A comparison of scaphoid-trapezium-trapezoid fusion and four-bone tendon weave for scapholunate dissociation

Load transmission characteristics of limited carpal fusions: a two-dimensional finite element study

Although limited carpal fusion is a choice of treatment in several wrist disorders, little is known about the biomechanics of these procedures, especially the loads carried by the ligaments. In a finite element study, four types of limited carpal fusions (scaphotrapeziotrapezoid, capitohamate, four corner fusion with and without scaphoid excision) were simulated and the loads carried by the ligaments were recorded. Measurements were repeated with and without implantation. The load transmission through the ligaments varied by the type of the fusion but, radioscaphoid and long radiolunate ligaments carried significantly more loads if not excised during the operation. Implantation did not affect the results in most cases. The model of the present study may be useful in preoperative planning.

A carpal ligament substitute part II: polyester suture for scapho-lunate and triqueto-lunate ligament reconstruction

Carpal ligaments are commonly injured and may lead to pain and disability. These ligaments are very difficult to repair, and the results are unpredictable; as a result, treatment options abound. A novel approach is presented here using a polyester suture, aiming to substitute these ligaments' function, rather than to repair them.

HERBERT SCREW FIXATION FOR THE TREATMENT OF SCAPHOLUNATE LIGAMENT RUPTURE

Complete rupture of the scapholunate ligament was treated by open reduction, ligament repair and internal splintage with a Herbert bone screw. After an average of 12 months, the screw was removed to allow full loading of the repair. In 33 procedures, there were 22 good and 11 poor results. In five cases with a poor outcome, the screw pulled or fractured out of the scaphoid or lunate. Grip and range of wrist motion improved in patients with a good outcome, and repair of the ligament was noted at all revision and open screw removal surgeries. A comparison of the good and poor results leads us to recommend this technique for patients with relatively recent injuries and light to moderate activity levels. Longstanding injuries and heavy occupational wrist loading led to poorer results.

Radiographic evaluation of the modified Brunelli technique versus the Blatt capsulodesis for scapholunate dissociation in a cadaver model

PURPOSE

A variety of soft tissue surgical procedures have been developed for treatment of scapholunate (SL) dissociation. The purpose of this study was to compare the degree of correction obtained (as measured on preoperative and postoperative radiographs) when performing the modified Brunelli technique (MBT) with that of the more commonly performed Blatt capsulodesis (BC) and to evaluate each technique after simulated wrist motion.

METHODS

Five cadaver wrists were used for this study. The SL interval, SL angle, and radiolunate angle were recorded radiographically, with the SL ligament intact, for each wrist in several loaded positions: neutral, flexion, extension, radial deviation, ulnar deviation, and clenched fist. The SL interosseous ligament was then completely incised, and the radiographic measurements were repeated to demonstrate SL instability. The radiographic measurements were then repeated after MBT reconstruction and after BC reconstruction. Additional radiographic measurements were taken after simulated wrist motion.

RESULTS

Sectioning of the SL ligament resulted in radiographic evidence of SL dissociation. Use of the MBT demonstrated improved correction of the SL interval and the SL angle in the clenched fist position, which was statistically significant when compared with BC. The correction for the SL angle was maintained on the MBT specimens with simulated wrist motion.

CONCLUSIONS

The results demonstrate that in this cadaver model, the MBT better restores the normal carpal relationship of the SL interval and SL angle when compared to the BC, as measured on radiographs. This correction might correlate with improved carpal dynamics and improved clinical outcomes.

Distal tunnel placement improves scaphoid flexion with the Brunelli tenodesis procedure for scapholunate dissociation

PURPOSE

Treatment of scapholunate dissociation remains difficult. The modified Brunelli procedure, a flexor carpi radialis tenodesis through the scaphoid and secured with dorsal wrist ligaments, has shown promising results. This study compares the biomechanical effects on scaphoid flexion and scapholunate gap between proximal and distal tunnel placement in the modified Brunelli procedure.

METHODS

Eight fresh-frozen cadaveric forearms were used. A dorsal approach to the wrist through the floor of the fourth compartment was used. Metallic markers were implanted into the scaphoid and lunate. Tunnels were drilled through the proximal and distal poles of the scaphoid. Wrists were positioned in neutral and loaded to 100 N through the wrist flexor and extensor tendons. Posteroanterior and lateral radiographs were taken with the scapholunate interval intact, with the scapholunate interval sectioned, and after the modified Brunelli tenodesis was performed through the proximal and then distal tunnels using Mersilene tape. Radiographs were analyzed for change in scapholunate angle and scapholunate gap. Multivariate analysis of variance was performed to assess statistical significance for each state compared with the intact wrist.

