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 Table of Contents  
Year : 2016  |  Volume : 2  |  Issue : 1  |  Page : 48-54

Defining patho-anatomy of the knee in congenital longitudinal lower limb deficiencies

Department of Orthopaedics, Sheffield Children's Hospital, Sheffield S10 2TH, UK

Date of Submission22-Mar-2016
Date of Acceptance03-May-2016
Date of Web Publication17-May-2016

Correspondence Address:
Caroline M Blakey
Department of Orthopaedics, Sheffield Children's Hospital, Western Bank, Sheffield S10 2TH
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2455-3719.182576

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Context: The osseous and soft tissue anatomy of the knee in congenital longitudinal lower limb deficiencies is important to consider, both in limb lengthening procedures and in soft tissue reconstruction.
Aims: Our study aims to further define the patho-anatomy of the knee in this group of patients.
Methods and Material: 24 children were reviewed clinically and radiologically. Osseous and soft tissue anatomy is described including MR imaging of 27 affected knees.
Results: Our results echoed those of previous authors, with dysplasia of the menisci and cruciate ligaments a frequent finding. However, the study demonstrated that a clear correlation between the osseous anatomy and soft tissue findings was not always seen.
Conclusions: MRI allows assessment of the cartilaginous epiphysis in younger children with longitudinal dysplasia and we would recommend systematic assessment of the knee prior to any surgical intervention.

Keywords: Congenital short femur, cruciate insufficiency, fibula hemimelia, knee, proximal focal femoral deficiency

How to cite this article:
Saldanha KA, Blakey CM, Broadley P, Fernandes JA. Defining patho-anatomy of the knee in congenital longitudinal lower limb deficiencies. J Limb Lengthen Reconstr 2016;2:48-54

How to cite this URL:
Saldanha KA, Blakey CM, Broadley P, Fernandes JA. Defining patho-anatomy of the knee in congenital longitudinal lower limb deficiencies. J Limb Lengthen Reconstr [serial online] 2016 [cited 2020 Jun 4];2:48-54. Available from: http://www.jlimblengthrecon.org/text.asp?2016/2/1/48/182576

  Introduction Top

The association between longitudinal deficiencies of the lower limb and dysplasia of the knee is well-described. Previous studies have explored both the clinical and arthroscopic findings in this group of patients. [1],[2],[3],[4],[5],[6] In 2005, Manner et al. proposed a radiographic classification of three osseous configurations, correlating radiographs with the magnetic resonance appearance of the cruciates in 34 knees. [7] A more recent publication describes the imaging of five patients with fibular hemimelia extending to abnormalities of the meniscus and posterolateral corner. [8] Magnetic resonance imaging (MRI) has the advantage of delineating the important soft tissue anatomy while remaining noninvasive.

Our study aims to further define the pathoanatomy of the knee in this interesting group of patients. We include MRI findings across the spectrum of congenital lower limb longitudinal deficiencies, fibular hemimelia, proximal focal femoral deficiencies, and congenital short femur occurring in isolation but also frequently in combination. This rare group of disorders includes not only deficiencies of bone but also anomalies of muscles, ligaments, and articular geometry, and management of these conditions can be difficult. In higher functioning individuals, congenital absence of the cruciate ligaments is often well-tolerated; however, cruciate reconstruction is described. [9] In those more severely affected, whereas previously ablative reconstruction was mainstay, as limb reconstruction techniques advance we also learn more about the associated complications. Among these, joint subluxations and dislocations can significantly affect the final outcome. We have seen this in our own unit with experience of more than 120 limb-lengthening procedures in children with longitudinal deficiencies, and this correlates with experience in other parts of the world. [2],[3],[4],[10],[11],[12],[13]

Defining the anatomy and its correlation with clinical symptoms is important to guide reconstruction but also to aid in the discussion of prognosis for children with congenital longitudinal lower limb deficiencies.

