Forces Transmitted Along Human Flexor Tendons During Passive and Active Movements of the Fingers

The in vivo forces in human digital flexor tendons were determined in 33 patients undergoing a carpal tunnel decompression surgery using a newly developed device. The tendons were tested in passive and active flexion, and flexing against resistance of up to 500 g. Forces in the range of 0.2 to 50 N were noted. Whilst the mean of these forces remained below the force normally required to dehisce a fresh modified Kessler repair, the range of values was such that we would only recommend early movement with great caution and under supervision.

Tendon graft--ulna fixation in distal radio-ulnar joint stabilisation; biomechanical comparison of three graft-bone fixation methods

A common distal radio-ulnar joint (DRUJ) stabilisation procedure uses a tendon graft running from the lip of the radial sigmoid notch to the ulnar fovea and through a bony tunnel to the ulnar shaft, before being wrapped round the distal ulna and sutured to itself. Such graft fixation can be challenging and requires a considerable tendon length. The graft length could be reduced by fixing the graft to the ulna using a bone anchor or interference screw. The aim of this study was to compare the strength of three distal ulna graft fixation methods (tendon wrapping and suturing, bone anchor and interference screw). Four human cadaveric ulnae were used. A tendon strip was run through a tunnel in the distal ulna and secured by: (1) wrapping round the shaft and suturing it to itself, (2) a bone anchor and (3) an interference screw in the bone tunnel. Load to failure was determined using a custom-made apparatus and an Instron machine. Maximum failure load was highest for the bone anchor fixation (99.3 +/- 23.7 N) followed by the suturing (96.2 +/- 12.1 N), and the interference screw fixation (46.9 +/- 5.6 N). There was no significant difference between the tendon suturing and bone anchor methods, but the tendon suturing was statistically significantly higher compared to the interference screw (P = 0.028). In performing anatomical stabilisation of the DRUJ fixation of the tendon graft to the distal ulna with a bone anchor provides the most secure fixation. This may make the stabilisation technique less demanding and require a smaller tendon graft.

A device to measurein vivoforces in human flexor tendons during carpal tunnel operations

An apparatus has been designed to measure the in vivo forces transmitted along human hand flexor tendons during carpal tunnel release procedures. The tendon will be run through three hooks, the central one of which is attached to a load cell. The rationale is that once these forces are known this will aid in the design of repair techniques and rehabilitation regimens. As a first stage, an in vitro validation study is presented using cord subjected to varying forces to mimic an in vivo flexor tendon under varying conditions of use. Our results show that we can accurately and reproducibly measure the force in the cord.

Forces transmitted along human flexor tendons--the effect of extending the fingers against the resistance provided by rubber bands

We wished to test the hypothesis that postoperative extension of repaired flexor tendons against rubber bands will reduce the stress on the repairs, and therefore the risk of rupture. During 24 routine carpal tunnel decompression operations the force in flexor tendons was measured using a load cell. The patients flexed and extended their fingers with and without a rubber band providing resistance to extension. We found no statistically significant difference between the force measured in the tendon with or without the presence of rubber bands. To conclude, we have shown that if the application of rubber band dynamic splintage after flexor tendon repair has any advantage, it is not by reducing the forces transmitted along the tendon during resisted extension or by aiding flexion.

Does the orientation of the distal radioulnar joint influence the force in the joint and the tension in the interosseous membrane?

OBJECTIVE

To investigate the effect of change in the orientation of the distal radioulnar joint on the force in the joint and the strain in the interosseous membrane.

DESIGN

Biomechanical study in fresh frozen cadavers.

BACKGROUND

The articular surfaces of the distal radioulnar joint may be orientated in parallel with the long axis of the forearm (a Type I joint) or at an oblique angle opening distally to the ulnar side (a Type II joint).

METHODS

Three cadaveric upper limbs were held on a custom built frame allowing measured rotation and axial loading across the wrist. Measurements of force in the distal radioulnar joint and strain in the interosseous membrane were taken and repeated after replacement of the distal radioulnar joint with prosthetic Type I and Type II joints.

FINDINGS

The force in the joint and the strain in the interosseous membrane increased with increasing load across the wrist (P < 0.0001). The force in the Type I joint was reduced compared to the normal or Type II joint. This difference was greater with increasing load and was significant at 8 kg (P < 0.001). The strain in the interosseous membrane was maximal at neutral forearm rotation and decreased with increasing pronation and supination.

