Tendon Excursion Research Articles

Application of spherical and cylindrical wrapping algorithms in a musculoskeletal model of the upper limb

In the modelling of the upper limb, many muscles cannot be represented as a straight line from origin to insertion due to the complex morphology causing them to wrap around passive structures. The majority of bony contours that form these obstructions can be described adequately as simple geometric shapes such as spheres and cylinders. A novel technique for the parameterisation of muscle paths as they wrap around such shapes has been developed for use in an upper limb model. The new method involves the definition of moving co-ordinate systems in which the path of a wrapped muscle does not move, allowing simplified specification. In addition, an analytical calculation of the wrapping path around a cylinder is presented over previous approximate methods. Muscle moment arms were pre-calculated from vector considerations and within SIMM by tendon excursion. Close agreement between the two suggests that the proposed implementations accurately follow the theoretical relationship and can be used with confidence in musculoskeletal models.

Method of determination of three dimensional index finger moment arms and tendon lines of action using high resolution MRI scans

High-resolution MRI scans, in conjunction with CAD software, were used to determine the three-dimensional moment arms and force vector direction cosines for 11 structures passing the interphalangeal and metacarpophalangeal joints of the index finger. The results are presented for five different angles of joint flexion for a single subject. The moment arm data obtained differ from previous studies, where results have been derived from tendon excursion techniques or geometrical models. These dissimilarities have been accounted for by the differences in experimental techniques.

Effect of pulley integrity on excursions and work of flexion in healing flexor tendons.

We investigated the effect of incision of a single critical pulley on excursions and work of flexion in healing flexor tendons. Forty-two long toes from 21 white leghorn chickens were used as the experimental model. Gliding excursions of the flexor digitorum profundus tendons and work of flexion of the long toes were studied 8 weeks after tendon repair to determine the functions of the healed tendons in intact, incised, or enlarged A2 pulleys. Eleven additional chickens (22 long toes) were used to obtain tendon excursion measurements in normal chicken toes. At 8 weeks, gliding excursions were statistically smaller in the intact pulley group than in the incised or enlarged pulley groups; the excursions were 73% +/- 4% for the intact pulley group, 88% +/- 9% for the incised pulley group, and 91% +/- 8% for the enlarged sheath group compared with the normal group. Work of flexion of the toes in the intact pulley group was statistically greater than that in the incised or enlarged pulley groups. Excursion efficiency of the flexor tendons was not statistically different among the toes receiving different treatments in the pulley. The results of this study demonstrate that release of a single pulley after repair of the tendons in this area improved gliding excursions of the tendons and reduced resistance to motion of the repaired tendons, and provide support for partial A2 pulley incision after repair of the tendons in the area of the pulley.

Palmar and digital flexor tendon pulleys.

Retinacular structures, called pulleys, maintain the flexor tendons of the hand in constant relationship to the joint axes and promote economy and efficiency in finger flexion. This system is composed of the transverse carpal ligament, the palmar aponeurosis pulley, and the digital flexor pulley system. Of these three components, the digital pulleys are the most critical to finger flexion. In their normal state, these pulley components are ideal in all aspects including configuration and location, which accomodates a 260 degrees arc of motion without impingement and with minimum friction while at the same time using muscle tendon excursion that is well within the natural range of the muscle. An absent pulley results in an increased moment arm and requires increased tendon excursion to produce the same arc of motion. Because muscle excursion is not a limitless factor and is directly proportional to muscle fiber length, the effectiveness of tendon excursion is dependent on maintenance of the critical relationship between pulleys and the adjacent joints. Preservation and reconstruction of this system is based on knowledge of the anatomy and an understanding of the relative functional significance of each component of the system.

