The Anterolateral Ligament of the Knee: Descriptive Anatomy and Clinical Correlation.

BACKGROUND: The anterolateral ligament is a fibrous structure in the anterolateral aspect of the knee. Recently this liagament of the knee has gained spotlight in anatomical and imaging studies and has been designated as a new ligament of the knee joint. The anterolateral ligament (ALL) has been postulated to be a restraint against the anterolateral instability of the knee resulting in a positive pivot shift test. The purpose of this study is to provide detailed anatomical characteristics of ALL in the Indian population.
MATERIALS AND METHODS: The qualitative and quantitative characteristics of the ALL were observed in 20 embalmed cadaveric specimens. In all but one left male knee specimen (95%) ALL was observed. After isolating the ALL, its length, thickness, width, and points of attachments and dimensions of lateral collateral ligament (LCL) were determined.
RESULTS: The ALL was consistently present in the anterolateral region of the knee separate from the joint capsule. Its proximal attachment to the femur is anterior and distal to the attachment of the LCL. Distally the superficial fibers of the ALL inserted close to the Gerdy's tubercle at the level of the fibular head, and the deeper fibers merged with the lateral meniscus. The mean length of the ALL was 43.35 mm ± 4.04 mm in flexion and 40.38 mm ± 4.35 mm in extension. The average width of the ALL was 6.98 mm ± 0.95 mm at its origin and 9.36 mm ± 1.07 mm at its insertion.
CONCLUSION: The ALL is hypothesized to affect internal tibial rotation and plays a role in the pivot shift phenomenon. ALL rupture could be responsible for rotatory laxity after isolated intraarticular reconstruction of the ACL.

Introduction

The knee joint is stabilized by a complex system of static and dynamic stabilizers.12345 There have been various studies which have tried to demonstrate the anatomy of the lateral aspect of the knee, but none have been able to demonstrate completely the structure and function of the ligamentous structures on the lateral aspect of the knee joint.

Segond1 in 1879 was the earliest to demonstrate an avulsion fracture pattern at the anterolateral proximal tibia as a result of forced internal rotation of the knee. In 1948, Last2 termed this structure the “short lateral ligament.” Terry3 and LaPrade4 have called this structure as the “capsulo-osseous layer of the iliotibial band.” LaPrade et al.4 called it the “mid-third lateral capsular ligament” and Campos et al.5 coined the term “lateral capsular ligament.” The structure which these authors are describing is the same, which is called the “anterolateral ligament of knee” (ALL).

Tear of the ALL leads to a pivot-shift phenomenon, which is an excessive anterior tibial translation and internal rotation laxity.67 However, this instability may also be caused by damage of other structures on the anterolateral aspect of knee demonstrated by Vincent et al.,8 Claes et al.,9 and Hughston et al.10

The aim of this study is to define the incidence and anatomical characteristics of the ALL of the knee in the Indian Population.

Materials and Methods

The qualitative and quantitative characteristic of the ALL were observed in 20 embalmed cadaveric specimens – 12 females (6 right and 6 left) and 8 males (4 right and 4 left). The specimens were obtained from the routine cadaveric teaching of the first professional medical students. The mean age of cadavers was 80.2 years. Specimens with gross deformities and surgeries of the knee were excluded.

The dissection was performed in a standardized manner. A large rectangular area on the lateral aspect of the knee was demarcated. The skin and subcutaneous tissue were dissected. The iliotibial band (ITB), extensor apparatus and the short head of biceps were cleared of subcutaneous tissue. A tenotomy of the Quadriceps tendon was done at the myotendinous junction. The ITB was carefully separated from its tibial attachment at the Gerdy's tubercle. The retropatellar pad of fat in the region was removed. The lateral collateral ligament (LCL) and the surrounding biceps femoris tendon were isolated carefully. All soft-tissue structures were incised from the lateral condyle. The tendon of popliteus was identified and cleared.

After isolation, the capsular thickening characteristic and similar to ALL was observed. It could be well demarcated from the anterior joint capsule. The following measurements were made using a digital calipers (150 cm DC-60 western, Zhejiang, China)–ALL length in flexion, ALL length in extension, ALL width at the origin, ALL width at insertion, LCL length, and LCL width. The distance between the center of the ALL insertion and Gerdy's tubercle was also measured.

Results

The ALL was found as a distinct ligamentous structure in 19 specimens (95%) separate from the joint capsule on the anterolateral aspect of the knee. In one left knee specimen of a male, ALL was absent. In 19 of the 20 specimens, it was identified as a flat band taking origin from the lateral femoral epicondyle only anterior to the LCL, posterior to the insertion of popliteus tendon. At the origin, the posterior fibers of ALL were in continuity with the origin of the anterior fibers of LCL [Figure 1].

Figure 1

Right knee lateral aspect showing reflected Biceps femoris: BCF, Iliotibial tract: ITT, anterolateral ligament: ALL, Fibular collateral ligament: FCL, Tendon of popliteus: PLT Blue Star –Gerdy's tubercle

This band was observed to be running obliquely downward and forward to the anterolateral aspect of the proximal tibia [Figure 2]. The deeper fibers merged with the periphery of the lateral meniscus [Figure 3]. After separating the ALL from the rim of the meniscus, the lateral inferior geniculate artery and vein were seen in between the lateral meniscus and the ALL [Figure 4: Blue circle].

