Transverse carpal ligament: its effect on flexor tendon excursion, morphologic changes of the carpal canal, and on pinch and grip strengths after open carpal tunnel release

Carpal tunnel mechanics and its relevance to carpal tunnel syndrome

The carpal tunnel is an elaborate biomechanical structure whose pathomechanics plays an essential role in the development of carpal tunnel syndrome. The purpose of this article is to review the movement related biomechanics of the carpal tunnel together with its anatomical and morphological features, and to describe the pathomechanics and pathophysiology associated with carpal tunnel syndrome. Topics of discussion include biomechanics of the median nerve, flexor tendons, subsynovial tissue, transverse carpal ligament, carpal tunnel pressure, and morphological properties, as well as mechanisms for biomechanical improvement and physiological restoration. It is our hope that the biomechanical knowledge of the carpal tunnel will improve the understanding and management of carpal tunnel syndrome.

Externally applied force helps reduce bowstring effect of flexors in patients with carpal tunnel release surgery

BACKGROUND

Patients with severe carpal tunnel syndrome (CTS) undergo carpal tunnel release (CTR) surgery to alleviate pressure in the carpal tunnel. However, the subsequent lack of the transverse carpal ligament (TCL) causes the bowstring phenomenon of the flexor tendons and increases the potential incidence of trigger finger.

OBJECTIVE

This study aimed to investigate the effects of various compressive forces on the flexor tendon and identify the appropriate force needed to mitigate the bowstring effect of those flexors.

DESIGN

Cross-sectional repeated measures comparison.

METHOD

Thirteen CTS patients who underwent CTR surgery were asked to flex the middle finger while applying different external compressive forces, just contact, 4N, and 8N force, over the carpal tunnel. Images of the flexor tendon within the carpal tunnel and at the metacarpal phalangeal (MCP) joint were recorded via ultrasound.

RESULT

Results show that the compression force limited the volar migration of the flexor tendon under maximal voluntary contraction (MVC) conditions. Entrance angles between the flexor tendon and metacarpal bone also decreased as the external compressive force increased.

CONCLUSIONS

Findings of this study may indicate that applying compression force on the carpal tunnel is useful for CTS patients and can inhibit the volar shift of the flexor digitorum superficialis (FDS) tendon after surgery, which may further prevent trigger finger.

Grip Strength Measurement for Outcome Assessment in Common Hand Surgeries

Grip strength has been used to evaluate the upper extremity functional status and clinical outcomes following upper extremity trauma or surgery. Understanding general recovery patterns of grip strengthening can be helpful in assessing the patients’ recovery status and in assisting in preoperative consultations regarding expectations for recovery. We summarize related studies on grip strength measurement and recovery patterns in common hand conditions, including carpal tunnel syndrome, cubital tunnel syndrome, triangular fibrocartilage complex injury, and distal radius fractures.

Release with or without reconstruction of the transverse carpal ligament for severe carpal tunnel syndrome: a randomized clinical trial

The objective of this study is to compare the clinical effectiveness of two surgical techniques in patients with severe unilateral idiopathic carpal tunnel syndrome. A total of 117 patients were randomized in two groups. In the experimental group ( n = 59) reconstruction of the transverse carpal ligament was performed after open retinaculum release (TCL reconstruction group). In the control group ( n = 58) only retinaculum release was performed (TCL release group). The primary outcome measure was grip strength; secondary outcome measures were pain and response to the Boston questionnaire. Significance was analysed using the t-test or Mann-Whitney test. At 6 months, the experimental group showed clinical and statistically significant improvement in grip strength and decrease in symptom severity. Retinaculum release with reconstruction of the transverse carpal ligament results in improvement of grip strength in the medium term when compared with open retinaculotomy in patients with severe unilateral idiopathic carpal tunnel syndrome.

LEVEL OF EVIDENCE

II.