  Patients and Methods Top

A database of children with complex limb deformities, treated in our unit, has been prospectively collected since 1980. From this database, we have been able to identify a cohort of 325 children with a longitudinal deficiency of the lower limb reviewed under our care. Search terms included longitudinal deficiency, congenital short femur, proximal focal femoral deficiency, tibial, and fibular hemimelia. Our radiology information database (radiology information system) was used to identify which of these children have had MRI of the affected knee to allow inclusion in the study. A total of 27 knees in 24 children were identified. All were children who had imaging as part of routine workup prior to lengthening procedures.

Basic demographic information was collated. Clinical findings on presentation were reviewed from case notes. These included the presence of symptoms relating to knee stability and findings of clinical laxity. Specific clinical tests included an anterior and posterior drawer, Lachman's test, and varus and valgus stress tests. Findings were compared to the contralateral knee, except in bilateral cases.

Plain radiography was available for all patients and deficiencies were classified accordingly.

Aitken designated femoral deficiencies into four groups based on the relationship between the acetabulum and the proximal end of the femur. [14] Class A is the least severe type where the femoral head is present and attached to the shaft by the cartilaginous neck which later ossifies. The femur is short. Occasionally a subtrochanteric pseudarthrosis can form defining Class A Type 2, a subdivision later included by Amstutz and Wilson. [15] In Class B, no osseous connection is seen between the head and the shaft, but the acetabulum remains adequate and contains the cartilaginous femoral head. The femoral segment is bulbous, distinct from the Class C where it has a tapered proximal end. In Class C, the acetabulum is severely dysplastic and no longer adequate, the femoral head is small or absent. Class D is the most severe with a complete absence of the acetabulum and proximal femur [Figure 1].
Figure 1: Aitken classification of proximal focal femoral deficiencies (A1) The femoral head may ossify late but it's presence is indicated by a well developed acetabulum. A subtrochanteric defect will also later ossify providing bony continuity. (A2) Occasionally a subtrochanteric pseudarthosis develops. (B) There is no cartilaginous connection between the head and the shaft of the femur and as such no bony continuity will develop. The acetabulum remains well formed due to the presence of the femoral head. (C) The actebulum is severely dysplastic and the femoral head is small or fails to develop. (D) There is severe shortening, the entire proximal femur fails to develop with a tapered tuft of bone proximal to the distal femoral epiphysis only

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Achterman and Kalamchi described fibular deficiencies, assessing the deformity according to the residual fibula length. [16] In Type 1, some fibula is present and can be subdivided into (a) mild proximal hypoplasia with intact ankle mortise or (b) 30-50% of proximal fibula absence with a dysplastic or absent ankle mortise. In Type 2, there is a complete absence of the fibula [Figure 2].
Figure 2: Achterman and Kalamchi classification of fibular deficiencies. (1A) Mild proximal hypoplasia with intact ankle mortise (1B) 30-50% of proximal fibula absence with a dysplastic or absent ankle mortise. (2) Complete absence of the fibula

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MRI was used to assess the anatomy of each knee. Osseous and ligamentous structures were defined as absent, hypoplastic, or normal. Abnormalities of the menisci were documented including the shape and position of each. These observations were made with the help of an experienced pediatric musculoskeletal radiologist. All scans were performed on a GE 1.5T Signa HDX Scanner (Siemens, Germany). The standard MRI protocol included FS PD sagittal, coronal, and axial sequences. Films prior to 2007 were scanned hard copy films, after this date digital imaging had been introduced in our unit.

  Results Top

There were a total of 27 knees (24 children) in our cohort, 8 girls and 16 boys. The mean age at the time of imaging was 12 years and 9 months (range: 1-14). Nine knees in seven children had predominantly femoral deficiencies and were all Type A Aitken. The remainder had predominantly fibular deficiencies. Eleven children had Achterman and Kalmachi Type Ia fibular hemimelia, and 7 had Type II fibular hemimelia. Among the 11 children with Type Ia fibular hemimelia, 6 also had mild congenital short femur. The femur was affected in four of the children with Type II hemimelia.

