MATHEMATICAL MODELING OF PELVIC MUSCLE FUNCTION IN PATIENTS WITH HIP JOINT ADDUCTION CONTRACTURE AT SINGLE-SUPPORT STANDING

Abstract

Long existing hip arthritis is accompanied by the development ofpain and contractures that cause contractile muscle spasm, reductionin the length of the adductor muscles and flexors of the thigh,relative overstretching of the abductor muscles, which over timeleads to changes in their structure. The result is weakness of thepelvic muscles, the clinical manifestation of which is a violationof postural balance — lameness, torso tilts while walking, changesin pelvic position, etc. Objective. To determine the effect of thehip joint adduction contracture on the ability to maintain balancestanding position with mathematical model. Methods: mathematicalmodel is worked out that represents the pelvis with the thigh andthe vectors of action of the adductor and abductor muscles. Themuscular effort required to maintain body balance during one-legstanding was normal and the hip position was set at 5° and 10°.Calculations were performed for patients weighing 70; 100; 120 kg.Results. It is determined that at the adduction contracture in 5°m. gracilis, m. add magnus, m. piriformis are not able to performthe functions of maintaining body balance due to the necessity todevelop greater efforts than their maximum possible, even at theminimal patient's weight. If the patient's weight exceeds 120 kg, thenalmost the entire muscular system of stabilization of the thigh worksbeyond its capabilities. The adduction contracture of 10° increasesthe required force of the thigh stabilizer muscles. The absolute valuesshowed an increase in their strength indicators. Conclusions.The adduction contracture of the hip joint causes a change in thebiomechanical conditions of the pelvic muscles due to changes inthe angles of action of the abductor muscles, reducing the effectivenessof their work to stabilize the pelvis. As the angle of adductioncontracture increases, there is a tendency for the pelvic musclesto work effectively. An additional factor that negatively affects thisindicator is the patient's overweight.