Scapholunate Advanced Collapse Research Articles

When and which treatment for scapho-lunate ligament lesions?

The lesions of the scapholunate ligament are some of the most frequently encountered in the wrist. Left untreated, the complete rupture of the ligament is followed by degenerative arthritis according to a well-defined pattern of progression through the wrist, eventually leading to multifocal arthrosis, a condition described as scapholunate advanced collapse (SLAC wrist). The scapholunate lesions are classified in stages according to the degree of the lesion established by imaging studies or arthroscopy and to the chronicity of the lesion. Both together essentially determine the healing potential and the prognosis, which rapidly decrease after six weeks from the initial trauma, thus indicating the importance of recognizing the acute or subacute lesion and directing the patient to the hand surgeon early enough. The therapeutic options are notably reduced and often of palliative nature in case of chronic lesions with secondary changes in the wrist mechanics or cartilage damage.

The prevalence of the extensor digitorum communis tendon and its insertion variants: a systematic review and meta-analysis.

The tendons of the Extensor Digitorum Communis (EDC) are frequently injured in hand trauma. Dislocation and spontaneous rupture can also occur during the course of wrist osteoarthritis and rheumatoid arthritis. The EDC exhibits many variations including splitting of its individual slips to the medial four fingers or their absence. The aim of this systematic review is to assemble evidence about the prevalence of the EDC and its variants on the dorsum of the hand. Twenty-four cadaveric studies met the inclusion criteria, providing data from a total of 2,005 hands. Meta-analysis yielded the following results: (a) for EDC-II (Index), the pooled prevalence estimates (PPEs) were 99.8, 98, 1.8, and 0.2% for the total, single, double, and triple slips, respectively; (b) for EDC-III (Middle), the PPEs were 100, 67.7, 24.2, 6, and 0.42% for the total, single, double, triple, and quadruple slips, respectively; (c) for EDC-IV (Ring), the PPEs were 100, 58.6, 29.1, 7.1, and 1.3% for the total, single, double, triple, and quadruple slips, respectively; (d) for EDC-V (Little), the PPEs were 63.2, 58.5, 10.4, 0.94, and 25% for the total, single, double, triple, and common 4th-5th slips, respectively. There were no significant differences in relation to hand side. Many EDC slip variants demonstrated some interaction with ancestry. A sound knowledge of EDC variants and their prevalences is paramount for assessing and treating hand injuries and disorders.

Scapholunate advanced collapse: a pictorial review

Teaching PointsScapholunate advanced collapse (SLAC) is the most common cause of osteoarthritis involving the wrist. Along with clinical investigation, radiological studies play a vital role in the diagnosis of SLAC wrist. Given that the osteoarthritic changes that are seen with SLAC occur in a predictable progressive pattern, it is important to understand the pathological evolution of SLAC to be able to recognise the associated progressive imaging findings seen with this disease process. Focusing on radiological findings, this article provides a pictorial review of the anatomy of the scapholunate interosseous ligament as well as the common terminology and biomechanical alterations seen in the pathway leading to the development of SLAC arthropathy. We will then discuss two additional common causes of SLAC wrist and their imaging findings, namely scaphoid non-union advanced collapse and calcium pyrophosphate dehydrate disease. In addition, we will provide a brief overview of the current treatment options of these pathological entities.• SLAC is the most common cause of osteoarthritis involving the wrist.• Arthritic changes of SLAC occur in a predictable progressive pathological and radiographic pattern.• Imaging is key for diagnosing, monitoring progression and assessing post-treatment changes of SLAC.

Arthroscopic Resection Arthroplasty of the Radial Column for SLAC Wrist.

