chapter 10: Patellar Dislocation
Treatment of permanent patellar dislocation is difficult, and simple extensor mechanism realignment (proximal, distal or both) is frequently insufficient. Often, there is significant degenerative change that further complicates treatment, particularly in older patients (Fig. 10.13).
In both the congenital and acquired forms of permanent dislocation, the main problem is an abnormal fibrotic band attaching to the superolateral aspect of the patella. The treatment for both of these conditions, when they involve dislocation of the patella, is rectus femoris lengthening, extensive lateral release, medial imbrication, and patellar tendon transfer. Gao et al noted 87.8% satisfactory results in 35 children treated in this manner (74). Langenskiold and Ritsila (75) have also noted favorable results following operative treatment of this condition in young people. Surgery is most successful in children with minimal degenerative change.
TECHNIQUE (FIG. 10.14)
A long anterolateral incision is necessary to explore all the factors that may potentially be involved. The incision should extend along the distal third of the thigh to the tibial tubercle, passing the patella at the level of the lateral condyle. Avoid making the incision too far lateral so that any procedures to reinforce the medial patellar structures can be carried out through the same incision. A long midline incision may be used if desired. After the superficial fascia has been incised, the following structures are systematically explored.
Fascia Lata. Frequently, an abnormal band is encountered attached to the superolateral corner of the patella. In any event, the normal fibers attached to the inferior third of the patella and the patellar tendon will require release to allow reposition. Some authors (44, 59) also recommend sectioning the iliotibial tract, which is inevitably tight and seems to fix the tibia in external rotation.
Vastus Lateralis. A thickened tendinous insertion into the superolateral corner of the patella may be concealed by overlying muscle fibers, in which case the insertion must be sought. It, too, is divided. Sometimes, the muscle itself appears diffusely fibrotic. In these cases, the vastus lateralis must be dissected free of the lateral and superior borders of the patella and the lateral border of the rectus femoris.
Rectus Femoris. Direct involvement is much less frequent, although secondary contracture frequently makes Z‑plasty lengthening necessary. It should be sutured under some tension, with the knee flexed 90 degrees. The vastus lateralis insertion may be used to reinforce the repair.
Synovium. The synovium may also be contracted or fibrosed to the lateral condyle, in which case release or even limited synovectomy may be required.
Each level of the release is determined by restriction of passive knee flexion and, in many cases, only limited releases are necessary. It is possible that even after sufficient lateral and superior release, the patella will be unstable because of insufficient development of the lateral condyle or trochlear sulcus. In this case, a medial restraint must be constructed. Possibilities include imbricating the medial retinaculum, advancement of the vastus medialis along the medial patellar border, and transposition of the sartorius into the medial patellar border. When the patient is skeletally mature, direct medial transfer of the tibial tubercle, using the Cox (51) modification of the Trillat procedure, may be very helpful.
If the condition is due to fibrosis of the vastus lateralis and/or intermedius due to multiple intramuscular injections in childhood, the actual fibrotic element may be well proximal to the knee. This can usually be determined on physical examination, in which case the fibrotic area is approached through a middle and proximal thigh, midlateral longitudinal incision, releasing the vastus lateralis and intermedius where indicated from their femoral and intermuscular septum origins. The degree of release and progression of the exploration to involve factors previously reviewed depends upon the achievement of flexion and proper tracking of the patella.
Postoperative management is a crucial phase of the treatment. The leg is placed in 90 degrees of flexion and immobilized in a Jones dressing with splints for several days. When the leg becomes comfortable, this is changed to a hinged long leg knee brace with extension stop at 0 degrees and flexion stop at 90 degrees. Continuous passive motion may be used selectively, but all patients are instructed in passive range of motion exercise. Active quadriceps exercise should generally be started early, if the repair will tolerate it. Satisfactory results (Fig. 10.15) can be anticipated, but if the quadriceps is lengthened, 6 months may be required to achieve active extension (64).
Chapter update 2010 (See references 76-88)
While the basic philosophy remains the same, it is important now to address the importance and proper place of medial patellofemoral ligament(MPFL) reconstruction. Tendon graft reconstruction of the MPFL is important when the medial support structure of the PF joint, including the MPFL, is deficient such that imbrication or advancement of this medial support structure is not likely to provide adequate restoration of support. In many patients, restoration of balance is most important, before restoring medial retinacular structure, whether by imbrication, advancement or reconstruction with tendon graft. In other words, retinacular structure alone should be viewed as passive support with limited, albeit important active function in aligning the PF joint. Attempting to alter patella tracking by forceful retinacular tethering or reduction to the central trochlea of a malaligned extensor mechanism using a medial tendon graft is likely to cause articular overload and permanent damage..
When articular damage is present, articular resurfacing makes sense in some patients at the time of restoring balance and retinacular integrity
The medial retinacular structures do heal (Reference 88), such that imbrication or advancement, after restoring balance of the extensor mechanism, makes sense.
Again, the emphasis here is to address extensor mechanism balance first, thus using, core stability training, orthotics, and tubercle transfer as needed to provide a balanced extensor mechanism, and then bring back retinacular restraints using what is needed, including imbrication or tendon graft MPFL reconstruction (Figure 10.16) selectively to maintain proper patella balance in the trochlea throughout range of motion, and during activity. Using this approach, trochleoplasty is very rarely necessary, as it does cause permanent articular damage. Nonetheless, we should look to further results of trochleoplasty in the hands of those who are stuying it. Verdonk’s results have shown mostly fair and poor results after trochleoplasty (89)
Inside Chapter 10: