Joint stiffness or contractures result from structural changes in muscles, tendons, ligaments, and skin, and are often caused by immobilization after trauma, surgery, or disease. In pathological conditions in which joint immobilization is necessary to manage the problem, the connective tissue, which is composed of a network of collagenous and reticular fibers, elastic fibers, fibrin, and ground substance, shortens and thickens, causing reduced range of motion (ROM). Additionally, in the presence of trauma, edema, or impaired circulation, new collagen fibers form in as little as 3 days, which further restricts motion. The length of the fibers can either increase or decrease, depending, respectively, on the presence or absence of an opposing force. This remodeling, or reorganization, of the connective tissue is well documented through research.
Historically, the following approaches have been employed to increase joint ROM and soft tissue extensibility (not all-inclusive): 1) manual physical therapy involving passive stretching with progressively greater loads of force; 2) continuous passive motion (CPM); 3) the application of casts at regular intervals; and 4) static splinting. Alternatively, various types of mechanical stretching devices have recently been employed to increase joint ROM within selected joints, including the shoulder, neck, back, finger, wrist, elbow, knee, ankle, and toe. Mechanical stretching devices are designed to permanently elongate the connective tissue. Devices are generally categorized according to their mode of action: 1) dynamic splinting systems that are low-load prolonged-duration stretch (LLPS) devices; 2) static progressive stretch devices (SPS); and 3) patient-actuated serial stretch (PASS) devices. These devices are classified by the US Food and Drug Administration (FDA) as Class I medical devices.
CLASSIFICATION OF MECHANICAL STRETCHING DEVICES
DYNAMIC LOW-LOAD PROLONGED STRETCH (LLPS) DEVICES
The goal of dynamic splinting is to stress scarred or shortened connective tissue with an LLPS to promote nontraumatic, more permanent tissue remodeling. Examples of dynamic splinting system products include Dynasplint Systems® (Dynasplint Systems, Inc., Severna Park, MD), Ultraflex™ (UltraflexSystems Inc., Pottstown, PA), LMB Pro-glide™ (LifeTec Inc., Wheeling, Il), and EMPI Advance Dynamic ROM® (Empi, St. Paul, MN). These devices are widely used in the national orthopedic and physical therapy community for selected populations. Dynamic splinting devices, when applied to the following joints, are an effective adjunct to physical therapy received in the clinical setting:
Commonly, when dynamic LLPS devices are used continuously for 6 to 12 hours per day for up to 4 months consecutively, the result is the permanent elongation of connective tissue and an increase in ROM.
The evidence shows the beneficial effects on health outcomes of dynamic LLPS devices, compared with other types of mechanical stretching devices. Neuhaus et al. (2012), in a prospective study, used dynamic splinting during the day and static extension splinting at night after extensor tendon laceration repairs in the fingers and in the thumb (entire thumb). Seventeen individuals with 19 lacerations were included; average time from injury to surgery was 12 days, and follow-up time averaged 96 days. Sixteen individuals achieved good or excellent results by 6 weeks. Fair results were reported in one individual. No complications were reported. Dynamic splinting systems were compared with controlled passive movement in 192 patients after repair of finger flexor tendon injuries. Total active movement was evaluated as excellent in 87% of those in the dynamic splinting group, while finger movement was evaluated as excellent in 75% of the passive movement group. It was concluded that dynamic splinting systems improved the outcome of the upper extremity, including ROM, grip strength, and function state of the hand, in repairs of the flexor tendons (Kitis et al., 2009). Dynamic splinting systems have also been compared with static splinting in a prospective, randomized controlled trial (RCT) in postoperative individuals after extensor tendon repair. The dynamic splinting group improved when compared with the static group in all areas of total active motion, grip strength, and forceful grip strength (Mowlavi et al., 2005).
RCTs, observational studies, case series, and medical community acceptance confirm the benefits of dynamic LLPS devices when used to relieve persistent joint stiffness that can occur after injury or surgery. A retrospective record review was conducted to evaluate the effect of Home Wrist Extension Dynasplint on 133 individuals with distal radius fractures. Improvement in active ROM was demonstrated for all individuals (Berner and Willis, 2010). Improvement was also noted in 86 patients who underwent a surgical procedure for extension deficits of the knee when Dynasplint Systems® (Dynasplint Systems, Inc., Severna Park, MD) was utilized. At follow-up of 4.6 years, the average extension had increased by 17 degrees (Freiling and Lobenhoffer, 2009).