Postoperative management of functionally restrictive muscular adherence, a corollary to surgical tenolysis: A case report

After a surgical release of adhered nongliding tendons, early active mobilization is encouraged to prevent the reformation of unfavorable adhesions that would limit functional tendon excursion. These restricting adhesions can also occur in non-synovial regions, such as within the flexor mass in the forearm. A “myolysis,” or release of muscle fibers from tethering adhesions, can be performed surgically to restore the muscle's gliding and lengthening properties. Postoperative management consists of treatment techniques that include low-load prolonged stress, differential tendon gliding, and active-resistive exercises, all of which are effective in restoring and maximizing a patient's active and passive range of motion to allow optimal mobility and performance. This case study demonstrates the successful management of a patient following a surgical myolysis, utilizing treatment techniques conceptually derived from postoperative tenolysis rehabilitation.

In vivo measurement-based estimations of the human Achilles tendon moment arm

The aim of the present study was to estimate and compare in vivo measurement-based Achilles tendon moment arm lengths at rest and during isometric plantarflexion maximum voluntary contraction (MVC) using the centre-of-rotation (COR) and the tendon-excursion (TE) methods. Both methods were based on morphometric analysis of sagittal-plane magnetic resonance images of the foot. Using the COR method, moment arms were obtained at ankle angles from 15 degrees of dorsiflexion to 30 degrees of plantarflexion in steps of 15 degrees, digitizing the perpendicular distance from a moving centre of rotation in the tibio-talar joint to the Achilles tendon action line. The TE method was based on measurement of calcaneal displacement along the tibial axis during 15 degrees rotations of the ankle joint, from 30 degrees of dorsiflexion to 45 degrees of plantarflexion. The two methods gave similar estimations at rest varying from 4.3 to 5.6 cm. Using the COR method, the Achilles tendon moment arm during MVC was larger by 1-1.5 cm (22-27%, P < 0.01) than the respective resting value. In contrast, no difference (P > 0.05) was found between the resting and MVC moment arm estimations of the TE method. The disagreement in moment arms during MVC may be attributed to differences in the assumptions made between the two methods. The TE method has more limitations than the COR method and its estimations during MVC should be treated with caution. Resting Achilles tendon moment arm estimations of the COR method should be multiplied by 1.22-1.27 when maximal isometric plantarflexion joint moments, musculotendon forces and stresses are predicted using modelling.

In vivo human tendinous tissue stretch upon maximum muscle force generation

In the present study, we examined the hypothesis that stretch of tendinous tissue in the human tibialis anterior (TA) muscle–tendon unit upon isometric dorsiflexion maximum voluntary contraction (MVC) varies along the entire tendinous component length. Ultrasound-based measurements of the excursions of the TA tendon origin and proximal end of the TA central aponeurosis were taken in the transition from rest to MVC in six men. Subtracting the TA tendon origin excursion from the excursion of the aponeurosis proximal end, the aponeurosis excursion was estimated. Estimation of the aponeurosis proximal region excursion was obtained subtracting the excursion of the insertion point of a central region fascicle on the aponeurosis from the whole aponeurosis excursion. Subtracting tendon excursion from the excursion of the central fascicle insertion point, the aponeurosis distal region excursion was estimated. Strain values were calculated dividing the excursions obtained by the original resting lengths. All excursions and lengths were measured in the mid-longitudinal axis of the TA muscle–tendon unit at the neutral anatomical ankle position. Tendon excursion and strain were 0.5±0.08 cm (mean±SE) and 3.1±0.2%, respectively. Aponeurosis excursion and strain were 1.1±0.15 cm and 6.5±0.6%, respectively. Aponeurosis distal region excursion and strain were 0.3±0.05 cm and 3.5±0.3%, respectively. Aponeurosis proximal region excursion and strain were 0.8±0.12 cm and 9.2±1%, respectively. Aponeurosis excursion and strain were larger by 110–120% ( P<0.05) compared with tendon. Aponeurosis proximal region excursion and strain were larger by 165–170% ( P<0.05) compared with aponeurosis distal region. These findings are in line with results from in vitro animal material testing and have important implications for theoretical models of muscle function.

