This in vivo study for the first time examined kinematics and kinetics of the hip joint during driver golf swings of patients who had undergone unilateral THA. During the driver swing at a mean maximum head speed of 31 m/s, the mean replaced hip rotations were approximately 20–30° and mean HCFs were 5 and 6.6 x BW at the lead and trail replaced hips, respectively. More than 60% of the %MVIC was found in both iliopsoas muscles, regardless of the surgical side. Being female, lower mHHS, and higher HCF of surgical side correlated with golf-induced pain of the replaced hip.
The 31 m/s of mean maximum head speed in unilateral THA patients was equivalent to that of a similar aged healthy cohort: mean 28.3–38.9 m/s.31-33An approximate mean of 20–30° of hip rotation during the driver swing in patients who underwent THA is also equivalent to that of the golf swing analyzed by the motion capture methods in normal hips: mean 20–60°.34,35 As in a previous study,12 the driver swing had comparable lead and trail hip rotations regardless of the surgical side, and no excessive deviation of rotational balance. Hip rotation during the golf swing of similar aged THA patients analyzed by the image-matching method was approximately 50°,12 which is greater than the 20–30° in the present study. The results may have been influenced by differences in the club used (grip only vs. driver club) and analysis method (image matching vs. motion capture).36,37 RoMs of the Flex-Ext and Add-Abd during the driver swing in this study were similar to those of the golf swing in healthy participants.34,35 In other words, club head speed and 3D hip RoMs were comparable to those of healthy participants, suggesting that THA had a positive effect on golf performance, including distance and handicap; this is supported by previous reports that most patients are able to play golf after THA, and mostly with an improvement in performance.1,10,11,38
The mean HCFs of the lead and trail replaced hips during the golf swing (5.5 and 6.7 x BW, respectively) were comparable, with a tendency of larger HCF of trail hips in both left THA and right THA, which was somewhat lower than the HCF while jogging at 6–8 km/h: 5.4–8.5 x BW.28,39 Although jogging has been classified as a high-impact sport, it has been reported to have no adverse effect on mid-term survival outcome in THA.5,40 The number of golf swing motions is much less than the number of steps taken while jogging and the repetition of loading cycles is significantly smaller. In addition, no negative effects on mid-term survival rate of implants have been previously observed in golfers.11,41 Thus, it is suggested that the golf swing is an acceptable motion in patients with unilateral THA, although it produces a high HCF for both lead and trail replaced hips, comparable to that of jogging. There have been no previous reports of HCF in normal participants and THA patients during a golf swing, the proximo-distal component of HCF showed a similar pattern and magnitude as the resultant HCF, consistent with the reported HCF of daily activities in THA patients.13
It has been reported that more than 60% of MVIC intensity should be used for effective muscle strengthening and that the range should be at least 40% to 60% to stimulate muscle strength adaptation.26,27 The driver swing may be useful as an iliopsoas strengthening exercise, because the %MVIC of the bilateral iliopsoas muscles is greater than 60%. Marta et al. demonstrated that the driver swing activated hip extensors in the order of strength of the biceps femoris long head, gluteus maximus, and semimembranosus in the lead leg (51–83%) and gluteus maximus, biceps femoris long head, and semimembranosus in the trail leg (67–100%), indicating a higher muscle activity of the trail leg,42 which was consistent with the present study, where more than 40% of %MVIC was found in the hip extensors (the biceps femoris long head and medial hamstring) of the trail leg, except in the bilateral iliopsoas muscles. However, overall, %MVIC values were higher in the Marta et al. report5 than in the present study, which may have been influenced by differences in the participants (mean 36-year-old healthy volunteers vs. mean 68-year-old THA patients), handicap (<5 vs. 8–45), and analysis methods (electromyogram vs. musculoskeletal modeling method). The biceps femoris long head and medial hamstring on the right side had approximately 40% of MVIC. Therefore, opposite-direction driver swings may be required to provide a level of muscle activation that balances the bilateral biceps femoris long head and medial hamstring muscular adaptations.
A significantly higher proportion of males were found in the patients without golf-related replaced hip pain compared to patients with pain, and male sex was a significant factor with a negative effect on golf-related replaced hip pain, consistent with previous reports on the association between sex and persistent pain after THA.43,44 The mean HCF on the surgical side for patients without golf-related replaced hip pain was 5.6 x BW, lower than 8.1 x BW for patients with pain and lower HCF was also a significant factor with a negative effect on golf-related replaced hip pain, which is consistent with a previous report that TKA patients experience less pain with lower loads applied to the knee when hitting the ball.9 Of golf swings, the minimalist golf swing and partial golf swing are designed to reduce the loading that hips experience throughout the swing.43,45,46 The minimalist golf swing, which requires torso rotation to be completed in a more upright position during the set-up, results in less hip extension and abduction moments while maintaining golf performance.29 The partial golf swing, which is adjusted to approximately 80% of full swing distance, requires limiting the natural weight shift of the swing to reduce lateral motion, resulting in a significant reduction in the peak horizontal ground reaction force of both legs.45,46 This reduction in joint loading resulting from swing adjustments may provide relief from hip pain during and after playing golf.
There are several limitations to the present study. First was the limitation of the small number of study patients. A larger number of patients might have revealed further kinematic and kinetic differences. In addition, we recruited recreational golfers from unilateral primary THA patients; therefore, findings in this study cannot be generalized to amateur or professional golfers. Furthermore, we only analyzed swings using a driver for our data collection. Therefore, we cannot make inferences as to kinematics and kinetics produced using other clubs. Finally, the patients performed their golf swing while barefoot and without a golf ball, which could have altered swing mechanics.