Force transmission through the wrist joint in Kienböck's disease: a two-dimensional theoretical study

Musculoskeletal Modeling of the Wrist via a Multi Body Simulation

In this study, three different musculoskeletal modeling approaches were compared to each other. The objective was to show the possibilities in the case of a simple mechanical model of the wrist, using a simple multi-body-simulation (MBS) model, and using a more complex and patient-specific adaptable wrist joint MBS model. Musculoskeletal modeling could be a useful alternative, which can be practiced as a non-invasive approach to investigate body motion and internal loads in a wide range of conditions. The goal of this study was the introduction of computer-based modelling of the physiological wrist with (MBS-) models focused on the muscle and joint forces acting on the wrist.

Changes in wrist joint contact area following radial shortening osteotomy for Kienböck's disease

We hypothesized that the contact area of the articular surface of the wrist joint could be evaluated using a custom-designed analytical program. The aim of the study was to compare the articular contact area of the wrist joint before and after radial shortening osteotomy for Kienböck’s disease. Nine wrists of 9 patients underwent radial shortening osteotomy for Kienböck’s disease. Computed tomography (CT) images of the wrist joint were reconstructed using a 3D reconstruction software package. Radioscaphoid and radiolunate joint contact areas and translation of the joint contact area from preoperative to postoperative were calculated using customized software. The mean Modified Mayo Wrist Score was significantly improved from 50.6 preoperatively to 83.3 at final follow-up (p < .001). Preoperatively, the pain was reported as severe in five wrists and moderate in four wrists, while at final follow-up, five patients were free from pain and four patients had mild pain with vigorous activity. The preoperative radioscaphoid joint contact area was 133.4 ± 49.5 mm² and the postoperative radioscaphoid joint contact area was 156.4 ± 73.1 mm². The preoperative radiolunate joint contact area was 194.8 ± 92.1 mm² and the postoperative radiolunate joint contact area was 148.3 ± 97.9 mm². The radial translation distance was 0.4 ± 1.2 mm, the dorsal translation distance was 0.6 ± 1.2 mm, and the proximal translation distance was 0.2 ± 0.4 mm. CT-based analysis revealed that the center of the contact area translated radially following radial shortening.

Anatomy, Biomechanics, and Loads of the Wrist Joint

The wrist is by far the most differentiated section of the musculoskeletal system. The spectrum of wrist injuries ranges from minor injuries to complex traumas with simultaneous loss of functions, resulting in enormous economic costs. A proper understanding of the anatomy and biomechanics is essential for effective treatment, whether conservative or surgical; this applies to the wrist no less than to other parts of the human body. Here; information on the wrist anatomy; kinematics; and biomechanical behavior is presented, commencing with a brief explanation of the structure of its hard and soft tissues. Eight carpal bones in combination with two forearm bones (radius and ulna) construct the wrist joint. The motion of the wrist joint is initiated by the muscles of the forearm, and strong and short ligaments ensure the stability of the wrist. All of these components are essential to bringing functions to the wrist joint because these structures allow wrist mobility and sustainability. In addition, the kinematics of the wrist joint is presented and different biomechanical model approaches. The therapeutic (surgical) restoration of the balance between the load–bearing capacity and the actual stress on a joint is the prerequisite for a lifelong and trouble-free function of a joint. Regarding the complex clinical problems, however, a valid biomechanical wrist joint model would be necessary as assistance, to improve the success of systematized therapies based on computer–aided model–based planning and intervention.

Biomechanical comparison of arthroscopic and open lunate excisions in the cadaveric wrist

BACKGROUND

In advanced Kienböck disease, unreconstructible lunate should be excised as a salvage procedure. There is a lack of information about the biomechanical approaches evaluating the carpal kinematics after lunate excision. We hypothesized that arthroscopic lunate excision would not break the ring structure of the proximal carpal row, preventing carpal instability. We aimed to investigate changes in carpal kinematics following arthroscopic and open lunate excisions.

METHODS

We used upper extremities from five fresh cadavers and simulated arthroscopic and open lunate excisions. Arthroscopic lunate excision was performed to preserve the attachment sites of intrinsic and extrinsic carpal ligaments to the lunate. Open lunate excision was conducted with sectioning of the intrinsic and extrinsic carpal ligaments. Using a three-dimensional space electromagnetic tracking device, rotation angles of the scaphoid and triquetrum and the change of scaphotriquetrum distance were measured under axial loading. We compared the rotation angles and the change of scaphotriquetrum distance among intact wrists, open, and arthroscopic lunate excisions.