Hypercholesterolemia Is Associated with the Subjective Evaluation of Postoperative Outcomes in Patients with Idiopathic Carpal Tunnel Syndrome Who Undergo Surgery: A Multivariate Analysis

BACKGROUND

Carpal tunnel syndrome is a compression neuropathy of the median nerve at the wrist; its symptoms include neuropathic pain and sensory and motor disturbance distributed by the median nerve. Carpal tunnel syndrome and hypercholesterolemia have similar backgrounds, but the effect of these similarities on postoperative outcomes has not been reported. Using multivariate analysis, the authors analyzed the relationship between prognostic factors, including the presence of hypercholesterolemia, and subjective postoperative outcomes of patients with idiopathic carpal tunnel syndrome.

METHODS

Of 168 hands with carpal tunnel syndrome that were treated surgically, 141 that were followed up and assessed 1 year postoperatively or thereafter were included. The mean postoperative follow-up period was 40.8 months. Surgery was performed through a small palmar skin incision under local anesthesia. The outcomes were postoperative symptoms, including pain and numbness, and overall Kelly assessment.

RESULTS

Preoperative numbness and pain resolved and alleviated in 94 of 141 hands and was diminished in 59 of 64 hands. Univariate analysis showed that postoperative numbness and Kelly assessment were significantly associated with hypercholesterolemia. Multivariate analysis showed that postoperative numbness was significantly associated with smoking and hypercholesterolemia, and Kelly assessment was significantly associated with smoking (adjusted OR, 3.3; 95 percent CI, 1.1 to 10; p = 0.04) and hypercholesterolemia (adjusted OR, 2.9; 95 percent CI, 1.4 to 6.3; p = 0.01).

CONCLUSION

Hypercholesterolemia, usually a systemic condition in sites other than the hand, is associated with the subjective evaluation of postoperative symptoms in patients with idiopathic carpal tunnel syndrome.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, III.

Effect of Wrist Position on Power Grip and Key Pinch Strength Following Carpal Tunnel Decompression

Power grip and thumb key pinch strength were measured pre- and immediately postoperatively in 30 patients with carpal tunnel syndrome while the wrist was in flexion and extension. The carpal tunnel decompression was performed under local infiltration with 1% lignocaine. Grip strength decreased more in wrist flexion than in wrist extension. No difference was found in thumb pinch strength. The authors conclude that some of the immediate postoperative loss of grip strength in wrist flexion can be attributed to prolapse of flexor tendons out of the carpal tunnel in this position.

In vivo tissue interaction between the transverse carpal ligament and finger flexor tendons

The transverse carpal ligament (TCL) is a component of the flexor pulley system of the wrist, keeping the flexor tendons in place by resisting their volar displacement. The purpose of this study was to investigate the in vivo biomechanical interaction between the TCL and flexor tendons in response to tendon tensioning with the wrist at various postures. In eight healthy subjects, the flexor digitorum superficialis and profundus tendons were tensioned by isometrically applying loads (5, 10, and 15N) to the index finger while the wrist posture was at 20° extension, neutral, 20° flexion, and 40° flexion. The TCL and flexor tendons were imaged at the distal carpal tunnel cross section using ultrasound. The volar-dorsal positions of the tendons, TCL arch height, and TCL-tendon distances were calculated. With increasing wrist flexion, the flexor tendons moved volarly, the TCL arch height increased, and the TCL-tendon distances decreased, indicating that the flexor tendons contacted the TCL and pushed it volarly. The TCL-tendon interaction was amplified by the combination of finger loading and wrist flexion. This study provides in vivo evidence of the biomechanical interaction between the TCL and flexor tendons. Repetitive TCL-tendon interactions may implicate the interacting tissues and the median nerve resulting in tissue maladaptation and nerve compression.

Biomechanical role of the transverse carpal ligament in carpal tunnel compliance

The transverse carpal ligament (TCL) is a significant constituent of the wrist structure and forms the volar boundary of the carpal tunnel. It serves biomechanical and physiological functions, acting as a pulley for the flexor tendons, anchoring the thenar and hypothenar muscles, stabilizing the bony structure, and providing wrist proprioception. This article mainly describes and reviews our recent studies regarding the biomechanical role of the TCL in the compliant characteristics of the carpal tunnel. First, force applied to the TCL from within the carpal tunnel increased arch height and area due to arch width narrowing from the migration of the bony insertion sites of the TCL. The experimental findings were accounted for by a geometric model that elucidated the relationships among arch width, height, and area. Second, carpal arch deformation showed that the carpal tunnel was more flexible at the proximal level than at the distal level and was more compliant in the inward direction than in the outward direction. The hamate-capitate joint had larger angular rotations than the capitate-trapezoid and trapezoid-trapezium joints for their contributions to changes of the carpal arch width. Lastly, pressure application inside the intact and released carpal tunnels led to increased carpal tunnel cross-sectional areas, which were mainly attributable to the expansion of the carpal arch formed by the TCL. Transection of the TCL led to an increase of carpal arch compliance that was nine times greater than that of the intact carpal tunnel. The carpal tunnel, while regarded as a stabile structure, demonstrates compliant properties that help to accommodate biomechanical and physiological variants such as changes in carpal tunnel pressure.

The relationship of trigger finger and flexor tendon volar migration after carpal tunnel release

It has been suggested that the increased frequency of trigger finger (TF) after carpal tunnel release (CTR) may be caused by the volar migration of the flexor tendons at the wrist altering the tendon biomechanics at the A1 pulley. This hypothesis has not been validated. We performed pre- and post-operative ultrasonography (USG) on the affected wrists of 92 patients who underwent CTR. Pre-operative USG was performed in neutral with no tendon loading; post-operative USG was performed in neutral unloaded and in various positions of wrist flexion whilst loading the flexor tendons with gripping. The mean volar migration of the flexor tendons after CTR was 2.2 (SD 0.4) mm in the unloaded neutral position. It was 1.8 (SD 0.4) mm in patients who did not develop TF and 2.5 (SD 0.5) mm in those who did (p = 0.0067). In loaded wrist flexion, the mean volar migration of flexor tendons after CTR in patients who did not develop TF and those who did was 2.1 and 3.0 mm in 0° flexion; 3.2 and 3.9 mm in 15° flexion; 4.3 and 5.1 mm in 30° flexion; and 4.9 and 5.8 mm in 45° flexion, respectively. There were significant differences between patients with and without TF at each flexion angle. Our data indicate that patients with greater volar migration of the flexor tendons after CTR are more likely to develop TF. This conclusion supports the hypothesis that the occurrence of TF after CTR may be caused by the bowstringing effects of the flexor tendons.

Quantification of the transverse carpal ligament elastic properties by sex and region

BACKGROUND

The transverse carpal ligament is an integral factor in the etiology of carpal tunnel syndrome. The purpose of this study was to report the biomechanical properties of this ligament and quantify sex-based differences and regional variation in tissue response. We hypothesized that the mechanical response would not be uniform across the surface, and that female ligament properties would have higher strain profiles and lower mechanical properties.

METHODS

Uniaxial testing of twelve (six males, six females) human fresh frozen cadaveric transverse carpal ligaments was carried out using an Instron Materials Testing Machine. Strain was measured via a non-contact optical method.

FINDINGS

The following biomechanical properties of the transverse carpal ligament were reported in this work: failure strain (male: 9.2 (SD 5.0), female: 15.5 (SD 7.1)%), strength (male: 4.9 (SD 1.5), female: 4.5 (SD 1.6) MPa), and modulus of elasticity (male: 52.9 (SD 19.6), female: 38.2 (SD 21.9) MPa). The radial side displayed significantly more strain at failure compared to ulnar (P<0.0001).

INTERPRETATION

The results of this study provide evidence that manipulative treatments should focus stretching on the radial half of the tissue, which experiences larger strains under uniform loading conditions. In addition, this work suggests possible sex-based differences in mechanical properties of the transverse carpal ligament, which could provide a basis for the development of improved non-surgical treatment methods for carpal tunnel syndrome. The results can also be applied to generate more accurate computational models of the wrist.

