Wrist kinematics after radiolunate arthrodesis.

INTRODUCTION: Analysis of carpal kinematics after radiolunate and radioscapholunate arthrodesis shows good preservation of midcarpal joint congruity and motion. However, no biomechanical data exist on carpal kinematics after radiolunate arthrodesis in the wrist. Purpose of this study was to examine the individual motion of scaphoid, capitate and triquetrum after simulated radiolunate arthrodesis. MATERIALS AND METHODS: Radiolunate arthrodesis was simulated in three fresh human cadaver wrists by means of Kirschner wires. Individual motion of the scaphoid, triquetrum and capitate relative to the radius was measured for extension/flexion and radial-ulnar deviation before and after arthrodesis. Photostereogrammetric measurement was carried out and the helical axis concept of motion was employed. RESULTS: Global wrist motion, corresponding to capitate motion, was found to be reduced 33-50 % for extension/flexion and 25-43 % for radial-ulnar deviation. Relative motion of the scaphoid for extension/flexion was found to be reduced 20 % more and for radial-ulnar deviation 10 % more than that of the capitate. Relative motion of the triquetrum for extension/flexion was found to be reduced 30 % more and for radial-ulnar deviation 20 % more than that of the capitate. The pattern of motion of the capitate hardly changed, and that of the scaphoid, only slightly. The triquetrum lost its rotational pattern of motion and gave way to tilting movements instead. The physiological function of the scaphoid between distal radius and distal carpal row was preserved. CONCLUSION: The presented data conform with the good clinical results obtained after radiolunate arthrodesis in the rheumatoid wrist and furthermore, encourage its use in the posttraumatic wrist.

Design aspects and clinical performance of the thrust plate hip prosthesis.

The thrust plate hip prosthesis (TPP) was conceived to maintain the physiological stress distribution in the proximal femur so as to prevent bone atrophy in this region, often encountered after implantation of conventional stem-type prostheses. A thrust plate of TiAlNb is firmly fixed to the neck of the femur by means of a forged CoCrMo bolt introduced through the lateral cortex, just below the greater trochanter, and through the metaphysis. A boss that contains the bolt head rests on the lateral cortex. A proximal extension from the thrust plate terminates in the ball head of the hip joint. Bone remodelling causes the initial prestressing of the structure (primary stability) to decline, but full integration of the thrust plate with the underlying host bone affords secondary stability. A total of 102 TPPs were implanted in the Cantonal Hospital, Chur, Switzerland, from 1992 to 1999 in 84 patients. The TPP was selected particularly for patients of the younger age group (26-76). Through its ability to load the medial cortex of the proximal femur in a physiological manner, the cortical bone in this region is preserved. The mean Harris hip score is 97 points and the survival rate 98 per cent, 144 months post-operatively.

Uncemented short-length diaphyseal segmental replacement prosthesis fixation--finite element analysis and long-term results.

INTRODUCTION: Extensively porous coated segmental replacement prostheses with intramedullary cementless fixation to bone over the whole length of stem often exhibit resorption of the surrounding bone due to stress-shielding. This makes them particularly susceptible to aseptic loosening. STUDY: A finite element analysis of the state of loading of a short-length fixation in a new prosthetic stem design has shown a definite advantage over long-length fixation. The stress pattern within the bone surrounding the prosthesis confirmed that shortening of the ongrowth area in length increases the stress values at the resection level significantly. This stem (Endlock) has been used for diaphyseal anchorage in the treatment of tumors in combination with an artificial joint of proven design in order to reduce stress shielding. RESULTS: No Endlock stem fractures or aseptic loosenings were observed at recent follow-up. The early clinical results comply with the theoretical assumptions. CONCLUSIONS: A short-length fixation system based on intramedullary anchorage of segmental replacement endoprostheses would possibly support physiologic adaptive processes more than fixation over the full length of the stem.

The self-locking Balgrist hip socket for cementless fixation: biomechanical principles and clinical results.

The Balgrist hip socket, initially made entirely of HDPE (high molecular weight polyethylene), now made of outer titanium alloy shell that faces the bone of the acetabulum has been in clinical use for 10 years. The purpose of this presentation is to illustrate the biomechanical principles that have governed this unique design and to present the clinical results that we have obtained until the end of 1991 with 717 implants. From 1982 to 1987 Balgrist HDPE sockets had been implanted for 346 hips, from 1984 to 1991 Balgrist Titanium alloy sockets have been implanted for 371 hips. The number of revision are 55 of 717 hips. 48 hips out of 55 were with Balgrist HDPE sockets. On the contrary, only 7 hips were with Balgrist titanium socket. The greatest benefit of Balgrist Titanium socket is the excellent mechanical lock with subchondral bone of the acetabulum.

Effect of selective capsulorrhaphy on the passive range of motion of the glenohumeral joint.

BACKGROUND: Capsulorrhaphy of the glenohumeral joint is a common surgical procedure for the treatment of instability caused by increased capsular laxity. The effect of capsulorrhaphy on the range of motion of the shoulder is poorly understood. METHODS: We simulated localized capsular contractures by selective capsular plications in eight human cadaveric shoulders and studied the effect of such plications on the passive range of glenohumeral abduction, flexion, and external and internal rotation in different degrees of abduction. A 0.5 or 1-N-m torque was applied to the humerus, and the range of glenohumeral motion was measured with electronic goniometers in three planes and compared with those of the intact shoulder. RESULTS: Anterosuperior capsular plication most markedly affected external rotation of the adducted arm, decreasing it by a mean of 30.1 degrees (p < 0.0001). Anteroinferior plication significantly reduced abduction by a mean of 19.4 degrees (p < 0.0001) and external rotation by a mean of 20.6 degrees (p = 0.0046). Posterosuperior plication mostly limited internal rotation of the adducted arm (mean decrease, 16.1 degrees, p = 0.0045). On the average, total anterior and total posterior plication each limited flexion by approximately 20 degrees (p = 0.005) and abduction by >or=15 degrees (p < 0.005), whereas total anterior plication limited external rotation by >30 degrees (p 20 degrees (p < 0.0001). Total inferior capsular plication restricted abduction (by a mean of 27.7 degrees, p = 0.0001), flexion, and rotation. Total superior plication restricted external rotation and flexion. CONCLUSIONS AND CLINICAL RELEVANCE: Localized plications of the glenohumeral joint capsule lead to predictable patterns of loss of glenohumeral mobility. If plication is planned, losses of movement can be anticipated. The findings of this study may assist surgeons in identifying the parts of the capsule that are contracted and that may need lengthening.

Friction between human finger flexor tendons and pulleys at high loads.

A method was developed to indirectly measure friction between the flexor tendons and pulleys of the middle and ring finger in vivo. An isokinetic movement device to determine maximum force of wrist flexion, interphalangeal joint flexion (rolling in and out) and isolated proximal interphalangeal (PIP) joint flexion was built. Eccentric and concentric maximum force of these three different movements where gliding of the flexor tendon sheath was involved differently (least in wrist flexion) was measured and compared. Fifty-one hands in 26 male subjects were evaluated. The greatest difference between eccentric and concentric maximum force (29.9%) was found in flexion of the PIP joint. Differences in the rolling in and out movement (26.8%) and in wrist flexion (14.5%) were significantly smaller. The force of friction between flexor tendons and pulleys can be determined by the greater difference between eccentric and concentric maximum force provided by the same muscles in overcoming an external force during flexion of the interphalangeal joints and suggests the presence of a non-muscular force, such as friction. It constitutes of 9% of the eccentric flexion force in the PIP joint and therefore questions the low friction hypothesis at high loads.

In vivo tendon force measurement of 2-week duration in sheep.