FINDINGS

No Significant differences in the rotation angle of the scaphoid and triquetrum or the change of scaphotriquetrum distance were found between intact wrist and arthroscopic lunate excision. The triquetrum significantly dorsiflexed and supinated in wrists with open lunate excisions compared with intact wrists. Significant differences in the change of scaphotriquetrum distance were found between intact and openly excised wrists and between arthroscopic and open excisions.

INTERPRETATION

Arthroscopic lunate excision potentially prevented kinematic change of the proximal carpal row under axial loading by maintaining the integrity of attachment sites of carpal ligaments.

Lunate loads following different osteotomies used to treat Kienböck's disease: A 3D finite element analysis

BACKGROUND

One of most accepted principles for treating Kienböck's disease before wrist degeneration settles in is to decompress the lunate by an osteotomy. Several osteotomies have been proposed since 1935. However, they are based on biomechanical hypotheses that are sometimes conflicting: This study compares the decompression effect of radius transverse shortening, radius lateral closing and medial closing wedge osteotomies, capitate shortening - with and without hamate shortening - and a Camembert-type radius wedge osteotomy with and without ulnar head shortening according to Sennwald.

METHODS

We built a 3D wrist model using finite elements that included the metacarpal, carpal and forearm bones. All wrist ligaments and Triangular Fibrocartilage Complex were incorporated in the simulation. Load was applied on the metacarpals with the forearm bones fixed. We then applied the different osteotomies to the model.

FINDINGS

When load was applied to the wrist, the osteotomies that best unloaded the lunate were the capitate shortening osteotomy combined with hamate shortening and the Camembert osteotomy combined with ulna shortening; the latter was the only osteotomy that completely unloaded the lunate.

INTERPRETATION

We think the association of the radius Camembert osteotomy and ulna Sennwald's shortening osteotomy is the most effective procedure to propose in Kienböck's disease.

Scaphotrapeziotrapezoid Arthrodesis Using Limited Wrist Fusion Plates in Kienböck's Disease

PURPOSE

The purpose of this study was to evaluate the clinical and radiological results of scaphotrapeziotrapezoid (STT) arthrodesis with a limited wrist fusion plate in patients with Stage IIIB Kienböck's disease (KD).

MATERIALS AND METHODS

A retrospective review was performed on nine patients with Stage IIIB KD who underwent STT arthrodesis between 2014 and 2017 at our institution. Clinical evaluations of the patients were made using the shortened quick version of the Disabilities of the Arm, Shoulder, and Hand (Q-DASH) Outcome Measure score (Institute for Work and Health, Toronto, ON, Canada) and grip strength measurements before surgery and at the final follow-up examination. All patients underwent computed tomography (CT) scan to confirm the union of the arthrodesis.

RESULTS

A complete union was obtained in all patients. The Q-DASH score was changed from 57.8 ± 8.2 points (range: 47.7 - 70.5) to 32.3 ± 17.3 points (range: 13.6 - 54.5) (p = 0.008). Similarly, the grip strength was improved significantly (p = 0.007).

CONCLUSIONS

The use of limited wrist fusion plates for STT arthrodesis in KD is a safe and effective treatment method that provides a high rate union and acceptable functional results.

Vascularized Bone Graft to the Lunate Combined With Temporary Scaphocapitate Fixation for Treatment of Stage III Kienböck Disease: A Report of the Results, a Minimum of 2 Years After Surgery

PURPOSE

To report the outcomes of patients with stage III Kienböck disease treated by vascularized bone graft (VBG) followed by temporary scaphocapitate (SC) fixation, a minimum of 2 years after surgery.

METHODS

Twenty-six patients (mean age, 35 years) with stage III Kienböck disease (16 with stage IIIA and 10 with stage IIIB), treated with VBG followed by SC fixation for 4 months, were retrospectively followed for at least 2 years (range, 24-121 months; mean, 61.8 months). The preoperative and postoperative assessments included range of motion (ROM) of the wrist, grip strength (GS), wrist pain, the modified Mayo wrist score (MMWS), carpal height ratio (CHR), Ståhl index (STI), and radioscaphoid angle (RSA). The outcomes of each assessment of the stages IIIA and IIIB groups at the final examination were compared with those before surgery.