The relevance of the moment arm of shoulder muscles with respect to axial rotation of the glenohumeral joint in four positions

Objective. This study was undertaken to determine the efficiency of the shoulder girdle muscles during axial humeral rotation based on measurements of the moment arms. Design. The instantaneous muscle moment arms of 10 shoulder muscles, including the three portions of the deltoid, the rotator cuff muscles, teres major, and the thoracohumeral muscle group, were measured during four specified glenohumeral rotations. Background. Axial humeral rotation is a commonly performed movement during activities of daily living and is a targeted motion of shoulder rehabilitation, particularly in those protocols emphasizing rotator cuff strengthening. An understanding of the function of the movers and stabilizers of the shoulder requires such basic information of muscle moment arms. Methods. The instantaneous moment arm values of the muscles were derived from the slope of the plot of tendon excursion versus glenohumeral joint rotation angle. Motion studied included axial rotation with the humerus elevated 90° in the coronal, scapular, and sagittal planes, as well as in the neutral position with the arm at the side. Results. Based on the findings, with the humerus in both neutral and elevated positions, the infraspinatus is potentially the most powerful external rotator, followed by teres minor and posterior deltoid. Subscapularis and possibly pectoralis major are the most effective internal rotators in this position. Conclusions. The moment arm in providing axial humeral rotation of 10 shoulder muscles in four planes were obtained. In general, the teres minor and infraspinatus had the largest moment arms in external rotation, and the subscapularis had the largest moment arm in internal rotation. The muscle function for axial humeral rotation was found to be modified by the plane of arm elevation. Relevance The data could be used for developing exercise programs in physical therapy.

Studies in flexor tendon wound healing: neutralizing antibody to TGF-beta1 increases postoperative range of motion.

The postoperative outcome of hand flexor tendon repair remains limited by tendon adhesions that prevent normal range of motion. Recent studies using in situ hybridization techniques have implicated transforming growth factor beta-1 (TGF-beta1) in both intrinsic and extrinsic mechanisms of repair. TGF-beta1 is a growth factor that plays multiple roles in wound healing and has also been implicated in the pathogenesis of excessive scar formation. The purpose of this study was to examine the effect of neutralizing antibody to TGF-beta1 in a rabbit zone II flexor tendon wound-healing model. Twenty-two adult New Zealand White rabbits underwent complete transection of the middle digit flexor digitorum profundus tendon in zone II. The tendons were immediately repaired and received intraoperative infiltration of one of the following substances: (1) control phosphate-buffered saline; (2) 50 microg neutralizing antibody to TGF-beta1; (3) 50 microg each of neutralizing antibody to TGF-beta1 and to TGF-beta2. Eight rabbits that had not been operated on underwent analysis for determination of normal flexion range of motion at their proximal and distal interphalangeal joints, using a 1.2-N axial load applied to the flexor digitorum profundus tendon. All rabbits that had been operated on were placed in casts for 8 weeks to allow maximal tendon adhesion and were then killed to determine their flexion range of motion. Statistical analysis was performed using the Student's unpaired t test. When a 1.2-N load was used on rabbit forepaws that had not been operated on, normal combined flexion range of motion at the proximal and distal interphalangeal joints was 93+/-6 degrees. Previous immobilization in casts did not reduce the range of motion in these forepaws (93+/-4 degrees). In the experimental groups, complete transection and repair of the flexor digitorum profundus tendon with infiltration of control phosphate-buffered saline solution resulted in significantly decreased range of motion between the proximal and distal phalanges [15+/-6 degrees (n = 8)]. However, in the tendon repairs infiltrated with neutralizing antibody to TGF-beta1, flexion range of motion increased to 32+/-9 degrees (n = 7; p = 0.002). Interestingly, a combination of neutralizing antibody to TGF-beta1 and that to TGF-beta2 did not improve postoperative range of motion [18+/-4 degrees (n = 7; p = 0.234)]. These data demonstrate that (1) the rabbit flexor tendon repair model is useful for quantifying tendon scar formation on the basis of degrees of flexion between proximal and distal phalanges; (2) intraoperative infiltration of neutralizing antibody to TGF-beta1 improves flexor tendon excursion; and (3) simultaneous infiltration of neutralizing antibody to TGF-beta2 nullifies this effect. Because TGF-beta1 is thought to contribute to the pathogenesis of excessive scar formation, the findings presented here suggest that intraoperative biochemical modulation of TGF-beta1 levels limits flexor tendon adhesion formation.

In vivo moment arm determination using B-mode ultrasonography

The tendon excursion of the tibialis anterior (TA) muscle was measured in vivo using B-mode ultrasonography in seven subjects under three force levels (0, 30 and 60% maximal voluntary contraction, MVC). For each force level, the TA moment arm ( m) was determined by calculating the derivative of the tendon excursion relative to the ankle angle ( a). A dynamometer controlled the ankle angle while force levels were monitored. The parametric model proposed by Miller and Dennis (1996), m= R sin( a+ Δ), where R is the largest moment arm and Δ represents the offset angle of R from 90°, was used in a least-squares fit of the relationship between moment arm and ankle angle. The R values at 0% MVC were significantly smaller than those at 30 and 60% MVC. The values of calculated moment arm at 0% MVC were not considered adequate estimates of the TA moment arm because of the possible confounding effect of the slackness of the relaxed muscle–tendon unit in more dorsiflexed positions. The moment arm values at 30 and 60% MVC were believed to provide reliable estimates of those of TA since the application of tension probably reduced the effects of the slackness of the muscle–tendon unit and tendon elongation on tendon excursion measurement at these force levels. Since the ultrasonographic technique is an in vivo application of the tendon excursion technique and therefore takes the functional meaning into consideration, it can yield more significant moment arms than other in vivo or cadaver techniques.

Tendon displacement assessment by pulsed Doppler tissue imaging: validation with a reciprocating string test target

After hand trauma and surgery, assessment of tendon excursion is important in reconstructive surgery and rehabilitation. Aimed as a more reliable alternative to traditional noninvasive methods, a colour Doppler imaging scanner was adapted to measure longitudinal tendon displacement. Displacement was quantified by integrating the velocity estimated from the zero-crossing rate of the Doppler signal. The system was tested by measuring displaced distances of a rubber string that was moved back and forth. At a determined optimal receiver gain, 1.5-cm string displacements were measured with less than ± 0.05-cm bias throughout an echo-signal dynamic range of 22 dB; standard deviations were around 0.05 cm. Regression analysis between measured and true displacements in the range 0.5–2.5 cm resulted in a best fit straight line with slope 0.927, intercept 0.041 cm and residual standard error of 0.06 cm. A transfer technique was conceived to ensure accuracy when measuring tendons in the body. This CDI-based pulsed Doppler system merits verification for measurement of tendon excursion in patients.

Effects of increased in vivo excursion on digital range of motion and tendon strength following flexor tendon repair.

Postoperative rehabilitation is an important factor in determining functional outcome following intrasynovial flexor tendon repair. We hypothesized that a rehabilitation protocol that produced increased in vivo excursion would lead to increased digital range of motion and tendon strength and decreased adhesion formation in a canine model. Ninety-six flexor digitorum profundus tendons from 48 dogs were cut transversely and repaired by a multistrand suture technique. Postoperative rehabilitation was performed daily with a low excursion-low force (1.7-mm average excursion; < 10 N force) or a high excursion-low force (3.6 mm excursion; < 10 N force) protocol. After death of the dogs at 10, 21, or 42 days, specimens were evaluated for digital range of motion, tensile mechanical properties, elongation of the repair site, and adhesion formation. Our data indicate that the range of motion of digits whose tendons were at low or high excursion was similar to that of controls. Increased in vivo tendon excursion due to synergistic wrist motion did not significantly affect ex vivo flexion of the distal and proximal interphalangeal joints or tendon displacement (p > 0.05). Similarly, tensile properties (ultimate load, repair site rigidity, and repair site strain at 20 N and at failure) and length of the gap at the repair site were not significantly affected by increased excursion (p > 0.05). Severity of adhesion formation was reduced slightly by increased excursion (p = 0.04). Our findings indicate that 1.7 mm of tendon excursion is sufficient to prevent adhesion formation following sharp transection of the canine flexor tendon and that additional excursion provides little added benefit.

