This is the editor's interpretation of a paper published in the orthopaedic literature in 2010 - our attempt to make relevant medical articles accessible to lay readers. A REPRINT WILL BE OBTAINABLE IF YOU ASK YOUR LIBRARY.
The paper is essentially a case report of a patient who at 32 years of age went to the doctors complaining of knee pain which she had experienced for about 10 years. She did not remember any injury to the knees and felt that the knee pain had developed without any particular provocation.
When the knees were X-rayed, it was noted that the tibial plateaux on both sides were flattened, on both sides the tibial spine was absent, and both of the femoral condyles on both knees were poorly developed. MRI scan revealed that the anterior cruciate ligament was absent on both sides, while the posterior cruciate ligament was present in both knee but was abnormal in structure.
During the examination, the doctors also noted incidentally that the patient had scoliosis, with the spine twisted in the chest area, and that both hips were abnormal (showing hip dysplasia, where the ball-and-socket joint was poorly formed and the ball slightly out of position within the socket).
The patient did not want surgery, and was treated conservatively, and on follow up 4 years later things were pretty much the same.
The authors presented the details and used the opportunity to explore the medical literature and discuss the issue of people born without the anterior cruciate ligament - what is known as congenital absence of the ligament.
The authors' discussion
The authors of this paper note that congenital absence of the cruciate ligament is very rare. The absent ligament may be the anterior cruciate ligament, the posterior cruciate ligament or both. The cause appears to be unknown at this time, but as the ligaments usually appear between the 8th and 10th week as an embryo it seems as if something goes wrong at this stage. Several reports in the literature associate congenital absence of the cruciate ligaments with dislocation of the knee in the womb, and the authors' interpretation of the literature is that the dislocation is a result of absence of the ligaments, rather than the cause.
Clearly, the finding of knee dislocation is fairly obvious, but usually the manifestation of absence of the cruciate ligaments is more subtle. The drawing on the right is a representation of a normal knee. The most common indicator on X-ray that something is wrong in the cruciate area is absence or hypoplasia (smaller than normal) of the tibial spine, which is normally seen on X-ray in the middle of the tibial plateau. The tibial spine seems to develop as a result of the normal development of the anterior cruciate ligament, to which it is attached. If the ligament fails to develop, then it seems that the tibial spine fails to develop also. In addition there are often other X-ray hints that something is wrong - the intercondylar notch may be flattened and the rounded condyles at the end of the femur bone incompletely developed and the tibial plateau may be flattened.
Usually the abnormalities are confined to the knee, but there are reports of associated hip dysplasia or scoliosis, and in this case the authors report the uncommon finding of a patient with the knee changes as well as both hip dysplasia and scoliosis.
The authors only briefly go into the management of patients with congenital absence of the cruciates, and basically their recommendation is to manage the problems according to the symptoms.