Aim: Robotic assisted total hip arthroplasty remains controversial, since wider exposure of the proximal femur and placement of the leg in maximal hip adduction and external rotation using a rigid leg-holder apparatus may impair significantly the hip abductors. Consequently, it is the purpose of this study to analyse and report both clinical outcome and hip abductor function following robotic assisted versus conventional total hip arthroplasty.
Material and methods: 36 robotic-assisted (CASPAR, Orto-Maquet, Rastatt, Germany) and 35 conventional cementless total hip arthroplasties were followed on average for 18 months regarding incidence of complications, Harris hip score, the scoring system according to Merle d'Aubigné and Postel, hip abductor function (using a spring-balance), and incidence of Trendelenburg's sign (according to the Kuhfuss-classification). Statistical analysis was performed in case of continuous data using the t test and the Mann-Whitney test, respectively, and in case of categorical data using Fisher's exact test and the chi-squared test, respectively. The level of significance was set as p < 0.05.
Results: Average duration of surgery (CASPAR: 100.6 min; conventional: 51.5 min; p < 0.0001) as well as average loss of haemoglobin (CASPAR: 4.5 mg/dL; conventional: 3.3 mg/dL; p = 0.0002) differed significantly, whereas the incidence of complications (CASPAR: two dislocations, one sciatic paresis, one deep infection; conventional: one dislocation, two fissures), revision rate (CASPAR: 5.6 %; conventional: 2.9 %), and incidence of heterotopic ossifications (CASPAR: 30.6 %; conventional: 17.1 %) was comparable following both procedures (p > 0.05). Improvement of the Harris hip score also was comparable in both groups (CASPAR: 40.9 to 86.1 points; conventional: 39.5 to 88.0 points; p = 0.21), whereas improvement of the score according to Merle d'Aubigné and Postel was significantly greater following the manual procedure (CASPAR: 10.1 to 16.0 points; conventional: 8.3 to 16.6 points; p < 0.0001). Differences between the two groups were also significant regarding hip abductor function (CASPAR: 76.1 %; conventional: 93.8 % of the contralateral hip; p < 0.0001) and incidence of Trendelenburg's sign (CASPAR: 61.1 %; conventional: 25.7 %; p = 0.0014).
Conclusion: The significant functional impairment following robotic assisted THA should be taken critically into consideration prior to initiating such procedure.