October 2011

Rotational mechanics: Bracing’s next frontier

Photo courtesy of Richie Brace

This two-part series explores the role of rotational forces in athletic injuries and the extent to which bracing can help control those forces and, in turn, prevent those injuries. This first installment ex­amines ankle sprains, PTTD, patello­femoral pain, and osteoarthritis.

By Cary Groner

Rotational forces play a role in all sorts of athletic injuries, from foot and ankle sprains right up the kinetic chain, but only recently have researchers begun to unlock their complex biomechanical secrets. Trainers and other clinicians, for that matter, are still deciphering how bracing strategies may contain or modify those forces to prevent injuries or help them heal once they’ve occurred.

Angst in the ankles

Consider the humble and ubiquitous ankle sprain. Subtalar joint inversion leads to simultaneous internal rotation of the talus and external rotation of the tibio-fibular mortise, which ruptures the anterior talo-fibular ligament (ATFL). In severe enough cases, the calcaneo-fibular ligament (CFL), the posterior tibiotalar ligament (PTTL), and articular cartilage may also be damaged.1 As it happens, while hiking last winter the author of this article incurred such a sprain (grade 3, in official jargon), and got a fresh perspective on rotational forces while crawling miles back to the trailhead through mud and cow dung. (One lesson: crawling is a lot easier when you’re a kid. Another: if you’re going to injure yourself so badly that you can’t walk, it’s best to do it early in the day, because around nightfall the coyotes begin to take an interest.)

A recent article in the Journal of Biomechanics sheds light on the forces that lead to this ligamental mayhem. A subject in a motion analysis lab, an elite 22-year-old female athlete performing cutting maneuvers, accidentally sprained her ankle and the whole process was recorded.2 The researchers reported that the ankle showed a sudden increase in inversion and internal rotation that peaked between 130 ms and 180 ms after initial contact; the internal rotation moment reached a peak of 64 Nm at 167 ms.

Could this have been avoided? As noted, scientists and clinicians continue to debate the extent to which bracing and taping are effective against torque. A 2004 paper, for example, reported that stabilization against inversion was the major function of ankle braces.3 The authors noted that ankle sprains occur in combinations of inversion, plantar flexion, and internal rotation; as a result, they wrote, “restriction of plantar flexion and internal rotation may also be an important function of the ankle brace.” A study from Drexel University compared four common ankle brace designs and found that only stirrup braces provided significant support in external rotation.4

“I would argue that any pathology of the foot and ankle has some relationship to inadequate dynamic control of transverse plane rotary displacement,” said Gary Wilkerson, EdD, ATC, a professor in the Graduate Athletic Training Education program at the University of Tennessee, Chattanooga.

A related issue is that if ankle braces affect proprioception, as some research suggests,5 this effect would not be evident in cadaver studies. And although a connection between proprioception and rotation seems intuitive, the extent to which enhanced proprioception might influence rotational forces in a preventive fashion has not been documented.

One variable that could factor into the discussion is whether braces have different effects—rotational or otherwise—in athletes with a history of sprains and in those without. A 2004 review and analysis in the Journal of Athletic Training suggested that the greatest benefits of prophylactic bracing or taping were associated with athletes who had a history of sprains.6 However, two more recent studies arrived at a different conclusion.7,8 Researchers from the University of Wisconsin-Madison found that prophylactic use of lace-up ankle braces significantly reduced risk of ankle sprain in high school basketball players7 and football players,8 regardless of players’ history of previous ankle sprain (see “Lace-up ankle braces reduce risk of sprain in basketball players regardless of history,” and “Tackling ankle sprains”).

Assessing the extent to which bracing affects rotational forces depends on how you define those forces, of course.

“Inversion is rotation at the ankle,” said Patrick McKeon, PhD, ATC, an assistant professor of athletic training at the University of Kentucky. “Both semirigid and lace-up braces have been shown9 to limit the total amount of inversion in controlled environments.”