STRUCTURAL CHANGES OF THE CARPAL TUNNEL, MEDIAN NERVE AND FLEXOR TENDONS IN MRI BEFORE AND AFTER ENDOSCOPIC CARPAL TUNNEL RELEASE

The purpose of this study is to investigate the structural changes of the carpal tunnel, median nerve, and flexor tendons in magnetic resonance imaging (MRI) before and after endoscopic carpal tunnel release (ECTR). We studied 36 hands undergoing ECTR. In MRI, the cross-sectional area of the carpal tunnel and the median nerve at the hamate and the pisiform levels were measured. The distance from the volar side of carpal bone to the median nerve or tendons and the volar displacement were measured. In post-operative MRI, the transverse carpal ligament could not be well delineated and the carpal tunnel was significantly enlarged both at the hamate and pisiform levels. The median nerve was enlarged at the hamate level. The median nerve and flexor tendons significantly moved to the volar side. The volar displacement of the median nerve and flexor digitorum superficialis in the long and ring fingers was greater than the other tendons.

GENDER DIFFERENCE IN CARPAL TUNNEL COMPLIANCE

The purposes of this study were to investigate the mechanical properties of the carpal tunnel and to examine carpal tunnel compliance as it related to gender difference. Twelve male and twelve female subjects without any neuromusculoskeletal disorders in the upper extremities participated in the study. Indentation testing was manually performed on the wrist volar to the transverse carpal ligament. Effective compliance was defined as the slope of the regression analyses of indentation force and displacement data. In the tested indentation force range (2.45–19.60 N), the displacement of females was 1.38 ± 0.25 mm, significantly smaller than that of the males, 1.82 ± 0.30 mm (p < 0.001). Regression analyses in the force range showed that the effective compliance for females, 0.075 ± 0.012 mm/N, was 26.3% lower than that for males, 0.101 ± 0.018 mm/N (p < 0.005). It was concluded that females have less compliant carpal tunnel than males. The gender difference in carpal tunnel mechanics may predispose females to detrimental compression of the median nerve and carpal tunnel syndrome.

Correlações entre força de preensão manual e variáveis antropométricas da mão de jovens adultos

O objetivo do estudo foi correlacionar a força de preensão palmar em diferentes posições de abertura, com variáveis antropométricas da mão. Participaram 73 voluntários de ambos os sexos (40 homens e 33 mulheres), com idade média de 23±4,61 anos. As medidas antropométricas largura da palma, comprimento do dedo indicador, espessura da palma, largura da mão, circunferência da palma e da mão foram realizadas bilateralmente. Para as medidas lineares, utilizou-se um paquímetro digital e, para as medidas de circunferência, a fita métrica. As medidas de força de preensão foram realizadas por meio de um dinamômetro hidráulico (UFTM) Jamar®. Os valores antropométricos foram correlacionados com as medidas de força nas cinco posições de abertura. Os homens e as mulheres tiveram maior força na mão direita e, entre as posições, a maior força dos homens foi na de número 3 (45,5±15,53 kgf) e das mulheres, na de posição 2 (25,5±6,28 kgf). Verificaram-se correlações significativas entre a força e os valores antropométricos nas medidas da largura da mão e circunferência da palma - que representam a maior medida transversal e o maior trofismo da mão, respectivamente, no grupo dos homens e a medida de comprimento do dedo, que representa a maior medida longitudinal no grupo das mulheres. Com isso, pode-se concluir que, para os homens, a maior força está relacionada à maior medida transversal e ao maior trofismo da mão e, para as mulheres, ao maior comprimento longitudinal da mão.

Current concepts of carpal tunnel syndrome: pathophysiology, treatment, and evaluation

The current concepts of carpal tunnel syndrome (CTS) with respect to its pathophysiology, treatment, and evaluation are discussed. With regard to the pathophysiology of idiopathic CTS, biomechanical studies to determine the kinematics of the flexor tendon, and the median nerve inside the carpal tunnel may provide valuable insights. Different degrees of excursion between the flexor tendons and the median nerve could cause strain and microdamage to the synovial tissue; this has been microscopically observed. A biomechanical approach for elucidating the events that trigger the development of CTS seems interesting; however, there are limitations to its applications. Endoscopic carpal tunnel release (ECTR) is a useful technique for achieving median nerve decompression. However, it is not considered superior to conventional open carpal tunnel release in terms of fast recovery of hand function. Unless the effect of inserting a cannula into the diseased carpal tunnel on the median nerve function is quantitatively elucidated, ECTR will not be regarded as a standard procedure for relieving the median nerve from chronic compression. The treatment of CTS should be evaluated on the basis of patient-oriented questionnaires as well as conventional instruments because these questionnaires have been validated and found to be highly responsive to the treatment. It should be noted that nerve conduction studies exclusively evaluate the function of the median nerve, whereas patient-oriented questionnaires take into account not only the symptoms of CTS but other accompanying pathologies as well, such as flexor tenosynovitis. In Japan, the number of CTS patients is expected to rise; this may be attributed to a general increase in the life-span of the Japanese and increase in the number of diabetic patients. Thus, more efforts should be directed toward elucidating the pathophysiology of so-called idiopathic CTS, so that new treatment strategies can be established for CTS of different pathologies.