RESULTS

In the intact wrist, the mean scapholunate gap was 1.6 mm +/- 0.1. With the scapholunate interval sectioned, the scapholunate angle increased by 26 degrees +/- 12 and gap increased to 4.2 mm +/- 1.2. With a proximal tunnel for the modified Brunelli procedure, the change in scapholunate angle decreased to 15 degrees +/- 10 and gap decreased to 1.8 mm +/- 0.3. With a distal tunnel for the modified Brunelli procedure, the change in scapholunate angle decreased to 4 degrees +/- 7 and gap decreased to 1.3 mm +/- 0.2.

CONCLUSIONS

These biomechanical data suggest that a tunnel exiting in the distal pole of the scaphoid results in better correction of scaphoid flexion when performing the modified Brunelli procedure.

Bone-tissue-bone repairs for scapholunate dissociation

Scapholunate dissociation is a commonly seen and treated form of carpal instability. Several surgical options have been used for the repair of scapholunate instability over the past 50 years. These have included benign neglect, reduction and percutaneous pinning, primary repair, partial fusions, tendon weaves, and combinations of these. Recent advancements in scapholunate repair and anatomy have been aimed at a more physiologic repair. Composite replacement of the entire scapholunate interval, similar to other tendon repairs seen in orthopedic surgery, has become popular. Bone-tissue-bone (BTB) autograft replacement from the foot has been used but the problems of a secondary surgical site have resulted in other graft site selections. Currently more commonly used grafts are bone-retinaculum-bone, third or second metacarpal-carpal bone, or hamate-capitate grafts, all performed with or without screw augmentation. Vascularized autograft replacement on pedicled grafts from the hand is being explored. This review discusses the surgeons' indications and technical details of the surgery. The lack of long-term outcome measurements for these BTB surgeries makes it difficult for the hand surgeon to determine the appropriate use of these treatment modalities, but early reports have indicated that the BTB graft will be an important part of scapholunate dissociation treatment.

A vascularized technique for bone-tissue-bone repair in scapholunate dissociation

Several surgical options have been used for the repair of scapholunate instability over the last 50 years. The many options have included neglect, reduction with percutaneous pinning, primary repair, partial fusions, tendon weaves, and others. Recent advancements in scapholunate repair and anatomy have been aimed at a more physiological repair. Composite replacement of the entire scapholunate interval similar to other tendon repairs seen in orthopedic surgery has become popular. Currently, more common hand-based grafts are bone-retinaculum-bone, third or second metacarpal-carpal bone or hamate-capitate grafts. There still exist some failures in the outcome after any of these procedures. This technique demonstrates the use of a vascularized autograft replacement on a pedicled graft. This procedure is the natural extension of the third or second metacarpal-carpal bone autograft, previously reported in the literature. The use of this proven graft, with a pedicle based on the intermetacarpal artery, may avoid some of the late complications seen with other autografts.

Scaphotrapeziotrapezoid arthrodesis for arthritis

The main indications for scaphotrapeziotrapezoid (STT) fusion are STT arthritis, rotary subluxation of the scaphoid, and Kienbock disease. The results of this procedure in the literature for each indication are discussed, as are the advantages, disadvantages,and alternative procedures. This article discusses the authors' surgical technique and results. The authors believe this procedure is a viable one in specific clinical scenarios.

The biomechanical effect of radial shortening on the radiocapitellar articulation

Repeated trauma to the radial head may be one of the causative factors in the genesis of osteochondritis dissecans of the capitellum. We measured the force, contact area and pressure across the radiocapitellar articulation of the elbow before and after radial shortening osteotomy in five fresh-frozen cadaver upper limbs with loads of 45, 90 and 135 N, respectively. Measurements were made on pressure-sensitive film placed in the radiocapitellar articulation with the forearm in the supinated, neutral and pronated positions before and after radial shortening. Radial shortening significantly reduced the mean force and contact area across the radiocapitellar articulation in all positions of the forearm.

A survey of the surgical management of acute and chronic scapholunate instability

PURPOSE

Scapholunate instability is a challenging problem and controversy persists among hand surgeons with respect to treatment choice. The purpose of this study was to evaluate the pattern of practice among specialized hand surgeons in the management of both acute and chronic scapholunate instability.