Figure 2

Left knee lateral aspect showing reflected Biceps femoris: BCF, Iliotibial tract: ITT, Anterolateral ligament: ALL, Fibular collateral ligament: FCL and Lateral femoral condyle: LFC

Figure 3

Right knee lateral aspect showing reflected Biceps femoris: BCF, Anterolateral ligament: ALL, Fibular collateral ligament: FCL Blue Star –Gerdy's tubercle, lateral meniscus lateral meniscus

Figure 4

Right knee lateral aspect showing reflected Biceps femoris BCF, Iliotibial tract ITT , anterolateral ligament ALL,Fibular collateral ligament FCL , Lateral Meniscus LM , cut end popliteus tendon PLT, Lateral femoral condyle LFC Lateral tibial condyle LTC Gerdyæs tubercle GT Encircled: Lateral inferior genicular Artery and Vein

Distal to the attachment with the lateral meniscus the ALL seems to fan out and increase in width. The ligament is inserted into the anterolateral aspect of proximal tibia posterior to the Gerdy's tubercle [Figures 1–3]. The insertion of ITB on the Gerdy's tubercle was completely distinct with no connecting fibers to ALL.

ALL was found to tense between 30°–90° of knee flexion and forced internal rotation.

The measurements in 19 cases the ALL was observed are mentioned in Table 1.

Table 1

Quantitative measurements of the anterolateral ligament, lateral collateral ligament, and distance from Gerdy’s tubercle

Number	Sex	Left/right	ALL L (F)	ALL L (E)	ALL-W (o)	ALL width (i)	DIFG	LCL (L)	LCL (W)
1	Female	Right	42.1	36.22	6.13	9.16	16.38	59.54	6.23
2	Female	Left	41.5	36.40	5.90	8.92	16.47	59.16	6.19
3	Female	Left	43.35	48.27	8.92	12.24	23.61	52.53	5.80
4	Male	Right	45.35	41.36	7.95	9.46	23.55	59.75	6.27
5	Male	Left	47.23	45.62	7.58	9.37	22.16	61.58	6.83
6	Female	Right	39.55	36.49	7.29	9.44	21.23	62.36	7.15
7	Female	Left	41.22	38.63	8.11	10.34	20.33	63.41	7.64
8	Male	Right	43.64	39.29	8.73	10.02	18.38	64.72	7.92
9	Male	Left	40.28	38.10	6.27	8.49	17.45	65.91	6.87
10	Female	Right	38.39	35.87	5.68	7.20	20.72	60.50	6.07
11	Female	Left	37.61	34.90	6.44	9.58	23.15	55.39	6.17
12	Female	Right	51.47	47.88	7.39	9.14	19.73	62.19	7.48
13	Female	Left	39.67	36.29	6.17	8.47	21.24	64.86	6.77
14	Female	Right	39.42	37.40	6.33	8.43	23.66	63.47	6.29
15	Female	Left	43.49	41.37	6.81	9.31	24.11	64.16	6.72
16	Female	Right	44.28	42.48	6.38	9.29	23.39	65.62	6.83
17	Male	Right	48.90	40.38	7.14	10.46	24.67	71.72	7.17
18	Male	Left	50.48	47.35	7.23	10.29	25.19	72.16	7.29
19	Male	Right	45.78	42.93	6.23	8.16	22.17	61.40	6.82
Mean			43.35	40.38	6.98	9.36	21.45	62.65	6.76

ALL = Anterolateral ligament, LCL = Lateral collateral ligament, ALL-L (F) = Anterolateral ligament length in flexion, ALL-L (E) = Anterolateral ligament length in extension, ALL-W (o) = Anterolateral ligament width at origin, ALL-W (i) = Anterolateral ligament width at insertion, DIFG = Distance between center of ALL insertion and GT, LCL (L) = Lateral collateral ligament length, LCL-W = Lateral collateral ligament width at center, GT = Gerdy’s tubercle

The mean length of the ALL was 43.35 mm ± 4.04 mm in flexion and 40.38 mm ± 4.35 mm in extension.

The mean width of the ALL at the origin was 6.98 mm ± 0.95 mm.

The mean width of the ALL at the insertion was 9.36 mm ± 1.07 mm.

The insertion of ALL was 21.45 mm ± 2.73 mm posterior to Gerdy's tubercle.

The mean length of LCL was 62.65 mm ± 4.70 mm.

The mean breadth of LCL was 6.76 mm ± 0.58 mm.

Discussion

The purpose of this study was to observe the presence of a ligamentous structure in the knee region in the Indian population, describe its qualitative and quantitative characteristics and correlate clinically.

This ligament has been investigated as intraarticular reconstruction after ACL repair fails to restore normal rotation movements of the knee. Even serial sectioning studies fail to reproduce pivot phenomenon after sectioning both the bundles of ACL.11 Even a well-done ACL reconstruction fails to stop the pivot phenomenon. This demonstrates the presence of another ligamentous factor which controls the pivot in the knee.

