Carpal tunnel syndrome impairs index finger responses to unpredictable perturbations.

The fine-tuning of digit forces to object properties can be disrupted by carpal tunnel syndrome (CTS). CTS' effects on hand function have mainly been investigated using predictable manipulation tasks; however, unpredictable perturbations are commonly encountered during manual tasks, presenting situations which may be more challenging to CTS patients given their hand impairments. The purpose of this study was to investigate muscle and force responses of the index finger to unpredictable perturbations in patients with CTS. Nine CTS patients and nine asymptomatic controls were instructed to stop the movement of a sliding plate by increasing index finger force following an unexpected perturbation. The electrical activity of the first dorsal interosseous muscle and forces exerted by the index finger were recorded. CTS patients demonstrated 20.9% greater muscle response latency and 12.0% greater force response latency compared to controls (p<0.05). The duration of plate sliding was significantly different between groups (p<0.05); the CTS group's duration was 142.2±5.8ms compared to the control group's duration of 133.1±8.4ms. Although CTS patients had increased muscle and force response durations comparatively, these differences were not statistically significant. Findings from this study suggest CTS-induced sensorimotor deficits interfere with accurate detection, processing and response to unpredictable perturbations. These deficits could be accounted for at multiple levels of the peripheral and central nervous systems. Delayed and decreased responses may indicate inefficient object manipulation by CTS patients and may help to explain why CTS patients tend to drop objects.

Effects of Carpal Tunnel Syndrome on Force Coordination and Muscle Coherence during Precision Pinch.

Carpal tunnel syndrome (CTS), caused by entrapment of the median nerve in the carpal tunnel, impairs hand function including dexterous manipulation. The purpose of this study was to investigate the effects of CTS on force coordination and muscle coherence during low-intensity sustained precision pinch while the wrist assumed different postures. Twenty subjects (10 CTS patients and 10 asymptomatic controls) participated in this study. An instrumented pinch device was used to measure the thumb and index finger forces while simultaneously collecting surface electromyographic activities of the abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles. Subjects performed a sustained precision pinch at 10% maximum pinch force for 15 sec with the wrist stabilized at 30° extension, neutral, or 30° flexion using customized splints. The force discrepancy and the force coordination angle between the thumb and index finger forces were calculated, as well as the ß-band (15-30 Hz) coherence between APB and FDI. The index finger applied greater force than the thumb (p < 0.05); this force discrepancy was increased with wrist flexion (p < 0.05), but was not affected by CTS (p > 0.05). The directional force coordination was not significantly affected by wrist posture or CTS (p > 0.05). In general, digit force coordination during precision pinch seems to be sensitive to wrist flexion, but is not affected by CTS. The ß-band muscular coherence was increased by wrist flexion for CTS patients (p < 0.05), which could be a compensatory mechanism for the flexion-induced exacerbation of CTS symptoms. This study demonstrates that wrist flexion negatively influences muscle and force coordination in CTS patients supporting the avoidance of flexion posture for symptom exacerbation and functional performance.

Changes in carpal tunnel compliance with incremental flexor retinaculum release.

BACKGROUND: Flexor retinaculum transection is a routine surgical treatment for carpal tunnel syndrome, yet the biomechanical and clinical sequelae of the procedure remain unclear. We investigated the effects of flexor retinaculum release on carpal tunnel structural compliance using cadaveric hands. METHODS: The flexor retinaculum was incrementally and sequentially released with transections of 25, 50, 75, and 100 % of the transverse carpal ligament, followed by the distal aponeurosis and then the antebrachial fascia. Paired outward 10 N forces were applied to the insertion sites of the transverse carpal ligament at the distal (hamate-trapezium) and proximal (pisiform-scaphoid) levels of the carpal tunnel. Carpal tunnel compliance was defined as the change in carpal arch width normalized to the constant 10 N force. RESULTS: With the flexor retinaculum intact, carpal tunnel compliance at the proximal level, 0.696 ± 0.128 mm/N, was 13.6 times greater than that at the distal level, 0.056 ± 0.020 mm/N. Complete release of the transverse carpal ligament was required to achieve a significant gain in compliance at the distal level (p < 0.05). Subsequent release of the distal aponeurosis resulted in an appreciable additional increase in compliance (43.0 %, p = 0.052) at the distal level, but a minimal increase (1.7 %, p = 0.987) at the proximal level. Complete flexor retinaculum release provided a significant gain in compliance relative to transverse carpal ligament release alone at both proximal and distal levels (p < 0.05). CONCLUSIONS: Overall, complete flexor retinaculum release increased proximal compliance by 52 % and distal compliance by 332 %. The increase in carpal tunnel compliance with complete flexor retinaculum release helps explain the benefit of carpal tunnel release surgery for patients with carpal tunnel syndrome.

Dynamic postures of the transverse metacarpal arch during typing.

The purpose of this paper is to describe the transverse metacarpal arch (TMA) during a dynamic typing task. Static/relaxed and dynamic typing TMA were collected from 36 right-handed females with musculoskeletal discomfort using a motion capture system. While the angle of right TMA static/relaxed posture (10.1° ± 5.5°) was significantly larger than the left (8.5° ± 5.6°) (P < .05), the right dynamic posture (10.6° ± 4.3°) was not significantly different from the left (10.3° ± 5.5°) (P = .66). Within both these mean scores, there was considerable individual variation, with some subjects demonstrating very flat TMA, and some very curved. The results indicate that TMA angular postures both for static/relaxed and dynamic typing are highly variable both between individuals and between individual hands.

Fiber orientation of the transverse carpal ligament.

