Age explains limited hip extension recovery at one year from total hip arthroplasty.

BACKGROUND: To investigate the dependency of the one-year recovery in gait after total hip arthroplasty on age and preoperative conditions.

METHODS: Longitudinal retrospective study on 20 elderly patients with unilateral total hip arthroplasty consequent to hip osteoarthritis, assessed by gait analysis before surgery (T0), 2weeks (T1), 6 (T2) and 12months (T3) post-surgery. A set of variables assessing primary gait deviations and compensatory mechanisms were extracted from gait analysis data. Their variations throughout the one-year period were analyzed through a repeated measures ANOVA. Their dependency on preoperative conditions (age, hip passive limitations and Thomas Test) at one year after surgery were assessed through a correlation analysis and an ANCOVA.

FINDINGS: Hip sagittal range significantly increased (P<0.05) after each measurement session from mean 21 (SD 10) degrees at T0, to 31 (6) at T1, to 34 (6) at T2 until 36 (4) degrees at T3. The peak of hip and ankle power generation significantly increased from T0 to T3, with a progressive reduction of compensatory mechanisms towards normal values. At T3, preoperative hip passive extension and Thomas Test score did not affect hip sagittal range during gait, while age did (P<0.05, R2 =0.36). Ankle and hip peak powers were also correlated with age (P=0.033 and P=0.008, respectively). In our sample, age was the main cause of hip sagittal joint range limitation.

INTERPRETATION: At one year from total hip arthroplasty, age affects hip joint limitations and gait recovery more than preoperative passive restrictions due to muscle shortening.