Kienböck disease is a common cause of chronic wrist pain, which is characterized by aseptic necrosis of the carpal lunate. Although its prevalence in the population is not high, it is not uncommon in hand surgery clinical work and seriously endangers the stability of the wrist joint, but so far, there is still more controversy about the etiology, imaging features and treatment of this disease, and more importantly, the problem of early diagnosis of this disease has not been well resolved. Therefore, further research and understanding of this disease is necessary. Lichtman summarized the clinical and radiological features and divided Kienböck disease into four stages: stage I patients often have recent carpal hyperextension injury, moderate wrist pain, often relieved in a few weeks, radiographs show basically normal structure and bone density of the lunar bones, but there can be linear or compression fractures, body layer photography helps to clarify suspected fractures; stage II patients clinically Stage II patients show recurrent wrist pain, swelling and pressure pain, and the X-ray shows a significant change in bone density of the lunate bone compared with other wrist bones, but basically normal in size, shape and anatomical relationship; in this late stage, the height of the radial side of the lunate bone is reduced as seen in anteroposterior radiographs; Stage III patients have approximately the same clinical manifestations as Stage II, only the stiffness and coagulation of the wrist joint is more obvious, and the X-ray shows collapse of the entire lunate bone, and The most obvious manifestation in the lateral radiograph is the dorsal palmar lengthening of the lunate. The pain and swelling of the wrist joint in stage IV patients may be mild, but the loss of wrist joint movement is typical. In addition to the features of stage III, the X-ray mainly shows comprehensive degenerative changes of the wrist joint, including narrowing of the joint space, formation of bone redundancy, subchondral sclerosis and even degenerative cysts. On this basis, stage III was divided into stage IIIA (normal correspondence between the navicular bone and the surrounding wrist bones) and stage IIIB (widening of the interphalangeal joint space, increased palmar flexion of the navicular bone, and ulnar deviation of the triangular bone) based on the correspondence between the navicular bone and the surrounding wrist bones. As research progresses, this disease has had many different expressions, such as ischemic necrosis of the lunar bone, chronic fibrous osteitis of the lunar bone, compression osteitis, traumatic osteoporosis and cystic bone atrophy. However, because it is difficult to have a name that more comprehensively summarizes the characteristics of this disease, the name Kienböck is still widely used to name it so far. The confusion of the names is an indication that the understanding of the disease is far from adequate, and the help of histopathology is needed to provide us with more direct and accurate information through clinical symptoms, signs and imaging examinations. In clinical practice, histopathology is known as the “judge” of the nature of the disease, because it can show us the nature of certain diseases. Histopathological studies of Kienböck disease are few and far between, but the limited studies that have been done have provided us with much valuable information. The use of surgical removal of the lunate bone in the treatment of some stage III patients has made possible the pathologic examination of the entire lunate bone. Foci of osteonecrosis were seen in all examined cases, manifesting as cavities, fat necrosis and bone loss. The destructive response includes resorption of the necrotic bone by osteoclast-type giant cells and the growth of granulation tissue into the necrotic area. In the early stages of stage III, osteonecrosis is mostly concentrated in the central area of the proximal lunate convexity; and the subchondral bone and articular cartilage in the necrotic area are only fractured and collapsed in the proximal lunate convexity. In almost all samples, a continuous three-layer structure of necrotic bone, osteoid (cartilage-like metaplasia), and granulation tissue was observed in multiple areas. In the osteoid zone, new bone formation by osteoblast-like cells present on the surface of the necrotic bone was observed. The boundary between the necrotic and osteoid zones can be clearly defined by Velaneuva-Goldner staining. In advanced specimens, however, the necrotic zone is mixed with the repaired zone and is difficult to distinguish, and multiple forms of fracture and collapse are present. Etiology There are many speculations about the etiology of this disease, and it is generally believed that it is the result of a combination of post-traumatic factors. The factors involved include the negative ulnar variation, the ulnar deviation angle of the distal radius, the status of the original blood supply to the lunate bone, the mechanism of injury, the age of the patient and the morphology of the lunate bone. Although there are also case reports of Kienböck disease associated with gout, SLE, sickle cell anemia and wrist flexion deformity due to cerebral palsy, a number of investigators have also clearly indicated that common factors causing osteonecrosis such as cortisol hormone use, vasculitis, vasculopathy, chronic alcoholism, hypercoagulable states and Caisson’s disease are not associated with lunar osteonecrosis. It is suggested that the etiology of Kienböck disease and