Surg Radiol Anat (2007) 29:303–311 DOI 10.1007/s00276-007-0215-3
O R I G I N A L A R T I CL E
Extensor retinaculum syndrome after distal tibial fractures: anatomical basis T. Haumont · G. C. Gauchard · L. Zabee · J.-M. Arnoux · P. Journeau · P. Lascombes
Received: 21 March 2007 / Accepted: 3 May 2007 / Published online: 15 May 2007 © Springer-Verlag 2007
Abstract Fractures of the distal extremity of the tibia include physeal injuries among teenagers and more complex fractures among adults. Displacement causes the compression of the muscles located between the distal tibia and the superior extensor retinaculum (SER). Among the muscles of anterior compartment of the leg, the extensor hallucis longus (EHL) is particularly vulnerable due to the amount of muscle Wbers extending under the SER. Consequently, a partial anterior compartment syndrome could result, aVecting only the distal portion located under the SER. In clinical practice, Mubarak measured the intramuscular pressure isolated under the SER and suggested the physio-pathological hypothesis of a compression of distal muscle Wbers. The aim of this study is to compare the ratios of anterior compartment muscle Wbers extending under the SER. Twenty legs were dissected in order to study how much of these muscles extend under the SER, their passages possibly dividing into two of the SER, as well as their vascularization and their innervation. On the last seven legs, the engagement of the muscles were measured in the spontaneous position and with a dorsal Xexion of 0°. The
posterior muscle Wbers of this compartment always descend lower than the anterior Wbers. EHL muscle Wbers and those of the inconsistent Wbularis tertius always extend under the retinaculum, unlike those of the tibialis anterior and of the extensor digitorum longus. The EHL muscle extends under the SER more than the other muscles. Its posterior Wbers are longer when this muscle goes through a dividing into two of the retinaculum. Its vascularization seems lesser, which could explain why this muscle tends to suVer more. The deep Wbular nerve innervates the anterior compartment of the leg, yet no nerve branches can be found under the upper edge of the retinaculum. In all cases, the muscle Wbers do not extend as much under the SER in a 0° of dorsal Xexion. This anatomical study allows us to explain why the EHL is more likely to suVer from this partial compartment syndrome and conWrms that when the latter occurs it is necessary, in all cases, to do emergency surgery opening the distal crural fascia and necessarily including the SER.
T. Haumont · L. Zabee · P. Journeau · P. Lascombes Service de Chirurgie Infantile Orthopédique, Hôpital Brabois-Enfants, 1, rue du Morvan, 54511 Vandoeuvre-lès-Nancy, France
Introduction
T. Haumont (&) · J.-M. Arnoux · P. Lascombes Laboratoire d’Anatomie, Faculté de Médecine de Nancy, 9, avenue de la Forêt de Haye BP 184, 54505 Vandoeuvre-lès-Nancy, France e-mail:
[email protected] T. Haumont · G. C. Gauchard INSERM, ERI11, Faculté de Médecine de Nancy, 9, avenue de la Forêt de Haye, 54505 Vandoeuvre-lès-Nancy, France
Keywords Ankle trauma · Compartment syndrome · Extensor hallucis longus · Extensor reticulum
Distal tibial fractures occur frequently. They can be divided into physeal injuries in teenagers, which represent 5% of fractures occurring in this age group [2], and often more complex fractures in adults. In fractures where the distal fragment is mainly displaced backward, an anterior compartmental syndrome of the leg muscles, limited to the extensor hallucis longus (EHL) and possibly the extensor digitorum longus (EDL), has been described [10] and observed in clinical practice. The EHL has the speciWc feature of occupying the distal portion of the leg, and its
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muscle Wbers extend far under the retinaculum in front of the ankle joint. As a result, they can be subjected to sustained compression between the fractured distal tibial metaphysis, from behind, and the superior extensor retinaculum (SER) in front, through a “cigar-cutter” type of mechanism. What results is an actual compartmental syndrome, which is limited to this muscle and cannot be explained by damage to its nerve branches, which never descend below the SER [5, 6, 13]. Clinical signs include pain in the lower leg, numbness of the Wrst commissure, which is witness of an aZicted deep Wbular nerve, and an active extension deWcit of the hallux. If the retinaculum is not opened, retraction of this muscle leads to a hallux erectus. Several classic studies have focused on anatomical descriptions of these anterior compartment muscles, with some authors concentrating particularly on variations in distal attachment with a great frequency of dividing [3, 7]. The study of the muscle–tendon junction was carefully detailed by Bonnel [1]. However, rare studies focus on the relationships between the muscles Wbers and the SER. As a result, the aim of this anatomical description is to describe the relationships between the muscle Wbers of the anterior compartment of the leg with the SER, to quantify the amount that lie under the SER, and to describe their vascularization in order to evaluate the quality of their trophism.