Carpal tunnel expansion by palmarly directed forces to the transverse carpal ligament

This study investigated the expansion of the carpal tunnel resulting from the application of palmarly directed forces to the transverse carpal ligament (TCL) from inside the carpal tunnel. Ten fresh-frozen cadaveric hands were dissected to evacuate the carpal tunnel, and thus to expose the TCL. A custom lever device was built to apply forces, ranging from 10 N to 200 N, to the TCL. Without force application, the carpal tunnel area was 148.4+/-36.8 mm2. The force application caused the TCL to form arches with an increase in cross-sectional areas of 33.3+/-5.6 mm2 at 10 N and 48.7+/-11.4 mm2 at 200 N, representing respective increases of 22.4% and 32.8% relative to the initial carpal tunnel area. The TCL length remained constant under the applied forces. It was found that the TCL arch formation was due to the narrowing of the arch width, which resulted from the migration of the bony insertion sites of the TCL. A geometrical model of the carpal tunnel was then developed to elucidate the relationships among the arch width, TCL length, arch height, and arch area. The model illustrated the effectiveness of carpal tunnel expansion by TCL elongation or arch width narrowing.

MRI assessment of recurrent carpal tunnel syndrome after open surgical release of the median nerve

OBJECTIVE

The purpose of this study was to retrospectively determine the accuracy of MRI in identification of the morphologic features of median nerve dysfunction after surgical release of the median nerve for carpal tunnel syndrome.

MATERIALS AND METHODS

Two blinded readers independently evaluated axial 1.5-T MR images for retinacular regrowth, morphologic characteristics of the median nerve, and presence of mass effect, fibrosis, and carpal tunnel decompression. All 47 patients (11 men, 36 women; mean age, 55 years; range, 27-81 years) had undergone open surgical release of the median nerve for carpal tunnel syndrome. Thirty-five patients had electromyographic evidence of recurrent carpal tunnel syndrome. The other 12 patients did not have electrophysiologic evidence of recurrent carpal tunnel syndrome and were the control group.

RESULTS

A statistically significant difference between the recurrent carpal tunnel syndrome and control groups was found for fibrosis (p = 0.009), nerve enhancement (p = 0.04), and median nerve width (p = 0.008) and ratio (p = 0.01) at the pisiform level.

CONCLUSION

MRI may be used in association with electromyography for accurate postoperative evaluation of the carpal tunnel.

Median nerve excursion in response to wrist movement after endoscopic and open carpal tunnel release

PURPOSE

To compare the perioperative kinematic effects of endoscopic versus open carpal tunnel release on longitudinal excursion (gliding) and volar displacement (bowstringing) of the median nerve at the wrist region in patients with idiopathic primary carpal tunnel syndrome.

METHODS

Sixteen hands of 13 patients were randomly assigned into 2 groups (group 1, endoscopic; group 2, open carpal tunnel release). For the measurement of gliding and bowstringing of the median nerve, a metallic marker was used. Before and after the division of the transverse carpal ligament, longitudinal excursion and volar displacement of the median nerve were calculated based on fluoroscopic imaging for each wrist. Movement was analyzed for the measurement of the marker locations.

