By Tamara Kittelson-Aldred, MS, OTR/L, ATP/SMS, and T. Sammie Wakefield, OTR/L (ATP retired)
What is a multi-joint muscle? A multi-joint muscle passes over more than one joint. As a result, what happens at one joint will affect the motion of the other joints. These complex visual-spatial concepts are difficult to grasp without three-dimensional teaching aids to accompany verbal explanations.

Understanding how these muscles and joints work is very important in wheelchair seating and 24-hour posture care and management, because the lumbar spine and below the knee joint are connected by multi-joint muscle groups with the pelvis caught in the middle. Often, those who would profit from this understanding are clients and family members who do not have knowledge of anatomy or may not even speak the same language. The use of a simplified anatomical model1 (SAM) can help everyone understand and communicate about therapeutic recommendations during treatment planning. This, in turn, will promote successful seating and positioning strategies. The SAM used for illustrations in this article intentionally omits the upper extremities and thorax to focus attention on the relationship between pelvic posture, leg and foot position, and their effects on spine and head orientation.

We will consider three muscle groups that have major effects on pelvic posture, and thus impact function throughout the body. Restricted motion in one or more of these important proximal muscle groups limits healthy pelvic movement and posture, the foundation of balanced sitting. This will have negative consequences that ripple up the spine, affecting head control, vision, breathing, swallowing, arm and hand function, as well as lower leg and foot position. More than one of these muscle groups may be affected in a single individual, resulting in complex seating needs. An understanding of these multi-joint movement patterns of the pelvis is key to successful, functional seating and positioning outcomes. Because of their complexity these muscle groups are not easy to understand. We will show how they work using a SAM and suggest how seating accommodations and 24-hour posture care management can minimize and improve problems caused by multi-joint muscle dysfunction.

Figure 1. The right string clamp of the SAM (foreground) demonstrates hamstring tightness that tilts the pelvis backward with knee extension. The spine and head follow.
Figure 1. The right string clamp of the SAM (foreground) demonstrates hamstring tightness that tilts the pelvis backward with knee extension. The spine and head follow.
Figure 2. Compensatory head-righting and vision reactions result in kyphotic posture.
Figure 2. Compensatory head-righting and vision reactions result in kyphotic posture.
Figure 3. SAM illustrates legs seeking support in supine when hip and knee extension is limited.
Figure 3. SAM illustrates legs seeking support in supine when hip and knee extension is limited.

Understanding Hamstrings

Hamstrings2 are the least complex of the three muscle groups we will discuss.

Limited hamstring length is commonly seen in people with high muscle tone and/or spasticity—for example, cerebral palsy, traumatic brain injury, and similar diagnoses. It is often obvious during mat assessments. The hamstring muscles attach at the bottom of the pelvis, pass over the back of the hip joint and the knee joint, and attach at the back of the lower leg behind the knee. The motion they cause is to straighten the hip and bend the knee joint. People who spend a lot of their waking hours in the seated position often have shortened (tight) hamstrings. People with shortened hamstrings are typically unable to fully extend their knees and hips at the same time, resulting in characteristic postures. A rounded back and posterior pelvic posture is a typical compensation in sitting when knees are not allowed to flex sufficiently. Sacral sitting and shearing caused by sliding forward to ease shortened hamstrings puts skin of the buttocks at risk for pressure injuries. This can occur when (a) seat length is too long or (b) foot supports are placed too far forward to allow appropriate knee flexion. (Figure 1 and 2) In supine lying, inability to extend the hips and knees together results in legs falling toward one side or the other (windswept), or into abduction or adduction. The legs are heavy, more than 35% of body weight for adults, and will seek support until they find it. This places stress on hip and knee joints, increasing risk of dislocations. (Figure 3)

Accommodating shortened hamstrings for successful seating.3 (Figure 4)

Specific techniques can be used when a person has shortened hamstrings, as follows:

• Allow sufficient knee flexion to foster relaxation in the shortened muscles.
• Plan careful placement of foot supports to allow comfortable positioning of the lower extremities without stretching knees into extension that will affect pelvic posture.
• Plan the seat length and shape to eliminate impingement on the hamstring tendons.
• Support the trunk—without restricting function.

Figure 4. Correct seat depth and foot placement allow more neutral posture of the SAM pelvis.
Figure 4. Correct seat depth and foot placement allow more neutral posture of the SAM pelvis.

Using night-time postural support to turn gravity into a corrective force for hamstrings4,5

In supine lying, risks to the hip and knee joints can be neutralized by harnessing gravitational forces pressing down to help straighten knees and hips gently. Muscle tone naturally relaxes in most people during sleep, plus growth hormone is primarily secreted at night—adding to the impact of a well-aligned sleeping position during growth spurts. Try these techniques:

• Place a soft support beneath the legs and on both sides to accommodate knee and hip flexion improving midline orientation. The support should be compressible to allow gentle straightening of the legs. (Figure 5)
• Provide lateral support at the hips and trunk beneath a fitted sheet, promoting symmetry and midline orientation, while distributing pressure throughout a large portion of the body.

Figure 5. SAM illustrates night positioning supports in place for tight hamstrings.
Figure 5. SAM illustrates night positioning supports in place for tight hamstrings.

Hip Flexors Explained

Hip flexors include a number of muscles. To simplify understanding of sitting and lying postures and the effect on the pelvis. We will discuss only the multi-joint hip flexors—those muscles that cross both the front of the hip and knee joint, and the muscle that crosses the front of the hip and attaches to the lumbar spine. These complex muscles join the femur and knee to the lumbar spine by way of the pelvis. Shortened hip flexors may be obvious during a mat evaluation and should be considered as a potential issue in people with muscular dystrophy, spina bifida, and other conditions characterized by low trunk tone.

The quadriceps femoris6 is a four-muscle group at the front of the thigh that flexes the hip and extends the knee. The rectus femoris flexes the hip. It works with the vastus lateralis, vastus medialis, and vastus intermedius synergistically to extend the knee. In the seated position, the quadriceps will assume a shortened position. A wheelchair user spends many hours in this position and, if trunk weakness or other issues cause forward leaning for stability, the person may develop shortened quadriceps that limit hip extension and knee flexion. In other words, a person with limited hip extension related to quadriceps tightness may require extension of the knees to avoid the pelvis being pulled into excessive anterior tilt. This promotes compensatory lumbar lordosis in order to maintain appropriate head orientation. (Figure 6)

Figure 6. Shortened quadriceps with trunk weakness, showing anterior pelvic tilt.
Figure 6. Shortened quadriceps with trunk weakness, showing anterior pelvic tilt.

The psoas major muscle joins the upper and lower parts of the human body, by attaching to the femur at one end and to all the lumbar and lowest thoracic vertebrae at the other. The psoas primarily flexes and externally rotates the hip and stabilizes the lumbar spine. But when shortened because of habitual postures related to trunk weakness, it will pull the pelvis forward into anterior tilt, increasing lumbar lordosis. Relevant factors include available flexion/extension of the hip-joint, degree of trunk weakness, and flexibility of the lumbar spine. An individual with a shortened psoas major may present sitting with anterior pelvic tilt, external hip rotation, and a sometimes extreme lumbar lordosis. (Figure 7)

Figure 7. SAM illustrates pelvic, hip and lumbar posture affected by a shortened psoas major.
Figure 7. SAM illustrates pelvic, hip and lumbar posture affected by a shortened psoas major.

Accommodating shortened hip flexors for successful seating

Specific strategies are used to accommodate shortened hip flexors in sitting as follows:

• Stabilize the pelvis with a contoured seat-cushion.
• Support the back of the pelvis with a back cushion, if possible angled to encourage a more posterior tilt.
• Add a pelvic belt at the ASIS to limit excursion of anterior tilt; four points of attachment often work well.
• Position foot supports to avoid tension on shortened hip flexors, knee extensors or in some cases, hamstrings.
• Allow slight external hip rotation to help reduce the tension in the shortened psoas major.
• Support the trunk—without restricting function! (Figure 8)

Figure 8. SAM illustrates accommodated seated posture for shortened hip flexors.
Figure 8. SAM illustrates accommodated seated posture for shortened hip flexors.

Using night-time postural support to turn gravity into a corrective force for hip flexors

As stated previously, in supine lying gravity can be harnessed to correct postural problems. In the case of hip flexors, gravitational forces applied consistently can help reduce lumbar lordosis and straighten knees and hips gently over time.