RESULTS

In both stages IIIA and IIIB groups, GS increased after surgery. Decrease of CHR and STI was associated with the increase of RSA in the stage IIIA group after surgery, while RSA decreased, although neither CHR nor STI significantly increased in the stage IIIB patients. No patient demonstrated deterioration of the wrist pain after surgery. Twenty-one of 26 patients had an improved MMWS grade at the final follow-up.

CONCLUSIONS

Vascularized bone graft combined with SC fixation for 4 months provided greater GS, pain relief, and functional improvement compared with before surgery in both stages IIIA and IIIB groups.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Trabecular bone patterning across the human hand

Hand bone morphology is regularly used to link particular hominin species with behaviors relevant to cognitive/technological progress. Debates about the functional significance of differing hominin hand bone morphologies tend to rely on establishing phylogenetic relationships and/or inferring behavior from epigenetic variation arising from mechanical loading and adaptive bone modeling. Most research focuses on variation in cortical bone structure, but additional information about hand function may be provided through the analysis of internal trabecular structure. While primate hand bone trabecular structure is known to vary in ways that are consistent with expected joint loading differences during manipulation and locomotion, no study exists that has documented this variation across the numerous bones of the hand. We quantify the trabecular structure in 22 bones of the human hand (early/extant modern Homo sapiens) and compare structural variation between two groups associated with post-agricultural/industrial (post-Neolithic) and foraging/hunter-gatherer (forager) subsistence strategies. We (1) establish trabecular bone volume fraction (BV/TV), modulus (E), degree of anisotropy (DA), mean trabecular thickness (Tb.Th) and spacing (Tb.Sp); (2) visualize the average distribution of site-specific BV/TV for each bone; and (3) examine if the variation in trabecular structure is consistent with expected joint loading differences among the regions of the hand and between the groups. Results indicate similar distributions of trabecular bone in both groups, with those of the forager sample presenting higher BV/TV, E, and lower DA, suggesting greater and more variable loading during manipulation. We find indications of higher loading along the ulnar side of the forager sample hand, with high site-specific BV/TV distributions among the carpals that are suggestive of high loading while the wrist moves through the 'dart-thrower's' motion. These results support the use of trabecular structure to infer behavior and have direct implications for refining our understanding of human hand evolution and fossil hominin hand use.

Risk Factors of Lunate Collapse in Kienböck Disease

PURPOSE

Not all patients with Kienböck disease progress to collapse of the lunate and carpal malalignment, but it is difficult to determine which patients are at risk. We aimed to identify demographic or anatomical factors associated with more advanced stages of Kienböck disease.

METHODS

We included all 195 eligible patients with Kienböck disease and available preoperative posteroanterior and lateral radiographs. We compared the mean age, sex distribution, mean ulnar variance, radial height, radial (ulnarward) inclination, palmar tilt, anteroposterior distance, and lunate type among the different Lichtman stages of Kienböck disease and performed ordinal logistic regression analysis.

RESULTS

We found that patients with more negative ulnar variance had more advanced stages of Kienböck disease (adjusted odds ratio, 1.4). An increase in age was also independently associated with a higher Lichtman stage of Kienböck disease (adjusted odds ratio, 1.02).

CONCLUSIONS

Our findings suggest that more negative ulnar variance may be related to a greater magnitude of lunate collapse in Kienböck disease. Additional long-term study is needed to confirm the longitudinal relationship of negative ulnar variance with progressive Kienböck disease.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic II.

Evaluation of midcarpal capitate contact mechanics in normal, injured and post-operative wrists

BACKGROUND

Scapholunate ligament injury is a commonly occurring carpal ligament injury. Pathology associated with scapholunate ligament injury depends on several factors such as the time after injury, type of injury (instability) and the development of osteoarthritis. The aim of this study was to investigate and compare contact mechanics in the lunocapitate and scaphocapitate joints in the normal, injured (scapholunate dissociation) and repaired (postoperative) wrist.

METHODS

Four human subjects with scapholunate ligament dissociation participated in this study. MR images of normal (contralateral), injured and postoperative wrists were obtained during relaxed condition and during active light grasp. Relaxed MR images were used to construct model geometry (bones with cartilage) for the capitate, lunate and scaphoid. Kinematic transformations were obtained by using image registration between the unloaded and functionally loaded image sets. Joint surface contact mechanics were then calculated.

FINDINGS

All contact measures (contact force, pressure, mean pressure and area) tended to increase with injury in both articulations. A significantly higher contact area was found in the injured scaphocapitate joint compared to normal. A significant increase in peak pressure was observed in the postoperative state compared to normal.

INTERPRETATION

Injury to the scapholunate ligament increased contact measures, suggesting a risk for onset of osteoarthritis in both the scaphocapitate and lunocapitate joints. Surgical repair appeared to restore most measures of contact mechanics to near normal values, more so for the lunocapitate joint when compared to scaphocapitate joint. The elevated postoperative peak pressures indicate the difficulty to fully restore joint mechanics.

Lunatum excision and scaphocapitate arthrodesis in Kienböck's disease

PURPOSE

The aim of this study was to compare functional results before and after lunatum excision and scaphocapitate arthrodesis (SCA) using an angular stable circular plate in patients with Lichtman's stage IIIB Kienböck's disease.

METHODS

The study included nine patients (six females and three males) with a mean age of 33.2 ± 11 years (range: 18-54 years). Clinical and radiological assessment before and after surgery included wrist extension and flexion, range of motion and grip strength, visual analogue scale (VAS) score to assess pain, modified Mayo wrist scores, and measurements of the scapholunate (SL) angle and modified carpal height ratio.

RESULTS

The mean follow-up period was 17.33 ± 4.69 months (range: 12-24 months), mean operation time was 56.67 ± 12.5 min (range: 45-75 min) and mean hospitalization time was 3.44 ± 1.13 days (range: 2-6 days). Preoperative mean wrist extension was 23.89° ± 4.17°, mean wrist flexion was 32.22° ± 5.07°, mean grip strength compared to the healthy side was 34% (range: 28-37%) and mean VAS score was 7.6 (range: 7-8). Modified Mayo wrist scores were poor in all of the nine patients. Post-operative mean wrist extension was 27.78° ± 4.41°, mean wrist flexion was 40.56° ± 4.64°, mean grip strength compared to the healthy side was 71% (range: 63-81%) and mean VAS score was recorded as 1.4 (range: 1-2). Modified Mayo wrist scores were good in five and moderate in four patients. No patients had non-union or additional surgery.

CONCLUSION

Lunatum excision and SCA using angular stable circular plate fixation provide pain relief with acceptable preservation of the range of motion.

Load distribution on the radio-carpal joint for carpal arthrodesis

BACKGROUND AND OBJECTIVE

Carpal fusions are useful for treating specific carpal disorders, maximizing postoperative wrist motion, hand strength, reducing pain and instability of the joint. The surgeon selects the appropriate treatment by considering the degree of stability, the chronicity of the injury, functional demands of the patient and former patient's outcomes as well. However there are not many studies regarding the load distribution provided by the treatment. So, the purpose of this study is to analyze the load distribution through the wrist joint with an arthrodesis treatment and compare the results with a normal wrist.

METHOD

To this end the rigid body spring model (RBSM) method was used on a three-dimensional model of the wrist joint. The cartilage and ligaments were simulated as springs acting under compression and tension, respectively, while the bones were considered as rigid bodies. To simulate the arthrodesis, the fused bones were considered as a single rigid body.

RESULTS

The changes on the load distribution for each arthrodesis agree with the treatment objective, reducing load transmission through a specific articular surface. For example, for SLAC/SNAC II most of the treatments reduced the load transmitted through the radioscaphoid fossae, almost by 8%. However, the capitolunate (CL) arthrodesis was the treatment that managed to keep the load transmitted through the radiolunate joint closer to normal conditions. Also, in treatments where the scaphoid was excised (3-corner, 4-corner and capitolunate arthrodesis), the joint surface between the lunate surface compensates by doubling the transmitted force to the radius.

CONCLUSIONS

The common arthrodesis for treating SLAC/SNAC II-III, reduces, in fact, the load on the radioscaphoid joint. Alternative treatments that reduce load distribution on the radiocarpal joint should be three corner and capitolunate arthrodesis for treating SLAC/SNAC-II; and for SLAC/SNAC-III four corners with scaphoid excision. On Kienbock's disease. Scaphocapitate (SC) arthrodesis is more effective on reducing the load transmission through the radiolunate and ulnolunate joints. All arthrodesis treatment should consider changes on the load transmission, and also bones' fusion rates and pain reduction on patient's outcomes.