However, discussions about motion at the foot and ankle are affected by the complexity of the joints and their motion, McKeon added.

“Beyond the frontal plane rotation associated with inversion, there is internal and external rotation of the foot in the transverse plane,” he said. “To further complicate things, the subtalar joint and the talocrural joint have their own unique planes and axes of rotation. I think that’s one reason we haven’t seen really strong evidence associated with bracing and rotation of the ankle; there may be a variety of mechanisms involved, including the sensory motor system, and the brace might be contributing through means other than just mechanical.”

PTTD

Rotational forces may also play a role in another common lower-leg problem, posterior tibial tendon dysfunction (PTTD), according to Christopher Neville, PT, PhD, an assistant professor of physical therapy education at SUNY Upstate Medical University in Syracuse.

“Tibial internal rotation is associated with hindfoot eversion, lowering of the medial longitudinal arch, and forefoot abduction,” Neville said. “All of these are likely components of Stage 2 flatfoot deformity and can lead to tibialis tendon problems. So when we think about in-shoe orthoses or bracing we have to consider how well we are taking into account these rotational components—the tibia influencing the continued motion into the foot.”

Research not specific to PTTD suggests that foot orthoses can help control tibial rotation. One study reported that both rigid plastic and accommodative orthoses significantly reduced tibial internal rotation.10 Another found that custom orthoses had the same effect.11

Orthoses may be helpful for managing PTTD regardless of the extent that they control rotation, of course. A couple of long-term studies have reported that both foot orthoses and ankle foot orthoses (AFOs) provided effective nonoperative treatment for PTTD patients, even though they didn’t specifically look at rotation.12,13

“The tissues that hold up the arch fail first, and then we overload the posterior tibial tendon, which may eventually rupture,” said Michael Pinzur, MD, a professor of orthopedic surgery and rehabilitation at Loyola University Medical Center in Maywood, IL. “So probably the foot orthosis slows and dampens that progression, and alters the loading in terminal stance.”

A 2009 study from the University of Southern California in Los Angeles found that a combination of custom foot orthoses and eccentric transverse-plane exercises was more effective than either intervention alone for improving pain and function in 36 patients with early-stage PTTD.14 This is consistent with research from Neville’s group suggesting that muscle weakness does not fully account for PTTD deformities.15

Based partly on experience and partly on the literature,16 Neville now believes that AFOs are probably more effective at controlling tibial rotational forces than in-shoe orthoses, both in general and in PTTD patients. To that end, in a case study of AFOs published in 2009, he reported that a custom model successfully addressed the patient’s flatfoot kinematics during gait, which is an important first step in treating PTTD;17 a larger study is now undergoing peer review.

Popular mechanics

To grasp why the field is so challenging, it helps to understand that axial rotation is intrinsic to human locomotion, is present all the way up the chain from the foot to the head, and is natural but complicated.

“In the gait cycle, the first thing that happens is that the foot lands in a supinated position on the outer portion of the heel,” Wilkerson explained. “When you’re in a supinated position, the tibia is externally rotated. Very rapidly the foot goes into a pronated position as the body’s center of gravity passes over the rearfoot. The arch begins to flatten to dissipate ground reaction forces, and as that happens the tibia rotates internally.”

That pulls the femur into internal rotation as well, but the femur may rotate even more than the tibia, which means that as the tibia is internally rotated relative to the ankle, it can simultaneously be externally rotated relative to the femur.

“People get confused as to which direction the tibia is rotating,” Wilkerson acknowledged. “It depends on the point in the gait cycle and which segment you’re relating the rotation to.”

As the foot pushes through the cycle and the heel rises, the foot bones interlock in a supinated position that creates the lever needed for push-off, and the tibia rotates externally again. These rotations cause subtle compensations in the femur, the pelvis, the lower back, the torso, the neck, and the head. The entire body rotates in complex ways during gait, in other words, but rotation that is too powerful, or poorly synched, can lead to problems. Understanding that motion is essential to preventing or healing injuries.