Materials and methods We obtained 20 legs from fresh, unembalmed adult cadavers. After an initial freezing to ¡18°C, the anatomical specimens were unfrozen, injected with a latex solution at the level of the femoral artery, and then dissected. The injection was given in the femoral triangle in such a way as to be able to do other anatomical studies on these specimens. The study was done macroscopically, with the naked eye, without any operating microscope. All dissections were carried out using the same technique: after exposition of the crural fascia, the SER, the inferior extensor retinaculum (IER) and the dorsal fascia of the foot, we opened the anterior crural compartment in the middle. Before doing so, we carefully pinpointed and marked the upper edge of the SER, which was diYcult: after humidifying the crural fascia, it was possible in low-angle light to locate the densiWcation of the fascia conjunctive Wbers. ModiWcation of its aspect made it possible to mark the upper edge of the SER. It should be noted that thickening of the fascia surrounding the ankle covers three reinforcements, the ligamentum transversum cruris or superior extensor retinaculum (SER), the ligamentum cruciatum cruris or inferior extensor retinaculum (IER), which has a “Y” shape, and the ligamentum laciniatum, which keeps the Xexor muscles, the posterior tibial vessels and the tibial nerve behind the medial malleolus [4].
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Each of the muscles of the anterior compartment were dissected: the tibialis anterior (TA), the extensor hallucis longus (EHL), the extensor digitorum longus (EDL), and the inconstant Wbularis tertius (3F). The anterior tibial artery and the deep Wbular nerve were dissected from their point of origin in such a way as to bring to light all the vascular-nervous pedicles for each of these four muscles and to count their nerves and vascular ramiWcations. All measures were made on the 20 feet in a spontaneous extension position, that is, at an average plantar Xexion of 30°. The seven Wnal feet beneWted from identical complementary measurements in a neutral position. We measured how much of these muscles, the muscle Wbers extended under the upper edge of the SER, which was called the “engagement”. We carried out this measurement for the anterior Wbers as well as for the posterior Wbers, because the latter always descend lower than the former (Fig. 1). These measurements were made as follows: the distance that separated the distal extremities of the muscular Wbers from the upper edge of the SER was measured in centimeters. The distance was deWned as negative when the muscles Wbers did not extend under the SER and they remained adjacent to the latter. The distance was, however, positive when the muscle Wbers extended under the SER (Fig. 2). The total length of the muscle Wbers studied was determined from their adjacent attachment to the muscle–tendon distal junction. As a result, the length of the distal tendon extending below the muscle Wbers was not considered, it not being involved in this hallux syndrome. The percentage of muscle under the SER therefore corresponds to the ratio of the muscle Wbers extending under the SER with regard to the total length of the Wbers of the considered muscle.
Fig. 1 Muscles of the anterior compartment of the leg. Opened superWcial fascia respecting the superior extensor retinaculum (LTC). For each muscle, the posterior muscle Wbers (PF) descend lower than the anterior Wbers (AF)
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305
Fig. 3 Example of a nerve branch from the deep peroneal nerve (DPN) destinated to the extensor hallucis longus (NbEHL)
Fig. 2 Measurement of the muscle Wbers extending under the superior extensor retinaculum (LTC). In this Wgure, the measurement of the most distal anterior Wbers of the extensor digitorum longus (EDL) is negative. The measurement of the most distal anterior Wbers of the extensor hallucis longus (EHL) is positive
For each of the four muscles, we also indicated whether or not its tendon passed through a dividing into two of the SER or if it stayed behind the SER. Vascular and nervous pedicles were dissected and we noted for each of the four muscles: – the number of nerve ramiWcations innervating them (Fig. 3) and whether or not a branch was located under the upper edge of the SER, – the number of arterial ramiWcations (Fig. 4). For each muscle, we calculated the length in centimeter on average were vascularized by an arterial ramiWcation, by calculating the ratio between the length of the muscle Wbers over the number of arterial branches. Photographs were taken for each specimen with a digital Nikon Coolpix 660 camera (2 million pixels) in macroscopic position with the only goal of having viable documents that could be veriWed. The statistical analysis was carried out with the help of non-parametric tests due to the low number of anatomical specimens (logiciel Statview, Abacus, Berkeley, CA). Regarding the percentage of the muscle laid under the SER and the dividing of the SER, the overall heterogeneity of the distributions of the four muscles was tested with the help of the Pearson ² test. Two on two distribution
Fig. 4 Arterial vascularization from the anterior tibial artery (ATa) of the anterior compartment’s constant muscles: anterior tibialis (AT), extensor digitorum longus (EDL) and extensor hallucis longus (EHL)
comparisons were carried out with the help of the exact Fisher test. Concerning the parameters of length of posterior muscle Wbers founded under the SER, whether or not
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they passed through a doubled SER, the percentage founded under the SER, and the number of centimeters of muscle vascularized per artery, we applied Kruskal–Wallis (H, overall heterogeneity) and Mann & Whitney (z, two to two comparisons) tests. The probability threshold set at P · 0.05 was used as an indicator of statistical signiWcance.
