CORR Insights®: Are the Choice of Frame and Intraoperative Patient Positioning Associated With Radiologic and Clinical Outcomes in Long-instrumented Lumbar Fusion for Adult Spinal Deformity?

Where Are We Now? Spine surgery has a long history of not adequately restoring or maintaining spinal sagittal balance. For example, hook-based distraction implants like Harrington rods [17] were a common cause of iatrogenic flatback syndrome. More recently, studies have shown poor restoration of lumbar lordosis in one- to two-level lumbar decompression and fusion procedures in patients with degenerative disease, along with the undercorrection of deformity in the larger reconstructions performed for adult spinal deformity [4, 9]. Both coronal and sagittal spinal deformities change with patient positioning [2, 3, 6, 7]. Options for prone positioning begin with the use of a regular OR table and towel rolls. Flexing the spine to unshingle the laminae and allow easier entry into the canal eventually evolved to specialized spine frames such as the Canadian (or Hastings) frame [16]. These “knee-chest” or “90-90” positions typically required hip and knee flexion. This positioning offered no major disadvantages in decompression-only and uninstrumented fusion procedures. However, with the advent of rigid, segmental instrumentation, surgeons have seen markedly reduced total and segmental lumbar lordosis. Newer frames, such as the Andrews and Wilson frames, can also be raised and lowered. Initial kyphosis for the decompression could be partially reversed to improve lordosis before final implant tightening [19]. Prone positioning also impacts blood pressure and cardiac function [8]. Introduced in 1967, the Relton-Hall four-poster frame decreased intraabdominal pressure to improve venous return and decreased intraoperative bleeding [18]. But since then, several variants on the original Relton-Hall frame have been introduced, most notably the modular Jackson frame, which incorporates four post supports for the patient with modular arm-boards, adjustable leg support, and radiolucent structural elements [1]. One echocardiographic study reported that Jackson frame positioning had less impact on cardiac index and stroke volume compared with Andrews and Wilson frames [5]. Other studies have concluded that by allowing the abdomen to suspend, the four-poster frame also improved lordosis in comparison with other options such as the Andrews frame [10, 21]. In the current study [14], the authors compared outcomes in patients with adult spinal deformity before and after transition from Wilson frame and a four-poster frame. Despite the unavoidable heterogeneity among patients with adult spinal deformity, the groups appeared reasonably well matched. At 2 years, there were no differences in PROMs. Radiographic parameters such as lumbar lordosis and sagittal vertical axis favored the four-poster group, as did blood loss. These findings comport well with what is known on the subject. The exact use of the adjustable Wilson frame and the impact of staged, anterior surgery on the ultimate alignment of these patients must be considered, so the differences found could vary in all-posterior surgical groups [11, 12]. The current study by Park et al. [14] reinforces the positive impact of four-poster frames over Wilson frames. The impact is notable in larger deformities, but surgeons should strongly consider their use even in short segment fusions for degenerative disease, where inadequate restoration of lordosis may contribute to long-term problems. Where Do We Need To Go? Future studies need to determine whether one four-poster frame, such as the Jackson frame, is superior to other frames. For example, newer four-poster frames offer mechanical hinges to allow greater control of the relative hip flexion and extension [20]. On the other hand, surgeons must also take into account the expenses associated with these frames. Given that 2-year PROMs do not differ between the groups, do the differences in blood loss and alignment justify the expense? In the absence of a clear benefit in PROMs, can other advantages, such as avoidance of osteotomies, be demonstrated? Can differences in adjacent segment degeneration or proximal junctional kyphosis be proven? When these investments are made, do the benefits of a stand-alone hinged spine frame outweigh its space requirements and cost? The degree to which intraoperative positioning will restore lumbar lordosis is not always clear preoperatively. Ideally, improvements in preoperative calculations of sagittal plane alignment will allow more specific surgery planning (such as adjunctive procedures from interbody implants or anterior releases to pedicle subtraction osteotomies). Corrections seem to vary by spinal segment as well. The L5-S1 level normally contributes 35% of normal lordosis, but may be less affected by prone positioning than upper lumbar lordosis [15]. Based on this, future studies need to determine which sagittal parameters are best addressed through intraoperative positioning and which require a change in surgical approach. It is increasingly clear that improving sagittal plane alignment is important in both one- and two-level fusions for degenerative disease and the much larger procedures seeking to address adult spinal deformity [13]. While proper positioning can both improve radiographic outcomes and patient safety, increased attention to its role makes sense, but, in many situations, positioning alone will not achieve the desired realignment. How Do We Get There? While randomized controlled trials can be helpful, the heterogeneity of patients with spinal deformity, including flexibility, bone quality, and body habitus, limit its usefulness in addressing the technical aspects of spinal reconstruction. While most general spine surgical registries do not typically capture granular details of spinal alignment or procedural details, such as the number and type of interbody implants or osteotomies, dedicated spinal deformity registries or modular additions for the general spine registries would allow a more detailed analysis of those steps most helpful in maintaining or restoring this alignment. Analysis of data from these registries could address questions such as: Is positioning or interbody fusion more useful in achieving appropriate lordosis at L5-S1? Can appropriate positioning decrease the need for posterior column or three-column osteotomies? Registries or large payor databases may offer insight into the gaps in our knowledge, including the impact of positioning and alignment on subsequent osteotomy surgeries and complications such as proximal junctional kyphosis. These data, in turn, could be used to assess the clinical and cost effectiveness of current four-poster frames and their newer iterations with adjustable, mechanical hinges. On a practical level, local quality and patient safety systems are important. When positioning-related complications are noted, surgeons should clarify their role in directing or directly participating in positioning. If these events recur, consider surgeon coaching on proper use of the surgical frame available or, perhaps, purchase a modern, modular system.

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