For the dynamic splinting of the toe, a well-designed RCT involving evaluation of the Dynasplint Metatarsophalangeal System® (MDS) (Dynasplint Systems, Inc., Severna Park, MD) for hallux limitus (i.e., loss of motion in the great toe) occurring after either bunionectomy or cheilectomy was reported by John et al. (2011). Fifty individuals with limited ROM of the first metatarsophalangeal (MTP) joint (i.e., great toe) within 2 months after surgery were randomly assigned to treatment or control groups. Duration of the study was 8 weeks. In addition to analgesics, orthotics, and home stretching exercises, the treatment groups also received treatment with Dynasplint Systems® (Dynasplint Systems, Inc., Severna Park, MD). Results found a significant difference in change in active ROM in the treatment group versus the control group. A greater difference occurred in individuals treated less than 2 months following bunionectomy or cheilectomy.
There is little evidence supporting the effectiveness of dynamic LLPS devices for the rehabilitation of joints other than finger, wrist, elbow, knee, and toe such as, but not limited to, shoulder, neck, back, and ankles. Furthermore, there is insufficient evidence in the published peer-reviewed literature to support the use of dynamic LLPS devices for the treatment of conditions such as, but not limited to, chronic joint stiffness or chronic fixed contractures caused by chronic conditions such as rheumatoid arthritis, neuromuscular disease, cerebral palsy, or plantar fasciitis. Sackley and Disler (2009) presented a systematic review of randomized trials for the treatment of foot drop and related contractures resulting from neuromuscular disease. Four studies with a total of 152 participants were included in the review. Among the modalities reviewed (physical, orthotic, and surgical treatments), night splinting of the ankle had no significant effect on muscle force or ROM in a trial involving 26 individuals with Charcot-Marie-Tooth disease. According to the authors, more evidence resulting from well-designed trials is needed to determine the appropriate intervention for foot drop in neuromuscular disease. Rose et al. (2010) examined six children with cerebral palsy who were treated with dynamic splinting combined with neuromuscular electrical stimulation for wrist or elbow contractures. Wrist ROM improved in one participant treated for a wrist contracture. An increase in passive elbow extension was found in two participants; however, no accompanying change in upper limb function was demonstrated. Khan et al. (2019) examined 18 systematic review/meta-analyses to evaluate the effectiveness of nonpharmacological interventions to improve limb spasticity. Although a range of interventions are available to improve spasticity, the authors found only low-quality evidence addressed in the peer-reviewed literature where ROM is improved through occupational, manual therapy with dynamic elbow extension splinting in individuals with stroke or other neurologic conditions. Additional studies are needed to better evaluate these interventions.
STATIC PROGRESSIVE STRETCH DEVICES
Static progressive stretch (SPS) devices apply stress relaxation and low-load stretch using components such as static line, turnbuckles, screws, and gears. These devices are designed to permanently lengthen shortened connective tissue. As the tissues lengthen in response to stress, the individual adjusts the splint to the new length. A typical session lasts 30 minutes and is repeated up to three times daily. Examples of SPS devices include Joint Active Systems® (JAS) splints (Joint Active Systems, Inc., Effington, IL) (JAS Elbow, JAS Shoulder, JAS Ankle, JAS Knee, JAS Wrist, and JAS Pronation-Supination); Static-Pro® (DeRoyal), Stat-A-Dyne® (Ortho-Innovations), AliMed® Turnbuckle Orthosis (AliMed), and Mayo Aircast® (DJO).