Scaphocapitate arthrodesis for treatment of late stage Kienbock disease

Symptomatic lunate collapse owing to Kienböck disease is difficult to treat. To define the potential role of scaphocapitate arthrodesis, we reviewed ten patients who underwent scaphocapitate arthrodesis for stage IIIB-IV Kienböck disease at a mean follow-up of 8.75 years (range 1.3-18.6). Clinical variables included ranges of motion, grip strength, pain, return to work, and QuickDASH (disabilities of the arm, shoulder and hand) scores. Radiographs were evaluated for union, carpal height, alignment, ulnar translation, and radiocarpal arthritis. The procedure resulted in functional ranges of motion and good grip strengths. Pain was substantially reduced. The mean QuickDASH score was 27 (range 9.1-56.3). Radiographic analysis showed union in nine patients, maintenance of carpal height with a corrected radioscaphoid angle, and no evidence of ulnar translation. The long-term clinical benefits of scaphocapitate arthrodesis for treatment of collapsed Kienböck disease are demonstrated. However, radiographic signs of radioscaphoid arthritis were often observed in patients with follow-up greater than 10 years.

Radial shortening osteotomy in advanced stages of Kienbock disease

Radial shortening osteotomy is a well-accepted treatment for Kienbock disease in stages I to IIIA. The usefulness of this procedure in more advanced stages of the disease is controversial. In this study, 27 cases of stage IIIB and IV of Kienbock disease underwent radial shortening osteotomy and were followed for a mean period of 54.9 months (9 to 117 mo). Twenty-four patients had stage IIIB and 3 patients had stage IV disease. Sixteen of the affected wrists were on the dominant side. All patients were evaluated clinically and radiologically at last follow-up. Modified Mayo Score was used for clinical evaluation. The measured radiologic parameters included carpal height ratio, Stahl index, and radioscaphoid angle. In stage IIIB, 41.6% of cases had good, 54.2 had fair, and 4.2 had poor result, whereas in stage IV all patients showed poor result. The mean range of flexion-extension was 84.4% of the unaffected side. Considering the percentage of preserved motion, this procedure seems to be a good alternative to partial fusion for stage IIIB when the patient is willing to preserve more degrees of motion. Although the number of patients with stage IV disease was limited in this study, poor result in all of them may show the uselessness of this procedure in stage IV.

Clinical and radiological results following radial osteotomy in patients with Kienböck’s disease

Radial osteotomy is currently advocated for patients with Lichtman’s stages II and IIIA of Kienböck’s disease; its place in the treatment of patients with stage IIIB disease remains controversial. The purpose of this study was to evaluate the medium-term results of this procedure and to compare the outcome in patients with stage IIIB disease and those with earlier stages (II and IIIA). A total of 18 patients (18 osteotomies) were evaluated both clinically and radiologically at a mean follow-up of 10.3 years (4 to 18). Range of movement, grip strength and pain improved significantly in all patients; the functional score (Nakamura Scoring System (NSSK)) was high and self-reported disability (Disabilities of Arm, Shoulder and Hand questionnaire) was low at the final follow-up in all patients evaluated. Patients with stage IIIB disease, however, had a significantly lower grip strength, lower NSSK scores and higher disability than those in less advanced stages. Radiological progression of the disease was not noted in either group, despite the stage. Radial osteotomy seems effective in halting the progression of disease and improving symptoms in stages II, IIIA and IIIB. Patients with less advanced disease should be expected to have better clinical results.

Computed tomography osteoabsorptiometry alterations in stress distribution patterns through the wrist after radial shortening osteotomy for Kienböck disease

PURPOSE

The distribution pattern of subchondral bone density is considered to closely reflect the stress distribution across a joint under physiological loading conditions. Our purpose was to determine alterations in the distribution pattern of subchondral bone density across the distal articular surfaces of the radius and the ulna in patients with Kienböck disease after radial shortening.

METHODS

We collected preoperative and postoperative computed tomography (CT) image data from 7 wrists of 7 patients who had undergone radial shortening for Kienböck disease. We measured the distribution of subchondral bone density through the distal articular surface of the radius and the ulna using a CT osteoabsorptiometry method. The obtained data were quantitatively assessed by calculating the high-density area ratio of the entire radiocarpal joint surface, scaphoid fossa, lunate fossa, and distal ulnar surface.

