Risk factors of de novo hyperextension developed after posterior cruciate ligament substituting total knee arthroplasty: a matched case-control study

Effect of mediolateral gap difference on postoperative outcomes in navigation-assisted total knee arthroplasty using an ultracongruent insert and the medial stabilising technique

PURPOSE

This study was aimed to compare the clinical, functional, and radiographic outcomes between symmetric and asymmetric extension and mediolateral gap balance after navigation-assisted (NA) total knee arthroplasty (TKA) using ultracongruent (UC) insets and the medial stabilising technique (MST).

METHODS

In all, 363 knees of 275 patients who underwent mechanical alignment-target NA TKA with MST between January 2015 and December 2017 were analysed. Patients were divided into balanced (extension mediolateral gap difference ≤ 2 mm) and tight medial (difference ≥ 3 mm) groups. Pre- and postoperative clinical, functional (range of motion, Western Ontario and McMaster University Osteoarthritis [WOMAC] index, Knee Society Knee Score [KSKS], and Knee Society Function Score [KSFS]) and radiographic (hip-knee-ankle [HKA] angle, femoral condylar offset, extension angle [a minus indicates hyperextension], and joint line distance) outcomes were compared between the groups. Student's t- or Chi-squared test was used to compare the outcomes.

RESULTS

Among the 363 knees analysed, 279 (77%) were assigned to the balanced group and 84 (23%) to the tight medial group. The preoperative HKA angle was significantly greater in the tight medial group than in the balanced group (9.7° ± 4.1° vs 14.3° ± 4.7°, P < 0.001). The postoperative WOMAC index, KSKS, and KSFS were similar between the groups. The change in the joint line distance was not significantly different (1.5 ± 3.7 vs 2.0 ± 3.3; n.s).

CONCLUSION

The clinical, functional, and radiographic outcomes, including joint line distance, were comparable between the tight medial and balanced group after mechanical alignment-targeted UC TKA with MST.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Hyperextension following two different designs of fixed-bearing posterior-stabilized total knee arthroplasty

PURPOSE

Hyperextension after total knee arthroplasty (TKA) is related to worse functional outcomes. Among the reported predictive factors, it is unclear whether prosthesis design affects postoperative hyperextension. Hence, our objectives were to (1) compare time-dependent changes of the extension angle following multi-radius (MR) and single-radius (SR) TKA and (2) assess predictive factors for the hyperextension.

METHODS

In this study, consecutive 136 MR TKAs and consecutive 71 SR TKAs performed by a single surgeon were reviewed. The extension angle was evaluated by digitized full-extension lateral radiographs at preoperative, 3 months and at 1 and 2 years after TKA. A positive value was defined as hyperextension. A multiple regression analysis was used to determine predictive factors for the extension angle and the risk of hyperextension > 5°.

RESULTS

The postoperative extension angle of both groups gradually increased during the first 2 years and the SR group finally progressed with 4.04° greater extension than the MR group (p < 0.01). The incidence of hyperextension > 5° in the SR group was 18.3% and for the MR group, 7.4% (p = 0.02). However, the Oxford knee scores was nonsignificant different between the groups (p = 0.15). Preoperative extension angle, sagittal femoral component angle (SFA) and SR prosthesis were predictive factors for the extension angle at 2 years after TKA and were also associated with hyperextension > 5°.

CONCLUSIONS

The extension angle of the SR group became significantly more extended than that of the MR group during the first two years after TKA. Hence, ideal extension position immediately after SR TKA may be different from that of the MR TKA prosthesis. The preoperative extension angle, SFA and SR prosthesis were factors that were associated with postoperative hyperextension.