METHODS

A mailed survey study was sent to the 1,628 members of the American and Canadian Societies for Surgery of the Hand. Hand surgeons were asked to complete a comprehensive management questionnaire that examined a surgeon's treatment algorithm in the clinical case of acute and chronic scapholunate instability. The algorithm included the choices of further investigation, timing of surgery, surgical approach, surgical procedure, fixation, and predicted outcome.

RESULTS

Of the 468 hand surgeons who responded to the survey the vast majority elected to perform surgery when confronted with a case of scapholunate instability. Early surgical intervention within 6 weeks of injury using an open dorsal approach was favored in both acute and chronic cases. The preferred surgical procedure in the acute case was scapholunate repair combined with a capsulodesis followed by scapholunate ligament repair alone. Favored management of the chronic case included Blatt capsulodesis alone, capsulodesis combined with a scapholunate ligament repair, or scaphotrapezium-trapezoid arthrodesis. A majority of surgeons used K-wire fixation, especially of the scapholunate and scaphocapitate in both acute and chronic cases.

CONCLUSIONS

This survey confirms a consensus for the early soft tissue surgical management of acute scapholunate instability using a scapholunate ligament repair with or without a capsulodesis. The management of chronic scapholunate instability is highly variable among respondents and the choice of either a soft tissue or bony procedure may depend to a large extent on intraoperative findings.

Remodeling of articular defects in an animal model

When treating displaced intraarticular fractures, the goal has been to restore normal articular cartilage contour to decrease local contact stresses that may lead to the development of posttraumatic osteoarthritis. To confirm observations that articular cartilage step-offs can remodel with time and to determine how the articular surface and subchondral bone remodels after an intraarticular fracture, joint surface changes were examined in a weightbearing sheep model with an intraarticular fracture. Articular surface pressure changes were observed across a 1-mm osteotomy. Twelve weeks after an intraarticular osteotomy, there was a decrease in differential pressure distribution between the normal articular cartilage and the depressed articular surface. Histologic analysis showed thinning of the articular cartilage on the high side of the osteotomy with collagen compression and bending of the collagen fibrils. On the low side of the osteotomy, increased chondrocyte cellularity and hypertrophy were observed. In addition, bending of collagen fibrils was observed in an unloaded state in an attempt to form a smooth overlapping shelf at the osteotomy site. Because intraarticular incongruency, with resultant joint contact pressure differences, seems to be involved in the development of posttraumatic arthritis, methods to improve cartilage remodeling may improve outcome after intraarticular fractures.

Scaphotrapeziotrapezoid fusion: long-term follow-up study

The long-term effectiveness of scaphotrapeziotrapezoid (STT) fusion is still controversial. We evaluated our clinical and radiological results of 30 STT fusions in 30 patients (average age 41 years; 23 males, 7 females). The follow-up period averaged 84 months. The indications were Kienböck's disease ( n= 23), isolated STT arthrosis ( n = 6), and dislocation of the trapezium ( n = 1). A total of 26 simultaneous associated procedures were performed. Excisional arthroplasty of the lunate was done in all 23 patients with Kienböck's disease. Of the 30 total patients, 5 had postoperative pain ranging from mild to severe; 4 patients were dissatisfied with the results. Postoperative ranges of motion of the wrist were 84% of extension and 91% of flexion compared with preoperative motion. The postoperative grip strength improved to 27 kgf from the preoperative value of 18 kgf. Altogether, 26 patients returned to their previous activities. All patients obtained uneventful STT fusion in an average of 11.2 weeks. Eight patients (27%) experienced postoperative complications; seven had radioscaphoid arthroses, five had trapeziometacarpal arthrodeses, and one had a flexor pollicis longus tendon rupture. Although radioscaphoid arthrosis occurred in 23% of this series after STT fusion, the results suggest that it is an effective procedure for Kienböck's disease and isolated STT arthrosis.

Scaphotrapeziotrapezoid arthrodesis: a follow-up study

PURPOSE

The purpose of this study was to review the results of 800 scaphotrapeziotrapezoid fusions performed over a 27-year period.

METHODS

The patients were evaluated for postoperative range of motion, grip and pinch strength, pain, return to work, arthritis, and complications.

RESULTS

The overall range of motion was 70% to 80% of the nonoperated side and strength was 69% to 89%. Of the patients 88% returned to previous employment. Arthritis developed in 1.8% of the patients. The overall complication rate was 13.4%.

CONCLUSIONS

Scaphotrapeziotrapezoid fusion is a viable treatment option especially for a high-functional-demand young population with significant wrist pathology. Complications, specifically nonunion, can be minimized with careful technique.

