In this paper its authors review the literature up to 2015 about dislocation of the patella. They note that patellar dislocation comprises 2-3% of knee injuries, and is the commonest cause of sudden bleeding into the joint (haemarthrosis in children) and the second commonest in adolescents after anterior cruciate ligament injury. In these injuries the patella usually pops out on the outer or lateral side, and 90% of them result in tearing of the medial patellofemoral ligament (MPFL). The injury does not respect gender, and usually occurs in young active individuals, peaking between 10-20 years of age and the first incident most commonly occurs in relation to sporting activities.
In combing the literature the investigators focused upon a number of relevant questions. The first of these was whether or not surgery to repair any damage shoud be undertaken after the first dislocation episode.
Should surgery be undertaken routinely after a first patellar dislocation?
After considering a number of studies, including a 2011 Cochrane Review, they note that most patients with a first-time patellar dislocation should be treated conservatively, ie without surgery, except if there are associated bony fractures.
What are the underlying risk factors for first-time dislocation of the patella?
The authors then turned their attention to identifying underlying risk factors for first-time dislocation. Despite choosing not to operate in most first-time dislocators, the literature advises that the patient be thoroughly investigated for those underlying anatomical factors that might have predisposed the person to such an incident. This usually involves MRI scanning. The following problems should be looked for:
Trochlear Dysplasia
In this condition there is an anomaly in the shape of the upper part of the groove of the femur where the patella normally rides. The authors describe the variations of the condition and also the various measurements on MRI that determine the extent of the problem. They offer a number of useful images of MRI in their discussion.
Patella alta
Increased TT-TG distance
Torsional abnormalities of femur and tibia.
Knock-knees (valgus deformity)
MPFL damage
There follows an unusual discussion of the investigation of the MPFL to determine the site and extent of any MPFL damage. MRI can help to determine if the MPFL is injured either with a partial tear or a full rupture, and whether the damage is more on the femoral side of the ligament or the patellar side.
Surgical treatment options
If the problem becomes recurrent, there are a number of options offered in the literature regarding surgical management. The authors point out that 'reefing' of the medial soft tissues and 'release' of the lateral retinaculum are no longer considered to be good treatment, primarily because the lateral release itself my lead to a secondary instability of the patella. Instead, surgeons are nowadays offering:
Medial Patellofemoral Ligament Repair
Repair or reconstruction of the MPFL would only be recommended if any underlying anatomical factors were minor. The authors note that repair instead of reconstruction of the MPFL is recommended in youngsters who still have open growth plates, as the femoral insertion of the ligament is in the region of the growth plate. For a repair, suture anchors might be used if the ruptures were near the bone, or ordinary sutures used if the ruptures were within the main substance of the ligament.
Medial Patellofemoral Ligament Reconstruction
The decision to undertake MPFL reconstruction should, according to the authors, be taken only after careful consideration of age and underlying anatomical issues. The graft is harvested from the patient's own gracilis, semitendinosus, quadriceps or patellar tendon and occasionally the distal adductor magnus tendon may be used, which they suggest has less morbidity (damage to the patient).
Tibial Tuberosity Transfer
Tibial tuberosity transfer (TTT) should be considered if is indicated in the presence of a pathologically increased TT-TG distance.
Trochleoplasty
Trochleoplasty is indicated for marked trochlear dysplasia, and is usually combined with an MPFL reconstruction.