The effect of gap formation at the repair site on the strength and excursion of intrasynovial flexor tendons. An experimental study on the early stages of tendon-healing in dogs.

Elongation (gap formation) at the repair site has been associated with the formation of adhesions and a poor functional outcome after repair of flexor tendons. Our objectives were to evaluate the prevalence of gap formation in a clinically relevant canine model and to assess the effect of gap size on the range of motion of the digits and the mechanical properties of the tendons. We performed operative repairs after sharp transection of sixty-four flexor tendons in thirty-two adult dogs. Rehabilitation with passive motion was performed daily until the dogs were killed at ten, twenty-one, or forty-two days postoperatively. Eight tendons ruptured in vivo. In the fifty-six intact specimens, the change in the angles of the proximal and distal interphalangeal joints and the linear excursion of the flexor tendon were measured as a 1.5-newton force was applied to the tendon. The gap at the repair site was then measured, and the isolated tendons were tested to failure in tension. Twenty-nine tendons had a gap of less than one millimeter, twelve had a gap of one to three millimeters, and fifteen had a gap of more than three millimeters. Neither the time after the repair nor the size of the gap was found to have a significant effect on motion parameters (p > 0.05); however, the ultimate force, repair-site rigidity, and repair-site strain at twenty newtons were significantly affected by these parameters (p < 0.05). Testing of the tendons with a gap of three millimeters or less revealed that, compared with the ten-day specimens, the forty-two-day specimens failed at a significantly (90 percent) higher force (p < 0.01) and had a significantly (320 percent) increased rigidity (p < 0.01) and a significantly (60 percent) decreased strain at twenty newtons (p < 0.05). In contrast, the tensile properties of the tendons that had a gap of more than three millimeters did not change significantly with time. Our data indicate that, in a dog model involving sharp transection followed by repair, a gap at the repair site of more than three millimeters does not increase the prevalence of adhesions or impair the range of motion but does prevent the accrual of strength and stiffness that normally occurs with time.

Treatment of flexor tendon injuries: Surgeons' perspective

Medical researchers continue to explore the flexor tendon's response to injury and repair. In recent years, hand surgery and therapy publications have focused on the biomechanics of suture techniques and the benefits of early postoperative motion on surgically repaired flexor tendons. Laboratory and clinical studies have shown that stronger suture techniques can withstand the strain of immediate active motion without a significant risk of tendon rupture or gap formation. Newly proposed therapy techniques and anatomic studies defining the effects of wrist and digital position on tendon excursion share the goals of achieving early motion and reducing restrictive adhesions. Clinical studies have evaluated the various imaging modalities used to diagnose postoperative adhesions. Other clinical surveys have detailed the use of pedicled autograft and allograft tendons in staged reconstruction. Histologic and immunologic researchers have concentrated on cellular activation patterns following tendon injury and the effects of pharmacologic agents, such as hyaluronan and aprotinin, on tendon healing and adhesion formation.

Effects of tenorraphy on the gliding function and tensile properties of partially lacerated canine digital flexor tendons.

