A total of 313 articles were identified in the original search, and two further articles were gleaned from other sources. After the removal of duplicates between databases, a total of 245 records were identified for title screening. After the exclusion of 157 papers on the basis of title, 88 records remained for abstract screening, of which 36 full texts were deemed relevant based on the inclusion and exclusion criteria.
Assessment of these full-text articles yielded 14 final articles for qualitative analysis (Figure.3) [1-5, 10-18]. Publication dates ranged from 1992 to 2016.
Only one of these articles was longitudinal [5] whist 12 were cross-sectional. The remaining article was a description of a surgical technique [18]. Seven of the articles reported manual measurements of the pelvis [3, 10-13, 15, 17] whereas 5 studies took measurements with radiographic images, a navigation system or imaging software [1, 2, 4, 14, 16] (Table.1).
Anatomy of the Psoas Valley
Subjects in this review
Ten articles in this review utilised cadaveric or skeletal hips from both male and female specimens [1, 3, 4, 10-15, 17]. Osmani et al. evaluated 3D-CT scans of live patients taken for colonography to make measurements of acetabular version [16]. Similarly in 2008, Vandenbussche et al. used CT scans of live hips to quantify the psoas valley [2]. Spiker et al. introduced the technique of arthroscopic psoas management related to the iliopsoas notch [18]. Finally, Domb et al. conducted study wherein all patients underwent hip arthroscopic surgeries due to a labral injury at the 3 o’clock position [5] (Table.1).
Definition
The 14 papers extracted put forward differing anatomical definitions of the anterior acetabular variable we have termed the ‘psoas valley’. A categorisation of these definitions were listed as below;
a) The notch between the anterior inferior iliac spine and the iliopubic eminence (notch between AIIS and IE)
Two studies found a notch between the anterior inferior iliac spine (AIIS) and the iliopubic eminence (IE) [11, 17]. Pellico et al. stated that the iliopsoas muscle passes anterior to this notch [11].
b) Psoas-U (Anterior labral sulcus)
The Psoas-U is another term that has been used in literature to describe the psoas valley. A more descriptive term used by Philippon et al. is the superior margin of the anterior labral sulcus, which they ascribe to the 3 o’clock position, relative to the centre of the acetabulum as the centre of the clock face. The Psoas-U is expressed as a concave impression of the anterior rim of the acetabulum, and relates anteriorly to the iliopsoas tendon [4]. Both Philippon et al. and Lee et al. vouch for the consistency of the Psoas-U 3 o’clock location, and in fact both use it as the key reference point in creating the clock face depiction of the acetabulum [4, 14]. Thus, like the previous ‘notch’ description, the Psoas-U has bony specifications and is related to the iliopsoas muscle, but it adds a cartilaginous bearing and has a more specific position in relation to the acetabulum.
c) Anterior wall depression
Only 1 study described an anterior wall depression. Kohnlein et al. detected three constant prominences and two depressions on acetabular bony rim, and defined one of the depressions as the anterior wall depression [13].
d) Psoas valley
Four studies defined the ‘psoas valley’ [1-3, 16]. Building on Maruyama et al’s work in distinguishing qualitative configurations of the anterior acetabular rim [15], Vandenbussche’s group aimed to quantify variations in acetabular rim morphology in cadavers, with particular focus on the psoas valley [1]. In the studies included in our review, they introduced the term ‘psoas valley’ for the first time.
e) Iliopsoas notch
Two papers found in the search do not extensively describe the psoas valley, and simply refer to it as the iliopsoas notch at the 3 o’clock position [5, 18].
Measurement
a) Depth
Six studies described the depth of the psoas valley and its anatomically equivalent notch [1-3, 11, 13, 17]. Pellico et al. and Sachdeva et al. defined the notch between the AIIS and IE, and measured it in a similar manner using calipers [11, 17]. The results were reported as 0.82 ± 0.16 cm and 1.26 ± 0.3 cm in males and 0.80 ± 0.195 cm and 1.02 ± 0.18 cm in females, respectively. Sachdeva et al. proposed that the different results in the two studies may be attributed to the different sets of populations, i.e. Spanish [11] and North Indians [17].
Kohnlein et al. expressed the values of the anterior depression in degrees; as a function of a geographical reconstruction of the acetabulum [13]. The pole of the acetabular hemisphere represented 0°, and the depth of the cup is tantamount to the latitude. The circle at 90° marks the equatorial level of the hemisphere. In the above measurement, the depth of the anterior depression was 81 ± 5 °, in other words, 9° below the level of a hemisphere.