In only one patient were symptoms of instability of the knee documented. Documentation of the knee examination was available in ten knees. In all, there was found to be some degree of laxity in the sagittal plane. All affected knees demonstrated valgus deformity and laxity in valgus stress of varying degrees.

Collateral ligaments were present in all knees. The lateral collateral ligament was found even in those cases of fibular hemimelia in which entire proximal fibula was absent. The distal attachment of lateral collateral ligament in these cases was to the lateral soft tissues including the deep fascia (iliotibial tract) and intermuscular septae of the lower leg.

The medial and lateral meniscus were normal in 19 and 16 knees, respectively. The posterior horn of lateral meniscus was found to be small in one. In 6 knees, both menisci were found to be hypoplastic. The medial and lateral menisci were found to be anteriorly united in 1 knee.

With regards to the osseous anatomy, the intercondylar notch was found to be absent in four knees and hypoplastic in nine. In these knees, both anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were also absent except in two cases where there was severe hypoplasia. The intercondylar notch was normal in 13 knees. Tibial spines were found to be absent in four knees and hypoplastic in ten. In these knees, the ACL was again either absent or hypoplastic in all but one case.

Full results of radiological findings are presented in [Table 1].
Table 1: Radiological results

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  Discussion Top

The presented study adds to current literature regarding the clinical, radiographic, and MRI findings in this rare condition. Since the inclusion criteria looked only at those children undergoing MRI as a part of their routine clinical workup, findings are heavily biased toward this group; however, it remains important that we continue to define the anatomy of the dysplastic knee.

The outcome of limb reconstruction in affected children can be markedly reduced if stability of the knee is not considered. Joint subluxation or dislocation is not infrequently reported with limb lengthening procedures. [10],[11],[12],[13],[17],[18],[19],[20],[21] Factors contributing to instability are important to define before embarking on extensive surgical reconstruction. The prevalence of joint subluxation has been reported between 3% and 7% for leg lengthening. [19] Congenital deficiency plays a significant role, exacerbated by imbalanced muscle tensioning during distraction. [22] In a study of femoral lengthening using the Wagner technique, seven out of 31 patients with leg length inequality suffered knee dislocations as a complication of femoral lengthening. [10] All seven dislocations occurred in those patients in whom the cause of leg length inequality was congenital femoral hypoplasia. A more recent series reported joint subluxation in 33% of congenital short femur lengthenings. [17] In those with abnormalities of primary and secondary restraints, the risk of knee subluxation can be reduced by protecting the joint with spanning external fixation and appropriate soft tissue release. [22] Subluxation despite the extension of the frame has been reported and the soft tissue release is critical. [17] Clinical examination identifies preoperative contracture and the muscles to be addressed. Posterior and posterolateral subluxation of the knee is most frequently seen secondary to the pull of the hamstrings and fascia lata. [22]

Manner et al. presented a valuable study comparing the osseous anatomy with MRI findings in a relatively large group of patients. [7] They suggest that the cruciate insufficiency may be predicted by plain radiography, in particular by the tunnel view. The age of patients in their series ranged from 7 to 24 with a mean age of 13. Plain radiography is of limited value in assessing the development of the articular geometry before bony maturity. Although the lateral and medial edges of femoral intercondylar fossa and the two tubercles (tibial spines) of the tibial intercondylar eminence just begin to appear at around 8 years in male and 6.2 years in female, differentiation of the tubercles of tibial intercondylar eminence and femoral intercondylar fossa only become clear by the age of 13 years in male and 10 years in female. Differentiation continues until a complete epiphyseal-diaphyseal fusion occurs. [23] Evaluating the dimensions of articulating ends of the femur and tibia directly from the MRI scans allows assessment of the actual cartilaginous epiphysis rather than just the ossified portion seen on the plain radiographs. Our results largely echoed those of previous authors. [7],[8] The intercondylar notch tended to be hypoplastic or absent where there was cruciate dysplasia, but we were unable to classify our patients into as well-defined groups as that proposed by Manner et al. [7] This was primarily demonstrated by three cases in which the intercondylar notch was normal despite ACL deficiency, and in one case, where the ACL was found to be normal in the presence of a severely shallow notch. Although we did not evaluate specific tunnel views, we would recommend systematic assessment of knee using MRI scan prior to any lengthening procedures in longitudinal deficiency, particularly in the skeletally immature.

