Intraarticular contact stresses with simulated ankle malunions

Management of Posterior Malleolar Fractures: A Systematic Review

Posterior malleolar fractures are relatively common and usually result from rotational ankle injuries. Although treatment of associated lateral and medial structures is well established, several controversies exist in the management of posterior malleolus fractures. We performed a systematic review of the current published data with regard to the diagnosis, management, and prognosis of posterior malleolus fractures. A total of 33 studies (8 biomechanical and 25 clinical) with >950 patients were reviewed. The outcome of ankle fractures with posterior malleolar involvement was poor; however, the evidence was not enough to prove that the size of the posterior malleolus affects the outcome. Significant heterogeneity was noted in the cutoff size of the posterior malleolar fragment in determining management. The outcome was related to other factors, such as fracture displacement, congruency of the articular surface, and residual tibiotalar subluxation. Indirect evidence showed that large fracture fragments were associated with fracture dislocations and ankle instability and, thus, might require surgical fixation. We have concluded that the evidence to prove that the size of the posterior malleolar affects the outcome of ankle fractures is not enough, and the decision to treat these fractures should be determined by other factors, as stated previously.

Contribution of the medial malleolus to tibiotalar joint contact characteristics

BACKGROUND

Isolated medial malleolus fractures are typically treated operatively to minimize the potential for articular incongruity, instability, nonunion, and posttraumatic arthritis. The literature, however, has not clearly demonstrated inferior outcomes with conservative treatment of these injuries. This study measured the effects of medial malleolus fracture and its resultant instability on tibiotalar joint contact characteristics. We hypothesized that restoration of anatomical alignment and stability through fixation would significantly improve contact characteristics.

METHODS

A Tekscan pressure sensor was inserted and centered over the talar dome in 8 cadaveric foot and ankle specimens. Each specimen was loaded at 700 N in multiple coronal and sagittal plane orientations. After testing fractured samples, the medial malleolus was anatomically fixed before repeat testing. Contact area and pressure were analyzed using a 2-way repeated-measure ANOVA.

RESULTS

In treated fractures, contact areas were higher, and mean contact pressures were lower for all positions. These differences were statistically significant in the majority of orientations and approached statistical significance in pure plantarflexion and pure inversion. Decreases in contact area varied from 15.1% to 42.1%, with the most dramatic reductions in positions of hindfoot eversion.

CONCLUSIONS

These data emphasize the importance of the medial malleolus in maintaining normal tibiotalar contact area and pressure. The average decrease in contact area after simulated medial malleolar fractures was 27.8% (>40% in positions of hindfoot eversion). Such differences become clinically relevant in cases of medial malleolar nonunion or malunion. Therefore, we recommend anatomical reduction and fixation of medial malleolus fractures with any displacement.

LEVEL OF EVIDENCE

Therapeutic Level V-Cadaveric Study.

FE analysis of stress and displacements occurring in the bony chain of leg

AIMS

The aim of this study was to assess how the stress shielding can influence the integrity and resistance of bones.

METHODS

With this purpose a complete FE model of the human leg was realised. A load of 700 N has been applied at the top of pelvis and the feet, at the tip, was rigidly fixed.

RESULTS

Obtained results reveal interesting consequences deriving by taking into account the complete bony chain.

CONCLUSION

A comparison among the literature data and our models can furnish a complete vision of the global spreading of the forces along the various bony components.

Realignment-lengthening osteotomy for malunited distal fibular fracture

PURPOSE

Persistent displacement of ankle fractures increases the stresses on the articular cartilage and leads to degenerative arthritis. Correction of the ankle mortise restores the normal ankle biomechanics and should prevent the development of degenerative joint disease.

METHODS

Seventeen patients were treated for symptomatic ankle joint due to malunited distal fibular fracture. There were eleven male and six female patients. Their ages ranged from 23 to 54 years (median 34 years). The procedure included transverse fibular osteotomy for restoration of the lateral malleolar alignment, acute distraction of the osteotomy to restore the fibular length with interpositional graft and reduction of subluxation of the distal tibio-fibular articulation. Internal fixation of the osteotomy was performed with plate and screws and trans-syndesmotic screws.

RESULTS

Fibular lengthening was performed in all cases and ranged from six to 12 mm (median eight millimetres). The American Orthopaedic Foot and Ankle Society score preoperatively ranged from 40 to 74 (median 60) and at follow up ranged from 50 to 95 (median 79). Progression of ankles arthrosis occurred in one patient leading to ankle arthrodesis as a secondary procedure. Results were satisfactory in 12 cases (70.6%), and unsatisfactory in five cases (29.4%) due to stiffness and pain in the ankle joint. The follow-up ranged from 24 to 45 months (median 31 months).

CONCLUSION

Corrective osteotomy of fibular malunion produces considerable improvement provided that the patient does not have significant degenerative changes before surgery. The use of athrodiastasis of the ankle as a secondary procedure may be of value to improve the outcome.

Posterior pilon fractures: a retrospective case series and proposed classification system

BACKGROUND

Posterior malleolus fractures occur in 7% to 44% of ankle fractures and are associated with worse clinical outcomes. Fractures that involve the posteromedial plafond extending to the medial malleolus have been described previously in small case series. Failure to identify this fracture pattern has led to poor clinical outcomes and persistent talar subluxation. The purpose of this study was to report our outcomes following fixation of this posterior pilon fracture and to describe a novel classification system to help guide operative planning and fixation.

METHODS

Eleven patients were identified following fixation of a posterior pilon fracture over a 4-year span; 7 returned at minimum 1-year follow-up to complete a physical examination, radiographs, and RAND-36 (health-related quality of life score developed at RAND [Research and Development Corporation] as part of the Medical Outcomes Study) and American Orthopaedic Foot & Ankle Society (AOFAS) ankle/hindfoot questionnaires. Patient records were reviewed to evaluate for secondary complications or operative procedures.

RESULTS

Our mean postoperative AOFAS ankle/hindfoot score was 82. Anatomical reduction of the plafond was noted radiographically in 7 of 11 patients, with the remainder demonstrating less than 2 mm of articular incongruity. Five of 7 patients demonstrated ankle and hindfoot range of motion within 5 degrees of the uninvolved extremity. Four complications required operative intervention; 2 patients reported continued pain secondary to development of CRPS.

CONCLUSION

The posterior pilon fracture is a challenging fracture pattern to treat, and it has unique characteristics that require careful attention to operative technique. Our results following fixation of this fracture pattern are comparable with results in the literature. In addition, a novel classification scheme is described to guide recognition and treatment of this fracture pattern.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Anterior distal tibia plafondplasty for exposure of the talar dome

BACKGROUND

It may be possible to avoid malleolar osteotomy for treatment of osteochondral talar lesions with chondrocyte transplantation techniques, where perpendicular approach to the talar surface is not required. We hypothesized that limited anterior distal tibial plafondplasty would allow access to most of the talar surface. We compared talar access with soft tissue exposure versus plafondplasty.

METHODS

Two soft tissue exposures (anteromedial and anterolateral) and two limited anterior distal tibial plafondplasties (anteromedial and anterolateral) were used on 12 cadaver lower-extremity specimens. Digital analysis was used to assess the accessible area.

RESULTS

Percentage of total talar dome surface area access increased significantly between soft tissue exposure and limited plafondplasty medially (22.3 +/- 6.3% versus 37.9 +/- 4.6%; p < 0.001) and laterally (22.4 +/- 7.7% versus 37.9 +/- 7.7%; p < 0.001). Percentage sagittal plane access also increased significantly between soft tissue exposure and limited plafondplasty medially 54.4 +/- 12.0% versus 81.3 +/- 9.7%; p < 0.001) and laterally (53.3 +/- 14.5% versus 80.9 +/- 12.8%; p < 0.001). Limited exposure to an additional 14.2 +/- 5% of the total talar surface area was possible. The posterior 10.6 +/- 8% was inaccessible.

CONCLUSIONS

A soft tissue approach with limited plafondplasty provided adequate exposure for the majority of the medial and lateral talar surface. Only the central posterior 10% of the talus was not accessed by this method.

CLINICAL RELEVANCE

It may be possible to avoid malleolar osteotomy by using limited plafondplasty to access the talar dome for treatment of osteochondral lesions if perpendicular access to the talus is not required.

Results of a computed tomography protocol evaluating distal third tibial shaft fractures to assess noncontiguous malleolar fractures

BACKGROUND

Intra-articular tibia fractures are reported to occur in 1% to 25% of tibia diaphyseal fractures. The objective of this study was to create a standard protocol to evaluate noncontiguous malleolar fractures associated with distal third tibial diaphyseal fractures using computed tomography (CT).

METHODS

Sixty-six patients with 67 distal third tibia fractures were treated at a level one trauma center from December 2005 to November 2007. These patients were then evaluated using a CT protocol to assess the ankle joint. There were 45 men and 21 women with average age of 44 years (range 18-69 years). All films were independently examined by two orthopedic traumatologists and one musculoskeletal radiologist.

RESULTS

Twenty-nine of 67 (43%) distal third tibial shaft fractures had associated intra-articular fractures determined by CT scan. There were 23 posterior malleolus fractures, 3 anterolateral fragments, and 3 medial malleolus fractures. Twenty-seven of 29 fractures (93%) were associated with spiral type fracture patterns (p = 0.001). Seventeen of 29 (59%) intra-articular fractures required operative fixation. Seventy-six percent were noncontiguous fractures. The radiologist detected 20 of 29 (69%) intra-articular fractures using high-resolution monitors, and the orthopedic surgeons averaged 13 of 29 (45%) using initial injury radiographs in the emergency department.

CONCLUSION

Plain radiographs are often insufficient for detecting posterior malleolus fractures in conjunction with ipsilateral distal third diaphyseal tibia fractures. Using a preoperative CT protocol for tibial shaft fractures can significantly improve the ability to diagnose associated intra-articular fractures that may not be evident on plain radiographs. Knowledge of these associated intra-articular fractures may prompt fracture stabilization and can prevent displacement during intramedullary nailing of tibia shaft fractures.

Effect of supramalleolar varus and valgus deformities on the tibiotalar joint: a cadaveric study

BACKGROUND

Distal tibia coronal plane malalignment predisposes the ankle joint to asymmetric load. The purpose of this cadaveric study was to quantify changes in pressure and force transfer in an ankle with a supramalleolar deformity.

MATERIALS AND METHODS

Seventeen cadaveric lower legs were loaded with 700 N after creating supramalleolar varus and valgus deformities. The fibula was left intact in 11 specimens and osteotomized in six. Tekscan© sensors were used to measure the tibiotalar pressure characteristics.

RESULTS

In isolated supramalleolar deformity, the center of force and peak pressure moved in an anteromedial direction for valgus and posterolateral direction for varus deformities. The change was in an anteromedial direction for varus and in a posterolateral direction for valgus deformities in specimens with an osteotomized fibula.

CONCLUSION

Two essentially different groups of varus and valgus deformities of the ankle joint need to be distinguished. The first group is an isolated frontal plane deformity and the second group is a frontal plane deformity with associated incongruency of the ankle mortise.

CLINICAL RELEVANCE

Our findings underline the complexity of asymmetric osteoarthritis of the ankle joint. In addition, results from this study provide useful information for future basic research on coronal plane deformity of the hindfoot and for determining appropriate surgical approaches.

Surgeon practices regarding operative treatment of posterior malleolus fractures

BACKGROUND

Operative indications for surgical treatment of posterior malleolar fractures associated with fractures of the distal fibula and tibia are not currently well defined. The purpose of the present study was to determine the current practice among orthopaedic surgeons regarding the management of posterior malleolus fractures.

MATERIALS AND METHODS

Web-based questionnaires were emailed to members of the Orthopaedic Trauma Association (OTA) and American Orthopaedic Foot and Ankle Society (AOFAS). Requested information included demographics and treatment preferences for five clinical scenarios with different fracture characteristics. Four hundred one respondents completed the survey (20% response rate). Ninety eight (24%) subjects had received specialty training in orthopaedic trauma, 199 (50%) in foot and ankle (F&A) surgery and six (2%) in both orthopaedic trauma and F&A surgery. Ninety five (24%) had either no or other specialty training.

RESULTS

The most frequently reported indication for fixation was not based on a fragment size threshold, but rather was ``depends on stability and other factors'' (56%). Trauma surgeons, those with less than 10 years experience, and those who treated more than five ankles fractures per month were significantly more likely to use factors other than size for indications (p = 0.026, <0.01, and <0.01, respectively). Despite this general response, fragment size still affected treatment decisions. A fragment comprising 50% of the articular surface was indicated for fixation by 97% of respondents, while a size of 10% would be treated by only 9% of respondents. For a posterior fragment with 20% articular involvement and a small free osteochondral fragment, fixation was deemed necessary by 44% of respondents. There were no differences in fellowship training, years of experience in practice, or ankle fracture volume per month in these three situations. A larger proportion of trauma trained surgeons considered fixation necessary compared to F&A trained surgeons in this case (p = 0.028). When posterior malleolus fixation was indicated for a large fragment, direct open reduction using the flexor hallucis longus -peroneal tendon interval was the most commonly selected approach in all cases. Trauma-trained surgeons were significantly more likely to choose antiglide plate fixation compared to screw-only fixation (p < 0.05).

CONCLUSION

In this survey study of trauma and F&A surgeons, significant variation existed regarding most aspects of posterior malleolar ankle fracture treatment. Most notably, factors other than fragment size most impacted surgical indications. Newer techniques such as direct exposure and plating of the posterior malleolus are chosen more frequently than traditional techniques of indirect reduction and percutaneous screw fixation.

Prediction of three-dimensional contact stress and ligament tension in the ankle during stance determined from computational modeling

BACKGROUND

Our goal was to quantify and visualize the three-dimensional loading relationship between the ligaments and articular surfaces of the ankle to identify and determine the stabilizing roles of these anatomical structures during the stance phase of gait.

MATERIALS AND METHODS

We applied discrete element analysis to computationally model the three-dimensional contact characteristics and ligament loading of the ankle joint. Physiologic loads approximating those at five positions in the stance phase of a normal walk cycle were applied. We analyzed joint contact pressures and periankle ligament tension concurrently.

RESULTS

Most ankle joint loading during the stance phase occurred across the articular surfaces of the joint, and the amount of ligament tension was small. The tibiotalar articulation showed full congruency throughout most of the stance phase, with peak pressure developing anteriorly toward the toe-off frame. Of the periankle ligaments, the deep deltoid ligament transferred the most force during the stance phase (57.2%); the superficial deltoid ligament transferred the second-most force (26.1%). The anterior talofibular ligament transferred force between the talus and fibula continuously, whereas the calcaneofibular ligament did not carry force during gait. The distal tibiofibular ligaments and the interosseous membrane were loaded throughout the stance phase.