Tendon tension in vivo may be determined indirectly by measuring intratendinous pressure, by using a buckle transducer or by measuring the tendon strain. All of these methods require appropriate calibration, which is highly dependent on various variables. To measure the tendon load in vivo during a period of 2 weeks in sheep, a measurement technique has been developed using a force sensor interposed serially between the humeral head and the tendon end. Within a supporting frame, a flexion-sensitive force transducer is subjected to three-point bending stress. The load is transmitted by sutures from the tendon end through a hole in the sensor frame, orthogonal to the force transducer. In this configuration, the sensor measures the tensile force acting on the tendon, largely independent of the loading direction. The sensor was screwed to the humeral head and connected to the tendon end which was previously released from its insertion site along with a bone chip, using sutures. Connecting wires passed subcutaneously to a skin outlet about 30 cm away from the transducer. The sensor output was linear to the measured load up to 300 N, with maximum hysteresis of 18% full scale. All sensors worked in vivo without drift over a period of up to 14 days with no change in the calibration data. Forces up to 310 N have been recorded in vivo with daily tension measurements. This study shows that serial tendon tension measurement is feasible and allows for reliable, repeatable recording of the absolute tendon tension at the expense of tendon integrity.

The effects of morphology and histopathologic findings on the mobility of the sacroiliac joint.

The sacroiliac joints of seven pelvic specimens were examined to determine functional, morphologic, and histopathologic aspects. The movements were measured in four intact pelvises (from two men and two women). The joint surfaces of all pelvises (from three men and four women) then were examined topographically by means of a photogrammetric method. After this, they were examined histologically to characterize any effects on function. The morphologic investigation revealed sex-specific differences. All joint surfaces from the female pelvises showed circular contours, the centers of which coincided with the iliac tuberosities. These morphologic characteristics were not discernible in the joint surfaces from the male pelvises; these had interlocking irregularities without a topographic pattern. As expected, this configuration involved distinct differences in mobility. Rotation of the sacrum was markedly less in the sacroiliac joints of men than in those of women.

Forces acting in the forefoot during normal gait--an estimate.

OBJECTIVE: To estimate forces acting along tendons and across the joints of the first and second rays of the forefoot during gait. DESIGN: Using recently published data on force distribution under the forefoot and relevant anthropometrical data, internal forces are calculated. BACKGROUND: It is of paramount importance to know the magnitude and direction of the forces acting within the most heavily loaded structures of the forefoot, especially when surgical treatment is envisaged. It can also be of major value in understanding the pathomechanics of certain disorders of the foot. As far as the author is aware, there is no such information presently available. METHODS: The ground force distribution during the second force peak of the stance phase was used with anthropometrical data (including lengths of lever arms of the tendons that cross the joints investigated) to determine conditions of equilibrium in the sagittal plane for each joint of the first and second rays. RESULTS: The flexor hallucis longus and brevis tendons exert about 52% and 36% body weight, respectively, and the peroneus longus muscle more than 58% body weight. The resultant force on the first metatarsal head amounts to about 119% body weight. The second metatarsal bone is subjected to a high bending moment with a resultant force of about 45% body weight acting on its head. The flexor digitorum longus and brevis forces are about 9% and 13% body weight, respectively. CONCLUSIONS: The high forces acting along the flexor tendons of the heavily loaded first ray support the so-called longitudinal arch of the foot. The second metatarsal bone is also heavily loaded, but more in bending. If the first ray with its powerful toe be deprived of its function, be it through muscular fatigue, disease, or trauma, the second metatarsal bone will probably also fail. RELEVANCE: Such information is necessary to understand the physiological function of the foot. It might also explain the development and manifestation of certain foot pathologies. Furthermore, it is of importance when considering surgical procedures in the treatment of forefoot disorders.

Loosening of the femoral component of the ICLH double cup hip prosthesis. A biomechanical investigation with reference to clinical results.

The cancellous bone in the proximity of the rim of the ICLH femoral cup may not only be subjected to an axial stress that is about three times the value physiologically encountered, but the cup also tends to move transversally away from the medial bone margin in this area. Hence, fracture of the trabecular structure in this area can occur, accompanied by cleavage formation. Across the gap which thus forms between cement and bone, the mating surfaces that are now no longer joined, probably move relative to each other with every subsequent walking cycle. This relative motion leads to bone resorption and the development of a thick intermediate layer of fibrous connective tissue that spreads until eventually the whole cup becomes loosened. In the meantime the bone further proximal probably undergoes atrophy due to mechanical inactivity. This presentation includes a biomechanical analysis which might explain the discouraging observations made in a series of forty-three implantations carried out between 1976 and 1979 in our clinic.

Physical equilibrium of the normal wrist and its relation to clinically defined "instability".