Background Symptomatic advanced scapholunate advanced collapse (SLAC) wrists are typically treated with extensive open procedures, including but not limited to scaphoidectomy plus four-corner fusion (4CF) and proximal row carpectomy (PRC). Although a minimally invasive arthroscopic option would be desirable, no convincing reports exist in the literature. The purpose of this paper is to describe a new surgical technique and outcomes on 14 patients who underwent arthroscopic resection arthroplasty of the radial column (ARARC) for arthroscopic stage II through stage IIIB SLAC wrists and to describe an arthroscopic staging classification of the radiocarpal joint for patients with SLAC wrist. Patients and Methods Data were collected prospectively on 17 patients presenting with radiographic stage I through III SLAC wrist who underwent ARARC in lieu of scaphoidectomy and 4CF or PRC. Fourteen patients (12 men and 2 women) subject to 1-year follow-up were included. The average age was 57 years (range 41 to 78). The mean follow-up was 24 months (range 12 to 61). Arthroscopic resection arthroplasty of the radial column is described for varying stages of arthritic changes of the radioscaphoid joint. Midcarpal resection was not performed. Results The mean Disabilities of the Arm, Shoulder, and Hand (DASH) score was 66 preoperatively and 28 at final follow-up. The mean satisfaction (0 = not satisfied, 5 = completely satisfied) at final follow-up was 4.5 (range 3 to 5). The pain level (on 0-10 scale) improved from 6.6 to 1.3. The total arc of motion changed from 124° preoperatively to 142° postoperatively following an ARARC. Grip was 16 kg preoperatively and 18 kg postoperatively. Radiographic stages typically underestimated arthroscopic staging. Although four of our patients appeared to be radiographic stage I, all were found to have arthritis involving some or all of the radioscaphoid articulation at the time of arthroscopy. Clinical Relevance Pain relief is rapid and remains consistent over time following ARARC. ARARC may be a viable surgical option for patients with SLAC wrist who desire a minimally invasive procedure. Radiographic stages underestimate the degree of arthritic change. Accurate staging requires arthroscopy. The indications and long-term outcome are not well defined; continued surveillance is warranted. Level of Evidence Level IV, Therapeutic study.

Vascularized Bone Grafting and Distal Radius Osteotomy for Scaphoid Nonunion Advanced Collapse

To determine the outcome of an alternative treatment for wrists with stages I to III scaphoid nonunion advanced collapse using a closing-wedge osteotomy of the distal radius and a vascularized bone graft for scaphoid reconstruction. Twelve patients with scaphoid nonunion advanced collapse (stage I, 3; stage II, 7; stage III, 2) treated with a vascularized bone graft interposition for the scaphoid and a closing-wedge osteotomy for the distal radius were retrospectively reviewed. Data were obtained and analyzed from the radiographs, and we assessed the pre- and postoperative range of motion, grip strength, visual analog scale pain score, as well as the Mayo and Disabilities of the Arm, Shoulder, and Hand (DASH) functional scores. Follow-up ranged from 2 to 11 years. All scaphoid nonunions united after an average of 9 weeks, and all osteotomies united after an average of 8 weeks. Although there was radiographic progression of the scaphoid nonunion advanced collapse stage in 5 of 12 cases, there was major improvement in visual analog scale pain score (from 6.1 to 0.8) and in both Mayo (from 64 to 85) and DASH (from 40 to 9) functional scores. The range of motion remained unchanged, and grip strength trended toward minor improvement. The carpal height was preserved, and the dorsal intercalated segmental instability was corrected. Scaphoid reconstruction with vascularized bone graft combined with closing-wedge distal radius osteotomy preserved wrist function for scaphoid nonunion advanced collapse. The method offers pain relief and does not compromise wrist motion or grip strength. Therapeutic IV.

Osteoarthritis of the Wrist

This article reviews pathogenesis and treatment of wrist osteoarthritis. Because there is no cure for osteoarthritis, treatment is directed at symptomatic relief. Surgical treatment is reserved for patients who have failed nonoperative modalities. This article reviews the surgical treatment of wrist osteoarthritis with an emphasis on selection of the appropriate procedure. Literature guiding surgical treatment with patient outcomes is reviewed.

Commentary on Akbar et al. Prevalence of carpal tunnel syndrome and wrist osteoarthritis in long-term paraplegic patients compared with controls

Commentary on Akbar et al. Prevalence of carpal tunnel syndrome and wrist osteoarthritis in long-term paraplegic patients compared with controls

