Arthritic knees with more than 10° valgus can have soft-tissue imbalance in flexion.

PURPOSE: Valgus knees have inferior outcomes compared to varus knees. There is little data regarding soft-tissue balance in flexion which may influence outcome in valgus knees undergoing TKA. The purpose of this study was to evaluate whether there is imbalance between medial and lateral flexion gaps in valgus deformity. A secondary aim was to compare soft-tissue balance in knees with valgus deformity less than 10° with those exceeding 10°. The null hypothesis was that there was no soft-tissue imbalance in 90° of flexion irrespective of magnitude of deformity.

METHODS

64 valgus knees (52 female and 12 male) with deformity from 0.5 to 27.5° (mean 188.77, SD 6.21) were studied in 54 patients (mean age 67.81 y, SD 8.69) undergoing navigated TKA. Medial and lateral gaps in extension and at 90° of flexion were compared (using Independent-samples t test) between knees with valgus < 10° with those > 10° using a validated dynamic method after resection of cruciates, menisci and osteophytes, and then after final trialling.

RESULTS

Mean initial medial-lateral (ML) gap difference in extension was 2.63 mm (SD 2.63) and 2.09 mm (SD 3.78) in flexion, being tighter laterally. Initial ML gap differences in extension and flexion correlated with valgus deformity (R =  - 0.514; p = 0.00001; R =  - 0.325; p = 0.01, respectively). Initial ML gap differences in extension correlated with those in flexion (R = 0.42; p = 0.0005). Mean ML flexion and extension gap differences were 1.30 mm (SD 3.67) and 1.26 mm (SD 1.92) in knees with < 10° valgus, and 3.17 mm (SD 3.71) and 4.29 mm (SD 2.45) in those > 10° valgus; p values were 0.026 and < 0.001 respectively.

CONCLUSION

The lateral flexion gap in valgus knees may be narrower than the medial flexion gap, especially in knees with > 10° deformity. This contrasts with native and varus knees, in which it exceeds the medial gap. This novel study indicates the need to identify valgus knees with lateral flexion gap tightness by distracting the posterior femoral condyles from the proximal tibia by dynamic stressing of the soft-tissues after resection of cruciates, menisci, and osteophytes, with the knee flexed to 90°. These findings, highlighting the need for restoring flexion gap balance, may improve the inferior outcomes in valgus knees.

LEVEL OF EVIDENCE: IV.