The rotational stability of the proximal carpal row was tested on six unembalmed human cadaver hand specimens. The physiological load conditions were stimulated by loading the wrist flexor and extensor tendons. Pure torque was introduced to the lunate, scaphoid and triquetrum, one at a time, by means of a dynamometer wrench, forcing the bones loaded to perform a flexion-extension motion. A truly stable state of equilibrium could be found in the normal wrist only under axial load. A uni-directional coupling was observed through the scapho-lunate ligament as a counteraction to a tendency for the lunate to extend and the scaphoid to flex. The triquetrum and lunate moved together, showing close coupling in both directions. As conclusion: a stable wrist can be defined as one which, while being loaded within a physiological range of stress, does not deviate from a stable state of equilibrium (the ability to return to a single position when disturbed) at any point within the whole physiological range of motion.

Kinematic analysis of relative motion within the proximal carpal row.

The motions of the scaphoid and triquetrum relative to the lunate have been studied on cadaver specimens. The helical axis concept was applied. The wrist motions performed were flexion-extension and radial-ulnar deviation. The results showed increased relative motion of the scaphoid towards terminal extension, and to a lesser amount in the case of the triquetrum, towards terminal flexion. The lunate might be considered as a keystone in the proximal carpal row when wrist stability is considered. It is doubly intercalated: longitudinally and transversely. Wrist ligaments co-ordinate the positioning of the bones in the mid-range of carpal motions, and restrict further motion in extreme positions of the wrist joint.

Foot function after ray resection for malignant tumors of the phalanges and metatarsals.

Four patients with malignant tumors of the proximal toe phalanx who had closed contact or direct involvement of the metatarsophalangeal joints or direct infiltration of the metatarsal bone were treated. Treatment included ray resection and reconstruction either by free microvascular fibula transfer, intermetatarsal bony fusion, or soft-tissue stabilization. Foot function was analyzed by Novel pedobarography. The four patients with a follow-up between 21 months and 8 years show almost normal gait. All patients have remained relapse free. If adequate margins can be achieved, ray resection and appropriate reconstruction may be an alternative to amputation.

Reconstruction of the first and second metatarsals with free microvascular fibular bone graft after resection of a Ewing sarcoma.

We report the case of a 12-year-old girl with a Ewing sarcoma originating from the first metatarsal of one foot. Because the girl and her parents refused amputation of the foot, we resorted to complete local resection and to reconstruction of the first and second metatarsals with a free microvascular fibular bone graft. At 3 1/2 years after surgery, the patient continues to walk without a limp, and the mechanical function of the forefoot has been largely restored, although considerable loss of function of the big toe is apparent. Details of the surgical technique and tumor management are described.

[Could biomechanical factors affect the etiology of Morton's neuralgia?]. / Des facteurs biomécaniques peuvent-ils influencer la genèse de la névralgie de Morton?

In the literature mechanical factors are considered as the most frequent etiology of Morton's disease. The pathology is a classical progressive fibrosis with rupture of nerve "fascicules" and/of arterioli, without nerve proliferation and without specific inflammatory factors. The deep intermetatarsal ligament and the bursae between the metatarsal heads are probably the most important factors in nerve irritation. In the literature there are few precise descriptions of the mechanism of irritation of the nerve, either by the bursae between the metatarsal heads, by the deep intermetatarsal ligament, or by the tendons of the lumbrical muscles which are close to the nerve. The aim of this study is an analysis of the mobility of these structures in both planes, by radiological evaluation in the erect position, after implantation of radiopaque pellets. The authors also present an hypothesis on the mechanism of the lesion.

8-year survivorship analysis and subjective results of 687 primary Balgrist hip sockets.

The Balgrist hip socket consists of an outer split ring in the form of a truncated cone, made of titanium, which is expanded by a tapered HDPE insert during implantation, thus ensuring firm primary press-fit and the possibility of retightening in the postoperative remodelling phase. Between November 1987 and October 1996, 687 primary Balgrist hip sockets were implanted in 555 patients. Five hundred and thirty-seven patients were investigated. Of these patients, 71.1% never had pain in the operated hip, 88.1% had no problems putting on their shoes, 76.2% were able to walk one or more hours. Furthermore, 91.7% are very or mostly content with the postoperative result. Nineteen hip sockets had to be revised until April 1997. With a 92.1% Kaplan-Meier survivorship rate after 8 years the Balgrist hip socket ranks among the most successful noncemented acetabular components.