Four-corner arthrodesis using distal radius bone grafting

Purpose The aim of the study was to review the clinical and radiographic results of four-corner arthrodesis for stages 2 and 3 scapholunate advanced collapse and scaphoid nonunion advanced collapse wrist using 3 Kirschner-wires (3K-wires) and bone graft from distal end of the radius. Patients and methods Twenty patients (scaphoid nonunion advanced collapse, n = 14; scapholunate dissociation, n = 6) underwent four-corner arthrodesis using 3K-wires and distal end radius bone graft and were evaluated for radiographic and clinical success using standard posteroanterior and lateral wrist radiographs and according to modified Mayo Wrist Scoring Chart at 6 and 12 months after surgery. Wrist pains, range of the wrist motion, and grip strength were evaluated at final follow-up. A total of 12 men and eight women were included and their average age at surgery was 38 years. In all, 14 wrists were right and six were left. Results Radiographic film assessment revealed union in all cases after an average period of 7 weeks, a well-preserved radiolunate articular interval at all stages of follow-up examination. Pain classification scores showed that 10 patients were pain free, nine patients complained slight pain with vigorous activities, and only one patient complained moderate pain with vigorous activities. The mean flexion improved from 42 to 70% of the normal side. The mean extension improved from 29 to 65% of the normal side. The mean ulnar deviation improved from 28 to 43% of the normal side. The mean radial deviation improved from 30 to 45% of the normal side. Grip strength significantly improved from 28% of opposite side preoperatively to 61% postoperatively. Complications occurred in three cases, radial impingement in one patient, ulnar neuritis in one patient, and superficial infection in one patient. Conclusion We have shown that four-corner arthrodesis using K-wires effectively achieves union, provides satisfactory pain relief, restores grip strength, allows return to original job, and preserves functional motion.

Associations of work activities requiring pinch or hand grip or exposure to hand-arm vibration with finger and wrist osteoarthritis: a meta-analysis

We systematically reviewed the epidemiologic evidence linking finger and wrist osteoarthritis (OA) with work activities requiring pinch or hand grip or exposure to hand-arm vibration (HAV). PubMed and Embase databases were searched up to June 2013. We selected studies assessing the associations of radiographic diagnosed finger and/or wrist joint OA with work activities involving pinch or hand grip or exposure to HAV. We used specific criteria to evaluate completeness of reporting, potential confounding, and bias. Pooled odds ratios (OR) were computed using random-effects meta-analyses. Of the 19 studies included, 17 were cross-sectional, 1 was a prospective cohort, and 1 a case-control study. The meta-analyses of studies that controlled their estimates for at least age and gender showed the associations of pinch grip work with proximal interphalangeal joint [OR 1.56, 95% confidence interval (95% CI) 1.09-2.23] and the first carpometacarpal joint OA (OR 2.10, 95% CI 1.06-4.17), but not with distal interphalangeal, metacarpalphalangeal, or wrist joints OA. Hand grip work and exposure to HAV were not associated with any finger or wrist OA. Epidemiological studies provide limited evidence that pinch grip may increase the risk of wrist or finger OA, but causal relation cannot be resolved because of cross-sectional designs and inadequate characterization of biomechanical strain to the hand and wrist.

English

Abstract Introduction Osteoarthritis is more common than any other joint disease, and patients often ask what the cause is, enquiring about environmental causes, such as previous occupation. The available literature suggests that factors such as increasing age, gender (female), obesity and genetics may all lead to the development of osteoarthritis of the hand or wrist. It is a multifactorial, heterogenous and complex disease. This review article presents the evidence that aging, female gender and hereditary factors are the most compelling culprits in the culmination of the primary hand and wrist osteoarthritis. Materials and methods Extensive literature search was carried out. Results As people age, the risk of developing osteoarthritis increases, with over 90% of those over 80 years of age being afflicted. For patients over the age of 60 years, the rate at which osteoarthritis progresses also increases. The prevalence of osteoarthritis at the base of the thumb has been shown to increase more rapidly in women than in men, with earlier peak prevalence in women. There is questionable evidence about hormonal links and hand osteoarthritis, rather chromosomes, genes and human leukocyte antigen-types are linked. Epidemiology of osteoarthritis of the hand and wrist

Radiological and Anatomical Study to Investigate Possibility of Relationship Between Scaphoid Fracture and Lunate Morphology