CONCLUSION

Force transmission through the ankle joint during the stance phase is predominantly through the articular surfaces, and the periankle ligaments do not play a major stabilizing role in constraining ankle motion. The medial ligaments have a more important role than do the lateral ligaments in stabilizing the ankle joint.

CLINICAL RELEVANCE

In addition to ligament insufficiency, other factors, such as varus tilt of the tibial plafond, may be important in the development of recurrent instability. Continuous loading of syndesmosis ligaments provides a theoretical basis for evidence of syndesmosis screw breakage or loosening. The analysis method has potential applications for clarifying ankle joint function and providing a basis for comparison between normal and abnormal joint conditions.

Patient-specific finite element analysis of chronic contact stress exposure after intraarticular fracture of the tibial plafond

The role of altered contact mechanics in the pathogenesis of posttraumatic osteoarthritis (PTOA) following intraarticular fracture remains poorly understood. One proposed etiology is that residual incongruities lead to altered joint contact stresses that, over time, predispose to PTOA. Prevailing joint contact stresses following surgical fracture reduction were quantified in this study using patient-specific contact finite element (FE) analysis. FE models were created for 11 ankle pairs from tibial plafond fracture patients. Both (reduced) fractured ankles and their intact contralaterals were modeled. A sequence of 13 loading instances was used to simulate the stance phase of gait. Contact stresses were summed across loadings in the simulation, weighted by resident time in the gait cycle. This chronic exposure measure, a metric of degeneration propensity, was then compared between intact and fractured ankle pairs. Intact ankles had lower peak contact stress exposures that were more uniform and centrally located. The series-average peak contact stress elevation for fractured ankles was 38% (p = 0.0015; peak elevation was 82%). Fractured ankles had less area with low contact stress exposure than intact ankles and a greater area with high exposure. Chronic contact stress overexposures (stresses exceeding a damage threshold) ranged from near zero to a high of 18 times the matched intact value. The patient-specific FE models represent substantial progress toward elucidating the relationship between altered contact stresses and the outcome of patients treated for intraarticular fractures.

Physical validation of a patient-specific contact finite element model of the ankle

A validation study was conducted to determine the extent to which computational ankle contact finite element (FE) results agreed with experimentally measured tibio-talar contact stress. Two cadaver ankles were loaded in separate test sessions, during which ankle contact stresses were measured with a high-resolution (Tekscan) pressure sensor. Corresponding contact FE analyses were subsequently performed for comparison. The agreement was good between FE-computed and experimentally measured mean (3.2% discrepancy for one ankle, 19.3% for the other) and maximum (1.5% and 6.2%) contact stress, as well as for contact area (1.7% and 14.9%). There was also excellent agreement between histograms of fractional areas of cartilage experiencing specific ranges of contact stress. Finally, point-by-point comparisons between the computed and measured contact stress distributions over the articular surface showed substantial agreement, with correlation coefficients of 90% for one ankle and 86% for the other. In the past, general qualitative, but little direct quantitative agreement has been demonstrated with articular joint contact FE models. The methods used for this validation enable formal comparison of computational and experimental results, and open the way for objective statistical measures of regional correlation between FE-computed contact stress distributions from comparison articular joint surfaces (e.g., those from an intact versus those with residual intra-articular fracture incongruity).

Osteotomy for salvage of the arthritic ankle

Ankle arthrodesis continues to be the procedure of choice for ankle arthritis. Coester and colleagues showed that arthrodesis is a significant risk factor for development of arthritis in the ipsilateral hindfoot and forefoot, however. Total ankle arthroplasty has gained significant interest but is not yet ideally suited for younger active patients because of unacceptable failure rates and complications. Osteotomies can play an important role in re-establishing normal alignment and potentially decreasing the rate of progression of wear on the articular surfaces and decreasing pain, which may allow more time before arthrodesis or arthroplasty are needed. The success of total ankle arthroplasty depends largely on the alignment of the foot and ankle and osteotomies can be used in a staged manner as part of a reconstructive effort including total ankle arthroplasty. Supramalleolar osteotomies can be used to align the tibia; alternatively, osteotomies in the midfoot and hindfoot can be used to balance the foot and ankle making them suitable for arthroplasty in an individual who perhaps would not otherwise have that treatment option. Further studies will continue to clarify the role and indications for osteotomies for treatment of ankle arthritis.

Contribution of articular surface geometry to ankle stabilization

BACKGROUND

Passive ankle stability under weight-bearing conditions has been found to depend substantially on the role of the articular surface geometry. In the present study, it was hypothesized that, in the ankle under axial loading, contact-stress changes in response to alterations of external load involve reproducible and specific patterns to maintain ankle stability.

METHODS

Six cadaver ankles with the peri-ankle ligaments intact were tested. Each specimen, held at several predetermined ankle positions under a primary one-body-weight axial force, was subjected to an additional secondary load. The secondary load-specifically, anterior/posterior shear force, inversion/eversion torque, or internal/external rotation torque-was applied independently, while motion associated with the two other secondary loading directions was unconstrained. Contact stress in the tibiotalar articulation was monitored by a real-time contact-stress sensor. Site-specific stress changes solely due to secondary loading at each load/position were identified by subtraction of the corresponding axial-force-only baseline distribution. The role of these stress changes in ankle stabilization was studied for each specimen by analyzing the data with a computer model of ankle geometry.