For example, foot pronation leading to tibial internal rotation may cause a valgus knee alignment, which increases stress on the ACL and MCL; tibial rotation and the associated rotation of the femur also contribute to knee osteoarthritis (OA) and patellofemoral pain syndrome (PFPS), Wilkerson said.

“Tibial rotation and oppositely-directed rotation of the femur are clearly major factors  in both OA and patellofemoral pain syn­drome,” he said.

Photo courtesy of American Orthopedics Manufacturing Corporation.

Wilkerson believes, like Neville, that control of tibial rotation requires components that contact both the foot and the leg, and to this end he’s developed a “subtalar sling” ankle taping procedure that he says effectively prevents ankle sprains.18

“With fixation on both the foot and leg segments, the spiraling effect of the tape causes the tape’s fibers to generate tension whenever there’s a tendency for rotation to occur,” he said. “Eternal rotation of the leg increases the tension in the system, which lifts the border of the foot, so you’re everting the foot when you externally rotate instead of inverting it.”

Wilkerson is also developing a brace that has this effect.

Not everyone agrees that ankle taping works this way, of course. According to Michael Pinzur, taping and bracing may have less to do with rotation than proprioception, particularly in cases of postinjury instability.

“Some patients have a perception of ankle instability when their ankles are clinically stable,” Pinzur said. “If you test their proprioception, though, it’s often impaired.”

In such cases, he refers patients to physical therapy to improve proprioception, and suggests taping to augment proprioception further.

Patellofemoral pain

Hip biomechanics appear to affect patellofemoral joint kinetics and kinematics, and this has implications for addressing issues that include anterior cruciate ligament injuries and patellofemoral pain (PFP). ACL issues will be addressed in Part 2 of this series.

PFP is the most common overuse injury in physically active people and occurs more than twice as often in women than in men.19 Research suggests that altered patellofemoral joint kinematics in women with PFP result from excessive femoral internal rotation, and that that rotation is a result of weakness in the hip extensors, abductors, and external rotators.20

As such, the problem could be influenced by strengthening, and recent research suggests that this approach could be effective. In a paper presented in September at the 2011 International Research Retreat on Patellofemoral Pain Syndrome in Ghent, Belgium, an international team of researchers reported that an eight-week regimen to strengthen hip abduction and external rotation improved pain and health status in women with PFP, versus a no-exercise control group—benefits that remained at six-month follow-up.21

“We want to control the hip and the femur, and to do that, I would always start with exercises,” said Christopher Powers, PT, PhD, director of the program in biokinesiology, and codirector of the Musculoskeletal Bio­mechanics Research Lab at the University of Southern California.

Other research suggests that this approach has potential, as well. In a study conducted at the University of Kentucky, investigators conducted gait retraining in 10 runners with PFP.22 Participants received real-time kinematic feedback related to hip adduction during stance while running on a treadmill; other variables measured included hip internal rotation, contralateral pelvic drop, and pain. The gait retraining resulted in a significant reduction in hip adduction and pelvic drop; and although the decrease in hip internal rotation didn’t reach statistical significance, it was 23% nevertheless. Moreover, the runners demonstrated significant improvements in pain and function.

The kinds of motion associated with PFP also appear to be amenable to bracing and taping strategies.23,24 One recent study, for example, found that taping, knee-sleeve bracing, and an elastic bandage all improved subjects’ control and function in step descent, suggesting a proprioceptive effect, but that the brace appeared to have a mechanical effect as well.25 U.K. researchers used a 10-camera video motion system to model the leg in six degrees of range of motion, according to lead author James Selfe, PhD, FCSP, a professor of physiotherapy at the University of Central Lancashire.

Transverse plane range of motion (ROM) was significantly decreased with bracing compared to a control condition, and a similar decrease with bracing compared to taping approached significance. All three interventions were associated with significantly less coronal plane ROM than the control condition.