compartment muscle that we occasionally found having anterior Wbers extending under the SER (3 cases out of 13). These muscle Wbers under the SER extended a length of 1, 1 and 4 cm. The EHL and the 3F always presented posterior muscle Wbers extending under the SER, unlike the TA and EDL (respectively, 75 and 80% of cases). Engagement of posterior muscle Wbers
Results Length of muscle Wbers Table 1 shows the results we observed regarding the length of the anterior and posterior muscle Wbers of the four anterior compartment muscles—TA, EHL, EDL and 3F—as well as how much of these Wbers extended under the upper edge of the SER. The posterior Wbers of these four muscles always descend lower than the anterior Wbers. The anterior Wbers of the TA, the EHL and the EDL never extend under the SER. The 3F is an inconstant muscle found 13 times out of 20 in our series (65%). This muscle is the only anterior
Table 2 presents the results we observed regarding how often the posterior muscle Wbers of the four anterior compartment muscles—TA, EHL, EDL and 3F—extended under the SER. We found an overall heterogeneity among the four muscles (² = 8.7, P = 0.037). The EHL and 3F muscles regularly extend under the SER, and therefore do so more frequently than the other two muscles, the TA and the EDL, with statistically signiWcant diVerences being observed between the EHL and the TA (P = 0.047), with a tendency towards signiWcance between the EHL and EDL muscles (P = 0.053). On the other hand, no statistically signiWcant diVerence was observed between the EHL and the 3F.
Table 1 Muscle Wbers extending under the superior extensor retinaculum, ankle in spontaneous extension TA
EHL
LAF
LPF
A ex
P ex
LAF
Foot no. 1
20
27
¡4
3
Foot no. 2
16
22
¡3
3
Foot no. 3
23
29
¡8
¡2
Foot no. 4
18
28
¡10
0
EDL LP F
A ex
P ex
11
19
¡5
9
17
¡4
11
19
9
22
3F
LAF
LPF
A ex
P ex
LAF
LPF
3
14
32
4
10
20
¡3
5
20
¡8
5
13
A ex
P ex
¡12
6
–
–
–
–
¡12
¡2
–
–
–
–
30
¡12
¡2
–
–
–
–
32
¡15
4
–
–
–
– –
Foot no. 5
20
30
¡5
5
15
26
¡4
7
22
30
¡2
6
–
–
–
Foot no. 6
21
30
¡8
1
13
24
¡2
9
20
35
¡10
5
28
36
¡2
6
Foot no. 7
21
29.5
¡7
1.5
13.5
27
¡5.5
8
20
30
¡9
1
20
32.5
¡9
3.5
Foot no. 8
20.5
27
¡7.5
1
13
25
¡6
6
12
30
¡15
3
25
33
¡2
6
Foot no. 9
19
27
¡5
3
15
26
¡2
9
15
18
¡10
¡7
25
31
0
6
Foot no. 10
22
32
¡6
4
16
28
¡5
7
12
26
¡16
¡2
29
32
1
4
Foot no. 11
25
30
0
5
12
25
¡3
10
16
36
¡10
10
–
–
–
–
Foot no. 12
26
32
¡3
3
14
26
¡4
8
24
35
¡4
7
–
–
–
–
Foot no. 13
18
26
¡6
2
15
25
¡3
7
19
33
¡8
6
19
33
¡8
6
¡8
2
14
26
¡8
4
17
36
¡15
4
17
36
¡15
4
0
3
17
29
0
12
15
30
¡4
11
15
30
¡4
¡7
0
26
37
¡5
7
19
32
¡9
4
30
36
1
Foot no. 14
21
31
Foot no. 15
19.5
24.5
Foot no. 16
22
29
11 7
Foot no. 17
21
30
¡6
3
21
33
¡6
6
14
34
¡13
7
14
34
¡13
7
Foot no. 18
19
27
¡8
0
15
22
¡5
2
16
34
¡13
5
16
34
¡13
5
Foot no. 19
21
26
¡9
¡4
15
25
¡3
7
21
34
¡11
2
32
39
0
7
Foot no. 20
23
29
¡5
1
21
37
¡7
9
18
30
¡10