RESULTS

In the cadaver experiment, anterior and posterior shear forces caused reproducible positive changes in articular contact stresses on the anterior and posterior regions, respectively. Similar changes with version torques occurred on the medial and lateral regions. Positive changes with internal/external rotation torques occurred at two diagonal locations: anterolateral and posteromedial, or anteromedial and posterolateral. In the model analysis, these stress-change patterns were found to be effective in ankle stabilization, and the levels of contribution by the articular surface were calculated as accounting for approximately 70% of anterior/posterior stability, 50% of version stability, and 30% of internal/external rotation stability.

CONCLUSIONS

The documented changes in contact stress illustrate the major role of articular geometry in passive ankle stabilization. The levels of contribution by the articular surface that we calculated are consistent with those reported in the literature. These findings support the conceptual mechanism of ankle stabilization by redistribution of articular contact stress.

Intra-articular contact stress distributions at the ankle throughout stance phase-patient-specific finite element analysis as a metric of degeneration propensity

A contact finite element (FE) formulation is introduced, amenable to patient-specific analysis of cumulative cartilage mechano-stimulus attributable to habitual functional activity. CT scans of individual human ankles are segmented to delineate bony margins. Each bone surface is projected outward to create a second surface, and the intervening volume is then meshed with continuum hexahedral elements. The tibia is positioned relative to the talus into a weight-bearing apposition. The articular members are first engaged under light preload, then plantar-/dorsi-flexion kinematics and resultant loadings are input for serial FE solutions at 13 instants of the stance phase of level walking gait. Cartilage stress histories are post-processed to recover distributions of cumulative stress-time mechano-stimulus, a metric of degeneration propensity. Consistency in computed contact stress exposures presented for seven intact ankles stood in contrast to the higher magnitude and more focal exposures in an incongruously reduced tibial plafond fracture. This analytical procedure provides patient-specific estimates of degeneration propensity due to various mechanical abnormalities, and it provides a platform from which the mechanical efficacy of alternative surgical interventions can be estimated.

Pathoanatomy of posterior malleolar fractures of the ankle

BACKGROUND

The functional outcome following ankle fractures that involve a posterior malleolar fragment is often not satisfactory, and treatment of this type of fracture remains controversial. Thorough knowledge of the pathologic anatomy of the posterior malleolar fracture is essential for planning appropriate treatment. Thus, we conducted a computed tomographic study to clarify the pathologic anatomy of the posterior malleolar fracture.

METHODS

Between 1999 and 2003, fifty-seven consecutive patients with a unilateral ankle fracture with one or more posterior fragments were managed at our hospital. We reviewed the patients' preoperative computed tomographic scans to determine (1) the ratio of the posterior fragment area to the total cross-sectional area of the tibial plafond and (2) the angle between the bimalleolar axis and the major fracture line of the posterior malleolus. Each fracture was categorized according to the location of the major fracture line on the computed tomographic image at the level of the tibial plafond.

RESULTS

The fifty-seven fractures were categorized into three types: (1) the posterolateral-oblique type (thirty-eight fractures; 67%), (2) the medial-extension type (eleven fractures; 19%), and (3) the small-shell type (eight fractures; 14%). Two of the eleven medial-extension fractures extended to the anterior part of the medial malleolus. A total of nine of the eleven medial-extension fractures actually consisted of two fragments [corrected] The conditions are not exclusive of one another; for example, in the case of one of the fractures exhibiting two fragments, the fracture also extended to the anterior part of the medial malleolus [corrected] The average area of the fragment comprised 11.7% of the cross-sectional area of the tibial plafond for posterolateral-oblique fractures and 29.8% for medial-extension fractures. In the cases of seven of the nine fractures that comprised >25% of the tibial plafond, the fracture line extended to the medial malleolus. The angles between the bimalleolar axis and the major fracture line of the posterior malleolus varied.

CONCLUSIONS

The fracture lines associated with posterior malleolar fractures appear to be highly variable. A large fragment extending to the medial malleolus existed in almost 20% of the posterior malleolar fractures in the current study, and some fragments involved almost the entire medial malleolus. Because of the great variation in fracture configurations, preoperative use of computed tomography may be justified. The information obtained from this study will be helpful for conducting basic research of this condition and for determining appropriate surgical approaches.

Articular fractures

Although injuries to articular cartilage may lead to radiographic osteoarthritis, pain, and decreased joint function, the actual effects of such injury and of its treatment on joint function are not completely understood. The mechanisms of repair after impact loading are different from those after frank disruption by fracture of the articular cartilage, but basic and clinical research both indicate that the resultant articular surface is prone to degeneration. The sensitivity of a joint to resultant incongruity varies considerably, depending on the thickness and modulus of the articular cartilage and the geometry of the joint. Also, factors other than articular congruity play a substantial role in determining outcomes after treatment. For these reasons, defining a single threshold for articular displacement that correlates with outcomes in all joints is not practical. Some articular fractures injure cartilage so severely that the joint will degenerate even with an accurate articular reduction. Also, radiographic evidence of osteoarthritis does not necessarily correlate with poor function. More reliable measurement techniques are needed to accurately assess how treatment affects arthritis, and factors other than articular congruity are needed to predict posttraumatic arthritis.