“The system allowed us to incorporate measurements of rotational and translational control,” Selfe explained. “We can measure the changes in range of motion, but we can’t necessarily explain why it’s happened. We think something is going on in terms of proprioception, and that the brace may introduce subtle alterations in pressure as well.”

A product called the SERF strap (Stability through External Rotation of the Femur), developed by Powers, has also gained attention for its potential to address patellofemoral and anterior knee pain. The strap is tensioned to pull the thigh into external rotation, thus limiting the extent to which the knee can collapse medially.

Photo courtesy of Townsend Design.

In a presentation at the 2009 International Patellofemoral Pain Syndrome Research Retreat in Baltimore, Powers and his colleagues reported that in five people tested (mean age, 32 years; four female), patients with PFP reported an average drop in pain of 50% while wearing the strap, which was also associated with significantly reduced hip internal rotation during step down, running, and drop jump tasks.26 At the 2011 retreat held in Belgium, a U.K. researcher reported that the SERF strap significantly reduced patients’ pain during single-leg squat and step landing, but that the apparent change in valgus associated with brace wear was more likely a result of measurement error than brace effect.27

“The brace is designed to control hip rotation, not necessarily knee valgus, even though they go together sometimes,” Powers commented. “In any case, this isn’t something you’d wear forever. I’d recommend it to calm down an acutely painful knee, or if an athlete had to compete at a high level and couldn’t take three weeks off to do exercises.”

In other cases, as noted above, Powers favors an exercise program to strengthen hip abduction and external rotation.

Osteoarthritis

In knee OA, the traditional view of bracing has been that it relieves pain by unloading the affected compartment. However, a 1999 Journal of Bone and Joint Surgery paper by Kirkley et al called this model into question by reporting that a neoprene sleeve was nearly as effective as an unloader brace for relieving pain.28

More recently, research has begun to focus on the role played by rotational forces in OA. For example, in 2005, Japanese researchers used a CT scanner to compare the knees of 114 patients with varus knee OA to a control group (n=20), and reported that those with more severe OA had larger rotational deformities.29 That same year, Swedish investigators reported that 14 patients with medial knee OA had decreased tibial internal rotation between 50° and 20° of flexion than did 10 asymptomatic individuals.30 Then, in 2006, researchers at Stanford reported abnormal varus/valgus rotations, observed between 10° and 90° of knee flexion, in 17 patients with knee OA compared to cadaveric controls.31

Given the evidence that braces relieve symptoms, it seems reasonable to conclude that they may affect these rotational forces to some extent, either biomechanically or proprioceptively. Researchers are only just beginning to explore that line of investigation, however.

“Using a brace that is basically cylindrical presents mechanical challenges if you want to control rotational forces,” said Tim Hewett, PhD, professor and director of research at the Ohio State University Sports, Health, and Performance Institute, and director of the Sports Medicine Biodynamics Center at Cincinnati Children’s Hospital. “In our research, we’ve found that unloader braces—especially the dual-strap, three-pressure point design—do appear to take load off the medial compartment of the knee joint. But the data regarding external or internal rotation is equivocal at best. You have relatively small excursions and you’re dealing with a high background of error in the transverse plane.”

A paper presented this year by researchers at New York’s Hospital for Special Surgery appeared to support the notion of brace-based rotational control.32 In seven patients with varus knee OA, a year of valgus bracing significantly reduced pain going up and down stairs, and nonsignificantly reduced walking pain, leading to an overall quality-of-life improvement of 43%.

“It is possible that the brace limits knee extension and alters rotations during gait, which may reduce joint pain by decreasing contact between the degenerated foci in the knee joint,” the authors concluded.

In that initial study, pain scores correlated primarily with peak external rotation moment. However, a continuation of the research in 15 patients led the authors to a slightly different conclusion—that medial joint space and peak adduction angle were the primary factors that predicted pain.33

“This suggests that therapy should target those variables,” said one of the study’s authors, Yatin Kirane, PhD, DOrth, a postdoctoral fellow in the Leon Root Motion Analysis Laboratory at HSS. “Ideally we want to increase the medial joint space and limit the peak knee adduction angle.”

