CORR Insights®: 2018 Frank Stinchfield Award: Spinopelvic Hypermobility Is Associated With an Inferior Outcome After THA: Examining the Effect of Spinal Arthrodesis

Where Are We Now?

The matched-pair study by Grammatopoulos and colleagues [5] addresses the spinopelvic relationship in patients with THA or THA and spinal arthrodesis. Many studies have tried to address this issue [4, 6] only to come away with mixed results.

The current study compares patient-reported outcome measures (PROMs) between those who underwent both THA and spinal arthrodesis and those who underwent only THA with no known spinal pathology. The authors found that in patients with spinal arthrodesis who underwent THA, spinopelvic hypermobility was associated with inferior results [5].

After examining some classic biomechanical principles, I believe that soft-tissue laxity could be responsible for some of the current study’s findings. I say this because articulations are involved in a chain. After a hip fusion, the lumbar spine above and the knee below are likely to undergo degenerative changes. If the hip is stiff and arthritic in a patient who is considering spine surgery, we probably should treat the hip first. Restoring hip mobility frequently will reduce low-back pain in patients who have both hip and spine arthritis. Looking at it the other way—as one may consider to be the analysis done in the study by Grammatopoulos and colleagues [5]—it seems to me that a patient with a fused lumbar spine will put more stress [4] on his or her hip, and may well develop spinopelvic laxity as a normal adaptation to compensate for the fusion.

Where Do We Need To Go?

Put in this context, surgeons need to decide which procedure to perform first. In the current study, a total of 42 patients (60 hips) underwent lumbar spinal arthrodesis and had a THA. Of the 60 THAs, 21 (35%) were performed before spinal arthrodesis and 39 (65%) were performed after spinal arthrodesis [5]. Future studies examining this patient population should determine whether those who had their spinal arthrodesis first had more dislocation or inferior PROMs than those patients who had their spinal arthrodesis after their THA.

Current approaches for postoperative management of this patient population call for early hospital discharge. Could this have some effects on periprosthetic tissue healing? I believe increased spinopelvic mobility is associated with an increase in hip loading and sliding distance, and in my view, a greater load on polyethylene bearings will mean more wear, more inflammation, and possibly more hip instability.

A good result is always the goal, but we should be mindful of the contradictory data on this subject, which makes obtaining quality results somewhat challenging. Perhaps poor acetabular orientation was not the only explanation for increased dislocation rate in this study [5]. Previous studies [3, 6] have concentrated on cup orientation—but what about the stem? Stem orientation could be as relevant as cup orientation in defining stability [2], and I wonder, based on my experience performing revisions, whether it played a role in the current study. Future research should determine the correct amount of femoral stem anteversion in patients with spinopelvic hypermobility undergoing THA after spinal arthrodesis. I am concerned—particularly for patients with obesity—that the abdomen might apply a rearward-directed force on the hip couple in deep flexion, risking a posterior dislocation. This may be especially important in overweight patients undergoing anterior THA approaches, where femoral exposure can be more of a struggle [1].

How Do We Get There?

Concentrating our research on geometrical aspects such as the head size, and cup and stem orientation is insufficient. Instead, we must consider the whole system, including the hip and muscles, soft-tissue healing around the total hip, obesity, surgical approach, biomaterials used in the bearing couple, and neuro-muscular control.

I recommend performing an EOS® (EOS Imaging Inc, Paris, France) imaging examination before a lumbar fusion. An EOS® exam defines the precise lumbar position, sacral tilt, and pelvic orientation, which could help the surgeon to determine the best orientation for the acetabular component. Additionally, for patients 65 years of age or older, the dual-mobility cup is effective in decreasing hip dislocation and in my opinion, may be better than a large femoral head, which decreases liner thickness and could accelerate wear and debris formation.