Revision of malunited ankle fractures

Malunion of an ankle fracture can lead to considerable pain and loss of function. Restoration of the normal anatomical alignments can restore function and minimize the onset of degeneration that will lead to severe arthrosis requiring an arthrodesis. This article outlines common causes of ankle malunion and treatment options.

Kinematic and contact stress analysis of posterior malleolus fractures of the ankle

OBJECTIVE

To determine if there are measurable dynamic contact stress aberrations and kinematic abnormalities (instability) that have not been observed in conventional static loading studies of posterior malleolar ankle fractures.

DESIGN

Cadaveric fracture model.

SETTING

Biomechanics laboratory.

INTERVENTION

Seven fresh cadaveric specimens were fixed in an unconstrained testing apparatus and loaded to one body weight. The ankle was moved from 25 degrees of plantarflexion to 15 degrees of dorsiflexion. The model included the intact ankle and four fracture simulations (50% fracture without internal fixation, 2 mm gap and step malreductions, and anatomically fixed).

MAIN OUTCOME MEASURE

Motion at the ankle was monitored with an electromagnetic tracking device, and intra-articular contact stresses were measured using a real-time stress sensor.

RESULTS

There were no kinematic abnormalities suggestive of tibiotalar subluxation in any of the fracture simulations. There was no increase in peak contact stress in any of the fracture models compared with the unfractured model. However, there was a shift in the location of the contact stresses to a more anterior and medial location following the fracture. When summed over the range of motion, these areas of cartilage bore significantly higher cumulative contact stresses relative to the nonfracture situation.

CONCLUSIONS

We found no talar subluxation and no increase in contact stresses near the articular incongruity, making it unlikely that these factors explain the increased incidence of arthrosis after trimalleolar fractures (OTA/AO classification 44 B3 fractures). Rather, we found that the joint remaining bears increased stress and that the center of stress shifts anteriorly, loading cartilage that normally sees little load.

Effects of isolated Weber B fibular fractures on the tibiotalar contact area

Fractures of the lateral malleolus can occur without rupture of the deltoid ligament or fracture of the medial malleolus. Controversy exists regarding the necessity of surgery on supination-external rotation stage II ankle fractures. Theoretically, as long as the medial structures are intact, the talus cannot displace enough to cause degenerative arthritis of the ankle joint. The purpose of this study was to measure changes in contact area between the tibial plafond and the talar dome with serial displacement of the distal fibula in both a lateral and a superolateral direction. Twelve cadaver lower extremities were used. Distal fibular fractures were replicated by creating an osteotomy. Displacement was accomplished with a customized apparatus that displaced and held the distal fibula in a malaligned position. Tibiotalar contact area was measured with pressure sensitive film at the following intervals of fibular displacement: 0 mm, laterally 2 mm and 4 mm, and then posteriorly and superiorly 2 mm and 4 mm. A servohydraulic testing apparatus was used to apply the same physiologic load to all limbs while measuring contact area. Key independent variables included the direction and amount of displacement of the distal fibula. Mean tibiotalar contact area decreased from baseline (no displacement) 361.1 mm2 (SD +/- 49.0) to 162.2 mm2 (SD +/- 81.3) and 82.6 mm2 (SD +/- 30.6) for 2 mm and 4 mm lateral displacement of the distal fibula respectively. With posterior/superior displacement of 2 mm and 4 mm mean tibiotalar contact decreased to 219.3 mm2 (SD +/- 56.7) and 109.2 mm2 (SD +/- 39.0), respectively. Statistical significance was found (P <.001) when comparing normal ankle alignment with displaced fractures at all levels of displacement.

Complications of open reduction and internal fixation of ankle fractures

This article discusses the complications after open reduction and internal fixation of ankle fractures. Complications are classified as perioperative (malreduction, inadequate fixation, and intra-articular penetration of hardware), early postoperative (wound edge dehiscence, necrosis, infection and compartment syndrome), and late (stiffness, distal tibiofibular synostosis, degenerative osteoarthritis, and hardware related complications). Emphasis is placed on preventive measures to avoid such complications.

The effects of tibial malrotation on the biomechanics of the tibiotalar joint

The effects of tibial malrotation on the biomechanics of the tibiotalar joint were studied using a cadaveric model loaded in an Instron 8521 materials testing device and a TEKScan I-Scan thin-film resistive ink pressure measuring system. Testing of 23 legs was performed using rotational conditions of 10 and 20 degrees internal and external rotation as well as neutral rotation. All rotational conditions were found to decrease joint contact area. Peak pressures were significantly greater with 20 degrees internal rotation as well as 20 degrees external rotation. Total load across the joint was significantly lower for both 10 and 20 degrees of external rotation. In conclusion, rotational deformity across the tibiotalar joint results in significant alteration of overall joint biomechanics and should be minimized whenever possible.