Studies involving SPS devices are case reports limited by lack of randomization, lack of controls, and small sample size (typically 8 to 40 individuals). Additionally, many studies report outcomes from the same set of individuals (Ulrich et al., 2010; Bonutti et al., 2010; McGrath et al., 2009). One study compared static progressive elbow splinting with dynamic splinting and found little difference in elbow extension or flexion between the groups (Lindenhovius et al., 2012). This is the only investigation of the elbow treated with an SPS device, and the study was flawed by a high dropout rate and lack of a control group comparing splints with active, self-assisted stretching exercises. Other studies and literature reviews that compared dynamic and static devices after tendon repair of the hand found similar results for both devices (Riggs et al., 2011) or improved outcomes for dynamic over static splinting (Kitis et al., 2012; Sameem et al., 2011). Although Hammond et al. (2012) found favorable outcomes with both devices, more tendon ruptures occurred, and more tenolysis procedures were required in the static group. Because of the lack of well-designed, well-conducted studies, conclusions cannot be reached regarding the effect of SPS devices on health outcomes.
In 2014, Ibrahim et al. conducted a randomized, controlled, double-blind study of SPS device efficacy in treating capsulitis of the shoulder. Sixty patients were randomly assigned into two groups: Group 1 received traditional physical therapy plus use of a static progressive stretch device; Group 2 received traditional physical therapy alone. Both groups received three traditional physical therapy sessions weekly for 4 weeks. In addition, the experimental group used an SPS device for 4 weeks. The device was to be worn for one 30-minute session daily for the first week; two 30-minute sessions per day during weeks 2 and 3; and three 30-minute sessions during week 4. The primary outcome was shoulder ROM, and the secondary outcome was function (measured by the Disabilities of the Arm, Shoulder and Hand [DASH] questionnaire) and pain (measured using a visual analogue scale [VAS]). After 4 weeks there was a significant increase in all ROM scores in the experimental group compared with the control group. The mean increase in active abduction was 76 degrees in group 1 compared with 47 degrees in group 2. Passive abduction increased by 65 degrees in group 1 vs. 37 degrees in group 2. Shoulder external rotation increased by 53 degrees in group 1 vs 30 degrees in group 2. Patients in both groups showed reduced pain at 4 and 12 weeks postintervention. Individuals in both groups showed functional improvement. At 12-month follow-up, significant differences were found between the groups in all outcome measures favoring the experimental group (P<0.001). The authors recognized study limitations. It is unknown whether improvements can be maintained over a longer period of time. Individual activity was not measured or controlled, concluding that additional studies are needed to compare SPS and dynamic splinting for treatment of individuals with adhesive capsulitis of the shoulder.
In 2015, Veltman et al. reported a systematic review of the literature to evaluate evidence for the best nonoperative treatment for posttraumatic elbow stiffness in adults. Eight studies with 232 elbows were included. The SPS device was used in four studies (160 elbows), and dynamic splinting was used in three studies (72 elbows). Only one RCT was included in the Veltman et al. study. Treatment protocols varied greatly between the groups, including length of time the orthoses were used. The authors indicated the need for large prospective randomized studies of SPS versus dynamic splinting focusing on duration of splint use per day, patient satisfaction, and other outcome factors that have not been studied.
Harvey et al. (2017) conducted a systematic review and meta-analysis of RCTs and other controlled trials to determine the effects of stretch on contractures in people with, or at risk of developing, contractures. The outcomes of interest included joint mobility, quality of life, pain, activity limitations, participation restrictions, spasticity, and adverse events. A total of 49 studies with 2,135 participants met the inclusion criteria. Study participants had a variety of neurological and nonneurological conditions. Studies compared stretch to no stretch, often delivered with standard care for the disorder or another cointervention (e.g., exercise or botulinum toxin injection in the case of spasticity). The stretch was administered in a variety of different ways including through passive stretching (self‐administered, therapist‐administered, and device‐administered), positioning, splinting and serial casting, and none of the studies performed stretch for more than 7 months. Of the 49 studies, 17 (787 participants) investigated the effect of splinting on joint mobility. The mean difference of splinting on joint mobility was 0 degrees (95% confidence interval [CI], -1 to 2; I2=28%; P=0.68). The authors concluded that the data do not support the hypothesis that any particular stretch intervention is superior to another, and that the effects of stretch did not differ between large and small joints. Furthermore, the authors concluded that stretch is not effective for the treatment and prevention of contractures and does not have short-term effects on quality of life and pain in people with non-neurological conditions, and the short-term and long-term effects of stretch on other outcomes in people with neurological and non-neurological conditions are not known.
