Optimized Prediction of Contact Force Application During Side-Lying Lumbar Manipulation

ObjectivesThe purposes of this study included the following: (1) to predict L3 contact force during side-lying lumbar manipulation by combining direct and indirect measurements into a single mathematical framework and (2) to assess the accuracy and confidence of predicting L3 contact force using common least squares (CLS) and weighted least squares (WLS) methods.MethodsFive participants with no history of lumbar pain underwent 10 high-velocity, low-amplitude lumbar spinal manipulations at L3 in a side-lying position. Data from 5 low-force criterion standard trials where the L3 contact force was directly measured were used to generate participant-specific force prediction algorithms. These algorithms were used to predict L3 contact force in 5 experimental trials performed at therapeutic levels. The accuracy and effectiveness of CLS and WLS methods were compared.ResultsDifferences between the CLS-predicted forces and the criterion standard–measured forces were 621.0 ± 193.5 N. Differences between the WLS-predicted forces and the criterion standard–measured forces were − 3.6 ± 9.1 N. The 95% limits of agreement ranged from 234.0 to 1008.0 N for the CLS and − 21.9 to 14.7 N for the WLS. During both the criterion standard and experimental trials, the CLS overestimated contact forces with larger variance than the WLS.ConclusionThis novel method to predict spinal contact force combines direct and indirect measurements into a single framework and preserves clinically relevant practitioner-participant contacts. As advanced instrumentation becomes available, this framework will enable advancements in training and high-quality research on mechanisms of spinal manipulative therapy.