Trabecular bone strain changes associated with cartilage defects in the proximal and distal tibia

Intraarticular fractures with cartilage defects can lead to post-traumatic arthritis (PTA). The purpose of this study was to determine how cartilage defects affect load transmission through subchondral trabecular bone in human cadaveric knees and ankles to further understand the pathomechanics of PTA. We created full-thickness cartilage defects in the meniscectomized proximal tibia and distal tibia and measured changes in trabecular bone strain using Texture Correlation. Texture Correlation compares high quality digital images made from contact radiographs of unloaded samples to images of the same sample under load to measure trabecular bone strain. Cartilage defects caused trabecular bone strain to decrease in the proximal tibia and increase in the distal tibia. The column of bone directly beneath the defect in the tibial plateau had the most significant reduction in strain. In the distal tibia, strain near the jointline and in the anterior third had the most significant increases in strain. The distal tibia had greater strain changes with small defects. The clinical course of intraarticular fractures of the proximal and distal tibia are markedly different. We postulate that disturbances in load transmission through the subchondral bone caused by cartilage defects may be important mechanical determinants of PTA.

Arthroscopic treatment of osteochondral lesions of the talar dome: a retrospective study of 48 cases

We treated 48 symptomatic osteochondral lesions of the talar dome arthroscopically. Of these, 18 patients had an osteochondral fracture with a loose fragment located in every case on the anteriolateral side of the talus. Treatment consisted of removal (16 cases) or fixation (2 cases) of the bone fragment. Thirty patients had chronic lesions (27 subchondral necrosis with a sequestrum and 3 extensive cysts). The lesion was posteromedial in 27 cases and the treatment consisted of removal of the sequestrum with curettage of the subchondral bone necrosis (27 cases) or transchondral drilling if the cartilage surface was intact (3 cases). All the patients were clinically and radiogically reviewed with a mean follow-up of 5 years (7 months to 11 years). Patients treated for an osteochondral fracture obtained significant better results (16 excellent or good results out of 18 cases) than those treated for chronic lesions (20 excellent or good results out of 30 cases). On radiographic examination, we noticed that, even at the longest follow-up, the bone healing was usually incomplete and the bone defect persisted indefinitely in case of extensive subchondral bone necrosis. The articular surface could be seen in 11 cases (8 computed arthrotomographies, 1 magnetic resonance imaging, and 2 second-look arthroscopies). The fibrous cartilaginous surface was apparently regular in 6 cases without any clear correlation with our clinical results. This study suggests that we must make a distinction between osteochondral fractures (recent or not healed) located in the anterolateral part of the talar dome, which carry a good prognosis, and necrotic lesions located medially, which are less likely to have a favorable outcome.

Measurement of surface contact area of the ankle joint

OBJECTIVE: To determine the distribution of contact area of the ankle joint with axial loading and in positions of maximal dorsiflexion, plantar flexion, supination, and pronation. We also tested the effects of extrinsic tendon loading and arch instability. DESIGN: Nine cadaveric feet were studied in the intact condition and following transection of ligaments to create arch instability. BACKGROUND: Assessment of ankle contact in various joint positions and degrees of instability is difficult to accomplish with conventional methods. METHODS: Displacement of the talus relative to the tibia was measured with a magnetic tracking device and tibiotalar joint contact from proximity calculations of digitized joint surfaces. RESULTS: Contact area did not change significantly from unloaded condition to 667 N load condition in the medial, central, and lateral zones. Central zone contact area decreased in plantar flexion by an average of 324 mm(2) (SD, 165 mm(2)) (P = 0.0004). Medial zone contact area decreased in plantar flexion by a mean of 55 mm(2) (SD, 28 mm(2)) (P = 0.0004), decreased in pronation by an average of 42 mm(2) (SD, 36 mm(2)) (P = 0.0086), and increased in supination by an average of 20 mm(2) (SD, 26 mm(2)) (P = 0.0430). Lateral zone contact decreased in plantar flexion by a mean of 124 mm(2) (SD, 57 mm(2)) (P = 0.0002). CONCLUSIONS: In plantar flexion, there was a decrease in contact area. Loading extrinsic tendons to the foot did not significantly increase ankle contact area, but arch instability caused a decrease in central and lateral zone contact area. RELEVANCE: This technique was used to assess joint contact characteristics in various loading conditions and will be useful for evaluating the extent to which treatment for ankle or hindfoot problems such as bracing or reconstruction operations restores normal joint contact.

Osteoarthritis of the ankle

Primary osteoarthritis of the ankle is a rare entity. Osteoarthritis of the ankle more commonly is seen secondary to trauma of the articular surface involving the normal biomechanics of the ankle. The causes are many and treatment consists of prevention of additional deterioration or treatment of that deterioration. The patient with osteoarthritis is plagued by chronic pain and decreased function. The surgical option for treatment includes soft tissue and bony debridement, ligamentous reconstruction, corrective osteotomy, arthrodesis, arthroplasty, or a combination of those treatments. The surgical treatment options are discussed and guidelines are provided for the treatment of ankle arthritis based on current concepts reported in the literature.

