The Hip Barely Moves During Joint Mobilization: What does that mean for clinicians?

In a popular video, a clinician demonstrates the vacuum phenomenon of the hip joint in a cadaver, moving the femoral head around to create suction and then pulling (clearly very hard) to demonstrate how strong that suction force can be. It prompts the question – if someone can apply that much force without any movement of the hip, what is happening during joint mobilization?

Seth Peterson, PT, DPT, OCS, FAAOMPT

The Motive Physical Therapy Specialists

Arizona School of Health Sciences, A.T. Still University

Moving the Hip Joint: Not an Easy Task

Several people have studied the amount of force required to move the hip joint, and they have found a similar answer: a lot. In a 2003 study,¹ posterior and anterior glides were applied to the hip joints of cadavers (measured with a force gauge) and found the hip moved a mean of 1.52 mm with 356 N (about 80 lbs) of force. The most the hip joint moved in this study was 2.90 mm.¹ For context, this is about the same amount of movement as a penny sitting on a nickel.

In an in vivo study using ultrasound on college students (because there’s always a study on college students), the average tangential glide during active hip flexion was about 54 mm, but the glide during the mobilization averaged only 2 mm with a force 50% of their body weight.² Again, it moved about the thickness of a nickel, which was only a very small percentage of its movement during active motion.² Finally, a study by Arvidsson³ using a long-axis distraction force, 400 N (about 90 lbs) was required to create any separation at all of the femoral head from the acetabulum.

If we set aside high velocity techniques, it is unlikely that clinicians are even getting close to these joint mobilization forces in clinical practice. In a study by Estebanez de Miguel et al, ⁴ researchers compared self-selected high force and low force joint mobilizations to the hip. The mean force applied in the “high force” group was 68.6 N (15 lbs).⁵ Not only is this amount of force unlikely to create any significant separation in joint surfaces, it is only around 25% of the force required to create ANY separation according to previous research.^1,2,3

So, case closed – right?

Hip Joint Mobilization Seems Pretty Effective–for Hip Osteoarthritis, At Least

Remember the randomized-controlled trial by Estabanez de Miguel et al?⁴ That study actually found that the high force group had significantly better outcomes than lower forces at improving hip joint range of motion in those with hip osteoarthritis.⁴ If hip joint mobilization was not doing anything, then there shouldn’t be a difference. A study has been done comparing sham joint mobilization with movement to the real thing, finding a substantial difference in immediate pain and range of motion in the mobilization group.⁶ Finally, a 2019 review determined that moderate level evidence existed (including 5 RCTs) that adding hip mobilization to treatment improves pain and range of motion in those with hip osteoarthritis.⁷ In other words, even though the hip joint is probably not moving a whole lot during the techniques, they outperform a sham, it appears that pulling harder might be more effective at improving pain and range, and adding it to treatment appears to improve outcomes in people with hip osteoarthritis.

Should We Add Hip Mobilization to Our Treatments or Stay Away From it?

Unfortunately, we are just not in a place where we can use an understanding of treatment mechanisms to guide our clinical decisions. There is little understanding about the mechanisms underpinning manual therapy approaches like joint mobilization of the hip. We know that contextual factors, such as patient factors, provider factors, and environmental factors can all influence the outcome of treatment.⁸ It appears that neurophysiological effects are probably a major reason for changes in pain or range of motion after manual therapy.⁸ However, these mechanisms are hard to measure, let alone predict.