A connection between lunate type has been described for medical conditions like Kienbock's disease as well as for wrist osteoarthritis, e.g. STT osteoarthritis. Aim of the Study to investigate the possibility of a relationship between lunate type and the type of wrist injury mainly localised to the scaphoid bone. 394 PA and lateral radiographs of the wrist (n = 394) were subjected to a detailed assessment by two independent surgeons. The X-rays were selected and analyzed from a computer and archive database run by St. Hedwig Hospital in Trzebnica, from the beginning of January 2011 till the end of December 2012. Most of the X-rays (69%) were obtained from citizens of Trzebnica District. In addition, detailed anatomical studies of the wrist bones were carried out on 20 human preparations fixed in ethanol. Lunate type I was found in 288 wrist radiographs (73%) and type II in the remaining 106 photos (27%). Various types of wrist injuries were diagnosed in 129 cases. These were mainly distal radius fractures, scaphoid fractures and isolated scapholunate instability. There exists a statistically confirmed relationship between scaphoid fracture and lunate type II as well as a connection between lunate type and gender. Anatomical examination of 20 wrists showed the presence of lunate type I in 11 cases and type I in 9 cases. 1. Lunate type II is more frequently encountered in men. 2. Scaphoid fractures are more common with lunate type II. 3. The joint surface for the hamate in lunate type II is 2-7 mm in width. 4. The presence of another articular surface for the hamate in lunate type II may contribute to the formation of degenerative changes in the lunohamate joint.

Rib Cartilage Graft for Posttraumatic or Degenerative Arthritis at Wrist Level: 10-Year Results

Background Posttraumatic arthritides of the radiocarpal joint, secondary to scaphoid nonunion advanced collapse (SNAC), scapholunate advanced collapse (SLAC), or Kienböck disease or in cases of intraarticularmalunion of the distal radius, are classically solved by some type of arthrodesis procedure. Osteochondral grafting provides a possible motion-sparing option that can diminish pain in the active patient. Description of Technique A chondrocostal graft harvested from the ninth rib was inserted and fixed with a plate in place of the articular defect in cases of a malunited intra-articular distal radius fracture (7 cases) or to replace the proximal pole of the scaphoid in cases of SNAC or SLAC (18 cases). In Kienböck disease, the graft was inserted as a free cartilage spacer (4 cases). Results Harvesting the graft from the ninth rib had minimal morbidity without pleural injury in the reported series. Graft union was achieved in all cases of fixation. No graft resorption or necrosis were observed on X-ray and magnetic resonance imaging (MRI) evaluation at the longest follow-up of 10 years. Histological analysis performed at the time of plate removal showed the vitality of the graft. Two thirds of the patients had excellent or good results using the Green and O'Brien score. Conclusions Reconstruction of a partially destroyed articular surface using a costal graft is reliable and provides an alternative option for resurfacing the articular surface with viable cartilage.

Clinical and Radiological Outcomes of Scaphoidectomy and 4-Corner Fusion in Scapholunate Advanced Collapse at 5 and 10 Years

This retrospective study examined clinical and radiological outcomes of scaphoidectomy and 4-corner fusion in patients with a scapholunate advanced collapse (SLAC) at 5 and 10 years. Partial wrist arthrodesis is commonly performed to treat wrist arthritis because it provides pain relief without sacrificing complete wrist motion. The purposes of this retrospective study were to evaluate clinical and radiological outcomes after scaphoidectomy and 4-corner fusion after more than 10 years of follow-up and to compare the midterm and long-term results. Forty-two patients were enrolled. The following were evaluated annually: pain (visual analog scale); Disabilities of the Arm, Shoulder, and Hand score; range of motion; grip strength; and Modified Mayo Wrist score. Bony union and arthritic changes in the radiolunate joint were also evaluated radiologically. Midterm and long-term results were compared. The mean (SD) follow-up period was 12.2 (1.43) years. Two patients were excluded from the study because of complications, so the final postoperative evaluation included 40 patients. Visual analog scale and Disabilities of the Arm, Shoulder, and Hand scores improved to a satisfactory level by 5 years after surgery and did not differ significantly between 5 and 10 years. Flexion, extension, and radial deviation were reduced after 5 years compared with preoperative measures, and no difference was found between 5 and 10 years. Ulnar deviation, pronation, and supination did not change significantly after surgery. Grip strength was significantly recovered from 29.7 (4.9) kg at 5 years after surgery to 32.1 (8.5) kg at 10 years. The Modified Mayo Wrist score improved significantly to 83.2 (4.1) at 5 years after surgery but did not differ significantly between 5 and 10 years. All cases showed radiological solid fusion, and the mean (SD) period of union was 9.34 (3.7) weeks. Further radiolunate arthritic change was verified in 2 patients, but Modified Mayo Wrist scores were fair. One patient experienced inexplicable pain; therefore, total wrist fusion was performed at 6 years after surgery. This retrospective cohort study of patients followed up for more than 10 years showed that the midterm and long-term results of 4-corner fusion for stage III SLAC were satisfactory, and arthritic changes in the radiolunate joint were minimal.

