Soft robotics-inspired sensing system for detecting downward movement and pistoning in prosthetic sockets: A proof-of-concept study.

BACKGROUND: Vertical displacement of the residual limb within transtibial prosthetic socket, often known as "pistoning" or downward movement, may lead to skin breakdowns and ulcers. Downward movement is particularly difficult to self-manage for diabetic individuals living with amputation because of diminished sensation in the residual limb from peripheral neuropathy. Therefore, a customizable sensor at the distal end that can alert the users when high-risk downward movement and pistoning occurs is urgently needed. OBJECTIVES: Presented herein for the first time is a lightweight, inexpensive sensing system inspired by soft robotics that can detect the occurrence and severity of downward movement at the distal end. METHODS: The sensing system consists of a multilayered torus-shaped balloon, allowing easy integration with pin-lock socket systems. The design allows sensing of vertical displacement without imparting high reaction forces back onto the distal end. A benchtop compression tester was used to characterize system performance. Systematic and parametric benchtop tests were conducted to examine the sensor's physical characteristics. Long-term (24-h) stability of the sensor was also recorded. RESULTS: Compared with water, air was determined to be a better medium with a higher linear full-scale span (FSS) because of its compressible nature. Repeatable 0.5-mm vertical displacements yielded a linear (>0.99 R2) FSS of 4.5 mm and a sensitivity of 0.8 kPa/mm. The sensing system is highly precise, with as low as 1% FSS total error band and average hysteresis of 2.84% of FSS. Over 24 h, a 4% FSS drift was observed. CONCLUSION: Sensing system characteristics, coupled with low-cost, customizable fabrication, indicates promising performance for daily use to notify and alert transtibial prosthetic users of downward movement and/or pistoning.

Air microfluidics-enabled soft robotic transtibial prosthesis socket liner toward dynamic management of residual limb contact pressure and volume fluctuation.

Residual limb volume fluctuation and the resulting contact pressures are some of the key factors leading to skin ulcerations, suboptimal prosthetic functioning, pain, and diminishing quality of life of transtibial amputees. Self-management of socket fit is complicated by peripheral neuropathy, reducing the perception of pressure and pain in the residual limb. We introduce a novel proof-of-concept for a transtibial prosthetic socket liner with the potential to dynamically adjust the fit between the limb and socket. The core of the technology is a small air microfluidic chip (10 cm3 and 10 g) with 10 on-chip valves that enable sequential pressurizing of 10 actuators in custom sizes to match the pressures required by the residual limb's unique anatomy. The microfluidic chip largely reduced the number of electromechanical solenoid valves needed for sequential control of 10 actuators (2 instead of 10 valves), resulting in the reduction of the required power, size, mass, and cost of the control box toward an affordable and wearable prosthetic socket. Proof-of-concept testing demonstrated that the applied pressures can be varied in the desired sequence and to redistribute pressure. Future work will focus on integrating the system with biofidelic prosthetic sockets and residual limb models to investigate the ability to redistribute pressure away from pressure-sensitive regions (e.g., fibular head) to pressure tolerant areas. Overall, the dynamic prosthesis socket liner is very encouraging for creating a dynamic socket fit system that can be seamlessly integrated with existing socket fabrication methods for managing residual limb volume fluctuations and contact pressure.

Outcomes of intra-articular calcaneal fractures: surgical treatment of 114 consecutive cases at a maximum care trauma center.

BACKGROUND: The aim of this retrospective monocentric study was to investigate the outcomes of surgically treated intra-articular calcaneus fractures in a maximum care trauma center. METHODS: One hundred forty patients who had undergone surgery for intra-articular calcaneal fractures between 2002 and 2013 were included. One hundred fourteen cases with 129 fractures were eligible to participate in the study of which 80 were available for a clinical and radiological follow-up. 34 patients were followed up by telephone interview only. Outcome measures included the American Orthopaedic Foot and Ankle Society (AOFAS) hindfoot score, Short Form 36 Health Status Survey (SF-36), complications, and subsequent surgeries. RESULTS: Mean follow-up was 91 months (range 12-183). The overall complication rate was 29% (37/129 ft). Disturbed wound healing (11%) and infection (5%) occurred most commonly. Non-union (4%) only occurred in smokers (p = 0.02). A high rate of posttraumatic subtalar arthritis (77%) and need for subsequent subtalar fusion (18%) without independent risk factors for subsequent subtalar fusion was found. The revision rate was high (60%) after primary fusion. Mean AOFAS-hindfoot score was 74 (Sanders I: 99, Sanders II: 74, Sanders III: 77, Sanders IV: 70). The postoperative Boehler angle improved significantly in all subgroups (p < 0.01). Patients with a decreased Boehler angle between postoperative images and the follow-up had significantly lower AOFAS hindfoot scores (p < 0.01). CONCLUSIONS: Our data can aid decision-making in the treatment of calcaneal fractures. We advocate to use primary subtalar fusion with caution due to the high revision rate. Smoking status should always be considered. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

Clinical and Radiologic Outcomes of Metatarsophalangeal Hemiarthroplasty: A Review of 12 Consecutive Cases.