2
32
36
4
8
TA tibialis anterior muscle, EHL extensor hallucis longus, EDL extensor digitorum longus, 3F Wbularis tertius, LAF length of anterior muscle Wbers, LPF length of posterior muscle Wbers, A ex number of centimeter the anterior muscle Wbers extend under the superior extensor retinaculum, P ex number of centimeter the posterior muscle Wbers extended under the superior extensor retinaculum, numbers in italic muscles passing through a divided superior extensor retinaculum
123
z = ¡2.4 P = 0.016 z = ¡0.9 NS P values are given NS not signiWcant
25.7 (20.8, 30.2)
14.5 (10.6, 20.0)
18.2 (14.2, 19.7)
H = 29.8 P < 0.001
z = ¡4.6 P < 0.001
z = ¡3.3 P = 0.001
z = ¡2.8 P = 0.005
z = ¡3.6 P < 0.001
z = ¡2.8 P < 0.005 z = ¡1.3 NS z = ¡4.1 P < 0.001 z = ¡0.9 NS z = ¡1.9 P = 0.058 z = ¡4.3 P < 0.001 H = 24.2 P < 0.001 6.0 (4.8, 7.0) 5.0 (3.5, 6.5)
10.0 (5.4, 12.4)
Table 4 presents the results observed regarding how often the posterior Wbers pass in a dividing into two SER, for the four TA, EHL, EDL and 3F muscles with their muscle Wbers extending under the SER. No statistically signiWcant diVerence was observed in the distribution of the four muscles (² = 3.9, NS).
% PF E
Dividing of the retinaculum
7.0 (5.0, 8.5)
Table 3 presents the results observed regarding the length of posterior Wbers when these Wbers extend under the SER, for the four muscles—TA, EHL, EDL and 3F. The table also includes the percentage of the posterior muscle Wbers that extend under the SER for each of these muscles. Regarding the length of the posterior muscle Wbers extending under the SER, the table shows that the EHL muscle Wbers extend under the SER signiWcantly more than those of the TA and EDL muscles. On the contrary, no signiWcant diVerence was observed between the EHL and 3F muscles. In addition, the table shows that the posterior Wbers of the TA muscle extend under the SER less than those of the 3F and EDL muscles. As for the proportion of the muscle extending under the SER, the table shows that the EHL muscle extends proportionally more than the other muscles, with statistically signiWcant diVerences being observed when compared with the three other muscles, TA, EDL and 3F. In addition the TA muscle extends under the SER proportionally less than the EDL and the 3F. However, no statistically signiWcant diVerence was observed between the EDL and the 3F muscles.
3.0 (1.6, 3.0)
Comparing of the engaged Wbers length
LPF E SER cm
For the seven Wnal anatomical specimens, between the spontaneous ankle position and the 0° Xexion position, we found a diVerence of muscle Wber extension under the SER of 1.7 cm for the TA, of 1.6 cm for the EHL, of 1.6 cm for the EDL and of 1.9 cm for the 3F. The posterior muscle Wbers of the TA, the EHL and the EDL no longer extend under the SER when the ankle moves from the spontaneous extension position to the 0° Xexion position.