Management of a partially lacerated digital flexor tendon within zone II remains controversial. To address this issue, we undertook an evaluation of the impact of tenorrhaphy on the gliding function and tensile properties of canine flexor tendons with lacerations involving either 30% or 70% of their cross-sectional area. Assessment of tendon excursion and joint rotation after 6 weeks of postoperative controlled passive mobilization failed to reveal any statistically significant benefit from tenorrhaphy on the gliding function. In fact, we demonstrated a significant negative effect of repair on tendons with 30% lacerations. Moreover, no significant differences between the structural properties or integrity of the repaired and nonrepaired tendons could be demonstrated. Thus, in light of the inherent tensile properties in these partially lacerated tendons, our data suggest that digital function of partially lacerated tendons of up to 70% of the cross-sectional area may be preserved without primary repair. However, additional work is needed to more definitively address this issue in a clinical context.

Wrist and digital joint motion produce unique flexor tendon force and excursion in the canine forelimb

The force and excursion within the canine digital flexor tendons were measured during passive joint manipulations that simulate those used during rehabilitation after flexor tendon repair and during active muscle contraction, simulating the active rehabilitation protocol. Tendon force was measured using a small buckle placed upon the tendon while excursion was measured using a suture marker and video analysis method. Passive finger motion imposed with the wrist flexed resulted in dramatically lower tendon force (∼5 N) compared to passive motion imposed with the wrist extended (∼17 N). Lower excursions were seen at the level of the proximal interphalangeal joint with the wrist flexed (∼1.5 mm) while high excursion was observed when the wrist was extended or when synergistic finger and wrist motion were imposed (∼3.5 mm). Bivariate discriminant analysis of both force and excursion data revealed a natural clustering of the data into three general mechanical paradigms. With the wrist extended and with either one finger or four fingers manipulated, tendons experienced high loads of ∼1500 g and high excursions of ∼3.5 mm. In contrast, the same manipulations performed with the wrist flexed resulted in low tendon forces (4–8 N) and low tendon excursions of ∼1.5 mm. Synergistic wrist and finger manipulation provided the third paradigm where tendon force was relatively low (∼4 N) but excursion was as high as those seen in the groups which were manipulated with the wrist extended. Active muscle contraction produced a modest tendon excursion (∼1 mm) and high or low tendon force with the wrist extended or flexed, respectively. These data provide the basis for experimentally testable hypotheses with regard to the factors that most significantly affect functional recovery after digital flexor tendon injury and define the normal mechanical operating characteristics of these tendons.

Biomechanical evaluation of wrist motor tendons after fractures of the distal radius.

We conducted a biomechanical study of changes in parameters of wrist motor tendons in fractures of the distal radius in 7 cadaveric extremities. Extra-articular distal radius fractures were simulated by distal radius osteotomy and fracture angulation was maintained by external fixators. Eight positions of the distal radius fractures were studied: dorsal angulation of 10 degrees, 20 degrees, 30 degrees, and 40 degrees and radial angulation of 5 degrees, 10 degrees, 15 degrees, and 20 degrees. Dorsal and radial angulation of the fractures were measured with respect to the shaft of the radius. Excursions of 5 principal wrist motor tendons extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris were recorded simultaneously with wrist joint angulation using a computer-assisted recording system. Data were collected from intact wrists and from wrists with fractures at each of 8 positions of angulation during wrist flexion and extension and radical and ulnar deviation. Moment arm of the wrist motor tendons was derived from tendon excursion and joint angulation. The results demonstrated that excursions and moment arms of principal wrist motor tendons are significantly affected by dorsal and radial angulation of distal radius fractures. Amplitude of changes in moment arms increased as the deformities became more severe. Statistical analysis revealed that dorsal angulation of 10 degrees or more significantly affected moment arms of all the prime wrist motors. Dorsal angulation of 30 degrees or 40 degrees changed the moment arms greatly. Radial angulation of 5 degrees did not affect moment arms of the tendons and angulation over 10 degrees had a statistically significant effect on the tendons. We conclude that deformities of distal radius fractures have a significant influence on the biomechanics of the wrist motors.