Kopydlowski et al. used the distance between a ruler, placed lateral to the 2 bony peaks that border the psoas valley, and the deepest point of the psoas valley (determined using a caliper) as a measurement of depth which came out to be 4.64 ± 1.62 mm [3]. Vandenbussche et al. established a pelvic coordinate system with the origin at the midpoint between the anterior superior iliac spines to analyse the position of the psoas valley along the acetabular rim [1, 2]. On each acetabulum, the articular surface and rim was digitised with a certain number of points. Using this coordinate system and digitised data, a two-dimensional plot of each individual acetabulum was produced with each point of inflexion labelled. The depth was defined as the distance between the trough of the psoas valley and the average heights of adjacent peaks [1] or between the psoas valley trough and the mean acetabular equator [2] which correspond to the above inflexion points. These values were 3.8± 2.0mm and 4.9± 2.0mm, respectively. (Table.1)
b) Width
The width was quantified in 2 papers [1, 3]. Vandenbussche et al. used the aforementioned coordinate system and defined the angle between two peaks adjacent to the psoas valley as its width, which was 71.0 ± 18.0° [1]. In another study, a ruler was placed lateral to the 2 bony peaks that border the psoas valley on the acetabular rim, and the width was measured with digital calliper, giving a value of 26.94 ± 5.03 mm [3]. Since previous studies have reported that the distance between the AIIS and IE is about 40mm [11, 17], it follows that the psoas valley spans more than half of this (Table.1).
c) Shape
Six papers described the shape of the psoas valley [1, 2, 10, 12, 13, 15]. All papers except one without a classification system, reported that the curved type was the most frequently observed configuration, seen in more than half of the subject acetabulae (58-79%). This was followed by angular, irregular, then straight [1, 2, 10, 12, 15]. Futhermore, two studies insinuate that a straight type may not exist [2, 13] (Table.1).
d) Location
Four studies described the location of the psoas valley [3, 4, 13, 14]. The location of anterior wall depression is indicated in the clockwise distribution from 1:00 to 12:00 with the acetabular notch as the caudal landmark for 6:00. In this clockface representation, the location of the anterior depression was 03:20 ± 20 min [13]. With the same measurement method, Kopydlowski et al. showed that the psoas valley was located in the anterosuperior quadrant of the acetabulum, with a mean location of 3.92 ± 0.42 o’clock anteriorly and 2.12 ± 0.77 o’clock posteriorly [3]. Philippon et al. set the midpoint of the transverse acetabular ligament as the 6 o'clock position, and the Psoas-U was located at 3:30 [4]. They also measured distances from the AIIS and reported 29.4 ± 3.4 mm to the midpoint of Psoas-U and 23.4 ± 2.9mm to the superior-most point of the Psoas-U. Lee et al., moreover, defined the Psoas-U at the 3 o’clock position and then, evaluated which position in plain radiographs corresponds to the Psoas-U in cadavers [14]. The Psoas-U was located a mean 26.9 ± 2.6mm proximal to the tear drop in anteroposterior (AP) view and 22.9 ± 4.8 mm anterior to the vertical line drawn through the centre of the acetabulum in false-profile (FP) view (Table.1).
e) Index of widening
Two studies defined the index of widening as the notch depth between the AIIS and IE divided by the maximum width of this notch multiplied by 100 [11, 17]. The index values in the two studies were reported as 20.73 ± 5.12 and 30.06 ± 6.72 in males and 22.48 ± 5.08 and 26.90 ± 6.06 in females, respectively. The difference between the values of these two studies may be linked to the different ethnicities of the population as noted above (Table.1).
f) Related factors
Factors related to the psoas valley and its synonyms are summarised in Table 2. The relationship with gender was the most frequently described (7 papers). Two papers reported no gender differences in depth [11, 13], while four papers showed that male valleys were deeper than female ones [1-3, 17]. Notably, there were no papers reporting that the female valley was deeper. There was no significant difference reported between genders in terms of location and shape [3, 13, 15].
Two papers evaluated the relevance of age, both reporting no correlation [2, 3]. As for differences between sides, most papers reported no significant difference, while Sachdeva et al. demonstrated that the index of widening was significantly higher on the left side [17]. However, with the same measurement method, another paper did not find a significant difference [11], hence this result may be influenced by differences among the ethnic groups of the subjects. As for other factors, Vandenbussche et al. found correlations between the depth of the psoas valley and acetabular parameters; positive with acetabular diameter and negative with the degree of acetabular anteversion [1, 2].