Synovial knee plica in newborn cadaver knee: a comparison between Anatomy and Arthro-TC

Plica sinovial de joelho em cadáveres de recém-nascidos: comparação entre Anatomia e Artro-TC

Abstracts

Em 52 joelhos de cadáveres de recém-nascidos, foi testada a validade da artro-TC de duplo contraste para o diagnóstico de plicas sinoviais normais, fazendo a comparação anatômica e artroscópica com comprovação histológica, objetivando tanto classificar e verificar a sua incidência como também sua relação com as raças. Os resultados encontrados mostram que a plica mediopatelar está, relacionada com as raças pardas, brancas e negras, respectivamente, em 60%, 40% e 9%. Em comparação com as raças parda e branca, a negra tem a tendência à não ter plicas sinoviais. A plica Infrapatelar foi a mais encontrada nos joelhos estudados 69%, seguida da suprapatelar 44% e a mediopatelar 31%. Não foram observadas plicas em 6% dos joelhos. A comunicação da bolsa suprapatelar com a articulação do joelho ocorre em 85 % das pessoas ao nascer. A plica infrapatelar tornou-se difícil de identificar, por estar envolvida em abundante gordura infrapatelar. A Artro-TC foi estudada e analisada por seis observadores, três radiologistas e três ortopedistas e seus resultados mostraram uma sensibilidade média de 72% com uma especificidade média de 60% para radiologistas, e uma sensibilidade média de 89% e especificidade média de 61%, para ortopedistas.

Joelho; Membrana sinovial; Bolsa sinovial; Artrografia; Plica sinovial

ORIGINAL ARTICLE

Synovial knee plica in newborn cadaver knee: a comparison between Anatomy and Arthro-TC

Henrique Mota Neto^I; José Alberto Dias Leite ^II

^ISBOT Accredited Member. Post-Graduate Student at Faculdade de Medicina da UFC

^IIAssociate Professor – Full Professor. Head Orthopedics Service of Hospital das Clínicas da UFC

^{Correspondence}

SUMMARY

Fifty-two newborn knees were used to verify the validity of the arthro-TC of double contrast for the diagnosis of normal synovial plicas, aiming at classifying and verifying their quantitative incidence and ethnic distribution.

The plica synovialis mediopatellaris was identified in brown (60%), white (40%) and black races (9%) in this study. The incidence in black people was quite low as compared to white and brown people. The most commonly found folds were the plica synovialis infrapatellaris (69%) followed by the plica synovialis suprapatellaris (44%) and plica synovialis mediopatellaris (31%). Plicas were not found in 6% of the knees. The communication of bursa patellares with the articulation of the knee is present at birth in 85% of newborns. Identification of plica synovialis infrapatellaris was difficult because it is covered by abundant fat tissue. Arthro-TC was studied and analyzed by six observers, three radiologists and three orthopedic surgeons. The results showed a medium sensibility of 72% and a medium specificity of 60% for radiologist versus 89% and 61% for orthopedist surgeons, respectively.

Key Words: Knee/anatomic and hystologic; Synovial membrane; Bursa, synovial; Arthrography; Synovial plicae

INTRODUCTION

Knee develops very early in fetuses, and is divided by thin synovial membranes called septa, which cause the medial, lateral and supra-patellar compartments. During the fourth to fifth fetal life month, these dividing septa are reabsorbed, and the knee joint turns into one single cavity. Incomplete reabsorption of these septa results in synovial folds; these embryonic remains are called plicae ^{(1,5,11,12,13,23,24,25,26)}. Thus, plicae are normal anatomical structures that represent vestiges of remainder knee embryonic development synovial membranes ^(5,11,25).

Development of knee joint was subject to many studies. Even though there is no consensus on how the common cavity is formed, it is widely admitted that the knee joint is originally made of these three compartments. This theory may explain how are formed the suprapatellar and infrapatellar plicae, but mediopatellar one remains uncertain. The embryologic study clarified the process of common cavity formation, with special reference to knee synovial plica formation and determined the incidence of synovial plica during fetal phase ⁽²³⁾.

Infrapatellar plica, or mucous ligament is present in almost all knees; it extends from the inter-condylean sulcus to the retropatellar fat tissue, parallel to the anterior cruciate ligament and is not responsible for any joint pathology ^{(2,5,7,9,24,25)}.

Suprapatellar plica is proximal to the patella and may extend from the anterior wall to the posterior one, and from medial to lateral; it generally has a communication orifice between proximal and distal portions, that is called "port" or "ostium", with a larger or smaller diameter, according to the synovial resorption degree ^(5,9). Mediopatellar plica is originated near to the suprapatellar one, and goes from the medial suprapatellar region, obliquely and descendently to the patella, anterior to the medial femoral condyle towards the retropatellar fat tissue, acquiring a triangular shape and smoothly sliding over the femoral condyles during flexion and extension of the knee joint ^(5,9,13).

Suprapatellar plica may be explained as originated from a septum between suprapatellar bursa and patellofemoral cavity. The infrapatellar plica may also be considered as a septum of the medial and lateral tibio-femoral cavity. On the other hand, it is believed that the mediopatellar plica is not a remain of a distinct and established embryonic phase compartment septum, but to be a remain of a mesenchimal tissue due to development circumstances ⁽²³⁾.

From physiopathological point of view, there is currently a consensus in grouping of these plicae as: suprapatellar, mediopatellar and infrapatellar, according to their position in relation to the patella, above, at the side or below to it ^(6,18,23,24). Other grouping methods divide these plicae into suprapatellar and infrapatellar, being the suprapatellar and mediopatellar plicae considered as a continuous structure that is different from the infrapatellar ^(3,16). Among the several origins of painful symptoms of the knee, we have the synovial plicae. The diagnosis of "symptomatic plica" is basically achieved by physical examination, with pain in the anterior region of the knee and the presence of a pop ^{(2,10,18,24,26)}. When diagnosed by means of arthroscopy, this can not be considered as gold standard since it is dependant of the examiner, pending on his/hers ability, interest and different criteria adopted by he or she, leading in the literature to a wide variation in the incidence of plica ⁽¹⁹⁾.

On the other hand, recent arthroscopy reports from different authors indicate that the most commonly leading to painful knees are the mediopatellar plicae ^(9,26). It is said that the clinical significance of infrapatellar and suprapatellar plicae is minimal ^(7,12,24).

Kim and Choe ⁽¹⁹⁾ mention age, knee side, gender and race as factors possibly influencing incidences and pattern distribution of plicae, stating that the racial difference that was found was caused by changes in how to interpret plicae findings; they didn’t notice significant difference in other factors.

Due to the wide range of symptoms affecting the knee, knowledge of its anatomy and arthro-tomographic interpretation are needed for a more precise understanding, identification and diagnosis of these synovial plicae. A precise diagnosis, well detailed with use of double-contrast Arthro-TC, is of paramount clinical importance and less expensive than MRI. So, Boven et al ⁽⁶⁾, evaluating 160 double-contrast Arthro-TC, found that: suprapatellar plica was occasionally seen, however was not included in the suprapatellar bursa in most of the exams; infrapatellar plica was seen, but of difficult correct description; mediopatellar plica was found in 47% of the exams.

Hoedge et al ⁽¹⁴⁾ found low correlation between arthro-tomography and arthroscopy results.

Nevertheless several works in adults by means of anatomical study ^{(3,11,17,23,25)}, arthroscopic study ^{(4,8,9,10,12,18,22,24,26,27)} and Arthro-TC ^(6,14) showing plicae morphologic changes and incidence, it is missed more detailed probing analysis, statistics and comparative in regard of these plicae.

As in the literature research it was not found any arthro-tomographic work in newborn cadaver, recognized as an absolute reference of normality regarding knee synovial plica, this work was made necessary in order to test the effectiveness of double-contrast Arthro-TC in comparison to the anatomic method, for diagnosis of normal synovial plicae, checking its presence as well as its incidence in the races white, brown and black, studying newborn cadavers.

CASES AND METHODS

The experimental study was performed in 26 newborn cadavers from the Departamento de Morfologia da Universidade Federal do Ceará. All cases were full term birth, with no congenital associated disease, and died at the Maternidade Escola Assis Chateaubriand nursery in their first 30 days of life; seventeen (65%) were male and nine (35%) female; five were white (19%), ten were brown (38%) and eleven black (43%). The studied specimens were the lower limbs, prepared by amputation by means of transversal cut at upper third of the thigh. The technique described by Boven et al ⁽⁶⁾ was applied. Studies were performed in two cadavers as initial study in order to determine the ideal amount of contrast and air to be injected, not included in this series.

By means of a 29G ½ " (12.7 mm x 0.33) hypodermic needle connected to a 10 ml disposable syringe, it was injected 4 to 5 ml of air, according to the knee size (Figure 1). Later, changing the syringe for one 1cc insulin syringe it was injected 0.2 ml of Pielograf ^® at 60% (sodium amidotrizoate and meglumine). Following, the limbs were manipulated in several directions, for diffusion of the contrast and placed into a 20º flexion, with the patella oriented upward, over a plastic Isopor^® mold and so accommodated to the tomographer gantry, model GE MEDICAL SYSTEMS SYERGY; KV=120; mA=100; DFOV=25,0 cm zoom (Figure 2).

A lateral escanogram with the grantry in a +10º inclination was performed, and 1 mm thick axial cuts were performed, established above the suprapatellar bursa and over the tibial plateaus (Figure 3). For each test this procedure was repeated and sent to three Radiologists and three Orthopedists for reporting the tomographies, with special attention to synovial plicae findings (Figures 4,5,6).

The macroscopic findings were fundamental for establishing the knee synovial plicae, and called "Gold Standard".

STATISTICAL ANALYSIS

Data bank was plotted in Excel and analyzed in Epi Info 6.04D software. It was used the Kappa index for statistical analysis.

RESULTS

A - Race

The incidence of synovial plica in blacks is 50%, in brown, 90% and in white, 100%. The incidence of mediopatellar plica is, in black 9%, in brown 50% and in white 40%; suprapatellar plica incidence in black was 41%, in brown 40% and in white 60% (Table 1). There is no statistically significant difference between the races in right and left knee mediopatellar plica (Table 2), however suprapatellar plicae did no have homogeneity for blacks in both genders (Table 3).

Knee of newborn cadaver of 11 blacks (43%), 10 brown (38%) and 5 white (19%) (Tables 2 and 3)

B - Anatomical study

The most frequent plica was infrapatellar (Figure 7), in 69% of the evaluated knee, followed by suprapatellar (Figure 8), in 44% and mediopatellar (Figure 7 and ⁹), in 31%. Twenty-six knees (50%) with mediopatellar plica were associated to infrapatellar plica. It was not found plica in 6% of the knee (Table 4). Regarding incidence of plica, there is no significant difference between right and left knees.

In Table 4, eight suprapatellar septa (15%) did not present a communication between the suprapatellar bursa and the knee cavity (Figure 10). The suprapatellar space has too many anatomical variations in articular cavity and suprapatellar bursa communication. This is wide or present small communication foramen in a curtain shape, in 85% of the knee (Figure 11).

C - Arthro-TC

Table 5 presents the synovial plica identification study in double contrast Arthro-TC examinations performed by Radiologists (A, B and C) and Orthopedists (D, E and F). Observers B and E had non-significant different results. Among the Radiologists, A found plicae in 40 knees (77%), B in 26 (50%) and C in 41 (79%); among the Orthopedists, D, E and F found 47 (90%), 25 (81%) and 45 (87%) knees respectively, better represented in (Graphic 1).

These results show a mean sensitivity of 72% and a 60% specificity among Radiologist observers, and 89% sensitivity with 61% specificity among Orthopedist observers (Table 6).

In Table 7, are displayed Kappa index diagnosis agreement to gold-standard. Observers B and E had no significant diagnosis agreement (p > 0.05). Observers D and F, were rated as "good and fair", and p < 0.01, while observers A and C had a weak Kappa index of p < 0.02.

The percentage of suprapatellar and mediopatellar grouped plicae, were found by the observer A 25 plicae (48%), B, 9 (17%) and C 26 (50%), with an average of 38%. For observer D 36 plicae (69%), E 37 (71%) and F 39 (75%). Average was 72% of these plicae (Table 5).

We would like to stress in this comparison the findings for mediopatellar plica: Gold-standard 31%, observer A 29%, B 2%, C, 27%, D, 29%, E 29%, F 37% (Table 10).

DISCUSSION

After Mayeda ⁽²¹⁾, in 1918, found plicae in 21% of the cadavers, Hohlmaum ⁽¹⁵⁾ in 1923, in 20%, Iino ⁽¹⁷⁾, in 1939, evaluating 67 adult cadaver knees reported mediopatellar plica in 55%. Pipkin ⁽²⁵⁾, in 1950, found in 78% of adult knee presenting a fusion of suprapatellar bursa to knee joint, calling this a suprapatellar plica, drawing interest from several investigators looking for more precision on this subject. Brody et al. ⁽⁷⁾ in 1963 state that, among the three more frequent knee plicae, infrapatellar one causes no articular problem. Cohen el al.⁽⁹⁾ state that suprapatellar plica has a minimal clinical significance, and several arthroscopic studies demonstrated that mediopatellar plica may rise symptoms, more frequently becoming pathologic. In our study we can state that 75% of the newborn would be subject to this syndrome in adult life, if these plicae were not further reabsorbed, being mediopatellar ones those with greater possibility.

As it was clear that mediopatellar plica had higher clinical significance, more attention was drawn to inform the incidence of this plica in the several studies. In a literature review, the informed incidence has a large range. Iino ⁽¹⁷⁾ reports a mediopatellar plica range from 20% to 55%. Sakakibara ⁽²⁷⁾ observed 35% to 55% in symptomatic knees, Hardaker et al. ⁽¹²⁾ stated that synovial plica may be pathologic without reaching the femoral condyle, and that the incidence of plicae may range from 18 to 60% in adult knees, according to the author. Amatuzzi et al. ⁽¹⁾, in 1990, presented an incidence ranging from 20 to 60%. In our study it was found an incidence ranging from 18 to 78%.

Other arthroscopic study researchers also informed their incidence: Mizumachi et al.⁽²²⁾ 25,6%; Aoki et al.⁽⁴⁾ 21,6%; Casscells⁽⁸⁾ 32,2%; Sakakibara⁽²⁷⁾ reported 45%; Patel⁽²⁴⁾ 18,5%; Hardaker et al.⁽¹²⁾ reported 20%; de la Caffiniere et al.⁽¹⁰⁾ 20%; Jackson et al.⁽¹⁸⁾ 60%; Cohen et al.⁽⁹⁾ 18%, Kim and Choe⁽¹⁹⁾ 72%. In this study we inform 31% of this plica incidence.

Nevertheless all this literature information, Apple et al. ⁽⁵⁾ report the suprapatellar plica to be of most common clinical relevance, in 20% of the population, while literature incidence of this plica ranges from 20% to 91.2% (Kim and Choe ⁽¹⁹⁾). It can so be noticed that there is not a consensus in synovial plica incidence.

Ogata and Uhthoff ⁽²³⁾ found in a 11 to 20 week fetal phase study, infrapatellar plica in 50% of the specimens, suprapatellar in 33% and mediopatellar in 37%. Also commented that only infrapatellar plica demonstrated an incidence reduction and that supra and mediopatellar ones do not vanish after formed; Kim and Choe ⁽¹⁹⁾ demonstrated in arthroscopy results an incidence of infrapatellar plica in 86%, suprapatellar in 87% and mediopatellar in 72%, with a complete septus pattern in 20.8%.

In our anatomical study were found infrapatellar plicae in 69% of the knee, suprapatellar in 44% and mediopatellar in 31%; for identification of mediopatellar plica, a similar finding was observed in double-contrast Arthro-TC examinations, with exception of Observer B, however, for suprapatellar plica identification, Orthopedist observers were close to the Gold-Standard, while the same was not observed among the Radiologists. These findings become important for literature for recording these plicae in a normal state at birth, when the joint did not have any external distress or physical erosion. When compared to adult arthroscopy incidence, that are below those reported in this work, this lead us to believe plicae keep being reabsorbed after birth. This hypothesis is supported by the observation of the data by Pipkin ⁽²⁶⁾ and Amatuzzi et al ⁽³⁾. The first one interpreted all plica findings as suprapatellar, while the second one grouped supra and mediopatellar, according to Hughston et al ⁽¹⁶⁾ grouping, as one single structure, while we actually believe mediopatellar plica does not originates from suprapatellar septum, here agreeing with Kim and Choe ⁽¹⁹⁾. Sometimes they are not even adjacent, as observed in this work. The mediopatellar incidence informed in this study includes a normality pattern for the joint. The statistics through arthroscopic study includes a given symptomatic set of adult knees, limiting the sample universe, not including healthy population; another factor also influencing the results was the range of plica interpretations as evaluated by different observers.

Regarding infrapatellar plica, our findings were similar to other authors ^{(1,5,9,12,24)} as stating that it is found in almost all knees. We informed that the incidence at birth is 69% and that this can be changed in adult life, since in this work it was found remains of the septum dividing the cavity in medial and lateral, with an incomplete differentiation in its inferior portion, leading us to believe that this reabsorption process may continue after birth.

Boven et al ⁽⁵⁾, states that suprapatellar plica is seen in Arthro-TC as a parallel to median wall line, and we believe with this author since it is considered to be a vision with the knee at 20º flexion, and the gantry with +10º inclination. He also states that it is difficult a correct description of the infrapatellar plica; we agree with him, however we could even though get good results through an intercondyllary vision. For this it is necessary to choose the attenuation coefficient searching for the right image, according to the gray scale, that is available in the tomographer. The mediopatellar plica can only be seen when special views are obtained.

Jackson et al ⁽¹⁸⁾, observed that a pathologic plica is a result of mechanical friction between the condyle and the patella, and Boven et al ⁽⁶⁾, based on the width and thickness of the plica, found that in 10 of the 63 mediopatellar plicae, that is, 16%, could develop as a pathologic plica, what was confirmed in only two of the cases. In this work we did not get to validate the criteria by Boven et al ⁽⁶⁾, since mediopatellar plicae had different characteristics not allowing us to establish a differential pattern. During dissection two thicker and wider mediopatellar plicae were found, interposing between the patella and the condyles, representing 12% of the total, however without significance in this study newborn group.

Ogata and Uhthoff ⁽²³⁾, demonstrated in their observation a reduction in infrapatellar plica incidence according to fetal evolution time. Kim and Choe ⁽¹⁹⁾, when publishing their plica incidence stated that the difference from the literature was due to race difference, however did not inform the race nor the incidence by patient race, a paramount importance information. Based in our study, brown and white races had a lower incidence of infrapatellar plicae (10 and 0%, respectively), while blacks had 36%.

We believe race has influence over determination of knee plicae, once our findings for mediopatellar plica showed a significant variation among them, stressing black race that presented a low incidence when compared to others. It is curious to observe the findings by Jackson et al ⁽¹⁸⁾, in Canadian an Japanese, stating that there was no difference in synovial plica incidence among these races, maybe because their study did not include blacks.

Since the 19th century with Malgaigne ⁽²⁰⁾ there is a concern to study the suprapatellar bursa. In the next century, in continuation to this study, Hohlbaum ⁽¹⁵⁾ and Pipkin ⁽²⁵⁾ informed the existence of a communication of this bursa with the knee cavity, in adults. It was also demonstrated by Gray and Gardner ⁽¹¹⁾ in fetuses, that it remains continuous with the knee joint in the fourth or fifth intra uterine life month, promoting a cavity at birth. Since then it is looked for a consensus on this communication incidence and on how do its embryonic remains behave. Harty and Joyce ⁽¹³⁾ demonstrated that the suprapatellar septum is seen in several forms in adult life and that it is rare that it completely divide the suprapatellar bursa from the remaining knee; Patel ⁽²⁴⁾ states that it is common a central communication called port, and Pipkin ⁽²⁵⁾, studying suprapatellar bursa communication reported 78% of plicae. Actually this would be the incidence of communication between the knee cavity and the suprapatellar bursa, what is similar to our findings.

However, suprapatellar plicae originated from these septa were of lower proportions, 44%, meaning that not all septum results in suprapatellar synovial plica. The incidence of patent embryonic structures in the general population is about 20% ^(24,25).

In this study it was not possible to confirm the statement that all knee joint is transformed into one single cavity at birth, since eight of 52 knees presenting suprapatellar septa had no perforation, and, when there was a communication, it as a central hole of a varied diameter, extending from median portion of suprapatellar bursa to the lateral condyle. It was also frequently seen multi-perforated septum, in a curtain shape, and embryonic remains of these septa loose in the joint. These findings lead us to believe that 15% of the people are born with imperforated suprapatellar septa, what is within the incidence presented by Kim and Choe ⁽¹⁹⁾ that ranged from 4.2 to 23%.

Infrapatellar plica rarely persists as a complete septum, however there are remains of it as a fenestrated septum or a series of fibrous bands ^(25,26). In this work we report one septum (2%) dividing the joint cavity into medial and lateral, with an incomplete reabsorption at its inferior portion.

Medial suprapatellar plica is more common, with an incidence of 20%, appearing as a molded fold, starting below the quadriceps tendon and extending towards the medial wall of the joint ⁽¹²⁾. With these characteristics, we grouped them as mediopatellar, and found it to be present in 31% of the studied knee.

Hodge et al ⁽¹⁴⁾, in a comparative study of double-contrast Arthro-TC and arthroscopy, found a 95% sensitivity and 100% specificity in the 23 studied patients. In this study the Radiologists reached an average of 73% of sensitivity and 60% of specificity, while Orthopedists had an average of 89% of sensitivity and 62% of specificity. We would like to add that, for getting better results it is necessary to be trained in arthrotomography.

Macroscopic anatomy was considered as Gold-Standard for knee plica diagnosis. This research is a prevalence indicator, and shows that through the study comparative to anatomy, that by means of arthrography it is possible to establish a safe standard for evaluation of the knee in synovial plica studies.

It is concluded that brown and white races have higher incidences of plicae, and are statistically more vulnerable to bearing pathologic synovial plicae that the black one. Factors as gender and knee side (right or left) did not present significant incidence levels; Arthro-TC is dependent of a well trained observer for getting better results; after birth, synovial plicae may continue to be reabsorbed, reaching a lower incidence in adult life.

CONCLUSIONS

1. Double-contrast Arthro-TC is a good method for identifying synovial plicae, given the observer is well trained.

2. Communication of suprapatellar bursa to the knee joint happens in 85% of the people at birth.

3. In comparison to White and Brown races, Black race has the lowest trend (9%) to have synovial plicae.

4. In newborn cadaver dissection normal plicae are found in the vast majority of the knee.

5. The most frequent plica was infrapatellar, followed by supra and mediopatellar, respectively.

Trabalho recebido em 17/09/2002

Aprovado em 05/11/2002

Work performed at Surgery Post-Graduation Program of Faculdade de Medicina da Universidade Federal do Ceará, UFC.

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Publication Dates

• Publication in this collection
  16 Apr 2003
• Date of issue
  Jan 2003

History

• Accepted
  05 Nov 2002
• Received
  17 Sept 2002