Mid-level constraint may correct coronal plane imbalance without compromising patient function in patients with...

Mid-level constraint (MLC) in Total Knee Arthroplasty (TKA) offer surgeons the opportunity to obtain a well-balanced varus-valgus balance in the setting of slight ligament imbalance. As such, we sought to evaluate patient reported outcome measures (PROMs), alignment correction, and rate of revision between the MLC group and a cohort of posterior stabilized (PS) knees in a cohort of patients with preoperative degenerative arthritis.

We performed a retrospective review of 57 MLC knees and 96 PS knees from a single manufacturer that were implanted by a single surgeon. We found the average age (68.91 vs. 68.40, p = 0.72), average BMI (30.88 vs. 29.14, p = 0.10), and gender breakdown (25:32 vs. 28:69, p = 0.08) to be comparable between the two cohorts. The latest follow-up was 4.0 years in the MLC group and 3.8 years in the PS group, p = 0.26.

The two cohorts inherently resulted in significantly different preoperative deformities (MCL knees: average varus deformity 13.75°, average valgus deformity 12.37°; PS knees average varus deformity 15.14°, average valgus deformity 10.8°). There were more valgus knees in the MLC group (36 vs. 22 (p < 0.001), respectively), but the postoperative alignment was the same. MLC cohort: preoperative varus group had 4.74° of valgus postoperatively, preoperative valgus group had 5.43° of valgus postoperatively. PS cohort: preoperative varus group had 5.40° of valgus postoperatively, preoperative valgus group had 4.80° of valgus postoperatively. We found a significant difference in Knee Injury and Osteoarthritis Outcome Score (KSCRS-Total) between the two groups (MLC 163.9 vs. PS 132.8, p = 0.003). There was no significant difference in terms of Range of Motion (ROM) (MLC 121° vs. PS 122°, p = 0.58), anterior knee pain (MLC 1.75 vs. PS 1.81, p = 0.39), or Pain VAS (MLC 25.1 vs. PS 28.6, p = 0.46). There was similar rate of revision between the cohorts (3.5% MLC vs. 2.10% PS, p = 0.13). There was no significant difference in manipulation rate (8.78% MLC vs. 9.40% PS, p = 0.38).

This study demonstrated that the use of MLC in TKA allows surgeons to correct preoperative deformities with equal or improved functional outcomes compared to PS knees. In general, we recommend that surgeons try to balance the knee and use the least amount of constraint possible but should consider MLC when needed and use such implants if they are unable to balance the varus-valgus gap.