Can Peak Plantar Shear Help Predict Diabetic Foot Ulcers?

A recent study in Diabetes Care finds that peak plantar shear is significantly higher in patients with a history of diabetic foot ulcers, and that shear is a risk factor for ulcers.

Researchers quantified peak plantar shear in nine patients with diabetic foot ulcers and 16 patients with diabetic neuropathy without previous ulcers as the patients walked barefoot over the Cleveland Clinic shear plate. While peak pressure was not significantly different between the two groups, the study notes peak plantar shear was significantly higher in patients with diabetic foot ulcers.

Study lead author Metin Yavuz, PhD, believes shear is at least as important as pressure is in ulcer pathomechanics. As he says, shear (particularly anteroposterior) acts back and forth under the foot during the same step, imposing braking and propulsive forces at the same region. He compares this to what happens to a straightened paper clip when it is bent back and forth numerous times, which obviously breaks the material ultimately.

Shear leads to abrasion, according to Dr. Yavuz, who is affiliated with the Department of Physical Therapy at the University of North Texas Health Science Center. He cites the analogy of a running chainsaw, saying it is quite easy to sever a branch when the engine is on as the chain applies repetitive shear. Furthermore, Dr. Yavuz notes plantar shear increases the temperature of the foot, in a similar way to rubbing hands, and elevated temperatures accelerate tissue breakdown.

While plantar shearing forces are an important factor in diabetic foot ulcer risk, Kevin Kirby, DPM, notes the verdict is still out as to whether physicians actually need to measure plantar shear forces clinically in order to design and utilize conservative and surgical treatments to treat diabetic ulcers. As technology improves and it becomes easier and more practical to measure discrete areas of high shear stress on the plantar foot, he asserts that further research will better reveal whether reducing shearing stress on the plantar foot is any more important than simply reducing areas of high plantar pressures on high-risk areas of the plantar foot in neuropathic patients.  

“As for now, I am not convinced that being able to measure discrete areas of plantar shearing forces will increase the therapeutic outcomes of the treatment of patients at risk for diabetic foot ulcers any more than simply measuring plantar pressures both barefoot and in-shoe, which technology easily allows us to do at this time,” says Dr. Kirby, an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif.  

Dr. Yavuz notes that assessing shear stress has always been a challenge not only in foot biomechanics but also in other engineering applications. He says while one can easily quantify plantar shear forces that act underneath the whole foot using force plates, a force plate will not inform physicians about how the shear force is distributed underneath the foot. Accordingly, one cannot quantify shear stresses using a force plate, according to Dr. Yavuz. Dr. Kirby also notes that for the average podiatrist who isn’t working in a research lab environment, there is currently no practical way for them to measure discrete areas of shearing forces on the plantar feet of their neuropathic patients.  

Dr. Yavuz and his team are working on a novel insole system designed to record shear stresses over the entire foot at a higher resolution.

“While concurrent measurement of plantar pressure and shear is quite challenging, we believe ever advancing technology will enable assessment of in-shoe triaxial plantar loading in the near future,” says Dr. Yavuz.

Can A Roll-On Cast Increase The Use Of TCCs?

By Brian McCurdy, Managing Editor

Although many consider the total contact cast (TCC) to be the gold standard of offloading for DFUs, physicians have cited issues with the use of the TCC. However, an abstract to be presented at the Symposium on Advanced Wound Care Spring (SAWC Spring)/Wound Healing Society (WHS) meeting in April notes that a roll-on TCC may be effective and easy to use.

In a three-year retrospective review, researchers examined 485 applications of the roll-on TCC in 71 patients with 133 wounds. More than 47 percent of the wounds were Wagner Grade 3 and 58.6 percent had active infections. Use of the roll-on TCC resulted in 79.7 percent of wounds resolving in 1.9 months on average with an average of 4.9 cast applications.