The effect of fibular malreduction on contact pressures in an ankle fracture malunion model

Nine fresh-frozen cadaveric specimens were disarticulated through the knee, and the soft tissues, except for the interosseous ligaments and interosseous membrane, were removed to the level of the ankle. The subtalar joint was secured with screws in neutral position (approximately 5 degrees of valgus). Contact pressures in the tibiotalar joint were measured with use of low-grade pressure-sensitive film, which was placed through an anterior capsulotomy. For each measurement, 700 newtons of load was applied to the specimen for one minute. The film imprints were scanned, and the contact pressures were quantitated in nine equal quadrants over the talar dome. A fracture-displacement device was secured to the distal end of the fibula; the device allowed for individual or combined displacements consisting of shortening, lateral shift, and external rotation of the fibula. The ankle was maintained in neutral flexion. The ligamentous injury associated with a pronation-lateral rotation fracture of the ankle was simulated by dividing the deep fibers of the deltoid ligament, the anterior-inferior tibiofibular ligament, and the interosseous membrane to a point that was an average of fifty-three millimeters proximal to the ankle joint. Baseline contact area and contact pressure in the joint were determined, followed by measurements after two, four, and six millimeters of shortening of the fibula; after two, four, and six millimeters of lateral shift of the fibula; and after 5, 10, and 15 degrees of external rotation of the fibula. The three types of displacement were tested individually as well as in combination. The simulated deformities were found to cause a shift of the contact pressure to the mid-lateral and posterolateral quadrants of the talar dome, with pressures as high as 4.1 megapascals. A corresponding decrease in the contact pressures was noted in the medial quadrants of the talar dome. The highest pressures were recorded for maximum shortening of the fibula, the combination of maximum shortening and lateral shift, the combination of maximum shortening and external rotation, and the combination of maximum shortening, lateral shift, and external rotation. In general, increases in each displacement variable corresponded to increasing contact pressures.

NOVEL Award 1996: 2nd prize Tenodeses do not fully restore ankle joint loading characteristics: a biomechanical in vitro investigation in the hind foot

OBJECTIVE: In order to understand the biomechanical consequences of ligament injuries and surgical reconstruction procedures, their effects on intra-articular loading in the ankle joint complex and Chopart joint line and on the plantar pressure patterns were investigated in vitro. METHODS: Twelve fresh-frozen lower leg specimens were freed of soft tissue down to the malleoli and prepared for accessing the talocrural, subtalar, talonavicular and calcaneocuboid joints. The specimens were fixed in a loading simulator and axially loaded with 600 N in six experimental conditions: intact; after cutting the anterior talofibular ligament; after additionally cutting the calcaneofibular ligament; after performing three common types of tenodeses, the Evans, Watson-Jones and Chrisman-Snook procedures. The intra-articular loading characteristics were determined with pressure sensitive film. Plantar loading patterns were measured with a capacitive EMED pressure distribution platform. RESULTS: Average intra-articular pressures were increased and were related either to decreased contact areas or to increased contact forces found in all joints after ligament resections and tenodeses. Plantar loading was increased under the medial aspect of the foot and decreased under the midfoot region. CONCLUSIONS: The results indicate that ankle ligament injuries, as well as surgical reconstructions by tenodeses, affect joint loading characteristics and may exacerbate joint degeneration. RELEVANCE: Excessive laxity of the ankle joint is considered a pre-arthrotic condition and is treated with various surgical procedures. Some of these procedures that utilize the tendon of the peroneus brevis have been shown to change joint kinematics. The aim was to evaluate joint loading characteristics and the potential danger of developing arthritis as a consequence of various tenodeses techniques. For this purpose, in vitro investigations are needed to directly determine intra-articular pressure measurements.

Calcaneal fractures cause a lateral load shift in Chopart joint contact stress and plantar pressure pattern in vitro

In order to evaluate the effects of the anatomical changes after calcaneal fractures on joint loading characteristics we investigated the effects of simulated calcaneal fractures on intra-articular loading in the Chopart joint and on plantar pressure patterns in vitro. Five fresh-frozen lower leg specimens were axially loaded with 500 N in three positions: neutral, 10 degrees plantarflexion and 10 degrees dorsiflexion. The loading characteristics were determined before and after creating a tongue-type fracture by osteotomy. Plantar loading patterns were measured with a capacitive pressure distribution platform. Intra-articular contact areas and pressures were recorded on pressure sensitive film introduced into the talonavicular and calcaneocuboid joint. Increased loading in the calcaneocuboid joint (+25%,p = 0.005) and decreased loading in the talonavicular joint (-16%,p = 0.01) corresponded to increased loading of the lateral aspects of the plantar surface. These findings were independent of the foot position. The results suggest that the effects of increased lateral foot loading which have been observed in calcaneal fracture patients (Rosenbaum et al., Clin. Biomech. 10, 345-351, 1995) are caused by changes in joint kinematics and do not appear to result from a protective gait pattern established after the injury.