osteonecrosis of the femoral head are not identical. The initial stage of Kienböck disease is only a small, partial osteonecrosis, mostly concentrated in the central area of the proximal lunate convexity, suggesting that the cause of the lesion may not be a complete disruption of the lunate blood supply, but more related to the stress load on the lunate bone. Thereafter, if the osteonecrosis is small and can be resorbed or repaired, the condition may improve; however, if the osteonecrosis is prolonged or enlarged, it will most likely interfere with the normal lunar blood supply, resulting in a vicious cycle of osteonecrosis, impaired blood supply, and more extensive osteonecrosis, eventually leading to irreversible lunar bone damage. Giunta et al. used CT bone resorption to study the mineralization of the subchondral bone of the radius, which is said to reflect its long-term stress distribution, and found that in normal subjects, stress concentrations were seen in both the navicular and lunar counterparts, whereas in Kienböck patients, mineralization in the lunar counterparts disappeared and the overall mineralization level was lower than in the normal group. This shows that the stress in the lunar bone is no longer high or even reduced after the onset of the disease. This seems to suggest that stress loading of the lunar bones may only play a role in the early stages of onset. Another much debated issue is whether Kienböck disease is associated with negative ulnar variation and ulnar deviation of the distal radius. Previous studies have suggested a close relationship between the three, and the fact that radial osteotomy to reduce or even eliminate negative ulnar variation and improve the distal ulnar deviation of the radius is effective in the treatment of early Kienböck disease also suggests a correlation; however, recent studies by Nakamura, Tsunoda, and Tian Guanglei have concluded that there is no significant correlation between the two. After comparing their study methods, it was found that the latter stratified and paired the patients by sex and age on the one hand to make the statistical results more convincing, but on the other hand the methods they used to measure the negative ulnar variation and the distal radial ulnar deviation angle differed, thus also affecting the comparison of the three statistical results. Previous studies have used the median axis of the radial stem as the standard and measured the angle between it and the tangent line of the distal radial articular surface as the distal ulnar deviation angle, and measured the vertical distance from the carpal articular surface of the ulna to the horizontal line past the ulnar point of the distal radius to determine the ulnar variation; Nakamura and Tsunoda used the Palmar concentric circle method to measure the ulnar variation; while the measurement method used by Guanglei Tian was to measure the ulnar variation past the distance of The distance from the lowest point of the distal ulnar articular surface to this vertical line was measured as the negative ulnar variation value, and the angle between the tangent line of the distal radial articular surface and the measurement standard line was used as the distal ulnar deviation angle. In this way, for the same patient, the Tian’s negative ulnar variance measurement will be larger than the former, while the distal radial ulnar deviation angle will be smaller; while for the concentric circle method, only when the radius of the concentric circles is large enough, the two arcs will be close to a straight line, and the measured value will be closer to the classical measurement, while when the radius of the concentric circles is small, the measured value will be larger than the classical measurement. This makes the proportion of negative ulnar variation significantly higher than the former in the normal population statistics, and the ulnar deviation angle of the distal radius is generally small, which may lead to the conclusion that the negative ulnar variation and ulnar deviation angle of the distal radius are not related to Kienböck disease. Of course, none of the above three measurements reflects the morphological characteristics of the distal radial articular surface well, and it seems crude to illustrate the complexity of the distal radial articular surface only by connecting two points into a straight line, so it remains to be explored how a more accurate measurement method can be developed. Since more studies have shown that Kienböck disease is associated with ischemia, it has even been suggested that 8-32% of the lunate bones have a unique blood supply only on the palmar side, and that interruption of this blood supply for various reasons (fracture, avulsion, or increased intra-articular pressure due to synovitis of the wrist, etc.) can lead to necrosis of the lunate bone. However, if it is the only interruption of the blood supply, it should lead to more extensive ischemic necrosis of the lunate bone and it is less likely that the necrosis will be accompanied by new bone repair, which does not seem to be consistent with the histopathological findings. Moreover, nuclear scans show nucleus concentrations in the majority of cases, suggesting that the arterial blood supply to the lunate bone is not completely interrupted, but rather there is a possibility of poor venous return. Therefore, it has been suggested that ischemia is not the initial cause of Kienböck disease, but rather the result of a stress abnormality in the lunar bone (called the “nutcracker