Static scapholunate dissociation: a new reconstruction technique using a volar and dorsal approach in a cadaver model

We used 4 fresh-frozen cadaver arms to assess a method of reconstruction we designed for static scapholunate dissociation. The dorsal scapholunate ligament, scapholunate interosseous ligament, radioscapholunate, and radioscaphocapitate ligaments were sectioned. Radiographs were taken before sectioning, after sectioning, and after reconstruction. Passive motion was also measured before sectioning and after the repair. The dorsal scapholunate ligament was repaired directly; the palmar radioscapholunate and radioscaphocapitate ligaments were reconstructed using a free flexor carpi radialis tendon autograft and Mitek mini suture anchors (1.8-mm diameter and 5.4-mm length; Mitek Products, Norwood, MA) for anatomic fixation. An independent board-certified hand surgeon analyzed the radiographs of the wrists taken before and after sectioning and after reconstruction. Assessment of the unsectioned wrists revealed an average scapholunate angle of 45 degrees. After scapholunate dissociation was created the average scapholunate angle was 71 degrees. Repair of the dorsal scapholunate ligament alone did not improve the scapholunate angle. Average scapholunate angle after repair of the dorsal scapholunate ligament and reconstruction of the palmar ligaments was 43 degrees. Average range of motion on flexion, extension, and radial and ulnar deviation before ligament sectioning and after reconstruction was unchanged at 54 degrees, 59 degrees, 19 degrees, and 40 degrees respectively. This technique shows an improvement in scapholunate angle on lateral radiographs, and passive motion remained relatively unchanged.

A preliminary study of joint surface changes after an intraarticular fracture: a sheep model of a tibia fracture with weight bearing after internal fixation

OBJECTIVE

To evaluate the changes in the articular cartilage and subchondral bone after an osteotomy designed to simulate an articular fracture.

DESIGN

The contribution of the cartilage and subchondral bone was evaluated twelve weeks after creating a 1.0-millimeter step-off in the medial plateau of the tibia of twelve adult domestic sheep. All animals surviving were labeled with fluorescent markers for bone production, oxytetracycline (fifty milligrams per kilogram), and calcein (twelve milligrams per kilogram) nine and 11.5 weeks after surgery. The knees were loaded in compression using an Instron materials tester with pressure-sensitive film to record joint contact pressures above and below the medial meniscus.

SETTING

The studies were performed in the research laboratories of the Orthopaedic Laboratory at Harborview Medical Center in Seattle, Washington and the Madigan Army Medical Center in Tacoma, Washington.

ANIMALS

Twelve adult domestic sheep.

INTERVENTION

An intraarticular osteotomy of the medial tibial plateau with 1.0 millimeter of displacement was performed. The osteotomy was stabilized with 3.5-millimeter lag screws.

MAIN OUTCOME MEASURES

The contact pressures of the knee joint and articular histology were evaluated twelve weeks after surgery. Samples of the articular cartilage were analyzed by light microscopy and electron microscopy to evaluate the response of the articular cartilage and subchondral bone of the differential joint loading because of the irregularity in the articular surface caused by the osteotomy.

RESULTS

The knees with an intraarticular step-off had two major contact areas with an intervening zone of reduced load corresponding to the edge of the depressed fragment. Coronal histologic sections through the articular surface showed the presence of thinning and fibrillation on the high side of the step-off and some compensatory hypertrophy of the cartilage. The subchondral bone was not responsible for restoring articular congruity because the rate of bone production was similar between the low side of the articular fracture (1.85 micrometers per day) and the high side of the fracture (1.67 micrometers per day). Scanning electron microscopy showed partial cartilage remodeling by deformation of the high side cartilage with bending of the vertical collagen fibrils, even in the unloaded state.

CONCLUSIONS

In this model with a small fracture displacement (1.0 millimeter), which was less than the thickness of the articular cartilage (1.5 millimeters), the contour of the joint improved despite residual articular surface incongruency after the fracture healing.

What is the Ideal Replacement for the Scapholunate Ligament in a Chronic Dissociation?

An ideal replacement for the scapholunate ligament has not been found. The carpometacarpal bone-ligament-bone complex at the base of the third metacarpal can be used as a replacement for the scapholunate ligament. A cadaveric study of matched scapholunate ligament and third metacarpal-capitate was carried out. Data for stiffness and strength were obtained from fresh frozen specimens tested to failure with a hydraulic distractor. The third metacarpal-scaphoid ligament most closely approximated the stiffness and the strength of the scapholunate ligament. Operative replacement of the scapholunate ligament with the third metacarpal-scaphoid replacement was accomplished. Clinically, the performance of the operation is facile and, in the present study, was not associated with increased morbidity or duration of surgery compared with other options.