RESULTS

The mean prerelease median nerve excursion during wrist range of motion was 20 mm (range, 10-28) in group 1 and 21 mm (range, 16-31 mm) in group 2. The mean postrelease median nerve excursion during wrist range of motion was 20 mm (range, 13-29) in group 1 and 18 mm (range, 8-26 mm) in group 2. There was no statistically significant difference in pre- and postrelease longitudinal excursion changes between the groups (p = .916 and p = .674, respectively). The mean prerelease volar displacement of the median nerve during wrist range of motion was 3 mm in group 1 and 4 mm in group 2; the postrelease mean values were 2 mm and 5 mm, respectively. There was no statistically significant difference between the groups with regard to pre- and postrelease volar displacement changes of the median nerve (p = .372 and p = .103, respectively).

CONCLUSIONS

This study demonstrated that the endoscopic release and open carpal tunnel release produce similar perioperative effects on longitudinal and volar movements of the median nerve.

The effect of wrist position on the relative motion of tendon, nerve, and subsynovial connective tissue within the carpal tunnel in a human cadaver model

The purpose of this study was to measure the effect of wrist position on the relative motion of the middle finger flexor digitorum superficialis (FDS) tendon, subsynovial connective tissue (SSCT), median nerve, and flexor retinaculum during simulated active finger motion. The relative motion of each tissue was measured by fluoroscopy in 10 human cadavers. Measurements were obtained for wrist positions of neutral (0 degree extension), 30 and 60 degrees of flexion, and 30 and 60 degrees of extension. The shear strain index (SSI) was defined as the difference in motion between two tissues (tendon, SSCT, or nerve) divided by tendon excursion, expressed as a percentage. The motion of the tendon, SSCT, and nerve in the 60 degree flexed position was significantly less than the motion in all other wrist positions (p < 0.001). The SSI at 60 degrees of flexion for tendon-SSCT and tendon-nerve were significantly increased compared with all other positions (p < 0.001). Because the SSCT and tendon are physically connected, a decrease in SSCT motion relative to the tendon would increase the shear strain on the SSCT with tendon motion. Thus, this result suggests that the SSCT may be predisposed to shear injury from activity done in 60 degrees of wrist flexion.

Carpal tunnel syndrome

Carpal tunnel syndrome is the most common compressive neuropathy of the upper extremity. As a result of median nerve compression, the patient reports pain, weakness, and paresthesias in the hand and digits. The etiology of this condition is multifactorial; anatomic, systemic, and occupational factors have all been implicated. The diagnosis is based on the patient history and physical examination and is confirmed by electrodiagnostic testing. Treatment methods range from observation and splinting, to cortisone injection and splinting, to surgical intervention. Both nonsurgical and surgical management provide symptom relief in most patients. The results of open and endoscopic surgery essentially are equivalent at 3 months; the superiority of one technique over the other has yet to be established.

Carpal tunnel syndrome--a comprehensive review

PURPOSE

To provide a comprehensive review of the management of carpal tunnel syndrome.

METHODS AND RESULTS

A systematic literature review is provided of the history, anatomy, pathophysiology, epidemiology, diagnostic criteria, investigative surgical techniques, results and complications for carpal tunnel syndrome.

CONCLUSION

Surgery for carpal tunnel syndrome requires meticulous attention to history-taking, investigation, counseling, training and surgical technique if unsatisfactory results and complications are to be avoided.

Wrist immobilization after carpal tunnel release: a prospective study

This prospective study evaluates the possible advantages of wrist imobilization after open carpal tunnel release comparing the results of two weeks immobilization and no immobilization. Fifty two patients with idiopathic carpal tunnel syndrome were randomly selected in two groups after open carpal tunnel release. In one group (A, n=26) the patients wore a neutral-position wrist splint continuosly for two weeks. In the other group (B, n=26) no wrist immobilization was used. Clinical assessment was done pre-operatively and at 2 weeks follow-up and included the two-point discrimination test at the second finger and two questionnaires as an outcome measurement of symptoms severity and intensity. All the patients presented improvement in the postoperative evaluations in the three analyzed parameters. There was no significant difference between the two groups for any of the outcome measurements at the final follow-up. We conclude that wrist immobilization in the immediate post-operative period have no advantages when compared with no immobilization in the end result of carpal tunnel release.

