Forces applied to the cervical spine during posteroanterior mobilization

There is little information on manual forces applied during cervical mobilization, a common treatment technique. Potential variability of applied forces between therapists and treatment occasions, and factors associated with different force applications are unknown. The purpose of this study is to establish the baseline mechanical properties of cervical spine mobilization and to determine if the applied forces are affected by the characteristics of therapists and mobilized subjects.

Physiotherapists (n = 116) applied 4 grades of posteroanterior mobilization to the premarked C2 and C7 spinous (central technique) and articular processes (unilateral technique, one right and one left) of 1 of 35 asymptomatic subjects. Techniques were performed in randomized order, and the first one was repeated after 20 minutes. Load cells attached to the treatment table recorded forces in 3 directions. Before mobilization, subjects' spinal stiffness at the C2 and C7 spinous processes was measured using a custom device. Analyses of variance with Bonferroni post hoc tests determined technique and grade differences, intraclass correlation coefficients the reliability between therapists, and linear regression the factors associated with forces.

Therapists apply distinct manual forces for different techniques and grades (P < .001). Variability between therapists is high, but intratherapist reliability is good (intraclass correlation coefficient [2,1] for different force parameters, 0.84-0.93). Mean peak forces increase from grades I to IV, ranging from 22 to 92 N for resultant forces. Greater vertical and caudad-cephalad forces are applied to C7 than C2 (P < .01), with higher mediolateral forces during unilateral techniques (P < .001). Male sex of the therapist or the mobilized subject is associated with higher forces, and C2 stiffness, thumb pain and postgraduate training with lower (P < .05).

These results quantify cervical mobilization forces, which will inform future research aimed at improving its application and clinical effectiveness.