INTERPRETATION

The force in the joint is greater with the Type II distal radioulnar joint. We believe this compressive force increases joint stability and this orientation of the articular surfaces should be considered in the design of a total distal radioulnar joint arthroplasty.

Measurement of sitting balance using the Manchester Active Position Seat (MAPS): a feasibility study

BACKGROUND

Evaluation of the effectiveness of therapy to improve sitting balance has been hampered by the limited number of sensitive objective clinical measures. We developed the Manchester Active Position Seat (MAPS) to provide a portable system to track change in the position of centre of force over time.

OBJECTIVES

(1) To investigate whether there is correspondence between the measurement of position change by a forceplate and by MAPS. (2) To explore whether and how MAPS measures changes in position when seated healthy adults change posture.

DESIGN

A feasibility study.

METHODS

(1) An adult subject sat on MAPS placed on top of a forceplate. The x and y coordinates of the centre of pressure recorded from the forceplate and centre of force from MAPS during movement were compared graphically. (2) Four adults sat on MAPS using a standardized starting position and moving into six sets of six standardized target postures in a predetermined randomized order. The absolute shift in centre of force from the starting position was calculated.

RESULTS

(1) The pattern of change of position over time was similar for the forceplate and for MAPS although there was a measurement difference, which increased with distance from the centre. (2) The direction of change of position corresponded to the direction of movement to the target postures but the amount of change varied between subjects.

CONCLUSIONS

MAPS shows promise as an objective clinical measure of sitting balance, but peripheral accuracy of measurement needs to be improved.

Objective measurement of use of the reciprocating gait orthosis (RGO) and the electrically augmented RGO in adult patients with spinal cord lesions

The purpose of the study was to measure objectively the home use of the reciprocating gait orthosis (RGO) and the electrically augmented (hybrid) RGO. It was hypothesised that RGO use would increase following provision of functional electrical stimulation (FES). Five adult subjects participated in the study with spinal cord lesions ranging from C2 (incomplete) to T6. Selection criteria included active RGO use and suitability for electrical stimulation. Home RGO use was measured for up to 18 months by determining the mean number of steps taken per week. During this time patients were supplied with the hybrid system. Three alternatives for the measurement of steps taken were investigated: a commercial digital pedometer, a magnetically actuated counter and a heel contact switch linked to an electronic counter. The latter was found to be the most reliable system and was used for all measurements. Additional information on RGO use was acquired using three patient diaries administered throughout the study and before and after the provision of the hybrid system. Testing of the original hypothesis was complicated by problems in finding a reliable measurement tool and difficulties with data collection. However, the results showed that overall use of the RGO, whether with or without stimulation, is low. Statistical analysis of the step counter results was not realistic. No statistically significant change in RGO use was found between the patient diaries. The study suggests that the addition of electrical stimulation does not increase RGO use. The study highlights the problem of objectively measuring orthotic use in the home.

Energy expenditure of walking for adult patients with spinal cord lesions using the reciprocating gait orthosis and functional electrical stimulation

A major factor influencing compliance with walking orthoses following spinal cord damage, is the energy requirement associated with them. We compared ambulatory energy expenditure in subjects using the reciprocating gait orthosis (RGO) with and without functional electrical stimulation (FES) of the thigh muscles at self selected walking speeds. Five adult subjects (median age 34 years, range 24-37) with spinal cord lesions ranging from C2 (incomplete) to T6 volunteered to participate in this study. All subjects were successful RGO users (median use 5.7 years, range 4.1-7.3). Walking speed (m/s), ambulatory energy consumption (J/kg/s) and energy cost (J/kg/m) were derived from oxygen uptake determined using the Douglas bag technique. We anticipated that subjects walking with FES would either: (a) walk at the same speed but reduce their energy cost or (b) increase their walking speed for the same (or less) energy cost. Walking speed and energy cost remained unchanged in one subject. One subject increased his walking speed by 14.0% and increased his energy consumption by 8.4%. His energy cost remained unchanged. Three subjects increased their walking speeds (by 12.4, 12.7 and 6.8%), energy consumption (by 25.9, 20.4 and 18.4% respectively) and energy cost (by 11.6, 6.8 and 10.5% respectively). We did not find a substantial benefit, in terms of energy expenditure, from the hybrid system when walking continuously for 5 min. We suggest that the hybrid system may be of greater benefit during prolonged walking, although other limitations, inherent in the RGO itself, may prevent an increase in compliance. Repetition of walking speed tests supported the reliability of our results. Tests on comparably aged, able-bodied subjects showed that an increase in energy cost of up to 5.8% was within the biological variability of the subject and the error of the methodology.