3F versus EDL
0 (0%)
3F versus TA
4 (20%)
13 (100%)
EHL versus 3F
16 (80%)
3F
EHL versus EDL
EDL
EHL versus TA
0 (0%)
Mann & Whitney test
5 (25%)
20 (100%)
Kruskal Wallis test
15 (75%)
EHL
3F M (Q1, Q3) n = 13
TA
EDL M (Q1, Q3) n = 16
No PF extension under SER n (%)
EHL M (Q1, Q3) n = 20
PF extension under SER n (%)
TA M (Q1, Q3) n = 15
Table 2 Distribution of the four muscles tibialis anterior (TA), extensor hallucis longus (EHL), extensor digitorum longus (EDL) and Wbularis tertius (3F) for their posterior muscle Wbers (PF) extending or not extending under the superior extensor retinaculum (SER), ankle in spontaneous extension
TA versus EDL
307 Table 3 Results expressed in median (M) associated with the Wrst (Q1) and third (Q3) quartiles, length parameters for posterior Wbers (LPF) when, with the ankle in spontaneous extension, these Wbers extend (E) under the superior extensor retinaculum (SER) and proportion of the muscle extended under the SER (%) for each of the four muscles: tibialis anterior (TA), extensor hallucis longus (EHL), extensor digitorum longus (EDL) and Wbularis tertius (3F)
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Surg Radiol Anat (2007) 29:303–311
Table 4 Distribution of the four muscle tibialis anterior (TA), extensor hallucis longus (EHL), extensor digitorum longus (EDL) and Wbularis tertius (3F) for extension of their posterior Wbers (PF) passing or not passing in a division (D) of the superior extensor retinaculum (SER), with the ankle in spontaneous extension PF D SER n (%)
PF ND SER n (%)
TA
10 (67%)
5 (33%)
EHL
7 (35%)
13 (65%)
EDL
8 (50%)
8 (50%)
3F
5 (38%)
8 (62%)
the posterior muscle Wbers, the Wbers that run through a doubled SER are signiWcantly longer than those which do not run through the doubled SER for the EHL and EDL muscles; on the other hand, no statistically signiWcant diVerence was observed for the TA and the 3F. Concerning vascularization of the TA, EDL and 3F muscles, no statistically signiWcant diVerence was observed, whether or not the muscle Wbers passed through a doubled SER. However, for the EHL, it appears that there are fewer centimeters of muscle vascularized per artery when the posterior Wbers pass through a doubled SER, which makes it much more fragile in cases of compression. All these muscles are directly vascularized from the anterior tibial artery.
Muscular vascularization Innervation Table 5 details for each anatomical specimen and each muscle, the number of arteries, the length of the posterior Wbers and the ratio of the average muscle length vascularized per artery. Table 6 presents the results observed regarding the length of the posterior Wbers and the number of vascularized centimeters per artery for the muscles that do and do not pass through a doubled SER. Regarding the length of
Innervation of the anterior compartment muscles depends on the deep Wbular nerve. We found a median of three nerve branches for the TA muscles (between 1 and 5), two branches for the EHL (between 1 and 3), one branch for the EDL muscle (from 1 to 3), and one branch for the 3F muscle (between 1 and 3). We found no branches taking root under the SER.
Table 5 Vascularization of the muscles anterior compartment of the leg TA Nb a
EHL LPF
C Cm/a
Nb a
EDL LPF
Cm/a
Nb a
3F LPF
Cm/a
Nb a
LPF
Cm/a
Foot no. 1
14
27
1.9
10
19
1.9
15
32
2.1
–
–
–
Foot no. 2
10
22
2.2
6
17
2.8
13
20
1.5
–
–
–
Foot no. 3
13
29
2.2
10
19
1.9
17
30
1.8
–
–
–
Foot no. 4
14
28
2.0
6
22
3.7
17
32
1.9
–
–
–
Foot no. 5
15
30
2.0
10
26
2.6
19
30
1.6
–
–
Foot no. 6
14
30
2.1
8
24
3.0
9
35
3.9
20
36
Foot no. 7
19
29.5
1.6
6
27
4.5
14
30
2.1
12
32.5
2.7
Foot no. 8
14
27
1.9
4
25
6.3
5
30
6.0
15
33
2.2
Foot no. 9
14
27
1.9
3
26
8.7
12
18
1.5
14
31
2.2
Foot no. 10
12
32
2.7
3
28
9.3
7
26
3.7
15
32
2.1
Foot no. 11
14
30
2.1
4
25
6.3
7
36
5.1
–
–
Foot no. 12
9
32
3.6
6
26
4.3
5
35
7.0
–
–
Foot no. 13
13
26
2.0
4
25
6.3
11
33
3.0
15
33
2.2
Foot no. 14
19
31
1.6
9
26
2.9
20
36
1.8
20
36
1.8
Foot no. 15
12
24.5
2.0
7
29
4.1
11
30
2.7
11
30
2.7
Foot no. 16
17
29
1.7
13
37
2.8
16
32
2.0
17
36
2.1
Foot no. 17
15
30
2.0
9
33
3.7
21
34
1.6
21
34
1.6
Foot no. 18
16
27
1.7
16
22
1.4
17
34
2.0
17
34
2.0
Foot no. 19
20
26
1.3
11
25
2.3
18
34
1.9
18
39
2.2
Foot no. 20
18
29
1.6
19
37
1.9
18
30
1.7
19
36
1.9
– 1.8
– –
TA tibialis anterior, EHL extensor hallucis longus, EDL extensor digitorum longus, 3F Wbularis tertius, Nb a number of arteries per muscle, LPF length of posterior muscle Wbers in cm, CM/a ratio LPF/Nb a representing the number of centimeter vascularized per artery, numbers in italic muscle passing in a divided superior extensor retinaculum (SER)