Any device that is non-removable and extends above the ankle will be successful in improving healing rates in the diabetic foot, according to James McGuire, DPM. As removable cast walkers made non-removable, such as the instant total contact cast, are as successful as the TCC, he postulates the roll-on TCC should work quite well. However, he cites cost concerns with the roll-on TCC, the fact that it is a bit flexible and does not provide a rigid leg cone, which is key to offloading the foot in a TCC.

Dr. McGuire cites good success with wound isolation type devices using cushion inserts under the area of the ulcer or felted foam padding in a non-removable cast walker or a TCC. As long as the cast is non-removable and the leg section of the cast is rigid and fits closely to the leg cone, the cast will be successful, notes Dr. McGuire, a Clinical Associate Professor in the Departments of Podiatric Medicine and Podiatric Biomechanics at the Temple University School of Podiatric Medicine.

Jeffrey Jensen, DPM, was part of the team that invented the roll-on TCC. Dr. Jensen’s goal was to make a total contact cast equivalent in function but easier to use, faster to apply and with a minimal learning curve. He cites his data from a poster presentation that a roll-on TCC had superior efficacy to a regular TCC.

“Those not using TCC likely are not educated in its use or familiar with the consensus documents supporting its use,” says Dr. Jensen, who is affiliated with the Diabetic Foot and Wound Center in Denver.

SAWC Spring/WHS will be held April 5–9 in San Diego. For more info, go to www.sawcspring.com .

Study Compares Bilateral With Unilateral TAR In Patients With Arthritis

By Brian McCurdy, Managing Editor

Bilateral end-stage ankle arthritis is more debilitating than unilateral arthritis but patients who had bilateral total ankle replacement (TAR) received as many benefits as those who had unilateral TAR, according to a study in the Journal of Bone and Joint Surgery.  

The authors compared preoperative, health-related quality of life in 53 patients with bilateral end-stage ankle arthritis and 106 patients with unilateral end-stage ankle arthritis. Preoperatively, authors found that patients with unilateral disease had a higher prevalence of post-traumatic arthritis while patients with bilateral disease had a higher prevalence of primary and secondary arthritis. The study authors found that patients who had either unilateral or staged bilateral TAR demonstrated improved Short Form (SF)-36 scores between the preoperative and postoperative evaluations.

Jeffrey E. McAlister, DPM, FACFAS, treats a mixture of active unilateral post-traumatic ankle arthritis and bilateral, metabolically-challenged patients with conditions such as rheumatoid arthritis. He states both types of patients typically do well with a stabilizing, gauntlet-type brace and periodic corticosteroid injections, but the post-traumatic patient typically will not withstand conservative treatment as long as the patient with bilateral ankle arthritis. Similar to the study findings, his bilateral ankle arthritis patients also have a lower preoperative SF-36 score and Dr. McAlister notes this is most likely due to the patients’ overall comorbidities rather than the isolated ankle pathology.

In his arthroplasty experience, patients with staged bilateral TAR have had similar or superior outcomes to those with unilateral TAR, according to Dr. McAlister, who practices in Phoenix. He emphasizes appropriate patient selection and perioperative expectations, observing that his unilateral post-traumatic TAR patients have higher expectations than those of the bilateral arthritis group.  

Dr. McAlister adds that his patients with bilateral ankle arthritis are usually in neutral alignment at the tibiotalar joint, making it less challenging to align the TAR accurately, and improve outcomes and implant longevity. Patients with post-traumatic arthritis may have retained hardware, periarticular cysts and difficult foot deformities, which ultimately play a role in the complexity of the case in comparison to those with a neutral foot and ankle.  

“We know that ankle arthroplasty works in the right hands,” says Dr. McAlister. “We know that it works in both post-traumatic and rheumatoid arthritis patients alike. This article helps us understand that despite the increased preoperative disability in the bilateral ankle arthritis group, outcomes are similar to a patient with unilateral ankle arthritis. This research aids in the paradigm shift from ankle fusion to ankle arthroplasty in the correct patient.”