RESULTS

At the mean postoperative period of 27 months, the mean high-density area ratio in the entire distal articular surface of the radius significantly decreased from 0.413 preoperatively to 0.141 postoperatively. The postoperative value in each fossa demonstrated a significant reduction from 0.253 to 0.096 in the scaphoid fossa and from 0.160 to 0.045 in the lunate fossa. No significant alteration in the value was found in the distal ulna at follow-up.

CONCLUSIONS

Our CT osteoabsorptiometry analysis suggests that the distribution of subchondral bone density in both scaphoid and lunate fossae notably decreases after radial shortening. This indicates that radial shortening unloads the lunate by reducing the actual stress across the distal articular surface of the radius in subjects with Kienböck disease.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Joint leveling for advanced Kienböck's disease

PURPOSE

The use of joint leveling procedures to treat Kienböck's disease have been limited by the degree of disease advancement. This study was designed to compare clinical and radiographic outcomes of wrists with more advanced (stage IIIB) Kienböck's disease with those of wrists with less advanced (stage II/IIIA) disease following radius-shortening osteotomy.

METHODS

This retrospective study enrolled 31 adult wrists (30 patients; mean age, 39 y), treated with radius-shortening osteotomy at 2 institutions for either stage IIIB (n = 14) or stage II/IIIA (n = 17) disease. Evaluation was performed at a mean of 74 months (IIIB, 77 mo; II/IIIA, 72 mo). Radiographic assessment determined disease progression. Clinical outcomes were determined by validated patient-based and objective measures.

RESULTS

Patient-based outcome ratings of wrists treated for stage IIIB were similar to those with stage II/IIIA (shortened Disabilities of the Arm, Shoulder, and Hand score, 15 vs 12; modified Mayo wrist score, 84 vs 87; visual analog scale pain score, 1.2 vs 1.7; visual analog scale function score, 2.6 vs 2.1). The average flexion/extension arc was 102° for wrists with stage IIIB and 106° for wrists with stage II/IIIA Kienbock's. Grip strength was 77% of the opposite side for stage IIIB wrists versus 85% for stage II/IIIA. Postoperative carpal height ratio and radioscaphoid angle were worse for wrists treated for stage IIIB (0.46 and 65°, respectively) than stage II/IIIA (0.53 and 53°, respectively) disease. Radiographic disease progression occurred in 7 wrists (6 stage II/IIIA, 1 stage IIIB). The one stage IIIB wrist that progressed underwent wrist arthrodesis.

CONCLUSIONS

In this limited series, clinical outcomes of radius shortening using validated, patient-based assessment instruments and objective measures failed to demonstrate predicted clinically relevant differences between stage II/IIIA and IIIB Kienböck's disease. Given the high percentage of successful clinical outcomes in this case series of 14 stage IIIB wrists, we believe that static carpal malalignment does not preclude radius-shortening osteotomy.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Conformational changes in the carpus during finger trap distraction

PURPOSE

Wrist distraction is a common treatment maneuver used clinically for the reduction of distal radial fractures and midcarpal dislocations. Wrist distraction is also required during wrist arthroscopy to access the radiocarpal joint and has been used as a test for scapholunate ligament injury. However, the effect of a distraction load on the normal wrist has not been well studied. The purpose of this study was to measure the three-dimensional conformational changes of the carpal bones in the normal wrist as a result of a static distractive load.

METHODS

Using computed tomography, the dominant wrists of 14 healthy volunteers were scanned at rest and during application of 98 N of distraction. Load was applied using finger traps, and volunteers were encouraged to relax their forearm muscles and to allow distraction of the wrist. The motions of the bones in the wrist were tracked between the unloaded and loaded trial using markerless bone registration. The average displacement vector of each bone relative to the radius was calculated, as were the interbone distances for 20 bone-bone interactions. Joint separation was estimated at the radiocarpal, midcarpal, and carpometacarpal joints in the direction of loading using the radius, lunate, capitate, and third metacarpal.

RESULTS

With loading, the distance between the radius and third metacarpal increased an average of 3.3 mm +/- 3.1 in the direction of loading. This separation was primarily in the axial direction at the radiocarpal (1.0 mm +/- 1.0) and midcarpal (2.0 mm +/- 1.7) joints. There were minimal changes in the transverse direction within the distal row, although the proximal row narrowed by 0.98 mm +/- 0.7. Distraction between the radius and scaphoid (2.5 mm +/- 2.2) was 2.4 times greater than that between the radius and lunate (1.0 mm +/- 1.0).

