Functional outcomes and implications of limb length discrepancy after total knee arthroplasty

Background
The occurrence and perception of LLD after TKA may lead to unsatisfactory results and its consequences are not well studied as the LLD occurring after THA. The objective of this study was to evaluate the incidence, magnitude, implications as well as functional outcomes of LLD in patients after TKA using the WOMAC (Western Ontario and McMaster Universities Arthritis Index) functional score 6 months after surgery.


Materials and Methods
This was a prospective case series study and included 34 cases. Cases were subjected to pre and postoperative clinical, radiological assessment to detect clinical LLD, flexion deformity (FD), radiological LLD, hip knee angle (HKA), and functional assessment using WOMAC score. The degree of osteoarthritis (OA) according to Kellegren Lawrence classification (KL) was assessed and documented. In addition, the polyethylene insert thickness was documented as well.


Results
Change in limb length occurred in the 38 (30 cases unilateral, 4 cases bilateral) knees with a mean increase of 1.3 cm ±SD 0.9. The mean improvement of the FD angle was 9.9° ± SD 8.7. The mean HKA before surgery was 11.2° ±SD 6.2 while the mean post-operative HKA was 2.7° ±SD 3.5. WOMAC score of cases included in the study with postoperative radiological LLD < 1 cm didn’t show a significant difference from that of cases with LLD≥ 1 cm. WOMAC score improvement after surgery didn’t correlate with perceived LLD. Also, age, sex, BMI, degree of arthritis, insert size, and FD showed no correlation with postoperative radiological LLD. Increased preoperative HKA showed a significant correlation with increased postoperative radiological LLD. There was a significant difference between postoperative radiological LLD in both groups (< 1 cm and ≥ 1 cm) regarding their postoperative perception of LLD.


Conclusion
This prospective case series study suggested that there is no significant correlation between LLD and the functional outcome after TKA. Patients with postoperative radiological LLD more than 1 cm are more likely to perceive LLD.