Network analysis reveals that total hip arthroplasty restores shared segmental motion before segmental...

Unilateral hip osteoarthritis (HOA) reshapes whole-body movement, and total hip arthroplasty (THA) restores function only partially-but conventional kinematic analyses fall short of characterizing how the body's distributed coordination reorganizes. Network analyses of inter-segment kinematic coupling offer a systems-level alternative, but they conventionally collapse the sign of coupling, treating two mechanically distinct relationships as equivalent: segments whose displacement amplitudes covary, rising and falling together, and segments whose amplitudes trade off, one displacing little while the other displaces a great deal. Here, we introduce a signed partial-correlation decomposition of marker-displacement coordination into parallel covarying $\left(W^{+}\right)$ and trading-off $\left(W^{-}\right)$ networks, applied to gait from 80 healthy adults and 106 HOA patients assessed before and 6 months after THA (ClinicalTrials.gov Identifier: NCT01907503). HOA reorganizes the two networks in opposite directions: covarying coordination loses modular structure and small-worldness, while trading-off coordination becomes more locally clustered and more small-world; global efficiency falls in both. This is consistent with pain-driven splinting that consolidates a few fixed trading-off configurations. Surgery acts predominantly on covarying coordination, partially restoring its topology, while the trading-off network's reorganization persists across the six-month post-surgical window-and on one measure, i.e., how broadly each segment spreads its trading-off partners, a deficit emerges during recovery that was absent before surgery. A node-level sign-balance metric shows that the proportion of each segment's coordination carried by covarying relationships returns to healthy values by 6 months, even though the underlying networks remain structurally altered. Standard post-surgical care thus restores the gross balance of coordination within 6 months, while the underlying architecture remains reorganized at that mid-recovery time-point-and, on at least one measure, consolidates further. Whether this reorganization reflects protective motor strategies, and whether training targeted at segmental differentiation would reverse it, are hypotheses that the present observational data raise but cannot test.