Can Total Knee Replacement Lengthen or Shorten Leg Length?
Yes, total knee replacement (TKR) typically lengthens the operated leg by an average of 5-7 mm, with the vast majority of patients (76-97%) experiencing some degree of leg lengthening rather than shortening. 1, 2, 3
Magnitude and Direction of Leg Length Changes
The average leg lengthening after TKR is 5.3-7.3 mm, with most patients experiencing lengthening rather than shortening 1, 2, 3
Approximately 76-97% of patients experience leg lengthening after TKR, while only 20% experience shortening, and 3-4% remain unchanged 2, 3
Maximum reported lengthening can reach up to 24.8 mm in cases with severe preoperative deformities 3
In revision TKR specifically, the average lengthening is 5.3 mm, with 76% of legs lengthened, 20% shortened, and 4% unchanged 2
Factors That Predict Greater Leg Length Changes
Preoperative deformity severity is the strongest predictor of leg length change:
Valgus knees experience the greatest lengthening (9.9 mm on average), compared to varus knees (7.2 mm) and normal alignment knees (4.1 mm) 3
The degree of varus deformity angle significantly correlates with leg length difference (p < 0.001) 1
Fixed flexion deformity is another significant predictor of leg length change (p < 0.001) 1
Both frontal and sagittal plane deformity corrections are independent risk factors for limb length modification (OR = 0.595 and OR = 0.396 respectively, p = 0.001) 3
Clinical Impact on Patient Outcomes
Contrary to what might be expected, leg lengthening after TKR is actually associated with improved clinical outcomes:
Increased leg length after revision TKR positively correlates with better clinical outcomes at both 3 months (r=0.22, p=0.044) and 1 year (r=0.26, p=0.027) 2
The improved outcomes are primarily due to better pain scores and increased stability, rather than improved range of motion 2
Good or excellent outcomes for pain and function are achieved in 89% of patients up to 5 years after TKR 4
Patient Perception and Resolution
Most patients who perceive leg length discrepancy after TKR experience resolution within 3 months:
Approximately 10% of patients perceive a leg length discrepancy postoperatively, which is actually lower than the preoperative rate 5
All patients who perceive postoperative leg length discrepancy experience resolution at a mean of 8.5 weeks (range 3-12 weeks) 5
The preoperative sensation of leg length inequality is the only significant predictor of postoperative perception (OR = 37.50, p = 0.0001) 3
A threshold value of 6.6 mm was identified as the point at which patients begin to perceive leg length modification 3
There is no correlation between actual mechanical axis alignment and perceived leg length discrepancy, suggesting perception is multifactorial 5
Critical Pitfalls to Avoid
Do not assume leg lengthening is a complication—it is typically associated with improved outcomes and pain relief 2
Reassure patients who perceive postoperative leg length discrepancy that resolution typically occurs within 8-12 weeks 5
Recognize that patients with severe valgus deformities (>183° HKA angle) will experience the greatest lengthening and may benefit from preoperative counseling 3
Weight-bearing anteroposterior and lateral radiographs are the initial imaging modality for evaluating alignment and component positioning if concerns arise 6, 7
Full-length hip-to-ankle standing radiographs should be obtained for comprehensive alignment assessment when leg length discrepancy is a concern 6, 7