Paper 13: Traction Application Method Influences Force and Distraction Parameters at Venting and Capsulotomy

OBJECTIVES: This study examined the effects of traction application method – either a standard peroneal post or a postless method -- on traction and distraction variables before and after venting and capsulotomy. A more robust understanding of the direct effects of each intervention under different traction conditions may inform clinical decisions about compartment access and/or methods of traction application. METHODS: Fluoroscopic images were taken before and after traction application, venting, and capsulotomy in primary hip arthroscopies by a single surgeon; these were used to measure distraction distances, which were each normalized to the diameter of the femoral head in the same image to account for the effect any purely positional differences across time points. Traction forces were also recorded at traction application, before/after venting, and before/after capsulotomy. Traction method, as well as sex and hamstring flexibility scores (known to influence degree of distraction) were assessed via standard least squares models for their effects on: 1) Instantaneous traction forces before venting, after venting, before capsulotomy, and after capsulotomy 2) Distraction differences -- expressed as % femoral head diameter -- between the neutral state and the values at these same interventions 3) The ratios of normalized distraction differences to traction forces at each intervention RESULTS: Both initial distraction and after-venting distraction values differed significantly with respect to sex (distraction: p<0.0001, venting: p<0.0001 ), and hamstring flexibility (distraction: p<0.0140, venting: p<0.0040), with larger distraction magnitudes in female and more flexible patients. After-capsulotomy distraction differed with sex (p<0.0001) and traction method (p<0.0056), with female and peroneal post-distracted patients exhibiting higher distraction magnitudes. All force values along the intervention trajectory (before and after venting, before and after capsulotomy) differed with respect to sex and traction method, but not with hamstring flexibility (Table1). Male patients and post-distracted patients exhibited higher forces. Distraction-traction ratios (distraction achieved per unit force applied) differed with respect to sex, traction method, and hamstring flexibility at all interventions – except for the after-capsulotomy ratio, which was unaffected by hamstring flexibility (Table 1). Higher values (more distraction achieved per unit force) were seen in more flexible patients, female patients, and patients distracted via the postless method. The differences between ratios before and after an intervention differed with respect to sex for venting (p<0.0106), and both sex and traction method for capsulotomy (sex: p<0.0001 traction: p<0.0379), representing more distraction achieved per unit force after capsulotomy in the post-distracted group, and for female patients at both interventions. CONCLUSIONS: The distraction results indicate that the posted and postless methods of traction application do not differ significantly in the magnitude of distraction achieved (except after capsulotomy), but depend more on patient flexibility. The fact that after-capsulotomy distractions are larger in the post-distracted group may point to differences in soft tissue strain patterns between traction application methods. Traction forces are higher in post-distracted group but yield lower distraction distances per unit force than the postless method overall; the exception to this pattern is the ratio taken after capsulotomy, which is higher in the post-distracted group. Taken together, these results may support a switch to postless methods and invite further investigation into the anatomical and mechanical patterns governing capsular integrity.