Just how braces alter rotational forces remains a subject of study, in any case.

“The effect of bracing is not conclusively established, to be honest,” Kirane acknowledged.

Some brace designs, he noted, move in a slightly oblique manner to allow a more natural rotation to occur.

“It seems that bracing may reduce muscle co-contractions of the quadriceps and the hamstrings,” said Richard Willy, PT, PhD, an assistant professor of physical therapy at Ohio University, and there is evidence to support this contention.34

Future research will likely clarify the mechanism, but at least investigators now have a better idea of what to explore.

Cary Groner is a freelance writer in the San Francisco Bay Area.

References

1. Wilkerson G. Inversion ankle sprains: Seeking optimal support. LER 2011;3(2):43-49.

2. Kristianslund E, Bahr R, Krosshaug T. Kinematics and kinetics of an accidental lateral ankle sprain. J Biomech 2011;44(1):2576-2578.

3. Omori G, Kawakami K, Sakamoto M, et al. The effect of an ankle brace on the three-dimensional kinematics and tibiotalar contact condition for lateral ankle sprains. Knee Surg Sports Traumatol Arthrosc 2004;12(5):457-462.

4. Siegler S, Liu W, Sennett B, et al. The three-dimensional passive support characteristics of ankle braces. J Orthop Sports Phys Ther 1997;26(6):299-309.

5. Ozer D, Senbursa G, Baltaci G, Hayran M. The effect on neuromuscular stability, performance, multi-joint coordination and proprioception of barefoot, taping or preventative bracing. Foot (Edinb) 2009;19(4):205-210.

6. Olmsted LC, Vela LI, Denegar CR, Hertel J. Prophylactic ankle taping and bracing: a numbers needed to treat and cost-benefit analysis. J Athl Train 2004;39(1):95-100.

7. McGuine TA, Brooks A, Hetzel S. The effect of lace-up ankle braces on injury rates in high school basketball players. Am J Sports Med 2011;39(9):1840-1848.

8. McGuine TA, Hetzel S, Wilson J, Brooks A. The effect of lace-up ankle braces on injury rates in high school football players. Am J Sports Med 2011 Sep 16 (epub ahead of print).

9. Cordova ML, Ingersoll CD, LeBlanc MJ. Influence of ankle support on joint range of motion before and after exercise: a meta-analysis. J Orthop Sports Phys Ther 2000;30(4):170-177.

10. McPoil TG, Cornwall MW. The effect of foot orthoses on transverse tibial rotation during walking. J Am Podiatr Med Assoc 2000;90(1):2-11.

11. Jenkins WL, Williams DS, Durland A, et al. Foot orthotic devices decrease transverse plane motion during landing from a forward vertical jump in healthy females. J Appl Biomech 2009;25(4):387-395.

12. Alvarez RG, Marini A, Schmitt C, Saltzman CL. Stage I and II posterior tibial tendon dysfunction treated by a structured nonoperative management protocol: an orthoses and exercise program. Foot Ankle Int 2006;27(1):2-8.

13. Lin JL, Balbas J, Richardson EG. results of nonsurgical treatment of stage II posterior tibial tendon dysfunction: a 7- to 10-year followup. Foot Ankle Int 2008;29(8):781-786.

14. Kulig K, Lederhaus ES, Reischl S, et al. Effect of eccentric exercise program for early tibialis posterior tendinopathy. Foot Ankle Int 30(9):877-885.

15. Neville C, Flemister AS, Houck JR. Deep posterior compartment strength and foot kinematics in subjects with stage 2 posterior tibial tendon dysfunction. Foot Ankle Int 2010;31(4):320-328.

16. Bellchamber TL, van den Bogert AJ. Contributions of proximal and distal moments to axial tibial rotation during walking and running. J Biomech 2000;33(11):1397-1403.