CONCLUSIONS

Carpal distraction has a significant (p < .01) effect on the conformation of the carpus, especially at the radiocarpal and midcarpal joints. In the normal wrist, external traction causes twice as much distraction at the lunocapitate joint than at the radiolunate joint.

A finite-element analysis of Kienbock's disease

A finite-element analysis model of the lunate was established using geometrical data obtained from cadaveric bones. The lunate cortex was modelled with triangular and quadrilateral elements and its intraosseous structure was represented either as a homogenous elastic structure or as an anisotropic network of cortical bone beams (trabeculae) with different orientations and thicknesses. Compressive loads applied to the metacarpus were distributed in the carpus against the fixed radius and ulna. The ulnar variance had a strong influence on the ratios radiolunate/ulnolunate total load and peak pressures. The distribution of internal stresses was markedly affected by the lunate uncovering index. The evolution of a simulated incomplete fracture was dramatically influenced by morphological parameters: with positive ulnar variance, the fracture did not progress, but in the presence of three associated conditions, negative ulnar variance, a high lunate uncovering index and angulated trabeculae, the fracture progressed and the proximal part of the lunate collapsed. This study supports the concept that some lunates are predisposed to Kienböck's disease because their anatomy induces abnormal internal stresses, which allow an incomplete fracture to progress, under heavy loading conditions, and cause progressive collapse and localised trabecular osteonecrosis.

Kienböck’s disease

Kienböck’s disease is a form of osteonecrosis affecting the lunate. Its aetiology remains unknown. Morphological variations, such as negative ulnar variance, high uncovering of the lunate, abnormal radial inclination and/or a trapezoidal shape of the lunate and the particular pattern of its vascularity may be predisposing factors. A history of trauma is common. The diagnosis is made on plain radiographs, but MRI can be helpful early in the disease. A CT scan is useful to demonstrate fracture or fragmentation of the lunate. Lichtman classified Kienböck disease into five stages. The natural history of the condition is not well known, and the symptoms do not correlate well with the changes in shape of the lunate and the degree of carpal collapse. There is no strong evidence to support any particular form of treatment. Many patients are improved by temporary immobilisation of the wrist, which does not stop the progression of carpal collapse. Radial shortening may be the treatment of choice in young symptomatic patients presenting with stages I to III-A of Kienböck’s disease and negative ulnar variance. Many other forms of surgical treatment have been described.

Predictors of clinical results of radial osteotomies for Kienböck's disease

The factors affecting the clinical results after radial osteotomies for Kienböck's disease are unknown. In the current study, we reviewed the data of 41 patients treated with radial osteotomies for Kienböck's disease and analyzed which preoperative factors significantly affected the clinical results of these procedures. Lateral closing wedge osteotomies of the radius were done for 22 patients (six patients with Lichtman Stage II disease, three patients with Lichtman Stage IIIA disease, 12 patients with Lichtman Stage IIIB disease, and one patient with Lichtman Stage IV disease) with zero or positive ulnar variance, and radial shortenings were done for 19 patients (four patients with Stage II disease, two patients with Stage IIIA disease, 12 patients with Stage IIIB disease, and one patient with Stage IV disease) with negative ulnar variance. The mean age of the patients at surgery was 36 years and the average followup was 38 months. To statistically assess the prognostic factors, multiple regression analysis focused on the postoperative clinical score as a dependent variable and preoperative patient data as independent variables. In the current analysis, patient age was the preoperative factor most clearly predictive of clinical results after radial osteotomies for Kienböck's disease. We think that the lower effectiveness of radial osteotomies must be considered in doing these procedures for elderly patients.

Lateral closing wedge osteotomy of the distal radius for advanced stages of Kienböck's disease

Seven patients with advanced Kienböck's disease, stage III-B and IV by Lichtman classification, who were treated with lateral closing wedge osteotomy of the distal radius were evaluated clinically and radiographically. The clinical results were correlated with radiographic changes. Five patients had stage III-B and 2 had stage IV disease; average follow-up period was 50 months (range, 24-93 months). Clinical results were good in 4 patients, fair in 2 patients, and poor in 1 patient based on Nakamura's postoperative clinical scoring system. The carpal-ulnar distance ratio and lunate-covering ratio increased and the radioscaphoid angle improved significantly. The improvements in radioscaphoid angle and Nakamura's postoperative clinical score showed a significant correlation. The satisfactory clinical outcome of lateral closing wedge osteotomy of the distal radius for advanced-stage Kienböck's disease can be attributed to the effects of the increased lunate-covering ratio and the improved radioscaphoid angle on carpal alignment.