The memory plate for four-corner fusion of scaphoid non-union advanced collapse

The aim of this study was to evaluate the clinical outcomes of the memory plates for four-corner fusion (FCF) of scaphoid non-union advanced collapse (SNAC). From 2005–2010, 11 cases of SNAC received FCF with the memory plate designed by the authors. At an average follow-up of 21 months, there were no non-unions and postoperative infections. One patient complained of dorsal impingement. The pain relief rate was 100% and the average grip strength increased from 11.3% preoperatively to 56.3% postoperatively of the contralateral side. The primary results of FCF with memory plates are promising. By its compressive property, the memory plate facilitates the arthrodesis with a lower complication rate.

Evidence of a Systemic Predisposition to Chondrocalcinosis and Association Between Chondrocalcinosis and Osteoarthritis at Distant Joints: A Cross‐Sectional Study

To determine whether there is a systemic predisposition to chondrocalcinosis (CC) and to examine the association between CC and osteoarthritis (OA) at distant joints. We performed a cross-sectional study embedded in the Genetics of Osteoarthritis and Lifestyle (GOAL) database (n = 3,170). All GOAL participants have had radiographs of the knees, hands, and pelvis performed. These were scored for OA at the knee, hip, wrist, and metacarpophalangeal (MCP) joints and for CC at the knee, hip, wrist, and symphysis pubis joints and for MCP joint calcification. Systemic predisposition to CC was established using cluster analysis. Odds ratios (95% confidence intervals) were used to examine the association between CC at the index and distant joints, CC and OA at the same joint, and index joint OA and distant joint CC. We adjusted for age, sex, and body mass index, and for distant joint OA, if required. Joints with CC clustered together. This was also observed when participants with OA were excluded from the analysis. CC at each joint was associated with CC at distant joints. Knee and wrist OA but not hip OA was associated with CC at the same joint. MCP joint OA was associated with MCP joint calcification. Knee OA was associated with CC at other joints, and this was independent of OA at the distant joint. There was no association between hip OA and distant joint CC. There is a systemic predisposition to the apparently sporadic CC. OA is associated with CC at the same joint and at distant joints, except hip OA, which is not associated with hip CC or with CC at distant joints.

Distribution of primary osteoarthritis in the ulnar aspect of the wrist and the factors that are correlated with ulnar wrist osteoarthritis: a cross-sectional study

The purpose of this cross-sectional study was to identify the distribution of primary osteoarthritis (OA) in the ulnar aspect of the wrist, and analyze the factors correlated with OA at this site. A total of 1,128 cases of skeletally mature Japanese patients were collected over a 3-year period. We analyzed the posteroanterior and lateral wrist radiographs of these patients for the presence of primary OA in the ulnar aspect of the wrist, including the distal radioulnar (DRUJ), radiolunate, ulnolunate, lunotriquetral, triquetrohamate, lunohamate, and lunocapitate joints. All joints were examined for the frequency of primary OA. Multivariate logistic regression was used to investigate the factors correlated with the presence of degenerative arthritis in the ulnar aspect of the wrist joint. Primary OA of the ulnar wrist was identified in 145 out of 1,128 cases (12.8%). Degenerative changes were most frequently identified in the DRUJ (12.3%), followed by the ulnolunate joint (8.1%). Variations in radial inclination (RI), carpal height ratio (CHR), and ulnar variance (UV) correlated with OA of the ulnar aspect of the wrist, with variations in UV showing the highest correlation. Primary OA of the ulnar wrist was most frequent in the DRUJ and second most frequent in the ulnolunate joint. UV correlated most with OA in the ulnar aspect of the wrist.

