Unilateral aplasia of both cruciate ligaments
© Balke et al; licensee BioMed Central Ltd. 2010
Received: 26 October 2009
Accepted: 25 February 2010
Published: 25 February 2010
Aplasia of both cruciate ligaments is a rare congenital disorder. A 28-year-old male presented with pain and the feeling of instability of his right knee after trauma. The provided MRI and previous arthroscopy reports did not indicate any abnormalities except cruciate ligament tears. He was referred to us for reconstruction of both cruciate ligaments. The patient again underwent arthroscopy which revealed a hypoplasia of the medial trochlea and an extremely narrow intercondylar notch. The tibia revealed a missing anterior cruciate ligament (ACL) footprint and a single bump with a complete coverage with articular cartilage. There was no room for an ACL graft. A posterior cruciate ligament could not be identified. The procedure was ended since a ligament reconstruction did not appear reasonable. A significant notch plasty if not a partial resection of the condyles would have been necessary to implant a ligament graft. It is most likely that this would not lead to good knee stability. If the surgeon would have retrieved the contralateral hamstrings at the beginning of the planned ligament reconstruction a significant damage would have occurred to the patient. Even in seemingly clear diagnostic findings the arthroscopic surgeon should take this rare abdnormality into consideration and be familiar with the respective radiological findings. We refer the abnormal finding of only one tibial spine to as the "dromedar-sign" as opposed to the two (medial and a lateral) tibial spines in a normal knee. This may be used as a hint for aplasia of the cruciate ligaments.
Aplasia of the cruciate ligaments is a very rare congenital pathology which was first described in 1956 by Giorgi as part of a radiographic study . It is typically associated with other congenital musculoskeletal disorders such as absent radius syndrome , congenital meniscal malformations [3–5] and most commonly with longitudinal deficiencies of the lower limbs (e.g. congenital short femur, and aplasia of the fibula or patella) [6–10]. Malformations of the cruciate ligaments can either affect the anterior cruciate ligament (ACL) only or both cruciate ligaments [11–15]. The deficiency can occur unilaterally [4, 5, 7, 9, 16–20] or affect both knee joints [6, 13, 14, 17]. We report on a patient with unilateral aplasia of both cruciate ligaments and point out the diagnostic pitfalls that possibly lead to therapeutic mistakes.
On clinical exam he had a free range of motion, no swelling and a slight valgus alignment. He had a positive posterior sag at 90° of flexion and a reduced medial step off when compared to the other side. His Lachman test was severely abnormal without a firm endpoint, pivot shift was slightly positive. His total anteroposterior laxity when measured with the Rolimeter (Aircast, Don Joy, Inc) was 6 mm and 22 mm with a resulting side difference of 16 mm. His collateral ligaments were stable. His further history revealed a status post medial growth plate closure at the medial femoral condyle at the age of 12 for a significant leg length discrepancy and a syndactylia of the second and third toe of his right foot.
Due to the clinical, surgical and MRI findings the patient was scheduled to undergo ACL and PCL reconstruction.
The patient was further treated conservatively and did well at a reduced activity level at last follow up.
There are only few reports about aplasia or hypoplasia of the cruciate ligaments in the literature. Since patients are usually adapted to the congenital anatomy of their knee joints [3, 14, 15] laxity is most likely a coincidental finding after trauma [6, 13, 14]. Usually patients do not complain of instability, although clinical tests (e.g. Lachman, anterior/posterior drawer) are highly positive for ligament insufficiency [12, 21–23]. The physician has to differentiate between objective laxity (positive tests for ligament insufficiency) and the subjective feeling of instability which is rarely reported by the patient.
Several radiological signs indicate aplasia of the cruciate ligaments. Common findings include hypoplasia of the tibial eminence [10, 23, 24], a hypoplastic lateral femoral condyle  and a narrow intercondylar notch [1, 16].
Manner et al. recently published a study on the typical radiological findings of patients with arthroscopically proven aplasia of the cruciate ligaments . They evaluated the associated pathological findings on MRI and tunnel view radiographs inaugurating a three stage classification system. According to their results the differentiation between trauma and aplasia of one or both cruciate ligaments may be made on plain radiographs according to differences in the notch width index, notch hight and changes in the lateral and/or medial tibial spine .
Our case demonstrates that the correct diagnosis may be missed in the clinical setup if a trauma is reported in the history and the contralateral knee is normal. A misleading information in this case was the previous arthroscopy report in which the specific finding of a severe notch deformity was not indicated. Also the external MRI report did not outline a deformity of the notch or the tibial spine. If the surgeon would have retrieved the contralateral hamstrings at the beginning of the planned ligament reconstruction procedure a significant damage would have occurred to the patient.
The history of the patient about his early childhood revealed on a more closer look that there were signs of congenital abnormalities suggesting other abnormalities in the symptomatic knee.
In the literature therapeutical options are discussed controversially. Some authors report good results after ACL reconstruction and consider ligament insufficiency as a mechanical problem responsible for instability [3, 12, 13]. Others prefer conservative treatment with physiotherapy and muscular training [7, 11, 15, 21, 23]. If surgical treatment is taken into consideration, it should include reconstruction of both ligaments, since reconstruction of the ACL alone results in posterior subluxation of the tibia and a fixed posterior drawer causing decreased knee extension and anterior knee pain [22, 25].
Ligament reconstruction in a case as described is technically hardly possible since there is no room in the knee for an additional ligament. A significant notch plasty if not a partial resection of one of the condyles would have been necessary to implant a cruciate ligament graft. However as this would be an absolutely arbitrary procedure it is most likely that this would not lead to a good knee stability.
Even in seemingly clear diagnostic findings the arthroscopic surgeon should take this rare abnormality into consideration and be familiar with the respective radiological findings.
Written informed consent was obtained from the patient for publication of this case report and any accompanying images.
Sincere thanks go to Maryam Balke, MD, for critical review and correction of the manuscript.
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