner quadriceps. Impact to the side of the patella. Twisting of the knee.
Signs and symptoms
Feeling of pressure under the patella. Pain and swelling behind the patella. Pain when bending or straightening the knee.
Complications if left unattended
Continued subluxations can cause small fractures in the patella, cartilage tears and put stress on the tendons. Failure to treat a subluxation could lead to chronic subluxations.
RICER. Anti-inflammatory medication.
Rehabilitation and prevention
During rehabilitation activities that do not aggravate the injury should be sought, such as swimming or biking instead of running. Strengthening of vastus medials and stretching vastus laterals will help correct the muscle imbalance that may cause this condition. A brace to hold the patella in p;ace may be needed when initially returning to activity. To prevent subluxations it is important to keep the muscles surrounding the knee strong and flexible and avoid direct impact to the patella.
Rarely surgery may be required to prevent recurring subluxations due to misalignment or instability.