In terms of clinical research, it would probably be more informative if researchers outlined the specific treatment target of each intervention, which some have already called for.⁹ For example, is hip joint mobilization being applied to increase range of motion or reduce pain? If we knew whether improving hip range of motion helped things like functional outcomes or reaching patient goals, we would then know whether it was a worthwhile treatment target. Only 36% of exercise trials for low back pain specified a treatment target, and often targeted things like strength, which we already know aren’t correlated with pain or disability outcomes.¹⁰ A 2021 consensus study identified 5 proposed targets of exercise interventions for back pain (improving function, improving quality of life, reducing pain, meeting patient-specific goals and reducing fear of movement).¹¹

At the end of the day, I believe we should come back to what we are trying to accomplish to help our patients. Although many of us might have heard or even grown up with the notion that joint mobilization is separating the hip joint, that’s probably not the case–at least not in a way that is significant. However, is our goal to move the hip joint a certain number of millimeters, or to help patients get more range of motion? Maybe our goal is to reduce the patient’s hip pain or help them squat deeper so they can more easily reach bottom cupboards or pick up their grandchildren. If that is the case, joint mobilization still appears to be a reasonable choice. You just might want to adjust your explanation for why that happens.

REFERENCES

1. Harding L, Barbe M, Shepard K, et al. Posterior-anterior glide of the femoral head in the acetabulum: a cadaver study. J Orthop Sports Phys Ther. 2003;33(3):118-125. doi:10.2519/jospt.2003.33.3.118
2. Loubert PV, Zipple JT, Klobucher MJ, Marquardt ED, Opolka MJ. In vivo ultrasound measurement of posterior femoral glide during hip joint mobilization in healthy college students. J Orthop Sports Phys Ther. 2013;43(8):534-541. doi:10.2519/jospt.2013.4487
3. Arvidsson I. The hip joint: forces needed for distraction and appearance of the vacuum phenomenon. Scand J Rehabil Med. 1990;22(3):157-161.
4. Estébanez-de-Miguel E, Fortún-Agud M, Jimenez-Del-Barrio S, Caudevilla-Polo S, Bueno-Gracia E, Tricás-Moreno JM. Comparison of high, medium and low mobilization forces for increasing range of motion in patients with hip osteoarthritis: A randomized controlled trial. Musculoskelet Sci Pract. 2018;36:81-86. doi:10.1016/j.msksp.2018.05.004
5. Estébanez-de-Miguel E, Caudevilla-Polo S, González-Rueda V, Bueno-Gracia E, Pérez-Bellmunt A, López-de-Celis C. Ultrasound measurement of the effects of high, medium and low hip long-axis distraction mobilization forces on the joint space width and its correlation with the joint strain. Musculoskelet Sci Pract. 2020;50:102225. doi:10.1016/j.msksp.2020.102225
6. Beselga C, Neto F, Alburquerque-Sendín F, Hall T, Oliveira-Campelo N. Immediate effects of hip mobilization with movement in patients with hip osteoarthritis: A randomised controlled trial. Man Ther. 2016 Apr;22:80-5. doi: 10.1016/j.math.2015.10.007. Epub 2015 Oct 31. PMID: 26559319.
7. Albertin, E. S., Miley, E. N., May, J., Baker, R. T., & Reordan, D. (2019). The Effects of Hip Mobilizations on Patient Outcomes: A Critically Appraised Topic, Journal of Sport Rehabilitation, 28(4), 390-394. Retrieved Jun 19, 2022, from https://journals.humankinetics.com/view/journals/jsr/28/4/article-p390.xml
8. Bialosky JE, Beneciuk JM, Bishop MD, et al. Unraveling the Mechanisms of Manual Therapy: Modeling an Approach. J Orthop Sports Phys Ther. 2018;48(1):8-18. doi:10.2519/jospt.2018.7476
9. Wood L, Ogilvie R, Hayden JA. Specifying the treatment targets of exercise interventions: do we?. Br J Sports Med. 2020;54(20):1235-1236. doi:10.1136/bjsports-2020-101981
10. Steiger F, Wirth B, de Bruin ED, Mannion AF. Is a positive clinical outcome after exercise therapy for chronic non-specific low back pain contingent upon a corresponding improvement in the targeted aspect(s) of performance? A systematic review. Eur Spine J. 2012;21(4):575-598. doi:10.1007/s00586-011-2045-6
11. Wood L, Bishop A, Lewis M, et al. Treatment targets of exercise for persistent non-specific low back pain: a consensus study. Physiotherapy. 2021;112:78-86. doi:10.1016/j.physio.2021.03.005