Functional alignment in total knee arthroplasty best achieves balanced gaps and minimal bone resections: an analysis comparing mechanical, kinematic and functional alignment strategies.

PURPOSE: Key concepts in total knee arthroplasty include restoration of limb alignment and soft-tissue balance. Although differences in balance have been reported amongst mechanical alignment (MA), kinematic alignment (KA) and functional alignment (FA) techniques, it remains unclear whether there are differences in gap imbalance or resection thicknesses when comparing different constitutional alignment subgroups. METHODS: MA (measured resection technique), KA (matched resections technique) and FA (technique based on the restricted KA boundaries) were compared in 116 consecutive patients undergoing 137 robotic-assisted cruciate-retaining total knee arthroplasties. The primary outcome was the proportion of balanced gaps (differential laxities ≤ 2 mm) for extension, flexion, medial and lateral gap measurements. Manual pre-resection laxity measurements were obtained for MA and KA and manual post-resection measurements were obtained for FA in 10° and in 90° of knee flexion. Secondary outcomes were resection depths and implant alignment. All outcomes were analysed per constitutional coronal alignment and joint line obliquity subgroups. RESULTS: The proportions of balance in all four gap measurements were 54.7%, 66.4% and 96.5%, with MA, KA and FA, respectively. Across all constitutional alignment types, FA achieved the highest proportion of balance. MA resected the least amount of bone from the medial tibial plateau. KA had femoral components in most valgus and most internally rotated, tibial components in most varus and was the most bone-preserving for the posteromedial femoral condyle. FA had the most externally rotated femoral components and was most bone-preserving for the distal femoral resections. CONCLUSION: The study shows that implant alignment to the mechanical axis or joint line anatomy (equal resections) alone does not guarantee a balanced total knee arthroplasty. FA resulted in the highest proportion of balanced knees across all analysed subgroups. Future research will consider whether one alignment philosophy leads to superior outcomes for different constitutional alignment subgroups. LEVEL OF EVIDENCE: Level II.

The Addition of Suture Tape to the Hamstring Graft Construct Does Not Reduce Instrumented Knee Laxity Following ACL Reconstruction.

Purpose: To establish the effect of the addition of suture tape to the hamstring graft construct through measurement of instrumented sagittal plane knee laxity at 6 months after anterior cruciate ligament reconstruction (ACLR). Methods: A retrospective analysis was undertaken of a consecutive series of primary ACLR performed between May 2017 and June 2019. Patients with concomitant or historic contralateral knee injury were excluded. Suture tape was included in the graft construct from the midpoint of the study period (May 2018). Sagittal plane knee laxity was quantified using the KT2000 arthrometer at 6 postoperative months. Mean side-to-side differences in sagittal plane laxity between the operated and contralateral, uninjured knees were compared for grafts with and without suture tape. Additional outcomes included comparison between suture tape application techniques (graft reinforcement versus augmentation), comparison between suture tape with and without iliotibial band (ITB) tenodesis and documentation of complications necessitating further surgery. Results: A total of 169 patients were eligible for inclusion. Seventy-two grafts included suture tape and 84 patients underwent concomitant ITB tenodesis. There was no significant difference in mean laxity between grafts containing suture tape (mean difference: 1.2 mm, SD: 2.6 mm) and those without (mean difference: 1.3 mm, SD: 2.1 mm), P = .83 (CI -.92 to 1.13). Neither were there significant differences in laxity when using suture tape with concomitant ITB tenodesis (mean difference: 1.1 mm, SD: 2.1 mm), P = .75 (CI -.79 to 1.09), or when comparing techniques: graft reinforcement (mean difference .9 mm, SD 2.6 mm); graft augmentation (mean difference: 1.5 mm, SD: 2.5 mm) P = .52 (CI -2.29 to 1.16). There were no complications associated with suture tape. Conclusions: The addition of suture tape to an autologous hamstring graft construct did not reduce instrumented sagittal knee laxity in the first 6 months after ACL reconstruction. As such, the clinical relevance of its use remains unknown. Level of Evidence: Level III, retrospective cohort study.

The importance of joint line obliquity: a radiological analysis of restricted boundaries in normal knee phenotypes to inform surgical decision making in kinematically aligned total knee arthroplasty.

