Medial proximal tibial angle at the posterior tibial plateau represents the pre-arthritic constitutional medial proximal tibial angle in anterior cruciate ligament-intact, advanced osteoarthritis of the knee

Restricted kinematically aligned total knee arthroplasty with an anatomically designed implant can restore constitutional coronal lower limb alignment

PURPOSE

Restricted kinematically aligned total knee arthroplasty (rKA-TKA) may not restore the constitutional varus alignment in most patients with knee osteoarthritis. This study aimed to investigate (1) the extent to which constitutional lower limb alignment can be restored by rKA-TKA using an anatomically designed implant and (2) which lower limb alignment parameters are associated with patient-reported outcome measures (PROMs).

METHODS

This study included 60 patients who underwent rKA-TKA using an anatomically designed implant. Radiographic alignment parameters, including mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), coronal hip-knee-ankle angle (HKA), coronal joint line obliquity (JLO), posterior tibial slope (PTS), single-leg standing knee flexion angle (KFA), sagittal JLO, and arithmetic HKA (aHKA), were evaluated preoperatively and postoperatively. The Western Ontario and McMaster Universities Arthritis Index (WOMAC) was used for clinical evaluation.

RESULTS

The mLDFA, MPTA, and aHKA showed no significant differences before and after surgery. Coronal HKA and PTS have significantly changed from 8.1 ± 8.7° and 9.9 ± 8.6° preoperatively to 3.5 ± 3.1° and 2.5 ± 2.0° postoperatively, respectively (p < 0.001 for each comparison). The postoperative WOMAC total score was significantly correlated with the KFA (r = 0.4063, p = 0.0034) and sagittal JLO (r = -0.3435, p = 0.0157). Postoperative KFA is a causal factor for the increased postoperative WOMAC total score (r = 1.416, 95% confidence interval: 0.491-2.342, p = 0.003).

CONCLUSION

rKA-TKA using an anatomically designed implant can restore constitutional coronal lower limb alignment, while postoperative KFA and sagittal JLO were associated with poor PROMs. Care should be taken for the postoperative KFA because it is a risk factor for poor PROMs.

LEVEL OF EVIDENCE

Level III, case-control study.

Long leg radiographs underestimate the degree of constitutional varus limb alignment and joint line obliquity in comparison with computed tomography: a radiographic study

PURPOSE

The purpose of this study was to understand if differences exist between computed tomography (CT) and long leg radiographs (LLR) when defining coronal plane alignment of the lower limb in total knee arthroplasty (TKA). It aimed to identify any such differences between the two imaging modalities by quantifying constitutional limb alignment (arithmetic hip-knee-ankle angle (aHKA), joint line obliquity (JLO) and Coronal Plane Alignment of the Knee (CPAK) type within the same population.

METHODS

A retrospective radiographic study compared pre-operative LLR and CT measurements in patients undergoing robotic-assisted TKA. The aHKA, JLO and CPAK types were calculated after measuring the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA). The primary outcomes were the mean differences in aHKA (MPTA-LDFA), JLO (MPTA + LDFA) and proportions of CPAK types between LLR and CT groups. The secondary outcomes were the differences in CT-derived MPTA values based on four different tibial sagittal landmarks.

RESULTS

After exclusions, 465 imaging sets were analysed in 394 patients. There was a statistically significant mean difference between LLR and CT, respectively, for both MPTA (87.5° vs. 86.2°; p < 0.01) and LDFA (88.7° vs. 87.3°; p < 0.01). There were also statistically significant differences for aHKA (- 0.2° vs. - 1.1°) and JLO (175.1° vs. 173.4°) for LLR and CT, respectively (both p < 0.01). CT increased the proportion of patients with CPAK Type I (constitutional varus aHKA, apex distal JLO) and CPAK Type II (neutral aHKA, apex distal JLO), and decreased numbers of CPAK Types III-VI. There were significant mean differences in the MPTA using varying sagittal landmarks.

CONCLUSION

Alignment determined by LLRs underestimates the magnitude of both constitutional varus alignment and joint line obliquity compared to CT, differences that notably increase the proportions of patients included in CPAK Types I and II. These distinctions are primarily due to underestimation of proximal tibial varus when measured on LLRs compared to CT, which more specifically defines articular weight-bearing points.

LEVEL OF EVIDENCE

III.