In our series, only one child was documented to complain of symptomatic knee instability. Clinical presentation of knee instability in this group is highly variable and does not always correlate with the presence of functional cruciates. [1],[2],[3],[4],[5] In a study of 66 patients with congenital longitudinal deficiencies, Roux and Carlioz found only 11 who described episodes of instability and of these, only two thought that such episodes were sufficiently frequent to be troublesome. [4] However, clinical laxity also appears to be an unreliable predictor of cruciate anatomy. In both our study and previously published reports, the Lachmann test did not always correlate with clinical history. [3] Anteroposterior laxity of knee was suggested to be very common in all forms of longitudinal deficiency and could be a reliable diagnostic sign during infancy when the radiological deficiency is barely evident. [5] Our anecdotal experience however suggests that more significant laxity at birth, prompting referral, and diagnosis is often no longer clinically significant as the child becomes older. MRI findings may show marked dysplasia with a complete absence of the cruciate ligaments despite relatively normal examination findings.

Roux and Carlioz documented absence or hypoplasia of the ACL and PCL in 95% and 60% of fibular hemimelia cases, respectively. [4] PCL lesions were not only less widespread but were also always less marked than those of the ACL. In our case series, the ACL was absent or at least hypoplastic in all children with PFFD and in 85% of children with fibular hemimelia. The PCL was absent or hypoplastic in 55% of femoral deficiencies and 50% of fibular deficiencies. PCL deficiency was always less extensive than ACL deficiency. Where PCL deficiency was present the ACL was found to be absent or hypoplastic invariably but the reverse was not the case, i.e. it is possible to have ACL deficiency without having any abnormality of PCL. These findings correlate with those of previous imaging reports that describe fibular hemimelia and the same appears to be true regarding femoral deficiencies. [7],[8] Gabos et al. describe successful early results in reconstruction in symptomatic congenital deficiency of the ACL, subsequent to limb lengthening procedures, in both femoral and fibular deficiencies. [9] Asymptomatic joint laxity may be unmasked during lengthening procedures.

In the absence of cruciates, secondary restraints become important in stabilizing the knee. Discoid menisci is a relatively common congenital abnormality and has been associated with longitudinal deficiencies. [4] The incidence of discoid meniscus is thought to be related to the severity of cruciate dysplasia. [7] Interestingly, we saw no discoid meniscus in our series. Hypoplasia of the menisci was noted in four knees, and focal hypoplasia of posterior horn of lateral meniscus in one knee. Yoong and Masour reported posterior horn hypoplasia in three patients and expressed concern regarding early wear in these patients. [8] Lesions of menisci associated with cruciate deficiency increase the potential for subluxation and dislocation when subjected to limb lengthening, but the long-term impact is unknown. In one case, we found the medial and lateral meniscus united to each other in anteriorly, to our knowledge previously unreported in this group.

  Conclusion Top

MRI of the knee in congenital longitudinal lower limb deficiencies demonstrates varying degrees of abnormality in both osseous anatomy and soft tissue constraints. The abnormalities of cruciates and menisci can influence treatment during limb reconstruction and prognosis and cannot reliably be predicted from plain radiography in the skeletally immature. It is important to consider the role of soft tissue releases and cross knee protection during lengthening, especially in these congenital disorders. [9]

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Conflicts of interest

There are no conflicts of interest.

  References Top

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Roux MO, Carlioz H. Clinical examination and investigation of the cruciate ligaments in children with fibular hemimelia. J Pediatr Orthop 1999;19:247-51.  Back to cited text no. 4
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Yoong P, Mansour R. Internal derangement of the knee in fibular hemimelia: Radiographic and MRI findings. Knee 2014;21:749-56.  Back to cited text no. 8
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  [Figure 1], [Figure 2]

  [Table 1]

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