chapter 8: Patellar Tilt‑Compression and the Excessive Lateral Pressure Syndrome (ELPS)
There are many reasons to believe that the lateral retinaculum causes and perpetuates many patellofemoral problems. There are several ways in which this may come about. First, we will develop the arguments for implicating the lateral soft‑tissue structures.
Many cases of ELPS demonstrate a clear difference in transverse passive movement. In these cases, the lateral retinaculum can be palpated and found to be thickened, indurated, and retracted. In these forms, the diagnosis, when searched for systematically, is not difficult. However, more frequently, the lateralizing forces of the lateral retinaculum are brought into play only during flexion and extension. In these cases, the transverse "play" in full extension may be normal. Flexion, however, results in excessive tightening of lateral soft‑tissue structures as the patella is brought into and over the trochlea. This may escape clinical detection but is evident in other aspects of the complete evaluation. Careful evaluation of lateral "tether" by elevating the lateral facet manually, as described by Kolowich (4), may be the most reliable clinical test for tilt (Fig. 8.14).
The dysplasias nearly always show evidence of excessive lateral modulating forces during skeletal development; lateral predominance (Wiberg Type III, Baumgartl type, and so on) single lateral facet, half‑moon patella, and congenital dislocation with secondary valgus deformity of the knee are examples. Autopsy studies (16‑18) show ulceration of patellar cartilage to be centered on the median ridge and the lateral facet, indicating that this is the localization for the effect of excessive forces. (The findings of surface changes elsewhere in the joint are not an argument against predominantly lateral excessive pressure.)
The direct evidence comes from specimens removed at surgery. If the lateral retinaculum is found to be tender preoperatively, the histology may show evidence of small nerve fibrosis.
This has been largely developed under the section on radiologic features. One aspect is worth developing here. Questions concerning the origin and natural history of bipartite patella are at the center of our subject. It is now generally accepted that the patella ossifies from a single center. Bipartite patella may be a type of stress fracture, with failure to reunite, or it may be the pathologic development of a secondary center, also under the influence of excessive stress. Of the bipartite patellae, 90% are localized to the superolateral corner of the patella, at the tendinous insertion of the vastus lateralis. Tripartite patella is rare, but those that we have seen have shown the second fragment to be localized to the inferolateral border of the patella in the region of the insertion from the fascia lata.
Rohlederer (19) supported this etiologic consideration when he reported a case of fusion of the bipartite fragment to the rest of the patella after simple release of the lateral retinaculum. It would be difficult to conceive a more elegant experimental situation to lend support to these concepts. Moreover, the development of a bipartite fragment may represent a method of reduction of the excess lateral pressure during growth. It is certain that many, if not most, bipartite patellae remain asymptomatic, only to be revealed at the time of injury or fortuitously by radiographs for other reasons. The nonrandom anatomic distribution of the bipartite and tripartite fragments seems to us to argue strongly in favor of mechanical factors in their production.
Confronted with a patient who has patellofemoral clinical, physical, and radiologic findings suggesting pain and tilt‑compression syndrome, the clinician may seek confirmation of the concept at the operating room table. Figure 8.15 shows the spontaneous separation of the lateral retinaculum with the knee in full extension. It has not been uncommon to observe a separation of 1.5 cm with the knee flexed to 90 degrees. The dynamic test for lateral tension is to reattach the lateral retinaculum, once it has been released, with a single 2‑0 suture. Upon flexing the knee to 90 degrees, the suture will normally hold unless there is excessive tension in the lateral retinaculum. Under this excessive tension, the suture will either break or pull out of the soft tissue. These observations confirm the considerable tension that can develop in these lateral structures. In the majority of cases, excessive retinacular tension is a major factor contributing to ELPS.
"The proof of the pudding is in the eating," said Don Quixote. The final argument is the most convincing. By relieving excessive lateral tension through surgical section of the lateral retinaculum, without any other surgical maneuver, it is possible to relieve many patients of their symptoms. Also, CT of patient patellofemoral joints before and after lateral release for patellar tilt shows that abnormal tilt is usually reversed to normal alignment (20), which again supports the belief that a tight lateral retinaculum causes and perpetuates patellar tilt. After considering all of the evidence, the clinician is led to the conviction that excessive tension in the lateral retinaculum is, indeed, a major contributing factor in most cases of ELPS.
Inside Chapter 8: