INTRODUCTION
The popliteal fossa presents an extensive topographical element on the posterior aspect of the knee, included between flexor muscles of the thigh and flexor muscles of the leg. The external contour of the popliteal fossa is diamond-shaped and covered with the popliteal fascia, which constitutes the roof of the popliteal fossa [1, 27]. The popliteal fossa is bounded superomedially by the semitendinosus and semimembranosus muscles, superolaterally — by the biceps femoris muscle, inferomedially — by the medial head of the gastrocnemius muscle, and inferolaterally — by the lateral head of gastrocnemius muscle and plantaris muscle [10, 25, 27, 30]. All the aforementioned muscles flex and stabilise the knee joint [18, 25]. Apart from this, the semitendinosus muscle, semimembranosus muscle, and lateral head of the gastrocnemius muscle all medially rotate the leg (endororation), while the biceps femoris muscle and medial head of the gastrocnemius are responsible for its lateral rotation (exorotation) [25, 27].
It should be emphasised that the floor of popliteal fossa is considerably greater than its roof. This is because the floor of the popliteal fossa extends as high as the adductor hiatus and as low as the tendinous arch of the soleus muscle [25, 27]. The floor of the popliteal fossa is composed of the popliteal surface of the femur, the articular capsule of the knee joint with its oblique popliteal ligament, and the popliteus muscle. According to Benniger and Delamarter [4], the oblique popliteal ligament is the very first constituent of the trifurcation of the semimembranosus tendon, and so it should be renamed the oblique popliteal tendon or expansion. The second expansion of this trifurcation ends on the anteroinferior aspect of the medial condyle of the tibia, the medial meniscus, and the medial collateral ligament of the knee, while the third one inserts onto the posteroinferior aspect of the medial condyle of the tibia and provides fibres to the individual fascia of the popliteus muscle.
The popliteal fossa communicates anteriorly through the adductor hiatus with the adductor canal. Superiorly, the popliteal fossa is freely continuous with the flexor compartment of the thigh. Of note, the soleus muscle resembles a kind of diaphragm by separating the popliteal fossa from the deep part of flexor compartment of the leg. Distally, the popliteal fossa communicates anteriorly with the extensor compartment of the leg due to the opening above the interosseous membrane of the leg that transmits the anterior tibial artery and veins. Deep to the tendinous arch of soleus muscle, both the tibial nerve and posterior tibial vessels leave the popliteal fossa end enter the deep part of the flexor compartment of the leg [4, 25, 27]. The posterolateral corner of the knee is largely stabilised by the biceps femoris muscle, the head of the fibula, the tendon of the popliteus muscle, and the popliteofibular ligament [9, 27]. Of note, there is also the plantaris muscle, which is a small vestigial muscle with an incidence of 80–93% [17, 21, 24].
The popliteal fossa is traversed vertically by the popliteal artery and vein, both encompassed by the popliteal sheath. At the superior angle of popliteal fossa, the sciatic nerve externally divides into the tibial and common fibular nerves. Not being included in the popliteal sheath, the tibial nerve freely winds from lateral to medial on the posterior aspect of the popliteal vessels. The common fibular nerve traverses from the superior to the lateral angle of the popliteal fossa, and after leaving the popliteal fossa at the level of the neck of the fibula it divides into the superficial and deep fibular nerves [8, 27]. The popliteal fossa accommodates the popliteal lymph nodes, of which the middle popliteal lymph nodes clothe the popliteal vessels, the articular popliteal lymph node is between the oblique popliteal ligament and the popliteal artery, while the saphenous popliteal lymph node adheres to the junction of the small saphenous vein with the popliteal vein [17, 24, 25, 27].
The muscles limiting the popliteal fossa may indicate relevant variations, characterised by anomalous muscle slips that cross neurovascular structures and cause entrapment syndromes. The third head of gastrocnemius joining its medial head is most frequently quoted as producing such clinical problems [1, 10]. On the other hand, Liu et al. [18] presented the coexistence of bilateral absence of both the semimembranosus and quadratus femoris muscles.
After reviewing the professional literature, we failed to find any morphometrical data concerning the popliteal fossa in the human foetus. Thus, we decided to morphometrically analyse the size of the popliteal fossa in human foetuses aged 17 to 29 weeks of gestation with the use of objective methods: digital image analysis and statistics. The present study provides new detailed numerical data of the popliteal fossa, to thoroughly understand its growth dynamics.
With relation to the popliteal fossa, we aimed to examine the following:
- the possible variability of the muscles limiting the popliteal fossa that may considerably influence its morphometrical parameters;
- its size by performing its linear and planar measurements in order to achieve age-specific reference intervals of examined parameters;
- the possible right-left and male-female differences in all examined parameters; and
- growth patterns for all examined parameters.
MATERIALs AND METHODS
The examined material comprised 31 foetuses of both sexes, 17 males and 14 females, at the age of 17 to 29 weeks of gestation, derived from spontaneous miscarriages and preterm deliveries. The foetal collection was from our Department of Normal Anatomy. The present examinations were approved by the Bioethics Committee of the Ludwik Rydygier Collegium Medicum in Bydgoszcz, and the Nicolaus Copernicus University in Bydgoszcz. The foetal ages were determined on the basis of the crown-rump length. Table 1 presents the characteristics of the examined foetal samples with their distribution regarding age, number, and sex.
|
Gestational age |
Crown-rump length [mm] |
Number of foetuses |
Sex |
||
|
Weeks |
Mean |
SD |
♂ |
♀ |
|
|
17 |
117.5 |
0.707 |
2 |
2 |
|
|
18 |
136.5 |
7.778 |
2 |
1 |
1 |
|
19 |
151 |
2.517 |
3 |
2 |
1 |
|
20 |
167 |
1.414 |
2 |
1 |
1 |
|
21 |
176 |
3.512 |
3 |
2 |
1 |
|
22 |
182.5 |
0.707 |
2 |
2 |
|
|
23 |
195 |
4.243 |
2 |
2 |
|
|
24 |
211.5 |
0.707 |
2 |
1 |
1 |
|
25 |
216.5 |
2.121 |
2 |
1 |
1 |
|
26 |
231 |
2.828 |
2 |
1 |
1 |
|
27 |
241.4 |
2.121 |
2 |
1 |
1 |
|
28 |
247.5 |
1.708 |
4 |
1 |
3 |
|
29 |
260.5 |
0.707 |
3 |
1 |
2 |
|
Total |
31 |
14 |
17 |
||
With the use of classical anatomical dissection on the posterior aspect of the lower limb, the popliteal fossa was bilaterally exposed. The photographic documentation of the popliteal fossae was prepared using a Canon EOS 70D(W), while for the morphometric analysis the NIS Elements AR 3.0 system was used. For each popliteal fossa, the following 11 parameters were defined and measured (Fig. 1A–C):
- length of superomedial boundary (mm), extending between the superior and medial angles of the popliteal fossa along the semitendinosus muscle;
- length of superolateral boundary (mm), extending between the superior and lateral angles of the popliteal fossa along the biceps femoris muscle;
- length of inferomedial boundary (mm), extending between the inferior and medial angles of the popliteal fossa along the medial head of gastrocnemius muscle;
- length of the inferolateral boundary (mm), extending between the inferior and lateral angles of the popliteal fossa along the lateral head of the gastrocnemius muscle;
- transverse diameter (mm), extending between the medial and lateral angles of the popliteal fossa;
- vertical diameter (mm), extending between the superior and inferior angles of the popliteal fossa;
- projection surface area (mm2), calculated semiautomatically after the popliteal fossa was outlined;
- superior angle (α) of popliteal fossa, between the semitendinosus and biceps femoris muscles;
- medial angle (β) of popliteal fossa, between the semitendinosus muscle and medial head of gastrocnemius muscle;
- inferior angle (γ) of popliteal fossa, between the medial and lateral heads of gastrocnemius muscle; and
- lateral angle (δ) of popliteal fossa, between the lateral head of the gastrocnemius muscle and the biceps femoris muscle.
All numerical data were subject to statistical analysis with the use of STATISTICA 13.0. Because of the normal distribution of numerical data, our results have been presented as means and standard deviations (SD). To compare right-left means and male-female means, Student’s t-test for dependent variables and Student t-test for independent variables were respectively used with one-way analysis of variance. The growth patterns of particular morphometrical parameters were examined using linear and nonlinear regression analyses. The growth dynamics of best fit was unequivocally characterised and selected by the greatest value of its coefficient of determination (R2). Statistically significant differences were considered at p < 0.05.
RESULTS
In the study material we found no variability concerning the skeletal muscles limiting the popliteal fossa, namely the semitendinosus, semimembranosus, biceps femoris, plantaris, and gastrocnemius muscles that all follow typically without extra muscle slips. As a result, the shape of each popliteal fossa was regular and diamond shaped.
The statistical analysis did not show any statistically significant male-female differences for all the parameters studied (p > 0.05), thus allowing us to aggregate them, without regard to sex (Tab. 2–6).
|
Parameter |
Regression formulae related to age |
R2 |
F |
P |
|
Superomedial border [mm] |
y = –44.421 + 24.301 × ln (age) |
0.897 |
535.1 |
= 0.00 |
|
Superolateral border [mm] |
y = –41.379 + 22.777 × ln (age) |
0.862 |
377.2 |
= 0.00 |
|
Inferomedial border [mm] |
y = –39.019 + 20.981 × ln (age) |
0.911 |
614.5 |
= 0.00 |
|
Inferolateral border [mm] |
y = –37.547 + 20.319 × ln (age) |
0.860 |
369.6 |
= 0.00 |
|
Length [mm] |
y = –69.790 + 38.730 × ln (age) |
0.901 |
548.7 |
= 0.00 |
|
Width [mm] |
y = –28.915 + 15.822 × ln (age) |
0.780 |
213.3 |
= 0.00 |
|
Surface area [mm2] |
y = –485.631 + 240.844 × ln (age) |
0.936 |
879.0 |
= 0.00 |
|
Gestational age [weeks] |
Number of foetuses |
Length of superomedial boundary |
Length of superolateral boundary |
||||||
|
Right |
Left |
Right |
Left |
||||||
|
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
||
|
17 |
2 |
6.205 |
0.219 |
6.320 |
0.099 |
5.395 |
0.064 |
5.540 |
0.028 |
|
18 |
2 |
6.875 |
0.191 |
6.945 |
0.021 |
6.040 |
1.457 |
6.045 |
1.407 |
|
19 |
3 |
9.230 |
1.127 |
9.550 |
1.190 |
8.820 |
1.134 |
9.110 |
1.169 |
|
20 |
2 |
9.745 |
0.926 |
9.765 |
0.841 |
10.495 |
0.530 |
9.995 |
0.078 |
|
21 |
3 |
10.270 |
0.242 |
10.980 |
0.554 |
10.27 |
0.806 |
10.650 |
0.860 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
22 |
2 |
10.115 |
0.106 |
10.540 |
0.099 |
10.575 |
0.488 |
10.175 |
0.219 |
|
23 |
2 |
11.525 |
0.658 |
12.000 |
0.226 |
10.350 |
0.523 |
10.925 |
0.954 |
|
24 |
2 |
11.410 |
0.778 |
10.680 |
0.481 |
10.445 |
0.290 |
10.885 |
0.035 |
|
25 |
2 |
10.635 |
0.573 |
10.945 |
0.672 |
10.715 |
0.530 |
10.175 |
0.205 |
|
26 |
2 |
11.870 |
0.014 |
11.500 |
0.608 |
12.785 |
0.346 |
12.290 |
0.438 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
27 |
2 |
13.035 |
0.643 |
13.380 |
0.848 |
12.845 |
0.346 |
13.085 |
0.021 |
|
28 |
4 |
14.570 |
0.360 |
14.715 |
0.184 |
13.765 |
0.396 |
13.320 |
0.454 |
|
29 |
3 |
15.220 |
0.382 |
14.935 |
0.106 |
13.145 |
0.106 |
13.225 |
0.219 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
Gestational age [weeks] |
Number of foetuses |
Length of inferomedial boundary |
Length of inferolateral boundary |
||||||
|
Right |
Left |
Right |
Left |
||||||
|
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
||
|
17 |
2 |
4.720 |
0.212 |
4.755 |
0.007 |
5.340 |
0.028 |
5.765 |
0.262 |
|
18 |
2 |
5.940 |
0.127 |
5.900 |
0.042 |
6.340 |
1.061 |
5.955 |
0.559 |
|
19 |
3 |
6.910 |
0.590 |
6.450 |
0.757 |
6.070 |
0.569 |
6.470 |
0.974 |
|
20 |
2 |
7.410 |
0.976 |
7.320 |
1.541 |
7.720 |
1.626 |
7.365 |
2.213 |
|
21 |
3 |
8.810 |
0.378 |
8.790 |
0.796 |
8.180 |
0.700 |
9.020 |
0.523 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
22 |
2 |
7.845 |
0.247 |
7.995 |
0.785 |
7.125 |
0.559 |
7.060 |
0.325 |
|
23 |
2 |
8.740 |
0.580 |
9.030 |
0.424 |
8.655 |
0.672 |
9.185 |
0.855 |
|
24 |
2 |
8.800 |
1.131 |
8.880 |
1.188 |
8.220 |
0.594 |
8.465 |
0.728 |
|
25 |
2 |
9.545 |
0.516 |
9.575 |
0.318 |
9.630 |
0.283 |
9.860 |
0.184 |
|
26 |
2 |
10.215 |
0.389 |
10.155 |
0.530 |
10.035 |
0.629 |
10.110 |
0.877 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
27 |
2 |
10.735 |
0.290 |
10.685 |
0.474 |
11.695 |
0.049 |
11.305 |
0.389 |
|
28 |
4 |
11.245 |
0.258 |
11.390 |
0.352 |
11.365 |
1.306 |
11.470 |
0.906 |
|
29 |
3 |
13.195 |
0.361 |
13.320 |
0.424 |
11.530 |
0.184 |
11.640 |
0.085 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
Gestational age [weeks] |
Number of foetuses |
Vertical diameter [mm] |
Transverse diameter [mm] |
||||||
|
Right |
Left |
Right |
Left |
||||||
|
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
||
|
17 |
2 |
10.665 |
0.488 |
10.765 |
0.021 |
4.530 |
0.071 |
4.695 |
0.035 |
|
18 |
2 |
11.745 |
0.389 |
11.605 |
0.304 |
5.155 |
0.205 |
5.190 |
0.297 |
|
19 |
3 |
14.420 |
0.734 |
14.130 |
0.784 |
5.030 |
0.358 |
5.060 |
0.325 |
|
20 |
2 |
17.245 |
1.492 |
16.455 |
1.195 |
5.020 |
0.679 |
4.835 |
0.318 |
|
21 |
3 |
17.290 |
1.124 |
18.160 |
1.200 |
7.050 |
1.603 |
6.810 |
0.111 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
22 |
2 |
17.350 |
0.891 |
17.140 |
0.749 |
6.260 |
0.509 |
6.130 |
0.551 |
|
23 |
2 |
19.600 |
0.085 |
20.130 |
0.523 |
6.790 |
0.042 |
6.600 |
0.382 |
|
24 |
2 |
19.015 |
0.276 |
18.680 |
0.594 |
7.635 |
1.534 |
7.560 |
2.164 |
|
25 |
2 |
21.495 |
1.421 |
20.845 |
0.671 |
8.510 |
0.099 |
8.865 |
0.035 |
|
26 |
2 |
22.515 |
3.472 |
22.050 |
1.457 |
8.460 |
0.198 |
8.475 |
0.403 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
27 |
2 |
21.335 |
1.860 |
20.975 |
1.619 |
9.680 |
0.113 |
9.460 |
0.622 |
|
28 |
4 |
24.055 |
0.044 |
24.075 |
0.561 |
8.400 |
0.290 |
8.235 |
0.191 |
|
29 |
3 |
23.035 |
0.544 |
22.695 |
0.502 |
10.735 |
0.191 |
10.890 |
0.184 |
|
(p < 0.01) |
(p < 0.01) |
||||||||
|
Gestational age (weeks) |
Number of foetuses |
Projection surface area [mm2] |
|||
|
Right |
Left |
||||
|
Mean |
SD |
Mean |
SD |
||
|
17 |
2 |
28.380 |
0.707 |
29.485 |
0.898 |
|
18 |
2 |
34.620 |
1.669 |
34.485 |
1.761 |
|
19 |
3 |
38.550 |
0.959 |
38.030 |
0.836 |
|
20 |
2 |
38.760 |
0.382 |
38.185 |
0.092 |
|
21 |
3 |
45.720 |
0.692 |
44.160 |
1.317 |
|
(p < 0.01) |
|||||
|
22 |
2 |
49.225 |
0.785 |
48.380 |
0.848 |
|
23 |
2 |
63.535 |
5.537 |
62.370 |
5.614 |
|
24 |
2 |
73.110 |
6.307 |
70.055 |
2.779 |
|
25 |
2 |
70.855 |
0.969 |
72.290 |
2.744 |
|
26 |
2 |
78.910 |
0.042 |
80.065 |
2.595 |
|
(p < 0.01) |
|||||
|
27 |
2 |
92.895 |
16.440 |
91.605 |
13.781 |
|
28 |
4 |
101.055 |
3.107 |
99.720 |
3.661 |
|
29 |
3 |
101.600 |
1.527 |
101.195 |
0.219 |
|
(p < 0.01) |
|||||
|
Gestational age [weeks] |
Number of foetuses |
Superior (α) angle |
Medial (β) angle |
Inferior (γ) angle |
Lateral (δ) angle |
||||||||||||
|
Right |
Left |
Right |
Left |
Right |
Left |
Right |
Left |
||||||||||
|
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
Mean |
SD |
||
|
17 |
2 |
38.17 |
0.707 |
42.075 |
6.230 |
134.66 |
5.508 |
141.08 |
12.098 |
34.85 |
10.797 |
22.60 |
2.446 |
133.69 |
8.534 |
136.4 |
2.659 |
|
18 |
2 |
36.53 |
7.001 |
36.655 |
7.163 |
134.30 |
7.530 |
130.33 |
6.484 |
34.08 |
10.472 |
44.77 |
1.704 |
126.28 |
3.649 |
133.72 |
0.035 |
|
19 |
3 |
39.65 |
4.643 |
39.65 |
5.282 |
129.04 |
1.0515 |
129.66 |
0.647 |
44.72 |
5.284 |
45.98 |
0.911 |
136.57 |
2.232 |
136.48 |
2.391 |
|
20 |
2 |
35.19 |
4.101 |
36.045 |
1.167 |
141.96 |
2.121 |
137.90 |
3.443 |
40.18 |
1.485 |
39.30 |
0.735 |
137.74 |
6.117 |
138.31 |
8.429 |
|
21 |
3 |
37.99 |
2.598 |
36.22 |
2.782 |
139.35 |
6.736 |
138.44 |
9.031 |
39.82 |
3.165 |
39.74 |
3.621 |
141.76 |
5.488 |
141.88 |
4.631 |
|
(p < 0.01) |
(p < 0.01) |
(p < 0.01) |
(p < 0.01) |
||||||||||||||
|
22 |
2 |
35.25 |
5.565 |
36.30 |
3.989 |
142.53 |
3.811 |
141.93 |
3.234 |
45.67 |
2.170 |
47.28 |
5.374 |
132.64 |
4.264 |
135.98 |
0.480 |
|
23 |
2 |
37.29 |
5.728 |
40.535 |
2.552 |
141.85 |
7.170 |
140.71 |
8.019 |
40.23 |
2.984 |
40.45 |
1.414 |
146.55 |
4.229 |
138.54 |
4.080 |
|
24 |
2 |
37.06 |
6.993 |
35.20 |
5.756 |
134.47 |
9.291 |
135.43 |
9.376 |
43.28 |
3.854 |
43.81 |
1.627 |
133.96 |
8.026 |
134.75 |
7.658 |
|
25 |
2 |
32.95 |
2.270 |
31.665 |
1.902 |
144.17 |
2.340 |
145.85 |
0.035 |
38.30 |
0.460 |
38.80 |
1.167 |
141.77 |
5.105 |
141.98 |
4.808 |
|
(p < 0.01) |
(p < 0.01) |
(p < 0.01) |
(p < 0.01) |
||||||||||||||
|
26 |
2 |
37.11 |
2.998 |
39.13 |
7.085 |
144.36 |
0.990 |
144.81 |
2.107 |
33.11 |
8.959 |
31.86 |
10.628 |
136.52 |
10.394 |
132.39 |
1.407 |
|
27 |
2 |
40.46 |
1.506 |
39.22 |
0.297 |
144.14 |
5.883 |
144.09 |
6.123 |
39.08 |
0.424 |
38.80 |
0.841 |
132.82 |
2.008 |
134.02 |
1.725 |
|
28 |
4 |
36.06 |
3.573 |
37.96 |
3.474 |
137.91 |
4.658 |
141.91 |
1.719 |
38.84 |
3.462 |
37.29 |
4.768 |
145.30 |
4.305 |
141.15 |
2.886 |
|
29 |
3 |
39.40 |
0.007 |
40.50 |
0.693 |
137.83 |
3.019 |
137.66 |
1.846 |
40.43 |
0.4957 |
40.47 |
0.778 |
135.58 |
1.895 |
136.32 |
1.527 |
|
(p < 0.01) |
(p < 0.01) |
(p < 0.01) |
(p < 0.01) |
||||||||||||||
Length values of the 4 boundaries of the popliteal fossa presented the following decreasing sequence: the superomedial, superolateral, inferolateral, and inferomedial ones.
The mean length of the superomedial boundary of the popliteal fossa (Tab. 3A) increased from 6.205 ± 0.219 mm at week 17 to 15.221 ± 0.382 mm at week 29 of gestation on the right, and from 6.321 ± 0.099 to 14.935 ± 0.106 mm, respectively, without right-left differences (p > 0.05). In the analysed period the mean length of the superomedial boundary of the popliteal fossa followed the natural logarithmic function y = –44.421 + 24.301 × ln (age) with R2 = 0.897 (Fig. 2A).
At the ages of 17–29 weeks of gestation, the mean length of the superolateral boundary of the popliteal fossa (Tab. 3A) increased its value from 5.395 ± 0.064 to 13.145 ± 0.106 mm on the right and from 5.54 ± 0.028 to 13.225 ± 0.219 mm on the left, without right-left differences (p > 0.05). The mean length of the superolateral boundary of the popliteal fossa modelled the natural logarithmic function y = –41.379 + 22.777 × ln (age) with R2 = 0.862 (Fig. 2B).
Between weeks 17 and 29, the mean length of the inferomedial boundary of the popliteal fossa (Tab. 3B) grew from 4.723 ± 0.212 to 13.195 ± 0.360 mm on the right and from 4.755 ± 0.007 to 13.320 ± 0.424 mm on the left, without right-left differences (p > 0.05). The mean length of inferomedial boundary of popliteal fossa computed the natural logarithmic function y = –39.019 + 20.981 × ln (age) with R2 = 0.911 (Fig. 2C).
The mean length of the inferolateral boundary of the popliteal fossa (Tab. 3B) revealed an increase in values from 5.34 ± 0.028 mm at week 17 to 11.53 ± 0.184 mm at week 29 on the right, and correspondingly from 5.765 ± 0.262 to 11.64 ± 0.849 mm on the left, without right-left differences (p > 0.05). The mean length of inferolateral boundary of popliteal fossa generated the natural logarithmic function y = –37.547 + 20.319 × ln (age) with R2 = 0.860 (Fig. 2D).
The vertical diameter of the popliteal fossa was approximately twice its transverse diameter. Between weeks 17 and 29 of gestation the mean transverse diameter of the popliteal fossa (Tab. 4) grew from 4.532 ± 0.070 to 10.735 ± 0.190 mm on the right and from 4.695 ± 0.035 to 10.891 ± 0.184 mm on the left, without right-left differences (p > 0.05). The mean transverse diameter of popliteal fossa followed the natural logarithmic function y = –28.915 + 15.822 × ln (age), with R2 = 0.780 (Fig. 2F).
The mean vertical diameter of popliteal fossa (Tab. 4) increased from 10.665 ± 0.488 mm at week 17 to 23.035 ± 0.544 mm at week 29 on the right, and correspondingly from 10.765 ± 0.021 to 22.695 ± 0.502 mm on the left. In the analysed period the mean vertical diameter of popliteal fossa displayed the natural logarithmic function y = –69.790 + 38.73 × ln (age), with R2 = 0.901 (Fig. 2E).
At the age range of 17–29 weeks, the mean projection surface area of the popliteal fossa (Tab. 5) grew from 28.381 ± 0.707 to 101.195 ± 0.220 mm2 on the right, and from 29.485 ± 0.898 to 101.195 ± 0.220 mm2 on the left. The mean projection surface area of popliteal fossa modelled the natural logarithmic function y = –485.631 + 240.844 × ln (age), with R2 = 0.936 (Fig. 2G).
The 4 angles of the popliteal fossa presented the following decreasing sequence: medial, lateral, superior, and inferior. Their values did not significantly change with foetal age (p > 0.05).
The mean superior (α) angle of the popliteal fossa (Tab. 6) between weeks 17 and 29 ranged from 38.172 ± 0.707° to 39.405 ± 0.007° on the right, and from 42.075 ± 6.230° to 40.500 ± 0.692° on the left, without statistically significant differences on either side or between the left and right sides. At the same time, the mean medial (β) angle of popliteal fossa (Tab. 6) ranged from 141.085 ± 12.099° to 137.665 ± 1.846° on the right, and from 134.665 ± 5.509° to 137.835 ± 3.019° on the left, without statistically significant differences on either side and between the left and right sides. The mean inferior (γ) angle of the popliteal fossa (Tab. 6) between weeks 17 and 29 changed from 24.855 ± 10.798° to 40.430 ± 0.450° on the right, and from 22.611 ± 2.447° to 40.470 ± 2.447° on the left, without statistically significant differences on either side and between left and right sides. The mean lateral (δ) angle of the popliteal fossa (Tab. 6) reached the values of 133.695 ± 8.535° at week 17 and 135.58 ± 1.896° at week 29 on the right, and, respectively, 136.412 ± 2.659° and 136.321 ± 1.527° on the left side, without statistically significant differences on either side or between left and right sides.
DISCUSSION
The present discussion was separated into the following 5 subdivisions: sex and laterality differences of the popliteal fossa and its limiting muscles; numerical data of the popliteal fossa in the growing human foetus; variability of the muscles limiting the popliteal fossa; morphometric studies of the muscles limiting the popliteal fossa in the human foetus; and clinical aspects of the popliteal fossa.
Sex and laterality differences of the popliteal fossa and its limiting muscles
In the material under examination, we found the size of the popliteal fossa to be independent of both the sex and laterality. Because we failed to find any morphometric study of the popliteal fossa in the professional literature, we could not develop a comprehensive discussion about the sex and laterality differences of the popliteal fossa. However, after reviewing the medical literature, we found the muscles limiting the popliteal fossa to be independent of sex and laterality. This referred to the plantaris muscle [24], the triceps surae muscle [15], the biceps femoris muscle [12], the semimembranosus muscle [2], and the semitendinosus muscle [3]. All the aforementioned muscles displayed a commensurate increase in length and width, expressed by linear growth patterns. Szpinda et al. [29] alone reported the only laterality differences with relation to the short head of the biceps femoris muscle. Neither sex nor laterality showed statistically significant differences in other skeletal muscles of the human foetus: the triceps brachii muscle [13], the biceps brachii muscle [28], and the rectus abdominis muscle [12] that extended typically from its origin to its insertion.
Numerical data of the popliteal fossa in the growing human foetus
Morphometric studies of the popliteal fossa may be helpful from both cognitive and clinical aspects. Dudek et al. [12] claimed that growing anatomical structures should be described accurately enough for clinical and prognostic purposes with segmental-linear models or one-function models. Furthermore, the degree of adjustment of model parameters and measurement results are strongly influenced by the function form, and especially by the size of anatomical structures. However, there are no reports in the professional literature to do with the size of the popliteal fossa in human foetuses. To the best of our knowledge, the present article is the first one to focus on the quantitative analysis on the popliteal fossa in the human foetus. Due to neither male-female nor right-left statistically significant differences (p > 0.05), we decided to aggregate numerical data concerning particular morphometric parameters and model only one growth pattern of statistical significance for each parameter. From a geometrical point of view, the diamond-shaped popliteal fossa presents a quadrangular with 4 sides and 2 diagonals. Having compared lengths of 4 boundaries of the popliteal fossa, we found the superomedial one to be greatest, the inferomedial one to be smallest, and the superolateral one to be greater than the inferolateral one. In the material under examination, all these diameters elongate with foetal age in accordance with natural logarithmic functions. The lengths of the superomedial, inferomedial, superolateral, and inferolateral boundaries of the popliteal fossa modelled the following natural logarithmic functions: y = –44.421 + 24.301 × ln (age), y = –39.019 + 20.981 × ln (age), y = –41.379 + 22.777 × ln (age), and y = –37.547 + 20.319 × ln (age), respectively.
As it transpired, the vertical diameter of the popliteal fossa was roughly twice its transverse diameter. In the study period, both vertical and transverse diameters of the popliteal fossa displayed the natural logarithmic growths: y = –69.790 + 38.73 × ln (age) and y = –28.915 + 15.822 × ln (age), correspondingly. Furthermore, the projection surface area of popliteal fossa increased in accordance with the natural logarithmic function y = –485.631 + 240.844 × ln (age).
Out of the 4 angles of the popliteal fossa, the medial one was greatest, the inferior one the smallest, while the lateral one was somewhat smaller than the medial one and approximately 3 times greater than the superior one.
The mean superior (α) angle of the popliteal fossa (Tab. 6) between weeks 17 and 29 ranged from 38.172 ± 0.707° to 39.405 ± 0.007° on the right, and from 42.075 ± 6.230° to 40.500 ± 0.692° on the left, without statistically significant differences on either side or between left and right sides. Since the statistical analysis showed their values not to significantly change with foetal age (p > 0.05), we could not model their growth patterns.
Variability of the muscles limiting the popliteal fossa
In the material under examination, we did not find any variability of the skeletal muscles limiting the popliteal fossa: the semitendinosus, semimembranosus, biceps femoris, plantaris, and gastrocnemius muscles all extended in a typical fashion. Okamoto et al. [20] found an anomalous muscle originating from the medial head of gastrocnemius, passing transversely subjacent to the popliteal fascia, and crossing posteriorly to the neurovascular structures of the popliteal fossa to finally end on the biceps femoris tendon. Such an atypical muscle must have been derived from the short head of the biceps femoris muscle because it was innervated by the common peroneal nerve. Kim et al. [16] presented a similar thin transverse muscle in the superficial region of the popliteal region that originated from the biceps femoris tendon and inserted onto the medial head of gastrocnemius muscle. It was innervated by a motor branch originating from the lateral sural cutaneous nerve and supplied by the sural artery.
The third head of the gastrocnemius muscle presents its most common variation [1, 5, 6, 10, 14], found in 1.7–5.5% of individuals [10]. The third head of the gastrocnemius muscle usually originates from the lateral epicondyle of femur, the lateral aspect of the popliteal surface of femur, and the articular capsule of the knee joint. It may sporadically originate from the long head of biceps femoris muscle, the lateral lip of linea aspera, the crural fascia, and even from the semitendinosus belly [5, 6, 10, 14]. The third head of the gastrocnemius muscle typically descends vertically subjacent to the popliteal fascia as the medial partner of the plantaris muscle, and it inserts onto the junction of the medial and lateral heads of the gastrocnemius muscle [10]. It may possess some separate origins and divide near its insertion to merge with the 2 heads of the gastrocnemius muscle. The biceps femoris muscle may either lack its short head or possess an extra head, originating from the ischial tuberosity, lateral lip of linea aspera, or the lateral epicondyle of femur. Sinav et al. [23] found atypical muscle slips that underlay the popliteal fascia and fascia lata, respectively. The first one arose from the inferior part of the long head of biceps femoris muscle and ended in the crural fascia, while the other started with the superior part of the long head of biceps femoris muscle and joined the semitendinosus muscle. Liu et al. [18] and Sussmann [26] reported the bilateral absence of the semimembranosus muscle. Chason et al. [7] observed the tensor fasciae suralis, the belly of which originated from the lateral aspect of the semitendinosus muscle and extended to the distal thigh. Its long tendon superficially crossed the superficial popliteal fossa, so as to merge with the most superficial part of the calcaneal tendon.
Morphometric studies of the muscles limiting the popliteal fossa in the human foetus
Dudek et al. [12] examined the growth dynamics of the biceps femoris muscle, which is the superolateral boundary of the popliteal fossa, in 67 human foetuses of both sexes with a crown-rump length of 130–237 mm. Szpinda et al. [29] examined the biceps femoris muscle in 30 human foetuses aged 17–30 weeks of gestation. The growth of its long head followed commensurately in both length and width, and modelled linear functions: y = –25.27 + 3.61 × age (R = 0.90) and y = –2.75 + 0.35 × age (R = 0.77), respectively. Of note, the growth of the short head of the biceps femoris presented statistically significant right-left differences. Its length modelled the linear functions: y = –10.09 + 1.86 × age (R = 0.79) on the right and y = –4.45 + 1.58 × age (R = 0.77) on the left. Correspondingly, its width followed the linear functions: y = –0.80 + 0.12 × age (R = 0.54) on the right and y = 0.73 + 0.04 × age (R = 0.25) on the left. The length of tendon of biceps femoris muscle increase proportionately: y = –9.85 + 1.41 × age (R = 0.90). Kadir et al. [15] performed a morphometric study of the gastrocnemius muscle in terms of its length, width, and thickness in 51 human foetuses of both sexes aged 15–40 weeks of gestation. The medial head of gastrocnemius proved to be longer, wider, and thicker than the lateral one. During the study period the length of the medial and lateral heads of the gastrocnemius muscle increased from 28.01 to 80.89 mm and from 14.77 to 53.54 mm, respectively. Yıldız et al. [32] examined the length and width of the plantaris belly and tendon in 24 human foetuses aged 17–40 weeks of gestation. The plantaris muscle was absent unilaterally in one male foetus and bilaterally in one female foetus, while the remaining plantaris muscles were typically structured with a relatively short belly and long tendon. When comparing the plantaris belly in the second and third trimesters of gestation, its mean length increased from 7.48 to 17.58 mm, while its mean width increased from 2.96 to 5.82 mm. As far as the plantaris tendon is concerned in the second and third trimesters of gestation, its mean length increased from 36.30 to 65.39 mm, while its mean width increased from 0.43 to 0.95 mm.
Badura et al. [2] examined the growth dynamics of the semimembranosus muscle in the human foetus that presents the superomedial boundary of the popliteal fossa. Both the length and width of the semimembranosus tendon modelled linear functions: y = 0.058 + 0.992 × age (R = 0.99; p < 0.05) and y = 0.068 + 0.940 × age (R = 0.98; p < 0.05), respectively. Another study by Badura et al. [3] concentrated on the foetal growth of the semitendinosus muscle that followed proportionately, as follows: y = 9.8971 + 1.7803 × age (R = 0.9752; p < 0.05) for length of the semitendinosus belly, y = –0.5495 + 0.207 × age (R = 0.8729; p < 0.05) for width of the semitendinosus belly, y = –8.1735 + 1.4421 × age (R = 0.9401; p < 0.05) for length of the semitendinosus tendon, and y = 0.0097 + 0.0442 × age (R = 0.8833; p < 0.05) for width of semitendinosus tendon.
Clinical aspects of the popliteal fossa
A thorough understanding of both the topography and contents of the popliteal fossa is critical in patients suffering from its injury and other pathologies [1]. Injuries of the popliteal fossa are sporadic, constitute only 2% of all surgical interventions around the knee, and mostly affect the plantaris muscle. Such a condition is clinically termed “tennis player’s leg” or “tennis leg” [21]. The injury of the plantaris muscle occurs most frequently while running or jumping and is caused by an eccentric load placed across the ankle with the extended knee [24]. Because of its long tendon and course with the calcaneal tendon, the plantaris muscle is commonly used for reconstruction of other tendons and ligaments, and it may contribute to Achilles tendinopathy [21]. Isolated or combined chronic injury of the posterolateral corner of popliteal fossa requires its reconstruction with reconstruction of any concomitant cruciate ligament injury [9]. Damage to the soleus muscle mostly results from running or springing and is characterised by a severe pain after breaks, including a night rest.
Supernumerary muscles positioned at the inferior part of the popliteal fossa constituted a much more frequent reason for entrapment of the popliteal vessels than those at the superior part of the popliteal fossa [6, 7, 14, 15, 19, 21]. The third head of the gastrocnemius muscle traverses the inferior part of the popliteal fossa and may exert a significant compressive effect on the adjacent neurovascular structures, usually resulting in popliteal vessel entrapment or compressive neuropathies, involving branches of the tibial and common fibular nerves [6, 10]. Partial resection of the third head of the gastrocnemius muscle is usually sufficient to relieve entrapped symptoms [14]. Kotian et al. [17] found a sporadic variation of the plantaris muscle to stem from a common origin with the further formation of 2 muscle bellies that crossed and entrapped the neurovascular bundle in the popliteal fossa. Olewnik et al. [21] presented an anomalous plantaris muscle that originated from the knee joint capsule, crossed posterior to the tibial nerve and the popliteal vessels, and might potentially compress the tibial nerve. Entrapment syndromes are characterized by a leg pain, tenderness in the popliteal fossa and decreased pulsations of the posterior tibial and dorsalis pedis arteries.
Chason et al. [7] and Montet et al. [19] emphasised that the tensor fasciae suralis muscle presents a sporadic cause of a popliteal mass, which must be differentiated from other pathological masses. Anatomical variations of the muscles limiting the popliteal fossa may be valuable for the surgical approaches in popliteal vessel syndromes [1]. Monotonous microtrauma of the pes anserinus, comprising tendons of the semitendinosus, gracilis, and sartorius muscles, may lead to chronic inflammation and later result in the development of degenerative changes in this region [22].
Neoplasmatic changes may be localised ain the popliteal region. Weschenfelder et al. [31] presented a desmoid tumour at the right popliteal fossa of a 34-year-old woman. This tumour surrounded the lateral head of the gastrocnemius muscle, involved the common fibular nerve, and infiltrated the head of fibula as far as the posterolateral aspect of the articular capsule of knee joint. Derzsi et al. [11] described a haemangioma of the left popliteal fossa in a 13-year-old child, who had previously undergone surgery because of congenital pes equinovarus.
CONCLUSIONS
In terms of morphometric parameters, the popliteal fossa in the human foetus displays neither male-female nor right-left differences.
In the popliteal fossa, growth patterns of its 4 boundaries, vertical and transverse diameters, and projection surface area all follow natural logarithmic functions.
All the morphometric data considered age-specific reference intervals, which may be conducive in the diagnostics of congenital abnormalities in the human foetus.
ARTICLE INFORMATION AND DECLARATIONS
Ethics statement
The present examinations were ethically approved by the Bioethics Committee of the Ludwik Rydygier Collegium Medicum in Bydgoszcz and the Nicolaus Copernicus University in Bydgoszcz.
Authors’ contributions
Mateusz Badura: concept, dissection, collecting data, statistical analysis, literature search, writing the article. Maria Dąbrowska: concept, dissection, collecting data, statistical analysis, literature search, writing the article. Anna Badura: statistical analysis, literature search. Monika Paruszewska-Achtel: dissection, literature search, writing the article. Magdalena Grzonkowska: dissection, literature search. Mariusz Baumgart: dissection, collecting data, statistical analysis. Michał Szpinda: writing the article, final approval of article.
Funding
None.
Conflict of interest
The authors declare that there is no conflict of interest.