In supine with shortened quadriceps, the principles are:

• Support the hips and lower legs, allowing relaxation of both hip flexors and knee extensors with midline orientation as much as possible.
• Place soft support beneath the lumbar spine for comfort and to reduce low back strain, while allowing gravity and muscle relaxation to provide gentle correction.
• The supports beneath knees and lumbar spine should be compressible. (Figure 9)

Figure 9. SAM illustrates supine lying with lower body support addressing shortened quadriceps.
Figure 9. SAM illustrates supine lying with lower body support addressing shortened quadriceps.

• Refer to Figure 5 for images of the lateral hip and trunk supports required for distribution of pressure as described previously.
In supine with shortened psoas major, the principles are:
• Support the hips in adequate flexion and slight external rotation to allow relaxation of the psoas major. This may require considerable hip flexion.
• Knees can be flexed or extended as much as is comfortable; the focus is on relaxation at the hips and spine.
• Soft support can be placed beneath the lumbar spine for comfort and to reduce low back strain, while allowing gravity and muscle relaxation to provide gentle correction toward reduction of the lordosis.

Figure 10. Illustration of supine lying with support for shortened psoas major.
Figure 10. Illustration of supine lying with support for shortened psoas major.

Complex principles involving multi-joint muscles surrounding the pelvis and influencing the posture and function of the entire body have been discussed in this article, and illustrated using a SAM. We have not discussed in-depth seating and positioning specific to the trunk, head, and upper extremities. These can only be appropriately addressed once issues related to pelvic posture are analyzed and understood. Similarly, the information in this article related to night-time therapeutic positioning is limited to specific concepts surrounding pelvic posture. It does not replace more in-depth understanding of 24-hour posture care management including specific techniques for upper body/spine protection and restoration, temperature regulation, and sleep hygiene in order to provide safe and effective interventions at night. See resources for further information about some of these topics. RM

Tamara Kittelson-Aldred, MS, OTR/L, ATP/SMS, is an occupational therapist, Assistive Technology Professional/Seating and Mobility Specialist. She earned certificates in advanced postural care through the Open College Network West Midlands, UK. She directs the Montana Postural Care Project and Eleanore’s Project, promoting 24-7 posture care and management and responsible wheelchair provision. Kittelson-Aldred has written and presented on these topics in the United States, Colombia, Jordan, and Peru, and has served individuals with complex neurodisabilities in Montana since 1983. She credits her daughter Eleanore, born with cerebral palsy and profound deafness, as her best teacher.

T. Sammie Wakefield, OTR/L (ATP retired), is an occupational therapist who has worked in seating and mobility for more than 37 years. She is a founding mother of New Hampshire ATECH — an assistive technology program that served clients in New Hampshire for more than 30 years. Now retired from paid work she continues her 13th year of volunteer work with Eleanore’s Project, sharing her knowledge and skills with students and therapists in Peru. Wakefield has degrees from Berea College and Texas Woman’s University. For more information, contact [email protected].

References

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2. Hamstring Muscle – An Overview. Science Direct Topics. Available at: https://www.sciencedirect.com/topics/medicine-and-dentistry/hamstring-muscle. Accessed August 2019.

3. Lange ML, Minkel JL. Seating and Wheeled Mobility: A Clinical Resource Guide. Slack Incorporated; 2018.

4. Kittelson-Aldred T, Hoffman LE. 24-Hour Posture Care Management: Supporting People Night and Day. Rehab Management, September 2017. https://rehabpub.com/2017/09/24-hour-posture-care-management-supporting-people-night-day/ Accessed August 2019.

5. Information about 24 hour posture care and management. Available at: https://posture24-7.org/. Accessed September 23, 2019.

6. Bordoni B, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Thigh Quadriceps Muscle. [Updated 2018 Dec 15]. In: StatPearls [Internet]. Treasure Island (FL):StatPearls Publishing; 2019 Jan-. Available at: https://www.ncbi.nlm.nih.gov/books/NBK513334/. Accessed September 23, 2019.

7. Penning L. Psoas muscle and lumbar spine stability: a concept uniting existing controversies. Eur Spine J. 2000;9(6):577-585.