This study indicates that the third carpometacarpal ligament approximates the mechanical properties of the scapholunate ligament and is a good alternative for replacement surgery.

Constraint and material properties of the subregions of the scapholunate interosseous ligament

The material and constraint properties of the dorsal, proximal, and palmar regions of the scapholunate ligament were studied using isolated bone-ligament-bone preparations from 24 adult intact cadaver wrists. Determinations of constraint to differential rotation and translation as well as failure strength were made using a servohydraulic testing machine incorporating an additional rotatory actuator. The dorsal region of the scapholunate ligament offered the greatest constraint to differential translation, while both the dorsal and palmar regions demonstrated statistically significant combined constraints to differential rotation between the scaphoid and lunate. The greatest yield strength was found in the dorsal region (260.3 N +/- 118.1 N), followed by the palmar region (117.9 N +/- 21.3 N) and the proximal region (62.7 N +/- 32.2 N).

Autograft replacements for the scapholunate ligament: a biomechanical comparison of hand-based autografts

An ideal replacement for the scapholunate ligament (SLL) has not been found. The carpometacarpal bone-ligament-bone complex at the base of the second and third metacarpal is proposed as a replacement for the SLL in this study. A cadaveric study of matched SLL, second metacarpal-trapezoid ligament, third metacarpal-capitate ligament, and dorsal periosteal retinaculum was performed. Stiffness and strength were obtained from fresh-frozen specimens tested to failure with a hydraulic distractor. The second metacarpal-trapezoid ligament and the third metacarpal-capitate ligament most closely approximated the stiffness and strength of the SLL. The dorsal periosteal retinaculum was significantly less stiff and was significantly weaker than the SLL. This study indicates that the second or third carpometacarpal ligaments are grafts that approximate the mechanical properties of the SLL.

Tarsal autografts for reconstruction of the scapholunate interosseous ligament: a biomechanical study

A biomechanical cadaver study was performed to identify a potential bone-ligament-bone autograft from the foot for reconstruction of the scapholunate interosseous ligament (SLIL). In this study the biomechanical properties of 9 dorsal tarsal ligaments and the anterior tibiofibular ligament were investigated and compared with those of the dorsal part of the SLIL. Fifteen fresh-frozen human cadaver feet and 14 fresh-frozen human cadaver wrists were used. In a Monsanto Tensometer testing apparatus (Monsanto Limited Instruments, Dorean Swindon, England) the complexes were uniaxially elongated at a constant velocity of 6.35 mm/min until rupture occurred. The stiffness and strength values for each tarsal ligament were calculated and compared with those of the dorsal part of the SL ligament. Analysis indicated that the third dorsal tarsometatarsal ligament (143 +/- 42 N) and the dorsal calcaneocuboid ligament (149 +/- 41 N) were comparable to the dorsal part of the SL ligament (141 +/- 20 N) while all other ligaments were stronger. The stiffness values of the third dorsal tarsometatarsal ligament (67 +/- 17 N/mm) and the dorsal calcaneocuboid ligament (55 +/- 14 N/mm) were comparable to the dorsal part of the SL ligament (61 +/- 6 N/mm). All the other ligaments had values that were higher than the dorsal part of the SL ligament. The strongest ligament appeared to be the medial dorsal cuneonavicular ligament (479 +/- 65 N), which had a stiffness value of 127 +/- 19 N/mm. Although the third dorsal tarsometatarsal ligament and the dorsal calcaneocuboid ligament are biomechanically most similar to the dorsal part of the SLIL, at present it is unclear how strength and stiffness values of ligaments are sustained following transplantation. From this selection of tarsal ligaments, the medial dorsal cuneonavicular ligament is the strongest ligament and it is therefore concluded that this ligament is the most suitable ligament to be used as an autograft for reconstruction of the SLIL.