PATIENT- ACTUATED SERIAL STRETCH DEVICES
PASS devices allow resisted active and passive motion within a limited range. PASS devices provide a low-level to high-level load to the joint, using pneumatic or hydraulic systems that can be manually adjusted by the individual. Examples of PASS devices include the End Range of Motion Improvement (ERMI) Knee Extensionater®, ERMI Elbow Extensionater®, ERMI Knee/Ankle Flexionater®, and the ERMI Shoulder Flexionater® (ERMI, Inc., Atlanta, GA). For individuals who have functional limitations in ROM who receive serial stretch devices and physical therapy, the evidence includes serial stretching with ERMI devices used to treat knee ROM. One small RCT and a larger retrospective comparative study have reported that high-intensity stretching with ERMI devices improved ROM more than lower intensity stretching devices in individuals who were postinjury or surgery. Other available data consist of retrospective case series that demonstrated improved ROM in individuals whose range had plateaued with physical therapy. The clinical significance of gains in this surrogate outcome measure is unclear. Aspinall et al. (2021) performed a systematic review to evaluate the effectiveness of medical stretching devices in the treatment of knee arthrofibrosis. The review included 13 studies with 558 participants who were status post knee surgery. In addition to physiotherapy and home exercises, participants were placed on continuous passive motion (CPM) and load control (LC creep) or displacement control [stress relaxation] (DCSR) stretching devices. The primary outcome measure in all studies was improved ROM. Secondary outcome measures included pain, stiffness, and physical function. In both the CPM device and manipulation under anesthesia group, a mean increase in ROM and Western Ontario McMaster Universities (WOMAC) Osteoarthritis Index Score (total scores and sub scores of pain, stiffness, and function) was reported between pretreatment evaluation and weeks 2 and 6 (P< 0.05). No difference was found between groups in total or sub scores. All studies reviewed used the universal goniometer (UG) to measure the primary outcome; however, the authors questioned the reliability and validity of the UG due to multiple evaluators involved in joint measurement. The systematic review indicates that load control and displacement control devices are effective in increasing ROM in the treatment of knee arthrofibrosis. Displacement control devices involving patient actuated serial stretching techniques may be more effective in increasing knee flexion than those utilizing static progressive stretch. CPM results were inconsistent and inconclusive due to sample size and heterogeneity of subjects; further research with RCTs is needed. However, the paucity of research in this field indicates that more RCTs are required to investigate the superiority of the different types of displacement-control stretching devices and which of these would be most effective for use in clinical practice and to compare these with standard physiotherapy treatment. The evidence is insufficient to determine that the technology results in an improvement in the net health outcome.
STRETCH MODALITIES ON THE TREATMENT AND PREVENTION OF CONTRACTURES
Katalinic et al. (2010) reviewed the effect of stretch modalities, including those that are self-administered and therapist administered, splinting, and casting on the treatment and prevention of contractures in 35 studies with 1,391 participants, and concluded that stretch has no clinically important effect on joint mobility in neurological or non-neurological conditions.
PREFABRICATED OR CUSTOM-FABRICATED MECHANICAL STRETCHING DEVICES
A prefabricated device is manufactured in quantity without a specific individual in mind. A prefabricated device may be trimmed, bent, molded (with or without heat), or otherwise modified (e.g., custom-fitted) for use by a specific individual. A device that is assembled from prefabricated components is considered prefabricated.
A custom-fabricated device is made for a specific individual. The process of making a custom-fabricated device starts with basic materials, including, but not limited to: plastic, metal, leather, or cloth in the form of sheets, bars, etc. Custom-fabricated devices entail substantial work, including cutting, bending, molding, and sewing, and may also incorporate some prefabricated components. The construction of a custom-fabricated device involves more effort than merely trimming, bending, or making other modifications to a substantially prefabricated item.
The peer-reviewed literature does not show advantages of custom-fabricated dynamic LLPS devices, except for the following indications:
- Deformity or abnormal limb contour
- Inability of individual to fit into a standard device so that effectiveness or individual compliance is compromised by poor fit
- Intolerance of the standard device secondary to skin breakdown