Carpal tunnel syndrome and development of trigger digit

Although the coexistence of carpal tunnel syndrome and trigger digit in the same hand is well documented, the interactive relationship between them is unclear. This study was conducted to examine the factors that may impact on the development of trigger digit in the hand with idiopathic carpal tunnel syndrome. One hundred and eighty-one patients were enrolled. Their gender, age, dominant side, severity of carpal tunnel syndrome, history or presence of trigger digit, and treatment type were recorded. The patients were evaluated for the presence of trigger digit at 1, 3, 6 and 12 months after surgery or the initial evaluation. Two hundred and sixty-five hands in 152 patients were included in the final assessment. Logistic regression analysis revealed that surgery was a significant risk factor for the onset of trigger digit and may accelerate development of trigger digit when carpal tunnel syndrome was mild to moderate, but not when it was severe. In severe disease, other unknown factors, such as hypertrophy of the flexor tenosynovium, may mask the effect of surgery.

The origins of the thenar and hypothenar muscles

This paper presents an anatomical study of the origins of the thenar and hypothenar muscles and postulates the causes of weakness and pillar pain following carpal tunnel release.

Biomechanics of the flexor tendons

This article examines basic tendon biomechanics, the anatomy and mechanics of digital flexor tendons, and the digital flexor pulley system. It also explores the various models that have tried to simulate the motion of the flexor tendons and several testing modalities that have been used. Finally, clinical applications are considered, including the biomechanics of flexor tendon repairs and tendon transfers. As we reach limits in the care of flexor tendon injuries, research into molecular, biochemical, and micromechanical methods of tendon repair will become the forefront of future investigation.

Ergonomic Pain--Part 2: Differential Diagnosis and Management Considerations

Work-related musculoskeletal disorders (MSDs) can produce ergonomic pain in several different regions of the body, including the shoulder, elbow, wrist and hand, lumbar spine, knee, and ankle/foot. Each family of disorders is distinctive in presentation and requires diagnosis-specific interventions. Because of the complex nature of these disorders, management approaches may not always eliminate symptoms and or completely restore patient function to a level found prior to symptom onset. As a consequence, ergonomic measures should be implemented to reduce the overload on tissue and contribute to patient recovery. However, functional limits may persist and the clinician must make further decisions regarding a person's functional status in the chronic stages of the patient's care.

Snapping wrist after surgery for carpal tunnel syndrome and trigger digit: a case report

We present a case of snapping dislocation of the flexor digitorum superficialis tendon to the small finger over the hook of the hamate that was noted after carpal tunnel release and trigger digit release.

Inflammation reduces physiological tissue tolerance in the development of work-related musculoskeletal disorders

Work-related musculoskeletal disorders (MSDs) cause substantial worker discomfort, disability and loss of productivity. Due to the difficulty in analyzing the tissues of patients in the early stages of work-related MSD, there is controversy concerning the pathomechanisms of the development of these disorders. The pathophysiology of work-related MSD can be studied more easily in animal models. The purpose of this review is to relate theories of the development of tissue injury due to repeated motion to findings of recent investigations in animals that address the role of the inflammatory response in propagating tissue injury and contributing to chronic or recurring tissue injury. These tissue effects are related to behavioral indicators of discomfort and movement dysfunction with the aim of clarifying key time points for specific intervention approaches. The results from animal models of MSD are discussed in the light of findings in patients, whose tissues are examined at a much later phase of MSD development. Finally, a conceptual model of the potentially negative impact of inflammation on tissue tolerance is proposed along with suggestions for future research directions.

Results of carpal tunnel release

We evaluated, by means of a prospective study, the results of carpal tunnel release both clinically and electrophysiologically in 188 patients with a carpal tunnel syndrome. A questionnaire was completed by patient and surgeon pre- and post-operatively (6 and 12 months after operation), when physical examination, electromyography and nerve conduction tests were also performed. Full pre- and post-operative results were available for 136 patients and 82% of the patients were satisfied with the results of the operation. Symptoms caused by median nerve compression showed the greatest improvement and no fixed patterns with regard to unsatisfactory results were found. If pain persisted in the wrist, many patients considered the operation to have been unsuccessful. Electrophysiological improvement occurred in all patients and at 12 months follow-up, median nerve conduction was normal in 21% of cases. Thus distal sensory latency remained abnormal in 79% of the patients, emphasizing the need for caution when recurrence of carpal tunnel syndrome is diagnosed in such cases.

