Zong Ming Li

RECONSTRUCTION OF THE INTEROSSEOUS LIGAMENT OF THE FOREARM REDUCES LOAD ON THE RADIAL HEAD IN CADAVERS

Excision of the radial head after fracture may be complicated by longitudinal radio-ulnar instability (Essex-Lopresti lesion) if the forearm interosseous ligament has also been torn. In such cases proximal migration of the radius occurs, and ulnar impaction at the wrist and radiocapitellar contact at the elbow may impair function. Although metal radial head arthroplasties are now used for irreparable radial head fractures, the long-term clinical outcome may still be unsatisfactory because of excessive radiocapitellar load causing pain. Interosseous ligament reconstruction might improve outcome by restoring normal load transfer from the radius to ulna, but the biomechanical effect of reconstruction has not been reported. This study evaluated forearm load transfer following interosseous ligament reconstruction with an Achilles tendon allograft in a cadaveric model with the radial head intact. Interosseous ligament reconstruction reduced proximal radius loading by transferring force to the proximal ulna, but force transfer by the reconstruction was only half that by the intact ligament.

Multi-directional strength and force envelope of the index finger

OBJECTIVE The purpose of this study was to biomechanically evaluate the motor function of the index finger based on multi-directional strengths. DESIGN An experimental apparatus was developed to measure force production of a digit at various points of force application along the digit and in any direction of force application within the transverse plane of the longitudinal axis of the digit. BACKGROUND Most existing tests of hand motor function are subjective, semiquantitative, and/or non-specific. METHODS Eight normal subjects with asymptomatic hands were tested. Maximum voluntary isometric contraction forces were measured at the middle of the proximal phalanx of the index finger in 16 directions that were evenly distributed within 360 degrees. RESULTS The highest force, 110.7 (SD 9.0) N, was generated in flexion, while the lowest force was generated in extension. The forces in extension, abduction and adduction were 37.6%, 97.9% and 79.3% of the flexion force, respectively. The area of the force envelope was 25739 (SD 3688) N-N. The average percentage quadrant areas, relative to the total force envelope area, for extension-adduction, extension-abduction, flexion-abduction, and flexion-adduction were 12.9%, 20.4%, 36.0%, and 30.8%, respectively. The average percentage quadrant areas for extension, abduction, flexion, and adduction were 9.1%, 33.3%, 35.6%, and 22.1%, respectively. CONCLUSION The current study provides an advanced level of quantification of hand motor function. RELEVANCE The methods may be used as a basis to detect changes in the motor function resulting from pathological conditions, disease progression, as well as rehabilitation and treatment of these disorders.

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.

Variability of Precision Pinch Movements Caused by Carpal Tunnel Syndrome

PURPOSE Carpal tunnel syndrome (CTS) impairs the performance of fine motor tasks of the hand, leading to clumsiness. Precision pinch by the thumb and index finger is a frequent task that requires the fine control of each digit as well as the coordination of the 2 digits. The purpose of this study was to examine the performance of precision pinch movements impaired by CTS. METHODS Sixteen CTS subjects and 16 gender- and age-matched control subjects were instructed to repetitively perform the precision pinch movement with the thumb and index finger. A marker-based motion analysis method was used to obtain the kinematic data of the thumb and index finger during the precision pinch movements. Pinch performance was quantified by the variability of tip positions, joint angles, and tip distance at the pinch closures in the repeated movements. RESULTS The CTS subjects performed the precision pinch movements less consistently compared with performance of the control subjects. The inconsistency was demonstrated by the increased variability of the tip positions of the 2 digits and the joint angles of the index finger. However, the variability of thumb joint angles was not significantly different between the 2 groups. The tip-to-tip distance, an indicator of thumb and index finger coordination, was relatively reproducible for both groups. Still, the CTS subjects showed a 50% greater variability of the tip distance compared with that of the control subjects. CONCLUSIONS Carpal tunnel syndrome impairs the performance of precision pinch movement as indicated by the increased variability. The results correlate with the observed clumsiness or lack of dexterity for patients with CTS.

Finger joint motion generated by individual extrinsic muscles: A cadaveric study

BackgroundOur understanding of finger functionality associated with the specific muscle is mostly based on the functional anatomy, and the exact motion effect associated with an individual muscle is still unknown. The purpose of this study was to examine phalangeal joints motion of the index finger generated by each extrinsic muscle.MethodsTen (6 female and 4 male) fresh-frozen cadaveric hands (age 55.2 ± 5.6 years) were minimally dissected to establish baseball sutures at the musculotendinous junctions of the index finger extrinsic muscles. Each tendon was loaded to 10% of its force potential and the motion generated at the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP) joints was simultaneously recorded using a marker-based motion capture system.ResultsThe flexor digitorum profundus (FDP) generated average flexion of 19.7, 41.8, and 29.4 degrees at the MCP, PIP, and DIP joints, respectively. The flexor digitorum superficialis (FDS) generated average flexion of 24.8 and 47.9 degrees at the MCP and PIP joints, respectively, and no motion at the DIP joints. The extensor digitorum communis (EDC) and extensor indicis proprius (EIP) generated average extension of 18.3, 15.2, 4.0 degrees and 15.4, 13.2, 3.7 degrees at the MCP, PIP and DIP joints, respectively. The FDP generated simultaneous motion at the PIP and DIP joints. However, the motion generated by the FDP and FDS, at the MCP joint lagged the motion generated at the PIP joint. The EDC and EIP generated simultaneous motion at the MCP and PIP joints.ConclusionThe results of this study provide novel insights into the kinematic role of individual extrinsic muscles.

Area and shape changes of the carpal tunnel in response to tunnel pressure

Carpal tunnel mechanics is relevant to our understanding of median nerve compression in the tunnel. The compliant characteristics of the tunnel strongly influence its mechanical environment. We investigated the distensibility of the carpal tunnel in response to tunnel pressure. A custom balloon device was designed to apply controlled pressure. Tunnel cross sections were obtained using magnetic resonance imaging to derive the relationship between carpal tunnel pressure and morphological parameters at the hook of hamate. The results showed that the cross‐sectional area (CSA) at the level of the hook of hamate increased, on average, by 9.2% and 14.8% at 100 and 200 mmHg, respectively. The increased CSA was attained by a shape change of the cross section, displaying increased circularity. The increase in CSA was mainly attributable to the increase of area in the carpal arch region formed by the transverse carpal ligament. The narrowing of the carpal arch width was associated with an increase in the carpal arch. We concluded that the carpal tunnel is compliant to accommodate physiological variations of the carpal tunnel pressure, and that the increase in tunnel CSA is achieved by increasing the circularity of the cross section.

Thumb force deficit after lower median nerve block

PurposeThe purpose of this study was to characterize thumb motor dysfunction resulting from simulated lower median nerve lesions at the wrist.MethodsBupivacaine hydrochloride was injected into the carpal tunnel of six healthy subjects to locally anesthetize the median nerve. Motor function was subsequently evaluated by measuring maximal force production in all directions within the transverse plane perpendicular to the longitudinal axis of the thumb. Force envelopes were constructed using these measured multidirectional forces.ResultsBlockage of the median nerve resulted in decreased force magnitudes and thus smaller force envelopes. The average force decrease around the force envelope was 27.9%. A maximum decrease of 42.4% occurred in a direction combining abduction and slight flexion, while a minimum decrease of 10.5% occurred in a direction combining adduction and slight flexion. Relative decreases in adduction, extension, abduction, and flexion were 17.3%, 21.2%, 41.2% and 33.5%, respectively. Areas enclosed by pre- and post-block force envelopes were 20628 ± 7747 N.N, and 10700 ± 4474 N.N, respectively, representing an average decrease of 48.1%. Relative decreases in the adduction, extension, abduction, and flexion quadrant areas were 31.5%, 42.3%, 60.9%, and 52.3%, respectively.ConclusionLower median nerve lesion, simulated by a nerve block at the wrist, compromise normal motor function of the thumb. A median nerve block results in force deficits in all directions, with the most severe impairment in abduction and flexion. From our results, such a means of motor function assessment can potentially be applied to functionally evaluate peripheral neuropathies.