effect”) that causes microfractures that interfere with the internal blood supply to the lunar bone. Of course, the characteristics of the distribution of the internal microvascular bed of the lunate bone and its influence in the various stages of Kienböck disease need to be further investigated. Diagnosis Because the early clinical presentation of this disease is not specific, its early diagnosis relies heavily on imaging. Early radiographs often do not provide valid evidence, whereas CT is more sensitive for fracture detection, and the recent use of 3D reconstruction of CT for the diagnosis of carpal disorders has given it a greater advantage in representing the morphology of the lunate bone and its relationship to all surrounding bones. Nuclear scanning is currently considered to be the most sensitive method of detection, showing nuclear concentration and delayed visualization of the lunate bone or its surroundings, or even the entire wrist joint, which may be due to vascular-rich granulation tissue during lunate bone repair and synovial inflammation imaging of the wrist joint. It has been reported that nuclear scans that show reduced nuclear aggregation and delayed imaging may be associated with a lack of lunar bone revascularization and bone repair, thus suggesting a poor prognosis. Although the sensitivity of this method is close to 100%, the specificity is not high. In contrast, the specificity of MRI is higher and, therefore, it has been suggested that nuclear scan should be used as an early screening method and MRI should be used as a basis for confirming the diagnosis. In recent years, the technology of MRI has continued to improve, with successive strides in surface coils, gradient hardware and pulse sequences, which, together with higher magnetic field strength, have made faster data acquisition, smaller fields of view and thinner tomography possible, and these have made the application of MRI in hand surgery possible. In MRI images normal bone marrow tissue appears as high signal due to its richness in fat and hematopoietic cells. If normal bone marrow tissue is replaced by necrotic bone, inflammatory tissue or other pathological tissue (such as Gaucher’s disease), the lesion area appears as low signal, and if the lesion develops into sclerosis and collapse, the lesion tissue remains as low signal. Therefore, focal or overall hyposignal lunar bones can be detected early in Kienböck disease. Further comparative histologic and imaging studies have shown that the clinical significance of T1- and T2-weighted images remains different, and although low signal in both is highly correlated with inactive bone on tissue biopsy (100% specificity, with some studies suggesting that T2-weighted images are more specific than T1-weighted images), high signal in T1-weighted images is mostly correlated with active bone (89% sensitivity), whereas high signal in T2-weighted images The high signal in the T2-weighted image was not always associated with active bone (sensitivity of 55%). In assessing treatment outcome and prognosis, although the hyposignal area of MRI does not suggest the histological content of the necrotic zone and does not distinguish between new bone and granulation tissue, if a hypodense arc is seen in the sagittal T1-weighted image, it is often suggested as a zone of tissue reaction surrounding the necrotic zone. Grade I: normal (isointense); Grade II: mildly reduced signal intensity in localized areas; Grade III: more extensive mildly reduced signal intensity; Grade IV: low signal with high signal or isosignal areas; Grade V: extensive low signal. It also concluded that increased signal intensity on postoperative T1-weighted images was significantly associated with improved radiographic performance of the lunar bone. Since five of the six patients in his study showed pure T2-weighted image signal enhancement at 2-5 months postoperatively, he speculated that T2-weighted images are more sensitive than T1-weighted images in detecting repair [26], which seems to be slightly contradictory to what was described above, but on closer analysis it is not, because this phenomenon occurs only in the early postoperative period (2-5 months) and may be related to soft tissue repair and recanalization, and The presence of high signal areas in the low signal areas of T2-weighted images is often associated with a good prognosis, while the presence of a large amount of isosignal in the low signal areas of the lunar bone in T1-weighted images suggests the recovery of lunar bone blood flow. Treatment Because the histopathological changes in early Kienböck disease (stages I, II, and IIIA) are only focal osteonecrosis in the area of stress concentration (the central area of the proximal lunate convexity) and are still reversible, treatment can be provided by various methods to reduce lunate stress and improve lunate blood flow, including wrist braking, bracing and external fixation, radial shortening/ulnar lengthening, and radial wedge osteotomy. radius, radial wedge osteotomy to improve the ulnar deviation angle of the distal articular surface, vascular or musculoskeletal flap implantation, cephalic hook fusion, and cephalic shortening. As mentioned earlier, stage I patients have no specific changes in clinical manifestations and radiographic examinations, and are difficult to distinguish from wrist sprains, and no prospective studies on their treatment have been seen. For the treatment of stage II and IIIA patients, most studies have reported that radial shortening, ulnar lengthening