Support of the talus: a biomechanical investigation of the contributions of the talonavicular and talocalcaneal joints, and the superomedial calcaneonavicular ligament

The goal of this study was to determine the magnitude of force transmission to the talus by its inferior articulations to provide insight into mechanisms involving acquired deformities of the hindfoot. Cadaver feet were mounted in a loading apparatus that applied axial force through the tibia and fibula as well as tensile loading of the tendons of extrinsic musculature. This also permitted positioning of the tibia in the sagittal plane. Eighteen specimens were tested in three selected positions of the gait cycle. In one series, pressure-sensitive film was inserted into the posterior and anteromedial facets of the talocalcaneal joint as well as into the talonavicular joint. In a second series, film was inserted between the talar head and the superomedial calcaneonavicular ligament. In stance position, the specimens were also tested without posterior tibial tendon (PTT) tension. Contact areas and force transmitted across the articulations were greatest in near toe-off position, in the posterior facet of the talocalcaneal joint. The talonavicular joint, the anteromedial facet of the talocalcaneal joint, and the calcaneonavicular ligament articulation showed sequentially decreasing amounts of contact area and force transmission. Mean pressures were similar across all articulations, except in the posterior facet in near toe-off position. From heel-strike to stance, to near toe-off, a trend to increasing contact area and force was noted. No difference in contact characteristics was found in the calcaneonavicular ligament articulation after PTT release. The contact force of the calcaneonavicular ligament against the talus was found to be much smaller than those of other talar articulations; however, its medially oriented direction must contribute to stabilization of the head of the talus against medial displacement. Loss of PTT tension was not found to alter the contact forces acting at the talar head in this model, which might indicate that it shares its talar stabilizing function with other structures.

Two reconstructive techniques for flatfoot deformity comparing contact characteristics of the hindfoot joints

The effect of two different methods of reconstruction of flatfoot deformity and the role of the posterior tibial tendon on the contact characteristics of the hindfoot joints were quantified using pressure-sensitive film. Each of 10 cadaver feet was loaded quasi-statically by an axial compressive force to simulate varying loads. First, a specimen was tested intact, then it was tested after sectioning the spring ligament and loading the specimen cyclically to create one type of flatfoot deformity. It was then tested again after reconstructing the deformity. Reconstructions used were the Dillwyn-Evans procedure (bone graft in osteotomy of the calcaneus) or the calcaneocuboid distraction arthrodesis (CCDA). We found that surgically produced flatfoot deformity altered mainly the talonavicular joint, by decreasing its contact area. The Dillwyn-Evans method had less effect on the talonavicular joint (altering 2 of 6 measured parameters) than the CCDA (3 of 6) and more effect on the anteriomedial facet (altering 3 of 6 parameters) than the CCDA (1 of 6). The Dillwyn-Evans method had more effect on the posterior facet (altering 2 of 6 measured parameters) than the CCDA (1 of 6). Function of the posterior tibial tendon had no effect on contact characteristics of the hindfoot joints after either type of reconstruction. These findings are based on measurements using a quasi-statically-loaded foot model at three selected positions, and results may be different with dynamic loading.

Isolated scaphotrapeziotrapezoid osteoarthritis: a possible radiographic marker of chronic scapholunate ligament disruption

This study was undertaken to describe 'isolated' osteoarthritis of the scaphotrapeziotrapezoid articulation in six patients with chronic scapholunate ligament disruption. Each patient included for study had scapholunate ligament disruption with secondary dorsal intercalated segmental instability. Secondary volar tilt of the scaphoid appeared to be limited in each case by impaction and development of osteoarthritis at the scaphotrapeziotrapezoid articulation. Isolated osteoarthritis at the scaphotrapeziotrapezoid articulation may accompany chronic scapholunate ligament disruption, its identification should trigger a search for associated scapholunate ligament disruption in the absence of a known systemic arthropathy.

Biomechanical analysis of capitate shortening with capitate hamate fusion in the treatment of Kienböck's disease

The biomechanical effects of surgical treatment options for Kienböck's disease have been compared. However, no study has included a direct analysis of capitate shortening along with capitate-hamate fusion (CSCHF). To investigate the biomechanical effects of CSCHF, a cadaver model of the upper extremity was used to determine radiocarpal articular pressure changes resulting from this procedure using pressure-sensitive film. Ten specimens were tested by placing each in an apparatus that applied load across the radiocarpal joint through the wrist flexor and extensor tendons. Testing was performed in 3 wrist positions (ulnar deviation, radial deviation, and neutral) combined with 3 forearm positions (pronation, supination, and neutral) and neutral flexion/extension. Radioscaphoid, radiolunate, and mean contact pressures in the entire radiocarpal joint were determined for each of the 9 wrist positions, both intact and after surgery. The radioscaphoid mean pressure increased in 6 of 9 positions and was unchanged in 3 positions. The radiolunate mean pressure decreased in 9 of 9 positions. The radiocarpal mean pressure increased in 2 of 9 positions and was unchanged in 7 positions. These data suggests that CSCHF increases radioscaphoid mean pressure, decreases radiolunate mean pressure, and has little effect on radiocarpal mean pressure.