17. Neville CG, Houck JR. Choosing among three ankle foot orthoses for a patient with stage II posterior tibial tendon dysfunction. J Orthop Sports Phys Ther 2009;39(11):816-824.

18. Wilkerson GB. Comparative biomechanical effects of the standard method of ankle taping and a taping method designed to enhance subtalar stability. Am J Sports Med 1991;19(6):588-595.

19. Taunton JE, Ryan MB, Clement DB, et al. A retrospective case-control analysis of 2002 running injuries. Br J Sports Med 2002;36(2):95-101.

20. Souza RB, Powers CM. Differences in kinematics, muscle strength, and muscle activation between subjects with and without patellofemoral pain. J Orthop Sports Phys Ther 2009;39(1):12-19.

21. Lyle M, Khayambashi K, Mohammadkhani Z, et al. effects of isolated hip abductor and external rotator muscle strengthening on pain, health status, and hip strength in females with patellofemoral pain. Presented at 2nd International Research Retreat on Patellofemoral Pain Syndrome, Ghent, Belgium, September 2011.

22. Noehren B, Scholz J, Davis I. The effect of real-time gait retraining on hip kinematics, pain and function in subjects with patellofemoral pain syndrome. Br J Sports Med 2011;45(9):691-696.

23. Selfe J, Thewlis D, Hill S, et al. A clinical study of the biomechanics of step descent using different treatment modalities for patellofemoral pain. Gait Posture 2011;34(1):92-96.

24. Van Linschoten R, van Middelkoop M, Heintjes EM, et al. Exercise therapy for patellofemoral pain syndrome: a systematic review. Presented at 2nd International Research Retreat on Patellofemoral Pain Syndrome, Ghent, Belgium, September 2011.

25. Selfe J, Chohan A, Hill S, Richards J. A clinical study of the biomechanics of step descent using three treatment modalities for patellofemoral pain. Presented at 2nd International Research Retreat on Patellofemoral Pain Syndrome, Ghent, Belgium, September 2011.

26. Powers C. The influence of femoral strapping on pain response, hip rotation and gluteus maximus activation in persons with patellofemoral pain. Presented at First International Patellofemoral Pain Syndrome Research Retreat, Baltimore, MD, April 2009.

27. Herrington L. The effect of a SERF strap on pain and knee valgus angle during unilateral squat and step landing in patellofemoral patients. Presented at 2nd International Research Retreat on Patellofemoral Pain Syndrome, Ghent, Belgium, September 2011.

28. Kirkley A, Webster-Bogaert S, Litchfield R, et al. The effect of bracing on varus gonarthrosis. J Bone Joint Surg Am 1999;81(4):539-548.

29. Matsui Y, Kadoya Y, Uehara K, et al. Rotational deformity in varus osteoarthritis of the knee: analysis with computed tomography. Clin Orthop Relat Res 2005;(433):147-151.

30. Saari T, Carlsson L, Karlsson J, Karrholm J. Knee kinematics in medial arthrosis. Dynamic radiostereometry during active extension and weight bearing. J Biomech 2005;38(2):285-292.

31. Siston RA, Giori NJ, Goodman SB, Delp SL. Intraoperative passive kinematics of osteoarthritic knees before and after total knee arthroplasty. J Orthop Res 2006;24(8):1607-1614.

32. Kirane Y, Zifchock RA, Hillstrom H. Correlation of kinematic, kinetic and radiographic variables with medial knee osteoarthritis pain following one year of valgus bracing. Presented at the annual meeting of the Orthopaedic Research Society, Long Beach, CA, January 2011.

33. Zifchock RA, Kirane Y, Hillstrom H, et al. Are joint structure and function related to medial knee OA pain? Clin Orthop Relat Res 2011;(469):286-273.

34. Ramsey DK, Briem K, Axe MJ, Snyder-Mackler L. A mechanical theory for the effectiveness of bracing for medial compartment osteoarthritis of the knee. J Bone Joint Surg Am 2007;89(11):2398-2407.

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