Non-structural misalignments of body posture in the sagittal plane

Human posture is commonly understood as the relationship between human body parts in the upright position. Particular body parts, such as the head and neck, the trunk, and the upper and lower limbs, are involved in the final body posture. A good body posture is considered (1) ergonomically advantageous while standing, (2) mechanically effective while moving, and (3) supportive for the normal function of internal organs. Body posture is described and considered in three reference planes: sagittal, coronal, and transversal [1, 2]. Kendall et al. proposed a definition of good human posture: “good posture is that state of muscular and skeletal balance which protects the supporting structures of the body against the injury or progressive deformity, irrespective of the attitude (erect, lying, squatting or stooping) in which these structures are working or resting. Under such conditions, the muscles will function most efficiently, and the optimum positions are afforded for the thoracic and abdominal organs” [3]. Such a comprehensive definition of body posture will not be used in this paper since the authors focused on the description of human posture in the upright standing position.

Poor posture is an imprecise term commonly used in the clinical practice to describe a relationship between various body parts which may be considered as faulty and which could stretch the spectrum from the non-perfect to pathological posture. It is postulated that poor posture can produce an increased strain on the supporting structures and less-efficient balance of the body over its base of support [3].

The most difficult task of describing good body posture concerns the sagittal plane alignment, while both the coronal and the transversal planes are usually considered symmetrical. In fact, the human being is symmetrical neither in the coronal nor in the transversal plane [3‐5]. However, this simplification is used in this paper for the clear presentation of the sagittal plane alignment.

The physiological sagittal spinal curvature represents a typical feature of good body posture in the sagittal plane. The cervical and the lumbar spine are curved anteriorly (lordosis), while the thoracic segment is curved posteriorly (kyphosis). The head remains horizontal, which denotes that the eye level corresponds to the horizontal plane, while the chin is positioned just above the sternum. The pelvis is inclined anteriorly, and the lower limb joints remain in a neutral position [1‐3].

The optimal body posture should represent the following alignment: the head line, beginning at the external auditory meatus (or at the mastoid process of the temporal bone), should run vertically through the acromion, the lumbar vertebral bodies, the promontory, then slightly posteriorly to the hip joint axis, slightly in front of the knee joint axis, and finish at the lateral malleolus or slightly in front of it. The course of this line in a good body posture overlaps the base line joining the center of gravity with the central point of the supporting area (Fig. 1) [4‐7].

As presented above, the detailed description of a good body posture in the sagittal plane is not explicit. Moreover, characterizing the deviations from a good posture can be ambiguous. The aim of this paper is to present the most common types of non-structural misalignments of body posture in the sagittal plane.

From a clinical point of view, the disturbances of human posture can be classified as non-structural or structural. The non-structural pathologies represent the main topic of this article and will be discussed in detail. The structural misalignments comprise specific clinical entities: idiopathic scoliosis, Scheuermann juvenile kyphosis, congenital vertebral malformation, sequels of spine osteomyelitis, spondylolisthesis, and other clinical entities that produce disorders of body posture, e.g., thoracic hyperkyphosis, flat back, and pelvis malposition. The said body posture disorders are known as “structural disorders,” as this term indicates the presence of morphological abnormalities within the bones and soft tissues (fascia, muscles, ligaments, tendons). Additionally, structural misalignments reveal a more severe clinical problem as they are less flexible and less prone to correction compared to the non-structural disorders. They require specific diagnostic and therapeutic approach and are not discussed in this paper apart from the differential diagnosis issue.

The clinical appearance of children with non-structural versus structural (e.g., Scheuermann disease) disturbances of body posture may be similar (Fig. 2 versus Fig. 3). Two boys, aged 12 and 14 respectively, diagnosed with the kyphotic posture (increased thoracic kyphosis, protraction of the head and shoulders), are presented in Figs. 2 and 3. Figure 2 shows the kyphotic posture reasonable due to the non-structural pathology, namely the combination of an incorrect postural habit and muscles’ hypo- and hyperactivity. Figure 3 presents the kyphotic posture due to the structural thoracic hyperkyphosis, which is a structural spinal deformity.

Differential diagnosis represents an important part of the evaluation of every child addressed for the so-called poor posture. Despite the modern imaging techniques, including digital whole-body radiography, computed tomography, or nuclear magnetic resonance, the basic clinical examination retains its value. For example, the functional testing allows assessing the flexibility of thoracic hyperkyphosis which reveals good in non-structural (Fig. 4a–c) versus poor in structural misalignment (Fig. 5a–c).