Wrist joint motion simulator

A computer controlled wrist joint motion simulator has been developed that actively moves forearms from cadavers through cyclic planar flexion-extension motions, planar radial-ulnar deviation motions, and combined motions such as circumduction. Hybrid position-force feedback control algorithms are used to determine the wrist flexor and extensor tendon forces necessary to achieve the desired motions. The simulator was used in a series of 12 fresh cadaver forearms to produce both flexion-extension and radial-ulnar deviation motions and was found to cause repeatable, physiological movements. In these experiments, the extensor tendon forces were greater than those of the flexors, typically by a factor of two.

Effects of intra-articular distal radius depression on wrist joint contact characteristics

Twelve cadaver extremities were used to study the effect of scaphoid and lunate facet depressions on the contact characteristics of the radiocarpal joint. Pressure-sensitive film was inserted into radiocarpal joints with varying degrees of depression, and the specimens were loaded statically in neutral position, radial deviation, and ulnar deviation. The film was removed and analyzed for contact area and pressure. The only statistically significant effect of a lunate fossa depression was an increase in scaphoid fossa pressure with a 3-mm step-off and the hand in neutral position. Scaphoid fossa depression had more significant effects. With a 1-mm scaphoid fossa depression, lunate fossa pressures increased in neutral position and in radial deviation. Lunate fossa contact area increased, compared to intact joints, in ulnar and radial deviation with 1-mm scaphoid fossa depressions and in all loading positions with 3-mm scaphoid fossa depression. Therefore, it appears that the most significant effect on radiocarpal joint contact characteristics occurs with a depression of the scaphoid side of the joint. Even with depressions as small as 1 mm, significant changes on the lunate side of the joint were observed.

Tibiotalar contact area and pressure distribution: the effect of mortise widening and syndesmosis fixation

An unconstrained cadaver ankle model was designed to reevaluate the effect of ankle mortise widening and syndesmotic fixation on the load-bearing characteristics of the tibiotalar joint. Tibiotalar contact area, centroid shift, and mean contact pressure were quantified using a pressure-sensitive film technique. Six fresh-frozen below-knee amputation specimens were axially loaded with 500 N in three positions: neutral, 10 degrees of dorsiflexion, and 20 degrees of plantarflexion. The tibiotalar contact area and centroid position for each specimen in its intact state were first determined and then compared with values obtained after syndesmotic fixation, mortise widening of 2 and 4 mm, and deep deltoid ligament transection. Syndesmotic fixation significantly decreased joint contact area but did not consistently affect centroid position. However, unlike earlier studies, which used more constrained ankle fracture models, mortise widening with or without deltoid rupture was not found to significantly affect contact area, centroid position, or joint contact pressure. When statically loaded, the talus moved to its position of maximal congruence in the mortise, rather than displacing laterally along with the lateral malleolus.

The scapholunate allograft: a biomechanical feasibility study

The feasibility of a new method for reconstruction of the isolated scapholunate ligament tear with a scapholunate allograft was studied biomechanically using a fresh cadaver upper extremity model. Seven specimens were first tested intact for wrist range of motion, contact characteristics of the radiocarpal articulation, and relative motion of the scaphoid with respect to the lunate. Then a segment consisting of the radial third of the lunate, the adjoining scapholunate interosseus ligament, and the proximal pole of the scaphoid was resected. This segment was matched to a donor allograft of similar size and geometry, which was then placed into the recipient carpus and secured with one central transverse Kirschner wire and two shorter interfragmentary Kirschner wires placed into the lunate and scaphoid. The allografted specimen was subjected to the same tests as the intact wrist. Results showed that there were no significant differences in wrist range of motion, radiocarpal articular surface contact area and pressure, and relative flexion-extension rotation between the scaphoid and lunate during passive radioulnar deviation between the intact and allografted wrists.

Contact areas and pressure distributions in the subtalar joint

We investigated how foot position and ankle arthrodesis affect the contact characteristics of the subtalar joint. Nine fresh-frozen specimens of amputated lower legs were used. Pressure-sensitive films were inserted into the anterior and posterior articulation of the subtalar joint. The contact areas and pressure for various foot positions and under axial loads of 600, 1200, and 1800 N were determined based on the gray level of the digitized film. In neutral position and under a 600 N load, the maximum contact pressure in the subtalar joint was 5.13 +/- 1.16 MPa. The contact area (1.18 +/- 0.35 cm2) was only 12.7% of the whole subtalar articulation area (9.31 +/- 0.66 cm2), and the total force (348.5 +/- 41.7 N) transmitted via this contact area was about 58% of the applied load (600 N). Dorsiflexion of the foot increased the contact area and the force transmitted, but decreased the average contact pressure in the subtalar joint, while the reverse occurred in plantar flexion. Eversion increased the subtalar contact stress, whereas inversion up to 10 degrees decreased it. Ankle joint arthrodesis shifted the contact areas in the subtalar joint posteriorly in all inversion/eversion positions. Moreover, total force transmitted through the subtalar joint as well as the contact pressure increased.