123
z = ¡0.45 NS
NS not signiWcant
P values are given
2.1 (2.0, 2.2) 33.5 (32.5, 36.0)
z = ¡0.15 NS z = ¡1.08 NS
2.0 (1.7, 2.9) 30.0 (28.0, 32.0)
z = ¡2.24 P = 0.025 z = ¡1.47 P = 0.141
2.9 (2.2, 4.2) 25.0 (21.3, 26.0)
z = ¡2.64 P = 0.008 z = ¡0.20 NS
2.0 (1.8, 2.2) 28.5 (26.5, 29.5)
z = ¡0.85 NS
ND
Discussion
z, P Mann & Whitney
29.3 (27.0, 30.5) D
2.0 (1.7, 2.1)
28.0 (26.0, 36.0)
4.3 (3.0, 8.1)
34.0 (31.5, 35.5)
2.4 (1.9, 4.1)
34.0 (31.9, 36.8)
2.2 (1.8, 2.7)
309
SER
Cm/a M (Q1, Q3) cm LPF M (Q1, Q3) cm LPF M (Q1, Q3) cm
Cm /a M (Q1, Q3) cm
LPF M (Q1, Q3) cm
Cm /a M (Q1, Q3) cm
LPF M (Q1, Q3) cm
Cm /a M (Q1, Q3) cm
3F EDL EHL TA
Table 6 Results expressed in median (M) associated with the with the Wrst (Q1) and third (Q3) quartiles of the length parameters for posterior Wbers (LPF) and the number of centimeter vascularized per artery (CM/a) for Wbers passing (D) or not passing (ND) through a division of the superior extensor retinaculum (SER) for each of the four muscles: tibialis anterior (TA), extensor hallucis longus (EHL), extensor digitorum longus (EDL) and Wbularis tertius (3F)
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Weakness of the EHL muscle, or “dropped hallux” syndrome, is recognized as a postoperative or post-traumatic complication [6, 12–14, 16]. Numerous authors have attributed this complication to a neurological deWcit of the deep Wbular nerve or of its branch(es) innervating the EHL. Several classical anatomical studies have studied the innervation of the anterior compartment muscles of the leg. Anatomical dissections of the deep Wbular nerve have shown that the Wrst branches destined to the TA and EDL muscles begun near the Wbular neck, while the EHL nerve run under the Wbular neck before reaching the EHL muscle for around 10 cm according to Satku [13], 15 cm according to Kirgis [6]. The length of this nerve branch is around 5 § 1.5 cm [5]. For Elgafy [5], 90% of the EHL muscles are innervated by only one collateral branch from the anterior tibial nerve, while we report a median of two nerve branches (between 1 and 3). According to this author, 63.6% of the EHL nerve branches enter from the Wbular side, 18.2% from the tibial side, and 18.2% from the front. In cases of one nerve branch near the Wbula, its proximity to this bone makes it very vulnerable during surgical Wbular removal. Although these observations of “dropped hallux” have clearly a neurological origin, Mubarak [10] hypothesized another mechanism, that of a partial and distal compartmental syndrome touching the distal muscle Wbers of the anterior compartment of the leg when these muscle Wbers are found under the SER. This partial compartmental syndrome is totally diVerent from the form which is normally found after a leg fracture and involves the entire anterior compartment of the leg or its proximal portion [8, 9]. From the study of six patients aged 6–15 years with a distal physeal injuries of the tibia, the intramuscular pressure measured beneath the SER by Mubarak was greater than 40 mmHg in all cases, while it was less than 20 mmHg in the other part of anterior compartment. Surgical treatment with opening of the SER led to clear improvement and even healing of this compartmental syndrome. This complication is not restricted to epiphyseal separation fractures among teenagers. It can also occur following ankle fractures in adults. Our surgical experience reveals that, during this fasciotomy, the tendon of the EHL muscle is widened, so that one can clearly see its posterior muscle Wbers extended under the SER, while the TA tendon is thicker, and without dissection we cannot see muscle Wbers extending under the SER. This is why we became interested by the description of the muscular portion found under the SER in the four muscles of the anterior compartment of the leg at a 30° plantar Xexion and in a neutral ankle position. Our study showed, that among the anterior muscles, the anterior