This study examined function, pain, satisfaction, and radiologic outcomes among patients treated with first metatarsophalangeal hemiarthroplasty. Patients were invited to participate in an outcome study conducted with questionnaires on subjective and objective outcomes and clinical and radiographic follow-up. A total of 12 patients (12 feet; mean patient age, 58.8±12.3 years) agreed to participate. Mean follow-up was 22.3±19.8 months. Of these patients, 7 were satisfied with the postoperative result. The mean visual analog scale pain score decreased significantly from 7.0±2.3 preoperatively to 3.5±3.3 postoperatively (P=.024). Mean passive range of motion of the first metatarsophalangeal joint was 32°±10° preoperatively, 93°±18° intraoperatively after implantation of the prosthesis and closure of the joint capsule, and 38°±19° at final follow-up (P=.26). Mean American Orthopaedic Foot and Ankle Society forefoot score increased significantly from 47.3±14.7 preoperatively to 71.8±15.2 at last follow-up (P=.033). During the follow-up period, 6 patients underwent additional procedures: 5 therapeutic joint infiltrations and 1 arthrodesis. No patients had radiologic loosening of the implant at final follow-up. Osseous dysplastic changes at the base of the proximal phalanx were noted among 6 of 11 patients (12 total cases) at final follow-up. Although first metatarsophalangeal hemiarthroplasty provided significant pain reduction at mean follow-up of 22.3 months, range of motion of the first metatarsophalangeal joint was not restored to anticipated levels and there were high rates of patient dissatisfaction and secondary interventions. [Orthopedics. 2018; 41(1):e64-e69.].

Sensitivity of knee soft-tissues to surgical technique in total knee arthroplasty.

Restricted range of motion and excessive laxity are both potential complications of total knee arthroplasty (TKA). During TKA surgery, the surgeon is frequently faced with the question of how tightly to implant the prosthesis. The most common method of altering implantation tightness is to vary the thickness of the polyethylene inlay after the bone cuts have been made and the trial components inserted. We have sought to quantify how altering the polyethylene thickness may affect post-operative soft tissue tension for a range of prosthetic designs. Four different prosthetic designs were implanted into fresh-frozen cadaveric knee joints. All four designs were implanted in the standard manner, with a 100 Newton distraction force used to set soft tissue balance. The tibiofemoral force was then recorded at 15° intervals throughout the passive flexion range. After the standard implantation of each prosthesis, the tibial component was raised or lowered to mimic increasing and decreasing the polyethylene thickness by 2mm and the force measurements repeated. Tibiofemoral force in extension correlated with implantation tightness for all prosthesis designs. Between 15° and 90° of knee flexion, all four designs were insensitive to changes in implantation tightness. Beyond 90° the effect was more notable in rotating platform mobile-bearing and cruciate-retaining prostheses than in posterior-stabilised mobile-bearing designs. The findings of this research may be useful in assisting surgical decision-making during the implantation of TKA prostheses.

Assessment of isometricity before and after total knee arthroplasty: a cadaver study.

Total knee arthroplasty (TKA) relies on soft tissue to regulate joint stability after surgery. In practice, the exact balance of the gaps can be difficult to measure, and various methods including intra-operative spreaders or distraction devices have been proposed. While individual ligament strain patterns have been measured, no data exist on the isometricity of the soft tissue envelope as a whole. In this study, a novel device was developed and validated to compare isometricity in the entire soft tissue envelope for both the intact and TKA knee. A spring-loaded rod was inserted in six cadaver knee joints between the tibial shaft and the tibial plateau or tibial tray after removing a 7 mm slice of bone. The displacement of the rod during passive flexion represented variation in tissue tension around the joint. The rod position in the intact knee remained within 1 mm of its initial position between 15 degrees and 135 degrees of flexion, and within 2 mm (+/-1.2 mm) throughout the entire range of motion (0-150 degrees). After insertion of a mobile-bearing TKA, the rod was displaced a mean of 6 mm at 150 degrees (p<0.001). The results were validated using a force transducer implanted in the tibial baseplate of the TKA, which showed increased tibiofemoral force in the parts of the flexion range where the rod was most displaced. The force measurements were highly correlated with the displacement pattern of the spring-loaded rod (r=-0.338; p=0.006). A simple device has been validated to measure isometricity in the soft tissue envelope around the knee joint. Isometricity measurements may be used in the future to improve implantation techniques during TKA surgery.

Tibiofemoral force following total knee arthroplasty: comparison of four prosthesis designs in vitro.

Despite ongoing evolution in total knee arthroplasty (TKA) prosthesis design, restricted flexion continues to be common postoperatively. Compressive tibiofemoral force during flexion is generated through the interaction between soft tissues and prosthesis geometry. In this study, we compared the compressive tibiofemoral force in vitro of four commonly used prostheses: fixed-bearing PCL (posterior cruciate ligament)-retaining (PFC), mobile-bearing posterior-stabilized (PS), posterior-stabilized with a High Flex femoral component (HF), and mobile-bearing PCL-sacrificing (LCS). Fourteen fresh-frozen cadaver knee joints were tested in a passive motion rig, and tibiofemoral force measured using a modified tibial baseplate instrumented with six load cells. The implants without posterior stabilization displayed an exponential increase in force after 90 degrees of flexion, while PS implants maintained low force throughout the range of motion. The fixed-bearing PFC prosthesis displayed the highest peak force (214 +/- 68 N at 150 degrees flexion). Sacrifice of the PCL decreased the peak force to a level comparable with the LCS implant. The use of a PCL-substituting post and cam system reduced the peak force up to 78%, irrespective of whether it was a high-flex or a standard PS knee. However, other factors such as preoperative range of motion, knee joint kinematics, soft tissue impingement, and implantation technique play a role in postoperative knee function. The present study suggests that a posterior-stabilized TKA design might be advantageous in reducing soft tissue tension in deep flexion. Further research is necessary to fully understand all factors affecting knee flexion after TKA.