PURPOSE: Restricted kinematic alignment (rKA) in total knee arthroplasty (TKA) aims to restore native soft tissue laxities while limiting alignment extremes that risk prosthetic failure. However, there is no consensus where restricted boundaries (RB) should be set. This study aims to determine the proportion of limbs in which constitutional alignment and joint line obliquity (JLO) would be restored with various RB scenarios, to inform decision making in rKA TKA. METHODS: The mechanical hip-knee-ankle (mHKA) angle, arithmetic hip-knee-ankle (aHKA) angle, lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were measured on radiographs of 500 normal knees. Incrementally wider RBs were then applied. The proportion of limbs within each increment was determined when RBs were applied only to HKA, or to HKA, LDFA and MPTA together. In addition, the proportion of limbs within published adjusted mechanical alignment (aMA) and rKA protocols were determined, as well as those within one, two and three standard deviations of the means for HKA, LDFA and MPTA. RESULTS: When restrictions to mHKA alone were applied, 74.0% and 97.8% of knees were captured with boundaries of ± 3° and ± 6° respectively. However, when the same boundaries to HKA were also applied to MPTA and LDFA, 36.2% and 91.0% of knees were captured respectively, highlighting the limiting effect that JLO has on restoration of normal knee phenotypes. When comparing previously published boundaries, aMA of 0° ± 3° captured 36.2%; rKA of 0° ± 3 for HKA and 85° to 95° for LDFA/MPTA captured 67.8%; rKA of - 5° to 4° HKA and 86°-93° for LDFA/MPTA captured 63%; and rKA of - 6° to + 3° for HKA and 84°-93° for LDFA/MPTA captured 85.4%. CONCLUSION: The greatest proportions of normal knee phenotypes were captured with boundaries that were centred around population means for HKA and JLO. Further, these findings demonstrate that restricting the JLO has a significant limiting influence on restoration of normal knee phenotypes beyond that of restricting HKA alone. LEVEL OF EVIDENCE: III.

Tibiofemoral dynamic stressed gap laxities correlate with compartment load measurements in robotic arm-assisted total knee arthroplasty.

AIMS: It is unknown whether gap laxities measured in robotic arm-assisted total knee arthroplasty (TKA) correlate to load sensor measurements. The aim of this study was to determine whether symmetry of the maximum medial and lateral gaps in extension and flexion was predictive of knee balance in extension and flexion respectively using different maximum thresholds of intercompartmental load difference (ICLD) to define balance. METHODS: A prospective cohort study of 165 patients undergoing functionally-aligned TKA was performed (176 TKAs). With trial components in situ, medial and lateral extension and flexion gaps were measured using robotic navigation while applying valgus and varus forces. The ICLD between medial and lateral compartments was measured in extension and flexion with the load sensor. The null hypothesis was that stressed gap symmetry would not correlate directly with sensor-defined soft tissue balance. RESULTS: In TKAs with a stressed medial-lateral gap difference of ≤1 mm, 147 (89%) had an ICLD of ≤15 lb in extension, and 112 (84%) had an ICLD of ≤ 15 lb in flexion; 157 (95%) had an ICLD ≤ 30 lb in extension, and 126 (94%) had an ICLD ≤ 30 lb in flexion; and 165 (100%) had an ICLD ≤ 60 lb in extension, and 133 (99%) had an ICLD ≤ 60 lb in flexion. With a 0 mm difference between the medial and lateral stressed gaps, 103 (91%) of TKA had an ICLD ≤ 15 lb in extension, decreasing to 155 (88%) when the difference between the medial and lateral stressed extension gaps increased to ± 3 mm. In flexion, 47 (77%) had an ICLD ≤ 15 lb with a medial-lateral gap difference of 0 mm, increasing to 147 (84%) at ± 3 mm. CONCLUSION: This study found a strong relationship between intercompartmental loads and gap symmetry in extension and flexion measured with prostheses in situ. The results suggest that ICLD and medial-lateral gap difference provide similar assessment of soft-tissue balance in robotic arm-assisted TKA. Cite this article: Bone Jt Open 2021;2(11):974-980.