Force transmission through the juvenile idiopathic arthritic wrist: a novel approach using a sliding rigid body spring model

Force transmission across the wrist during a grasping maneuver of the hand was simulated for three children with juvenile idiopathic arthritis (JIA) and for one healthy age-matched child. Joint reaction forces were estimated using a series of springs between articulating bones. This method (i.e., rigid body spring modeling) has proven useful for examining loading profiles for normally aligned wrists. A novel method (i.e., sliding rigid body spring modeling) designed specifically for studying joint reaction forces of the malaligned JIA wrist is presented in this paper. Loading profiles across the wrist for the unimpaired child were similar using both spring modeling methods. However, the traditional fixed-end method failed to converge to a solution for one of the JIA subjects indicating the sliding model may be more suitable for investigating loading profiles of the malaligned wrist. The results of this study suggest that a larger proportion of force is transferred through the ulno-carpal joint of the JIA wrist than for healthy subjects, with a less than normal proportion of force transferred through the radio-carpal joint. In addition, the ulnar directed forces along the shear axis defined in this study were greater for all three JIA children compared to values for the healthy child. These observations are what were hypothesized for an individual with JIA of the wrist.

Kienbock's disease: diagnosis and treatment

Kienbock's disease, or osteonecrosis of the lunate, can lead to chronic, debilitating wrist pain. Etiologic factors include vascular and skeletal variations combined with trauma or repetitive loading. In stage I Kienbock's disease, plain radiographs appear normal, and bone scintigraphy or magnetic resonance imaging is required for diagnosis. Initial treatment is nonoperative. In stage II, sclerosis of the lunate, compression fracture, and/or early collapse of the radial border of the lunate may appear. In stage IIIA, there is more severe lunate collapse. Because the remainder of the carpus is still uninvolved, treatment in stages II and IIIA involves attempts at revascularization of the lunate-either directly (with vascularized bone grafting) or indirectly (by unloading the lunate). Radial shortening in wrists with negative ulnar variance and capitate shortening or radial-wedge osteotomy in wrists with neutral or positive ulnar variance can be performed alone or with vascularized bone grafting. In stage IIIB, palmar rotation of the scaphoid and proximal migration of the capitate occur, and treatment addresses the carpal collapse. Surgical options include scaphotrapeziotrapezoid or scaphocapitate arthrodesis to correct scaphoid hyperflexion. In stage IV, degenerative changes are present at the midcarpal joint, the radiocarpal joint, or both. Treatment options include proximal-row carpectomy and wrist arthrodesis.

Force distribution through the wrist joint in patients with different stages of Kienböck's disease: using computed tomography osteoabsorptiometry

The pattern of subchondral bone density has been considered to reflect the stress distribution that occurs under physiologic loading conditions. To determine the force distribution through the wrist joint with Kienböck's disease in living subjects, we applied a computed tomography osteoabsorptiometry and investigated the subchondral bone density pattern across the radio-carpal joint of 6 normal subjects and 10 patients suffering from Kienböck's disease (Lichtman's stage IIIA, 5 patients; stage IIIB, 5 patients). A single density maximum was found in each scaphoid and lunate fossa in all normal subjects. Among the subjects with Kienböck's disease, the current analysis demonstrated that the density maximum area significantly increased in the scaphoid fossa and decreased in the lunate fossa from stage IIIA to IIIB group. These findings indicate that the load is shifted away from the lunate to the scaphoid with the progression of Kienböck's disease in living subjects.

Lateral closing wedge osteotomy for treatment of Kienböck's disease. A clinical and biomechanical study of the optimum correcting angle

A retrospective clinical analysis of 20 patients who underwent a lateral closing wedge osteotomy of the radius as an adjuvant procedure to a radial recession in the treatment of Kienböck's disease is reported. The functional outcome is compared to the results of a simplified two-dimensional articulating force analysis (Rigid Body Spring Model) based on radiographs of the wrist of the same patients taken before and after surgery. At an average follow-up of 39 months, wrist function was excellent in 4 patients, good in 9, moderate in 6, and poor in one patient. A significant positive correlation between functional improvement and percent reduction of the calculated peak pressure at the radiolunate interval was found. This was maximal in patients with wedge osteotomies between 5 and 10 degrees.