Chronic repetitive reaching and grasping results in decreased motor performance and widespread tissue responses in a rat model of MSD

This study investigated changes in motor skills and tissues of the upper extremity (UE) with regard to injury and inflammatory reactions resulting from performance of a voluntary forelimb repetitive reaching and grasping task in rats. Rats reached for food at a rate of 4 reaches/min, 2 h/day, and 3 days/week for up to 8 weeks during which reach rate, task duration and movement strategies were observed. UE tissues were collected bilaterally at weekly time points of 3-8 weeks and examined for morphological changes. Serum was tested for levels of interleukin-1alpha (IL-1) protein. The macrophage-specific antibody, ED1, was used to identify infiltrating macrophages and the ED2 antibody was used to identify resident macrophages. Rats were unable to maintain baseline reach rate in weeks 5 and 6 of task performance. Alternative patterns of movement emerged. Fraying of tendon fibrils was observed after 6 weeks in the mid-forelimb. After 4 weeks, a general elevation of ED1-IR macrophages were seen in all tissues examined bilaterally including the contralateral, uninvolved forelimb and hindlimbs. Significantly more resident macrophages were seen at 6 and 8 weeks in the reach limb. At 8 weeks, serum levels of IL-1alpha increased significantly above week 0. Our results demonstrate that performance of repetitive tasks elicits motor decrements, signs of injury and a cellular and tissue responses associated with inflammation.

Laminar configuration of the transverse carpal ligament

We investigated the laminar configuration of the transverse carpal ligament, using 77 hands from 44 donated cadavers. According to the running directions and attachments of the fiber bundles composing the ligament, we identified four basic bundle patterns: proximal transverse, distal transverse, radial oblique, and ulnar oblique. Although these patterns often coexisted and the bundles were somewhat intermingled, a specific pattern was very evident in several laminae. Laminae with the distal transverse bundle pattern were the thickest and were reinforced by additional fibers which originated from the palmar aponeurosis and were deeply inserted into the lamina. Based on the laminar configurations of the superficial and deep layers and their composite fiber bundles, we classified the ligaments into four types. Type I, in which distal transverse and ulnar oblique laminae predominated in every layer, was the most common (44.2%), while another large group (41.6%) exhibited type II ligaments, comprising distal transverse and ulnar oblique laminae in the superficial layer and proximal transverse and radial oblique laminae in the deep layer. Thus, in almost half of the patients (type II), the strong distal transverse lamina is likely to be excised during the final step of endoscopic carpal tunnel release because of its superficial localization. This could be a major reason for the frequent occurrence of incomplete release. Moreover, the almost universal superficial ulnar oblique bundle pattern (observed in type I, II, and III ligaments), predisposes to scarring, which may cause radial shifting of the ulnar neurovascular bundle and may affect the palmar branch of the median nerve. We conclude that the interindividual variability seen in the results of endoscopic carpal tunnel release, including minor complications, depends partly on configurational variations in the laminar arrangement of the transverse carpal ligament.

Pathophysiological tissue changes associated with repetitive movement: a review of the evidence

Work-related musculoskeletal disorders (WMSDs) represent approximately one third of workers' compensation costs in US private industry, yet estimates of acceptable exposure levels for forceful and repetitive tasks are imprecise, in part, due to lack of measures of tissue injury in humans. In this review, the authors discuss the scope of upper-extremity WMSDs, the relationship between repetition rate and forcefulness of reaching tasks and WMSDs, cellular responses to injury in vivo and in vitro, and animal injury models of repetitive, forceful tasks. The authors describe a model using albino rats and present evidence related to tissue injury and inflammation due to a highly repetitive reaching task. A conceptual schematic for WMSD development and suggestions for further research are presented. Animal models can enhance our ability to predict risk and to manage WMSDs in humans because such models permit the direct observation of exposed tissues as well as motor behavior.