The transverse carpal ligament is the volar roof of the carpal tunnel. Gross observation shows that the ligament appears to have fibers that roughly orient in the transverse direction. A closer anatomical examination shows that the ligament also has oblique fibers. Knowledge of the fiber orientation of the transverse carpal ligament is valuable for further understanding the ligament's role in regulating the structural function of the carpal tunnel. The purpose of this study is to quantify collagen fiber orientation within the transverse carpal ligament using the small angle light scattering technique. Eight transverse carpal ligament samples from cadaver hands were used in this study. Individual 20-µm sections were cut evenly along the thickness of the transverse carpal ligament. Sections of three thickness levels (25%, 50%, and 75% from the volar surface) were collected for each transverse carpal ligament. Fibers were grouped in the following orientation ranges: transverse, longitudinal, oblique in the pisiform-trapezium (PT), and oblique in the scaphoid-hamate (SH) directions. In analyzing the fiber percentages, the orientation types for the different thickness levels of the ligament showed that the transverse fibers were the most prominent (>60.7%) followed by the PT oblique (18.6%), SH oblique (13.0%), and longitudinal (8.6%) fibers.

Biomechanics of the transverse carpal arch under carpal bone loading.

BACKGROUND: Carpal tunnel release and conservative interventions are widely used in clinical therapies of carpal tunnel syndrome. The efficacy of these treatment and interventions mainly lies in the exploitation of the mechanical properties of carpal tunnel. This study investigated the structural mechanics of the transverse carpal arch using cadaveric hands. METHODS: Paired force was applied to the insertion sites of the transverse carpal ligament at both the distal (hamate-trapezium) and proximal (pisiform-scaphoid) levels of the carpal tunnel. The two pairs of forces were simultaneously applied in an inward or outward direction when the transverse carpal ligament was intact and transected. Transverse carpal arch and carpal tunnel compliance in response to the forces were analyzed. Three-way repeated measures ANOVA were used to examine the effect of the transverse carpal ligament status (intact/transected), the level of the carpal tunnel (distal/proximal) and the force application direction (inward/outward) on the biomechanics of the transverse carpal arch. FINDINGS: Transverse carpal ligament plays a stabilizing role in resisting outward deformation of the carpal tunnel. The carpal tunnel at the proximal level is more flexible than the carpal tunnel at the distal level. The carpal tunnel is more compliant under the inward force application than under the outward force application. INTERPRETATION: The understanding of carpal tunnel mechanics potentially helps to improve the existing strategies and to develop alternatives for the treatment of carpal tunnel syndrome.

The influence of mechanical loading on osseointegration: an animal study.

Osseointegration of implant provides a stable support for the prosthesis under functional loads. The timing of loading is a critical parameter that can govern the success of the osseointegration of implant. However, it is not clear whether the early loading can affect the success of osseointegration, or whether the no-loading healing period can be shortened. This paper presents an animal study conducted to investigate how external loads influence the osseointegration at the initial stage of healing. Titanium implants were inserted into the goat tibia laterally, and different axial loadings were applied to the implants in 4 weeks after surgery. After the 2 weeks period of early loading, animals were sacrificed and the tibia bones with the implants were cut off from the bodies. Then mechanical test was employed to find out the differences in the pull-out force, and shear strength at the bone-implant interface between the non-loaded and the loaded implants. The implant-bone interfaces were analyzed by histomorphometric method, SEM (scanning electron micrograph) and EDS (energy density spectrum). The results indicated that the bone-implant interface did not well integrate 4 weeks after surgery, and the fibrous tissue could be found at the interfaces of the specimens without loadings. While the results of loaded specimens with 10 N axial force showed that that parts of the interface were well integrated, indicating that the early mild loading may play a positive role in the process of the osseointegration. The results support that a certain range of external loading would influence the process of osseointegration, and appropriate mechanical loading can be applied to shorten the osseointegration period after surgery.

Biomechanical and histological evaluation of the application of biodegradable poly-L-lactic cushion to the plate internal fixation for bone fracture healing.

BACKGROUND: Internal plate fixation of fracture can provide favorable mechanical environment for fracture fragments. However, osteoporosis under the plate is often found, and refracture may occur after the plate is removed. There are two different opinions about the bone loss beneath the plate: first is the stress shielding effect brought by the rigid fixation, and the second is the insufficient blood supply of the bone caused by the placement of the plate. In this paper, we tried to achieve a favorable condition for the fracture healing by inserting a kind of biodegradable cushion, through which the stress shielding effect and the interruption of the bone blood supply could be relieved at the same time. METHODS: Animal models of internal fixation for tibia diaphyseal fracture with the placement of the poly-l-lactic (PLLA) cushion between the plate and the bone were established; a series of in vitro investigations and finite element (FE) analysis were performed to evaluate the effect of this new internal fixation system. FINDINGS: During both the initial and 50% healing periods, the extent of stress shielding of the fracture zone decreased due to the use of the PLLA cushion. Especially for the 50% healing stage, the insertion of the PLLA cushion on alleviating the stress shielding of the bone tissue between the inner two screws directly under the plate is more apparent than that at the initial healing period. Meanwhile, radiological and histological coloration results demonstrated sooner callus growth and better trabecular rearrangement of the fracture zone in the PLLA group with the degradation of the PLLA cushion during the healing periods. INTERPRETATIONS: This study showed that the use of the PLLA cushion at the initial period did not impair the stability of the whole system, which provides a favorable mechanical environment for the following fracture healing. On the other hand, its superiorities on alleviating stress shielding effect and interruption with the blood supply of the bone tissue beneath the plate contributed to the favorable fracture healing conditions in PLLA group with the degradation of the materials.