Appendix e-1

Outcome of leg crossing dependent on time

Patients who crossed their legs after day 15 did not have a better outcome anymore, none of these patients attained a Barthel index outcome above 15 of 100 points (figure e-1). This figure additionally illustrates that leg crossing contralateral to the lesion did not have an even better outcome.

Demographic and morbidity data

Patients who crossed their legs and their controls did not differ in demographic data or underlying stroke syndromes and comorbities (table e-1).

Force considerations in leg crossing

A combination of movements including leg elevation (M. iliopsoas) and adduction (including the M.adductor longus, magnus, brevis and M. gracilis) is needed to cross one’s legs. An electromyographic study investigating the influence of common postures on abdominal muscle activity revealed that leg crossing reduced the activity of the oblique abdominals but not the activity of the rectus abdominise1.

To illustrate the amount of force needed for leg crossing we calculated the torque and force for an average male leg:

Voluntary force is clinically rated into the 6 MRC grades, ranging from full force (5) to complete plegia (0). For leg crossing, a minimal force of 3 (elevation against gravity) is needed in the hip flexor muscles and a minimal force of 2 (movement without gravity) is needed in the adductor muscles. These force considerations are important for the evaluation of stroke patients, because they may have pareses. The amount of force required for leg crossing (hip flexion of an outstretched leg) depends on the body properties of the individual patient. The weight of the leg represents approximately 19% of the total body weighte2, the center of mass is located on the leg axis at approximately 38% from its proximal ende3. Assuming an averagee4 body weight of 78.5 kg and leg length of 0.812 m, a torque of 45 Nm in the hip joint or an external force of 56 N applied at the foot is required to elevate the outstretched leg (see figure e-2).

e-References

e1. Snijders CJ, Slagter AH, van Strik R, Vleeming A, Stoeckart R, Stam HJ. Why leg crossing? The influence of common postures on abdominal muscle activity. Spine (Phila Pa 1976) 1995;20:1989-1993.

e2. Söll H. Biomechanik in der Sportpraxis. Schorndorf: Hofmann, 1982.

e3. Clauser C, MCConville J, Young J. Weight, volume, and center of mass of segments of the human body. Technical Report AMRL-TR-69-70 (AD-710 622). Aerospace Medical Research Laboratory, Aerospace Medical Division, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio, August 1969.

e4. Flügel B, Greil H, Sommer K. Anthropologischer Atlas / Grundlagen und Daten. Alters- und Geschlechtsvariabilität des Menschen. Frankfurt/Main: Edition Wötzel, 1986.


Figure legends

Figure e-1: Days to cross and outcome

Relation of time course until first leg crossing (“days to cross”) on outcome (Barthel Index). Crossing of the leg contralateral (green circles) to the lesion did not change prognosis as compared to ipsilateral crossing (blue circles). The dashed line at day 15 indicates an arbitrary cut off, where prognosis does not improve with leg crossing (no outcome with Barthel index >15/100).

Figure e-2: Forces in Leg crossing

Panel A shows the forces that are needed for leg crossing.

The leg of an average male weighs approx. 14.9 kg (19 % of 78.5 kg). Gravity must be overcome in order to elevate the leg. The torque in the hip joint required for hip flexion of the horizontally outstretched leg can be computed as a product of the distance between the hip and the center of gravity (CoG) of the leg (lever arm (r), approx. 38% of the leg length, measured from greater trochanter (T) to foot sole (S)) and the gravity force, M = r x FG. For an average male with leg length of 0.812 m this results in M = 45 Nm. Since the leg works as a lever with its pivot at the hip joint, the amount of externally applied force necessary to elevate the leg depends on its point of application. At the CoG the force would be equal to the weight of the leg (i.e. 146 N corresponding to the mass of 14.9 kg for an average male); at the foot less force would be required because of the longer lever arm. For an average male a vertical force of approx. 56 N would have to be applied at the foot to elevate the leg.

Panel B shows the legs of one of the authors (JR) in the typical position assumed by the patients (legs crossed at ankle level).

Table e-1: Demographic and morbidity data

Etiologies of the severe strokes in the leg crossing group (“cross”) as compared to controls. (EVD = extraventricular drainage; SAB = subarachnoid bleeding).

n / Sex / Age
(years) / Comorbities / Localisation / Type of Stroke
Pneumonia / Sepsis / EVD / Craniotomy / Endocarditis / myocardial infarction / pacemacer / Pulmonary embolism / posterior circulation / middle cerebral artery / SAB
cross / 34 / 15 female
19 male / 56.9 + 14.0 / 11 / 3 / 3 / 6 / 1 / 2 / 1 / 0 / Total 11
Infarction 11
Bleeding 0 / Total 16
Infarction 9
Bleeding 7 / 7
control / 34 / 12 female
22 male / 57.1 + 14.9 / 7 / 2 / 3 / 6 / 0 / 3 / 1 / 1 / Total 15
Infarction 12
Bleeding 3 / Total 14
Infarction 11
Bleeding 3 / 5