Pressure–morphology relationship of a released carpal tunnel

We investigated morphological changes of a released carpal tunnel in response to variations of carpal tunnel pressure. Pressure within the carpal tunnel is known to be elevated in patients with carpal tunnel syndrome and dependent on wrist posture. Previously, increased carpal tunnel pressure was shown to affect the morphology of the carpal tunnel with an intact transverse carpal ligament (TCL). However, the pressure–morphology relationship of the carpal tunnel after release of the TCL has not been investigated. Carpal tunnel release (CTR) was performed endoscopically on cadaveric hands and the carpal tunnel pressure was dynamically increased from 10 to 120 mmHg. Simultaneously, carpal tunnel cross‐sectional images were captured by an ultrasound system, and pressure measurements were recorded by a pressure transducer. Carpal tunnel pressure significantly affected carpal arch area (p < 0.001), with an increase of >62 mm2 at 120 mmHg. Carpal arch height, length, and width also significantly changed with carpal tunnel pressure (p < 0.05). As carpal tunnel pressure increased, carpal arch height and length increased, but the carpal arch width decreased. Analyses of the pressure–morphology relationship for a released carpal tunnel revealed a nine times greater compliance than that previously reported for a carpal tunnel with an intact TCL. This change of structural properties as a result of transecting the TCL helps explain the reduction of carpal tunnel pressure and relief of symptoms for patients after CTR surgery.

Directional Coordination of Thumb and Finger Forces during Precision Pinch

The human opposable thumb enables the hand to perform dexterous manipulation of objects, which requires well-coordinated digit force vectors. This study investigated the directional coordination of force vectors generated by the thumb and index finger during precision pinch. Fourteen right-handed, healthy subjects were instructed to exert pinch force on an externally stabilized apparatus with the pulps of the thumb and index finger. Subjects applied forces to follow a force-ramp profile that linearly increased from 0 to 12 N and then decreased to 0 N, at a rate of ±3 N/s. Directional relationships between the thumb and index finger force vectors were quantified using the coordination angle (CA) between the force vectors. Individual force vectors were further analyzed according to their projection angles (PAs) with respect to the pinch surface planes and the shear angles (SAs) within those planes. Results demonstrated that fingertip force directions were dependent on pinch force magnitude, especially at forces below 2 N. Hysteresis was observed in the force-CA relationship for increasing and decreasing forces and fitted with exponential models. The fitted asymptotic values were 156.0±6.6° and 150.8±9.3° for increasing and decreasing force ramps, respectively. The PA of the thumb force vector deviated further from the direction perpendicular to the pinching surface planes than that of the index finger. The SA showed that the index finger force vector deviated in the ulnar-proximal direction, whereas the thumb switched its force between the ulnar-proximal and radial-proximal directions. The findings shed light on the effects of anatomical composition, biomechanical function, and neuromuscular control in coordinating digit forces during precision pinch, and provided insight into the magnitude-dependent force directional control which potentially affects a range of dexterous manipulations.

Complex, multidimensional thumb movements generated by individual extrinsic muscles

The objective of this study was to investigate three‐dimensional thumb joint movements produced by individual extrinsic thumb muscles. Ten cadaveric arms were dissected to expose the musculotendinous junctions of the flexor pollicis longus (FPL), abductor pollicis longus (APL), extensor pollicis brevis (EPB), and extensor pollicis longus (EPL). Each muscle/tendon was loaded to 10% of its maximal force capability whereas three‐dimensional angular movements of the carpometacarpal (CMC), metacarpophalangeal (MCP), and interphalangeal (IP) joints were obtained simultaneously. We found that each extrinsic muscle produced unique joint angular trajectories in multiple directions. The FPL, APL, EBP, and EPL generated two, two, three, and six movements, respectively. The extrinsic muscles all together generated eight movements among the multiple thumb joints. High interjoint coordination was shown between the MCP joint flexion and IP joint flexion by FPL loading, as well as between the MCP joint extension and IP joint extension by EPL loading. High intrajoint coordination was observed between extension and supination at the CMC joint by the APL, EPL, and EPB. We concluded that each muscle produces movements in multiple joints and/or in multiple anatomical directions. The findings provide a novel insight into the biomechanical roles of the extrinsic muscles of the thumb.