Abstract
Background:
Acetabular cup positioning1, 2, leg length discrepancy3 and global offset4 are important parameters associated with outcomes following total hip arthroplasty (THA). Deviation from an accepted range of values for each of these parameters can lead to significant complications including nerve injury, low back pain, abnormal gait, increased dislocation rate, and bearing surface wear. The primary purpose of this study was to assess whether the use of the MAKO™ robotic hip system is reliable in predicting post-operative radiographic measurements of cup inclination, cup anteversion, leg length change, and global offset change in THA.
Materials and Methods:
All robotic-assisted THAs performed using the MAKO™ system between June 2011 and Dec 2012 were reviewed. A single surgeon performed all cases through a mini-posterior approach. The intra-operative measurements of cup inclination and anteversion angles, leg length change, and global offset change recorded by the MAKO™ system were compared to the post-operative radiographic measurements.
Results:
Sixty one cases met the inclusion and exclusion criteria. A strong inter- and intra-observer correlation was found for the radiographic measurements of cup inclination, cup anteversion, leg length discrepancy and global offset (r > 0.8 with p < 0.001 for all). Comparison between the MAKO™ and the radiographic measurements showed mean differences in inclination of 3.2° ± 2.7° (CI95 = 0.7), mean differences in anteversion of 3.8° ± 2.6° (CI95 = 0.7), mean differences in leg length change of 3.5 ± 2.6 mm (CI95 = 0.7), and mean differences in global offset change of 4.5 ± 3.7 mm (CI95 = 1.0). 85.2% of MAKO™-measured inclination angles were within 5° of radiographic measurements, and 96.7% within 10°. 65.6% of MAKO™-measured anteversion angles were within 5° of radiographic measurements, and 98.4% within 10° (Figure 1). 69.4% of MAKO™-measured leg length change measurements were within 5 mm of radiographic measurements, and 100% within 10 mm. 71.4% of MAKO™-measured global offset change measurements were within 5 mm of radiographic measurements, and 91.8% within 10 mm (Figure 2).
Conclusion:
The MAKO™ robotic hip system showed good predictive value for cup inclination and anteversion angles, leg length change and femoral offset change measurements done post-operatively on plain radiographs. Further refinement of the MAKO™ system would be expected to make it more accurate in predicting the post-operative parameters mentioned.