In reply

There are many solutions to this problem, and we commend Dr Bunata's comments. Our thoughts are that a loop can be made too tight, as can a sutured tendon segment. Adhesions will probably prevent any significant excursion of tendon through the loop. The key to full tendon hood excursion includes having the repair graft perpendicular to the extensor tendon with the finger in midrange of motion. Following repair, the surgeon should pull on the extensor tendon and ensure full extension of all three joints. Additionally, he should check that full flexion occurs without lateral deviation of the extensor tendon. Suturing to or around the lateral band has the advantage of being less likely to restrict motion, but the disadvantage of a less secure purchase for maintaining a centralized extension tendon in full flexion. Proximal interphalangeal motion in our patients was normal.

The triangular fibrocartilage complex: An important component of the pulley for the ulnar wrist extensor

The extensor carpi ulnaris (ECU) tendon is the only wrist motor tendon that broadly connects with the triangular fibrocartilage complex (TFCC) of the wrist. The goal of this study was to determine the biomechanical effect of the TFCC on the function of the ECU. The effect of avulsion of the TFCC on the changes in mechanics of the ulnar wrist extensor tendon was investigated in 8 fresh-frozen cadaver forearms. Excursion of the ECU tendon was continuously recorded over the functional range of wrist extension and ulnar deviation in intact wrists, wrists with ulnar styloid fractures, wrists with TFCC release from the distal ulna, and after excising the distal ECU tendon sheath. The ECU tendon demonstrated a 30% increase in excursion during wrist extension after release of the TFCC from its attachment on the distal ulna. During 60 degrees of wrist extension, excursion of the ECU tendon was 4.8+/-1.9 mm in the intact wrists and 6.3+/-2.0 mm after TFCC release. This change in excursion represented 1.4 mm of bowstringing for the ECU tendon during 60 degrees of wrist extension. Further incision of the distal part of the extensor sheath produced only 6% increase in excursion of the ECU. Results of this study suggest that the TFCC is an important component of the pulley for the ulnar wrist extensor. These findings imply that disturbance of the wrist extensor after TFCC injury may potentially contribute to abnormal loading and force transmission through the ulnar wrist and the TFCC, and support the growing consensus that integrity of the TFCC should be restored in the presence of TFCC injuries.

The effect of fracture malunion at the mid-shaft of the metacarpal on the extrinsic muscle forces

Objective. To investigate the combined effect of dorsal angulation and shortening in metacarpal mid-shaft fracture malunions on the extrinsic flexion and extension muscle forces. Design. An experimental study on human cadavers. Background. Malunion of the metacarpal mid-shaft fractures are common sequelae and can result in angular deformities of the shaft, bone shortening, or as in most cases, a combination of both in several variations. The degree of the loss of function or efficiency depends on the extent of the malunion. This would also have a bearing as to whether surgical intervention is necessary. Methods. Experiments were performed on the second metacarpal in eight fresh normal cadaver hands. The extrinsic tendon forces to obtain full flexion and extension of the digit were measured at a fixed tendon excursion. The intact metacarpal was used as the experimental control. An oblique osteotomy was done on the mid-shaft of the metacarpal and combinations of bone shortening (0–5 mm) and dorsal angulation at the mid-shaft of the metacarpal (0–60 °) were simulated. The tendon forces were then measured again as a percentage of the control, given the same excursion. Results. The extension force was found to increase with increasing dorsal angulation and decrease with increasing bone shortening. While the flexion force decreased with increasing dorsal angulation and shortening. Dorsal angulation had a greater effect than bone shortening on the extension and flexion forces. Conclusion. Simulated malunion metacarpal fractures in human cadavers, has an effect on the efficiency of the measured extensor and flexor forces. In extension, dorsal angulation was found to increase the force required for the same amount of excursion. However, with added bone shortening, the extension force required decreased. This could be a compensatory mechanism in malunion metacarpal fractures. In flexion, a lower force was required with bone shortening and dorsal angulation for the same excursion.