An Alternative Treatment Option for Scaphoid Nonunion Advanced Collapse (SNAC) and Radioscaphoid Osteoarthritis: Early Results of a Prospective Study on the Pyrocarbon Adaptive Proximal Scaphoid Implant (APSI)

Scaphoid nonunion advanced collapse (SNAC) and radioscaphoid osteoarthritis are difficult to treat. Options include proximal row carpectomy (PRC), four corner fusion (4CF) and wrist arthroplasty or arthrodesis. However, with inevitable disease progression, a significant proportion of patients undergo total wrist fusion. This reduces function by abolishing wrist movement. We review the preliminary results of a pyrocarbon interpositional radiocarpal implant in a small cohort of patients from our prospective study and challenge the assumption that there are no surgical alternatives. This study prospectively studied 12 consecutive pyrocarbon Interpositional arthroplasty day cases over 3 years. Patients were assessed using level of pain, ranges of motion, grip strength, key pinch, type of and time to return to work and the disabilities of the arm, shoulder and hand (DASH) score, both preoperatively and postoperatively. Radiographs were also taken and patient satisfaction recorded. All 12 patients could be contacted and were satisfied with their surgery. There were no immediate, early or late postoperative complications associated with the procedure. Promising results were noted in terms of pain, ranges of motion, grip strength, key pinch, type of and time to return to work, DASH scores, photographs and radiographs. The mean follow-up was 18 months, range between 11 months and 3 years. Our early results are encouraging, warrant further and longer studies and support the use of pyrocarbon implants as a primary procedure in what is a generally young and active subgroup of patients.

AB1048 Does chondrocalcinosis associate with a different radiographic phenotype of osteoarthritis?

BackgroundSome studies suggest that the structural changes in joints with osteoarthritis (OA) and co-existing radiographic chondrocalcinosis (CC) are distinct from joints with OA alone. However, other studies suggest that there...

A Minimal Wrist Arthroplasty for Early Wrist Osteoarthritis

Background The most common forms of salvage surgery for wrist arthritis of any stage are four corner fusion and proximal row carpectomy. Younger, high demand patients with early arthritis may not be candidates for this type of salvage surgery. We describe a technique and preliminary case series of a minimal radiocarpal arthroplasty aimed at patients with initial and isolated wrist arthritis (stage 1). This procedure does not preclude any procedure that may become necessary in the future. Patients A series of nineteen male heavy laborers with scapholunate advanced collapse (SLAC grade 1-2) wrist osteoarthritis that felt the wrist arthritis was prohibiting their function enough to warrant surgery, but were unwilling to undergo a salvage procedure, were treated with the technique. The average age was 57.2 (± 7.7) years. The average follow up period was 40.3 months (9-63 months). All patients returned to heavy labor. No revision surgery was needed within the follow up period. Range of motion (ROM) and grip strength did not significantly improve. Patient satisfaction was high despite imperfect results. Conclusions Minimal arthroplasty as described may provide a temporary solution for active patients with symptomatic early wrist arthritis who are not candidates for salvage wrist surgery. Longer -term follow up as well as investigation of additional stabilization procedures is necessary.

Excellent Results After Bone Grafting and K-Wire Fixation for Scaphoid Nonunion Surgery in Skeletally Immature Patients

Scaphoid nonunion is relatively rare in children and adolescents, and no long-term follow-up has been reported. Retrospective follow-up study. Eleven patients (10 boys and 1 girl), mean 15.2 (13.9-15.9) years of age, with scaphoid nonunion and open growth plates were operated with bone grafting, Kirschner-wire fixation and 12 weeks of cast immobilization. Bony union, degenerative wrist changes, and restoration of the carpal architecture were assessed with CT and radiographs. Clinical parameters included active range of motion, grip strength, key pinch strength, and subjective outcome scores (quick disabilities of arm, shoulder and hand (DASH), visual analog scale). The patients were followed up after mean 6.9 (3.1-15.1) years; all patients attended. Radiographs and CT confirmed healing of all nonunions, the carpal anatomy was restored, and the wrists were rated as 0 according to the scaphoid nonunion advanced collapse, without degenerative changes. The clinical result was excellent with visual analog scale at rest = 1, at activity = 6, and quick DASH score = 3.3. Active range of motion and grip strength were insignificantly reduced (14 degrees and 2 kg); the key pinch strength remained similar. Healing of a scaphoid nonunion can be expected in adolescents after open reduction, Kirschner-wire fixation, bone grafting, and plaster immobilization, resulting in pain relief and excellent wrist function without degenerative changes after longer term follow-up. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.