and radial wedge osteotomy can achieve more satisfactory results. In an ex vivo study, Gong Xu et al. showed that cephalic shortening redistributed the stresses through the radial carpal joint, reducing the compressive stresses in the cephalic bone by an average of 77.5% and increasing the tensile stresses in the navicular bone by an average of 79.1%, thus effectively reducing the axial stresses transmitted through the cephalic bone to the lunar bone. Chuinard and Zeman suggested that cephalic hook fusion would reduce the proximal displacement of the skull and reduce compression of the “softened” lunate bone, thus avoiding lunate fragmentation and collapse. In this procedure, the proximal displacement of the cephalic bone should not exceed 2 mm, and if the displacement already exceeds 2 mm, cephalic hook fusion with lunar bone replacement may be used. The efficacy of vascular or musculoskeletal flap implantation is controversial. It is currently believed that it is difficult to effectively improve the blood flow to the lunate bone with simple drilling and bone grafting. Other experimental studies have concluded that despite the implantation of vascular bundles, the rate of osteogenesis lags far behind the rate of resorption of dead bone and is not effective in preventing softening and collapse of the lunar bone. The histopathological changes in advanced Kienböck disease (stages IIIB and IV) are more extensive osteonecrosis, fragmentation and collapse of the lunate, and general degenerative changes of the wrist joint. This makes it difficult to implement treatment options that attempt to salvage the lunate bone through surgical approaches. Few treatments are widely accepted for these patients, and the more commonly used procedures include lunate removal, prosthetic implantation, tendon suspension, myoball filling, wrist arthroplasty, various intracarpal fusions, and proximal row carpal resection. The lunate bone removal surgery has been carried out for more than half a century. Although its recent results are good, the late displacement of the cephalic bone to the proximal side can lead to disturbance of the relationship between the remaining carpal bones, so in recent years it has been used less alone and replaced by the implantation of various prostheses, the commonly used prostheses are alloy prosthesis, acrylic prosthesis and silicone prosthesis. Although the implantation of the prosthesis can prevent the displacement of the cephalic bone and maintain the wrist height, there are problems of wear and tear, dislocation and foreign body reaction. It has also been reported that there is a reduction in wrist height in the late stage due to the small or soft myoballs. As for the choice of intracarpal fusion, Almquist concluded that the navicular lunar fusion has a high percentage of nonunion and is not suitable for cases in which the lunate has been fragmented; the cephalic navicular lunar fusion is also inappropriate at this time because the lunate has mostly collapsed and the radial surface is uneven, so performing fusion of the distal side of the lunate is not helpful; whereas the radial navicular lunar fusion is not only stable, but also maintains a moderate range of motion, and in When performing this procedure, the articular surfaces of the lunar and cephalic bones must be well preserved. Recently, Watson has recommended the use of large and small pollicis and navicular fusion to relieve pressure on and stabilize the lunar bone, with good results. Early results are better with proximal row carpal resection, but joint changes and pain can occur in the late stages. In contrast, most patients with Kienböck disease are young and middle-aged, so total wrist arthroplasty is not widely available. Total wrist fusion is certainly effective in wrist stabilization and pain relief for cases where other treatments have failed. In addition to the above causal treatments, there are also symptomatic treatments such as neurectomy, in which the nerves cut are the dorsal interosseous nerve, the palmar interosseous nerve, the radial nerve and the articular branch of the ulnar nerve. This procedure not only can significantly reduce the wrist pain, but also can basically maintain the wrist mobility and grip strength in the near future, but at the same time, because the wrist joint loses the protection of the pain mechanism, the occurrence and progress of osteoarthritis is faster. Through the analysis of the histopathology of Kienböck disease, combined with epidemiological data and many clinical case reports, it is tentatively believed that the etiology of the disease may be closely related to the abnormal lunar bone stress, and that ischemia and necrosis, as important links in the pathological process, do not seem to be its main initiating factors. Due to the lack of specificity of the early clinical manifestations, nuclear scan can be used as a screening tool for suspicious cases, and MRI is used as an early diagnostic basis, but the use of MRI as a prognostic assessment has yet to be further clinically validated. In terms of treatment principles, it is advisable to promote lunate repair by reducing lunate stress and improving lunate blood flow in the early stage; in the late stage, the aim is to reduce pain and maintain wrist height and grip strength as much as possible at the expense of lunate and/or partial wrist motion; neurectomy can be considered for elderly patients and non-manual workers; and total wrist fusion can be the final solution for cases in which all the above treatments fail.