Tensions in the palmar ligaments of the wrist. I. The normal wrist

We developed a method for measurement of the in situ tensions in the ligaments of the palmar side of the wrist in cadaver specimens. The technique is based on deflecting the ligaments transversely (i.e., perpendicular to their longitudinal axis) using an instrumented probe. Based on measurement of the load required to deflect the ligament, magnitude of the transverse deflection, and axial length of the ligament, the axial tension in the ligament can be determined without otherwise disturbing it. The tensions in 8 palmar ligaments in 10 functional positions of the wrist in each of 5 fresh cadaver specimens were assessed. The position of the wrist was monitored, but the specimen was not loaded. We concluded that (1) the palmar ligaments are in tension, even with the wrist in neutral position and unloaded; (2) the following ligaments act as passive stabilizers: in neutral the triquetrocapitate and distal part of the radioscaphocapitate, in radial deviation the radiolunate, in ulnar deviation the ulnolunate, in pronation the proximal part of the radioscaphocapitate, in supination the ulnolunate, and in extension the ulnolunate, radiolunate, and radioscaphocapitate; (3) in any position some ligaments are in a state of greater tension than others. The radiolunate, ulnolunate, radioscaphocapitate had the greatest tension; and the lunotriquetral, trapeziocapitate, and scaphocapitate had the least.

Contact characteristics of the subtalar joint: load distribution between the anterior and posterior facets

The pressure distribution properties of the normal talocalcaneal joint were studied in 13 fresh cadaver specimens using pressure-sensitive film. The film was inserted into the joint through a posterior approach for the posterior facet and an anteromedial approach for the anterior/middle facet. Specimens, comprising the distal half of the tibia and fibula and the intact ankle and foot, were positioned in neutral in the sagittal plane. In the coronal plane, specimens were positioned in neutral, inversion, or eversion, and the contact characteristics were determined in varying positions, with and without loading the fibula, under axial loads of 350 N, 700 N, 1,050 N, and 1,400 N. The transducers were video imaged for quantitative analysis of area and pressure. The contact/joint area ratio increased significantly with applied load in the posterior facet [e.g., in eversion from 0.336 (SD = 0.195) at 350 N to 0.631 (SD = 0.225) at 700 N], as did the proportion of the contact area greater than 6 MPa, indicating an increase in contact pressure. The contact/joint area ratio was significantly lower in inversion than in any other position of the foot; however, high-pressure zones were similar, indicating that higher pressures occur in inversion. In the anterior/middle facets both contact/joint area ratio and high pressure/contact area ratios increased significantly to 700 N, but not with further load increase. At 350 N the anterior/middle facet contact area was 31% that of the posterior facet, yet it carried 63.3% of the load of the posterior facet, so its mean contact pressure was 1.44 MPa compared with 0.93 MPa for the posterior facet.(ABSTRACT TRUNCATED AT 250 WORDS)

Contact characteristics of the subtalar joint: the effect of talar neck misalignment

In this study we determined the effects of misalignment of the talar neck on the contact characteristics of the subtalar joint. Each of seven fresh cadaver lower extremities was mounted in a loading jig and a vertical load was applied, 90% of which was directed through the tibia and 10% through the fibula. The foot was allowed to displace freely in the horizontal plane so that relative rotations, known to occur in the subtalar joint, would not be prevented. Pressure-sensitive film, inserted into the posterior and anterior/middle articulations, was used to quantify changes in contact characteristics. After testing in the normal condition, the talar neck was osteotomized and stabilized with internal and external skeletal fixation. Contact characteristics were then determined in each of the following stages: anatomic realignment, or with 2-mm displacement of the talar neck either dorsally, medially, laterally, or complex (dorsal and varus) with respect to the body of the talus. Measurements showed no significant changes in overall contact area or high pressure area in the posterior facet, although four of the seven specimens demonstrated increased localization of the contact area into two discrete regions. The combined anterior/middle facet, on the other hand, was significantly unloaded by all but medial displacement of the talar neck. An extraarticular load path and/or increased loading directly on the talonavicular joint was presumed to account for the loss of load transfer in the talocalcaneal joint.