Abstract
Background:
Coronal malalignment occurs frequently in total knee arthroplasty (TKA) and reduces implant longevity and function. Designed to improve consistency and efficiency, patient- specific positioning guides (PSPG) generated from preoperative imaging studies represent a paradigm shift from manual instrumentation (MI) and intraoperative computer navigation.
Purposes:
We compare the efficacy of PSPG to MI in (1) restoring mechanical axis of the extremity and (2) achieving neutral alignment of the femoral and tibial components.
Methods:
We retrospectively examined 696 postoperative anteroposterior standing long-leg radiographs after TKA (545 PSPG, 151 MI) by two surgeons. Coronal alignment was assessed by determining the zone in which the overall mechanical axis (OMA) passed through the knee, measuring the hip-knee-ankle (HKA) angle between the tibial and femoral mechanical axes, and finally, noting the alignment of the femoral and tibial components with respect to their mechanical axes.
Results:
The OMA passed through the central third more frequently with PSPG than MI for both surgeons (JHD: 86.6% vs. 77%, p = 0.02; AVL: 86.4% vs. 74.5%, p = 0.11). For the senior author, while percent of HKA outliers >3ï,° was similar between PSPG and MI, the mean error from neutral for these patients was significantly less with PSPG than MI (4.50ï,° vs. 5.25ï,°, p = 0.0031). The tibial component demonstrated no significant difference between PSPG and MI. With PSPG, average individual deviation from neutral for the femoral component was significantly less (0.91ï,° vs. 1.34ï,°, p = 0.0005) and had fewer outliers >2ï,° (4.9% vs. 19.6%, p = 0.017).
Discussion:
Improved coronal alignment in total knee arthroplasty (TKA) is associated with greater patient satisfaction, better functional scores and increased implant longevity [11,30,31,36]. Recently, preoperative three-dimensional imaging and custom manufacturing have enabled the development of patient-specific positioning guides (PSPG). Designed to improve consistency and efficiency, PSPG represents a paradigm shift away from intramedullary and extramedullary guides, or manual instrumentation (MI), and an evolution from intraoperative computer-assisted navigation (CAN). Even in the hands of experienced surgeons, MI frequently results in significant component angulation and mechanical axis malalignment [32].
Multiple studies support the restoration of a neutral axis as a critical factor in implant performance and potential longevity of total knee arthroplasty [2, 3, 5, 18, 41, 44]. Intraoperative CAN has been shown to improve precision and accuracy of alignment compared to MI with a reduction in the number of outliers (less than 3ï,° varus/valgus) [32, 38] and the amount of blood loss [39], but is hindered by time-consuming landmark registration, increased operative length [7], greater cost, the risk for stress fracture, pin loosening, and a substantial learning curve [6, 22, 29, 43].
Patient-specific positioning guides, on the other hand, purportedly eliminate many of the disadvantages of CAN while still allowing the bone resections to match the measured overall mechanical axis.
While accurate and precise alignment guides are potent tools in restoring the proper overall mechanical axis, they are not a substitute for careful preoperative planning, good clinical and intraoperative judgment, appropriate soft tissue balancing, and precise implantation technique. Nevertheless, patient-specific positioning guides can provide the first step in the right direction to a successful TKA.
Conclusions:
Patient-specific positioning guides can assist in restoration of the mechanical axis with reduction in outliers.
Level of Evidence: Level III, retrospective case-control study