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muscle Wbers of the TA, EHL and EDL muscles never extend under the SER. However, in cases where 3F muscles exist, their anterior muscle Wbers occasionally extend under the SER (3 cases out of 13). Posterior muscle Wbers of the EHL and 3F regularly extend under the SER to a large degree, while it is frequent for the other two muscles, occurring in 75% of cases for the TA and 80% for the EDL. Thus, the average length of the posterior Wbers found under the SER, when they do, is 2.7 cm for the TA, 6.8 cm for the EHL, 5.2 cm for the EDL and 6.6 cm for the 3F, which respectively represents an average of 10, 26 and 16% of their length for the three former muscles in a spontaneous ankle position. When the foot is at 0°, the posterior Wbers extend less under the SER in all cases, with an average length, depending of the muscles, of 1.5–2 cm. However, the EHL muscle remains particularly exposed in cases of compression of its muscle Wbers to a compartmental syndrome localized under the SER, because one fourth of its length, on average, is mechanically susceptible to be injured, even when the foot is straightened up. This Wrst part of our study conWrms that the EHL muscle is fragile, compared to the other muscles, in cases of ischemic damage or of a partial compartmental syndrome of the distal part of the leg. In addition, the dissection showed the pathway followed of the muscle in doubled SER in 60% of the cases for the TA muscles and in more than one third of the cases for the other muscles: EHL (35%), EDL (40%) and 3F (38.5%). When there is a doubled SER, the amount of muscle Wbers under the SER was larger for the EHL and EDL muscles than when in absence of division, which makes them more vulnerable to a compartmental syndrome, in these cases, 29% (25–30%) of EHL lies under the SER, while the average is 25% in absence of divided SER. We suppose that a distal partial ischemia could be accompanied by a broader ischemia when the muscle passes through a split. This could explain the reason for certain patients to have more after than others an extensor retinaculum syndrome with a “dropped hallux” syndrome. In any case, the portion of the muscle Wbers located under the SER always diminishes when the foot was straighted up at 0°. The majority of cases of dropped hallux syndrome occured after a long waiting period. Thus, immobilization of the injured ankle at 0° is probably a means to decrease the risk of partial compartmental syndrome, in correlation with Weiner’s intercompartmental pressure measurements [15] which found the lowest leg pressure when the ankle was immobilized in a cast between 0° and 37° of dorsal Xexion. Vascularization of the anterior compartment muscles of the leg was studied by Pillet [11], who noted that “when sensitive-motor ischemia occurs, paralysis of the hallux, preceding of the TA and the EDL.” This vascularization
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mainly depends on the anterior tibial artery, the branches are arranged ladder-like, and are between 0.5 and 1 mm in diameter. According to Pillet, the three muscles receive 9–14 arterioles for the TA, 10–14 for the EDL and 6–8 for the EHL, respectively. Our measurements are relatively similar, with an average of 14 arterioles for the TA, 14.5 for the EDL, 17 for the 3F and 7.5 for the EHL. Pillet insists on the lack of intra-muscular longitudinal anastomosis which, when it exists, predominates in the upper third of the TA and at the proximal half of the EDL. However, we must relate the number of arterioles to the weight of each of the concerned muscles, and Pillet Wnds a proportional value in 5 feet with average weights of 98 g for the TA, 72 g for the EDL and 32 g for the EHL. However, endeavoring to measure the length of the muscle segment vascularized per arteriole, we found 4 cm for the EHL versus 2 cm for the TA and 2.8 for the EDL (whether or not it extended under the SER). Thus, this length is signiWcantly longer for the EHL in relation to the other muscles, and this measurement increases even more when the latter muscle passes through a doubled SER: 5.3 cm when doubled for 3.3 when not. The vascular fragility is clearly greater for the EHL muscle in case of compression under the SER. To summarize, the muscles exposed to a compartmental syndrome are therefore those whose Wbers extend under this SER that means, the EHL and the 3F in all cases, but less consistently also the TA and the EDL. However, the amount of the proximal muscle portion of these two latter muscles is enough to explain that a very distal and partial injury has no clinical repercussions. The 3F muscle extends under the SER consistently and for a large portion (nearly 20% of the length of its posterior Wbers), but its vascularization is better and in cases of injuries, the clinical diagnosis is very diYcult. On the other hand, the EHL muscle, which has an average of 25% of the length of its muscle Wbers located under the proximal limit of the SER, runs a greater risk of suVering in cases of compression and leading to an easier clinical diagnosis.
