Change in lower limb length following total knee arthroplasty.

Background: Length variations of the lower limbs after total knee arthroplasty (TKA) constitute a poorly evaluated parameter and can be associated with worse functional outcomes. The objectives of this study were to: (1) describe the variations in the lower limb length after TKA according to the digital accuracy of the computerized navigation system used for prosthesis implantation, (2) describe patient sensation of limb length modification at 3 months postoperatively and to identify its risk factors, (3) identify factors affecting lower limb length modification and to analyze the predictive value causing in the patient the sensation of lower limb discrepancy.

Hypothesis: We hypothesize that there may be a lower limb length discrepancy after TKA, which may cause some distress to the patient.

Patients and methods: This prospective study included 100 TKAs implanted with navigation gap-balanced adjusted mechanical alignment. Were compared the length of the lower limb before and after implantation and the patient's changes in leg length perception at 3 months postoperatively. A subgroup analysis was performed according to preoperative knee deformities: varus knee was an HKA < 177 °, normal knee was an HKA between 117° and 183 ° and valgus was an HKA >183 °.

Results: Ninety-seven out of 100 patients experienced lengthening compared to the preoperative ipsilateral length, and twenty-three experienced lengthening greater than 10 mm. The mean lengthening was 7.3 mm (maximum 24.8 mm). Lengthening was significantly greater in valgus knees 9.9 mm [range, 2.0-24.8] than in varus 7.2 mm [range, 1.46-19.4] and normal knees 4.11 mm [range, 0.4-11.4] (p < 0.05). The correction of frontal and sagittal deformation were risk factors for limb length modification (OR = 0.595; 95% CI [0.544-0.816] [p = 0.001], OR = 0.396; 95% CI [0.351-0.653] [p = 0.001]). Twenty-two patients reported a sensation of limb length change: 11 (50%) reported equalization, whereas the remainder reported lengthening with a leg length difference. The preoperative sensation of lower limb length inequality was the unique factor affecting the patient's perception post-surgery (OR = 37.50; 95% CI [9.730-144.526] [p = 0.0001]). A threshold value of 6.6 mm was identified for the sensation of limb length modification.

Conclusion: Navigation is a tool for describing ipsilateral leg length variations after TKA. These variations are significant and perhaps explain some patient dissatisfaction. A partial correction of the frontal deformity according to the knee phenotype could limit the risk of modification of the native length.

Level of evidence: IV; Descriptive therapeutic prospective study.