Long-term results with the uncemented thrust plate prosthesis (TPP).

The long-term clinical results of a novel concept for total joint replacement called the Thrust Plate Prosthesis (TPP) are presented. Only a restricted number of patients were provided with this new prosthesis (115 at the Orthopedic Department, Canton Hospital, Chur, and 47 at the Department of Orthopedic Surgery, University of Zurich). All patients have undergone clinical and radiological follow-up covering a period from 1980 to 1991. The basic feature of the Thrust Plate Prosthesis is the direct load transfer to the medial cortical bone of the femoral neck, and this has been unchanged since 1978. Titanium alloy has been used since 1986. The good clinical and radiological results are confirmed by a histological examination of an 8-year-old implant: In the crucial area of load transfer newly formed bone can be seen in direct contact with the thrust plate without fibrous tissue in between. The clinical results and histological findings have confirmed the validity of the biomechanical principle of the TPP. The TPP is therefore to be considered a true alternative to the conventional hip prosthesis. In contrast to the conventional intramedullary anchored stem prosthesis the TPP requires the removal of a minimum amount of bone stock, which is certainly important in young patients.

[Static anterior glenohumeral subluxation following coracoid bone block in combination with pectoralis major transfer: a case report and biomechanical considerations]. / Subluxation antérieure statique de l'épaule après butée pré-glénoïdienne et transfert du grand pectoral. A propos d'un cas et considérations biomécaniques.

We report the case of a patient who experienced post-traumatic static anterosuperior subluxation of the shoulder. The displacement worsened after surgical treatment associating a preglenoid bone block and pectoralis major transfer. We studied the lines of action of the conjoint tendon on an anatomic model. The biomechanical study demonstrated that alone, the coracoid bone block did not provoke the anterior glenohumeral subluxation. On the contrary, the compression components of the humeral head into the glenoid cavity increased and could not explain the worsening dislocation. Inversely, the tendon of the pectoralis major passed in front of the conjoint tendon because of the absence of the subscapularis and could have been the cause of the aggravated anterior subluxation.

The Balgrist hip socket for cementless fixation in primary total hip replacements and in acetabular revisions.

The results of 532 hip arthroplasties in which an uncemented Balgrist hip socket had been used in 387 primary total hip replacements and in 145 acetabular revisions were reviewed after a maximum of six years. The socket consists of two tapered parts, namely an expansive outer titanium-alloy split ring and an insert of polyethylene. The mean age of the patients at the time of operation was 54.3 years in primary hip replacements, and 64.7 years in acetabular revisions. Acetabular deficiency according to the AAOS classification was found in 21% of the primary arthroplasties, and in 80.7% of the acetabular revisions. Using Kaplan-Meier survivorship analysis, with the use of prosthesis revision as the endpoint of failure, the survival rate at five years was 99% in primary arthroplasties, and 88.7% in acetabular revisions. Our data suggest that the unique socket design of the Balgrist hip socket gives very satisfactory clinical results not only in primary hip replacements but also in acetabular revisions even with various acetabular defects.

The mobility of the sacroiliac joint in healthy subjects.

A three-dimensional stereophotogrammetric method is described for measuring the mobility of the sacroiliac joint, which was based on preliminary two-dimensional in vitro experiments. The investigations were carried out with intraosseous markers in 24 healthy volunteer male (15) and female (9) subjects having an age range of 20 to 50 years. Considerable intra- and inter-individual variability was found for both the measurements of rotation and translation. The position and direction of the movement axes showed wide variations, but a basic pattern could always be recognized. The average values for rotation and translation were low, being 1.8 degrees / 0.7 mm for the males and 1.9 degrees / 0.9 mm for the females. No statistically significant differences could be demonstrated with respect to either sex or age. On the basis of the measurement results, it is postulated that there is pathological sacroiliac joint movement when rotation is more than 6 degrees and translation more than 2 mm. This increased mobility seems to be of greater clinical significance than reduced mobility.