1. PATELLA SUBLUXATION

This condition usually presents itself in the adolescent especially in those individuals who perform sporting activities. Patella subluxation indicates a tendency of the patella (kneecap) to loose track and dislodge outwards. However, these episodes only last for a split second after which the patella usually falls back into its groove. Patients often experience a sharp and intense pain and significant knee swelling may occur within minutes.

Patella instability may be due to a variety of reasons, which can be either dynamic or static. Dynamic problems include muscle or ligament weakness and imbalance, patella mal-alignment and gait abnormalities. Static or structural problems relate to bony deformities of either patella or femur. An abnormally flat groove (trochlea hypoplasia), a malformed patella and/or a patella which is sitting to far up on the femur (patella alta) are structural problems which create an unfavourable environment frequently leading to symptoms of patella instability. If the patella appears to displace frequently it is quite likely that the patients suffers from any of the aforementioned abnormalities. The clinician classifies such patients as 'habitual dislocators'.

It is important to perform a thorough examination and assessment, which should always include radiographs of the patello-femoral joint. Lateral, as well as skyline or Merchant views are often sufficient in providing the clinician with baseline measurements like patella height and positioning and trochlea configuration. Sometime additional investigations such as MRI or CT scans are required. Especially dynamic CT scans often helpful in determining the reasons for the patella subluxation, as they not only demonstrate any structural deformities but also highlight possible mal-tracking or patella tilt.

Depending on the patients age different types of surgical procedures have been proposed. Due to the difference in patients and the variety of abnormalities, a cookbook approach should be avoided in favour of individually tailored treatment. Care should be taken to advise all patients of the possible long-term problems relating to such surgical procedures as the outcome may sometimes be unpredictable. Recovery time can take up to 18 months depending on the degree of malformation and the extent of surgery. Procedures may involve soft-tissue re-alignment and reefing, patella-tendon re-routing (Roux-Golthwait), tibial tuberositas transfers (Elmslie-Trillat, Fulkerson), trochlear plasty (Albee), patella osteotomy (Deliss) and patella distalisation. It is beyond the scope of this site to detail all of these procedures in detail and the reader is referred to the classic textbooks on this topic (Fox, DelPizzo 'The patello-femoral joint' McGraw-Hill 1993, Fulkerson 'Disorders of the Patello-Femoral Joint' Williams & Wilkins 2003). The reader may also look at 'PATELLA MAL-ALIGNMENT' in the section 'KNEE PAIN IN ADULTS' and at 'PATELLA RE-ALIGNMENT SURGERY' in the section 'KNEE SURGERY EXPLAINED'.

2. PATELLA DISLOCATION

Occasionally the patella may not get back on its own and remain dislocated on the outer aspect of the knee. In these circumstances, medical help should be sought immediately to reduce the patella. In these circumstances the clinician will most likely place the leg into a long leg cylinder cast keeping the knee straight for 2 to 4 weeks to allow healing of any torn soft tissues.