In some individuals, the combination of the two aforementioned sagittal misalignments can be noted in the form of kyphotic-lordotic posture (Fig. 8) [3]. In this case, the influence of kyphotic and lordotic posture on the musculoskeletal system is combined [3, 7].

The authors would like to emphasize that difficulties in planning corrective exercises can occur in the kyphotic-lordotic posture. For instance, in lordotic posture, the abdominal muscles are lengthened and therefore should be shortened, while it is not recommended in the kyphotic posture. Although providing therapeutic schemata extends beyond the content of this paper, this example illustrates accurately the need for a nuanced physiotherapy: shortening the lower part of the abdominals (e.g., by moving upward their attachment to the pubic symphysis and iliac crest) while increasing the length of their upper part (Fig. 8).

In a good body posture, balance should be maintained between the strength and the flexibility of the antagonistic muscles, for instance, between the hip flexors and the extensors or between the muscles of anterior and posterior part of the pectoral girdle [1‐3, 6‐10, 23].

According to the classification proposed by Kendall et al., muscles can be assessed in respect to their length and strength. Consequently, e.g., in lordotic posture, among others, the abdominal muscles, the gluteus maximus, the posterior part of gluteus medius, and hamstrings are lengthened. On the other hand, the erector spinae in the lumbar spine, quadratus lumborum, and hip flexors are shortened [3]. The authors suggested that the muscles which are excessive in length are usually weak and require strengthening, while these muscles that are too short are usually strong and maintain antagonistic muscles in a lengthened position [3]. According to our experience, this description of muscle function, based on the direct connection between the lengthening or shortening of muscles and their weakness or strength, respectively, is often taken into consideration while planning corrective exercises by many clinicians. A clinically important question remains: does the muscle lengthening mean that they prove weak, and does the muscle shortening correspond to their increased strength like in the classification proposed by Kendall et al.? The answer was attempted to be given with the detailed classification of muscles presented in the paper [9, 10].

Figure 12 presents a boy whose anterior pelvic tilt is increased, which means that his hamstrings are probably lengthened and, according to Kendall et al., weak. It suggests that during corrective exercises these muscles should be strengthened. However, two functional tests performed by the boy (the long sitting test and the popliteal angle test) reveal interesting information [3, 7, 27]. Figure 13 presents the boy performing the maximal active knee extension while keeping the hip flexed at 90° (the popliteal angle test). The test indicates decreased hamstring flexibility. Accordingly, taking into consideration only the result of this test, the hamstrings would have to be stretched. Figure 14, in turn, shows a maximal trunk forward bending during the long-sitting test. The result of the test suggests the decreasing flexibility of hamstrings and trunk. However, the trunk flexion in sitting on the stool (knees flexed) indicates a good range of motion of the trunk, which confirms the limited flexibility of hamstrings (Fig. 15).

The abovementioned tests revealed the shortening of the hamstrings (Figs. 13 and 14). However, according to Fig. 12 and the description of the lordotic posture in the literature [3, 27], these muscles should be lengthened in this type of faulty posture. This question may be answered with the use of the muscle classification proposed by Bergmark and Richardson et al., which indicates that muscle lengthening may not be related to muscle weakness but can be analyzed in respect to its hyper- or hypoactivity [9, 10]. Taking into consideration the imbalance between the gluteus maximus muscle (hypoactive) and the hamstring muscles (hyperactive) (described detailed in the section “Lordotic posture”), the specific postural physiotherapy should not comprise hamstring exercises aimed at their strengthening (according to Kendall et al. [3]) or stretching (according to functional tests results). The exercises should be focused rather on reducing their activity through regaining the activity of the stabilizers including, in this example, the gluteus maximus [7‐10]. Furthermore, the lengthened muscles should not be simply strengthened, but they should be shortened, so the exercises should be performed in the so-called internal (not full) range of motion [10].

In consequence, when planning the corrective exercises, it is important to verify not only the length of the muscles but also their function (hyper- or hypoactivity). It is also important to plan the exercises based on (1) the individual evaluation of the posture, especially when the characteristics of the posture does not match any of the four types presented in the paper, and (2) the analysis of the posture in the usual position for a particular subject in which she/he spends most of the time during a day (e.g., sitting, position at work or while learning, position during learning or hobby).

The authors of this paper focused on the sagittal misalignments of the body posture and their relations with the muscular system. The paper is not discussing the relation of body posture with other factors: psychosocial, nutritional status, structural disorders, or fascial system. We did not discuss the important role of postural education to obtain the good results of corrective exercises.

Further studies are needed to verify a long-term influence of various types of non-structural sagittal misalignments of body posture on the disturbances in the muscular and skeletal system and the functional and structural status of the body.