The reciprocating gait orthosis: long-term usage patterns

OBJECTIVE

To investigate the frequency of nonusage of the reciprocating gait orthosis (RGO) in 85 patients supplied between 1986 and 1993. Reasons for nonusage and usage patterns were examined.

DESIGN

Nonusage was determined from patient records and clinical knowledge. Patients were surveyed using a detailed questionnaire to produce information on usage patterns.

SETTING

All patients had been treated as hospital outpatients.

PATIENTS

Most patients had congenital or acquired spinal cord lesions. Postal questionnaires were sent to 81 patients 5 to 55 years of age (mean 20.4 years). Thirty-five patients replied.

RESULTS

At a mean follow-up of 5.4 years, 71% of patients were classified as nonusers. Of the 35 respondents to the questionnaire (mean follow-up 5.5 years, range 4 to 7 years), 20 patients were nonusers. Median usage was 27 months in patients under age 18 and 24 months in adult patients. Significant differences were observed between nonusers and users in the areas of perception of the RGO as a functional tool, independence, and reliability and between the adult and the under 18 groups in the areas of weekly usage, function, independence, and reliability.

CONCLUSION

The high level of nonusage of the RGO has implications for prescription practice. Identifying reasons for nonusage and acknowledging differences in use between age groups will help in patient assessment.

The role of an adhesive (Histoacryl) in tendon repair

Two in vitro experiments have been done comparing various techniques of tendon repair. These include repairs using an adhesive, 2-butyl cyanoacrylate (Histoacryl), and repairs by the modified Kessler technique, using 4/0 braided polyester and 4/0 stainless steel. Mechanical analysis has shown that by replacing the circumferential suture of a modified Kessler tendon repair with Histoacryl, the tensile strength of the repair and the force needed to produce a gap can be increased by 30% to 40%. This improvement was statistically significant (P < 0.05).

The mechanical strength of various suture techniques

The mechanical strengths of five techniques of tendon repair have been evaluated using human cadaver tendons. A modified Kessler repair with a peripheral circumferential suture and the method of Becker were found to require the greatest load to produce gapping, but the Becker and Savage repairs withstood the highest load before failure.

A clinical evaluation of plaster-of-Paris and eight synthetic fracture splinting materials

A number of new synthetic orthopaedic splinting materials, all claiming substantial advantages over the traditional plaster-of-Paris, have been introduced in recent years. However, although their properties have been extensively measured in the laboratory, little has been documented concerning their performance in clinical use. This study was therefore initiated as a comparative evaluation of the clinical characteristics and ease of use of these relatively expensive materials in the fabrication of below-knee weight-bearing casts. The study encompassed nine materials--seven based on water-activated polyurethanes, one thermoplastic and plaster-of-Paris, and involved a total of 203 patients. It was concluded that plaster-of-Paris should be used for all routine splinting applications, but that in cases in which cast weight, cast bulk, or the time to bearing weight is important, a synthetic material, chosen principally on the basis of cost, is indicated.

The effect of ultrasound on the healing of repaired cockerel tendon: is collagen cross-linkage a factor?

The acid solubility of the collagen of cockerel tendon demonstrates a similar degree of intermolecular acid-labile cross-linkage to that found in adult human tendon, implying similar maturity of the collagen. By contrast, rabbit tendon collagen demonstrates a dissimilar degree of cross-linkage suggesting immaturity of the collagen. Since this cross-linkage is likely to be related to mechanical properties, the cockerel may well be a better animal model than the rabbit for the study of tendon healing. The application of ultrasound to sutured cockerel tendons produced no change in the mechanical strength of the tendon at six weeks, or its propensity to form adhesions, relative to untreated control sutured tendons. This contrasts with the decrease in strength after ultrasound found by previous workers using rabbits.

An evaluation of suture materials used in tendon surgery

The following suture materials have been evaluated for their suitability for use in flexor tendon repairs: 4/0 gauge monofilament and multifilament stainless steel, mono-filament nylon, monofilament polypropylene, monofilament polybutestor, braided polyester, braided polyglycolic acid and a monofilament polyglyconate. These were investigated for their tensile strength (both knotted and unknotted), their extension to failure and knot-holding properties. Stainless steel and monofilament polyglyconate appeared to be the most suitable in that they had high tensile strengths, both knotted and unknotted, and had good knot-holding security. The only disadvantages are that stainless steel is difficult to use and monofilament polyglyconate is absorbable. Polypropylene and braided polyester, although having lower tensile strengths, are reasonable alternatives.

The Effect of Ultrasound on the Healing of Repaired Cockerel Tendon: Is Collagen Crosslinkage a Factor?

The acid solubility of the collagen of cockerel tendon demonstrates a similar degree of intermolecular acid-labile cross-linkage to that found in adult human tendon, implying similar maturity of the collagen. By contrast, rabbit tendon collagen demonstrates a dissimilar degree of cross-linkage suggesting immaturity of the collagen. Since this cross-linkage is likely to be related to mechanical properties, the cockerel may well be a better animal model than the rabbit for the study of tendon healing.

The application of ultrasound to sutured cockerel tendons produced no change in the mechanical strength of the tendon at six weeks, or its propensity to form adhesions, relative to untreated control sutured tendons. This contrasts with the decrease in strength after ultrasound found by previous workers using rabbits.

An Evaluation of Suture Materials Used in Tendon Surgery

The following suture materials have been evaluated for their suitability for use in flexor tendon repairs: 4/0 gauge monofilament and multifilament stainless steel, mono-filament nylon, monofilament polypropylene, monofilament polybutestor, braided polyester, braided polyglycolic acid and a monofilament polyglyconate. These were investigated for their tensile strength (both knotted and unknotted), their extension to failure and knot-holding properties. Stainless steel and monofilament polyglyconate appeared to be the most suitable in that they had high tensile strengths, both knotted and unknotted, and had good knot-holding security. The only disadvantages are that stainless steel is difficult to use and monofilament polyglyconate is absorbable. Polypropylene and braided polyester, although having lower tensile strengths, are reasonable alternatives.

Is callus calcium content an indicator of the mechanical strength of healing fractures? An experimental study in rat metatarsals

Changes in the mechanical properties and the calcium content of healing fracture callus were followed, using rat metatarsals. By 24 weeks post-fracture the mean ultimate tensile stress and elastic modulus were still less than half that of the contralateral unfractured bone, whereas the mean torsional modulus had almost reached that of the unfractured bone. The calcium content of the callus formed immediately between the fractured ends of the bone showed changes which coincided with the increases in mechanical strength and the moduli, thus measurement of callus calcium content would enable the prediction of the strength of a healing fracture.

Development and clinical application of an external fixator monitoring system

A monitoring system for measuring movement occurring in a dynamic external fixator used to treat fractures is described. The system measures shortening during fracture healing, micromovement at the fracture site on weight bearing and detects pin loosening. The method of calibration including cadaver experiments is presented. The clinical application is described and the reasons for measuring movement are discussed.

Non-suture repair of tendons

A set of metal clamps cooled by liquid nitrogen were developed to hold the ends of tendons during in vitro tension tests. These were then used to determine the strength of whole human tendons, and human tendons repaired in vitro by sutures or by cyanoacrylate glues with or without suturing. The mean ultimate load of the intact human tendons was 1065 N, and the ultimate stress was 99.02 MN m-2. The repairs gave values of 0.3-2.3% of those of intact human tendon. Tendons were then repaired in vivo by a Kessler suture technique using braided polyester sutures with or without augmentation by a butyl cyanoacrylate glue (Histoacryl). At six months post-repair all tendons were as strong as the unoperated contralateral tendons. The glue augmented sutures were stronger than those not so augmented. A scanning electron micrograph of a tension tested glued tendon showed that it had failed by cohesive failure, i.e. failure of the inter-glue bonds rather than failure at the glue/tendon interface.

Experimental study in rat metatarsals to determine whether callus vascularity is an indicator of the mechanical strength of healing fractures

Changes in the mechanical properties and percentage area of blood vessels of healing fracture callus were followed using rat metatarsals. By 24 weeks after fracture the mean ultimate tensile stress and elastic modulus were still less than half that of the contralateral unfractured bone, whereas the mean torsional modulus had almost reached that of the unfractured bone. The percentage area of blood vessels declined from five days post-fracture and showed no changes which coincided with the increases in mechanical strength or moduli. We conclude that studies of vascularity would not justify a prediction of the strength of a healing fracture.

The comparative properties of plaster of Paris and plaster of Paris substitutes

Modern casting materials are becoming available in an increasing and bewildering variety. A series of tests has been devised to investigate the properties of these materials. They have been tested for strength, flexibility, lamination, fatigue life and radiolucency. Their properties have been compared with those of plaster of Paris in order that the role of the newer materials can be defined. It is suggested that the tests described might form the basis of a standard from which user trials could be designed to appraise the value of these materials in clinical practice.