Conclusion From our dissections, it appears that the EHL muscle has a strong probability of being altered in cases of a partial compartmental syndrome under the SER after a fracture of the distal extremity of the tibia in teenagers or in adults, Wrst due to the amount of posterior muscle Wbers that lies under the SER, and secondly due to the fewer number of arterioles that supply it. Certain subjects seem to run a greater risk of this syndrome than others, in particular when the EHL muscle passes in a divided retinaculum. Keeping the ankle at 0° is a well-known rule for
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immobilization in orthopedics and traumatology. This position could also prevent a partial compartmental syndrome of the leg. When such syndrome occurs, it needs an urgent surgical release with opening the distal crural fascia, which must in all cases include the superior extensor retinaculum. References 1. Bonnel F (2005) Le complexe muscle–tendon (bases anatomiques et concept biomécanique), vol 87, pp 229–261. Expansion ScientiWque Française, Paris 2. Bracq H, Chapuis M, Violas P (1997) Fractures du cou-de-pied de l’enfant. Encycl Méd Chir Appareil locomoteur, 14-088-b-10, p 4. Elsevier, Paris 3. Denk CC, Oznur A, Sürücü HS (2002) Double tendons at the distal attachment of the extensor hallucis longus muscle. Surg Radiol Anat 24:50–52 4. Drake RL, Vogl W, Mitchell AWM (2005) Gray’s anatomy for students. Elsevier, Philadelphia, pp 569–570 5. Elgafy H, Ebraheim NA, Shaheen PE, Yeasting RA (2002) Extensor hallucis longus innervation. Clin Orthop 398:245–251 6. Kirgis A, Albrecht S (1992) Palsy of the deep peroneal nerve after proximal tibial osteotomy. J Bone Joint Surg 74-A:1180– 1185
311 7. Le Double AF (1897) Variation du système musculaire de l’homme, vol 2, pp 301–328. Schleicher Frères, Paris 8. McQueen MM, Court-Brown CM (1996) Compartment monitoring in tibial fractures. J Bone Joint Surg 78-B:99–94 9. McQueen MM, Christie J, Court-Brown CM (1996) Acute compartment syndrome in tibial diaphysal fractures. J Bone Joint Surg 78-B:95–98 10. Mubarak SJ (2002) Extensor retinaculum syndrome of the ankle after injury to the distal tibial physis. J Bone Joint Surg 84-B:11– 14 11. Pillet J, Cronier P, Mercier P, Moreau P, Boscher Y Taviaux R, Lescalie F (1984) L’artère tibiale antérieure et vascularisation des muscles de la loge antérieure de la jambe. Application au syndrome de la loge antérieure de la jambe. Bull Assoc Anat (Nancy) 68:223–231 12. Robinson CM, O’Donnell J, Will E, Keating JF (1999) Dropped hallux after the intramedullary nailing of tibial fractures. J Bone Joint Surg 81-B:481–484 13. Satku K, Wee JT, Kumar VP, Ong B, Pho RW (1992) The dropped big toe. Ann Acad Med Singapore 21:222–225 14. Shingade VU, Jagtap SM, Ranade AB (2004) Weakness of extensor hallucis longus after removal of non-vascularised Wbula as an autograft. J Bone Joint Surg 86-B:384–387 15. Weiner G, Styf J, Nakhostine M, Gershuni DH (1994) EVect of ankle position and a plaster cast on intramuscular pressure in the human leg. J Bone Joint Surg 76-A:1476–1481 16. Wiggins HE (1975) The anterior tibial compartmental syndrome. A complication of the Hauser procedure. Clin Orthop 113:90–94
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