The ALL has been variably described as the anterior oblique band by Campos et al.5 or the lateral capsular ligament by Johnson.12 Terry3 and LaPrade4 all have labeled it as the capsule-osseous layer of the iliotibial tract. We are in concurrence with the nomenclature by Vincent et al.8 and Claes et al.9 and call it the ALL of the knee.

In this study, the ALL was observed in 19 of the 20 specimens dissected (95%). The joint capsule was situated anterior to it. The ALL was easily demarcated from the surrounding joint capsule. It had similar length, breadth, and had comparable values to recent studies.89 However, Musahl et al.13 in their recent editorial have reported only a discrete capsular thickening in 30% of cases.

Similar to results of Claes et al.9 and Vincent et al.,8 the femoral attachment of the ALL on the lateral femoral epicondyle was anterior to and in line with the attachment of the LCL. This was in contrast to Dodds et al.14 who found ALL to arise 8 mm proximal and 4.2 mm posterior to lateral femoral epicondyle.

In our cadavers, distally the ligament appeared to widen and gain distal attachment close to the Gerdy's tubercle (the insertion of the ITB). The deeper and medial fibers of the ligament merged with the lateral meniscus. This observation is concurrent with the previous reports by Helito et al.15 Vincent et al.,8 and Claes et al.9 Claes et al. have named this part the meniscofemoral part and distal to it the meniscotibial part of ALL.

The attachment of ALL to the lateral meniscus may have a role in the injuries of the lateral meniscus, especially peripheral tears. ALL may thus prevent anteroposterior translation and prevent extrusion of the meniscus during flexion. Terry3 and LaPrade4 documented a clear association of rupture of ALL with ACL injury.

ALL was found to get taut at between 30°–90° of knee flexion and forced internal rotation. This observation is in concurrence with Segond,1 who described extreme amounts of tension during forced internal rotation. The bony avulsion of the ALL is often regarded as pathognomonic of ACL injuries. This bony avulsion of ALL could provide a clue to role of ALL in rotatory knee instability patterns observed in many ACL deficient knees (i.e., pivot shift phenomenon).

Dodds et al.14 observed that the ALL crosses the middle of the LCL when the knee was flexed. Further similar to our observations they found that the ALL broadens out close to its tibial attachment.

The insertion of the ALL in Indians is similar to the observations by Claes et al.,9 Vincent et al.,8 Dodds et al.14 The tibial attachment of the ALL was constant and observed to be posterior to the Gerdy's tubercle. A summary of the measurements of ALL in our study in comparison to other authors has been done in Table 2.

Table 2

Summary of dimensions of anterolateral ligament in previous studies and our study

Authors	Number of specimens and incidence of ALL	ALL L (mm)	ALL W (mm)	ALL T (mm)	Tibial insertion
Vincent et al.8	10 cadavers, 30 TKRs 100%	34.1±3.4	8.2±1.5	2-3	5 mm from articular margin posterior to GT
Claes et al.9	41 cadavers, 97%	38.5±6.1 (extension)	8.3±2.1 (at origin)	1.3±0.6 (at joint line)	6.5±1.4 mm from articular margin
		41.5±6.7 (90° flexion)	6.7±3.0 (at the joint line)
			11.2±2.5 (tibial insertion)		21.6±4.0 mm posterior to GT
					23.2±5.7 mm anterior to FH
Dodds et al.14	40 cadavers, 83%	59±4	5±0		11±2 mm from joint line
					18±3 mm from GT and 17±3 mm from FH
Helito et al.15	20 cadavers, 100%	37.3±4.0	7.4±1.7	2.7±0.6	4.4±1.1 mm from distal articular margin
Caterine et al.16	19 cadavers and 10 MRI,100%	40.3±6.2	5.1±1.8 (above meniscus)	1.4±0.6	11.1±2.4 mm from joint line
			8.9±2.5 (below meniscus)		23.4±3.4 mm from GT
					23.9±5.5 mm from LCL insertion
Stijak et al.17	14 cadavers 50%	41±3	4±1	1	Midway between the GT and the FH
Our study	20 cadavers, 95%	40.38±4.35 (extension)	6.98±0.95 (at origin)		21.45±2.73 mm posterior to GT
		43.35±4.04 (90° flexion)	9.36±1.07 (at insertion)

ALL = Anterolateral ligament, ALL-L = Anterolateral ligament length, ALL-W = Anterolateral ligament width, ALL-T = Anterolateral ligament thickness, GT = Gerdy’s tubercle, FH = Fibula head, DIFG = Distance between center of ALL insertion and GT, LCL = Lateral collateral ligament, MRI = Magnetic Resonance Imaging, TKRs = Total knee replacements

The fibers of the ITB are a completely separate entity from the ALL, there being no anatomical continuity between the two.

Conclusion

The study demonstrates the existence of the ALL and defines its anatomical features and measurements in the Indian Population. Due to its attachments and tension observed in it during forced internal rotation it is hypothesized to play a role in maintaining the anterolateral stability of the knee. Further, the tear of the ALL may also be implicated in peripheral lateral meniscus tears.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.